Shaped article and composite material and method for producing same |
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| 申请号 | EP81103363.8 | 申请日 | 1981-05-04 | 公开(公告)号 | EP0042935B2 | 公开(公告)日 | 1997-09-10 |
| 申请人 | DENSIT A/S; | 发明人 | Bache, Hans Henrik; | ||||
| 摘要 | |||||||
| 权利要求 | |||||||
| 说明书全文 | Densified systems containing homogeneously arranged ultrafine particles, for brevity termed DSP in the following specification and claims, were described and defined in detail for the first time in EP-A1-0 010 777. The present invention relates to important further developments of the DSP systems, including new types of DSP systems. DSP systems give rise to hitherto unattainable mechanical qualities, including strength, density, and durability, of materials and articles based on such systems and make it possible to establish such articles and materials by advantageous novel methods which broaden the possibilities of establishing advanced micro structures of constructional materials for a great variety of applications. In a very brief form the basic principle of DSP systems comprises placing ultrafine bodies or particles having a size of from about 50 Å (5 nm) to about 0.5 µm in homogeneous arrangement in the voids between substantially densely packed bodies or particles having a size of from about 0.5 µm to about 100 µm and being at least one order of magnitude (power of 10) larger than the respective ultrafine particles. Some essential characteristics of the DSP systems are contained in the following five points:
In the present context, the terms "bodies" and "particles" refer to domains with physical boundaries, the term "physical" referring to specific properties, e.g., mechanical, electrical, optical, or chemical properties. Shaped articles comprising a DSP matrix may be defined in general as shaped articles comprising a coherent matrix, the matrix comprising
The bodies or particles A and B are solid bodies or particles. The inter-particle substance I may be solid, or it may be a gas phase or liquid phase substance, provided that when the inter-particle substance in a shaped DSP article is not solid, the necessary "gluing" to retain the shape of the article is provided by particle-to-particle bonding. Thus, the substantially coherent structure of the matrix of the above-defined DSP articles of the may be due to the homogeneously arranged or densely packed bodies or particles A being combined with each other to form a coherent structure, or due to solid particles B as stated above being combined with each other to form a substantially coherent structure, or both the ultrafine particles A and the particles B in the shaped articles may each be combined with each other to form coherent structures, and/or particles A being combined with particles B to form the coherent structure. The combination between the particles A or between the particles B or between particles A and/or particles B may be of any character which results in a coherent structure. In systems comprising cement particles as particles B and silica dust particles (as defined below) as particles A the coherent structure is formed due to partial dissolution of the solid particles in the aqueous suspension from which the articles are made, chemical reaction in the solution, and precipitation of the reaction product, the silica dust being less reactive in this regard than the cement. In this connection it is noted that depending on the identity of the particles A and B, also other mechanisms imparting coherence may have been responsible for the coherence of the matrix, such as melting or sintering, etc. The chemical reaction mentioned above may be one which takes place between the particles A or their dissolved constituents, or between the particles B or their dissolved constituents, or between particles A and B or between constituents of particles A and particles B. A substantially coherent structure may also be established by solidifcation of other inter-particle substance, e.g., by solidification of a melt or liquid, such as physical solidification, including solidification of a metal or glass melt, and chemical solidification, including polymerization, e.g. to form a plastics substance. Shaped articles comprising a matrix having a substantially coherent structure comprising homogeneously arranged or densely packed particles A together with densely packed particles of Portland cement were obtainable in the known art only by compaction in a high stress field, typically by high pressure powder compaction. Hence, one very interesting class of shaped DSP articles comprises shaped articles produced by shaping in a low stress field of less than 5 kg/cm2, preferably less than 100 g/cm2, and having a matrix of a substantially coherent structure comprising homogeneously arranged or densely packed particles A or a coherent structure formed from such homogeneously arranged or densely packed particles A, and densely packed particles B, at least 20% by weight of the densely packed particles B being Portland cement particles, or a coherent structure formed from such densely packed particles B. Another way of defining the class of shaped DSP articles having homogeneous arrangement of particles A between densely packed particles B of which at least 20% by weight are Portland cement particles is by referring to the dimensions of the article. Such articles having a correspondingly dense packing between the particles B and having at least one dimension of at least 1 m and a minimum cross section of at least 0.1 m2 are not believed to have been made in practice, prior to the invention of the DSP systems, by high pressure powder compaction technique. Another way of expressing this kind of DSP article is by defining that the articles have a complex shape that does not permit its establishment through powder compaction. Finally, when the particles B have a molecular structure different from the particles A, such as will most often be the case in practice, such structures in which at least 20% by weight of particles B are Portland cement and which otherwise comply with the definition stated above, could not have been made using traditional techniques irrespective of the size or shape of the structures. While it may have been possible in powder compaction techniques to obtain a combination of the two systems comprising homogeneously arranged or densely packed particles A and densely packed particles B, this would have involved crushing of the larger particles during the compaction process to result in the smaller particles and hence, would have meant that the larger particles and the smaller particles would have identical molecular structure. One very interesting feature of the DSP materials is that it is possible to establish structures of the types discussed above with inherently weak particles and inherently weak additional bodies which would have lost their geometric identity (would have been crushed or drastically deformed) by the known art treatment in a high stress field. This makes it possible to establish dense structures with materials not previously available therefor. The principles of dense packing are dealt with in detail in the following section "Principles of dense packing". In the present specification and claims, the terms "ultrafine silica particles" and "silica dust" are intended to designate SiO2-rich particles having a specific surface of about 50,000-2,000,000 cm2/g, especially about 250,000 cm2/g. Such a product is produced as a by-product in the production of silicium metal or ferrosilicium in electrical furnaces and comprises particles in a particle size range from about 50 Å (5 nm) to about 0.5 µm, typically in the range from about 200 Å (20 nm) to about 0.5 µm. In EP-A1-0 010 777, the particles A and B of the DSP materials are, in general terms, characterized as solid particles having particles sizes typically between, 50 Å (5 nm) and 0.5 µm and 0.5 µm and 100 µm, respectively. The said EP-A1-0 010 777 mainly discloses compact-shaped particles, typically relatively hard materials such as Portland cement, lime, fly ash, and colloid silica. However, also weak materials easily deformable under stress of below 5 kg/cm2 are mentioned as particles B. According to the present invention, the bodies A and B may be of any shape, a typical useful shape being elongated rod-like shapes where the minimum dimensions are 0.5-100 µm. The length of the bodies B may be of arbitrary size larger than the transverse dimensions, such bodies typically being chopped fibers or whiskers having a length/diameter ratio from 1000:1 to 5:1, or continuous fibers such as wires. In the present specification, the term "bodies" designates bodies of any of the above-mentioned possible shapes, including particle shape, elongated shape, plate shape, or fiber or continuous fiber or wire shape, and the term "particles" generally designate compact-shaped particles, but may also encompass angular particles and somewhat flattened out or elongated shapes within the normal understanding of the definition scope of the term "particles". The dense packing as discussed in the section "Principles of dense packing" is related to the geometry of the particles and the type of packing or shaping process. Thus, with simple mixing or casting technique, a volume concentration of 10% of elongated bodies B may often be considered high and will constitute dense packing when the mixing or casting technique according to which the DSP materials containing such bodies have been established is a simple mixing or casting technique, whereas the corresponding volume concentration with parallel arrangement of fibers B in filament winding may be as high as 40-70%. Dense packing of bodies and particles is essential in connection with DSP systems. As an example, the essential feature of Portland cement-based DSP materials is dense packing of cement particles, combined with the incorporation of ultrafine particles in the voids between the cement particles. In connection with the creation of volumetrically stable DSP concrete and mortar, it is also desirable to pack sand and stone as tightly as possible with the spaces between the aggregates filled as tightly as possible with dense DSP paste. This packing is not uniquely defined, but depends on the shape of the bodies or particles in question, on the size distribution, and on the method of compaction. The packing density depends on the particle shape, so that the more angular, oblong, and rougher the particles, the lower will be the density. In connection with Portland cement DSP paste, the large particles (cement) will typically have a cubicle-angular shape, with moderate packing capacity. (The shape of cement particles depends on the production method (grinding). From the point of view of packing, spherical cement would be ideal. Such cement could be produced by nucleation and growth in liquid phase). The ultrafine powder, on the other hand, consists of sphericals formed by condensation from gaseous or liquid phase. The spherical shape results in ideal packing properties. Densely packed elongated bodies, such as fibers, will typically be arranged in a much more open structure than compact-shaped particles (vide Figure 4) unless special precautions are taken (vide Figure 5). The effect of the particle size distribution can be illustrated by discussing binary mixes (large particles and small particles) as opposed to multi-component mixes. Dense packing of particles dominated by the geometry of the particles (without influence from surface forces) has been treated worldwide in the literature dealing with particulate technology in various fields, for example in "Particulate Technology, Clyde Orr, Jr. 1966, The MacMillan Company, New York, and "Principles of Particulate Mechanics", Brown and Richards, 1970, Pergamon Press. It is characteristic that packing of particle systems in which surface forces are insignificant is independent of the absolute particle size and depends only on the shape of the particles, the relative size distribution, and the mechanical way in which the particles are placed. This means that regular packing of equal spheres results in the same volume fraction of solids content (for example, 0.52 for cubic packing and 0.74 for hexagonal packing) irrespective of the absolute size of the spheres. The density of the packing is strongly influenced by the relative particle size distribution, that is, the ratio between the various particle sizes. Thus, Brown and Richards (loc. cit.) report classical experiments with binary packings of spherical particles with various size ratios where the volume fraction of solids content increases from about 0.63 for packing of each of the individual particle size fractions to 0.70 for a mixture of large and small particles with a size ratio of 3.4:1 and to 0.84 for a mixture of large and small particles in a size ratio of 16:1. The density of the packing is also strongly influenced by the mechanical compaction method. Simple pressure compaction will normally not lead to very dense packing of particle systems in which the particles retain their geometric identity (that is, are not crushed or heavily deformed). Normally, denser packing is obtained by shear deformation, repeated shear deformation, or balanced vibration, all with application of a small normal pressure to secure that the repeated deformation finally results in a more dense structure. For this reason, it is not possible to state dense packing in terms of one unique quantity. The "dense packing" referred to in the present specification is to be understood as substantially such a dense packing which would be obtained in systems without locking surfaces by influences of the above types such as shear deformation and balanced vibration. The densest packing is obtained with a high ratio between large and small particles, typically in excess of 20. For small diameter ratios, the maximum packing density is reduced because of the wall and barrier effect (vide Figures 37 and 43) which gains increasing importance with increasing ratio of fine particles to coarse particles. Without the wall and barrier effect, 100% dense packing could be achieved in multi-component mixed by continuously filling the spaces between the particles with fiber particles. In practice, where the ratio between largest and smallest particles is limited, for example to about 104-105 for concrete or cement-based DSP with up to 10 mm aggregate and fine cement fraction of 1 µm, and for the DSP, also ultrafine silica particles having a mean particle size of about 0.1 µm, a marked wall effect and barrier effect would occur if the number of discrete particle fractions were more than 3 or 4, which would result in a far from ideal packing. There seems to be no theory that enables the drawing-board design of the grading curve that will give optimum packing. Hence, the solution seems to be a compromise between a few-component packing with little wall effect and barrier effect, on the one hand, and multi-component packings, on the other hand. In each particular case, the optimum packing may be assessed by preliminary physical compaction tests. However, some general principles may usually be utilized:
The dense packing of bodies or particles where surface forces are eliminated is strongly dependent on the kinematics of the arrangement of the bodies. For example, fibers may be arranged in what is considered dense packing in the context of the present application by 1) a simple mixing and casting process (vide Figure 4), 2) sedimentation (vide Figure 31), and 3) filament winding as illustrated in Figure 5. The density or fiber concentration is strongly increasing from 1) via 2) to 3). Typical fiber concentration values obtainable by the three methods are 5, 20, and 60 per cent by volume, respectively. Thus, it will be understood that the dense packing is the combined effect of the particle or body shape and the way the particles or bodies have been arranged, that is, the kinematics, under conditions where the particle or body concentration is insignificantly influenced by surface forces such as in the DSP systems with effective dispersing agent incorporated. An essential part of the establishment of a DSP system is the overcoming of surface forces between the small particles and bodies to secure the important dense packing. For cement-based DSP, the question of obtaining dense particle packing is, thus, essentially a question of overcoming locking surface forces between the cement particles and the ultrafine particles in aqueous dispersion. For particles of compact, rounded shape, held together by surface forces, the forces required to separate two particles in point contact or to perform mutual sliding are proportional to the particle dimension (d) and the surface tension (γ) The surface tension γ is defined as 1) the surface tension between the liquid meniscus and surrounding fluid (usually air) when cohesion is caused by the meniscus or 2) the work required to create one unit area of new surface by removing plane-parallel faces from the contact area to infinite distance. On the assumption that separation and sliding resistance dominate over rolling resistance, the yield stress of a powder (which is proportional to the force acting on a particle, divided by the area of the particle) can be written This qualitative model has played a great role in the choice of strategy for the production of dense, strong, cement-bound materials, including DSP, where depiction of the particle packing as a function of pd/γ has been used. The quantity pd/γ is a measure of the extent to which external stresses (p) are able to overcome internal cohesion (γ/d). Ultrafine particles subjected to surface forces are typically packed in a very open structure if the packing takes place under moderate external pressure. This is a case of compaction of a particulate system with very low, dimensionless compaction pressure pd/γ, resulting in a correspondingly low particle concentration. Denser packing can be achieved by 1) heavier compaction, 2) reduction of surface forces, for example by means of surface-active agents, or 3) selection of larger particles. For very high values of pd/γ, the effect of surface forces is practically overcome, cf., for example, a pile of stones. Here, the particle packing is principally a question of particle geometry, particle friction and the way in which the compaction is made, i.e., by vibration. The production of extremely strong and dense concrete requires a binder of very fine particles arranged in dense packing. However, in normal circumstances, the combination of small particles, locking surface forces and moderate compaction load does not permit the production of such a dense structure. According to the DSP principle, the locking effect of surface forces in cement-based materials is practically completely eliminated by means of dispersing agents, thereby enabling ideal geometrical arrangements with packing of small, spherical particles between larger particles to ensure a very dense structure despite the fact that the small particles packed between the cement particles are about 1/100th the size of normal cement particles (silica dust with an average diameter of 0.1 µm). Thus, according to the DSP principle, efficient dispersing agents are utilized to change the ultrafine particle-based materials into a condition where the packing density has become purely a geometrical and kinematic problem, known from the theory of packing of large-size particles. According to a particular aspect of the present invention, it is also possible to perform compaction of the DSP particles in higher stress fields, cf. the following section "Shaping in a high stress field". Utilizing compaction in high stress fields, it is possible to successfully establish DSP systems based on the smallest particle size in the range stated for particles A, that is 50-200 Å (5-20 nm), where surface forces (γ) according to the model For other methods of arranging fine bodies or particles, such as sedimentation, similar principles may be utilized, only the mathematical models being different. Thus, the dense arrangement by sedimentation of small fibers is dependent upon whether the force of gravity acting on the fiber is able to overcome the surface forces which tend to fix or lock the sedimenting fiber (such locking or fixation is typically a fixation in an absolutely undesired position unparallel to other fibers) so that the sedimenting fiber will obtain a desired position substantially parallel to already sedimented fibers (vide Figure 31). The dispersion of fine particles by use of surface active agents is well explained in general terms in the literature on colloidal and surface science. The purpose of using a surface active agent is to establish such repulsive forces against adjacent particles that the repulsive forces become able to overcome the mutual attraction caused by London/van der Waals forces and possibly other attraction forces. By this measure, it is attempted to eliminate blocking between the particles, thus ensuring the sliding of the particles relative to each other which is absolutely essential for the establishment of dense packing in a low stress field. According to classical theory, two repulsive mechanisms are normally considered: electrical repulsion caused by generation of electrical diffuse double layer in the medium surrounding the particles (cf. the D.L.V.O. theory), and steric hindrance where particles are prevented from coming together (e.g. prevented from flocculation) due to the presence of adsorbed layers of another compound on their surface. Such adsorbed layers may be molecules from the medium, or they may be surfactant molecules. The physical interaction of the adsorbed molecules as the particles approach each other acts as a barrier to flocculation. It is believed that steric hindrance effect is the dominant factor in cement dispersed in water under the influence of typical concrete superplasticizers, but that also electrical repulsion enter into the mechanism as an extra contribution. Experience over many years indicates that a pure electrical repulsion effect is insufficient to prevent flocculation of Portland cement in water (probably due to a high concentration of divalent, trivalent counterion (Ca++ and Al+++), which, according to the Hardy-Schultz rule, compresses the diffused double layer, and perhaps also due to formation of direct chemical bonds (or bridges). It seems likely that an efficient dispersion of ordinary Portland cement in water is strongly dependent on dispersing agents securing efficient steric hindrance. Achievement of a good dispersion of ultrafine silica, e.g. having an average size of 0.1 µm, in water is basically much simpler than the achievement of a similar dispersion of the much coarser Portland cement (typically with average particle size of 10 µm). Thus, an efficient dispersion of colloid silica in water (without salt content) is obtained by pH control (pH typically above 7 or 8) is reported in Surface and Colloid Science, editor Egon Matijeviec, Ralph K. Iler, 1973, John Wiley & Sons). Practical experimental experience with the fine silica dust used in the working examples (specific surface area about 250,000 cm2/g) demonstrates the same general behaviour. Thus, 1:1 mixture of silica dust and tap water (by weight) and a 2:1 mixture of silica and 3% sodium tripolyphosphate aqueous solution both result in slurries with moderate viscosity which are easily mixed in low shear mixers or by hand. However, attempts to combine such silica/water systems with Portland cement result in a pronounced flocculation. Thus, the addition of a small amount of easily flowable Portland cement/water slurry (typically a water:cement ratio of 1) to a large batch of silica/water slurry of the types and concentrations mentioned above (e.g. typically 1 part of cement slurry to 10 parts of silica/water slurry) results in a drastic stiffening which renders any further mixing impossible. This demonstrates that the solutes in the water generating from the cement destroy the dispersion of the ultrafine silica particles. The precise mechanism of bond formation between the silica particles is not known, but the explanation is likely to be along the lines of reduced double layer repulsion and formation of various types of direct bonds or bridges. By the use of concrete superplasticizers, such as sodium salt of a highly condensed naphthalene sulphonic acid/formaldehyde condensate, of which typically more than 70% consist of molecules containing 7 or more naphthalene nuclei, it is easy to obtain an extremely good dispersion of the combined ultrafine silica/Portland cement/water system, making the dense packing of the binder possible in a low stress field. Hence, the success of superplasticizers in ultrafine particle/cement/water DSP systems is not due to their ability to disperse ultrafine particles in water (indeed, other surfactants are even better for this purpose), but due to the fact that they are able to provide a good dispersion of the silica in the specific Portland cement/water environment. The present invention relates to the preparation of ultra strong cement-based DSP materials. The strength of ordinary concrete depends primarily on the quality of the cement binder which binds together sand and stone, and only to a smaller degree on the quality of the sand and stone as long as normal sound materials are concerned. The reason for this is that the binder is the weak link in normal concrete and that ruptures predominantly occur through the binder, without passing the sand and stone particles. In textbooks on concrete design, this is clearly expressed by assuming, as a first approximation, that the strength is a function solely of the composition of the binder (expressed as the cement concentration in the cement-water suspension through the reciprocal value:the "water-cement ratio") without including the amount and quality of the sand and stone in the models. In concrete where the strength of the sand and stone is no longer high in relation to the strength of the binder, both the strength of the binder and the strength of the sand and stone will be of importance to the strength of the composite material. This is known for traditional lightweight aggregate concrete where the stone material consists of light, porous, relatively weak material. In this case, the inherent strength of the stone has equal importance to the strength of the mortar in the mathematical expression for the strength of the concrete: With the development the new, very strong cement-based DSP binders, as disclosed in EP-A1-0 010 777, concrete and mortar with a hitherto unknown strength have been obtained. Thus, EP-A1-0 010 777 discloses water-cured, wet cylindrical test specimens having a diameter of 10 cm and a height of 20 cm and showing a compressive strength of 146.2 MPa for a concrete after 169 days' storing at 20°C and 179 MPa for a mortar cured at about 60°C for 4 days. Both the concrete and the mortar were prepared from easily flowable masses cast with slight mechanical vibration. Traditional quartz sand and, for the concrete, granite stone, were used. These strengths were compared with the highest strength disclosed in the relevant technical literature: 120.6 MPa measured on test cylinders of the same dimensions as above and consisting of concrete with a water/cement ratio of 0.25, a cement content of 512 kg/m3 and a content of "Mighty" (a concrete superplasticizer which is further characterized below) 150 in an amount of 2.75% of a 0.42% solution, calculated on the weight amount of cement, the samples having been stored for one year prior to the testing of compressive strength. (Kenichi Hattori, "Superplasticizers in Concrete, Vol. I, Proceedings of an international Symposium held in Ottawa, Canada, 29-31 May, 1978, edited by V. M. Malhhotra, E. E. Berry and T. A. Wheat, sponsored by Canada Centre for Mineral and Energy Technology, Department of Energy, Mines and Resources, Ottawa, Canada and American Concrete Institute, DETROIT, U.S.A). The investigation of rupture surfaces in connection with the strength measurements disclosed in EP-A1-0 010 777 indicated that the sand and stone materials used were not strong in comparison with the binder such as would have been the case in normal concrete, as the rupture proceeded, to a large extent, through the sand and stone particles. This indicated the possibility of producing even stronger concrete by combining the use of the DSP binder with the use of much stronger sand and stone materials. This is a principle which does not have any significant effect in connection with normal concrete, such as explained above. Thus, the present invention relates to DSP systems which are even stronger than the DSP materials disclosed in EP-A1-0 010 777, to shaped articles made with such systems, and to composite materials and methods for making such systems. In accordance with this, concrete and mortar were prepared with the DSP binder, using, as sand and stone material, e.g., refractory grade bauxite and silicon carbide, both of which are much stronger than ordinary concrete sand and stone, vide Examples 1 and 4. The concrete and the mortar were prepared from easily flowable masses and had extremely high strength (the compressive strength of the cylindrical concrete specimens with diameter 10 cm and height 20 cm cured at 60°C for 4 days was 217 MPa). This is more than 50% higher than the strength of the very strong concrete with traditional sand and stone, bound together with the new strong cement binder (146.2 MPa, cf. EP-A1-0 010 777) and more than 80% higher than the highest strength which has, to the applicants' best knowledge, been obtained with concrete fabricated with traditional soft mass casting and curing technique using traditional superplasticized cement binder (120.6 MPa, cf. Hattori, loc. cit). The new high quality material of the invention also showed an extremely high rigidity (dynamic modulus of elasticity of 109,000 MPa) which is about 60% higher than for high quality concrete using the DSP binder and quartz sand and granite stone, cf. Example 1 of EP-A1-0 010 777. The mortar with sand of refractory grade bauxite was even stronger and more rigid than the concrete (the compressive strength of cylindrical specimens with diameter 10 cm and height 20 cm cured at 80°C for 4 days was 248 MPa and the dynamic modulus of elasticity was as high as 119,000 MPa, cf. Example 4). The compressive strength is 38% higher than the strength of the strongest mortar hitherto prepared with the DSP binder and quartz sand (179 MPa, vide Example 9 of EP-A1-0 010 777 and more than twice as high as the strength of the above-mentioned strong concrete reported by Hattori (120 MPa). Still stronger cement-based DSP materials of the present invention have been made with the strong sand and stone materials, vide Example 5 where the strength was 268.3 MPa. Hence, the DSP concrete material of the present invention is of a hitherto unknown quality obtained by using extremely strong sand and stone material together with the extremely strong DSP binder, whereby
Together with the advantages with respect to easy production which are associated with the DSP binder, the incorporation of the particularly strong sand and stone materials opens up the possibility of a wide range of new and improved products. Another very interesting aspect of the ultra strong cement-based DSP materials is the ratio between the strength σ and the density ρ, which is the key parameter in the construction of large structures such as towers, bridges, etc., where the maximum possible size is proportional to this ratio. The stress/density ratio of cement-based DSP materials and, in particular, of DSP materials comprising strong sand and stone, is far higher than that of ordinary concrete or high quality concrete and even higher than the stress/density ratio of structural steel. An aspect of the invention may be defined as a process for preparing a shaped article or part of a shaped article, comprising combining
and thereafter, if necessary or if desired, respectively, combining the resulting mass with particles and/or bodies of the type mentioned above (B, C, D) by mechanical means to obtain the desired distribution of the components, and finally casting the resulting mass in the desired shape in a stress field, optionally with incorporation of particles C and/or additional bodies D during the casting. JP-A-49 125 428 published on November 30, 1974 (Application No. 48-38075) discloses a method for preparing high strength concrete by adding 2-30 weight parts of pozzolanic material (which may be the same kind of ultrafine silica as used in the examples of the present application) to 100 weight parts of cement and further adding calcium sulphate in an amount of 2-6 weight parts per weight part of alumina component in the pozzolanic material, moulding in the ordinary way and curing at high temperature or under high pressure with high temperature, in order to obtain a reaction between the pozzolanic/calcium sulphate material with calcium hydrate to produce cement gel or ettringite. The specification of the patent application discloses the use of a concrete superplasticizer, but the data given in the specification do not indicate that homogeneous arrangement of the ultrafine particles has been obtained. DE-A1-2 731 612 discloses the use of sodium tripolyphosphate as dispersing agent for producing a binder containing 25% by weight of aluminous slag of particle size of 5-50 µm, 38% by weight of vitrious silica of a particle size from 100 Å to 0.1 µm, and 37% by weight of Fontainebleau sand of a particle size of 5 µm, the water/powder ratio being as low as 0.175. The mortar prepared from this mix showed a compressive strength after 20 days of 120 MPa (the testing conditions and specimen dimensions are not stated). However, the materials disclosed in DE-A1-2 731 612 do not seem to show the essential homogeneous distribution of the particles A. According to the present invention, sand and stone materials are used which are stronger than the sand and stone materials used in ordinary concrete. Typically, concrete sand and stone consist of ordinary rock such as granite, gneiss, sandstone, flint and limestone comprising minerals such as quartz, feldspar, mica, calcium carbonate, silicic acid etc. Various kinds of comparison tests may be used to assess that particular sand and stone materials are stronger than ordinary concrete sand and stone, e.g.
It is difficult to specify unambiguous relations between such strength and hardness results for the sand and stone and the ability of the sand and stone to impart strength to the concrete or the mortar. Generally, it must be anticipated that sand and stone with higher hardness, abrasion strength, strength in composite structure etc., yields a higher concrete strength provided
In Examples 1, 3, 4, and 5, sand and stone materials with considerably higher strength and hardness than ordinary concrete have been used: Refractory grade bauxite containing 85% Al2O3 (corundum) and silicon carbide were used. Both materials have considerably higher hardness than the minerals in ordinary sand and stone. Thus, both corundum and silicon carbide are reported to have a hardness of 9 according to Moh's hardness scale, and then a Knoop indentor hardness is reported to be 1635-1680 for aluminum oxide (corundum) and 2130-2140 for silicon carbide, while quartz, which is one of the hardest minerals in ordinary concrete sand and stones, has a Moh's hardness of 7 and Knoop indentor hardness of 710-790 (George S. Brady and Henry R. Clauser, Materials Handbook. 11th ed., McGraw-Hill Book Company). The high strength of these materials compared to ordinary concrete sand and stone has been demonstrated by powder compaction tests (Example 3) and by tests with mortar and concrete with silica-cement binder where the materials were used as sand and stone (Examples 1, 4 and 5). Many other materials than the two above-mentioned materials may, for course, be used as strong sand and stone materials. Typically, materials with a Moh's hardness exceeding 7 may be used, e.g. topaz, lawsonite, diamond, corundum, phenacite, spinel, beryl, chrysoberyl, tourmoline, granite, andalusite, staurolite, zircons, boron carbide, and tungsten carbide. The hardness criterion could, of course, also be stated as Knoop indentor hardness where minerals having values above the value of quartz (710-790) must be considered strong materials compared with the minerals constituting ordinary concrete sand and stone. For the assessment of the strength of sand and stone, the technique described in Examples 1, 4, and 5 involving embedding the sand and stone in question in a specified cement/silica matrix produced and tested in a specified manner may be used: Concrete produced from ordinary concrete sand and stone (granite stone and quartz sand) and silica/cement matrix substantially identical with the one used in Example 1 had compressive strengths about 120-160 MPa (vide EP-A1-0 010 777). Therefore, it seems reasonable to characterize stone and sand increasing the compressive strength of the concrete to 170 MPa as strong compared to ordinary concrete sand and stone. With refractory grade bauxite sand and stone, however, cf. Example 1 of the present description, strengths of 217.5 MPa were obtained, for which reason values above 200 MPa can be taken as a realistic and desirable goal for a preferred material. Analogous experience has been obtained with cement/silica mortar where materials with substantially identical cement/silica matrix yielded compressive strengths of 160-179 MPa for quartz sand mortar (vide Example 9 in EP-A1-0 010 777) and 248 and 268 MPa, respectively, for mortar with sand of refractory grade bauxite (Examples 4 and 5, respectively, of the present description). It would seem reasonable to characterize sand which increases the mortar strength to above 200 MPa as strong compared to the strength of normal sand, and also, it seems reasonable to state strengths above 220 MPa as a goal which is both desirable and obtainable with the preferred materials. For the evaluation of aggregates having a particle size exceeding 4 mm, the concrete technique from Example 1 is used. For the evaluation of sand having a particle size of less than 4 mm, the mortar technique, cf. Example 9 in EP-A1-0 010 777 and Examples 4 and 5 in the present description (composite as for bauxite mortar) is used, whereby, in the particular mixes, the same volume of sand and stone is to be incorporated, not the same weight amount of sand and stone. The preparation, the curing, and the testing are performed as in the examples mentioned. The above-mentioned testing methods, and the particular way in which certain of the tests are performed, form the basis of the definition of useful and preferred particles C referred to in the claims. The additional bodies D having at least one dimension which is at least one order of magnitude larger than the particles A may, in principle, be bodies of a solid (such as discussed in greater detail below), a gas (such as in gas concrete) or a liquid. The bodies may be compact shaped bodies (such as sand, stone, gas bubbles, or liquid bubbles), plate-shaped (such as mica), or elongated (such as fibers or reinforcing bars or wires). Due to the possibility of shaping the articles in question in a "gentle" way in a low stress field, such bodies may, in contrast to what happens in any known art compaction processes which might achieve dense packing in ultrafine particle systems, substantially retain their geometric identity during the shaping. In this context, retainment of geometric identity indicates that the bodies in question are not subjected to any substantial crushing or drastic deformation. A typical example is a solid body in the form of a hollow particle, or a fiber which in powder compaction or other high stress field treatment would be crushed or drastically deformed, but which in the much lower stress field in which the articles of the invention may be formed is capable of avoiding such deterioration. Examples of additional bodies D which are advantageously incorporated in shaped articles comprising the DSP matrix, in particular the cement-based DSP matrix, are sand, stone, polystyrene bodies, including polystyrene spheres, expanded clay, hollow glass bodies, including hollow glass spheres, expanded shale, perlite, natural lightweight aggregate, gas bubbles, metal bars, including steel bars, fibers, including metal fibers such as steel fibers, plastic fibers, glass fibers, Kevlar fibers, asbestos fibers, cellulose fibers, mineral fibers, high temperature fibers and whiskers, including inorganic nometallic whiskers such as graphite whiskers and Al2O3 whiskers and metallic whiskers such as iron whiskers, heavy weight components such as particles of baryte or lead or lead-containing mineral, and hydrogen-rich components such as hollow water-filled particles. When the shaped articles comprise additional bodies D, it may be attractive for optimum strength and rigidity or for other purposes to obtain dense packing of the additional bodies. The easily deformable (easily flowable) DSP matrix permits a considerably denser arrangement of additional bodies than was obtainable in the known art. Especially the incorporation of fibers is of great interest due to the unique capability of the DSP matrix with respect to anchoring fibers. In this context, it should be mentioned that the much denser structure in the shaped articles comprising the DSP matrix will result in a virtual insulation of fibers otherwise subjected to chemical attack from the constituents of the matrix or from the surroundings. The fibers used in the shaped articles may be of any configuration such as chopped single fibers, or continuous fibers or yarns or ropes, or roving or staple fibers, or fiber nets or webs. The particular type and configuration of fiber will depend upon the particular field of use, the general principle being that the larger the dimensions of the shaped article, the longer and coarser are the fibers preferred. The improvement of the fixation of fine fibres makes it possible to fabricate strongly improved fiber composite materials based on mixing, into the material, a larger amount of chopped fibers than in corresponding materials based on common matrices. To secure a good fiber performance in the known art matrices, it is necessary that the chopped fibers have a certain (high) length to diameter ratio, the so-called aspect ratio. In normal matrices it is, however, difficult to intermix and arrange fibers with large aspect ratios-in other words, the smaller the aspect ratio is, the easier it is to incorporate the fibers and arrange them in a suitable way in the cast matrix, and the higher volume of fibers can be incorporated. For example, chopped polypropylene fibers with cross dimensions of approximately 30 µm, usually have a length of 12-25 mm (aspect ratio more than 500) when employed as reinforcement in ordinary cement matrices. A far better utilization of the same type of fibers is obtained in the DSP matrix, such as described in Example 2 of EP-A1 010 777. In Example 2 of EP-A1-0 010 777, very favorable fixation and resulting strength properties were obtained even though the fiber length was only 6 mm. With the DSP matrix, it seems possible to reduce the length of chopped fibers and, hence, the aspect ratio, with a factor of 10 or more (compared to chopped fibers of ideal or reasonable aspect ratios for use in normal matrices) and, accordingly, to utilize this reduced aspect ratio to incorporate a larger amount of fibers in the composite material and/or secure a better fiber arrangement in the cast matrix. Among the most important shaped articles according to the invention are the ones in which the particles B comprise at least 50% by weight of Portland cement particles, especially the ones in which the particles B essentially consist of Portland cement particles. These shaped articles will typically contain silica dust particles in a volume which is about 5-50% by volume, in particular 10-30% by volume of the total volume of the particles A and B and will typically contain sand and stone as additional bodies to form mortar or concrete of extremely high qualities with respect to mechanical strength, frost resistance, etc., and/or fibers, especially metal fibers, including steel fibers, mineral fibers, glass fibers, asbestos fibers, high temperature fibers, carbon fibers, and organic fibers, including plastic fibers, to provide fiber-reinforced products showing a unique anchoring of the fibers such as discussed further above. With particular reference to fibers which are subject to chemical deterioration, for example glass fibers which are subject to deterioration under highly alkaline conditions, it is an important advantage of the DSP matrix that such fibers, both during the curing of the material and in the final cured material, become much better protected against influence from the environment, due to partial dissolution of the silica dust with resulting partial neutralization of the alkaline environment, and due to the micro-dense "jacketing" around the fibers conferred by the ultrafine particles and the coherent structure formed therefrom which very substantially contributes to static conditions in the glass fiber environment, substantially avoiding any migration of alkaline material against the fiber in the final cured matrix. When the shaped articles of the invention comprising the cement-based DSP matrix are of large sizes, they are preferably reinforced with reinforcing steel such as bars or rods or steel wires or fibers. Reinforcements in pre-stressed constructions involving the DSP matrix are especially valuable. Due to the very gentle conditions under which the articles can be shaped, the reinforcement bodies can retain their geometric identity during the shaping process. With the considerably increased strength of the matrix of the invention and the strongly improved fixation of fibers and bars in the matrix, possibilities for producing new classes of reinforced and fiber reinforced cement based articles and materials are provided:
The reinforcing possibilities mentioned may, of course, be combined in many ways, for example by making a thin cover of semi-brittle reinforced material on a large load bearing member, or by use of high quality steel wires as secondary reinforcement (mainly placed perpendicular to the main reinforcement) in large pre-stressed members. With the strong sand and stone (bodies C) embedded in the matrix in accordance with the present invention, the resulting high quality DSP materials may be characterized in that they have a compressive strength of
By introducing ultrafine particles in the voids between densely packed particles, for example silica particles having a specific surface area of 250,000 cm2/g in the voids between cement particles having a diameter about 5 µm, a structure is obtained which shows an increased resistance against internal mass transport in the form of fluid transport (gas or liquid) between the particles and against mass diffusion in the pore liquid. The squeezing of liquid from saturated particle systems depends on the compression of the particle skeleton-typically depending on whether sliding between the particles is possible-and on the flow of liquid through the channels between the particles. In connection with shaping of cement-silica-water suspensions, internal liquid transport in the fresh material is of decisive importance. The resistance against viscous flow of fluid between particles in systems of particles of geometrical similarity varies inversely as the square of the particle diameter. This means that the time for a given liquid transport under a given pressure gradient in two geometrically similar particle-liquid systems with a particle size of 1:50 is 2500 times higher in the fine grained system than in a system with particles are 50 times as large. A similar effect is obtained by filling the pore volume between large particles with ultrafine particles, as it is the cross-section dimensions of the resulting channels between the particles which are mainly responsible for the resistance to the flow. The effect of particle size on water retention is further illustrated in Figures 6, 7 and 8. These facts are well-known, and it is also known art to reduce the internal liquid transport in cement/water systems by introducing so-called "thickeners" in the water in the form of ultrafine particles or polymers such as Methocell. Because of the dominating effect of locking surface forces, it will, however, normally not be possible to combine the uses of 1) very dense cement packing and 2) ultrafine particles in an easily flowable aqueous suspension. However, with an extremely high dosage of a dispersing agent, such as a superplasticizer, this is possible. Thus, easily flowable cement paste, mortar and concrete with densely packed cement particles and containing 10-30 per cent by volume of silica dust, calculated on cement+silica dust, with water/cement+silica-ratio of 0.15-0.20 by weight can be made. This results in several advantages compared to the known methods: In the known art production of high quality concrete and mortar using relatively high dosages of superplasticizer, an easily flowable mass having a low water/cement-ratio (for example 0.25) is obtained. The mass is poured into moulds where it is compacted under the influence of gravity and optionally also mechanical vibration. However, during this process, the heavier cement, sand, and stone particles will tend to arrange themselves in an even more dense packing, while water migrates upwardly, the so-called bleeding, vide Figure 7. Accordingly, for such known systems with very efficient cement dispersion obtained in the use of relatively high dosages of superplasticizer, a marked bleeding is normally observed in spite of the low water/cement-ratio-especially if the process is accompanied by vibration. This phenomenon may for example be critical in the casting of concrete roads with superplasticized concrete as bleeding results in a surface sludge of high water content, and hence results in a road surface which has a lower quality than the intended abrasion layer. Internal liquid separation is also critical in casting of reinforced concrete with superplasticizer. The liquid separation may result in a bleeding at the underside of the reinforcement, which reduces the fixation of the reinforcement and reduces the protection against chemical attacks. By introducing, in accordance with the principles of the present invention, ultrafine particles, for example 5-15% of silica dust having the above-mentioned particle size, between the densely packed cement particles, and using a high dosage of superplasticizer, a drastic delay of the bleeding process is obtained, theoretically corresponding to 100-1000 times slower water movement (vide Figure 8). In practice, this means that bleeding has been obviated, considering that the chemical structuring process normally starts and develops much faster. In order words, by combining high dosage of superplasticizer with silica dust, it becomes possible in practice to produce superfluidized high quality concrete, mortar and cement paste without bleeding. This is of special interest in connection with pre-stressed constructions, where the above-mentioned principles can be utilized for producing high quality non-bleeding, easily flowing injection mortar (grouting mortar) which gives extremely good protection of the tendons and secures an extremely good mechanical fixation, vide the more detailed discussion of this aspect below. In the production of certain cement products, for example asbestos cement panels, the known art technique presently used is either a slip-casting technique (in which surplus liquid is pressed out from an aqueous slurry through filters, cf. the Magnani process in which the pressing is established via a vacuum system) or a high pressure extrusion of a moist powder (where a traditional thickener (Methocell) has been added to obviate the otherwise hardly avoidable internal liquid transport at the outlet and the consequent blocking of the system by particle interlocking). With the DSP materials, it becomes possible to produce such materials in a low stress field by simple rolling processes or extrusion without liquid exchange with the surrounding when a high amount of superplasticizer is incorporated in the mass together with ultrafine particles. While it might seem possible to employ similar rolling or extrusion processes with cement materials with high amount of superplasticizer incorporated, but without the concomitant use of ultrafine particles which is characteristic to this aspect of the present invention, such materials-although they could be made easily flowable with a low water/powder-ratio (but not quite as low as with ultrafine, well dispersed particles)-would, due to the large size of the cement particles, show a marked tendency to local water expulsion in the stressed zones, such as at the rollers or at the outlet in extrusion, with resulting blocking of the particles. This has been observed in practice in experiments with a laboratory extruder with superplasticized, fine grained cement and with superplasticized ordinary cement plus an additive of a fine filler which was finer than the cement, but considerably coarser than the above-mentioned ultrafine silica dust. In both cases, the material had a sandy performance and could not be extruded due to blocking. With an ultrafine silica powder incorporated in the superplasticized cement system in accordance with the DSP principles, such expulsion of water is delayed with a factor of the order of 100-1000 (as calculated from theoretical considerations). The appearance of the cement silica material containing a high amount of superplasticizer is toughly-viscous and cohesive during rolling, while corresponding superplasticized products without the ultrafine silica powder typically appear as friction materials with a tendency to local water expulsion with resulting particle blocking during rolling or extrusion. Easily flowable superplasticized cement materials containing ultrafine silica particles are one aspect of the DSP principle and show a much better internal coherence than corresponding superplasticized easily flowable cement materials without ultrafine silica particles. This is believed to be due to the fact that local liquid transport which contributes to separation, is drastically reduced in the materials with the ultrafine silica particles. (This is illustrated in Figure 10, which illustrates a demonstration of internal coherence of a fluid to plastic mortar. The influence of streaming water (4 liters per minute) for typically 5 to 30 minutes will not result in any visible washing away of material from the mortar). Many advantages are obtained in this manner. For example, the existing possibilities of producing underwater concrete by simple pouring the fresh concrete into the water are considerably improved. Such a technique is known per se and especially developed with superplasticizing additives (without ultrafine powder). However, with ultrafine, well-dispersed silica powder in accordance with the DSP principles, the process is now much more attractive and shows correspondingly extended potential fields of utility. The resistance against internal liquid transport increases with the density of the packing of the ultrafine particles in the voids between the coarse particles. Thus, it is expected that fluidized powder materials consisting of well+dispersed Portland cement (s=4000 cm2/g) and silica dust (s=250,000 cm2/g) will show considerably better internal coherence, higher resistance to internal liquid flow and bleeding, and better processability in rolling and extrusion with 20-40 volume per cent of silica dust than at 5-10 per cent. However, the experience so far obtained indicates that even very small amounts of ultrafine silica dust (typically 1-5%) incorporated between densely packed particles B), in particular in densely packed Portland cement structures may have a marked improving effect compared to similar materials without silica dust. The articles of the invention may be shaped in a low stress field from a composite material comprising
It is to be noted that although the amount of surface active dispersing agent (i.e. concrete superplasticizer) is defined herein by stating the conditions which must be fulfilled in order that the amount be sufficient to disperse the particles in a low stress field (which, expressed in another way, indicates the use of an extremely high amount of the surface activity dispersing agent), this does not mean that the composite material is necessarily used in a low stress field; it may also be used in a higher stress field. Articles with densely packed particles A are obtained from a composite material of the above type where the particles A are present in a volume substantially corresponding to dense packing to fill the voids between the particles B when densely packed. The surface-active dispersing agent is present in an amount sufficient to allow dense packing of the particles A) in a low stress field of less than 5 kg/cm2, preferably less than 100 g/cm2, and the ideal amount of the dispersing agent is one which substantially corresponds to the amount which will fully occupy the surface of the particles A. Figure 2 in EP-A1-0 010 777 shows ultrafine silica particles covered with a layer of a dispersing agent, a so-called superplasticizer "Mighty", the composition of which is described below. Under the assumption that the superplasticizer is absorbed in a uniform layer at the surface of the silica spheres, the calculated thickness, with reference to applicant's own experiments, was 25-41 Å, corresponding to a volume of 14-23% of the volume of the spheres. It is to be noted that a surplus of the dispersing agent over the amount which will fully occupy the surface of the ultrafine particles, will not be advantageous and will only tend to take up too much space in the composite material. Any type of concrete super-plasticizer which in sufficient amount will disperse the system in a low stress field is useful for the purpose of the invention. The concrete superplasticizer type which has been used in the experiments described in the Examples to obtain the extremely valuable results in Portland cement-based systems is of the type comprising alkali and alkaline earth metal salts, in particular a sodium or calcium salt, of a highly condensed naphthalene sulphonic acid/formaldehyde condensate, of which typically more than 70% by weight consist of molecules containing 7 or more naphthalene nuclei. A commercial product of this type is called "Mighty" and is manufactured by Kao Soap Company, Ltd., Tokyo, Japan. In the Portland cement-based silica dust-containing composite materials according to the invention, this type of concrete superplasticizer is used in the high amount of 1-4% by weight, in particular 2-4% by weight, calculated on the total weight of the Portland cement and the silica dust. Other types of concrete superplasticizers useful for the purpose of the present invention appear from Example 2. Portland cement-based composite materials of the type defined above will often contain additional fine particles of suitable size and size distribution together with the Portland cement particles, such as fine sand, fly ash, and fine chalk, to obtain even more dense binary structures formed from the particles B in accordance with the principles discussed above. Both with respect to its unique shaping and workability properties as discussed above and illustrated in greater detail in the examples below, and with respect to its capability of gently fixing and, in the final shaped state, extremely effectively micro-locking or micro-jacketing any incorporated additional bodies, the composite material shows uniquely advantageous properties which have not previously been reported or indicated for any material, and hence, such novel and extremely useful composite materials constitute important aspects of the present invention. Interesting materials prepared according to the invention are Portland cement-based materials containing, as additional bodies, bodies selected from the group consisting of polystyrene bodies, including polystyrene spheres, expanded clay, hollow glass bodies, including hollow glass spheres, expanded shale, perlite, natural lightweight aggregate, gas bubbles, fibers, including metal fibers such as steel fibers, plastic fibers, glass fibers, Kevlar fibers, asbestos fibers, cellulose fibers, mineral fibers, high temperature fibers and whiskers, including inorganic nonmetallic whiskers such as graphite whiskers and Al2O3 whiskers and metallic whiskers such as iron whiskers, heavyweight components such as baryte or lead or lead-containing mineral, and hydrogen-rich components such as hollow water-filled particles. Sand and/or stone as sole additional bodies will result in important novel mortar and concrete composite materials. Important composite materials of the present invention are the materials in which the particles A are silica dust particles having a specific surface area of about 50,000-2,000,000 cm2/g, in particular about 250,000 cm2/g, and the particles B comprise at least 50% by weight of Portland cement. In these composite materials, the dispersing agent is a concrete superplasticizer in a high amount resulting in the above-defined dispersing effect. In accordance with the principles discussed above, the composite material for making the articles of the invention has a very low ratio between water and cement and any other particles B+silica dust, this ratio being 0.12 to 0.30 by weight, preferably 0.12 to 0.20 by weight, and the silica dust may be present in a volume which is 5-50% by volume, in particular 10-30% by volume, of the total volume of the particles A+B. In accordance with a special aspect of the invention, the composite material is packed and shipped as a dry powder, the addition of the liquid, typically water, being done on the job. In this case, the dispersing agent is present in dry state in the composite material. This type of composite material of the invention offers the advantage that it can be accurately weighed out and mixed by the producer, the end user just adding the prescribed amount of liquid and performing the remaining mixing in accordance with the prescription, e.g., in the manner described in Example 11 in EP-A1-0 010 777. The invention also relates to a process for preparing a shaped article or a part of a shaped article, said process comprising the steps listed above. It should be noted that the low stress field stated defines the amount of dispersing agent to be used and does not necessarily mean that the process is in fact carried out in a low stress field. However, the fact that it can be performed in a low stress field constitutes one of the main advantages of the process, and preferred low stress fields (which are preferably below 5 kg/cm2 and more preferably below 100 g/cm2) used for shaping the mass are: gravity forces acting on the mass, such as self-levelling out of a cast soft mass, or forces of inertia acting on the mass, such as in centrifugal casting, or contact forces, such as pressure compaction, rolling or extrusion, or the simultaneous acting of two or more of the above forces, such as in combined vibration and pressure compaction. Also, oscillating forces with a frequency between 0.1 and 10' Hz may be used to shape the mass, the oscillating forces being of the type described above, such as forces from mechanical or hydraulic vibrator, or such oscillating forces may be combined with non-oscillating forces such as in combined vibration and pressure compaction. The liquid used in the process is water, and the dispersing agent is often added together with the water so that an aqueous solution of the dispersing agent is added, but it is also within the scope of the present invention to incorporate the water separately from a solution of the dispersing agent, the dispersing agent being combined with the water in the mixing process. It is characteristic that a mixture conforming with the above-stated definition will have a very "dry" appearance during the mixing stage until it converts into a viscous plastic mass, this "dryness" being due to the low fluid content. The fabrication technique for producing the shaped articles according to the invention must naturally be specially adapted to the specific type of composite material in question and the specific type of shaped articles in question. There are, however, some general trends:
Introduction of the dispersing agent as a dry powder to the dry mix before adding water seems to be an equally valuable way of producing the casting mass of the invention. This was demonstrated in Example 11 of EP-A1-0 010 777 where this procedure was used, resulting in a mortar with substantially the same flowability and appearance as one made from almost the same components, but mixed as described above with addition of the dispersing agent as a solution to the pre-wetted mix (vide Example 9, Mix No. 1, of EP-A1-0 010 777. For any specific system, there is a level at which the system is saturated with superplasticizer and over which there is no beneficial effect in adding further superplasticizer. This saturation point increases with decreasing water/(cement+silica dust) ratio. Above this level, the material is not sensitive to the amount of dispersing agent.
Firstly, as the structure is more densely packed, the solidification will be faster (early strength). Secondly, the solidification may be influenced by the rather large amount of dispersing agent which is necessary in order to obtain the specific structure. In the Portland cement-silica-Mighty systems high early strength was obtained, but a modest retardation of the curing was noted (4-8 hours). In the actual Portland cement-silica-Mighty systems, it was shown, such as could be predicted from the expected calcium silicate hydrate structure to be formed, that extremely good quality could be obtained by curing at as well approximately 20°C, 80°C and 200°C (autoclave), which means that the novel matrix is useful for traditional low temperature curing, heat curing, and autoclave treatment. Heat curing (which in normal concrete leads to slightly smaller strength than curing at low temperature) probably seems to be the most promising curing technique for the material of the present invention. In accordance with what has been stated above, the volume of liquid incorporated in the process is preferably so that substantially no liquid escapes from the mass during the shaping process, which results in several advantages in comparison with known processes where liquid, typically water, is removed from the sludge during the shaping process, typically by some kind of filter pressing operation. While the process of the invention can be said to constitute completely new technology, it can also be considered as a valuable modification of existing tehnology. For example in the preparation of fiber cement products according to the Magnani process, shaping (from a dilute cement/fiber/water slurry) through rolling is performed, with concomitant removal of water by suction. When incorporating ultrafine particles and the extremely high amounts of dispersing agents in the mass to be procesed in accordance with the principles of the present invention, these known technologies can be modified to produce, by extrusion or rolling at a shaping pressure of up to 100 kg/cm2, an (even more dense) material from a viscous/plastic mass which already shows the final low water content so that no water or substantially no water is removed from the mass during the shaping process, and hence, no suction arrangement is required. As indicated above, additional bodies D may (like the bodies C and, to a certain extent, the bodies B) be incorporated at various stages during the process, and these additional bodies D are of the various types discussed in great detail in the preceding text, the only limitation being, of course, that some type of additional bodies such as reinforcing bars or tendons in prestressed concrete can only be incorporated during the casting stage and not in any previous stage. Unique improved possibilities of submersed, in particular underwater construction comprise pouring a cement paste, mortar or concrete of the type of the present invention in the form of a coherent mass into a liquid, typically into water in the sea, a harbour or a lake, and allowing the mass to displace part of the liquid and arrange itself as a coherent mass. Other possiblities of utilizing the extraordinary shapeability properties of the viscous to plastic mass are to shape articles by spraying, painting, or brushing to shape layers on other articles or to shape an article layer by layer, injection or simple hand application of a layer of the mass on a surface and conforming the mass to the shape of the surface. Centrifugal casting technique is another attractive shaping method useful in connection with the process of the invention. In the same manner as disclosed in EP-A1-0 010 777, the articles of the present invention may be further subjected to impregnation to further increase their strength and improve their properties. This method is claimed in Claims 51-56. The preferred materials and methods for performing the impregnation are the same as disclosed in EP-A1-0 010 777. When the particles A are to be densely packed in the materials of the present invention, they are preferably of a size of from 200 Å (20 nm) to about 0.5 µm. While particles A used in the Examples were SiO2 particles formed from vapour phase (in connection with the production of silicium metal in an electric furnace), also other ultrafine SiO2-containing particles may be used, in particular the particles mentioned in EP-A1-0 010 777. However, also in connection with the present invention, the particles formed by growth from a vapour phase are preferred. A novel application of concrete, mortar and similar materials has been made possible with the extremely strong, room temperature-mouldable materials of the present invention, namely the molding of articles with an external shell and an internal part which is totally or partly filled with the strong materials of the present invention (concrete, mortar, paste, etc., reinforced or non-reinforced). This makes it possible to combine desired specific surface properties of the articles (chemical, optical, thermic, mechanic, magnetic etc.) with good bulk properties (especially high mechanical strength and rigidiy) and simple preparation technique (separate preparation of shell with subseqeunt introduction of flowable concrete, mortar or paste). This constitutes a particular aspect of the present invention. There is a number of advantages and potential advantages associated with separate preparation of hollow shells which are completely or partially filled with the materials of the present invention:
On solidification of the cement-based DSP material, a volume contraction takes place as is the case with ordinary cement paste. The volume contraction is considerably higher for the new binder material, 2% against 0.5-1% for ordinary cement paste. This contraction may result in undesirable crack formations and change of shape. The volume contraction is due to the fact that water is being consumed during the chemical structure formation and that the reaction products formed have a smaller volume than the components from which they are formed. This results in internal cavitations and thus internal liquid menisci, causing tensile stresses in the liquid phase which compress the powder mass. The finer the powder material the higher the meniscus-determined tensile stresses and thus the contractions forces. Therefore, when using powder which is 50-100 times finer than cement, considerably stronger contraction force prevail than in ordinary cement paste. This is, e.g., known from draining out of soil, where fine clay shows a distinctive volume contraction, while coarse sand does not substantially change its volume. The volume contraction is also strongly dependent on the hydration products formed, e.g., calcium silicate hydrate, during the hardening, especially their ability to create internal contraction stress when less strongly bound water is moved for being consumed elsewhere in the hydration process. Various precautions may be used or contemplated to reduce or eliminate the volume contraction of the binder, reduce the volume contraction of the composite material and/or reduce or eliminate possibly damaging effects of the volume contraction of the binder especially crack formation.
Due to its extreme tightness and mechanical strength, the material made possible by this invention is useful in a wide range of articles, examples of which are a sheet or panel of thin-walled plane or corrugated shape, such as sheets or panels of the same shapes as the known art asbestos cement products; a pipe; a tube; a refractory lining (e.g., applied as a complete lining) or a refractory lining component (such as a building stone for a refractory lining); a protecting cover (e.g. to protect other materials against chemical influences) such as a cheap protecting cover applied on steel, e.g. steel tubes or pipes, or on ordinary concrete products so as to supply concrete products with a noble surface which is strong, abrasion resistant, and acts as a sealant against influence from the surrounding environment, protecting covers on masonry, pavements and roads, utilizing the same beneficial characteristics of the novel material, and protecting covers on roofing panels or tiles, or on containers; a roofing material such as a roofing panel or tile; an electrically-insulating member; a nuclear shielding for protection against radioactive action (for radioactive-based reactor constructions, etc.) a seafloor structure for deep water applications; a machine part; a sculpture; a container; an in situ cast oil well wall; or a load-bearing member in structural engineering utilizing the extreme strength qualities of the material and its resistance to climatic influence, such as a beam, a shell or a column, typically as reinforced concrete, especially as pre-stressed concrete. Seafloor structures for deep water applications, e.g. spherical containers to withstand large hydrostatic pressures require concretes of a high strength, high durability and low permeability. "Polymers in concrete", ACI Publication SP-40-1973, P 119-148, report model tests on small 16 inches diameter spherical hulls made of high quality polymer-impregnated concrete for deep water applications. Full impregnation was obtained by a complicated drying vacuum outgassing-pressure procedure which is, in practice, limited to small size members. With the materials and processes according to the present invention, it is now possible to produce such structures in large scale (several meters in diameters) with a similar high quality material by a simple fabrication technique. Examples of articles of the invention are the following structures which may be produced by casting adjacent to or between surfaces: Large electric insulators are today made from glass or ceramic materials, especially because of the excellent insulating properties of these materials. It is of special importance to prevent currents along and in the surface layers. Besides, large insulators demand high mechanical strength and a good ability to absorb mechanical energy. This is difficult to obtain with brittle materials such as glass and ceramics to which it is difficult to impart "toughness" by reinforcement (due to the fact that they are shaped from fluid masses at high temperatures and solidify under relatively great volume changes). However, in accordance with this aspect of the present invention, high material strength and good ability to absorb mechanical energy may be obtained in such large electrical insulators by producing large hollow jackets or shells of glass or ceramics which are fortified with reinforced high quality DSP concrete, mortar or paste prepared by casting of soft mass (injection, etc.); the reinforcement may be placed in advance in the interior of the jacket or shell (large steel bars, etc.), or the reinforcement may be part of the casting mass (e.g. chopped fibers). It is contemplated that this will make it possible to realize a cheaper production of large insulators in the sizes in which they are produced nowadays, and to produce far larger insulators than those known today. Furniture, shelves, doors, etc. which, due to requirements concerning appearance, tactile sensation, cleanability, chemical durability, etc., require special surface properties combined with good mechanical bulk properties (strength, toughness) may be prepared from hollow membes of plastic, metal and the like (e.g. prepared by extrusion) which are filled with a reinforced DSP binder by pouring, injecting etc. Strongboxes and other strong containers which may be produced by filling the cavities in doors and walls with the DSP material by casting of soft mass (injection etc.); all or parts of the internal reinforcement and hard components (e.g. bauxite stone) may be placed in advance. Containers for radioactive waste in which the radioactive waste is cast into the above-mentioned strong materials, by injecting a paste or mortar of the DSP materials into the container room in which all or part of the reinforcement, the radioactive waste in solid form and various rigidity-imparting elements (e.g. bauxite stones) have been placed in advance. Very large sculptures of desired surface materials, which in an inexpensive way may be given the required mechanical strength by filling a thin shell with reinforced mortar or concrete prepared according to the principles mentioned in the previous examples. Load-bearing constructions with special requirements for surface materials (pillars, walls, floors, roof elements etc.). Ship hulls with an exterior and an interior of materials with special properties (e.g. smooth exterior and heat insulating interior) where the necessary part is filled with reinforced DSP concrete, mortar or paste by injection etc. Tubes with an exterior and an interior comprising materials with special properties (e.g. acid resistant interior and heat insulating exterior) where the interspace between the tube walls is filled with reinforced DSP concrete, mortar or paste by injection etc. As mentioned above, there is a number of advantages and potential advantages associated with separate preparation of hollow shells which are completely or partially filled with the DSP materials. In this connection, it should be emphasized, e.g., that very large thin-walled members with monolithic reinforced load-bearing core may be prepared. For example, it is possible to produce long stretches of tubes with monolithic strong reinforced core in the tube walls (for example, in connection with lines of the sea floor where tubes having hollow walls of plastic or the like are correctly positioned, the interspace being filled with stone and reinforcement, whereafter, the tubes are filled with DSP paste or mortar by injection). Other members which may be prepared in this manner are ship hulls, large building sections, tunnel linings and the like. The possibility of producing, with a simple casting technique and at room temperature, reinforced concrete, mortar and paste with very high strength and acceptable toughness makes it possible to produce members which are traditionally produced of metal. Such members are in particular large load-bearing members traditionally produced as metal castings (covers, lids, large valves, load-bearing machine parts, etc.) and structural members (masts, beams, and the like). The high hardness of the DSP materials, combine with the fact that they can easily be made tough through fiber reinforcement, makes it possible to use the materials as milling or grinding bodies and abrasion aggregates, typically produced by ordinary casting of soft mass, extrusion, or compression. A specially promising production for producing articles of DSP is compressing shaping from DSP materials of the invention having a plastic to stiff plastic consistency. This is a fast process which requires considerably less mold material than ordinary casting, and which permits the preparation of products of a considerably higher quality than is obtainable by ordinary casting, considering that the water/powder ratio is considerably lower in compression shaping (typically 0.08 to 0.13 versus 0.20 in ordinary casting of cement/silica paste-based articles), and which permits incorporation of more fibers and finer fibers in the compression-shaped masses (thus, e.g. the compression shaping of plastic cement/silica paste is performed using up to 6 per cent by volume of glass fibers of diameter 5 pm and length 12 mm). Prior to the compression shaping, the semi-finished product is formed which subsequent to the compression becomes the desired article. The semi-finished product is formed by mixing processes and various forms of pre-treatments (e.g., extrusion or rolling) to ensure a desired fiber orientation and a desired starting shape of the semi-finished product. The semi-finished product is placed in a press, a rolling mill or the like the faces of which facing towards the product ensures that the compressed articles obtain the desired shape. Examples are shown in Figures 24 to 30. By moving one or several parts of the compression tool, the material is pressed into the cavity, thus forming the desired article having the desired shape. Upon removal from the compression faces, the shaped article may be withdrawn from the press to a lesser or greater extent supported by mechanically stable molds, the requirements to the stabilizing molds being dependent upon the mechanical stability of the compressed material, the geometry of the article (size and shape), external influences subsequent to the compression (gravity, vibrations, etc.) and the requirements concerning the dimension and shape tolerances of the article. In the present context, the term "semi-finished product" designates the bodies which, on compression are converted into the compression-shaped articles. The semi-finished articles may be formed from the above-described components (particles, fibers, other components, liquids, etc.) and may, likewise, be shaped in one of the above-described processes for shaping the finished article (extrusion, rolling, vibro pressing, spraying, etc.) or by compression shaping (when the production is performed by successive compression shaping operations). The semi-finished products may be formed from various partial components which, in the compression operation, are shaped to form a unitary product. Thus, e.g., panel-shaped articles having specific fiber arrangements may be formed by placing layers of thin extruded panels (with the fibers substantially oriented in the direction of the extrusion) in suitable and desired orientation relative to each other, such as illustrated in Figure 25, and desired articles to be incorporated, such as electrical resistance units, tubes, cables, sockets, reinforcements etc, or various other parts (steel panels, wood bodies, etc.) may be cast into the resulting article in the compression shaping, such as illustrated in Figures 24-27. As mentioned above, the compression is performed by moving one or several parts of the compression tool relative to the material to be shaped, and thus pressing the material into the desired shape. Often, the shaping cavity is closed all over, and the material is made to fill all of this room by being pressed against non-resilient mold sides. This is a compaction process. In other cases, the compression is performed in cavities which are not completely closed on all sides. An important example of this is the compression process termed extrusion where material is pressed out of an orifice having a specified cross section, thus resulting in an article having said cross section, or by a stamping which is often a local compression shaping. A specially interesting technique is rolling with flexible rollers. As previously mentioned, there will normally not be any pressing out of liquid from the blank to the surroundings, which is one of the substantial advantages of the DSP casting mass. However, using drained compression, it becomes possible to construct a new type of materials consisting of coarse components (large in comparison with the particles B) arranged in dense packing corresponding to what may be obtained with the components in question in a compression process (possibly vibropressing) glued together by means of a high quality DSP paste. The specimen consisting of the coarse components is compressed in one of the following manners:
In the first-mentioned case, the compression is, such as mentioned above, accompanied by liquid expulsion. The compression apparatus is adapted to be able to drain the expelled liquid without any substantial interference with the compression process. Using processes of this kind, it becomes possible to produce articles having a good stability immediately after compaction. After the compression shaping, a specimen having a more or less stable shape has been formed. Dependent upon the stability, various degrees of support of the specimen may be utilized:
The specimen and the supporting means may be combined in the press, part of the shaping surface being a mold which, subsequent to the compression, accompanies the specimen as a shape support (the molds may e.g., be thin compression-shaped metal bodies) or which is brought into contact with the specimen in a separate process after the specimen has left the press. In many cases, the compressed specimen is surface-treated immediately after the compression, primarily to prevent drying out in the further processing. The surface treatment may be performed by application of curing compounds to avoid evaporation, which may, e.g. be applied by brushing, smearing, spraying, etc., or by application of evaporation-impeding removable film, after the specimen has left the press or in connection with the compression process by transfer from the shaping surfaces of the press. In many cases, the above-mentioned supports may also be utilized in the application of a surface treatment, or may render a surface treatment superfluous, or the support may constitute the surface treatment (e.g., a ceramic shell applied in the press). Finally, the compression may be accompanied by processing securing some kind of solidification of the specimen-in addition to the solidification resulting from the pressure itself. As examples may be mentioned simultaneous application of heat (by heat transfer from the press or by electro or micro wave heating) or eliciting of polymerization of a polymerizable component included in the liquid phase. A cement/water-based DSP composite material of the invention may be retarded with respect to its chemical structure formation and/or stabilized with respect to its shape by freezing the DSP composite or the semifinished product. In this manner, the composite material or the semi-finished product can be pre-mixed or pre-shaped, respectively, and thereafter transported to a desired site of use where the structure-forming process can be allowed to proceed further by thawing the product, possibly combined with subsequent shaping. The DSP material subjected to this process may be pre-shaped in any of the manners described in the present specification. Shaping of DSP materials of the invention may also be performed in a high stress field, typically between 5 and 100 MPa, in special cases, between 100 and 1000 MPa, and in extreme cases between 1000 and 10000 MPa. The high stress shaping will usually be combined with a pre-shaping of the DSP material at lower stress, typically designed to achieve
The high stress field shaping may typically be applied during solidification e.g. by hot or cold pressure sintering, or-typically for cement products-by structure formation during hydration. By the high stress field shaping, denser structures are obtained. It is known to shape articles in high stress fields by powder compaction, pressure sintering, etc., but in these known methods, it is not easy and in most cases not possible to obtain a desired predesigned micro structure. Utilizing the structure formation techniques of the present invention in a superplasticized material in a low stress field, the desired particle/fiber arrangement may be pre-designed, whereafter the high stress treatment may be performed on the thus pre-arranged structure. Articles which are typically made by means of the high stress shaping are, e.g., machine parts which are to be subjected to high stress, aircraft or spacecraft parts which are to be subjected to extreme mechanical loads, and other articles which are subject to severe conditions during their use, including highly fiber loaded articles combining extreme resistance and hardness with high tensile strength and ductility. An especially interesting technique is to combine the high stress field shaping with various pre-arrangement methods which are described in the section "Compression shaping of DSP". The various semi-manufacture production methods described in that section can suitably be combined with a post-treatment of the semi-finished article in a high stress field. Especially, the high stress field shaping of DSP makes it possible to combine high hardness and abrasion resistance with a high degree of ductility (obtained by high fiber load), which are properties which it is normally very difficult to combine by means of known art techniques. The DSP composite of the invention and/or DSP semi-manufacture may be in a field of 5-100 MPa, in special cases 100-1000 MPa, and in extreme cases 1000-10000 MPa. A DSP material of the invention, e.g. a cement-based DSP material may also be solidified at a high stress level, typically at 0-5 MPa, for example by solidification between platen members in a press. In special cases, the solidification may be performed at higher stress levels, such as 5-100 MPa, and in very special cases at stresses between 100 and 1000 MPa or even between 1000 and 10000 MPa. If desired, the solidification in a high stress field may be combined with treatment of the DSP composite material prior to shaping by high shear treatment, for example by passage, optionally repeated passage, through narrow nips of multiple rollers, in accordance with the technique described in EP-A1-0 021 682. The names "Mighty", "Lomar", "Melment", "Betokem", and "Sikament" are trademarks. The materials used in this Example were as follows: White Portland cement:
Silica dust Fine spherical SiO2-rich dust. Specific surface (determined by BET technique) about 250,000 cm2/g, corresponding to an average particle diameter of 0.1 µm. Density 2.22 g/cm3. Bauxite Refractory grade calcined bauxite, 85% Al2O3, density 3.32 g/cm3 for sand 0-4 mm, 3.13 g/cm3 for stone 4-10 mm. Mighty A so-called concrete superplasticizer, sodium salt of a high condensed naphthalene sulphonic acid/formaldehyde condensate, of which typically more than 70% consist of molecules containing 7 or more naphthalene nuclei. Density about 1.6 g/cm3. Available either as a solid powder or as an aqueous solution (42% by weight of Mighty, 58% by weight of water). Water Common tap water. Preparation of cylindrical concrete specimens from wet concrete mixed with silica dust/cement binder and calcined bauxite sand and stone: Concrete specimens were prepared from one 23 liters batch of the following composition: Mixing Coarse aggregate, cement and Mighty powder were dry-mixed in a 50 litre paddle mixer for 5 minutes. Thereafter, the silica dust was admixed, and mixing was continued for 10 minutes. The water was added, and the mixing was continued for approx. 10 minutes. Fresh concrete The concrete was soft and easily workable. Casting 6 concrete cylinders, diameter 10 cm, height 20 cm and 2 slabs (40×30×5 cm) were cast at 20°C. The specimens were vibrated for 10-30 seconds on a standard vibrating table (50 Hz). Curing Immediately subsequent to casting, the closed molds for the cylinders were submersed in water at 60°C and cured for 5 days. The slabs were covered with plastic film and cured one day at 20°C in air after which they were submersed in water at 60°C and cured for 4 days. After curing, the specimens were demoulded and stored in air at 20°C and approx. 70% relative humidity until testing (testing was performed within a period of 30 days subsequent to the heat treatment). Testing Density, sound velocity, dynamic modulus of elasticity, compressive strength and stress/strain curve were determined for the 6 concrete cylinders (stress/strain curves were determined for two specimens only). In the table below, the test results are shown. Experiments were made with various concrete superplasticizers in order to determine the water demand to obtain the fluid to plastic consistency of the mass to be cured. The following types of superplasticizers were used:
In all the series, the following common components were used (with reference to one batch): The SPT-amounts were determined so that the content of dry matter was at least 82 g per mixture. A somewhat greater dosage was used with Betokem and Sikament. The following components were different: The mixing was performed in a kneading machine with planetary movement, using a mixing blade. The following procedure was followed:
The water demands, that is, the amount of water used in the various mixes in order to obtain the specified consistency, were ascertained by trial mixing. The water demands appear from Table II below. The consistency was evaluated by measuring the spreading of a cone of the material formed by pouring the material into a 5 cm high brass cone mould with bottom diameter 10 cm and upper diameter 7.1 cm on a flow table with brass surface for use in testing hydraulic cement (ASTM C 230-368) and removing the mold. The diameter of the material was measured a) immediately subsequent to removal of the mold, b) after 10 strokes, and c) after 20 strokes. The consistency was considered to be of the desired value for diameters of about 12 cm after 10 strokes and of 14 cm after 20 strokes. The experiments can be compared with the experiments in Example 7 in EP-A1-0 010 777, series 1, Table V. Sand, cement, and silica amounts are the same as in that Example, the silica dust and the cement, however, originating from later batches. Another difference is that in Example 7 of EP-A1-0 010 777, Mighty powder was used and was dissolved immediately prior to mixing, whereas in the present experiment a Mighty solution delivered from the manufacturer was used. It will be noted that the water demand in all cases with high dosage of superplasticizer was low, ranging from 500 g in Example 7 in EP-A1-0 010 777 to 600-650 g for Melment in the present experiment, corresponding to water/powder ratios of 0.15-0.19 by weight. This to be compared with 1200 g of water and water/powder ratios of 0.36 in mortar without superplasticizer. It will be noted that there are minor differences between the water demands of the various types of superplasticizer, Mighty being among the best. All of the superplasticizers, however, appear to result in the extremely good flow properties of cement+silica dust binder with very low water content, which are characteristic to the materials of the present invention and of EP-A1-0 010 777. The purpose is to evaluate the resistance of various sand and stone materials to deformation on powder compaction, and in particular, to compare natural concrete aggregates with particularly strong and hard materials. Quartz sand 0.25-1 mm, quartz sand 1-4 mm, crushed granite 4-8 mm, refractory grade bauxite 0-4 mm, refractory grade bauxite 4-10 mm, silicon carbide 0.5-2 mm (Qual. 10/F PS-K Arendal Smelteværk A/S, Ejdenhavn, Norway). The individual fractions of particles are relatively uniformly graduated, corresponding to the ratio between the largest and the smallest grain size (particle size) substantially not exceeding 4. Samples of the individual sand and stone fractions were compressed by uniaxial die pressing. The compaction equipment consists of a cylindrical die cylinder open in both ends, and two cylindrical pistons (diameter of the die cylinder 30 mm, powder height on filling about 32 mm and after finished compression 16-23 mm depending upon the type of powder). Dry materials were poured loosely in the die cylinder. The compaction was performed in an Instron testing machine having constant compaction rate (5 mm/min) up to a compaction pressure of 350 MPa, whereafter the pressure was released by moving the piston in opposite direction. During the compaction and release, force/displacement curves were plotted. From the curves of force/displacement, comparisons of compaction pressure to obtain identical "density" was performed for the individual materials. The results appear from Table III below. It will be noted that the compaction pressure to obtain same degree of compaction is considerably higher for the hard materials (bauxite and silicon carbide) than for materials usually used as additives in concrete (granite and quartz). The powder compaction technique is suitable for comparing the strength of particles, provided the various particle materials or particle compositions have about the same particle geometry and provided that the particle size is relatively large in comparison with the dimensions of the die cylinder. These conditions have been reasonably fulfilled in the experiments with quartz sand and fine bauxite (in these cases, the particles are compact, rounded and small). In the experiments with granite stone and coarse bauxite, the particle/die ratio was somewhat too large (about 0.2-0.3) for permitting a direct comparison between the results of the test with quartz sand and with fine bauxite. On the other hand, mutual comparison of the two is reasonable. It is difficult to compare the results of the experiments with silicon carbide with the remaining results, considering that this powder material, in contrast to all the other materials, had very sharp edges. Two different types of mortar mixes were prepared, both on the basis of low alkali sulphate resistant Portland cement, silica dust, and Mighty, but with different types of sands, namely refractory bauxite and silicon carbide (Qual. 10/F PS-K, Arendal Smelteværk A/S, Ejdenhavn, Norway). The purpose was to investigate mechanical properties of mortar made with very strong sand, compare Example 3, and with the very strong silica/cement binder described in EP-A1-0 010 777. In all the mixes, the following common components were used (with reference to one batch): For the bauxite mortar, the following components are used: For mortar with silicon carbide the following components were used: The amounts of sand, cement and Mighty used (after volume) are the same as the amounts used in Example 9 in EP-A1-0 010 777. In the mortar with bauxite, the water amount was also the same as in Example 9 in EP-A1-0 010 777, whereas the water amount in the mortar with silicon carbide was considerably higher. This was due to the fact that the silicon carbide sand had very sharp edges and therefore required a more easily flowable silica/cement paste and/or a larger amount (by volume) of paste. For each of the two types of mortar, two batches were prepared, one having the composition as stated above, the other one of double size. The mixing was performed in a kneading machine with planetary movement, using a mixing blade. The following procedure was followed:
The mortar mixtures behaved like highly viscous fluids and were cast in cylindrical molds (height 20 cm, diameter 10 cm) on a standard vibrating table (50 Hz). The casting time was about 1 minute. The specimens (in closed molds) were cured in water at 80°C for 4 days. Density, sound velocity, dynamic modulus of elasticity, compressive strength and stress/strain curve were determined. The compressive strength and the stress/strain curves were determined on a 500 tons hydraulic press using a rate of stress change of 0.5 MPa per second. The results obtained appear from Table IV: Stress/strain measurements were performed on two specimens from each series. The samples were loaded to about 60% of their rupture of load and were thereafter released, whereafter they were again loaded up to rupture without recording of stress/strain. A few of the samples were loaded and released several times. The stress/strain curve for the bauxite mortar was practically a straight line throughout the complete measuring range (0-150 or 160 MPa) with a slope (secant) corresponding to a modulus of elasticity of 84300 MPa. On repeated loading and unloading, only insignificant hysteresis was noted. The stress/strain curves for the mortar with silicon carbide (measuring range 0-100 MPa) bent somewhat with initial slope corresponding to a modulus of elasticity of 86000 MPa and modulus of elasticity at the pressure of 100 MPa of 72000 MPa. On repeated loading of 100/120/140/160 MpP, a specimen of the silicon carbide mortar showed marked hysteresis indicating internal structure deterioration. The compressive strength for mortars with bauxite did not seem to be significantly influenced by pre-loading up to 150-160 MPa, whereas the strength of the mortar with silicon carbide was considerably lower for the samples which have been previously loaded. The values of the compressive strength for the pre-loaded specimens of the silicon carbide mortar were, therefore, not included in the results in Table IV. It will be noted that the mortar with bauxite sand is extremely strong and rigid, having compressive strengths of 248 MPa (maximum value for two of the specimens were 254.2 MPa corresponding to a load of more than 200 tons). The rupture proceeded to a large extent through the bauxite sand, indicating the possibility of producing even stronger mortar by utilization of even stronger sand materials. The compressive strength of the mortar with silicon carbide was considerably lower (184.3 MPa) and is not much higher than for the corresponding mortar containing quartz sand (160-179 MPa, cf. EP-A1-0 010 777, Example 9) which might seem strange in view of the great hardness and strength of silicon carbide per se. The reason is undoubtedly that the mortar with silicon carbide used considerably more water than the mortar with bauxite and the mortar with quartz sand referred to in EP-A1-0 010 777. This results in a considerably weaker binder. The water/powder ratio (total water in relation to cement+silica by weight) was 0.149 for the bauxite or quartz mortars and 0.179 for the silicon carbide mortar. The rupture proceeded to a large extent outside the silicon carbide particles. This, compared with the bending stress/strain curve and the large hysteresis (which is characteristic to brittle materials where the particles are considerably stronger than the matrix) indicate the possibility of obtaining considerably higher strength by improving the matrix. This can be achieved by reducing the water/powder ratio to, e.g., 0.13-0.15, which is possible by using a somewhat coarser silicon carbide sand and/or larger amount of cement and silica. Additional 16 cylinders of the bauxite mortar have been prepared with the same composition and using the same technique as above with the exception that the bauxite was from a later batch. The purpose was to examine various mechanical properties. At first, density, sound velocity and dynamic modulus of elasticity were determined on all 16 specimens. As a guidance, the tensile strength was determined on two of the specimens. The results are shown below. The same density as above was found, while sound velocity and dynamic modulus of elasticity were somewhat lower. The reason for this is unknown, but is believed to be due to an error in the determination of the time for travelling of sound impulse (either in the test on page 27 or the test above). The strengths were slightly higher than above. The highest value of 268.1 MPa corresponds to a load of 214.6 tons and a pressure of 2732 kg/cm2. A bauxite mortar was prepared having the same composition and using the same technique as mentioned in Example 4 with the exceptions
From each of the four batches 4 cylinders (height 20 cm, diameter 10 cm) were cast. Density, sound velocity, dynamic modulus of elasticity and stress/strain curve were determined using the technique described in Example 4. The results appear from below Table V. The stress/strain curve is shown in Figure 14, together with a similar curve for ordinary concrete normally considered to be of very high quality (compressive strength 72 MPa). It is seen that the bauxite-cement-silica mortar has a compressive strength (270 MPa) approximately four times higher than that of traditional high quality concrete and a modulus of elasticity (slope of the curve) approx. twice as high. One of the specimens had a compressive strength of 282.7 MPa and a density of 2861 kg/m3 which corresponds to a stress/density-ratio of 98812 (m/s)2. The load of the cylinder corresponds to the base load of a 10076 meter high prism prepared from the material. (By way of comparison it may be mentioned that the yield load of high quality structural steel (400 MPa) corresponds to the base load of a 5200 meter high steel prism). In the drawing,
Reference is made to the drawing, where like numerals generally designate like parts. In Figure 1, which illustrates a typical DSP matrix structure 10, 12 designates substantially densely packed particles B, e.g., Portland cement particles, and 14 designates homogeneously arranged and optionally densely packed particles A, e.g., particles of silica dust homogeneously dispersed in water by means of a concrete superplasticizier, or a coherent unitary structure formed from such particles and from solid inter-particle substance formed by chemical reaction between solutes generating from the cement particles. The system shown in Figure 1 has typically been established by gentle mechanical means, e.g. by shear or vibration, or simply under the influence of gravity. In Figure 2, the particles B(12) comprise larger particles and smaller particles, with gap grading between the particles B. The system of Figure 2 has typically been established using the same means as described in connection with Figure 1. However, in Figures 1 and 2, 14 may also designate ultrafine particles which have been homogeneously arranged by means of a surface active agent in accordance with the fluid DSP system establishment processes of the invention, but which are now surrounded by an inter-particle substance which is different from the fluid by means of which the particles were arranged and which has been introduced by exchange of the original fluid by infiltration. In Figure 3, compressible bodies 12, e.g. polystyrene spheres constitute the densely packed particles B, and homogeneously arranged or densely packed particles A, typically rigid small particles surrounded by inter-particle substance, fill the voids between the adjacent densely packed gas bodies B. However, Figure 3 also illustrates the case where the bodies 12 are compressible bodies of a larger size than the particle B size, and 14 is a solidified DSP paste which, in itself, comprises substantially densely packed particles B with homogeneously arranged and optionally densely packed particles A and inter-particle substance in the voids between the particles B, the DSP paste, hence, having a structure as illustrated in Figure 1 or Figure 2. In Figure 4, fibers or elongated particles 12 constitute the densely packed bodies B, and homogeneously arranged and optionally densely packed particles A in inter-particle substance fill the voids between the densely packed bodies B. In this case, the dense packing of the bodies B refers to dense packing as obtained by simple mixing and casting with the maximum fiber load limited by the mixing and shaping process only. Also, in this case, the inter-particle substance may be a substance which is different from the fluid by means of which the particles were arranged, the inter-particle substance now present being a substance introduce by exchange of the original fluid by infiltration. In Figure 5, the densely packed fibers or elongated bodies 12 show a dense packing of bodies B referring to a most efficient manner of establishing dense packing of non-compressible fibers: parallel placing of the elongated bodies or fibers with homogeneously arranged and optionally densely packed particles A in the interspace between the densely packed bodies B. This structure has been established, e.g., by filament winding of the fibers 12 immersed in a slurry of homogeneously dispersed and optionally densely packed particles A. The structure shown in Figure 5 is typical of the structure desired in ultra high quality, highly fiber-loaded stress and abrasion resistant materials where the inter-particle fluid between particles A which are, e.g., densely packed microfine metal particles, has been replaced, by infiltration, with a strong inter-particle substance, e.g., a metal or a polymer. In Figure 6, Portland cement particles 16 form an open flocculant structure in an aqueous phase in the absence of surface active agents. Figure 7 illustrates how such a system will normally show a tendency to sedimentation of the cement particles when the flocculating tendency is eliminated by means of a superplasticizer. Figure 8 illustrates, in further enlarged scale, a DSP paste system, e.g. a cement/ultrafine silica system with superplasticizer where the voids between the cement particles 12 are filled with a suspension of ultrafine silica particles 18 which are substantially densely packed in the suspension. 20 designates the inter-particle substance, in this case, e.g., superplasticizer solution. In such a system, the tendency to sedimentation of the particles is minimized due to the extremely slow water flow around the ultrafine particles in accordance with classical hydrodynamics. Figure 9 illustrates a fine reinforcing fiber 22 embedded in a DSP matrix 10, e.g., a cement-based DSP matrix. By using such a cement-based DSP matrix instead of ordinary cement paste, the mechanical fixation of the reinforcement is increased even more than the strength, this increase being one or several orders of magnitude. This is because the dimensions of the "roughness" or "wave configuration" of the fiber which are necessary to obtain "mechanical locking" of the fiber in the matrix are reduced one to two orders of magnitude, which also means that in the DSP matrix, it becomes possible to obtain mechanical locking of fibers which are one to two orders of magnitude smaller than the smallest fibers which can be mechanically locked in ordinary cement paste. Figure 10 demonstrates the surprising internal coherence of the fresh fluid to plastic cement-based DSP mortar 24 placed on a supporting glass plate 26 under vibration (50 Hz-10 s) and then kept under flowing tap water (rate of outflow about 4 liters per minte). In this demonstration, the mortar is typically kept under the flowing water for periods of 2-30 minutes without any visible washing out of the components thereof. The mortar was prepared as described in Example 9 of International Patent Application No. PCT/DK79/00047. Figure 11 illustrates the repair of a bridge construction 28 in flowing water 30 a river by underwater injection. Between a base structure 34 of ordinary concrete 36 and a foundation 38, erosion cavities 40 had exposed wood piles 32, incurring danger of severe damage of the piles. Easily flowing cement-based DSP paste 24 was pumped through one of drilled holes 42 into the cavity 40. Due to its higher density, the DSP paste displaced water from the cavity 40 and rose into the remaining holes 42, completely filling the cavity and the holes and forming a new cover, also on top of the foundation. All casting was performed under water, and the river flow over the freshly case DSP concrete, which, however, had such a high degree of internal coherence that substantially no washing out occurred. Figure 12 illustrates the repair of a wall element 44 of a subwater tunnel under a bay. An easily flowable DSP material 24 was filled into the cavity to be repaired. The cavity had a complicated shape and was heavily reinforced with steel reinforcement 46. The DSP material was introduced from one side through a hose 50 and rose at the other side of an existing concrete wall 36 and filled the cavity between the concrete wall and formwork 48. Figure 13 illustrates casting of a lining of high abrasion resistance inside a steel pipe 52 used for transportation of powder (coal). A plastic tube 54 filled with sand 56 with placed in the interior of the pipe and was kept in position by means of bracings 58. A steel fiber-reinforced DSP material 24 based on Portland cement and refractory grade bauxite was poured into the pipe 52 under slight external vibration and completely filled the space between the steel pipe 52 and the inserted plastic tube 54. After curing of the DSP material, the sand was removed, and the plastic tube was pulled out. Figure 14 is a stress-strain diagram recorded during compression testing of 10 cm diameter, 20 cm high cylinders of ordinary high quality concrete and DSP mortar with sand consisting of up to 4 mm refractory grade bauxite, respectively. The DSP material was Densit-S™ from Aalborg Portland, Aalborg, Denmark. The compression strengths measured were 72 and 270 MPa, respectively. Figures 15, 16 and 17 illustrate compaction of DSP concrete or mortar in a vessel 62 where a surplus of fluid DSP paste 68 is squeezed out of the mass and flows past aggregates 64 and the passage between a piston 66 and the wall of the vessel 62 as the piston is moved down. Hereby (Figure 16), the aggregate skeleton is compressed. After compression, the surplus of paste is removed (still with load on the piston). Hereafter, the piston is removed, and the aggregate skeleton expands slightly (elastic spring back), pulling the paste 68 slightly into the voids (a suction) whereby inwardly curved paste/gas interfaces are formed, which, due to surface forces, stabilize the compacted drained material. Figure 18 illustrates rolling of a plastic DSP material 68 by means of a pair of rollers 70 of an elastic material with a spacer member 72 inserted between the rollers to form a semi-manufactured plate or sheet of DSP material which may be further shaped. Figures 19 and 20 illustrate the shaping of such a semi-manufacture plate or sheet 74 between halves 76 of a compression mold (which may in themselves be made from a DSP material) to form a tube section 80. Figure 21 illustrates the extrusion of a DSP material. From an extruder die 82, an extruded string 84 of DSP material passes a support 86 where electrical components 88, e.g. resistance components, are inserted into the V-shaped extruded string. The string is cut by means of a cutter 90, and the resulting sections 92 are thereafter compressed in a compression mold 76 to form DSP-encapsulated components 94. Figure 22 illustrates compression shaping of DSP material 68 between a lower and an upper mold part 96 and 98, respectively and Figure 23 illustrates the compression shaping of a large kitchen table/wash basin element from DSP material 68 in a large mold 100, 102. Figure 24 illustrates the preparation of a reinforced DSP panel member by compaction of fresh rolled plates 110 and 112 of cement based DSP on each side of a steel reinforcing grid 108 in a press 104, 106. Figure 25 illustrates the preparation of a sandwich element of fiber-reinforced DSP material where the fiber orientation in the upper component 110 is perpendicular to the fiber orientation in the lower component 112. Figures 26 and 27 illustrate embedding sanitary tubing 114 or heating tubing 116 in DSP construction elements. In Figure 28, a fresh rolled plate cement-based DSP material is cut into bricks or tiles 120 by means of a grid-like cutter. Figure 29 illustrates barrier effect when a large body or particle 221 close to a wall 223 impedes small particles 18 from entering into the narrow space between the large particle of diameter D and the wall. The size of the space not accessible to the particles 18 is designed f. Figure 30 illustrates wall effect showing particles 258 adjacent to a wall 256. The particle concentration is lower in the narrow space adjacent to the wall than in the bulk. The thickness of the narrow space adjacent to the wall is approximately 1 particle diameter. Figure 31 illustrates the sedimentation of rod-shaped particles 248 in a liquid 250. Sedimentation from a liquid with a low concentration of particles or fibers in the absence of surface forces results in a rather dense packing due to the fact that the fibers are allowed to turn freely into horizontal position without interference with settling neighbouring particles. |
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