Mix for rural and road building and process for the preparation thereof

The present invention relates to a mix for rural and road building and to a process for preparing the same.

More particularly the present invention relates to an essentially inorganic or mineral mix for rural and road building, based on a mixture of inert and incoherent materials stiffened by a binder comprising an interlacement of acicular crystals of aluminocarbonates produced "in situ" in said mix.

It has been found that by effecting the formation of crystals of such aluminocarbonates in suitable mixtures of inert, incoherent materials which can be found easily in nature, mixes may be obtained which are characterized by excellent mechanical properties and which, therefore, can be used in the field of rural and road building.

Accordingly the present invention provides a mix for use in rural and road building, comprising the following components:

• (a) at least one silicate containing alumina and calcium;
• (b) at least one carbonatic rock;
• (c) a crystallization orientator; and
• (d) optionally, a basicity regulator,

Preferably the mix comprises

20 to 80% by weight, with respect to (a+b), of the above component (a);

80 to 20% by weight, with respect to (a+b), of at least one carbonatic rock;

0.1 to 15% by weight with respect to the sum of components (a) and (b), of component (c); and

0.1 to 15% by weight, with respect to the sum of components (a) and (b), of component (d).

Suitable examples of modified silicates, i.e., silicates in which the hydrolysis by atmospheric agents has just started, are tectosilicates, phyllosilicates, inosilicates, neosilicates, sorosilicates, clays (illite) and granite.

Suitable examples of carbonatic rocks are limestone, dolomite, marble and calcite.

As the substance capable of orienting (initiating) the salt crystallization for the mix of the present invention, urea is used.

As the formation of aluminocarbonate crystals is effected in a basic medium, it is preferred that the mixture, before the thermal treatment, has a pH of at least 7, preferably of from 9 to 12.

If use is made of a basicity regulator, this regulator can be selected, e.g., from those of natural origin (such as basic metamorphic rocks), those of artificial origin (such as lime), and from those coming from a chemical synthesis (such as soda, ammonia and the like). Said regulator is generally used in amounts which allow to obtain the above pH values.

The components of the mix of the present invention are mixed to give rise to a plastic and moldable mixture.

The water necessary to obtain said mixture is used in amounts which depend on the kind of starting materials employed and on the granulometric distribution thereof. Generally, however, said amount ranges from 5 to 70% by weight, based on the total composition.

The thus obtained mixture is treated thermally at not too high a temperature for times sufficient for removing the excess water and for increasing the initial rate of aluminocarbonate crystallization. The most suitable temperatures are above 30°C and preferably range from about 35 to about 60°C.

Since the crystallization of the aluminosilicates can also take place (although slowly) at temperatures below 30°C, mixes according to the present invention can also be obtained by removing the excess water from the mixture by natural evaporation at room temperature, generally ranging from 5 to 25°C.

The mix of the present invention generally shows an ultimate tensile compression stress at 180 days (measured according to UNI 6132) of 5 to 20 MPa, an ultimate tensile bending stress at 180 days (according to UNI 6133) of from 1 to 4 MPa and a water absorption by dipping (7 days) of less than 50% by weight, most frequently of from 10 to 25% by weight.

The mix of the invention tends to develop considerable mechanical resistance over time and therefore it can be used as layer for road foundations or for preparing building blocks, suitable for use in the builing of anti-desert barriers, anti-wind barriers, etc.

The process for preparing a shaped article comprises the steps of dry mixing the following components:

• (a) at least one silicate containing alumina and calcium;
• (b) at least one carbonatic rock;
• (c) a crystallization orientator; and
• (d) optionally, a basicity regulator,

• (ii) kneading said components with water;
• (iii) shaping the mixture into the desired article; and
• (iv) drying the shaped article at a temperature from 5°C to 60°C.

Since it is very favourable to mix the above solid components in granular form with a granulometric distribution which serves to reduce the empty space inside the mix to a minimum and which allows to obtain a high degree of compaction, it is preferred to use materials in the form of granules having a diameter below 25 mm, up to 80% by weight of said materials having a granulometry below 0.2 mm.

The following examples serve to further illustrate the present invention without limiting the scope thereof.

EXAMPLE 1

100 g of dry powder of clay (illite), 400 g of powder of ground granite, 480 g of limestone, 10 g of nitrogen-containing fertilizer containing 40% of urea and 10 g of 50% aqueous sodium hydroxide were mixed with 500 ml of water.

The solid components of the mixture showed a granulometric distribution below 5 mm and, more particularly, 35% by weight of said components had a granulometry below 0.2 mm.

The mixture was then tamped into a cylindrical die having a diameter of 100 mm and a height of 100 mm, whereafter it was treated for 4 hours at 55°C in a dry environment and for 4 hours at 55°C in an environment having a relative humidity above 60%.

Then the die was opened and the material was kept for 60 days at 20°C in an environment having a relative humidity above 60%.

In a compression test the thus prepared sample showed a compression strength of 1.6 MPa.

EXAMPLE 2

Example 1 was repeated, except by using 470 g of limestone.

The obtained sample showed a resistance to compression of 2.3 MPa.

EXAMPLE 3

Example 1 was repeated, except by using 20 g of calcium hydroxide instead of the sodium hydroxide.

The obtained sample showed a resistance to compression of 2.5 MPa.

EXAMPLE 4

Example 1 was repeated, except by using 460 g of ground limestone.

The obtained sample showed a resistance to compression of 2.8 MPa.