LU88487A1 - Compositions for stabilizing soils and method for stabilizing soils with such a composition - Google Patents

Description

Brief Description filed in support of a request for

PATENT

at

Luxembourg on behalf of: ETABLISSEMENTS BOCAHUT s'.A.

TOP LOCATION

F-59440 AVESNES SUR HELPE (Nord) FRANCE

for; COMPOSITION FOR SOIL STABILIZATION THUS

THAT METHOD OF STABILIZING SOILS WITH SUCH A COMPOSITION

PATENT

Company known as: ETABLISSEMENTS BOCAHUT

"Composition for stabilizing soils and method for stabilizing soils with such a composition"

The present invention relates to a composition for stabilizing floors, in particular pavement foundations, in particular motorways.

In the context of road engineering, the first phase of the construction of a roadway conventionally corresponds to earthworks carried out using special machines which consist of stripping certain parts in relief and recovering spoils which are used to fill the holes (backfill) so as to obtain a relatively flat surface.

In the particular case of fine, moist soils, in particular sandy loam soils, it is necessary, before the realization of the upper layers of the pavement, to provide a stabilization treatment allowing in particular to confer on the soil an immediate bearing capacity authorizing traffic of the site.

This stabilization is conventionally obtained thanks to the use of lime which acts essentially on three levels: - by supplying dry product, - by consumption of the quantity of water necessary for the chemical hydration of quicklime into slaked lime, - by evaporation under the action of the heat released following the exothermic nature of this reaction.

In addition, lime acts by flocculating the clays and therefore by making the soil more brittle, and by hydrating the calcium silicates and aluminates which it can, if necessary, contain.

However, such a treatment is not without drawbacks and must in particular often be followed by an additional treatment, in particular with cement so as to obtain an improvement over time in the mechanical characteristics of the soil.

To remedy this drawback, attempts have been made in accordance with the invention to replace this conventional treatment with another, more satisfactory treatment.

We thus had the idea of using fly ash which corresponds to a product available in large quantities, constituting in particular a by-product often discarded from the operation of thermal oil or coal power plants, including l activity as back-up plants seems set to grow in the years to come.

The chemical composition of fly ash depends on their origin: for example, they may contain potassium carbonate, carbonate and calcium and magnesium phosphates, silica, aluminum silicate or iron and manganese oxides.

Fly ash from thermal power plants is, however, generally stored in a wet state to prevent it from flying away and contains, on average, a proportion of humidity of the order of 20 to 40% and sometimes even s '' raise up to around 55%.

This feature makes it necessary to provide a drying operation before any implementation.

In accordance with the invention, we had the idea of carrying out this operation, thanks to the addition of quicklime.

The invention therefore relates to a composition for stabilizing soils, in particular road surfaces, in particular of motorways, characterized in that it contains in weight proportion between 25 and 80% fly ash and between 20 and 40% lime.

The fly ash used in accordance with the invention is preferably constituted by a product coming from thermal power stations, in particular coal or fuel oil and having a moisture content of between 20 and 55%.

Experience has shown that ash from coal-fired power plants such as, for example, those from the Pont sur Sambre thermal power plant, the main constituent of which is aluminum silicate, makes it possible to obtain particularly satisfactory performance.

It should be noted that lime is previously added to fly ash in the form of quicklime; however, part of it is "consumed" to dry wet fly ash in accordance with the well-known chemical hydration reaction of quicklime to slaked lime (CaO + H = 0 -> Ca (OH) 2) highly exothermic which occurs almost immediately to give a mixture endowed with pozzolanic properties which can be assimilated to cement. Consequently, when it is used for treating the soil, the lime contained in the composition is in the form of a mixture of quicklime and slaked lime.

The composition in accordance with the invention proves to be particularly advantageous for stabilizing soils, in particular silty-sandy or clayey soils having a high moisture content, of the order of 22 to 24 I.

Indeed, in the case of such soils, it is necessary to provide a double treatment first with lime to obtain, in addition to the necessary lift, a homogeneous and optimal water content, then with cement.

This conventional stabilization process has the drawback, however, of being able to be implemented only in two stages, and therefore of requiring two successive passes, which greatly increases its cost price.

However, the composition according to the invention allows, thanks to the application of lime and fly ash, to replace this double treatment by stabilization in a single step and therefore being able to be implemented in a single pass, for at least the same result.

However, it is not entirely excluded to carry out a lime pretreatment on this type of soil if the latter does not yet have the characteristics necessary to be treated with the lime / ash mixture.

According to a preferred characteristic of the invention, the composition contains, in proportion by weight, between 25 and 45% of fly ash, between 20 and 40% of a mixture of quicklime and slaked lime, and between 25 and 45 V fine limestones with a particle size less than 80 μ.

As already indicated, the lime is in fact in the form of a mixture on the one hand of quicklime and on the other hand of slaked lime which has already reacted with the humidity possibly present in the initial fly ash.

However, it is imperative that the proportion of quicklime is sufficient to treat soil moisture.

By way of nonlimiting example, a composition containing in weight proportions approximately 35% fly ash, approximately 30% lime and approximately 35% fines has been found to be particularly satisfactory in use.

In accordance with this preferred characteristic, part of the fly ash is therefore replaced by fine limestones (filler) which generally correspond to a dust removal product which is in suspension and stored in a silo.

The addition of this product makes it possible to obtain a specific surface close to that of cement.

The invention also relates to a process for stabilizing floors, in particular pavement foundations, in particular motorways, by which the ground to be stabilized is treated, in a single step, with the composition described above.

According to another characteristic of this process, the soil to be stabilized is treated by spreading the composition on the ground and kneading it over a height of approximately 30 cm.

Claims (3)

1) Composition for stabilizing soils, in particular road surfaces, in particular motorways, characterized in that it contains, in proportion by weight, between 25 and 80% fly ash and between 20 and 40% lime . 2) Composition according to Claim 1, characterized in that the fly ash has a moisture content of between 20 and 55%. 3 °) Composition according to any one of claims 1 and 2, characterized in that the fly ash come from thermal power stations, in particular with coal or fuel oil. 4th) Composition according to any one of claims 1 to 3, characterized in that it contains in weight proportion between 25 and 45% of fly ash, between 20 and 40% of a mixture of quicklime and slaked lime, and between 25 and 45 hours of fine limestones with a particle size less than 80 μ. 5 °) Composition according to claim 4, characterized in that it contains in proportion by weight about 35% of fly ash, about 30% of lime and about 35% of fines. 6 °) A method of stabilizing soils, in particular pavements, especially motorways, characterized in that the soil to be stabilized is treated, in a single step, with a composition according to any one of claims 1 5. according to claim 6, characterized in that the soil to be stabilized is treated over a height of approximately 30 cm.