FR2572743A1 - Base course (layer) or carriageway foundation course (layer) - Google Patents

Abstract

a. Base course (layer) or carriageway foundation course (layer). b. Characterised in that it comprises, in weight per cent, 88 to 92% of a crushed limestone rock, 4 to 6% of preground slag, 4 to 6% of flue dust and 0.5 to 1.5% of lime, the rest being made up of water, and these various components being mixed by means of a mixing operation known per se. c. The invention is applicable to the road industry.

Description

Basement or foundation layer
The present invention applies to the road industry, and more specifically relates to the base layers or foundation layers of roadways.

 Conventionally, it is known that roads or motorways consist of a base layer which is covered by the actual coating on which vehicles circulate (tar, concrete slabs ...).

 -The qualities sought for the base layer are to have good resistance to stresses of all kinds, associated with a thickness which is as small as possible, in order to reduce the cost of manufacturing the road.

 To meet these requirements, at first glance contradictory, the base layers of conventional pavements generally contain approximately 85% of crushed limestone rock recomposed so as to have a continuous particle size from 0 to 20 mm, approximately 15% of granulated slag consisting of blast furnace slag which swims on the molten metal therefore by by-products of metallurgical processing operations having a composition based on silicate, and 1% quicklime, the rest being water.

 The above-mentioned mixing is commonly carried out in mixing plants, using silos and hoppers corresponding to the various components.

 To improve the characteristics of these conventional foundation layers, it has been proposed to replace the granulated slag with pre-ground slag. We have, for example, obtained foundation and base layers giving every satisfaction from the point of view of resistance to stresses by mixing 90% of crushed 0/20 limestone, 10% of pre-ground slag and 1% of lime in excess.

 This composition has, if compared to the composition defined above, the advantage of requiring less slag, significantly more expensive than crushed limestone.

 However, this advantage is partially diminished by the need to provide an additional operation for grinding the slag.

 From these known compositions, the invention proposes to develop a base layer or foundation layer of roadway having satisfactory resistance to stresses, for a minimum thickness, and this, from inexpensive starting materials.

 For this purpose, the base layer or foundation layer of roadway according to the invention is characterized in that it comprises, in percentage by weight, 88 to 92 X of a crushed limestone rock, between 4 and ó of pre slag crushed, between 4 and 6% of fly ash and between 0.5 and 1.5% of lime, the rest being constituted by water, these various components being mixed by the implementation of a mixing operation known in itself.

 This composition makes it possible, surprisingly, by replacing part of the pre-ground slag with fly ash, in particular with silico-aluminous fly ash, and therefore with a less expensive material, to obtain high performance layers, making it possible to reduce the thicknesses of pavements built so far, for an equal quality, and consequently to significantly reduce the costs of the construction works launched by the various public authorities.

 In fact, the fly ash which comes from the dust removal from the fumes, are quantitatively important residues from thermal power plants, numerous and scattered all over the territory, and can always be obtained very easily and for a low cost price.

 On the contrary, industrialists do not always have satisfactory slag on hand, and it is often necessary to import it, which results in a significant shortage in transport and foreign currency, not to mention the need to carry out an additional operation. grinding.

 According to another characteristic of the invention, the crushed limestone rock has a continuous particle size of 0 to 20 mm.

 According to another characteristic of the invention, limestone rock has a specific weight between about 2.65 and 2.80.

 According to another characteristic of the invention, the base layer contains between 5 and 7% of water, this percentage varying as a function of climatic conditions and dependent on the content of manufacturing water and the natural humidity of the constituents.

 According to another characteristic of the invention, the pre-ground slag has a particle size between 0 and 2 mm.

 Particularly favorable results have been obtained by preparing a slag in such a way that 12% by weight is capable of passing through a sieve at 80 microns.

 According to another characteristic of the invention, the lime contains about 90% of free lime with a particle size between 0 and 0.2 mm.

 The characteristics of the composition which is the subject of the invention will be described in more detail with reference to the example below of such a composition.

EXAMPLE
Particularly satisfactory use has been made of a base layer having the following composition
- 90% of a hard limestone crushed from Avesnois (Frasnien) meeting the following characteristics - Specific weight varying from 2.65 to 2.80 - Los Angeles 20 - Micro Deval in the presence of water on the fraction 10 / 14
equal to 9.8, - Sand equivalent on fraction 0/6 greater than 50.

- 5% of a granulated slag from the GUSTAVE BOEL metallurgical factories in LA LOUVIERE (BELGIUM), ground using "Babbitless" bar mills,
- 5% fly ash from the PONT S / SAMBRE (NORD) thermal plant,
- 1% quicklime from vertical gas lime kilns of the Maertz type,
- 6.5% water.

Claims (6)

 10) Base layer or foundation layer of pavement characterized in that it comprises, in percentage by weight, 88 to 92% of a crushed limestone rock 4 to 6% of pre-ground slag, 4 to 6% of fly ash and 0.5 to 1.5% lime, the remainder being water, and these various components being mixed by the implementation of a kneading operation known in itself.  20) Base layer or foundation layer of roadway, according to claim 1, characterized in that the crushed limestone rock has a particle size 0/20 (reconstituted formula) from 0 to 20 mm.  30) Base layer or foundation layer of roadway, according to any one of claims 1 and 2, characterized in that the limestone rock has a specific weight between, approximately, 2.65 and 2.80.  40) Base layer or foundation layer of roadway, according to any one of claims 1 to 3, characterized in that it contains between 5 and 7% of water.  50) Base layer or foundation layer of roadway, according to any one of claims 1 to 4, characterized in that the pre-ground slag has a particle size between 0 and 2 mm with 12% less than 80 microns.  60) Base layer or foundation layer of roadway, according to any one of claims 1 to 5, characterized in that the lime contains, approximately, 90% of free lime and that its particle size is between 0 and 0.2 mm.