WO2004063115A2 - Light cementitious materials based on carpet by-products and method of producing such materials - Google Patents

Abstract

The invention relates to a cementitious material comprising carpet by-products, in particular used carpets. The inventive cementitious material has the same spreading properties as standard materials. In addition, the mechanical properties of said material increase after the setting phase and during the hardening phase when the latter is performed in free air and without water, unlike standard cementitious materials which require a constant supply of water in order for the mechanical properties thereof to reach the expected levels. The invention also relates to a method of preparing one such cementitious material.

Description

 LIGHTWEIGHT CEMENT MATERIALS BASED ON CARPET BY-PRODUCTS AND PROCESS FOR PRODUCING SUCH MATERIALS

The technical field of the present invention is that of cementitious materials. More specifically, the present invention relates to a cementitious material having improved lightening properties. Even more precisely, the present invention relates to a cementitious material comprising carpet by-products, in particular used carpets.

The amount of household waste produced by industrialized societies is constantly increasing. This waste constitutes significant pollutants.

Saving the environment therefore requires appropriate recycling of waste, but also by ending the storage of this waste in open landfills.

Among household waste, used carpets represent a significant part. Indeed, carpets constitute a significant amount of synthetic waste, which has mainly been stored in landfills. However, since this waste is non-biodegradable, its storage in landfills cannot constitute a viable solution, without taking into account the fact that landfills are going to disappear.

Carpet recycling is therefore an obligation. However, these products are part of waste that is difficult to recycle.

This is explained in particular by their composition. Indeed, carpets generally comprise two support layers made of polymers, joined together by means of a latex loaded with mineral constituents and an upper layer of synthetic textile fibers. Thus, carpets include three main constituents: polymer fibers, latex and mineral constituents, whose physical and chemical characteristics are very different, which greatly complicates recycling.

On the other hand, the structure of the carpets also makes it very difficult to physically separate the different elements. Also, today the reprocessing of used carpets consists essentially of their transformation under various presentations: cut carpet, shredded, granulate / plastdensification or fine powder.

Some of these processed products are then used as fuel in cement factories. However, such use can only represent at most around 10% of the total amount of carpet to be reprocessed.

One factor limiting the use of used carpets and in particular of their transformation by-products described above is that they are of an unpleasant appearance and are often loaded with a large number of impurities making them unhealthy. The prior art however reports the use of processed carpet waste. Thus the document WO-A-00/06638 describes a composition based on asphalt and a residue consisting of a mixture of polypropylene, styrene-butadiene and calcium carbonate. This residue is obtained following the depolymerization of nylon 6 in carpet waste, at medium pressure. Asphalt acts as a binder. Such a composition is used as road asphalt, asphalt covering membrane, molding composition, etc.

If such a composition has improved mechanical properties, it remains expensive and time-consuming to implement, due to the need to depolymerize nylon 6.

Wang et al. {Journal of Material Science; 29 (1994) 4191-4199) describe the use of recycled fibers from used carpets as reinforcing fibers in concrete. These fibers are the polypropylene fibers contained in the carpets, disassembled from the “backing” constituted by styrene-butadiene and calcium carbonate.

The disadvantage of this technique is that it requires a prior step of separation of the fibers. However, such a separation cannot be envisaged at a reduced cost.

It therefore appears in the light of this inventory that the field of reprocessing of household waste is awaiting an effective means of recycling used carpets, without intermediate stages of separation of components of the carpet and above all without prohibitive additional cost .

In addition, the cement sector is awaiting new cementitious materials with certain improved properties.

There are already on the market, concretes with such improved properties. Apart from conventional constituents, these concretes contain additives used for insulation and lightening. These additives are for example expanded polystyrene, expanded vermiculite, expanded clay, expanded shale, etc.

However, the use of such additives in cementitious materials greatly increases their cost price. Furthermore, the use of additives such as expanded polystyrene has several major drawbacks.

In fact, the process for preparing cementitious materials conventionally comprises the following steps: o an implementation step consisting in mixing and kneading the various constituents of the cementitious material together; o a shaping step consisting in pouring the cementitious material into a mold; o a setting stage during which the cementitious material passes from the liquid state to the solid state; and a consolidation step during which the cementitious material sees its mechanical properties increase. However, additives such as polystyrene are used in the form of very light particulate fillers which float when incorporated into concrete paste. After the concrete has been formed and during the setting phase, these charges tend to rise and concentrate on the surface of the concrete. This then weakens the consolidated concrete, due to the significant reduction in mechanical properties. Another disadvantage of existing cementitious materials is that they require, during the consolidation phase, a regular supply of water so as to allow the increase in mechanical properties.

The cement industry therefore awaits materials with improved insulation and lightening characteristics compared to traditional cement materials and equivalent to those of existing additive materials, while retaining acceptable mechanical properties, with a cost of returns less.

Thus, one of the essential objectives of the present invention is to remedy the drawbacks stated above, by proposing a cementitious material comprising a non-negligible proportion of carpet by-products. Another object of the present invention is to provide a cementitious material having acceptable mechanical properties to allow its use in the field of public works and roads.

Another objective of the present invention is to provide a cementitious material with a limited cost price. In order to achieve these objectives, the inventors had the merit, on the one hand, of having had the idea of using products for the reprocessing of this carpet waste, in particular as additives in materials for building and works public and in particular in cement materials such as concrete or mortar.

Quite unexpectedly, the inventors have been able to demonstrate that cementitious materials comprising carpet by-products and having spreading properties equivalent to traditional materials, see their mechanical properties increase after the setting phase and during the consolidation phase, when it is done in the open air and without the addition of water; and this unlike traditional cementitious materials, which require a constant supply of water to see their mechanical properties reach the expected values.

The present invention therefore satisfies the abovementioned objectives by proposing, firstly, a cementitious material comprising carpet by-products. By carpet by-products is meant the products obtained by cutting, grinding, and possibly compacting the carpets.

By compacting is meant cold compression of roughly precut carpet waste so as to reduce its volume. By cementitious material is meant any material produced by the cement industry, such as concrete, mortar or even cement.

Preferably, these by-products come from used carpets. Advantageously, the proportion of carpet by-products in the cementitious material according to the invention is between 5 and 20% by weight. According to a remarkable characteristic, the cementitious material has, according to its formulation, a compressive strength of between 1 and 10 MPa.

The compressive strength measurements are carried out according to standard NF P 18-406.

According to another remarkable characteristic, the cementitious material has, according to its formulation, a density reduced by at least 5% and preferably by 5 to 30% compared to a non-additive concrete; this for the final product dried at room temperature until equilibrium is reached.

According to another remarkable characteristic, the cementitious material according to the invention has a flexural strength greater than 2 MPa. According to a variant of the invention, the cementitious material also comprises, as an additive, at least one constituent taken from the group comprising, for example, plasticizers, plasticizers such as polysulfonates or any equivalent product known to those skilled in the art. job.

Another object of the present invention relates to a process for producing the cementitious material described above, this process consisting in using carpet by-products.

Preferably, the size of the carpet by-products used in the present process is less than 10 mm, preferably less than 5 mm and more preferably still less than 1 mm. According to another characteristic, the water / cement ratio used in the process according to the invention is advantageously between 0.4 and 0.9.

Advantageously, the carpet by-products are introduced during the implementation step, after mixing the basic constituents of the cementitious material, namely cement, water, sand or aggregates as it be a mortar or concrete.

To obtain a consistency and spreading properties equivalent to those of traditional cementitious materials, it appeared necessary to introduce a greater quantity of water into the cementitious material according to the invention. However, against all wait, this significant proportion of water has in no way affected the mechanical properties of the consolidated cementitious material.

According to another remarkable characteristic of the process according to the invention, it is found that during the setting phase of the cementitious material, the particles are retained in suspension, allowing said cementitious material to maintain a homogeneous structure.

By particles is meant sand particles or aggregates depending on whether it is a mortar or concrete.

According to another remarkable characteristic of the process according to the invention, the consolidation phase is carried out in the open air and without the addition of water. In fact, the water supplied during the implementation step is sufficient to hydrate the cementitious material.

Indeed, quite advantageously, during the consolidation phase, the hydration of the cementitious material is obtained by the release of water by the carpet by-products. According to a remarkable characteristic of the process according to the invention, the gain in value of compressive strength, during the consolidation phase after 28 days at 20 ° C. in air, is at least 100%.

Another object of the present invention relates to the use of by-products of used carpets for the production of cementitious materials. Yet another object of the present invention relates to articles obtained by the shaping of the cementitious material, in particular by casting in prefabrication or casting on site or molding, such as for example plates or any article capable of being used for example as curb or partitions.

Other details and advantages of the invention will appear more clearly in the light of the examples given below, only for information and for illustration.

EXAMPLES:

The by-product studied comes from the crushing of used carpets. The product is supplied in two forms, either as ground material with dimensions varying from 2 to 5 mm, or in powder form from 50 to 250 microns.

EXAMPLE 1: STUDY OF DUBETONAVECDUBROYAT

1-1 / Formulation study

1-1.1 / Estimation of the absorption of the material Tests were carried out to determine the absorption rate of the material. The test consists of soaking a dry sample of 20 g in water for 1 h, then draining and wringing it out. The absorption rate is determined as a percentage relative to the initial dry mass of the sample. This test gives orders of magnitude for the water retention capacity of the ground material. The means of the results obtained are collated in Table 1 below.

Table 1: Water absorption rate by the ground material

Table 1 shows that the ground material can contain between 80% to 270% of its weight in water. This high absorption rate can only considerably influence the consistency of the dry concrete.

1-1.2 / Concrete formulation with addition of ground material

1-1.2.1 / Dosages studied

Twelve formulations containing crushed used carpets were studied by varying the dosage in crushed and / or the Water / Cement ratio (W / C). The addition of the ground material was first carried out in progressive dosages in the reference concrete whose W / C ratio is constant and equal to 0.55. Then, higher dosages were used, but by increasing the W / C ratio, in order to keep the initial rheological behaviors close (between 0-lh).

Table 2 summarizes the different formulations studied.

Table 2: Formulations studied

1-1.2.2 / Manufacturing procedure

The mixing of the various constituents (aggregates, sand and cement) is carried out dry for approximately two minutes before adding the water. The ground material is then added to the fresh concrete and the mixing continues for approximately two minutes.

1—1.3 / Tests on fresh concrete

Different tests are carried out on the finished concrete immediately after mixing in order to characterize its rheology and its physical properties. The tests are as follows: penetrant test, measurement of the percentage of air trapped in the concrete and measurement of the density.

1-1.3.1 / Density and percentage of air trapped

The measurements of the percentage of air and the density of the fresh concrete were carried out using an airmeter. Other density measurements of hardened concrete were also taken from certain 11 x 22 cylindrical specimens (11 cm in diameter and 22 cm in height) dried to constant mass in an oven at 70 ° C or in a air-conditioned room (20 ° C, RH = 50%).

Table 3 summarizes the different density measurements and the percentage of air trapped in fresh concrete:

Table 3: Percentages of occluded air and densities of fresh concrete

The table above shows an increase in the percentage of air occluded with the increase in the dosage of ground material. The percentage of trapped air can reach 18%. Indeed, without being bound to theory, the ground material consisting on the one hand of fibers (polyamide) and on the other hand of foam (calcium carbonate), behaves like a sponge thus promoting water retention and air. The direct consequence of the increase in the percentage of air retained in the material is the decrease in the density of the concrete.

The density of B12 concrete is around 1.78 t / m ³ on average. This decrease can be explained on the one hand by the increase in voids and on the other hand by the high W / C ratio.

Additional measurements have been made on concrete after evaporation of the water by drying under different conditions. The results obtained are collated in Tables 4 and 5 below.

In the case of oven drying, evaporation can be considered very effective, so we find that the variation in density is even greater.

Table 4: Densities of dried 11 x 22 test pieces

Ml = density before drying (t / m) M2 = density after drying (t / m)

Table 5: Variation in density according to the drying conditions

The measurements carried out on 11 x 22 test pieces dried to constant mass, grouped in Tables 4 and 5 above show that the density decreases with drying.

It would also seem that the ground material promotes the creation of a network of connected pores. This property can be the source of interesting acoustic and thermal properties.

It appears that the concretes obtained have a significant reduction rate compared to standard concretes: weight gain of 30% for concrete B 12.

1-1.3.2 / Penetrant testing

The penetrant test is carried out using transparent PVC tubes with a diameter of 8 cm. The concrete is poured in three times over a height of 150 cm, vibrated each time for 15 seconds. The tubes are left in an air-conditioned room for approximately 2 hours. The height of the water film at the upper surface is then measured, which is the consequence of the solid part of the mixture settling under the effect of gravity. The following table 6 gives the results obtained for this test:

Table 6: Height of the drained water film

The values obtained are close, without it being possible to distinguish a significant variation between the concretes. A priori the structure of the ground material made it possible to keep the material in suspension, which limited this phenomenon.

1-1.4 / Formulations retained:

At the end of the formulation study, two formulations were selected for the study of mechanical properties. The first consists of concrete with a low grind strength dosage: 5% by weight of the cement, or 16.25 kg / m ³ with an E / C ratio = 0.65 (concrete B6). The second is a concrete with a high dosage: 20% by weight of the cement, i.e. 65 kg / m ³ with an W / C ratio = 0.87 (concrete B12). These two formulations make it possible to compare two dosages, low and high with a concrete without addition with close initial consistency.

1-2 / Mechanical properties:

The mechanical properties of the two formulations B6 and B12 were evaluated by two tests, simple compression on 11 x 22 cylindrical specimens and traction by bending on plates 5 x 14 x 56 cm. The evolution of the modulus of elasticity was also monitored on several deadlines 1, 2, 7 and 28 days after pouring.

Compressive strength

The simple compression test is carried out on 11 x 22 specimens surfaced with sulfur. The test specimens are stressed in force at a speed of 5 kN / sec according to the standard

(NF P 18-406). In order to follow the evolution of the resistance over time, the resistance was measured at different stages of hardening 1, 2, 7, 28 and 56 days. Table 7 gives the different measures taken: Table 7: Measurement of the compressive strength on 11 x 22 test pieces

The compressive strength results show a remarkable increase in the resistance of concrete kept in the open air.

Furthermore, it can be seen that the resistance values of concrete kept in the open air are always higher than that of concrete kept in water.

It also appears that the results obtained for concrete B12 in terms of mechanical properties are better than a good number of lightened concretes on the market, for an equivalent rate of reduction.

1-3 / Permeability of concrete

Capillary rise

In order to establish the influence of the ground material on the permeability of the concrete, capillary rise tests were carried out on cylindrical specimens made from concretes B6 and B12.

The test is carried out on 11 x 22 test pieces kept in water for the first 7 days and then dried at 70 ° C to constant mass. These test pieces are then immersed in water over a height of 1 cm delimited by a ribbon around the test piece. The upwelling is assessed by weighing taken at different times. Table 8 gives the different measurements of the masses of the test pieces as well as the cumulative masses of water absorbed by the different concretes. Table 8: Masses of water accumulated in the test pieces by capillary rise

EXAMPLE 2: DUMORTIER STUDY WITH LAPOUDRE

This part concerns the study of the addition of by-product in its powder form in mortars and is limited only to a comparison between a first mortar with a low powder dosage and a second with a high powder dosage. The characteristics of these mortars, the workability, the percentage of trapped air and the density in the fresh state are presented as well as the mechanical properties in compression. 11-1 / Formulation

11-1.1 / Estimated water absorption rate of the powder

This estimation is done by the same method as that used in Example 1. Thus a 20 gram sample is soaked in water until the sample is saturated.

The masses of the drained and drained sample are taken, the absorption rate is then calculated as a percentage relative to the initial mass. The results are presented in Table 9 below.

Table 9: Estimated rate of water absorption by the powder

We observe that the values obtained are very close to those obtained for the ground material

11-1.2 / Formulation of mortars

By analogy to the formulations studied for concretes B6 and B12, two mortars are studied, Ml dosed in powder at 5% and M2 dosed at 20% by weight of cement. Table 10 gives the composition of one cubic meter of these mortars.

Table 10: Composition of one cubic meter of mortar

The sand and cement are first dry mixed for about 1 minute before adding the water. The mixing continues for approximately 1 minute. The powder is gradually introduced by hand and kneaded for approximately 2 minutes. 11-2 / Tests on fresh mortars

Density and percentage of air

The density and the percentage of air trapped in the mortar were measured using an air meter intended for mortars. Table 11 gives the percentages of occluded air:

Table 11: Percentage of air

As with concrete, we make almost the same observations, the percentage of air increases with the increase in powder dosage. We also find that these percentages for Ml and M2 have values close to those obtained for concretes B6 and B12 respectively.

As for the density, we also note the decrease in this parameter with the increase in the powder dosage.

Table 12 summarizes the density values of the mortars in the fresh state and in the dry state, after drying at 20 ° C. and RH 50%.

Table 12: Density

The measured densities reflect a reduction of 5 to 30% of the mortars obtained compared to traditional mortars 11-3 / Tests on hardened mortars

11-3.1 / Resistance to compression

Mortar specimens (6 x 12 cm) were tested in compression at different times 1, 2, 7, 28, 56, and 100 days. They were kept either in a swimming pool or in an air-conditioned room (t = 20 ° C, RH = 50%) and this until maturity. After surfacing, the compressive strength is measured using a hydraulic press at a loading speed of 0.5 MPa / sec.

Table 13: Measurements of the compressive strength of mortars

Equivalently to concrete, it is found that the values of compressive strength obtained for consolidated mortars, preserved in air, are better than those obtained for consolidated mortars, preserved in water.

We also observe that, while the compressive strength values obtained for mortars kept in water tend to decrease at the end of consolidation (60 days), those obtained for mortars kept in air continue to progress.

Conclusion:

It appears that the addition of this product appreciably modifies the behavior of concretes and mortars, both in the fresh state and in the hardened state. During the first hours, it is observed that the ground material and the powder act as a "water reservoir" linked to their capacity to mobilize the water of the mixture. These materials indeed have a very high porosity and consequently a high absorbency. These products therefore make it possible to regulate the initial rheology of a concrete "whatever" the dosage of water. The additions also lead to a decrease in the density and an increase in the amount of air trapped within the material and this is according to the dosage of by-product used. The increase in the percentage of occluded air and the amount of water used does not prevent the concretes and mortars tested from exhibiting generally better mechanical properties than the existing lightweight concretes and mortars.

Concrete and mortar with added product then has the double advantage of light materials while allowing production and implementation on site.

Claims

1. Light cement material characterized in that it includes carpet by-products. 2. Cement material according to claim 1, characterized in that the by-products are obtained from used carpets. 3. Cement material according to one of claims, characterized in that the proportion of carpet by-products is between 5 and 20% by weight. 4. Cement material according to one of the preceding claims, characterized in that it has a compressive strength of between 1 and 10 MPa. 5. Cement material according to one of the preceding claims, characterized in that it has a density reduced by at least 5% and preferably by 5 to 30% compared to a non-additive concrete. 6. Cement material according to one of the preceding claims, characterized in that it has a flexural strength greater than 2 MPa. 7. cementitious material according to one of the preceding claims, characterized in that it also comprises, as an additive, at least one constituent taken from the group comprising, for example, fluidizers, plasticizers. 8. Method for producing a cementitious material according to one of claims 1 to 7, characterized in that it consists in using carpet by-products. 9. Method according to the preceding claim, characterized in that the size of the carpet by-products is less than 10 mm, preferably 5 mm and more preferably still 1 mm. 10. Method according to one of claims 8 or 9, characterized in that the water / cement ratio used is between 0.4 and 0.9. 11. Method according to one of claims 8 to 10, characterized in that the carpet by-products are introduced after mixing the constituents of the cementitious material. 12. Method according to one of claims 8 or 11, characterized in that during the setting phase of the cementitious material, the particles are retained in suspension, allowing said cementitious material to maintain a homogeneous structure. 13. Method according to one of claims 8 to 12, characterized in that the consolidation phase is carried out in the open air and without the addition of water. 14. Method according to one of claims 8 to 13, characterized in that during the consolidation phase, the hydration of the cementitious material is obtained by the release of water by the carpet by-products. 15. Method according to one of claims 8 to 14, characterized in that during the consolidation phase, the gain in value of compressive strength is at least equal to 100%. 16. Use of carpet by-products for the production of cementitious materials. 17. Articles obtained by shaping the cementitious material according to one of claims 1 to 7 or obtained from the process according to one of claims 8 to 15.