EP2411580A1

EP2411580A1 - Synthetic aggregate with photocatalytic properties for road use and production method thereof

Info

Publication number: EP2411580A1
Application number: EP10715981A
Authority: EP
Inventors: Xavier Bricout; Jean Eric Poirier
Original assignee: Colas SA
Current assignee: Colas SA
Priority date: 2009-03-25
Filing date: 2010-03-25
Publication date: 2012-02-01
Also published as: FR2943664A1; WO2010109146A1; CA2756644A1; US20120006231A1

Abstract

The invention relates to a synthetic aggregate with photocatalytic properties for road use, consisting of a collection of particles each comprising a matrix formed by a binder containing at least photocatalytic particles and a particulate mineral material. The invention also relates to the production method thereof and to the use of same in a pollution-reducing road surface course having excellent tyre grip.

Description

Synthetic granulate with photocatalytic properties for road application, and its production process

The present invention relates to a synthetic granulate with photocatalytic properties for road application, as well as its production method, and a wearing course which incorporates it.

In order to have both a long service life and a maximum level of safety for users, the wearing course of a roadway must have particular mechanical and physicochemical properties, such as, for example, traffic resistance and suitability. tire adhesion in dry or wet conditions.

The adhesion of tires on a wearing course mainly depends on the surface condition of the road surface. Thus, on wet pavement, this surface state must allow the rupture of the film of water that forms between the roadway and the tires.

The micro-roughness of the aggregate on the surface of the pavement wearing course largely determines the surface condition of the pavement. The higher the micro-roughness of the aggregate, the better the adhesion of the tires to the wearing course. In order to maintain a high microroughness of the aggregate throughout its life, it must therefore have certain surface characteristics, including good resistance to abrasion and polishing. Document FR 2 858 614 thus discloses a process for producing synthetic aggregates from crushed concrete formulations, whose microroughness is greater than that which can be found in natural rocks, and which have a high resistance to abrasion. Such aggregates are intended for roadway portions requiring maximum adherence of the tires on the wearing course. However, over time, there is a fouling of the surface of the roadway and aggregate by dirt from both the immediate environment of the roadway and the traffic of vehicles and the pollution that arises therefrom. This results in a gradual decrease in the apparent micro-roughness of this aggregate, and therefore a gradual loss of the adhesion properties of the tires on the wearing course. An object of the invention is to provide a synthetic granulate having excellent microroughness which is maintained over time, so as to ensure permanent adhesion properties.

This goal is achieved by the production of a synthetic granulate with photocatalytic properties. Indeed, its photocatalytic properties give the granulate a superhydrophilic and self-cleaning surface with respect to any organic pollution, and thus allow the maintenance of its excellent microroughness over time.

Indeed, the presence of photocatalyst particles on the surface of the aggregate, associated with UV and visible solar radiation, allows the decomposition of organic molecules to the surface of the photocatalyst particles. These self-cleaning properties increase with the micro-roughness of the aggregate.

By superhydrophilic surface is meant a surface that has a total affinity with water, which has the effect of detaching the soil that is deposited on the surface, whether mineral or organic.

However, a wearing course is particularly exposed to pollution: combustion residues, tire marks or other dirt are deposited on its surface and contribute to its fouling. It has been observed that particles of photocatalyst can completely or partially decompose these soils, and facilitate their evacuation. Despite its high resistance to abrasion, the synthetic aggregate with catalytic properties will undergo, like any granulate, an inevitable polishing of its surface over time, especially under the action of traffic. The presence of photocatalyst particles in the matrix of the granulate allows it to retain its self-cleaning and superhydrophilic properties over time, by renewing the surface as wear. As the roughness of the surface is not clogged with dirt, the micro-roughness of the granulate is maintained, and the adhesion properties of the tires on the wearing course also remain.

The synthetic granulate of the invention consists of a set of grains, each comprising, included in a matrix formed by a binder, at least photocatalyst particles and a particulate mineral material. The invention therefore relates to a synthetic granulate with photocatalytic properties for road application, consisting of a set of grains, each comprising, included in a matrix formed by a hydraulic binder or pozzolanic, at least photocatalyst particles and a particulate mineral material. which is a sand, the synthetic granulate having a particle size d / D with D between 4 and 10. In a first embodiment of the invention, the matrix formed by a first binder, which comprises the particulate mineral material and the photocatalyst particles, constitutes the heart of the grains of the synthetic granulate.

In a second embodiment of the invention, the matrix formed by a second binder, which comprises the particulate mineral material and the photocatalyst particles, is on the surface of the grains of the synthetic granulate, where it constitutes a layer of coating, the heart of the grains of the synthetic granulate then being constituted by the grains of a starting granulate.

The photocatalyst is advantageously a semiconductor compound, preferably titanium dioxide. Among the various allotropic forms of titanium dioxide, the preferred forms are rutile, anatase and brookite, and more particularly the anatase form.

It will thus be possible to use the photocatalysts known under the following names:

Hombikat® UV100 (Sachtleben), Kronos® VLP7000 (Kronos), Kronos® VLP7500 (Kronos), Kronos® VLP7101 (Kronos) and Aeroxide® P25 (Evonik). Preferably, the photocatalyst Hombikat® UV100 (Sachtleben) will be used.

In the first embodiment of the invention, when the photocatalyst is titanium dioxide, the synthetic granulate preferably comprises between 0.5 and 50% by weight of photocatalyst particles relative to the total weight of the grains, and advantageously between 5 and 15% by weight relative to the total weight of the grains.

In the second embodiment of the invention, when the photocatalyst is titanium dioxide, the synthetic granulate preferably comprises between 0.02 and 40% by weight of photocatalyst particles relative to the total weight of the grains, and advantageously between 0.2 and 12% by weight relative to the total weight of the grains.

Advantageously, the particulate mineral material has a hardness greater than that of the matrix in which it is included and forms hard inclusions in the grains of the granulate. These inclusions form asperities on the surface of the grains of the aggregate, and are responsible for the micro-roughness of the granulate. In order to allow optimum adhesion of the tires on the wearing course, it is desirable that the relief of the grains conforms to the surface of the tires, thus creating a large contact surface. Advantageously, the particulate mineral material comprises particles having a size of less than 1.5 mm, preferably of between 1 and 1.2 mm, thus forming indentations of about 200 μm at the surface of the grains. To ensure the durability of the asperities formed by the particles of the particulate mineral material, it is preferable that the latter has a good mechanical quality. As a result, the particulate mineral material is preferably derived from a source rock having good mechanical properties, and in particular good resistance to wear and fragmentation. Any naturally occurring rock with a Los Angeles coefficient value less than 12 and a Micro-Deval coefficient of less than 20 is preferred.

The particulate mineral material is preferably sand, particularly gneiss sand or dioritic sand. The particulate mineral material may also be a mixture of several particulate mineral materials.

The starting granulate used in the second embodiment of the invention may be any granulate, natural or synthetic, in accordance with a use in a wearing course according to standard NF EN 13043.

The first binder forming the core matrix of the grains of the synthetic granulate is a hydraulic binder or pozzolanic in the sense of the standard NF P15-108.

The second binder forming the matrix of the coating layer on the surface of the grains of the synthetic granulate is also a hydraulic binder or pozzolanic in the sense of the NF P15-108 standard. It may or may not be identical to the first binder forming the matrix of the heart of the grains of the synthetic granulate. In order to obtain a good development of their mechanical performances, notably resulting in a good adhesion of the inclusions in the matrix, these first and second binders preferably comprise a cement and a silica fume.

In order that the synthetic granulate is not intrinsically sensitive to photodegradation, in addition to the particulate mineral material, all the additional constituents which form the grains are preferably of a mineral nature.

The production of the synthetic granulate according to the first embodiment of the invention is carried out by the following steps:

(a) manufacturing a mortar comprising a particulate mineral material, a first binder, and photocatalyst particles;

(b) curing said mortar;

(c) crushing said granular mortar; and

(d) curing said mortar grains; whereby said synthesis granulate is obtained. Step (a) of the process can be implemented according to two methods.

According to the first method, in step a), said photocatalyst particles are mixed simultaneously with firstly said first binder and with said particulate mineral material. According to this first method, a particulate mineral material is provided on the one hand, and on the other hand elements for forming a first binder are provided, on the other hand, particles of photocatalyst are also provided, and then a quantity of photocatalyst is mixed simultaneously. predetermined said particulate mineral material with a predetermined amount of said photocatalyst particles and with a predetermined amount of each of said elements for forming a first binder, whereby a mortar comprising, in a matrix formed by a first binder, both photocatalyst particles and inclusions corresponding to the particulate mineral material.

According to the second method, in step a), said photocatalyst particles are mixed with said first binder prior to mixing with said particulate mineral material. According to this method: on the one hand, a particulate mineral material is provided, on the other hand, elements are provided for forming a first binder, which elements comprise particles of photocatalyst, and then a predetermined quantity of said particulate mineral material is mixed with a predetermined amount of each of said elements for forming a first binder, whereby a mortar comprising, in a matrix formed by a first binder, both photocatalyst particles and inclusions corresponding to the particulate mineral material is obtained.

Preferably, the main elements intended to form the first binder of the mortar are chosen from cements, silica fume, superplasticizers and water. In practice, the matrix formed by the first binder comprises a cement, thus making it possible to obtain a mortar with a high compressive strength. The superplasticizer makes it possible to limit the water / cement ratio.

As mentioned above, the photocatalyst particles are either incorporated in the elements intended to form a first binder, or mixed simultaneously with the other constituents of the mortar. In these two cases, the amount of photocatalyst is determined such that the photocatalyst particles represent between 0.5 and 50% by weight, advantageously between 5 and 15% by weight, relative to the total weight of the synthetic granulate obtained. Step (b) of the process is a curing step which corresponds to a treatment of the mortar to manage the exchange of water and / or heat with the external environment. In practice, a cure prevents dehydration of the matrix and instead promotes hydration that tends to consolidate. Consequently, the conditions (time and temperature) in which a cure is practiced determine the consolidation of the matrix and therefore of the mortar. To show a high roughness in the mortar, it is essential that the mortar is hydrated, but that the cure for this hydration is not too long. Indeed, a crushing after a cure of short duration allows to expose a number of inclusions and thus to obtain a high roughness.

In practice, the mortar is advantageously hydrated by a cure which corresponds to a succession of two courses. The duration of the second treatment is limited, so that the consolidation of the matrix is just sufficient so that, on the one hand, the inclusions adhere sufficiently in the matrix without being detached during the crushing and that, on the other hand, the fractures caused by crushing can reveal a rugged facies. It should be noted that in the case of a cementitious matrix, the sand inclusions combine with the cement to form lime silicates within the mortar. Thus a second too long cure would lead to an extremely strong adhesion between the inclusions and the matrix, thus favoring the appearance of intergranular ruptures within the inclusions, synonymous with facies much smoother and therefore lower roughness.

For the same purpose of multiplying the number of asperities, the particles of substantially micrometric size called fines will have been advantageously removed by successive washings of the particulate mineral material before mixing with the first binder. Step (c) of the process is a crushing step of the mortar, performed after the second cure. The crushing is carried out several times, then the crushed mortar is screened in a sieve making it possible to select grains of size between 0 and 10 mm. Step (d) of the process is a curing step of the mortar grains obtained after crushing. This third treatment advantageously makes it possible to complete the hydration of the cement which began during the second treatment, to perfect the hardening of the matrix within the crushed mortar and thus to consolidate the grains obtained after crushing. This maturation leads to the development of adhesion inclusions / matrix to ensure good bonding of the particulate mineral material and the first binder and thus to limit the risk of detachment inclusions. After this stage (d) of the third cure, the mortar matures and consolidated grains are obtained.

The production of the synthetic granulate according to the second embodiment of the invention is carried out by the following steps: (e) coating a starting granulate with a coating composition comprising a particulate mineral material, a second binder, and photocatalyst particles; (f) recovery of the grains obtained by an anti-gluing agent or mobilization of the grains during the first days; and (g) curing said coating composition; whereby said synthesis granulate is obtained.

The starting granulate used in step (e) of the process is preferably characterized by a particle size d / D with d representing the smallest dimension in mm and D the largest dimension in mm such that d is between 0 and 4 and D is between 4 and 10.

In a particular case of the second embodiment of the invention, the starting granulate is identical to the synthetic granulate produced according to the first embodiment of the invention, except that the mortar is not loaded with particulate matter. photocatalyst. This therefore amounts to carrying out the following steps: (a) manufacturing a mortar comprising a particulate mineral material and a first binder;

(b) curing said mortar;

(c) crushing said granular mortar;

(d) curing said mortar grains; whereby said starting granulate used in step (e) of the process is obtained.

In this particular case, steps (b), (c) and (d) above are identical to steps (b), (c) and (d) of the method corresponding to the first embodiment of the invention, and step (a) above is carried out as follows: on the one hand, a particulate mineral material is provided, on the other hand, elements are provided for forming a first binder, and then a predetermined quantity of said particulate mineral material is mixed with a predetermined quantity of each of said elements intended to form a first binder. whereby a mortar comprising, in a matrix formed by a first binder, inclusions corresponding to the particulate mineral material is obtained. The coating composition used in step (e) of the process can be obtained by two methods. According to the first method, said coating composition is obtained by simultaneous mixing of said photocatalyst particles with said second binder and with said particulate mineral material. According to this method, a particulate inorganic material is provided on the one hand, and elements for forming a second binder are provided on the other hand. Photocatalyst particles are also provided on the other hand and a predetermined quantity is then mixed simultaneously. said particulate mineral material with a predetermined amount of said photocatalyst particles and with a predetermined amount of each of said elements for forming a second binder, whereby a coating composition comprising a particulate mineral material, a second binder, and photocatalyst particles. According to the second method, said coating composition is obtained by simultaneously mixing said photocatalyst particles with said second binder prior to mixing with said particulate mineral material. According to this method: - on the one hand a particulate mineral material is provided, on the other hand, elements are provided for forming a second binder, which elements comprise photocatalyst particles, then a predetermined quantity of said particulate mineral material is mixed with a predetermined amount of each of said elements for forming a second binder, whereby a coating composition comprising a particulate mineral material, a second binder, and photocatalyst particles is obtained. Preferably, the main elements for forming the second binder of the coating composition are selected from cements, silica fume, superplasticizers and water. In a particularly preferred manner, the second binder is identical to the first binder.

As mentioned above, the photocatalyst particles are either incorporated in the elements for forming a second binder, or mixed simultaneously with the other constituents of the coating composition. In both cases, the quantity of photocatalyst is determined so that the photocatalyst particles represent either between 0.5 and 50% by weight, advantageously between 5 and 15% by weight, relative to the total weight of the coating composition, or between 0 , 02 and 40% by weight, advantageously between 0.2 and 12% by weight, relative to the total weight of the synthetic granulate obtained.

Step (e) of the process is carried out as follows: a starting granulate is provided on the one hand, and on the other hand a coating composition obtained according to one of the two methods described above is provided. above, - mixing in a kneader a predetermined amount of said starting granulate with a predetermined amount of said coating composition, whereby grains are obtained coated by said coating composition. The amount of the coating composition to be introduced into the kneader is calculated from the specific surface of the starting granulate. This is to cover each grain of the starting granulate with a coating layer of thickness preferably between 0.1 and 3 mm and preferably between 0.5 and 1.5 mm.

Step (g) of the method is a curing step, identical to step (d) of the method corresponding to the first embodiment of the invention.

Prior to this curing step, a step (f) is carried out in which the grains coated with the coating composition are covered with an anti-adhesive agent. This step is necessary to prevent grain agglomeration during the subsequent cure step (g).

This anti-slip agent may be chosen from mineral powders such as calcareous or siliceous fillers. It can also be liquid, and corresponds for example in this case to silicone oil or paraffin oil. Finally, they may be concrete deactivating agents capable of blocking the setting phenomenon on the surface.

Alternatively, in the case where no anti-sticking agent is available, it is possible to obtain a similar result by regularly mobilizing the grains during the first days after their manufacture, so as to break the bonds that could have occurred. train them during this time. After these steps (f) and (g), the synthetic granulate is obtained whose grains consist of a core coated with a consolidated coating layer. The synthetic granulate is then screened in a sieve to select the size of the grains.

The present application finally relates to the use of synthetic granulate with photocatalytic properties in a de-polluting wearing course. Finally, the present invention relates to a cleansing surface layer obtained by mixing a granulate and a bituminous binder of which part of the granulate, preferably all, is a synthetic aggregate as defined above. A wearing course is obtained from a mix comprising a mixture of a granulate, a bituminous binder and optionally additives and / or fillers. According to the invention, at least a portion of the aggregates are synthetic aggregates with photocatalytic property. The synthetic granulate has a particle size d / D with d is between 0 and 8, preferably between 0 and 4 and D is between 4 and 10, preferably between 5 and 10, and better between 6 and 10. The layer In general, the rolling composition comprises 3 to 10% by weight of bituminous binder and 60 to 95% by weight of aggregate relative to the total weight of the wearing course.

Other features and advantages will become more apparent from the examples which follow, given by way of illustration and not limitation.

Examples

I. First embodiment of the invention

The two compositions indicated in Table 1 below are given by way of example of compositions making it possible to obtain a synthetic granulate with photocatalytic properties according to the first embodiment of the invention.

The compositions are expressed in kg of material for one cubic meter of concrete.

Table 1: Compositions making it possible to obtain a synthetic granulate with photocatalytic properties according to the first embodiment of the invention.

By considering Example 1, a quantity substantially equal to 943 kg / m ³ of gneiss sand is mixed simultaneously with an amount equal to 210 kg / m ³ of photocatalyst particles and with a total amount substantially equal to 1021 kg / m 2. ³ elements for forming the first binder and water. Prior to mixing, the gneiss sand has preferably undergone sieving on a sieve of 1.5 mm to retain as particles only sand grains of size preferably less than or equal to 1.5 mm.

The mortar is obtained by mixing the aforementioned quantities, and by performing the first cure, then the second cure. It is then crushed and sieved to select grain size preferably between 6.3 and 10 mm. These are then subjected to the third cure.

By considering Example 2, a quantity substantially equal to 840 kg / m ³ of dioritic sand is mixed simultaneously with an amount equal to 280 kg / m ³ of photocatalyst particles and with a total amount substantially equal to 101 1 kg / m 2. ³ elements for forming the first binder and water.

As for Example 1, prior to mixing, the dioritic sand has preferably undergone sieving, but rather on a sieve of 1 mm to retain as particles only sand grains of size preferably less than or equal to 1 mm. The same steps as those carried out for the mortar of Example 1 are then carried out.

Such a synthetic granulate with photocatalytic properties has extremely interesting properties which allow it to be used in wearing courses which are both depolluting and having excellent adhesion properties of the tires.

II. Embodiment of the invention

The two compositions indicated in Table 2 below are given by way of example of compositions making it possible to obtain a synthetic granulate with photocatalytic properties according to the second embodiment of the invention.

Table 2: Compositions making it possible to obtain a synthetic granulate with photocatalytic properties according to the second embodiment of the invention. Considering Example 3, a coating composition is prepared by mixing an amount equal to 990 kg / m ³ of gneiss sand with a quantity equal to 240 kg / m ³ of photocatalyst particles and with a substantially equal total amount. at 1015.2 kg / m ³ of elements intended to form the second binder and water.

As for Example 1, prior to mixing, the gneiss sand was preferably sieved on a sieve of 1.5 mm.

The synthetic granulate A is obtained by mixing one ton of 4/6 chippings of dioritic nature in a kneader with 1200 kg of the coating composition of Example 3, and then covering the coated grains obtained with an anti-gluing agent such as Formwork oils or the like and the agents for inactivating the concrete, by effecting the final cure of the coating composition. We get a ton of gravel 5/7.

Whereas in Example 4, a coating composition is prepared by mixing an amount equal to 910 kg / m ³ of sand with diorite an amount equal to 180 kg / ^m3 of photocatalyst particles and a total amount substantially equal to 1079 kg / m ³ of elements intended to form the second binder and water.

As for Example 2, prior to mixing, the dioritic sand was preferably screened on a 1 mm sieve.

Synthetic granulate B obtained by mixing one ton of chippings 2/8 in a kneader which is coated with 1600 kg of the coating composition of Example 4, and then covering the coated grains obtained with an anti-adhesive agent as defined above, by effecting the final cure of the coating composition, and finally by sieving to select grains of size preferably between 6.3 and 10 mm.

Such a synthetic granulate with photocatalytic properties has extremely interesting properties which allow it to be used in depolluting wearing courses which have excellent tire adhesion properties.

According to this embodiment, the necessary quantities of photocatalyst are less important than for the first embodiment.

Claims

1. Synthetic granulate with photocatalytic properties for road application, consisting of a set of grains, each comprising, included in a matrix formed by a hydraulic or pozzolanic binder, at least photocatalyst particles and a particulate mineral material which is a sand , the synthetic granulate having a particle size d / D with D between 4 and 10.

2. Synthetic granulate according to claim 1, characterized in that said photocatalyst particles are particles of titanium dioxide, preferably anatase titanium dioxide.

3. Synthetic granulate according to claim 1 or 2, characterized in that the matrix formed by a first binder, which comprises the particulate mineral material and the photocatalyst particles, constitutes the core of the grains of the synthetic granulate.

4. Synthetic granulate according to claim 3, characterized in that it comprises between 0.5 and 50% by weight of photocatalyst particles relative to the total weight of said grains, preferably between 5 and 15% by weight.

Synthetic granulate according to claim 1 or 2, characterized in that the matrix formed by a second binder, which comprises the particulate mineral material and the photocatalyst particles, is on the surface of the grains of the synthetic granulate, where it constitutes a coating layer, the core of the grains of the synthetic granulate then being constituted by the grains of a starting granulate.

6. Synthetic granulate according to any one of the preceding claims, characterized in that said first binder and said second binder are both hydraulic binders or pozzolanic, identical or not.

7. A process for producing a synthetic granulate with photocatalytic properties for road application according to any one of claims 1 to 4, characterized in that it comprises the following steps:

(a) manufacturing a mortar comprising a particulate mineral material, a first binder, and photocatalyst particles; (b) curing said mortar;

(c) crushing said granular mortar; and

(d) curing said mortar grains, to obtain said synthetic granulate.

8. A method according to claim 7, characterized in that step b) curing said mortar corresponds to a succession of two cures.

9. A process for producing a synthetic granulate with photocatalytic properties for road application according to any one of claims 1 or 5, characterized in that it comprises the following steps: (e) coating a starting granulate with a coating composition comprising a particulate mineral material, a second binder, and photocatalyst particles;

(f) recovery of the grains obtained by an anti-gluing agent or mobilization of the grains during the first days; and

(g) curing said coating composition.

10. Depollifying tread layer obtained by mixing the synthetic granulate according to any one of claims 1 to 6 with a bituminous binder, characterized in that the synthetic granulate has a particle size d / D with D between 4 and 10.