FR3031051A1 - CONCRETE SLUDGE TREATMENT - Google Patents

Abstract

The present invention relates to a method of treating concrete sludge (BB) comprising a drying phase (P1) of concrete sludge (BB) in order to reduce the water content of said sludge (BB) in a range between 15 and 30 %, an upgrading phase (P2) comprising: a) a first screening (S3) of dry concrete sludge (BB) in order to recover, from said sludge (BB), a first product (PDT1), called rejection (GR ), consisting of elements greater than or equal to 22.4 millimeters, and a second product (PDT2) consisting of elements smaller than 22.4 millimeters, and b) a second screening (S4) of said second product (PDT2) to separate elements of size less than 8 millimeters, namely sands (SA), elements of sizes between 8 and 22.4 millimeters, called agglomerates (AG).

Description

TECHNICAL FIELD AND PRIOR ART The object of the present invention relates to the treatment of concrete sludge, and more particularly the cleaning and recycling of concrete sludge. One of the objects of the present invention is to enhance the concrete sludge by allowing in particular a reuse of sand and grit from the sludge. The present invention thus has many advantageous applications, particularly in the various sectors of the public works industry by allowing for example the recycling of concrete sludge such as those from the settling tanks of concrete plants.

Other advantageous applications can of course be considered in the context of the present invention. Regulations on waste treatment are becoming more and more stringent in the industry. Thus, for both ecological reasons and economic reasons, industrialists are forced to limit or even eliminate their waste and their discharge into water. The Ready Mixed Concrete Industry, also known by the acronym "BPE", must also comply with these regulations. The players in this market must set up solutions to value concrete sludge.

This sludge comes mainly from the return of concrete from construction sites, the cleaning of "top trucks", or the cleaning of production tools and especially mixers. Today, these sludges are discharged on concrete areas located near several settling ponds, which are serially aligned one after the other.

The water from this sludge settles largely in the first basin, then in the other following basins. Until now, no effective solution has really been put in place to valorize this sludge. OBJECT AND SUMMARY OF THE PRESENT INVENTION The present invention aims to improve the situation described above by providing a solution for upgrading concrete sludge in an industrial environment. Classically, these sludges consist of a heterogeneous mixture of chippings, sands, cement fines, agglomerates of sand and fines, and often adjuvants diluted in water sludge.

One of the objectives of the present invention is in particular to separate the different products above in order to valorize them. To this end, the present invention relates to a method of upgrading concrete sludge which comprises a drying phase and a treatment phase.

The drying phase advantageously comprises drying the concrete sludge to reduce the water content of the sludge in a range of between 15 and 30%. The treatment phase comprises: a first screening of the dry concrete sludge in order to recover, from the sludge, a first product, called rejection, consisting of elements of size greater than or equal to a first determined particle size threshold, and a second product, referred to as a serious product, consisting of elements of size less than said first particle size threshold, and a second screening of the second product in order to separate the elements of size smaller than a second determined particle size threshold, namely the sands, elements, called chippings, the size of which is between the second and first size thresholds. Advantageously, the first threshold is greater than the second threshold. Thus, thanks to this succession of technical steps, characteristic of the present invention, it is possible to separate the refusal, the chippings and the sands. This dry treatment allows recovery of concrete sludge while avoiding significant consumption of water necessary for washing chippings. Indeed, without water supply, the treatment proposed in the context of the present invention allows to separate, from the concrete sludge, the refusal, sands and chippings.

Advantageously, the first granulometric threshold is equal to a value between about 15 to 28 millimeters; preferably, the first granulometric threshold is substantially equal to 22.4 millimeters. Advantageously, the second granulometric threshold is equal to a value of between 4 and 12 millimeters; preferably, the second granulometric threshold is substantially equal to 8 millimeters. The agglomerates are generally formed of fine sands and cement, which form between them, mostly on chippings, solid blocks of small dimensions.

In order to eliminate agglomerates and to recover "clean" chippings, the treatment phase comprises crushing, or crumbling, during which the agglomerates are crushed and the layer is removed around said chippings. Advantageously, the treatment phase comprises, following the crushing, a third screening of the agglomerates in order to separate the cleaned grit from a third product composed of sand and cement. At the end of this treatment, the process according to the present invention makes it possible to separate, as a function of their particle size, the following products: the rejection (approximately 10% in estimated proportion) with a particle size greater than a first determined threshold; sand (approximately 55% in estimated proportion) with a particle size smaller than a second determined threshold; and - "clean" gravel (approximately 35% in estimated proportion) with a grain size between the two thresholds.

Thus, the "clean" sands and gravel obtained at the end of this treatment can be reused for example in the manufacture of concrete; the concrete sludge is thus recoverable thanks to the treatment above. Advantageously, the drying phase comprises aeration of the concrete sludge, for example by ventilation, called natural ventilation.

Optionally, the drying phase comprises: - storage of the concrete sludge under a covered tunnel, and / or - spinning of the concrete sludge. Correlatively, the present invention relates to the use of the method as described above for the recovery of sludge from a settling basin of a concrete plant. The present invention further relates to an upgrading plant for concrete sludge, suitable for implementing the method described above, which advantageously comprises: a storage platform for drying concrete sludge in order to reduce the water content sludge in a range of between 15 and 30%, and a processing platform comprising: a) a first screen configured to recover from the dried concrete sludge a first product, called a rejection, consisting of elements of greater than or equal to a first determined particle size threshold, and a second product consisting of elements smaller than said first particle size threshold, and b) a second screen configured to separate, from the second product, the elements of size less than a second defined granulometric threshold, namely the sands, elements, called chippings, the size of which is between uxth and first granulometric thresholds.

Advantageously, the processing platform comprises crushing means having a pair of compression rollers having a substantially identical diameter, the direction of rotation is opposite to allow the cleaning of chippings by crushing agglomerates. The spacing between each roller may advantageously be adjustable in order to improve the cleaning efficiency and to adapt the treatment to the particle size of the treated product. The speed of rotation of the rolls can also be variable, always with the aim of improving the quality of the finished product. The installation advantageously comprises a set of means configured for the implementation of any of the steps of the method described above. Thus, by its different structural and functional aspects, the present invention makes it possible to remedy the various disadvantages stated in the state of the art by proposing a specific installation for a dry treatment of concrete sludges, and in particular those resulting from settling ponds of concrete plants, in order to valorize these sludges. Brief description of the appended figures Other characteristics and advantages of the present invention will emerge from the description below, with reference to FIGS. 1 and 3, which illustrate an embodiment of this embodiment devoid of any limiting character and in which: FIG. 1 is a flowchart illustrating the method of upgrading concrete sludge according to an exemplary embodiment of the present invention; FIG. 2 represents a schematic view of an installation according to an exemplary embodiment of the present invention; and FIG. 3 represents a schematic view of the crushing means according to an example of the present invention. DETAILED DESCRIPTION OF AN ADVANCED EMBODIMENT A method for upgrading concrete sludge and the plant for carrying out this process will now be described in the following with reference to Figures 1 and 3.

It is estimated that concrete sludge accounts for about 4% of concrete production. Thus, for 100m3 of concrete produced, the materials to be treated represent about 4m3, or about 8 tons of sludge to be treated. Today, the recovery of concrete sludge does not exist in the process 5 currently in place. Indeed, after settling, it is generally enough to send the waste to landfills. It is therefore understandable that the valorization of these sludges represents a major stake for the concrete industry, these muds representing until now a true loss. Valuing concrete sludge BB is one of the objectives of the present invention.

In the example described here, the BB concrete sludge that is to be upgraded is sludge from the settling ponds of the concrete plants. This is one example among other possible examples. In this example, according to the present invention, the sludge BB from the settling ponds is transported and then unloaded by tipper trucks directly onto a PS storage platform of the installation 100. This storage platform PS is configured to perform a pretreatment of the sludge and allow the adequate drying of this sludge. In the example described here, the method according to the present invention provides a drying phase P1 on this PS platform.

During this phase P1, the sludge is stored on this platform PS during a step S1; they are preferably moved at least once using a construction machine of the type for example loaders, hydraulic excavators on tires or caterpillars. This displacement S2 of the sludge during this phase P1 makes it possible to ventilate the material; such aeration, by natural ventilation, accelerates the drying process.

It is also observed that this movement of material has the advantage of breaking some of the uncured lumps. In the example described here, the storage step Si is done by storing the sludge in a covered tunnel. The use of such a tunnel has the advantage that the natural ventilation considerably accelerates the drying time while protecting the sludge from bad weather.

The tests carried out by the Applicant have furthermore shown that the storage height of the BB sludge has a direct influence on the drying speed of the sludge. Thus, in the example described here, the drying phase P1 is optimal by carrying out a storage If sludge BB over a height greater than 4 meters.

From a water content of between 15 and 30% defined on the granular fraction 0-8 millimeters, the "dry" sludge can pass on the processing platform PT to move to a treatment phase P2. This tolerated water content is defined as a function of the absorption of the granular fraction 0-8 millimeters and the nature of the aggregates (for example hard limestone, siliceous, sillico-limestone, etc.). As soon as the sludge BB reaches this level, these sludges are therefore considered ready for the treatment phase P2. In the example described here, the treatment phase P2 firstly comprises the succession of a first S3 and a second S4 screening of the dry concrete sludge BB. The first screen S3 makes it possible to obtain a first PDT1 and a second PDT2 produced. This first product PDT1, called GR refusal, consists of elements greater than or equal to 22.4 millimeters; this value taken here as an example corresponds to the first granulometric threshold. For this first threshold, the selection of a value between 15 to 28 millimeters can be considered here. The second product PDT2, called serious, is then routed to a second screen 20 for a second screen S4 in order to separate the elements of size less than 8 millimeters, namely SA sands, elements of sizes between 8 and 22.4 millimeters, called AG gravel. This value of 8 millimeters is taken here as an example and corresponds to the second granulometric threshold. For this second threshold, the selection of a value between 4 to 12 millimeters can be considered here. It was found by the Applicant that the operation performed in a "Trommel" type screening tunnel has the disadvantage of fouling the chippings. Indeed, the rotation of the materials on themselves leads to fouling of elements whose size is greater than 8 millimeters. Thus, these steps S3 and S4 are performed using screens 10 and 20, flat on two or three floors, depending on the granular range to be targeted. Preferably, these are sieves called "piano strings".

In this example, the first screen 10 preferably has a screening area of at least 5 m 2 in order to obtain a correct evacuation of the fines. These two stages S3 and S4 thus make it possible to recover, from the BB sludge: rejections: approximately 10%, pebbles and agglomerates of fines: approximately 45%, and sand: approximately 45%. In this example, the elements obtained after the second screening have a size of between 8 and 22.4 millimeters; they are particularly important for the manufacture of concrete.

These elements contain in particular GV chippings and agglomerates of sand and fine. However, following the second screening, more than 15% of fines and agglomerated and friable elements composed of cement or slag extracted from the cleaning of the settling ponds are present in these elements.

However, the finer the material contains and the friable elements, the more the manufacture of the concrete requires water. The addition of water in the concrete manufacturing process has the direct effect of reducing the strength of the concrete. The product resulting from this second screening is therefore not recoverable in the state. To overcome this problem, the manufacturer of the BPE die could provide a larger cement dosage, which is unsatisfactory. Thus, following these screens S3 and S4, the presence of friable elements does not allow to reuse the second product in a concrete manufacturing process. The friable elements contained in the second product PDT2 must be eliminated. The present invention overcomes this problem by performing a specific treatment. More particularly, in the example described here, the treatment phase P2 comprises crushing or crumbling S5 using means 30. In the example described here, this crushing S5 is carried out after a drying time depending on the climatic conditions. (and in particular according to the ambient hygrometry rate), the location of the storage and the effectiveness of the previous treatment, that is to say the greater or lesser number of soft elements in the second product. PDT2. More particularly, in the example described here, the crushing S5 is triggered when fines glued to GV grit detach from a simple shock or friction. The triggering of this step S5 is therefore based on feedback. The Applicant submits that the measurement of water content is not sufficiently reliable here to determine whether or not the second product is ready for recovery. This step S5 comprises conveying agglomerates AG, by means of conveyor belt or crawler excavator means, to a feed hopper 31 as illustrated in FIG.

In the example described here and illustrated in FIG. 3, under this feed hopper 31 are two pairs of rollers 32 each having a substantially identical diameter and an inverted direction of rotation so as to allow crushing of the friable elements. around the SG gravel.

Such an arrangement of rollers 32 with bibs 33 allows crumbling of the SG gravel. Preferably, the rollers 32 are made of a semi-rigid deformable material such as rubber (tires). An inverter can be provided for regulating the rotational speed of the rollers 10 (not shown here). In an exemplary embodiment not illustrated here, the distance between the rollers 32 of each pair of rollers is adjustable in order to adapt the efficiency of the treatment. It is thus possible to envisage the passage of sand SA between the rollers by setting the distance to a minimum.

The presence of two pairs of stepped rollers 32 as illustrated in FIG. 3 makes it possible to increase the efficiency of the treatment if necessary. A single pair of rollers or even more than two pairs of rollers may be provided one above the other. The crushed products are recovered by a receiving hopper 34. In an embodiment not shown here, an impact chamber, composed of a closed hopper with a rotating pallet inside to propel the aggregates on the interior walls of the container. the hopper, can complete the installation, especially when the product is difficult to clean. In such an embodiment, the box is positioned in place of the receiving hopper 34.

Thus, whether in this mode or in the other, the friable elements surrounding the gravel GV are crushed by the means 30, in particular by passing through the pair of rollers 32. After such a passage through the means 30, the product resulting from the cleaning is then screened again by a third screen 40 during a step S6. At the end of this third screening S3, the fine elements containing a large sulphate content are removed with the sand; the gravel GV from this step S3 thus have an acceptable content of fine elements, which allows its reuse, especially for the manufacture of concrete. In the example described here, following this succession of steps, the products resulting from the sludge treatment are decomposed as follows: 3031051 9 - refusal (elements of size greater than or equal to 22.4 millimeters): approximately 10%, - elements of size between 8 and 22.4 millimeters: about 35%, and - sand: about 55%. The second treatment phase with S5 crushing and S6 screening makes it possible to refine the product for good sludge recovery. It is then expected that the various products resulting from this treatment will be stored and sent to the various sectors in accordance with the standards in force. The present invention thus makes it possible to dry treat all the sludge from the settling tanks, so that they can be reused completely in 10 different processes of the Public Works sector. More particularly, the present invention allows BPE manufacturers to implement a solution in accordance with environmental rules for recovering waste concrete sludge from the settling tanks of concrete plants; the present invention makes it possible in particular to valorize this sludge and to obtain products suitable either for being reintegrated in a conventional manufacturing circuit or for considering a new range of products. The installation of a plant 100 according to the present invention is in accordance with ICPE 2515; such an installation enables BPE producers to guarantee the evacuation and recovery of concrete sludge.

The installation of such an installation 100 also makes it possible to reduce the environmental taxes that are generally payable for discharges into water and sludge waste. The present detailed description relates directly to a use of the sludge recovery process from a settling basin of a concrete batching plant. Of course, this application example is one example among other examples. Those skilled in the art will understand that the treatment applied here on concrete sludge can be used for other applications. It should be observed that this detailed description relates to a particular embodiment of the present invention, but in no case this description is of any limiting nature to the object of the invention; on the contrary, its purpose is to remove any imprecision or misinterpretation of the claims that follow.

Claims (10)

REVENDICATIONS1. A method of upgrading concrete sludge (BB) comprising: - a drying phase (P1) of concrete sludge (BB) in order to reduce the water content of said sludge (BB) in a range between 15 and 30%, - a treatment phase (P2) comprising: a) a first screening (S3) of dry concrete sludge (BB) in order to recover, from said sludge (BB), a first product (PDT1), called rejection (GR), consisting of elements of size greater than or equal to a first determined particle size threshold, and a second product (PDT2) consisting of elements of size less than said first particle size threshold, and b) a second screening (S4) of said second product (PDT2) in order to separating the elements of size smaller than a second determined particle size limit, namely the sands (SA), elements, called agglomerates (AG), whose size is between said first and second grain size thresholds, said first threshold being greater than udit second threshold. 2. The method of claim 1, wherein the first particle size threshold is equal to a value between the order of 15 to 28 millimeters, preferably substantially equal to 22.4 millimeters. 3. The method of claim 1 or 2, wherein the second granulometric threshold is equal to a value between about 4 to 12 millimeters, preferably substantially equal to 8 millimeters. 4. Method according to any one of claims 1 to 3, said agglomerates (AG) being in particular composed of gravel (GV) surrounded by a layer of sand and cement, wherein the treatment phase (P2) comprises a crushing (S5) during which the agglomerates are crushed and the layer is removed around said chippings (SG). 5. Method according to claim 4, comprising, after crushing (S5), a third screen (S6) agglomerates (AG) to separate the cleaned grit (SG) of a third product (PDT3) composed of sand and cement. 3031051 11 6. Method according to any one of claims 1 to 5, wherein the drying phase (P1) comprises an aeration (S2) of concrete sludge (BB), by ventilation. The method of any one of claims 1 to 6, wherein the drying step (P1) comprises storage (S1) of the concrete sludge (BB) under a covered tunnel. 8. Use of the method according to any one of claims 1 to 7 for the recovery of concrete sludge (BB) from a settling basin of a concrete plant. 10 9. Recovery plant (100) for concrete sludge (BB) comprising: - a storage platform (PS) for drying concrete sludge (BB) in order to reduce the water content of said sludge (BB) in a range between 15 and 30%, and - a processing platform (PT) comprising: a) a first screen (10) configured to recover from said dried concrete sludge a first product, called a refusal, consisting of elements of size greater than or equal to a first determined particle size threshold, and a second product consisting of elements smaller than said first grain size threshold, and b) a second screen (20) configured to separate, from the second product, the size elements. less than a second determined particle size threshold, namely the sands, elements, called agglomerates (AG), the size of which is between said first threshold being greater than said second threshold, said premie r threshold being greater than said second threshold. 10. Installation (100) according to claim 9, comprising means configured for carrying out the method according to any one of claims 2 to 7.