FR2917082A1 - Additive, useful to prepare cement based composition containing concrete, mortar or cement, comprises particles of iron (II) sulfate dry heptahydrate - Google Patents

Abstract

Additive for cement based composition comprising concrete, a mortar or a cement, comprises particles of iron (II) sulfate dry heptahydrate, which does not comprises more than 20 wt.% of the particles and having a granulometric size of 200 mu m, comprising at least 20 wt.% of iron (II) sulfate dry heptahydrate having granulometric distribution of 100-200 mu m. Independent claims are included for: (1) a cement based composition comprising concrete, mortar or cement, comprising the additive; and (2) a preparation of the composition comprising mixing the iron (II) sulfate dry heptahydrate particles with the cement.

Description

ADDITIVE FOR CEMENT-BASED COMPOSITION

  The present invention relates to an additive for a cementitious composition, such as a concrete, a mortar or a cement, comprising particles of iron (II) sulfate heptahydrate.

  It is well known in the cement industry that the soluble chromium (VI) content should be as low as possible. Thus, current regulations (European Directive 2003/53 / EC) require that the concentration of chromium (VI) soluble in cement be less than 2 ppm.

  A common method for obtaining a reduced chromium (VI) content cement thus consists in adding to the cement ferrous sulphate - or ferrous sulphate (FeSO4) -, insofar as the Fe2 + ions make it possible to reduce the Crs ions +

  The iron sulphate used is either heptahydrate (FeSO4,7H2O) or monohydrate (FeSO4, H2O). Iron sulphate heptahydrate is more soluble in water than iron sulphate monohydrate, however it generally has coarser particles than iron sulphate monohydrate. In addition, the Applicant has shown that the wet form of iron (II) heptahydrate sulphate - called copperas or green vitriol in English - is poorly adapted as it is to the mixture with the cement, insofar as it can form agglomerates making handling and solubilization difficult. The iron sulphates heptahydrates dry - denominated free flowing heptahydrate ferrous sulphate in English language - currently available on the market all have relatively large particle sizes, with 70 to 90% by weight of the product consisting of particles having a particle size greater than 200 μm. The particle size of these iron sulphate heptahydrate particles results in the appearance of spots due to incomplete dissolution of the large iron sulphate particles followed by oxidation (rust stain) on the facings of the materials comprising cement. In order to avoid this phenomenon, coarse iron sulphates are usually added at the mill inlet in the case of open circuit mills or at the separator inlet in the case of closed circuit mills.

  When iron sulphate is added at the mill or at the separator inlet, the iron sulphate particles are co-milled with the constituents of the cement and turn into very small particles. These small particles of iron (II) sulphate heptahydrate, because of a large surface area / volume ratio, are more subject to oxidation or aging and thus lose their effectiveness vis-à-vis the reduction of chromium (VI ) over time.

  To guarantee a soluble chromium (VI) content of less than 2 ppm for a sufficient period of time and thus to compensate for the loss of efficiency over time, the amount of iron sulphate which is incorporated in the cement is much greater than the amount of iron sulphate theoretically required to reduce soluble chromium (VI). Currently the dose of ferrous sulphate heptahydrate added in the cement varies widely, between 300 and 1000 ppm of ferrous sulphate dry heptahydrate (ie between 60 and 200 ppm of Fe2 + ion) per ppm of soluble chromium (VI), this depending on the shelf life of the desired cement (the values mentioned correspond to a minimum shelf life of two months). This overdose generates a significant additional cost and a risk concerning a possible modification of the properties of use of the cement or materials derived from it, such as concretes or mortars.

  There is therefore a need for a process to increase the stability of iron sulfate dry heptahydrate and to reduce the amount of iron sulfate to be incorporated into a cement (for example in order to reduce the soluble chromium (VI) contained in this cement). Therefore, one of the objects of the present invention is an additive for a cementitious composition, such as a concrete, a mortar or a cement, comprising particles of iron (II) sulfate dry heptahydrate, said particles of iron (II) sulfate dry heptahydrate comprising not more than 20%, preferably not more than 10%, advantageously not more than 5% by weight of particles having a particle size greater than 200. According to a particularly preferred embodiment, at least 20%, preferably at least 50%, advantageously at least 75% by weight of iron (II) dry heptahydrate sulfate particles have a particle size distribution of between 100 μm and 200 μm. pm. It is theoretically possible to obtain up to about 99% of iron (II) dry heptahydrate sulfate particles having a particle size distribution of between 100 μm and 200 μm. In general, at most the percentage of particles of iron (II) heptahydrate sulfate having a particle size distribution of between 100 μm and 200 μm is high, at most the amount of iron (II) sulfate heptahydrate dry to incorporate the cement is weak, for a result at least equivalent.

  Applicants have unexpectedly discovered that dry iron (II) sulfate particles in the above-mentioned particle size distribution have a better efficiency over time in reducing soluble chromium (VI). Advantageously, the additive consists of a powder of iron (II) sulfate dry heptahydrate (for a minimum shelf life of the composition of two months).

  Another object of the present invention is a cementitious composition, such as a concrete, a mortar or a cement, comprising an additive according to the invention. Preferably, said composition is a cement. According to a particularly preferred embodiment, the abovementioned cement is a Portland cement, a composite cement, any cement defined in the EN 197 standard, or any cement defined in the ASTM C-150 and C-595 standards.

  Advantageously, this composition contains a dosage by weight of additive according to the invention, such that the amount of iron (II) dry heptahydrate introduced into the composition is less than 60 ppm of iron (II) per ppm of chromium (VI) soluble.

  According to a preferred embodiment, the composition according to the invention has a chromium (VI) content of less than or equal to 2 ppm during a storage period of at least two months, preferably at least two months. nine months, said storage period of up to twelve months. Another object of the invention is a process for obtaining the aforementioned composition, said process comprising a step of mixing iron (II) heptahydrate sulfate particles with a cement.

  Another object of the invention relates to the use of an additive according to the invention for preparing a composition based on cement, such as a concrete, a mortar or a cement.

  Granulometric size selection can be carried out according to one or other of the known methods for controlling the particle size: grinding / selection, agglomeration of fine particles or controlled recrystallization.

  The present invention makes it possible to overcome the drawbacks of the state of the art, and more particularly to reduce significantly, compared with prior art techniques, the amount of iron sulphate which it is necessary to incorporate into a cement in order to to reduce the soluble chromium (VI) contained in this cement, by incorporating in the cement only a moderate quantity of an additive, while obtaining satisfactory results. The reduction of the amount of iron sulphate used allows undeniable economic gains and makes it possible to avoid, as mentioned above, the possible risks related to possible changes in the use properties of the cement or materials derived therefrom. , such as concretes or mortars.

  The invention thus provides a solution for improving the durability of iron sulphate on the reduction of chromium (VI) soluble in cement, unlike the state of the art.

  Alternatively, tin sulfate or manganese sulfate could be used instead of iron (II) sulfate, since these compounds have similar chromium (VI) reducing properties and exhibit relative instability. when they are added to the cement.

  According to the present invention iron (II) sulfate is in dry heptahydrate form (FeSO4, 7H2O). Indeed, this dry heptahydrate form of the iron (II) sulfate particles, in combination with the specific particle size distribution according to the present invention, results, surprisingly, in an excellent stability of the sulphate particles of Fe2 + ions (in mixture with a cementitious composition) that can ensure the reduction of Cr6 + ions over a longer period of time, while using smaller amounts of iron (II) heptahydrate sulfate. By way of example, the Applicant has unexpectedly discovered that the monohydrate form (FeSO 4, 1H 2 O) does not make it possible to maintain the amount of chromium (VI) below 2 ppm whereas the dry heptahydrate form continues to limit this amount of chromium (VI) below the aforementioned limit threshold, under equivalent treatment conditions.

  The cementitious composition according to the invention is substantially stable during a storage period of at least two months, preferably at least nine months and up to twelve months under the usual conditions of cement storage, in particular in bag.

  By "substantially stable" it is meant that sufficient Fe2 + ions are available to reduce the amount of soluble chromium (VI) to less than 2 ppm. The additive of the invention is useful as an additive for cements. By way of cement, any type of cement may be used, in particular Portland cements, composite cements, any cement defined in the EN 197 standard, or any cement defined in the ASTM C-150 and C-595 standards. The additive according to the invention can be added at any time during the manufacture of the cement. This additive may be added or as a separator inlet in the case of closed circuit mills, or directly to the finished product. This latter solution is preferred in that it limits the attrition actions on the surface of the particles. The additive can also be added in silos or in transport tanks, or in the final concrete or mortar.

  The amount of iron (II) sulphate heptahydrate sulfate particles is relatively small, compared to the amount of iron sulphate that was previously required to compensate for the loss of time efficiency of iron sulphate. .

  The particles according to the invention have no noticeable effect on the conditions of use of the cement, which is therefore used quite conventionally.

  Alternatively, the iron (II) sulfate particles may be coated, for example with polymers such as alginate or gelatin.

  Synthesis of the additive according to the invention The additive is obtained according to one of the following three methods: grinding / selection to a particle size of less than about 200 μm of an iron sulfate heptahydrate marketed for cement application; grinding / screening to a particle size ranging from about 100 μm to about 200 μm of a commercially available iron sulfate heptahydrate for the cement-agglomerating application using an organic binder of fine particles (<100 μm) obtained by grinding of an iron sulphate heptahydrate marketed for cement application Examples of the effectiveness of the additive according to the invention on the reduction of the soluble chromium (VI) of a cement Incorporation protocol into the cement of the cement additive according to the invention Various amounts of iron (II) sulfate monohydrate or dry heptahydrate powder are added to the cement according to the tests, the iron (II) sulphate samples used being different. particle sizes, for comparison purposes. Comparisons between various forms of iron sulphates are always made at the same quantities of iron (II) introduced by the amount of chromium (VI) soluble in the cement. A cement incorporating the additive according to the invention is prepared by mixing this additive with the cement and homogenizing by passing 45 minutes of the mixture in a mixer marketed under the trademark Turbula.

  The soluble chromium (VI) content of the treated cement is determined immediately or after subjecting the treated cement to an accelerated aging protocol described below.

  Accelerated Aging Protocol: High Moisture This test consists in placing in a tank a bed of cement powder containing iron sulphate: the mass of cement is approximately 600 grams and the height of the bed is 1 cm. This tray is then placed in a chamber maintained at 20 C and 100% relative humidity. The tank remains 24 hours in this chamber, then the measurement of soluble chromium (VI) is carried out. We measure to 1 day.

  This accelerated aging protocol constitutes severe (extreme) storage conditions for cement. Also, the observation of a "good" behavior of a cement (in terms of low chromium content (VI)) in the conditions of accelerated aging means a fortiori that said cement will necessarily also have a good behavior under conditions of usual storage / storage. Chromium (VI) measurement procedure The determination of chromium (VI) is carried out according to draft standard PR NF EN 196-10 May 2005 "Methods of testing cement - Part 10: determination of chromium cement content ( VI) soluble in water ". Products tested in the various examples described below The various iron sulphates tested were prepared based on various commercial products currently used in cement plants to reduce the soluble chromium (VI) of the cement. More specifically, these commercial products have been crushed and / or sieved to obtain the different granulometric ranges of interest.

  The following products were tested: 3 iron sulfates (II) dry heptahydrates (hereinafter referred to as hepta A, hepta B and hepta C), 20 - 2 iron (II) sulphates monohydrate (hereinafter referred to as mono D and mono E).

  The hepta A product is marketed by Kemira Pigments oy, hepta B and mono D products are marketed by Ferro Duo GmbH and hepta C and mono E products by Kronos International Inc. Experimental chromium reduction results ( VI) soluble

  EXAMPLE 1 Advantage of 0-200 μm Qranulometric Selection A 152.5N CEM cement containing 9.5 ppm soluble chromium (VI) is used, to which 47 ppm of ferrous iron per ppm of soluble chromium (VI) is added. of two iron sulfates dry heptahydrates obtained from commercial products at different particle sizes. The treated cement is subjected to the accelerated aging protocol described above.

  The results are presented in the appendix, in Table 1. The results of Table 1 show that, even under very unfavorable conditions after an accelerated aging test, the use of iron sulfate particles dry heptahydrate, particle size substantially less than 200 microns allows a much more effective reduction in the soluble chromium (VI) content of a cement, than the use of iron sulfate particles dry heptahydrate of size between 0 and 100 microns.

  Example 2. Advantage of a Size Selection 100 μm-200 μm A 152.5N CEM cement containing 9.5 ppm of soluble chromium (VI) is used, to which 47 ppm iron (II) per ppm of chromium (VI) is added. soluble various iron sulphate dry heptahydrates obtained from commercial products, to different sizes granulometric. The treated cement is subjected to the accelerated aging protocol presented above.

  The results are presented in the appendix, in Table 2.

  The use of particles of iron sulphate dry heptahydrate with a particle size ranging between 100 and 200 μm systematically leads to values of soluble chromium (VI), measured after an accelerated aging test, which are lower than those obtained with the use of iron sulphate heptahydrate particles of particle size smaller than 200 μm, with identical amounts of ferrous iron introduced.

  EXAMPLE 3 Advantage of a Quantum Selection 100um-200um of an Iron Sulphate Dry Heptahydrate

  A CEM 152.5N cement, containing 15 ppm of soluble chromium (VI), is used, to which are added various iron sulfates dry heptahydrates or monohydrates obtained from commercial products, at different particle sizes. Iron (II) sulphates monohydrate are obtained from thermal or chemical processes. The different iron sulphates heptahydrates or monohydrates are added to the cement in order to obtain either 45 ppm of iron (II) sulphate per ppm of soluble chromium (VI) or 30 ppm of iron (II) per ppm of chromium (VI ) soluble. The treated cement is subjected to an accelerated aging protocol.

  The results are presented in the appendix, in Table 3.

  The results in Table 3 show that the advantage obtained with the dry heptahydrate iron sulphate by particle size selection ranging between 100pm and 200pm does not apply to iron sulfate monohydrate. In addition, the dry heptahydrated iron sulphate with a particle size ranging between 100 μm and 200 μm is considerably more durable than iron sulphate monohydrate as it is (mono E) with identical amounts of iron (II) introduced by quantity of chromium (VI). ) soluble in cement.

  Example 4. Advantage of a size selection 100um-200um of an iron sulphate dry heptahydrate

  A CEM 152.5N cement containing 9.5 ppm of soluble chromium (VI) is used, to which are added various iron sulfates heptahydrates dry or monohydrated obtained from commercial products, to different sizes granulometric. The treated cement is subjected to the accelerated aging protocol described above.

  The results are presented in the appendix, in Table 4.

  The results in Table 4 also show, on a cement different from the previous example, that the advantage obtained with dry heptahydrate iron sulphate by particle size selection of between 100 μm and 200 μm does not apply. to iron sulphate monohydrate.

  EXAMPLE 5. Advantage of a 100μm-200μm size selection of an iron sulphate dry heptahydrate and reduction of the dose

  A CEM 152.5N cement containing 9.5 ppm of soluble chromium (VI) is used, to which are added, at different dosages, various dry iron sulfates heptahydrates obtained from commercial products, with a particle size ranging from 100 to 200. pm. The treated cement is subjected to the accelerated aging protocol described above. The results are presented in the appendix, in Table 5. The results of Table 5 show that the use of ferrous sulphate heptahydrate particles of particle size between 100 μm and 200 μm effectively reduces the chromium content. (VI) soluble a cement, even by greatly reducing the amounts of ferrous iron added compared to the doses commonly used in the state of the art ranging between 60 and 200 ppm of ferrous iron per ppm of chromium (VI) soluble.

  Example 6. Obtaining a 100 μm particle size selection at 200 μm of an iron sulfate dry heptahydrate with particles obtained by agglomeration of small particles

  A CEM 152.5N cement containing 9.5 ppm of soluble chromium (VI) is used.

  The particle size fractions tested are obtained by agglomerating fine iron sulphate heptahydrate fine particles obtained from hepta product A. Iron sulphate heptahydrate particles having 80% (by mass) of particles smaller than 100 μm are introduced into a fluidized bed and a solution of 1% CarboxyMethylCellulose (CMC) is sprayed at a flow rate of about 10g / min so as to introduce between 0.2 and 0.3% of CMC in iron sulfate dry heptahydrate. During fluidization, the temperature of the product is maintained at about 35 ° C.

  Particles of iron sulfate dry heptahydrate of size selected between 100 and 200 μm, obtained by gluing small particles, are as effective as monoparticles of iron sulfate dry heptahydrate of the same size. The results are presented in the appendix, in Table 6.

  In summary, the desired 100-200 micron size for improved iron sulfate dry heptahydrate time efficiency over the reduction of soluble chromium (VI) can be achieved by iron (II) heptahydrate or iron sulfate (II) monoparticles. agglomeration of fine particles of iron (II) sulfate dry heptahydrate, as shown in FIG.

Table 1 Iron Sulfate Test Assay Size of the Additive: Particles 47 ppm Fe 2+ per ppm soluble Cr (VI) in ppm soluble ppm (VI) measured after accelerated aging protocol iron sulfate particles (II) heptahydrate 0-100 2.6 sec, obtained from hepta B iron sulfate (I1) heptahydrate 0-200 0,1 sec, obtained from hepta B iron sulfate particles (II) ) heptahydrate 0-100 2.9 sec, obtained from the product hepta C iron (II) sulfate particles heptahydrate 0-200 1.5 sec, obtained from the product hepta C Table 2 iron sulphate tested assay size of the additive: particles 47 ppm Fe 2+ per ppm Cr (VI) soluble in Nm ppm Cr (VI) soluble measured after accelerated aging protocol particles of iron (II) sulfate heptahydrate 0 200 3.2 sec, obtained from the product hepta A particles of iron (II) sulfate heptahydrate 100-200 0.5 sec, obtained from the pro duit hepta A particles of iron (II) sulphate heptahydrate 0 200 1.5 sec, obtained from the product hepta C iron (II) sulfate particles heptahydrate 100 200 0.1 sec, obtained from the product hepta C 11 Table 3 iron sulfate tested additive particle size in μm in ppm Fe 2+ per ppm soluble Cr (VI) 45 30 ppm Cr (VI) soluble measured after accelerated aging protocol iron sulfate particles (II) heptahydrate 100-200 0.2 0.4 sec, obtained from the product hepta A iron (II) sulfate particles heptahydrate 100-200 0.1 No dry results, obtained from the product hepta B particles of iron sulphate (II) monohydrate, 100-200 No result 6.7 obtained from the mono product D iron (II) sulphate particles monohydrate, 0-100 6.3 No results obtained from the mono E product Table 4 iron tested additive dosage size: particles 47 ppm Fe 2+ per ppm Cr (VI) soluble in p m ppm Cr (VI) soluble measured after accelerated aging protocol particles of iron (II) sulfate heptahydrate 100-200 0.1 sec, obtained from the product hepta B particles of iron (II) sulfate heptahydrate 100-200 0 , 1 sec, obtained from the product hepta C particles of iron (II) sulfate monohydrate, 100-200 4, 3 obtained from the mono D product particles of iron (II) sulfate monohydrate, 100-200 3,3 obtained from the mono product E 12 105 Table 5 Iron sulfate tested Dosage size of the additive particles in ppm Fe 2+ per ppm Cr (VI) in soluble pm 47 35 24 12 ppm Cr (VI) soluble measured after accelerated aging protocol iron (II) sulfate particles 100-200 0.5 0.8 2 No dry heptahydrate, obtained from the product result hepta A iron (II) sulfate particles 100-200 0.1 0, 1 0.1 1.9 dry heptahydrate, obtained from product hepta B iron (II) sulfate particles 100-200 0.1 0.2 1.9 No heptahyd dry error, obtained from the product result hepta C Table 6 iron sulfate tested: size of the additive dosage: particles obtained in a fluidized bed, by particles 47 ppm Fe 2 * per ppm bonding with CMC fines particles in pm of soluble Cr (VI) obtained from iron (II) sulphate 100-200 dry heptahydrate hepta A soluble ppm Cr (VI) measured after accelerated aging protocol test n 1: 100-200 <0, 1 test n 2 100-200 <0.1 13 10 15 20

Claims (10)

  An additive for a cementitious composition, such as a concrete, a mortar or a cement, comprising particles of iron (II) sulphate dry heptahydrate, said particles of iron (II) sulphate dry heptahydrate not comprising more of 20%, preferably not more than 10%, advantageously not more than 5% by weight of particles having a particle size greater than 200 μm.   2. The additive according to claim 1, wherein at least 20%, preferably at least 50%, advantageously at least 75% by weight, of the iron (II) dry heptahydrate sulfate particles have a particle size distribution of between 100 μm and 200 pm.   3. Additive according to claim 1 or 2, said additive consisting of a powder of iron (II) sulfate dry heptahydrate.   4. A cementitious composition, such as a concrete, a mortar or a cement, comprising an additive according to any one of the preceding claims.   5. Composition according to the preceding claim, said composition being a cement.   6. Composition according to the preceding claim, said cement being a Portland cement, a composite cement, any cement defined in EN 197, or any cement defined in ASTM C-150 and C-595 standards.   7. A composition according to claim 5 or 6, said composition containing a dosage by weight of additive according to any one of claims 1 to 3, such that the amount of iron (II) sulfate heptahydrate dry introduced into the composition is lower than at 60 ppm iron (II) per ppm soluble chromium (VI), for a minimum retention period of two months composition.   8. Composition according to one of claims 5 to 7 having a chromium (VI) content less than or equal to 2 ppm during a storage period of at least two months, preferably at least nine months , said storage period being up to twelve months.   9. A process for obtaining a composition according to any one of claims 4 to 8, said method comprising a step of mixing iron (II) heptahydrate dry sulphate particles with a cement.   10. Use of an additive according to one of claims 1 to 3 for preparing a cementitious composition, such as a concrete, a mortar or a cement.