FR2917083A1 - "ADDITIVE FOR CEMENT-BASED COMPOSITION" - 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

CEMENT COMPOSITION ADDITIVE 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 small 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 Cr6 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 stains 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. For the purposes of the present invention, the expression "dry iron (II) heptahydrate sulfate particles" means particles of dry iron (II) heptahydrate sulphate, that is to say, not coated with at least one layer of at least one polymer-type outer coating, or iron (II) heptahydrate sulfate particles coated with at least one layer of at least one polymer-type outer coating, with the exception of iron sulfate particles (II) dry heptahydrate coated with gelatin or with alginic acid or a derivative thereof.

  Dry, non-coated, dry iron (II) heptahydrate sulfate particles are preferably used.

  According to a particularly preferred embodiment, at least 20%, preferably at least 50%, advantageously at least 75% by weight, of the particles of iron (II) heptahydrate sulfate, have a particle size distribution of between 100 μm and 200 μm. .

  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) sulphate heptahydrate dry having a particle size distribution between 100 pm and 200 pm is high, at most the amount of iron (II) sulfate heptahydrate dry to incorporate the cement is weak, for a result at least equivalent.

  Applicant has unexpectedly found that the dry iron (II) sulfate particles in the aforementioned particle size distribution have a better time efficiency in reducing the 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 subject of the present invention relates to 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) sulphate dry heptahydrate introduced into the composition is less than 60 ppm of iron (II) per ppm of chromium. (VI) soluble, for a minimum shelf life of two months composition. 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 nine month, said storage period of up to twelve months. Another object of the invention consists in a process for obtaining the abovementioned composition, said process comprising a step of mixing particles of iron (II) sulphates dry heptahydrate with a cement. Another object of the invention relates to the use of an additive according to the invention for preparing a cementitious composition, 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 particle size: grinding / screening, 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 to the 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 in 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. ci, such as concretes or mortars.

  The invention therefore 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, or a mixture of at least two compounds selected from the group consisting of iron (II) sulfate, dry heptahydrate, tin sulfate, and sodium sulfate. Manganese are used in place of iron (II) sulphate, since these compounds have similar chromium (VI) reduction properties and exhibit relative instability when added to cement.

  According to the present invention iron (II) sulfate is in dry heptahydrate form (FeSO4, 7 H2O). 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 (mixed with a cementitious composition) that can provide for 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 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 low, 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. According to an alternative to the present invention, it is possible to use an additive for a cementitious composition, such as a concrete, a mortar or a cement, comprising particles of iron (II) sulfate dry heptahydrate coated with gelatin or with alginic acid (or one of its derivatives), in which at least 15%, preferably at least 50%, advantageously at least 75% by mass weight of the iron sulphate particles ( II) dry heptahydrate coated have a particle size distribution of between 100 μm and 200 μm.

  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 an iron sulphate heptahydrate marketed for the agglomerating application with the aid of an organic binder of fine particles (<100 μm) obtained by grinding Heptahydrate iron sulfate 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 35 Incorporation protocol into the cement of the cement According to the invention, various amounts of iron (II) sulphate monohydrate or dry heptahydrate powder are added to the cement, 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 5 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 humidity This test consists of putting a bed of cement powder containing iron sulphate in a tank: the mass of cement is about 600 grams and the height of the bed of material is 1 cm. This tray is then placed in a chamber maintained at 20 C and at 100% relative humidity. The tank remains in this chamber for 24 hours, then the soluble chromium (VI) is measured. 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 (VI) content) under the conditions of accelerated aging means a fortiori that said cement will necessarily also have a good behavior under conditions usual storage / storage. 25 Chromium (VI) measurement procedure Chromium (VI) measurement is carried out according to the 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 works to reduce the soluble chromium (VI) of the cement. More specifically, these commercial products have been crushed and / or sieved in order 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), 2 iron (II) sulphates monohydrate (hereinafter referred to as mono D and mono E).

  Hepta A is marketed by Kemira Pigments oy, hepta B and mono D are marketed by Ferro Duo GmbH and hepta C and mono E by Kronos International Inc.

  Experimental Results of Reduction of Soluble Chromium (VI) Example 1. Advantage of Size Selection 0-200 pm

  A CEM 152.5N cement containing 9.5 ppm of soluble chromium (VI) is used, to which 47 ppm of ferrous iron are added per ppm of soluble chromium (VI) of two dry iron sulfates heptahydrates obtained from commercial products. to 15 different size 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 in Table 1 show that, even under very unfavorable conditions after an accelerated aging test, the use of dry heptahydrate iron sulfate particles with a particle size of substantially less than 200 μm allows a much more efficient reduction of the soluble chromium (VI) content of a cement, that the use of iron sulfate particles dry heptahydrate of size between 0 and 100 pm.

  Example 2. Advantage of a particle size selection 100 μm-200 μm

  A 152.5N CEM cement containing 9.5 ppm soluble chromium (VI) is used, to which 47 ppm iron (II) per ppm soluble chromium (VI) of various iron sulphate dry heptahydrates obtained from commercial products, to different size sizes. 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 granulometric selection 100um-200pm of an iron sulphate dry heptahydrate

  A 152.5N CEM cement, containing 15 ppm soluble chromium (VI), was used, to which various dry iron sulfates or monohydrated iron sulfates obtained from commercial products, at different particle sizes, were added. Iron (II) sulphates monohydrate are obtained from thermal or chemical processes. The various iron sulfates, dry 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 dry heptahydrate iron sulphate by particle size selection between 100 μm and 200 μm does not apply. to iron sulphate monohydrate. In addition, the dry heptahydrate 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 100μm-200μm dialulose selection of an iron sulfate dry heptahydrate

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

  The results are presented in the appendix, in Table 4.5 The results in Table 4 also show, on a cement different from the previous example, that the advantage obtained with the iron sulphate heptahydrate dried by particle size selection particle size between 100 μm and 200 μm does not apply to iron sulphate monohydrate. Example 5. Advantage of 100μm-200μm Size Selection of Iron Seed Heptahydrate Sulfate and Decrease of Dosage A 152.5N CEM cement containing 9.5 ppm soluble Chromium (VI) was used, to which was added, various assays, various iron sulfates dry heptahydrates obtained from commercial products, particle size ranging from 100 to 200 μm. The treated cement is subjected to the accelerated aging protocol described above.

  The results are presented in the appendix, in Table 5.

  The results in Table 5 show that the use of ferrous sulphate heptahydrate particles with particle size ranging between 100 μm and 200 μm effectively reduces the soluble chromium (VI) content of a cement, even by greatly reducing the amounts of ferrous iron added relative to the doses commonly used in the state of the art, ranging from 60 to 200 ppm of ferrous iron per ppm of soluble chromium (VI). EXAMPLE 6. Obtaining a Quantum Selection 100 μm - 200 μm of an iron sulfate dry heptahydrate with particles obtained by agglomeration of small particles

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

  The particle size fractions tested are obtained by agglomerating fine particles of iron sulphate dry heptahydrate obtained from the product hepta A. Particles of iron sulphate dry heptahydrate 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 sulphate heptahydrate solubility over time in the reduction of soluble chromium (VI) can be achieved by iron (II) sulphate heptahydrate or iron (II) sulfate monoparticles. agglomeration of fine particles of iron (II) sulfate heptahydrate dry, as shown in Figure 1.

  Table 1 Iron sulfate test assay size of the additive: Particles 47 ppm Fe 2+ per ppm Cr (VI) soluble in pm ppm Cr (VI) soluble measured after accelerated aging protocol iron (II) sulphate heptahydrate 0-100 2.6 sec, obtained from the product hepta B particles of iron (II) sulphate heptahydrate 0 200 0.1 sec, obtained from the product hepta B iron sulphate 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 size assay of the additive: particles 47 ppm Fe 2+ per ppm Cr (VI) soluble in pm ppm Cr (VI) soluble measured after accelerated aging protocol iron (II) sulfate particles heptahydrate 0-200 3, 2 sec, obtained from the product hepta A particles of iron (II) sulfate heptahydrate 100 200 0.5 sec, obtained separately ir hepta product A particles of iron (II) sulfate heptahydrate 0-200 1.5 sec, obtained from the product hepta C particles of iron (II) sulfate heptahydrate 100-200 0, 1 sec, obtained from the Hepta product C 12 Table 3 iron sulfate tested additive particle size assay in ppm Fe 2+ per ppm Cr (VI) soluble in pm 45 30 ppm Cr (VI) soluble measured after protocol accelerated aging particles iron (II) sulphate 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 result, obtained from hepta product B particles of iron (II) sulphate monohydrate, 100-200 I 6.7 obtained from the mono D product No iron sulphate (II) particles monohydrate, 0-100 6.3 No results obtained from the mono E product Table 4 iron sulfate tested additive dosage size: particles 47 ppm Fe per ppm Cr (VI) solubl e in pm ppm soluble Cr (VI) 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 iron (II) sulfate particles monohydrate, 100-200 4.3 obtained from the mono product D iron (II) sulfate particles monohydrate, 100-200 3 , 3 obtained from the mono product E 13 5 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 hepta hydrated dry, obtained from the product hepta C result 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 14 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. Additive according to claim 1, in which at least 20%, preferably at least 50%, advantageously at least 75% by weight, of the iron (II) heptahydrate sulfate particles have a grain 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) sulphate 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. 30   7. 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. 25 10   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. Process for obtaining a composition according to any one of claims 4 to 8, said method comprising a step of mixing particles of iron (II) sulfates dry heptahydrate 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.