MXPA96004713A - Fluid control of compositions of ceme - Google Patents

Abstract

The present invention relates to a process for quickly changing the fluidity of a fluid cement composition, characterized in that it comprises adding thereto an aqueous dispersion of at least one honeycomb polymer comprising pendant carboxylic portions.

Description

FLUID CONTROL OF CEMENT COMPOSITIONS This invention relates to cement compositions and more particularly to cement compositions with predetermined flow characteristics. Cement mixtures are required to be fluid or workable for at least part of their lives. This allows them to be easily placed before their "setting" (becoming rigid) and subsequently hardening (sometimes called "setting") (the formation of a hard material through a complex series of hydration reactions). The fluidity or practicality of cement compositions such as concretes or mortars can be measured, for example, by the settlement test, defined in ASTM C143. Achieving sufficient fluidity for a sufficiently long period can be difficult under some conditions, and it can happen that a cement composition loses fluidity too quickly and sets before the composition is in place, with unfortunate consequences. The plasticizers and superplasticizers recognized in the art can not rectify this problem.

REF: 23002 In the PCT / EP co-pending patent application 93/01910, it has been suggested that the use of a two-component system can produce considerable improvements. In such a system, polyalkylene oxide and a selected plasticiser or superplasticizer are added to the cement compositions in the mixing, and a condensate of beta-naphthalene sulfonate ("BNS") is added just before application. The polyalkylene oxide and the (super) plasticizer give increased fluidity (allowing, for example, that the composition be pumped-easily or to flow to an adequate degree around a complicated formwork or structure) and the BNS abruptly reduces fluidity ( causing a sudden loss of flow and setting). The composition may then be conveniently hardened, or, in special cases such as spray application (such as "torch-on"), setting or hardening is augmented by known accelerators. It has now been found that the fluidity of the cement compositions can be varied by the use therein of certain materials. There is provided, therefore, according to the present invention, a process of rapid alteration of the fluidity of a fluid cement composition, comprising the addition thereto of an aqueous dispersion of at least one honeycomb polymer which comprises carboxyl portions outstanding. By "honeycomb" polymer is meant a branched polymer comprising a spinal polymer from which a number of arms depend. The term is well known in the art (as, for example, in "Polymer Science Dictionary" by M.S.M. Alger (Elsevier, 1989)). In the honeycomb polymer used in the present invention, the protruding arms of the spinal column (whose chemical nature is too irrelevant) are portions that possess carboxylic groups. These portions may be up to 100 units long and may comprise monomeric residues of, for example, (meth) acrylic acid, maleic acid or fumaric acid. It should be noted that polymerized and saturated acids such as poly (meth) acrylic acid are not honeycomb polymers. A preferred backbone is a random addition copolymer in which one of the monomers from which the copolymer was prepared comprises more than one, and preferably two, polymerizable double bonds. The spine also preferably comprises styrene. For the polymers of this invention "styrene" includes styrene itself and substituted styrenes such as alpha-methyl-styrene, ethyl-styrene-no, dimethyl-styrene and the commercially available mixed isomers such as "vinyl-toluene". It is possible to use styrene with more than one polymerizable double bond, for example, divinyl benzene, but such monomers should comprise not more than 5% by weight of styrene. The preferred monomer is styrene, but other styles may also be used in combination. The monomer with more than one double bond can be selected from monomers such as isoprene, butadiene, chloroprene and various diallyl monomers such as diallyl phthalate and diallyl adipate. The preferred monomer is butadiene, but, again, more than one monomer can be used. A preferred copolymer is a styrene-butadiene copolymer. Such a copolymer (which may have outstanding polymerizable double bonds and / or intrachain) may be copolymerized by grafting monomers containing carboxyl groups such as acrylic acid, methacrylic acid, maleic acid or fumaric acid. Examples of the preferred copolymers are styrene-buta-diene copolymerized with acrylic acid and styrene / butadiene / maleic acid (or fumaric) terpolymer. The polymers of this invention have molecular weights greater than 20,000, and are solid at room temperature. They also have a limited solubility in water, being rather dispersible (never completely soluble), but they are highly soluble in alkaline media (such as a fluid cement mixture). In the case of poly (meth) acrylic acid and polymers that are inherently soluble in water, it is possible to prepare such polymers in such a way that the necessary solubility is achieved, for example, in the form of particles. These are added to the cement mixture as an aqueous dispersion of less than 5% by weight solids. Typical examples of available commercial materials are those available under the trademark "Synthomer" (eg Synthomer Chemie GmbH, Frankfurt / Main, Germany). A particularly suitable example is "Synthomer" 9523 (a copolymer of methacrylic acid-styrene-butadiene). Another commercially available product is "Polyacryl" AD (eg Polygon Chemie AG, Olten, Switzerland). The aqueous dispersion can be used in any cement composition where it is practical to add the dispersion immediately before the time when the fluidity change is required. A particular case is in the spraying of a cement composition on a substrate. In this case, the dispersion of the aqueous polymer is added by means of a spray nozzle through which the composition is sprayed. It is important to note that, in the case of sprayed or particulate cement compositions, where rapid strength development is desired, it is essential to use an accelerator. Threcrete accelerators are well known in the art and are described in, for example, "Concrete Admixtures Handbook" (VS Ramachandran, Ed., Noyes 1984) on page 547. Typical examples are silicates (especially sodium silicate or glass). water) and alkali metal aluminates. However, in a surprising and especially valuable aspect of the invention, it has been found that a combination of an acrylic polymer dispersion such as the type previously defined herein and a particular chemical compound, can give excellent performance in sprayed cement compositions. . The invention therefore provides a process for rapidly changing the fluidity of a fluid cement composition, comprising the addition thereto of an aqueous dispersion of at least one polymer comprising protruding carboxyl portions and an accelerator selected from at least one hydroxide of aluminum and aluminum hydro-xysulfate. The invention also provides a mixture for sprayed cement compositions, consisting of water, the polymer as described hereinabove and an accelerator selected from at least one of aluminum hydroxide and aluminum hydroxysulfate. The invention further provides a method for forming a layer of cement composition on a substrate by spraying, wherein a mixture as defined hereinabove is added to the composition immediately before spraying. In this aspect of the invention, it is possible to use in the aqueous dispersion any polymer comprising protruding carboxyl portions. Examples are addition polymers comprising monomer units derived from carboxylic acid monomers such as (meth) acrylic acid and maleic and fumaric acids. Acrylic polymers are preferred, more preferably. You get poly (meth) acrylic acid. However, the most preferred polymers are the honeycomb polymers defined hereinbefore. This aspect of the invention confers considerable advantages. It is found that the composition can be applied in thick layers, which harden in a very short time, thereby consistently reducing sag and fall. Furthermore, it is found that rebounding (the tendency for at least a portion of a sprayed cement composition to bounce off a substrate upon impact) is very small and in some cases is virtually absent. An additional advantage lies in the fact that the aluminum compounds are non-alkaline and are much less dangerous in use.

The use of aluminum hydroxide as an alkali-free accelerator in the torrette has been suggested in the art. European Patent No. 0076927 describes a mixture of aluminum hydroxide and aluminum sulfate. However, it has been found that aluminum hydroxysulfate works particularly well and is therefore the preferred accelerator. This can be mixed with aluminum hydroxide and / or sulfate, but it is preferred to use it alone. A preferred material is commercially available as "Gecedral" L (eg Giulini Chemie GmbH, Ludwigshafen / Rhein, Germany). The relative amounts of the components can be varied as follows: hydroxysulfate / aluminum hydroxide 15-25 parts by weight polymer (solids) 5-10 parts by weight water 80-65 parts by weight In a preferred mixture, the aluminum hydroxysulfate, the polymer and the water are used in the respective proportions by weight of 20, 8 and 72 parts. The mixture is prepared by stirring the accelerator in the aqueous polymer dispersion and adding water if necessary. It can be injected into a spray nozzle. In a further embodiment of this invention, the operation of the sprayed cement compositions can be further enhanced by the addition to the cement composition, prior to spraying, of at least one chemical compound that forms a chelate with calcium. The use of such compounds in the spray cement compositions is known from co-pending British Patent Application No. 2,240,334 (the subject of which is incorporated by reference herein). In this description, the usual accelerators for the decoy are referred to as suitable for use. However, the combination of the calcium chelating agents of this invention with a mixture as described hereinabove gives results that are superior to those obtained by the use of the mixture alone. The calcium chelating agents for use in this invention may be any such agents, but the preferred agents are phospho-acid derivatives, more particularly those comprising carboxyl, hydroxyl or amino groups. An example of the carboxyl group containing class is "Bayhibit" (trademark) (eg Bayer AG, Leverkusen, Germany.

Examples of the material containing hydroxyl or amino groups are the commercially available material "Dequest" (trademark) (eg Monsanto Co. San Luis, United States). A list of "Dequest" materials suitable for use in the work of this invention is given below.

- "Dequest" 2000: aminotri (methylene phosphonic acid) - "Dequest" 2006 pentasodic salt of aminotri (methylene phosphonic acid). - "Dequest" 2010 1-hydroxyethylidene-1, diphosphonic acid - "Dequest" 2016 tetrasodium salt of 1-hydroxyethylidene-1,1-diphosphonic acid - "Dequest" 2041 ethylenediaminotetra (methylene phosphonic acid - "Dequest" 2047 calcium / sodium salt of ethylenediaminetetra (methylene phosphonic acid) - "Dequest" 2051 hexamethylenediaminotetra (methylene phosphonic acid) - "Dequest" 2054 potassium salt of hexamethylenediaminetetra (methylene phosphonic acid) - "Dequest" 2060 diethylenetriaminepenta (methylene acid) phosphonic) - "Dequest" 2066 sodium salt of diethylenetriaminepenta - (methylene phosphonic acid) It is permissible to use two or more of these materials.Other materials that perform this chelating function and which are useful in the work of the invention include: hydroxylated acids and its salts, for example, salicylic, citric, lactic, gluconic, tartaric, mucic, and glucoheptanoic acids; polycarboxylic acids and their salts, including organic acids, liraeric, for example, maleic, fumaric, itaconic, succinic, malonic and phthalic acids and the polyacrylic, polymethacrylic and polyfumáric acids, the polymerized acids which are preferably of low molecular weight; - antioxidants, for example, ascorbic and isoascorbic acids; polymers, for example, copolymers of acrylic acid containing sulfonic acid and polyhydroxysilane groups, these polymers preferably having a low molecular weight; - aldoses and ketoses, for example, sugar and corn syrup and lignosulfates, for example, calcium lignosulfonate; - inorganic complexing agents, for example, phosphates and borates; organic complexing agents, for example, EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid); and - zeolites.

Again, it is permissible to use mixtures of two or more of these materials. Preferred materials of this type are hydroxycarboxylic acids, polycarboxylic acids, phosphates, and mixtures thereof. Preferred materials are mixtures of at least one phosphonic acid derivative and at least one other calcium chelating compound. Since many of these calcium chelating compounds that do not belong to the group of the phosphonic acid derivatives also have water-reducing properties, these also increase the compressive strength of the hardened concrete. A typical combination is a derivative of phosphonic acid with gluconic acid or a salt thereof. Especially preferred materials are mixtures of one of the phosphonic acid derivatives previously listed, with citric acid and salts thereof, in particular aminotri (methylene phosphonic acid) and citric acid, or a salt thereof. The preferred proportions of the aforementioned phosphonic acid derivatives to citric acid are from 1: 1 to 2: 1. The principles of the use of these calcium chelating agents are found in British Patent GB 2,240,334 and reference should be made to this document in relation to the amount of calcium complexing compound, to be used in any particular group of circumstances, but as a general rule, compounds are used at a ratio of 0.1 to 5.0%, preferably 0.4 to 2% by weight of the cement + any mineral-mixtures present (for a complete guide to mineral mixtures, see Ramachandran op.cit.p.303 ). When a calcium chelating agent is used according to this invention, it is mixed in the initial mixture before pumping. The compositions and processes of this invention are useful in spraying cement compositions by "wet" and "dry" methods, but these work best in the "wet" method where water is added to the mixing stage before of the pumping. The aspect of the invention in which the calcium complexing agent is used is particularly suitable for the "wet" method. Sprayable cement compositions using this invention form thick layers that "set" quickly and can be sprayed again without any problem. The characteristics of rebound are particularly good, as are the development of resistance and long-term resistance. The invention is further described with reference to the following examples, in which all parts are expressed by weight.

Example A mixture of concrete for spraying is constituted as follows Cement Portland 450 parts Sand 1 mm maximum 600 parts Aggregate 8 mm maximum 1200 parts Microsilica densified2 40 parts ex. Perimoser Zementwerk, Austria 2 ex. ELKEM A / S, Norway The water is added to give a W / C (water to cement ratio) of 0.50. To this is added 0.8% by weight, of the weight of the cement, of a superplasticizer based on styrene-maleic anhydride copolymer ("Rheobuild" (registered trademark) 3520 is used (eg MBT, Zürich Switzerland)). To the portions of this mixture were added various amounts of a mixture of water, aluminum hydroxysulfate "Gecedral" L and acrylic dispersion "Synthomer" 9523 in the percentages in weights of 72: 20: 8, respectively. The amounts used were as follows: Portion 1 3.0% by weight of cement Portion 2 5.88% by weight of cement Portion 3 10.0% by weight of cement Portion 4 5.0% by weight of cement These portions are all injected into the spray nozzle when the mixture is sprayed. Furthermore, 0.3% by weight solids stabilizer "Delvo" (registered trademark) (eg MBT, Zurich, Switzerland) is incorporated in Portion 4 in the mixing stage. It is found in all cases that it is possible to spray thick layers without falling or sinking and almost without bouncing. The rapid "setting" allows a substrate to be sprayed again within 2-3 minutes and can therefore be quickly constituted substantial layers. The strength of the concrete as measured by a penetrometer is as follows: Age of the Torcrete Serving 1 Serving 2 Serving 3 Serving 4 minutes N / mma N / mm3 N / mm2 N / mma 5 0.25 6 0.18 7 0.25 8 0.31 10 0.31 0.39 0.39 12 0.25 15 0.47 0.60 20 0.39 0.31 0.68 25 0.39 0.68 30 0.39 '35 0.52 0.93 0.80 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. A process for rapidly changing the fluidity of a fluid cement composition, characterized in that it comprises the addition thereto of an aqueous dispersion of at least one honeycomb polymer comprising protruding carboxyl portions.

2. A process according to claim 1, characterized in that the honeycomb polymer is a random addition copolymer, in which one of the monomers from which the copolymer was prepared, comprises more than one, and preferably two , double polymerizable links.

3. A process according to claim 1 or claim 2, characterized in that the monomer comprising more than one double bond is butadiene.

4. A process according to any of claims 1 to 3, characterized in that the honeycomb polymer comprises styrene.

5. A process according to any of claims 1 to 4, characterized in that the honeycomb polymer is a graft copolymer having a styrene and butadiene backbone, and side chains comprising monomer units derived from the selected monomer of acrylic acid, methacrylic acid, maleic acid, and fumaric acid.

6. A process for rapidly changing the fluidity of a fluid cement composition, characterized in that it comprises the addition thereto of an aqueous dispersion of at least one polymer comprising protruding carboxylic portions, wherein the aqueous dispersion further comprises an accelerator selected from at least one one of aluminum hydroxide and aluminum hydroxysulfate.

7. A process according to claim 6, characterized in that the polymer is selected from copolymers comprising residues of acrylic and methacrylic acid, and honeycomb polymers comprising protruding carboxyl portions.

8. A method for forming a layer of cement composition on a substrate, by spraying through a spray nozzle, characterized the method because an aqueous dispersion is added to the composition in the nozzle as described in accordance with any of the claims 1 to 7.

9. A process according to claim 8, characterized in that at least one compound that forms a chelate with calcium is added to the cement composition before spraying.

10. A mixture for sprayed cement compositions, characterized in that it consists of water, the polymer as described according to any of claims 1 to 8, and an accelerator selected from at least one of aluminum hydroxide and aluminum hydroxysulfate.