Cement plasticiser compositions based on polymerisable carboxylic acids and cementiferous compositions containing them

Abstract: Disclosed are cost effective cement compositions having superior flow characteristics imparted by the incorporation of a copolymer of an ethylencially polymerisable carboxylic acid, an alkyl ester of a ethylenically polymerisable carboxylic acid and, optionally, a third ethylenically unsaturated comonomer.

Description: This invention relates to cementiferous compositions and to additives for use in such compositions, which additives improve the physical characteristics such as the flow and workability of such compositions. The cementiferous compositions with which this invention is concerned include concretes which comprises cement, coarse and fine aggregates and water; cement pastes which comprise cement and water, and mortars which comprise cement, sand and water; lime, sand and water, or mixtures containing both lime and cement. The invention is also applicable to high-pressure, steam-cured concretes comprising cement, aggregate and water; lime or limestone and siliceous materials such as silica flour and water. The additives with which this invention is concerned are sometimes referred to as plasticisers and/or superplasticisers for concrete. Their purpose is to improve the flow characteristics of the cementiferous compositions containing them so that they may be pumped or effectively poured to fill all the spaces in a mould or other structure and yet not have their strength characteristics weakened by the inclusion of excessive amounts of air which, in certain circumstances, would be undesirable. In addition, these additives can be used to design cementiferous compositions with a reduced water content. This permits the production of concretes having higher compressive strength when cured and also adequate flow properties for certain applications. Various additives for use in cementiferous compositions have been previously proposed, including for example, lignosulphonates and sodium naphthalene sulphonate formaldehyde condensates. Details of such materials are set out in "Chemical Admixtures for Concrete" by M R Rixom, published by E and F N Spon Limited, London, and by the Halstead Press, a division of John Wiley and Sons Incorporated of New York, USA, where, at page 34, various known additives are considered. GB-A-1 538 103 discloses a set-inhibited calcium sulphate hemihydrate plaster, wherein a copolymer of acrylic acid or a water-soluble salt thereof having a molecular weight within 2000 to 75000 is comprised for inhibiting premature setting. The set-promoting composition for inducting the setting of the plaster comprises at least one iron, copper or aluminium salt. In GB-A-2 018 737 there are disclosed homogeneous, uncured cementiferous compositions which comprise a hydraulic cement, water and acid copolymers having selected proportions of carboxyl groups. The polymers are said to be water-dispersible, and contain carboxyl groups in an amount of at least 50 mg KOH/gram of polymer. Preferred polymers have a molecular weight of greater than 100000. US-A-4 460 720 reveals a cement plasticizer composition comprising alkali metal polyacrylates having a molecular weight from 500 to 25000 in combination with either an alkali or alkaline earth metal polynaphthalene sulfonate-formaldehyde condensate or a mixture of an alkali or alkaline earth metal polynaphthalene sulfonate-formaldehyde and an alkali or alkaline earth metal lignin sulfonate. Various polymeric materials have been evaluated as plasticiser additives for cementiferous compositions and it has been found that certain polymers and their soluble salts comprising polymerisable carboxylic acids and the hydroxyalkyl esters of such acids have a definite utility in this application. Such polymers are described in European Patent specification 0097513. The applicants have now discovered that comparable results can be obtained using more cost effective copolymers which do not contain hydroxy esters. This invention relates to the use of a water soluble copolymer or soluble salt thereof having a molecular weight of 1,000 to 15,000 consisting essentially of: i) about 33 to about 95 mole % of an ethylenically polymerizable carbocylic acid and ii) from about 67 to about 5 mole % of an alkyl (C1 to C8) ester of an ethylenically polymerizable carboxylic acid as the sole plasticizing additive in cementiferous additive compositions. In accordance with a further embodiment of the invention, we have found that the copolymer may be further improved with respect to its use as a more cost effective plasticizer additive by the copolymerisation therein of a third ethylenically unsaturated monomer. Examples of suitable monomers are vinyl esters such as vinyl acetate and vinyl propionate; maleate and fumarate (C₁ to C₈) esters and diesters; allyl alcohol; ethylene; aromatic vinyl compounds such as styrene; vinyl alcohol (obtained by hydrolyzing a vinyl acetate based polymer); and mixtures thereof. Surprisingly, the addition of this third monomer, while substantially lowering the cost of the polymer, has been found to have little or no deleterious effect upon the efficiency of the polymer as a plasticiser, even when added at levels as high as bout 50% by weight of the copolymer. Thus, the invention also relates to a Plasticizer additive specifically adapted for use in a cementiferous composition, said additive consisting essentially of an aqueous solution of a polymer or soluble salt thereof having a molecular weight of 1,000 to 15,000 consisting essentially of: i) from 45 to 90 mole % of an ethylenically unsaturated carboxylic acid; ii) from 5 to 50 mole % of an alkyl (C1 to C8) ester of an ethylenically unsaturated carboxy acid; and iii) from 5 to 50 mole % of a third ethylenically unsaturated comonomer selected from the group consisting of vinyl esters, maleate and fumerate (C1 to C8) esters and diesters, allyl alcohol, ethylene, aromatic vinyl compounds, vinyl alcohol and mixtures thereof. The cementiferous composition will preferably contain from about 0.01% to about 2.5% by weight of the copolymer with respect to the cement component. In accordance with a further aspect of this invention, there is provided a plasticiser additive composition comprising an aqueous solution of a copolymer on soluble salt thereof comprising from about 45 to 90 mole % of the ethylenically polymerisable carboxylic acid and from about 5 to about 50 mole % of the ester. The plasticiser additive may also contain 5 to 50 mole % of a third ethylencially comonomer as described above. These plasticiser additives may contain anti-foaming agents or air entraining agents, accelerators and other components conventional in the art. These additives, if present, are employed in effective amounts, for example anti-foaming agents are generally used in the range of about 0.1 to 2% by weight of the copolymer of salt thereof. Suitable anti-foaming agents include tributylphosphates, dibutyl phthalate, various water insoluble alcohols and silicone derivatives. Suitable accelerators include, for example, sodium thiocyanate and triethanolamine, used generally at levels of about 15 to 35% by weight of the copolymer. The invention also includes a process for making cementiferous composition wherein the plasticiser additive defined is added to the composition components during mixing. The ethylenically unsaturated carboxylic acids suitable for use herein include acrylic, maleic, methacrylic, crotonic, fumaric, itaconic, citraconic and aconitic acids and mixtures thereof. However the acids are not restricted to being mono or dicarboxylic. Acrylic, maleic and methacrylic acids are preferred. The preferred esters are the methyl, ethyl, propyl and butyl derivatives. Preferred copolymers are those of acrylic acid with ethyl acrylate or methyl methylacrylate with the copolymer of acrylic acid and methyl methacrylate being most preferred. As noted previously, in the broadest scope of the invention, the mole percentage of the acid in the copolymer is 33 to 95%, preferably 60 to 85% with the ester comprising the remainder of the polymer. In the embodiment wherein a third ethylenically unsaturated comonomer is present, the acid is used in amount of 45 to 90 mole %, preferably 60 to 80%, the ester in an amount of 5 to 50 mole %, preferably 10 to 30, and the third comonomer is an amount of 5 to 50 mole %, preferably 10 to 30%. Suitable polymers may be made by the copolymerization of the alkyl ester with the ethylenically unsaturated acid and, optionally the third monomer, using methods known in polymerisation technology. The resultant copolymer or terpolymer may be neutralised with a suitable base such as sodium hydroxide or other soluble base to form a soluble salt and diluted with water to the required concentration for use in the cementiferous compositions and plasticiser additives provided by this invention. Representative salt cations are preferably alkali metal, eg. sodium, potassium, alkaline earth metals eg. calcium, magnesium, organic bases, eg. amines and their derivatives, and ammonia. Absolute molecular weights of the polymers of this invention have not been determined. However, apparent molecular weights as calculated relative to sodium polyacrylate standards have been determined using gel permeation chromatography. The apparent molecular weight of the copolymer is within the range of 1000 to 15000, preferably 1000 to 9000. Precise molecular weights have not been determined for all the copolymers used but in some cases viscosity determinations have been carried out. The preferred viscosity is less than 30 cps as a 15% by weight aqueous solution in 1 molar NaCl as measured by a Brookfield viscometer model LVT with UV adaptor at 65 rpm and 25°C. The water soluble copolymer or salt thereof is used as a plasticiser additive in cementiferous compositions in amount of 0.01 to 2.5% by weight, preferably 0.03 to 2.0%. Examples Examples of sodium salts of the copolymers and terpolymers and their application in cementiferous compositions will now be given to illustrate but not limit the invention. The cement mix used in the tests had the composition: Portland cement 350 Kg/m³ gravel (20 mm) 780 Kg/m³ gravel (10 mm) 330 Kg/m³ sand 700 Kg/m³ water/cement ratio 0.57 The aggregate (gravels and sand) was placed in a mixer with half the water and mixed for 30 seconds. After standing for 1 minute the mixer was restarted and the cement component added over 30 seconds. The remainder of the water was then added and mixing continued for a further 2 minutes. The plasticiser polymer admixture (if present) was then added at a level of 0.12% by weight, ie as 0.4% w/w of 30% w/w solution, of cement component and the whole mixed for a further 1 minute. The cementitious compositions prepared were tested for slump, plastic density, compressive strength and setting time according to British Standard 1881. The flow properties were tested by the method of DIN 1048. Twelve copolymers and terpolymers were prepared and tested as their sodium salts against a copolymer sodium salt disclosed in European patent specification 0097513 as standard. Appropriate measurements were also made on the two base cementiferous compositions not containing an admixture. The twelve examples and standard copolymer had the compositions set out in Table I. The sodium salts of the polymers were prepared at 30% w/w solutions and 0.25% w/w tributyl phosphate added as anti-foamer. These admixtures were tested at a level of 0.4% w/w of cement using two cement bases indicated as Base 1 and Base 2 in Table II. This Table quotes the properties of the cementiferous compositions prepared. It will be seen that the copolymers of the invention improve the properties of the cement bases and are as effective as known more expensive hydroxy ester containing polymers.

Claims: Use of a Water soluble copolymer or soluble salt thereof having a molecular weight of 1,000 to 15,000 consisting essentially of: i) about 33 to about 95 mole % of an ethylenically polymerizable carboxylic acid and ii) from about 67 to about 5 mole % of an alkyl (C₁ to C₈) ester of an ethylenically polymerizable carboxylic acid as the sole plasticizing additive in cementiferous additive compositions Use of the water soluble copolymer or soluble salt thereof according to claim 1 wherein the salt cations are selected from alkali metal, preferably sodium, potassium, alkaline earth metals preferably calcium, magnesium, organic bases, preferably amines and their derivatives, and ammonia. Use of the water soluble copoylmer or soluble salt thereof according to claim 1 or 2 wherein the copolymer or salt is used in an amount from about 0,01 % to about 2,5% by weight with respect to the cement component. Use of the water soluble copoylmer or soluble salt thereof according to any preceding claim wherein the acids defined in paras (i) and (ii) are selected from acrylic, maleic, methacrylic, crotonic, fumaric, itaconic, citraconic and aconitic acids and mixtures thereof. Use of the water soluble copoylmer or soluble salt thereof according to any preceding claim wherein the esters of para (ii) are selected from the methyl, ethyl, propyl and butyl derivatives. Use of the water soluble copoylmer or soluble salt thereof according to any preceding claim wherein the copolymers are those of acrylic acid with ethyl acrylate or acrylic acid with methyl methacrylate. Cementiferous compositions comprising, as a plasticizer additive, a water soluble polymer or soluble salt thereof having a molecular weight of 1,000 to 15,000 consisting essentially of i) from about 45 to 90 mole % of an ethylenically polymerizable carboxylic acid, ii) from about 5 to about 50 mole % of an alkyl (C₁ to C₈) ester of an ethylenically unsaturated carboxylic acid, and iii) from about 5 to about 50 mole % of a third ethylenically unsaturated comonomer selected from the group consisting of vinyl esters, maleate and fumerate (C₁ to C₈) esters and diesters, allyl alcohol, ethylene, aromatic vinyl compounds, vinyl alcohol and mixtures thereof. Compositions according to claim 7 wherein the third monomer is vinyl acetate, allyl alcohol, vinyl alcohol, styrene and mixtures thereof. Composition according to claim 7 or 8, wherein the salt cations are selected from alkali metal, preferably sodium, potassium, alkaline earth metals preferably calcium, magnesium, organic bases, preferably amines and their derivatives, and ammonia. Compositions according to claim 7, 8 or 9 containing from about 0.01 % to about 2.5 % by weight of the copolymer or salt with respect to the cement component. Compositions according to any of claims 7 to 10 wherein the acids defined in paras (i) and (ii) are selected from acrylic, maleic, methacrylic, crotonic, fumaric, itaconic, citraconic and aconitic acids and mixtures thereof. Compositions according to any of claims 7 to 11 wherein the esters of para (ii) are selected from the methyl, ethyl, propyl and butyl derivatives. Compositions according to any of claims 7 to 12 wherein the copolymers are those of acrylic acid with ethyl acrylate or acrylic acid with methyl methacrylate. Use of a plasticizer additive as the sole plasticizing additive in a cementiferous composition, said additive consisting essentially of an aqueous solution of a copolymer, or soluble salt thereof, having a molecular weight of 1,000 to 15,000 consisting essentially of: i) about 33 to 95 mole % of an ethylenically polymerizable carboxylic acid and ii) from 67 to 5 mole % of an alkyl (C₁ to C₈) ester of an ethylenically polymerizable carboxylic acid. Use of a plasticiser additive according to claim 14 where there is additionally present an effective amount of anti-foaming agent. Use of a plasticizer additive according to claim 15 wherein the anti-foaming agent is selected from the group tributyl phosphates, dibutyl phthalate, water-insoluble alcohols and silicone derivatives. Use of a plasticizer additive according to claim 14, 15 or 16 wherein the amount of anti-foaming agent in the composition is in the range of 0.1 % to 2.0 % by weight of the copolymer or salt thereof. Use of a plasticizer additive according to any of claims 14 to 17 wherein there is additionally present an accelerator. Use of a plasticizer additive according to claim 18 wherein the accelerator is sodium thiocyanate or triethanolamine. Use of a plasticizer additive according to claim 18 or 19 wherein the accelerator is present in an amount of 15 to 35 % by weight of the copolymer. A plasticizer additive specifically adapted for use in a cementiferous composition, said additive consisting essentially of an aqueous solution of a polymer or soluble salt thereof having a molecular weight of 1,000 to 15,000 consisting essentially of: i) from 45 to 90 mole % of an ethylenically unsaturated carboxylic acid; ii) from 5 to 50 mole % of an alkyl (C₁ to C₈) ester of an ethylenically unsaturated carboxylic acid; and iii) from 5 to 50 mole % of a third ethylenically unsaturated comonomer selected from the group consisting of vinyl esters, maleate and fumerate (C₁ to C₈) esters and diesters, allyl alcohol, ethylene, aromatic vinyl compounds, vinyl alcohol and mixtures thereof. A plasticizer additive according to claim 21 where there is additionally present an effective amount of anti-foaming agent. A plasticizer additive according to claim 22 wherein the anti-foaming agent is selected from the group tributyl phosphates, dibutyl phthalate, water-insoluble alcohols and silicone derivatives. A plasticizer additive according to claim 21, 22 or 23 wherein the amount of antifoaming agent in the composition is in the range of 0.1 % to 2.0 % by weight of the copolymer or salt thereof. A plasticizer additive according to any of claims 21 to 24 wherein there is additionally present an accelerator. A plasticizer additive according to claim 25 wherein the accelerator is sodium thiocyanate or triethanolamine. A plasticizer additive according to claim 25 or 26 wherein the accelerator is present in an amount of 15 to 35 % by weight of the copolymer. A process for the preparation of a plasticized cementiferous composition comprising adding to a cementiferous material a plasticiser additive as claimed in any of claims 21 to 27.

Inventors: BAINBRIDGE PETER, HOARTY JOHN TERENCE, MONTAGUE PETER GRAHAM, BAINBRIDGE, PETER, HOARTY, JOHN TERENCE, MONTAGUE, PETER GRAHAM
Applicants: NAT STARCH CHEM INVEST, NATIONAL STARCH AND CHEMICAL INVESTMENT HOLDING CORPORATION
Application year: 1987
Main classification: C04B24
IPC codes: C04B24, C04B22, C08L33