Water retention aids

Abstract

In mortars, concretes and stuccos, cellulose ether can be replaced as a water retention aid by an alkali-soluble acrylic polymer that contains repeating units derived from: (a) 20 to 50 weight percent (meth)acrylic acid monomers; (b) 30 to 60 weight percent alkyl (meth)acrylate monomers; and (c) 5 to 30 weight percent ethylene glycol acrylate monomers; and (d) no more than 20 weight percent other unsaturated monomers, wherein the weight percentages are based on the total weight of the acrylic polymer.

Description

[0001] WATER RETENTION AIDS

[0002] F1ELD

[0003] This disclosure generally relates to the field of concrete, mortar, grout and stucco.

[0004] INTRODUCTION

[0005] Concrete, mortar, grout and stucco (called cementitious mixtures) are typically prepared in two stages. First, a dry mix that contains cement, filler and solid particulate additives (“dry components”) is blended together. Second, water is added to the dry mix to make a wet mix, which can be further formulated into the final cementitious mixture. The dry mix is stable as long as it remains sufficiently dry; it can be stored for long periods and transported easily. The wet mix can start to cure due to the presence of added water and must be used before it becomes unworkable.

[0006] The major components of the dry mix are filler and cement. The dry mix components may also include small quantities of other additives, such as water retention aids, organic binders, starch ethers, fibers, air entrainment agents, curing accelerators, curing retarders, defoamers and pigments.

[0007] Water retention aids prevent water from settling out or otherwise separating from dry ingredients in the wet mix. In this way, the water retention aids improve cement hydration and curing of the wet mix, improve adhesion of the wet mix to substrates and control the open time and workable life of the wet mix.

[0008] The most common water retention aid is cellulose ether. Cellulose ether is made by an energy-intensive, high-waste process. Further, the performance of cellulose ethers in cementitious mixtures can vary widely based on naturally-occurring variations in the cellulose starting materials. It would be desirable to identify alternate water retention aids that can be made with consistent quality by a simple, low-waste process.

[0009] SUMMARY

[0010] One aspect of this invention is an alkali-soluble acrylic polymer that comprises repeating units derived from:

[0011] (a) 20 to 50 weight percent (wt%) of (meth)acrylic acid monomers;

[0012] (b) 30 to 60 wt% alkyl (meth)acrylate monomers; and

[0013] (c) 5 to 30 wt% ethylene glycol (meth)acrylate monomers; and

[0014] (d) no more than 20 wt% other unsaturated monomers, wherein the weight percentages are based on the total weight of the acrylic polymer.

[0015] A second aspect of this invention is a process to make an alkali-soluble acrylic polymer comprising performing an emulsion polymerization of: (a) from 20 to 50 wt% (meth)acrylic acid monomers;

[0016] (b) from 30 to 60 wt% alkyl (meth)acrylate monomers; and

[0017] (c) from 5 to 30 wt% ethylene glycol (meth)acrylate monomers; and

[0018] (d) no more than 20 wt% other unsaturated monomers, in an aqueous medium that contains an emulsifying quantity of surfactant and a polymerization initiator, wherein weight percentages are based on the total weight of monomers.

[0019] A third aspect of this invention is a process to extend the water retention of a cementitious wet mix that contains filler, cement and optionally other dry components mixed with water, comprising the step of incorporating into the wet mix an alkali-soluble acrylic polymer from the first aspect of the invention.

[0020] A fourth aspect of this invention is a cementitious mixture comprising the following dry components (a)-(c):

[0021] (a) filler;

[0022] (b) cement;

[0023] (c) at least 0.01 wt% of an alkali-soluble acrylic polymer, based on the total weight of dry components, wherein the alkali-soluble acrylic polymer comprises repeating units derived from:

[0024] (i) 20 to 50 wt% (meth)acrylic acid monomers;

[0025] (ii) 30 to 60 wt% alkyl (meth) acrylate monomers; and

[0026] (iii) 5 to 30 wt% ethylene glycol (meth)acrylate monomers; and

[0027] (iv) no more than 20 wt% other unsaturated monomers, and wherein the weight percentages of repeating units are based on the total weight of the acrylic polymer, and optionally water.

[0028] A fifth aspect of this invention is a cured cementitious mixture comprising:

[0029] (a) filler;

[0030] (b) cured cement; and

[0031] (c) an alkali-soluble acrylic polymer as described in the first aspect of the invention.

[0032] Alkali-soluble acrylic polymers of this invention can be made simply and inexpensively with consistent properties by ordinary emulsion polymerization using known and readily available monomers. In some embodiments of cementitious mixtures, the alkali-soluble acrylic polymers can provide water retention comparable to cellulose ethers. DETAILED DESCRIPTION

[0033] Acrylic Polymers and their Synthesis

[0034] Some embodiments of the present invention relate to an alkali-soluble acrylic polymer that can be substituted for cellulose ether as a water retention aid in a cementitious mixture. Tire alkali- soluble acrylic polymer is a copolymer that is synthesized from (meth)acrylic acid monomers and (meth)acrylate monomers as described further herein. In an acidic environment, the alkali-soluble acrylic polymer can form an emulsion wherein the acrylic polymer chains are contained within dispersed particles. In a basic environment, the acid moieties in the acrylic polymer are ionized, and the acrylic polymer swells and can dissolve into the aqueous phase. Depending on the concentration of dissolved polymer, the viscosity of the aqueous phase may increase.

[0035] For the purposes of this application, “(meth)acrylic acid” refers to either acrylic acid or methacrylic acid or a mixture of both acrylic acid and methacrylic acid. In some embodiments, (meth)acrylic acid monomers consist essentially of acrylic acid. In some embodiments, (meth)acrylic acid monomers consist essentially of methacrylic acid. In some embodiments, (meth)acrylic acid monomers are a mixture comprising acrylic acid and methacrylic acid, in which methacrylic acid makes up at least 10 wt% of the mixture or at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%. In some embodiments, (meth)acrylic acid monomers are a mixture comprising acrylic acid and methacrylic acid, in which acrylic acid makes up at least 10 wt% of the mixture or at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%. In some embodiments, (meth)acrylic acid monomers may further contain small amounts of other alkyl acrylic acids such as ethacrylic acid; in some embodiments, the concentration of other alkyl acrylic acids is no more than 10 wt% or no more than 5 wt% or no more than 2 wt% or no more than 1 wt% or essentially 0 wt% (no measurable concentration).

[0036] Like (meth)acrylic acid, “(meth)acrylate” refers to either acrylate or methacrylate or a mixture of both acrylate and methacrylate. In some embodiments, (meth)acrylate monomers consist essentially of acrylate. In some embodiments, (meth)acrylate monomers consist essentially of methacrylate. In some embodiments, (meth)acrylate monomers are a mixture comprising acrylate and methacrylate, in which methacrylate makes up at least 10 wt% of the mixture or at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%. In some embodiments, (meth)acrylate monomers are a mixture comprising acrylate and methacrylate, in which acrylate makes up at least 10 wt% of the mixture or at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt%. In some embodiments, (meth)acrylate monomers may further contain small amounts of other alkyl acrylates such as ethyl acrylate; in some embodiments, the concentration of other alkyl acrylates is no more than 10 wt% or no more than 5 wt% or no more than 2 wt% or no more than 1 wt% or essentially 0 wt% (no measurable concentration).

[0037] The acrylic polymer contains from 20 to 50 wt% of repeating units derived from (meth)acrylic acid monomers. In some embodiments, the acrylic polymer contains at least 22 wt% repeating units derived from (meth)acrylic acid monomers or at least 24 wt% or at least 25 wt%. In some embodiments, the acrylic polymer contains at most 45 wt% repeating units derived from (meth)acrylic acid monomers, or at most 42 wt% or at most 40 wt% or at most 38 wt% or at most 36 wt% or at most 35 wt%. In some embodiments, the (meth)acrylic acid monomers comprise primarily (more than 50 wt%) methacrylic acid.

[0038] The acrylic polymer contains from 30 to 60 wt% repeating units derived from alkyl (meth)acrylate monomers. The alkyl (meth)acrylate monomers comprise alkyl esters of acrylic acid and / or methacrylic acid. In some embodiments, the alkyl (meth)acrylate monomers consist essentially of alkyl esters of acrylic acid, and in some embodiments, the alkyl (meth)acrylate monomers consist essentially of alkyl esters of methacrylic acid. In some embodiments, the alkyl (meth)acrylate monomers comprise a mixture of alkyl esters of acrylic acid and alkyl esters of methacrylic acid. In some embodiments, the alkyl portion of the alkyl ester contains on average at most 8 carbon atoms or at most 6 carbon atoms or at most 4 carbon atoms. The alkyl portion of the alkyl ester contains at least 1 carbon atom, and in some embodiments contains on average at least 2 carbon atoms. In some embodiments, the alkyl portion is a methyl, ethyl, propyl or butyl group. Examples of suitable alkyl (meth) acrylate monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate or butyl methacrylate. In some embodiments, the alkyl (meth)acrylate monomers comprise primarily (more than 50 wt%) ethyl acrylate.

[0039] In some embodiments, the acrylic polymer contains at least 35 wt% repeating units derived from alkyl (meth)acrylate monomers, or at least 40 wt% or at least 45 wt% or at least 48 wt% or at least 50 wt%. In some embodiments, the acrylic polymer contains at most 58 wt% repeating units derived from alkyl (meth)acrylate monomers, or at most 56 wt% or at most 54 wt%. In some embodiments, more than 50 wt% of the alkyl (meth)acrylate monomers are ethyl acrylate.

[0040] The acrylic polymer contains from 5 to 30 wt% repeating units derived from ethylene glycol (meth)acrylate monomers [“EG(M)A monomers”], which are selected from hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-alkoxyethyl acrylate, and / or 2-alkoxyethyl methacrylate. For example, the EG(M)A monomers may meet Formula 1 in some embodiments:

[0041] R1

[0042] ( 1) H2C = C-CO2-CH2CH2O-R2 wherein each R1is independently hydrogen or a methyl group and each R2is independently hydrogen or an alkyl end cap group. In some embodiments, R2is a hydrogen atom (H) and contains no carbon atoms. In some embodiments, R2is an alkyl moiety that contains at least 1 carbon atom. In some embodiments, R2contains on average at most 8 carbon atoms or at most 6 carbon atoms or at most 4 carbon atoms or at most 2 carbon atoms. In some embodiments, R2is a methyl, ethyl, propyl or butyl group. In some embodiments, R2is a methyl group.

[0043] In some embodiments, the EG(M)A monomers consist essentially of hydroxyethyl acrylate, and in some embodiments, the EG(M)A monomers consist essentially of hydroxyethyl methacrylate. In some embodiments, the EG(M)A monomers consist essentially of 2-methoxyethyl acrylate, and in some embodiments, the EG(M)A monomers consist essentially of 2-methoxyethyl methacrylate. In some embodiments, the EG(M)A monomers comprise a mixture of hydroxyethyl acrylate and / or hydroxyethyl methacrylate and / or 2-methoxyethyl acrylate, and / or 2-methoxyethyl methacrylate. In some embodiments, the acrylic polymer contains at least 8 wt% repeating units derived from EG(M)A monomers, or at least 10 wt% or at least 12 wt% or at least 13 wt%. In some embodiments, the acrylic polymer contains at most 28 wt% repeating units derived from EG(M)A monomers, or at most 26 wt% or at most 25 wt%.

[0044] The acrylic polymer may optionally contain up to 20 wt% repeating units derived from other ethylenically unsaturated monomers. Examples of suitable monomers include styrene, vinyl acetate, vinyl alcohol, acrylonitrile, acrylamide, alkyl acrylamides, 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate, sodium vinylsulfonate, phosphoethyl methacrylate, and vinyl chloride. In some embodiments, the acrylic polymer contains no more than 15 wt% repeating units derived from other monomers, or no more than 10 wt% or no more than 5 wt% or no more than 3 wt% or no more than 2 wt%. In some embodiments, the acrylic polymer may contain essentially no repeating units derived from other monomers (0 wt%).

[0045] The above-named monomers are commercially available, such as from The Dow Chemical Company. See, for example “Solutions for Emulsion Polymerizations,” published by The Dow Chemical Company (2018).

[0046] In some embodiments, the alkali-soluble acrylic polymer is a random copolymer. In some embodiments, the acrylic polymer meets Formula 2: wherein:

[0047] • each R1is independently hydrogen or a methyl group; • each R is independently an alkyl group in an alkyl (meth)acrylate repeating unit as previously described;

[0048] • each R2is independently hydrogen or an alkyl end cap group;

[0049] • M is hydrogen or a substituent that is appropriate for a comonomer in an acrylic polymer, such as an alkyl group, an aryl group, a hydroxyl group or an amide group;

[0050] • x represents a number of repeating units derived from (meth)acrylic acid monomers, representing on average from 20 to 50 wt% of the polymer;

[0051] • y represents a number of repeating units derived from alkyl (meth)acrylate monomers, representing on average from 30 to 60 wt% of the polymer;

[0052] • z represents a number of repeating units derived from ethylene glycol (meth)acrylate monomers, representing on average from 5 to 30 wt% of the polymer;

[0053] • m represents a number of repeating units derived from other monomers, representing on average from 0 to 20 wt% of the polymer.

[0054] In some embodiments of Formula 2, the illustrated repeating units are randomly distributed within the polymer.

[0055] In some embodiments, the acrylic polymer has a number average molecular weight of at least 100,000 g / mol or at least 200,000 g / mol or at least 300,000 g / mol or at least 500,000 g / mol or at least 1,000,000 g / mol. In some embodiments, the acrylic polymer has a number average molecular weight of at most 1,000,000 g / mol or at most 500,000 g / mol or at most 300,000 g / mol.

[0056] The monomers are selected such that the acrylic polymer is alkali-soluble, which means soluble in water with a pH of 10, as measured according to the Test Methods. Cementitious environments are alkaline, and the alkali-soluble acrylic polymer can dissolve in them to interact effectively with water. The acrylic polymer is soluble up to at least 1 g / 100 g in water with a pH of 10. In some embodiments, the acrylic polymer is soluble up to at least 10 g / 100 g in water with a pH of 10 or at least 20 g / 100 g or at least 30 g / 100 g. The solubility limit of some acrylic polymers may be difficult to measure, because the viscosity of the solution increases with increasing concentration of acrylic polymer. In some embodiments, the acrylic polymer forms a stable emulsion in an aqueous acidic environment, such as in water with a pH of at most 3 or at most 6.

[0057] The acrylic polymers may be obtained using known processes for the polymerization of the appropriate acrylic monomers. A commonly known process is emulsion polymerization of suitable monomers in the presence of emulsifiers and an initiator. Emulsion polymerization may offer advantages for some acrylic polymers used in this invention. Emulsion polymerization can yield higher molecular weights for some acrylic polymers, as compared to other polymerization methods. Further, some emulsions that contain acrylic polymers can easily be dried to form redispersible powders, which can easily be included in a dry mix. Polymers made by emulsion polymerization are often called emulsion polymers. Emulsion polymerization processes are well-known and described in numerous publications, such as Emulsion Polymerization of Acrylic Monomers, published by Rohm and Haas Company, (1966) which is available at https: / / ia600709.us.archive.org / 35 / items / emulsioiipolymeri00rohm / emulsioiipolymeri00rohm.pdf; Lovell et al, Fundamentals of Emulsion Polymerization, 21 Biomacromolecules 4396-4441 (2020); and Juaregui, Thesis: Synthesis and Optimization of Emulsion Polymers published by California Polytechnic State University, San Luis Obispo (2016).

[0058] Emulsion polymerization takes place in an aqueous medium, which contains surfactants that act as emulsifiers. Monomers are polymerized in the medium, initiated by a free radical initiator or a redox initiator. The selection and proportions of the monomers in the emulsion polymerization reflect their desired proportions in the resulting polymer, as previously described. In some embodiments, the monomer emulsion contains at least 20 wt% monomers or at least 30 wt% monomers or at least 40 wt% monomers or at least 50 wt% monomers or at least 60 wt%. In some embodiments, the monomer emulsion contains at most 80 wt% monomers or at most 70 wt% or at most 60 wt% or at most 50 wt%.

[0059] Examples of appropriate surfactants for use as emulsifiers are commercially available from The Dow Chemical Company under the DOWFAX™ and TRITON'™ trademarks. See, for example “Solutions for Emulsion Polymerizations,” published by The Dow Chemical Company (2018). In some embodiments, the weight ratio of emulsifiers to monomers is at least 0.5 wt% or at least 1.0 wt% or at least 1.5 wt%. In some embodiments, the weight ratio of emulsifiers to monomers is at most 2.0 wt% or at most 2.5 wt% or at most 3.0 wt%.

[0060] Examples of suitable initiators include free radical initiators and redox initiators. Examples of free radical initiators include organic peroxides such as benzoyl peroxide and t-butyl hydroperoxide and azo compounds such as azobisisobutyronitrile (AIBN) or azobismethylbutyronitrile (AMBN). Examples of redox initiators are described in Sarac, “Redox Polymerization”, 24 Prog. Polym. Sci. 1149-1204 (1999). In some embodiments, the weight ratio of initiator to monomers is at least 0.05 wt% or at least 0.1 wt% or at least 0.15 wt%. In some embodiments, the weight ratio of initiator to monomers is at most 0.3 wt% or at most 0.25 wt%.

[0061] In many embodiments, the emulsion polymerization is carried out at a temperature of at least 50°C or at least 60°C or at least 70°C or at least 75°C. In many embodiments, the emulsion polymerization is earned out at a temperature of at most 95°C or at most 90°C. Pressure is not critical, as long as the blend of water, emulsifiers and other ingredients is stable; in most embodiments, ambient pressure is convenient. In many embodiments, the reaction mixture is agitated to provide good mixing.

[0062] The result of the emulsion polymerization is a polymer emulsion, which contains particles of the acrylic polymer suspended in the aqueous solvent with emulsifiers. In some embodiments, the average particle size of the polymer is at least 50 nm or at least 70 nm or at least 90 nm. In some embodiments, the average particle size is at most 500 nm or at most 250 nm or at most 150 nm. In some embodiments, the concentration of acrylic polymer in the polymer emulsion is at least 10 wt% or at least 15 wt% or at least 20 wt%. In some embodiments, the concentration of acrylic polymer in the polymer emulsion is at most 40 wt% or at most 45 wt% or at most 50 wt%.

[0063] In some embodiments, the acrylic polymer may be retained and used as a polymer emulsion.

[0064] In some embodiments, the polymer emulsion may be spray-dried to form a powder comprising the acrylic polymer. Spray-drying equipment is commercially available with instructions for its use, and spray-drying is described in many publications such as: Santos et al., “Spray Drying - A Overview”, available at: http: / / dx.doi.org / 10.5772 / intechopen.72247; “Spray Dry ManuaD published by Bete Performance Spray Engineering at www.BETE.com; and More Swati et al, “Review on Spray Drying Technology” 4(2) IJPCBS 219-225 (2014). Acrylic polymer powders may be easier to store and transport and may optionally be added to a dry mix before water is added.

[0065] Use as Water Retention Aids

[0066] Acrylic polymers of this invention may be used as water retention aids in cementitious mixtures (dry mix or wet mix). Powders that contain the acrylic polymer may be added to the dry mix before water is added. Alternatively, powders or emulsions that contain the acrylic polymer may be added to the wet mix after water is added. Alternatively, powders or emulsions that contain the acrylic polymer may be added to water before the water is added to the dry mix.

[0067] The cementitious mixtures contain filler, cement and optionally other additives as dry components. (“Dry components” are any components of the cementitious mixture that are normally solid at up to 40°C and atmospheric pressure.)

[0068] Fillers for cementitious mixtures usually contain inorganic particles. The particle sizes of the filler vary depending on the intended use of the cementitious mixture. Mortar, grout and stucco fillers generally contain sand. US standards for masonry filler are listed in ASTM C144 and in AASHTO M 45-15. Concrete fillers generally contain aggregate, a mixture of sand and gravel of various sizes. US standards for concrete aggregate filler are listed in ASTM C33 and AASHTO M 6 / M 80. See also, Kousmata et al., Design and Control of Concrete Mixtures, Chapter 6 “Aggregates for Concrete” (2016). In some embodiments, the filler may also contain pozzolans such as fly ash, calcined kaolin, pumices, or fumed silica; pozzolans and their use in cementitious mixtures are well-known and described in US Patent 9181131B2. In some embodiments, the filler may also contain inorganic pigments such as titanium dioxide, other metal oxides or carbon black. In some embodiments, the filler may also contain organic fibers or particles.

[0069] In some embodiments, the cementitious mixture contains at least 50 wt% filler, based on the dry components and excluding water, or at least 60 wt% or at least 65 wt% or at least 70 wt%. In some embodiments, the cementitious mixture contains at most 85 wt% of filler, based on the dry components and excluding water, or at most 80 wt%. In some embodiments, the cementitious mixture contains at least 50 volume percent filler, based on the dry components and excluding water, or at least 55 volume percent or at least 60 volume percent. In some embodiments, the cementitious mixture contains at most 85 volume percent of filler, based on the dry components and excluding water, or at most 80 volume percent or at most 75 volume percent.

[0070] The ASTM recognizes five categories of cement: Type 1 (ordinary Portland cement); Type 2 (moderate sulfate resistant cement); Type 3 (rapid hardening cement), Type 4 (low heat cement) and Type 5 (high sulfate resistant cement). Any of these cements may be used in cementitious mixtures of this invention. In some embodiments, the cement is ordinary Portland cement. In some embodiments, the cement is a variation of ordinary Portland cement, known as white cement. In some embodiments, the cement is a more specialized cement, such as a high alumina cement or a calcium sulfoaluminate cement. Suitable cements are commercially available.

[0071] The cementitious mixture should contain enough cement to effectively bind the dry components together. In some embodiments, the cementitious mixture contains at least 15 wt% cement or at least 20 wt%, based on the dry components and excluding water. In some embodiments, the cementitious mixture contains at most 50 wt% cement or at most 40 wt% or at most 35 wt% or at most 30 wt%, based on the dry components and excluding water.

[0072] Examples of other additives that may optionally be included in the cementitious mixtures include starch ethers, rheology modifiers, air-entraining agents, accelerators, retarders, superplasticizers and defoamers.

[0073] • Starch ethers, such as hydroxypropyl starch ether, can improve the anti-sagging and anti-slip performance of the wet mix, as well as lengthening open time and providing a smoother surface. Appropriate starch-ethers are commercially available, such as under the Aquaion name.

[0074] • Rheology modifiers, such as bentonite clay, organically-modified clay, attapulgite, fumed silica and precipitated calcium carbonate, can modify the viscosity and shear thinning behavior of the wet mix. Suitable rheology modifiers with instructions for their use are commercially available.

[0075] • Air-entraining agents cause the formation of small air-bubbles in the wet mix, which can improve its resilience under freeze-thaw cycles. Air-entrainment agents are frequently surfactants. Suitable air-entrainment additives with instructions for their use are commercially available.

[0076] • Accelerants speed the setting of the wet mix. They may be especially useful in cold-weather use. Examples of common accelerants include calcium nitrate, calcium nitrite, calcium formate and certain aluminum compounds. Accelerant formulations with instructions for their use are commercially available. • Retarders slow the setting time of the wet mix. Examples of common retarders include calcium, sodium and ammonium salts of lignosulfonic acid, hydroxycarboxylic acids, carbohydrates, lead oxides, zinc oxides, phosphates, borates and fluorates. Retarder formulations with instructions for their use are commercially available.

[0077] • Superplasticizers allow the production and use of wet mix with lower water content.

[0078] Examples of superplasticizers include sulfonated melamine-formaldehyde condensates, sulfonated naphthalene-formaldehyde condensates, modified lignosulfonates and polycarboxylate ethers. Superplasticizer formulations with instructions for their use are commercially available.

[0079] • Defoamers can reduce air-entrainment and voids in the wet mix. Examples of defoamers include mineral oils, polyglycols and polyethersiloxanes. Defoamers with instructions for their use are commercially available.

[0080] In some embodiments, the cementitious mixture contains at most 10 wt% of the other additives or at most 5 wt% or at most 2 wt%, based on the dry components and excluding water. In some embodiments, the cementitious mixture contains no measurable content of the other additives (essentially 0 wt%) or at least 1 wt% or at least 2 wt%, based on the weight of dry components and excluding water.

[0081] The cementitious mixture contains the alkali-soluble acrylic polymer in a quantity suitable to increase the water retention of the cementitious mixture. In some embodiments, the cementitious mixture contains at least 0.01 wt% alkali-soluble acrylic polymer, based on the total weight of dry components, or at least 0.03 wt% or at least 0.05 wt% or at least 0.1 wt% or at least 0.15 wt% or at least 0.2 wt% or at least 0.25 wt% or at least 0.3 wt%. In some embodiments, the cementitious mixture contains at most 2 wt% alkali-soluble acrylic polymer, based on the total weight of dry components, or at most 1 wt% or most 0.5 wt% or most 0.4 wt% or most 0.4 wt%.

[0082] In some embodiments, the cementitious mixture contains no more than 0.15 wt% cellulose ether, based on the weight of dry components and excluding water, or no more than 0.1 wt% or no more than 0.08 wt% or no more than 0.05 wt% or no more than 0.02 wt% or no more than 0.01 wt%. In some embodiments, the cementitious mixture contains essentially no cellulose ether (0 wt%). In some embodiments, the cementitious mixture contains at least 0.01 weight percent cellulose ether.

[0083] In some embodiments, some or all of the dry components are preblended to make a dry mix before the dry components are mixed with water to form a wet mix. In some embodiments, some of the dry components, particularly additives, may be omitted from the dry mix and either may be added to the water before it is blended in to form the wet mix or may be added into the wet mix after it is formed.

[0084] To make the wet mix, water is blended with the dry components in a quantity sufficient to fully wet the dry components and provide a cementitious mixture that is homogeneous and has desirable workability and viscosity. In some embodiments, dry components are blended to make a dry mix and then water is added to the dry mix, but other orders of mixing are also possible. The optimum quantity of water varies depending on the dry components and their intended use, and can be readily determined by experimentation. In some embodiments, the amount of water is at least 15 wt% of the weight of the dry components, or at least 20 wt% or at least 25 wt%. In some embodiments, the amount of water is at most 60 wt% of the weight of the dry components, or at most 50 wt% or at most 40 wt% or at most 30 wt%.

[0085] In some embodiments, the wet mix has a water retention of at least 92 percent, when measured according to the Test Methods, or at least 94 percent or at least 95 percent or at least 96 percent or at least 97 percent or at least 98 percent. There is no maximum desired water retention, but in many cases retention over 99 percent is unnecessary.

[0086] The wet mix may be used in a variety of suitable applications. Non-limiting examples include:

[0087] • Concrete wet mix may be cured in molds to form solid structures, such as pavement, pavers, floors, blocks, walls, pillars or other concrete articles.

[0088] • Mortar may hold bricks, blocks, tiles or other structural elements in place.

[0089] • Stucco may coat a wall or form a layer in an exterior insulation and finish (EIFS) system. After it is applied, the cementitious mixture is permitted to dry and cure. The time needed to dry and cure varies significantly depending on the selection of dry components in the wet mix, the quantity of water, the thickness of the application, and the temperature and humidity at which the drying and curing occur. In many embodiments, the cementitious mixture dries to the touch in a few hours or less, and can be weight-bearing in a day or two. On the other hand, curing to full strength may take many days.

[0090] After curing is complete, the cured cementitious mixture reflects the contents of the wet mix used to make it. The cured cementitious mixture contains filler, cured cement, optionally additives, and residual acrylic polymer of this invention.

[0091] Test Methods

[0092] Unless stated otherwise, measurements listed in this application are made using the following test methods:

[0093] Water Retention Test

[0094] A wet mix mortar is freshly prepared by combining 65g sand and 35g cement to create a dry mix. Separately, a fluid mixture comprising the water retention aid (WRA) and water is prepared separately subject to the constraints that (1) the amount of WRA that is added should equate to the desired final weight fraction in the mortar (0.3 wt%), and (2) the final ratio of water to dry mix in the mortar, including water entering through WRA, should be roughly 0.22. The mortar preparation step is as follows:

[0095] 1. Fluid mixture (water + WRA) is added to the dry mix

[0096] 2. Mix for 1 minute

[0097] 3. Rest for 3 minutes

[0098] 4. Mix for 1 minute

[0099] 5. Rest for 4.5 minutes

[0100] 6. Mix for 30 seconds

[0101] An aluminum ring is placed in the center of a filter paper circle on a flat nonabsorbent surface. The ring has an inner diameter of 55 mm and a depth of 10 mm. The paper is Whatman grade 2294 filter paper with a diameter of 110 mm and a base weight of 556 g / m2. The ring is completely filled with a sample of the mortar, which weighs about 55 to 65g. The sample is allowed to rest for 30 minutes. The water taken up by the filter paper is then determined gravimetrically and subtracted from the initial amount of water in the mortar to obtain the water retention value.

[0102] Examples

[0103] The following examples illustrate specific embodiments of the invention, but do not limit the broadest scope of the invention. The materials in Table 1 are used for the Examples:

[0104] Table 1

[0105] Synthesis of Polymers

[0106] The monomers listed in Table 2 are emulsion polymerized according to the following process: SLS (8.4 g, 28 wt% aqueous solution) and water (386.25 g) are charged into a 2-L, 4-neck round bottom flask equipped with a water condenser, overhead stirrer and a thermocouple, placed under nitrogen and heated to 88°C.

[0107] A monomer emulsion is prepared by mixing together SLS (5.60 g, 28 wt% aqueous solution) and water (203.75 g) in a glass jar at ambient temperature. The desired monomers as shown in Table 2 are added in the following order: (meth)acrylate monomer, EG(M)A monomer (HEMA, HPMA or

[0108] SBEM), (meth) acrylic acid monomer (MAA or AA), followed by any other monomers. The weight ratio of monomers for each example is selected to reflect the proportions shown in Table 2, and the total mass of monomers of monomers is selected to provide a final acrylic polymer emulsion having the solids content in Table 2. A portion of the monomer emulsion (27.45 g) is added to the round bottom flask while stirring. Immediately after the monomer emulsion is added, a mixture of APS initiator (0.38 g in 7.50 g water) is added to the kettle, followed by a water rinse (2.5 g). At the exotherm peak, a solution of aqueous APS (0.15 g in 30 g of water) and the remainder of the monomer emulsion are added to the round bottom flask over 1.5 hours while the contents are maintained at 85 °C. After 1.5 hours, the monomer emulsion and APS vessels and feed lines are rinsed with water, and the reaction mixture is stirred for 5 min at 85 °C. An aqueous solution of APS (0.13 g in 32.5 g of water) is added over 15 min. The contents are cooled to 75 °C, and dilution water (10 g) was added.

[0109] Cooling is continued to 30 °C, and remaining free monomer in the round bottom flask is chased during cooling by addition of 0.15% active ferrous sulfate heptahydrate (1.83 g), followed by addition of 70% aqueous t-butyl hydroperoxide (0.2 g diluted in 6.25g water) over 15 minutes and rinsed with water (1.25 g), concurrent with addition of isoascorbic acid (0.28 g in 6.25 g water) over 15 minutes, and rinsed with additional water (1.25 g). Then the t-butylhydroperoxide and isoascorbic acid additions were repeated one time as described above.

[0110] The final polymer emulsion is filtered successively through 100 mesh and 325 mesh screens. The approximate solids content of the polymer emulsion is shown in Table 2, and the polymer emulsion has a pH of 2.5 to 3.5.

[0111] The polymers are tested for water retention according to the Test Methods. Results are shown in Table 2. The samples labeled as “IE” represent Inventive Examples according to some embodiments of the present invention, and the samples labeled as “CE” are comparative examples.

[0112] Table 2

[0113] * Water retention of cellulose ether at 0.3% concentration is 98% a - from 31 to 34 weight percent.

Claims

CLAIMS:

1. A cementitious mixture comprising the following dry components (a)-(c):(a) filler;(b) cement;(c) at least 0.01 weight percent of an alkali-soluble acrylic polymer, based on the total weight of dry components, wherein the alkali-soluble acrylic polymer comprises repeating units derived from:(i) 20 to 50 weight percent (meth)acrylic acid monomers;(ii) 30 to 60 weight percent alkyl (meth)acrylate monomers; and(iii) 5 to 30 weight percent ethylene glycol (meth)acrylate monomers; and(iv) no more than 20 weight percent other unsaturated monomers, and wherein the weight percentages of repeating units are based on the total weight of the acrylic polymer, and optionally water.

2. The cementitious mixture of Claim 1 wherein the alkali- soluble acrylic polymer contains from 20 to 40 weight percent repeating units derived from methacrylic acid .

3. The cementitious mixture of Claim 1 wherein, in the alkali-soluble acrylic polymer, the alkyl portion of repeating units derived from alkyl (meth)acrylate monomers contains on average 1 to 6 carbon atoms.

4. The cementitious mixture of Claim 1 wherein, in the alkali-soluble acrylic polymer, the repeating units derived from alkyl (meth)acrylate monomers are derived primarily from ethyl acrylate.

5. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer contains from 45 to 58 weight percent repeating units derived from alkyl (meth) acrylate monomers.

6. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer contains from 10 to 30 weight percent of repeating units derived from ethylene glycol (meth)acrylate monomers that meet Formula 1 :wherein each R1is independently hydrogen or a methyl group and each R2is independently hydrogen or an alkyl end cap group that contains no more than 6 carbon atoms.

7. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer contains on average no more than 2 weight percent repeating units derived from “other unsaturated monomers” other than (meth)acrylic acid monomers, alkyl (meth) acrylate monomers, and ethylene glycol (meth)acrylate monomers.

8. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer is a random copolymer.

9. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer meetsFormula 2:wherein:(a) each R1is independently hydrogen or a methyl group;(b) each R is independently an alkyl group;(c) each R2is independently hydrogen or an alkyl end cap group;(d) M is hydrogen or an alkyl group, an aryl group, a hydroxyl group or an amide group;(e) x represents a number of repeating units derived from (meth)acrylic acid monomers;(f) y represents a number of repeating units derived from alkyl (meth)acrylate monomers;(g) z represents a number of repeating units derived from ethylene glycol (meth) acrylate monomers; and(h) m represents a number of repeating units derived from other monomers.

10. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer is a random copolymer wherein:(a) from 20 to 40 weight percent of repeating units are derived from methacrylic acid monomers;(b) from 45 to 58 weight percent of repeating units are derived from ethyl acrylate monomers; and(c) from 10 to 30 weight percent of repeating units are derived from ethylene glycol acrylate monomers that meet Formula 1R1(1) H;C = C-CO CH,CH2O-R wherein each R2is independently hydrogen or a methyl, ethyl, propyl or butyl group; and(d) no more than 2 weight percent of repeating units are derived from other unsaturated monomers.

11. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer has a weight average molecular weight from 200,000 g / mole to 1,000,000 g / mole.

12. The cementitious mixture of Claim 1 wherein the alkali-soluble acrylic polymer is an emulsion polymer.

13. The cementitious mixture of Claim 1 further comprising from 0.01 to 0.1 weight percent cellulose ether.

14. The cementitious mixture of any one of Claims 1 to 13 which contains the following dry components:(a) from 50 to 85 weight percent of the filler;(b) from 15 to 50 weight percent of the cement;(c) from 0.05 to 1 weight percent of the alkali-soluble acrylic polymer(d) no more than 0.05 weight percent cellulose ether; and(e) optionally other additives, wherein all weight percentages are based on the total weight of dry components excluding water.

15. The cementitious mixture of Claim 14, wherein the mixture is a wet mix that comprises from 20 to 50 weight percent water, based on the weight of dry components, and has a water retention of at least 92 percent.

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