Cement modifiers acrylic emulsions

The formulation of cementitious products with use of powdered acrylics is accomplished through dry blending. After gaining information on cement-modifying acrylics, let us now gain an idea of two broad spec-trums of such acrylics acrylic-cement repair mortars and acrylic-cement protective coatings. These discussions are equally applicable to acrylic emulsions as well as to powdered acrylics. 

Acrylic modifiers for cement impact strength and adhesion to substrates are discussed in reference 211. Both water-soluble acryHc and acrylic emulsion polymers are used in tHe ceramic industry7 as temporary7 binders, deflocculants, and additive components in ceramic bodies and glazes (212) (see Ceramics). 

Table 5.1 outlines useful properties, products and application areas of acrylic systems. Key market segments are coatings based on methacrylates as well as emulsions and water-based sealants. Acrylic emulsions and redispersible powders as cement modifiers offer many useful products for several end-uses. However, the high cost of acrylic has limited their use as cement modifiers. The use of water-based acrylic systems is increasing because of their non-toxic and environmentally friendly nature. 

Acrylic emulsions (or acrylic latices) are characterised as high-solids polymers having a film-forming temperature at or below room temperature (Lavelle, 1986). They have excellent hydrolysis resistance compared with other resins and are well suited as modifiers for portland cement mortars. Studies have shown that certain acrylic latices impart excellent workability at lower water demand, thin section adhesion and toughness, improved flexural strength and tensile strength and outstanding adhesion (Lavelle, 1983). 

Commercial grades are designed for specific end-uses, for example there are separate grades for trowel-applied products and for sprayable products. Cement systems modified with acrylic emulsion are used in numerous applications, as listed below ... 

Table 5.7 Physical properties of commercial acrylic emulsions used as cement modifiers...

The acrylic resins may be so polymerized that a resultant product may be obtained which can be dispersed in water to form a true polymer emulsion. Such a product is now available as a cement mortar modifier. By dry blending this resin with appropriate cementitious materials, it is possible to formulate a one-package acrylic modified cement mortar. Addition of water to the dry blend will produce a mortar with superior adhesion and physical strength properties. 

In addition to the use of dry acrylic powders in cement mortars, other typical uses for these modifiers are in cement toppings, ceramic tile adhesives, ceramic tile grouts, white masonry paints and cement block fillers. It is obvious that these compounds are more convenient to use with the simple addition of water, than those compounds requiring the addition of a latex emulsion. As improvements are made in these dry powders, there will be more emphasis on this type of compound. At the present time, the dry powder acrylics are more costly than the latex emulsions on a dry solids basis. 

B) Polymer-cement concrete is a modified concrete in which a part of the cement binder is replaced by organic polymer. It is produced by incorporating a monomer, prepolymer, or dispersed polymer latex into a cement-concrete mixture. The process technology used is similar to that of conventional concrete and has the advantage that it can be cast in place for field applications. Most of the polymer-cement-concrete composites are based on different kinds of lattices obtained especially by emulsion polymerization. The lattices are aqueous emulsions containing polymer particles such as SBR, NBR, PVAc, copolyesters of AA-MAA, and PAA-PMAA-SBR. The compatibility of SBR, PVAc, and acrylic lattices with Portland cement produces particular characteristics that led to wide use of this component as polymer-concrete composites. 

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