Cement modifiers

P. F. Tsytsymushkin, S. R. Khajrullin, A. P. Tamavskij, G. S. Glyant-seva, G. G. Iskandarova, and B. V. Mikhajlov. Plugging solution for oil and gas wells—contains plugging cement, modified methylcellulose, mono-substituted sodium phosphate and water. Patent SU 1740627-A,... 

Fig. 11.10 SEM photographs of the surfaces of the cements modified with MPS and various kinds of calcium salts after soaking in SBF for 7days.

Mori, A., Ohtsuki, C., Sugino, A., Kuramoto, K., Miyazaki, T., Tanihara, M. and Osaka, A. (2003)Bioactive PMMA-based bone cement modified with methacryloxypropyltrimethoxysilane and calcium salts — Effects of calcium salts on apatite-forming ability. Journal of the Ceramic Society of Japan, 111, 738-742. 

Surfactants enable the polymer particles to disperse effectively without coagulation in the mortar and concrete. Thus, mechanical and chemical stabilities of latexes are improved with an increase in the content of the surfactants selected as stabilizers. An excess of surfactant, however, may have an adverse effect on the strength because of the reduced latex film strength, the delayed cement hydration and excess air entrainment. Consequently, the latexes used as cement modifiers should have an optimum surfactant content (from 5 to 30% of the weight of total solids) to provide adequate strength. Suitable antifoamers are usually added to the latexes to prevent excess air entrainment increased dosages causes a drastic reduction in the air content and a concurrent increase in compressive strength [87, 92-94]. 

Generally, polymer latexes used as cement modifiers are not toxic, are safe materials to handle and require no special precautions. However, because they have an excellent adhesion to various materials, even to metals, all the equipment and tools such as mixers, trowels, and vibrators should be washed down or cleaned immediately with water after use. For concrete requiring formwork, it is advisable to use the most effective mold-release agents, e.g., silicone wax or grease [87, 96]. 

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. 

Figure 5.8, which is the result of extensive research by Rohm Haas (1991), illustrates the comparative durability of polymer-modified cements. A comparative study carried out by Rohm Haas (1989) of different cement modifiers concluded with the following results ... 

Acrylic latices have been used successfully for more than 35 years to modify portland cement composites. The use of solid grade acrylic cement modifiers has become common during the past few years. Both of these types will be discussed later in this section. The level of polymer modification is measured as a ratio of polymer solids by weight of cement. A 15%-20% modification represents the range for optimum performance lower modification levels may prove acceptable for certain product applications (Rohm Haas, 1989). 

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

In recent years solid grade acrylic cement modifiers have become more popular, for many reasons ... 

Table 5.8 Typical physical properties of acrylic redispersible powers. Source Tsai, M.C., Burch, M.J. and Lavelle, J.A., Solid grade acrylic cement modifiers, in Polymer Modified Hydraulic Cement Mixtures, ASTM STP 1176 (eds L.A. Kuhlam and D.G. Walter), Table 1 published by the American Society for Testing and Materials, Philadelphia, PA, 1993...

Application areas for powdered acrylics as cement modifiers are as follows ... 

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. 

Rohm Haas (1989) Cement Modifier Trouble Shooting Guide, Philadelphia, PA. 

Rohm Haas (1991) Which Cement Modifier Modifies Best , Philadelphia, PA. 

Render Cementitious repair mortar cements modified with polymers are included in this category. 

Figure 11.4 (A) Diagenetic environments and typical cements (modified from Fliigel, 1978). (B) Formation of beachrock in relation to other cemented coastal deposits (schematic).

Asphalt concrete Aggregate - Hot mix asphalt - Cold mix asphalt - Seal coat or surface treatment Asphalt cement modifier Mineral filler... 

Methyl cellulose is very popular as a water-soluble polymer used as a cement modifier, and has been widely used in the field of adhesive polymer-modified mortars for ceramic tiles since the early 1960s.( In this case, die polymer content (to the cement used) is 1% or less. Shibazakil l showed that other polymers, such as hydroxyetfayl cellulose and polyvinyl alcohol (poval) are effective for the water-soluble polymer-modified mortars. 

Shibazaki, T., Properties of Masonry Cement Modified with Water-Soluble Polymers (in Japanese), Semento-Gijutsu-Nempo 17, pp. 194-199 (Jan. 1964)... 

Polymer-modified mortar and concrete are prepared by mixing either a polymer or monomer in a dispersed, powdery, or liquid form with fresh cement mortar and concrete mbctures, and subs uently curing, and if necessary, the monomer contained in the mortar or conoete is polymerized in situ. The polymers and monomers used as cement modifiers are shown in Fig. 2.1. 

Several types of polymer-modified mortars and concretes, i.e., latex-redispersible polymer powder-, water-soluble polymer-, liquid resin-, and monomer-modified mortars and concretes, are produced by using the polymers and monomers shown in Fig. 2.1. Of th, the latex-modified mortar and concrete are by far the most widely used cement modifiers. 

The principle of modification of cement mortar and concrete with redispersible polymer powders is almost the same as that of latex modification except that it involves the addition of redispersible polymer powders. Mostly the redispersible polymer powders are used by dry mixing with the cement and aggregate premixtures, followed by wet mixing them with water. During the wet mixing, the redispersible polymer powders are reemulsified in the modified mortar and concrete, and behave in the same manner as the latexes for cement modifiers. 

Polymer latexes are generally classified into the following three types by the kind of electrical charges on the polymer particles, which is determined by the type of surfactants used in the production of the latexes cationic (or positively charged), anionic (or negatively charged) and nonionic (not charged). The formulations for emulsion polymerization of typical polymer latexes as cement modifiers are listed in Table 3.2.f l... 

In general, polymer latexes are copolymer systems of two or more different monomers, and their total solid content including polymers, emulsifiers, stabilizers, etc. are 40 to 50 % by weight. As seen in Fig. 3.2, most commercially available polymer latexes for cement modifiers are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried. The polymer latexes that are underlined in Fig. 3.2 are the main ones that are in general use today in the world. Table 3.3 gives the... 

Table 3J, Formulations for Emulsion Polymerization of Typical Polymer Latexes as Cement Modifiers. ( 1991, American Concrete Institute, Sprinted widi pemussion.)...

Figure 3.2 Commercially available polymer latexes for cement modifiers.

Table 33 Chemical Structures of Main Polymer Latexes for Cement Modifiers.

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