Polymer-modified mortars

Polymer modified Portland cement mortars are used in a range of primary construction and concrete and mortar repair appHcations (Fig. 8-31) [86, 90]. 

They are appHed in bridge decking and airport runway apphcations, in repair applications, where the mortar layer can be as much as 5-8 cm thick, in industrial floor screeds, where up to a 5 cm layer is appHed over standard concrete, in fine screeds or patching compounds, where up to 1.5 cm of repair mortar is appHed on floors, in self-leveHng underlayments, where thickness from 2-3 cm to feather edging are common. 

Fundamentals of concrete and Portland cements, hydration chemistry and classification of admix agents were reviewed by Kosamatka, Panarese and Soroka [84, 85]. 

Polymers are added to Portland cement based mortar systems for a number of reasons. Firstly, polymers improve the key properties of the fresh, non hardened mortar, i.e. adhesion, workability and open time. Polymer additives also tend to have a plasticizing effect on cementitions mortars, there by reducing the amount of added water to achieve needed workability and mortar flow properties. Minimizing added water results in fewer capillary pores, lower porosity and stronger cements. Secondary, the properties of a hardened cement mortar are improved. Properly selected 

Improved tensile, compressive and flexural strength are generally reahzed in polymer modified cement mortars, provided sufficient levels of defoamer are added to counteract the tendency of emulsion polymer additives to induce excessive foam generation. 

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Of the several types of the polymer-modified mortars and concretes used for various construction applications, latex-modified mortar and concrete are by far the most widely used materials. Latex-modified mortar and concrete are prepared by mixing a latex, either in a dispersed liquid or as a redispersible powder form with fresh cement mortar and concrete mixtures. The polymers are usually added to the mixing water just as other chemical admixtures, at a dosage of 5-20% by weight of cement. Polymer latexes are stable dispersions of very small (0.05-5 pm in diameter) polymer particles in water and are produced by emulsion polymerization. Natural rubber latex and epoxy latex are exceptions in that the former is tapped from rubber trees and the latter is produced by emulsifying an epoxy resin in water by the use of surfactants [87]. 

Unlike unmodified mortars, which require laborious moist curing conditions for optimum strength properties, polymer-modified mortars should be air-cured at ambient temperature and relative humidity. 

Unlike polymer-modified mortars, unmodified mortars require moist cure for optimal effect. ASTM codes. C = cohesive failure A = adhesive failure. 

Y.Ohama, T.Demura, T.Sato, Water Resistance and Hot Water Resistance of Polymer- Modified Mortars Containing... 

Polymer-modified mortars can be obtained by replacing part of the mixing water with a synthetic latex (e. g. styrene butadiene or acrylate) to the mix. Although the binder is still cementitious, and thus alkalinity is guaranteed, the latex may improve the workability, the waterproofness, the carbonation and chloride resistance, the tensile and flexural strength of the repair mortar [8]. It can also reduce the modulus of elasticity, increase the bond to the substrate, reduce the rate of drying out and thus the rate of shrinkage. 

In the 1960s, styrene-butadiene rubber-, polyacrylic ester-,l and poly(vinylidene chloride-vinyl chloride)- modified mortars and concretes became increasingly used in practical applications. Since the 1960s, the practical research and development of polymer-modified mortar and concrete have been considerably advanced in various countries, particularly U.S.A., U.S.S.R., West Germany, Japan, and U.K. Consequently, a considerable number of publications including patents, books, papers, and reports have appeared. Of these, the main and important studies are as follows ... 

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. 

Considerable research and development of polymer-modified mortar and concrete were conducted in the world in the 1970s. In the 1980s, the polymer-modified mortar and concrete became the dominant materials in the construction industry. At present, they are used as popular construction materials in the advanced countries. 

JISA1171 Method of making test sample of polymer-modified mortar in the laboratory... 

JISA1172 Method of test for strength of polymer-modified mortar... 

Table 1.3 BSs for Concrete-Polymer Composites (including Polymer-Modified Mortars).

Table 1.4 JCI Standards for Test Methods for Polymer-Modified Mortars.

Method of test for adhesion durability of polymer-modified mortar after warm-cool cycling... 

Method of test for resistance of polymer-modified mortar to rapid fteezing and thawing... 

Table 1.5 Standard Specifications and Guides for Polymer-Modified Mortars and Concretes in U. S., Germany, Japan, and RILEM.

Architectural Institute of Japan (AU) Guide for the Use of Concrete-Polymer Composites (1987) JASSs (Japanese Architectural Standard Spedficatiotls) Including the Polymer-Modified Mortars JASS 8 (Waterpr ing and Sealing) (1993) JASS 15 (Plastering Work) (1989) JASS 18 (Paint Work) (1989) JASS 23 (Spray Finishing) (1989)... 

Ohama, Y., Study on Properties and Mix Proportioning of Polymer-Modified Mortars for Buildings (in Japanese), Report of the Budding Research Institute, vol. 65 (Oct. 1973)... 

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. 

Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation (coalescence of polymer particles and the polymerization of monomers) proceed well to yidd a monolithic matrix phase widi a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrbc phase, resulting in the superior properties of polymer-modified mortar and conoete compared to conventional. 

Polymer-Modified Mortar Test Compressive strength Not less than 100kgVcm2(9.8MPa)... 

Calculated firom unit weight of polymer-modified mortars. ... 

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