Latex-modified concrete

In general, at low latex dosage levels, the creep strain and creep coefficient of latex modified concrete and mortar are considerably smaller than those of ordinary cement cement, mortar and concrete [94, 98]. The low creep is probably due to the low polymer content which may not affect the elasticity, but increases the strength by improving the binding capacity of the matrix as well as providing better hydration through water retention in the mortar and concrete. The coefficient of thermal expansion at about 9-10 x 10 is very similar to that of concrete, which is 10 x 10 6 [87, 94, 99]. 

Bordeleau, D., Pigeon, M., Banthia, N. (1992) Comparative Study of Latex-Modified Concretes and Normal Concretes Subjected to Freezing and Thawing in the Presence of a Deicer Salt Solution, ACI Materials Journal, Nov.-Dee. 1992, pp. 547-553. 

American Concrete Institute (ACI) ACI 548.IR-92 Guide for the Use of Polymers in Concrete (1992) ACI 548.4 Standard Specification for Latex-Modified Concrete (LMC) Overiays(1992) ACI 546.1 R Guide for Repair of Concrete Bridge Superstructures (1980) ACI 503.5R Guide for the Selection of Polymer Adhesives with Concrete (1992)... 

Ramakrishnan, V., Latex-Modified Concretes and Mortars, A Synthesis of Highway Practice, NCHRP Synthesis 179, Transportation Research Board, National Research Council, Washington D.C. (Aug. 1992)... 

When the coloring of latex-modified mortar and concrete is required, alkali-resistant, weatherproof pigments are used. Furthermore, it is important that the pigments do not obstruct the stability of polymer latexes and the hydration of cements. Alkali-resistant glass, steel, polyamide, polypropylene, polyvinyl alcohol (poval), aramid and carbon fibers are employed as mixable reinforcements. Reinforcing bars for ordinary cement concrete are also used for the reinforcement of the latex-modified concrete. 

The mix proportions of most latex-modified concretes cannot be easily determined in the same manner as those of latex-modified mortars because of many factors considered in the mix design. Normally, the polymer-cement ratio of the latex-modified concrete ranges from 5 to 15%, and the water-cement ratio from 30 to 50%. A rational mix design system developed for the latex-modified concrete by Ohama is described below. 

Slump control factor (by volume)=Vp+Vw (Ifisn ) Vc, Vp, Va, Vw, Vs, Vg Volumes of cement, polymer, air, water, sand, and gravel per unit volume of latex-modified concrete, respectively (l/m )... 

The slump (St) of latex-modified concrete can be predicted with every polymer type and at each sand-aggregate ratio by using slump control factor (q>) as follows ... 

The water-cement ratio (W/C) and unit cement content (C) of latex-modified concrete can be generally expressed as a function of the binder-void ratio (a) with every polymer type at each polymer-cement ratio by the following equations ... 

Figure 3.4 Chart showing mix design procedure for latex-modified concretes.

According to Fig. 3.4, the procedure for determining the mix prr rtions of latex-modified concrete is carried out according to the following stqrs ... 

Calculate the quantities of the different materials required to design a mix for a latex-modified concrete for an anticorrosive floor. 

Tables 3.7 and 3.8 give the ACI (American Concrete Institute) suggested guidelines for the mix proportions of latex-modified concretes for bridge deck applications and patching work respectively.l J Also, Standard Specification ACI 548.4.1 1 provides a guideline for the mix proportions of SBR-modifled concrete overlays, for new construction as well as repair and rehabilitation, of highway bridge decks as shown in Table 3.9.

Table 3.7 ACI Suggested Guidelines for Mix Proportions of Latex-Modified Concrete for Bridge Deck y plications. ( 1992, American Concrete Institute, Reprinted with permission.)...

As seen in the Fig. 4.4,t l the water-cement ratio of latex-modified concrete at a given slump is markedly reduced with an increase in the polymer-cement ratio. This water reduction effect is found to contribute to strength development and a drying shrinkage reduction. 

Figure 4.6 Polymer-cement ratio vs. air content of latex-modified concretes.

Table 4.4 Relationship Between Various Strengths of Latex-Modified Concretes. 

Figure 4.21 Relation between binder-void ratio and compressive strength of latex-modified concretes.

The modulus of elasticity in compression and Poisson s ratio of latex-modified concretes are listed in Table 4.5. [ 1 The modulus of elasticity generally tends to decrease with a rise in the polymer-cement ratio. The Poisson s ratio of PAE- and SBR-modified concretes is nearly equal to that of unmodified concrete regardless of the polymer-cement ratio, but that of PVAC-modified concretes increases with rising polymer-cement ratio. 

Conflicting data exist on the creep behavior of latex-modified mortar and concrete. The creep characteristics of SBR- and PAE-modified concretes reported by Ohamal l are represented in Fig. 4.40. Like ordinary cement concrete, the relationships between loading time (t) and creep strain (ec) or creep coefficient (< )) (i.e., creq) strain/elastic strain ratio) of the latex-modified concretes fit approximately the expression ... 

Figure 4.40 Loading time vs. creep strain and creep coefficient of latex-modified concretes.

According to the data of Solomatovfi i on latex-modified concrete using a copolymer of vinyl acetate and didutyl maleate, the wet-cured conaete is more liable to affected by freeze-thaw cycles than the dry-cured concrete. 

Sprinkel, M. M., Twenty-Year Performance of Latex-Modified Concrete Overlays, Polymer-Modified Hydraulic-Cement Mixtures, STP-1176,pp. 141-154, American Society for Testing and Materials, Philadelphia (1993)... 

Of various polymer-modified mortar and concrete, latex-modified mortar and concrete have superior properties, such as high tensile and flexural strengths, excellent adhesion, high waterproofhess, high abrasion resistance, and good chemical resistance, compared to ordinary cement mortar and concrete. Accordingly, they are widely used in many specialized applications in which the ordinary cement mortar and concrete have been employed to a lesser extent till now. In these applications, the latex-modified mortar is widely used rather than the latex-modified concrete from the viewpoint of a balance between their performance and cost Typical applications of the latex-modified mortar and concrete are listed in Table 9.1. 

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