Concrete Mixtures

The incorporation of a latex (an aqueous emulsion of a polymer) into a cement mix makes it possible to achieve both an intimate blend of the 

Variation of Compressive and Tensile Strength of Portland Cement Mortars with Polymer Latex Modification  

Polymer latex type Compressive strength, psi Tensile strength, psi 

Composition, parts by weight Mean value of force to rupture, kg 

The improvements in properties noted may be linked to several factors the reduction made possible in the water/cement ratio, a reduction in gross porosity, the entrainment of air as a fine dispersion, and specific interactions or bonds with the cement gel. Using electron microscopy, Wagner (1965, 1966, 1967) and Aignesberger et al (1969) have shown that melamine and vinyl resins form networks that interpenetrate the network formed by the cement gel. Also, using similar techniques, Pierzchala (1969) concluded that poly(vinyl acetate) effectively becomes a constituent of the cement gel, and makes it chemically resistant, even to hydrofluoric acid. 

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Construction. The addition of PEO to concrete has been a subject of several iavestigations (172). Research studies and patent Hterature suggests that PEO can be used as a pumping aid to concrete where the lubricity of PEO allows concrete to be pumped to longer distances (173—176). In addition, PEO is also used to disperse the water more uniformly ia the concrete mixture that promotes better uniformity of the concrete mixture. Eormulations ia the constmction industry are proprietary and not easily available. 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

Time of setting of concrete mixtures by penetration resistance Compressive strength of cylindrical concrete specimens Flexural strength of concrete (using simple beam with third-point loading)... 

Vassiladou EE (1993) Utilization of fly and bottom ash as a partial fine aggregate replacement in asphalt concrete mixtures. Symposium proceedings Recovery and Effective Reuse of Discarded Materials and By-products for Construction of Highway Facilities. Federal Highway Administration, FHA 101... 

Several different materials and installation systems are available and include various types of proprietary materials, plasters containing perlite or ver-miculite, concrete mixtures, or lightweight concretes. The selected material and installation system, encasement, or surface application should provide protection for the expected fire duration. For more information refer to Chapter 7, Section 7.3.2. 

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]. 

Such effects increase with an increase in the polymer content or the polymer-cement ratio (the weight ratio of total solids in a polymer latex to the amount of cement in a latex-modified mortar or concrete mixture). However, at levels exceeding 20% by weight of the cement in the mixture, excessive air entrainment and discontinuities form in the monolithic network structure, resulting in a reduction of compressive strength and modulus [87, 94, 95]. 

When added at dosage of 2% by weight of cement to a concrete mixture with 460 kg m of cement without adjustment for the volume of the water introduced by the admixture, the concrete s slump and porosity are increased. However, when substituted for an equal volume of water, the SRA has little or no effect on concrete slump. It does have a slight retarding effect on the rate of hydration and may extend the setting time up to about an hour. The admixture also affects the air content of fresh concrete and therefore when used in air-entrained concrete, the air-entraining admixture dosage must be increased to achieve a specified air content. 

The choice of a particular option or options is determined by the desired set time and rate strength development. Accelerated time of setting is usually achieved by increasing the heat of hydration of the concrete mixture. Selection of appropriate chemical admixtures enables the production of cold-weather concrete mixtures with both accelerated setting and early-age strength development characteristics, similar to that obtained with plain... 

Although previous investigations [132, 134, 135] have shown that increased soluble alkalis could have an important influence on the AVS, more recent work [136, 137], however, indicates that soluble alkalis per se do not influence the production of the AVS. It is only when the sulfate level (inherent or by extraneous addition) is high that the AVS production is difficult. An increase in the soluble-alkali content of cement has been found to improve significantly the stability of AVS, particularly in concrete mixtures to which a superplasticizer (SP) is added [138]. 

Design and Control of Concrete Mixtures (1978). Engineering Bulletin of the Portland Cement Association, Skokie, Illinois, USA. 

Hover, C.K. (1998). Concrete mixture proportioning with water-reducing admixtures to enhance durability a quantitative model, CANMET/ACIInternational Workshop on Supplementary Cementing Materials, Superplasticizers and Other Chemical Admixtures, Toronto, Canada, April 6-1. 

Based on the above, the determination of the optimum binder content for SEA concrete mixtures can be summarized as follows ... 

Larrard, F.De Concrete Mixture Proportioning. Routledge, New York. NY. 1999. Marchand. J. and J.P. Skalny Materials Science of Concrete, The American Cerantie Society. Westerville. OH, 1999. 

Cold-weather concrete mixtures incorporating non-chloride antifreeze accelerating admixtures have been used in a number of projects. Two of these projects are profiled. All the concrete mixtures described below were treated with the sodium-thiocyanate-based CWA mentioned earlier. These projects illustrate the impact of this admixture on normal concrete mixtures containing Class C fly ash, since fly ash typically delays time of setting and, hence, would not be a logical choice for cold-weather concrete. 

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