Study of modifications of latex-modified concrete system
Abstract
The major impetus of this study was the indication in 1986 that latex-modified concrete for highway bridge deck overlays would not be exempt from Federal requirements that mandate the use of fly ash in concrete at the contractor's option. Since there had been essentially no engineering evaluation or controlled research on the effects of fly ashes on such concretes, an early indication of any potential deleterious effects was imperative. Tests were performed to determine the effects on chloride permeability, freezing-thawing resistance, strength, bond, and dynamic modulus of elasticity of latex-modified concretes resulting from incorporation of fly ash. In addition, pore size distribution and microstructure were studied on latex-modified cement pastes containing fly ash. Four different representative fly ashes of both Class F and Class C types were used in this study at replacement levels of 15% and 25% by weight of cement. The results indicated that not only did fly ash not degrade the overall performance characteristics of ordinary latex-modified concrete, its inclusion significantly improved chloride permeability and generally improved cement paste pore structure and bond to underlying concrete. A method was developed to permit visualization of the three dimensional latex network on scanning electron microscopy. It was found that fly ash affects this network. The network is somewhat more dense with fly ash, and individual fly ash particles are anchored to the network. Investigations were also conducted on possible modifications of latex-modified concrete incorporating various combinations of latex, superplasticizer, and silica fume. It was found that incorporation of superplasticizer improved the properties of the latex-modified concrete significantly; that satisfactory latex-modified concrete could be produced with reduced latex contents, thus providing significant materials cost savings; and that latex-modified concretes with silica fume and superplasticizer were not uniformly superior to ordinary latex-modified concretes, problems with stickiness and paste pore structure being observed.
Degree
Ph.D.
Advisors
Diamond, Purdue University.
Subject Area
Civil engineering|Materials science
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