A study on type K expansive cement paste and concrete, and the influence of silica fume
Abstract
A study of the expansion characteristics of Type K expansive cement pastes was undertaken in order to establish the requirements for a mixture proportioning procedure and observe the effect of expansion on its properties. The effects of expansive clinker particle size distribution, steel reinforcement, and water-cement ratio on the expansion characteristics were investigated. An attempt was made to improve upon some of the properties of type K expansive cement pastes by the addition of silica fume. A study on the physical and chemical properties of the pastes containing silica fume was also undertaken. Paste studies were complemented by studies on mortar and concrete. Statistical models were developed from experimental data to predict the unrestrained expansion magnitude and duration of expansion of expansive cement pastes. Specific results of the study indicate that the microstructure of the expansive cement pastes was more porous than conventional portland cement pastes. Prolonged expansion resulted from coarse particle expansive clinker, and this caused significant damage to the paste microstructure. Restraining the expansion by steel reinforcement was not very effective in decreasing the paste porosity. The addition of silica fume accelerated the initial expansion of the paste and shortened the expansion duration. Thus, the expansive process was more efficient with the addition of silica fume and several of the paste properties were improved. Specifically, the pore structure was modified so as to make the system more impermeable to water and deleterious chemicals. The resistance to sulfate attack was also significantly improved. The study on the hydration chemistry of pastes revealed that expansion was terminated when ettringite stopped forming. In pastes without silica fume, this resulted due to the depletion of SO$\sbsp{4}{2-}$ in the pore solution. However, the termination of ettringite formation in pastes containing silica fume seemed to be related to the decreased OH$\sp-$ concentration in the pore solution, that perhaps decreased the reactivity of the aluminate phases. The study on concrete mixtures revealed that addition of silica fume decreased its permeability to chloride ions. Higher shrinkage and creep was observed for concrete mixtures containing silica fume.
Degree
Ph.D.
Advisors
Cohen, Purdue University.
Subject Area
Civil engineering
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