Investigation of plastic shrinkage cracking in fiber-reinforced concrete and shrinkage-compensating cement concrete

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Eikamp, Jordan Cornelius
Major Professor
Shafei, Behrouz
Phares, Brent
Taylor, Peter
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Civil, Construction, and Environmental Engineering
Excessive pore water pressure development in early-age concrete may lead to plastic shrinkage cracking in a restrained concrete specimen. As the water evaporation rate exceeds the bleeding rate, negative capillary pressure builds in concrete while it is still in the semiplastic stage. When the capillary pressure exceeds the relatively low tensile strength of early-age concrete, plastic shrinkage cracking occurs. Plastic shrinkage cracking allows water and corrosive agents to penetrate the concrete surface from an early age, which may lead to corrosion of steel rebar, particularly in freeze-thaw climates in which deicing salts are common. The aim of this research is to study the effects of concrete mix design as well as fiber reinforcement on plastic shrinkage cracking. The plastic shrinkage cracking behavior is quantified by measuring capillary pressure and strain in concrete with varying doses of Type K expansive cement, which are analyzed in relation to plastic shrinkage crack development. In addition, cracking potential of polypropylene fiber reinforced concrete (FRC) is determined by measuring cracking age, tensile strength, and compressive strength of FRC. For this purpose, restrained concrete plastic shrinkage tests, ring tests, split cylinder tests, and compression tests are performed. The experimental test results indicate a direct relationship between capillary pressure and plastic shrinkage cracking. The addition of Type K expansive cement tends to increase the rate at which capillary pressure develops, while simultaneously reducing plastic shrinkage-induced strain and mitigating the development of plastic shrinkage cracking in concrete. In FRC specimens, the plastic shrinkage cracking potential is reduced due to the increased tensile strength provided by fibers, particularly when compared with the low strength of early-age concrete. The addition of polypropylene fibers as concrete reinforcement provides addition early-age tensile strength to FRC which helps to reduce the risk of plastic shrinkage cracking. Based on the tendency of Type K expansive cement and polypropylene fibers to mitigate plastic shrinkage cracking, the outcome of this research is expected to contribute to address the long-standing issue of early-age cracking in reinforced concrete structures.
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