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STUDY OF THE REACTION BETWEEN FLY ASH AND CALCIUM HYDROXIDE.

STUDY OF THE REACTION BETWEEN FLY ASH AND CALCIUM HYDROXIDE. Jenny Lau Eik Lang and Joseph Biernacki, Tennessee Technological University, Cookeville, Tennessee. The demand for concrete is increasing every year due to the rapid development of constructed infrastructure around the world. Consequently, large-scale industrial production of cement results in high amounts of carbon dioxide ([CO.sub.2]) being released into the atmosphere. In order to reduce the amount of [CO.sub.2] produced while supplying enough cement to the construction industry, materials such as fly ash can be used to partially substitute for cement in concrete. Fly ash, a common waste material produced by the combustion of coal and one of the world's most commonly used pozzolans, is characterized by an ability to react with hydrated lime from cement to form a hardened cementitious material. Although fly ash has been in concrete for many years, the fundamental chemical and physical changes that occur in these systems are still not clearly under stood. To predict the performance of fly ash and other blended cements in concrete by using materials science-based mathematical simulations, detailed knowledge of the chemical and physical changes that happen during hydration are needed. However, this can be very complicated due to the complex system of chemical reactions that take place in the process of cement hydration. To simplify the process, instead of investigating the reaction between Portland cement and fly ash, a model system containing calcium hydroxide (CH), a by-product of cement hydration, and fly ash was studied. When mixed with water and CH, fly ash reacts by forming cementitious products similar to those produced by hydration in Portland cement phases. Recent studies suggest that the rate of the reaction may be controlled by the surface of CH as shown by an increasing consumption rate of CH content of the system. Several hypotheses, such as the effect from particle proximity (transport distance between particles) and pH consistency, have bee n proposed to account for these observations. The objective of this research was to test these hypotheses, to better understand the reaction mechanism between fly ash and CH hydroxide, and to calibrate various parameters in existing hydration models for the accurate prediction of fly ash-CH interaction.
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Author:DYCUS, PATRICIA; VISCO, DON
Publication:Journal of the Tennessee Academy of Science
Article Type:Brief Article
Geographic Code:1U6TN
Date:Jan 1, 2000
Words:367
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