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Utilization of fly ash-portland cement binary systems to control alkali-silica reaction

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2019
Çelen, Ahmet Ziya
The highly alkaline pore solution of the portland cement concrete is not an ideal environment for certain reactive aggregates with poorly-crystalline or amorphous silica phases. In this environment, these aggregates partially or completely disintegrate resulting in formation of a hydrophilic, amorphous gel mainly composed of alkalis and water from the pore solution of the hydrated cement matrix and silica from the aggregates. The newly formed alkali-silica reaction (ASR) gel can expand by absorbing huge amounts of water irreversibly, becoming a significant problem if the gel is confined in a matrix such as hardened cement paste. Expansion of the gel can result in localized internal stresses that cannot be relieved by movement of the ASR gel into to the present voids of the matrix leading to extensive micro-cracks in the concrete. Eventually, ASR can cause critical loss of stiffness, impermeability and strength of concrete. The focus of this thesis is evaluating the ASR performance of portland cement/fly ash binary mortars. For this purpose, a total of 13 fly ashes with a wide range of chemical and mineralogical composition are selected from the leading thermal power plants in Turkey (Tunçbilek, Çatalağzı, Afşin Elbistan, İçdaş, Kemerköy, Yatağan and Yeniköy). The ASR performance of such a variety of Turkish fly ashes has not been investigated at this level before. An in-depth analysis of the impact of chemical and mineralogical differences of the fly ashes on the ASR performance of binary Portland cement/fly ash mortars are also conducted.