Identification of Reactive Aggregates Using Neutron Diffraction and Development of Methods to Reduce the Alkali-silica Reaction Expansion

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Abstract The alkali-silica reaction (ASR) involves reactive siliceous aggregates and highly alkaline concrete pore solution producing an expansive alkalisilicate gel, which can imbibe water and then expand. Many dams, reinforced concrete bridges, and pavements require continuous repair or replacement because of cracks caused by this deleterious reaction. Concrete deterioration caused by the ASR has been investigated for many years, however, an understanding of the mechanisms underlying this expansion is still limited. The objective of this proposal is to establish a holistic study of the rocks that causes ASR and then develop chemical admixtures that reduce this expansion. The investigation will be done at various scales, from the molecular to the engineering level. The theoretical model will be validated through rigorous experimental research to quantitatively characterize rock aggregates, their microstructure, and the resulting gel. An important technique to study the bulk deformation properties of mineral components in rocks will be the time-of-flight neutron diffraction facilities at Los Alamos National Laboratory. We will also perform chemical and physical tests on these rocks and on concrete samples to establish a comprehensive and reliable methodology to identify reactive rocks for concrete structures. New chemical admixtures will be studied to reduce or eliminate the expansion in concrete. The results of this research will provide critical information for the aggregate and concrete science and industry.