Thermo-chemo-mechanics of ASR expansion in concrete structures

The critical nature of the alkali-silica reaction (ASR) on premature concrete deterioration requires the quantitative assessment, in time and space, of the chemomechanical impact of ASR expansion on the dimensional stability of concrete structures. In particular, the coupled problem of heat diffusion and ASR kinetics can be critical, as the ASR is a thermoactivated chemical reaction. The quantitative analysis of these coupled effects on both material and structural level is the main objective of this paper. Starting from the governing micromechanisms of ASR expansions, a chemoelastic model is developed that accounts for ASR kinetics and the swelling pressure exerted by the ASR reaction products on the skeleton. This chemoelastic model is a first-order engineering approach to capture timescale and magnitude of ASR expansion. It is shown that the realistic prediction of ASR structural effects requires the consideration of two timescales: (1) a latency time associated with the dissolution of reactive silica; and (2) a characteristic time associated with the ASR product formation. In addition, a dimensional analysis of the governing equations reveals that the ASR deterioration of “massive” concrete structures is driven by the simultaneous activation of heat diffusion and reaction kinetics within a surface layer defined by a characteristic ASR heat diffusion length. In turn, in “slender” structures, it is the simultaneous activation of moisture diffusion and ASR kinetics that drives the surface layer delamination. This is illustrated through finite-element case studies of ASR effects in structures of different dimensions: a concrete gravity dam and a bridge box girder.