Thermo-chemo-mechanics of ASR expansion in concrete structures

The critical nature of the alkali-silica reaction (ASR) on premature concre te deterioration requires the quantitative assessment, in time and space, o f the chemomechanical impact of ASR expansion on the dimensional stability of concrete structures. In particular, the coupled problem of heat diffusio n and ASR kinetics can be critical, as the ASR is a thermoactivated chemica l reaction.;The quantitative analysis of these coupled effects on both mate rial and structural level is the main objective of this paper. Starting fro m the governing micromechanisms of ASR expansion, a chemoelastic model is d eveloped that accounts for ASR kinetics and the swelling pressure exerted b y the ASR reaction products on the-skeleton. This chemoelastic model is a f irst-order engineering approach to capture timescale and magnitude of ASR e xpansion. It is shown that the realistic prediction of ASR structural effec ts requires the consideration of two timescales: (a) A latency time associa ted with the dissolution of reactive silica; and (2) a characteristic time associated with the ASR product formation. In addition, a dimensional analy sis of the governing equations reveals that the ASR deterioration of "massi ve" concrete structures is driven by the simultaneous activation of heat di ffusion and reaction kinetics within a surface layer defined by a character istic ASR heat diffusion length. In turn, in "slender" structures, it is th e simultaneous activation of moisture diffusion and ASR kinetics that drive s the surface layer delamination. This is illustrated through finite-elemen t case studies of ASR effects in structures of different dimensions: a conc rete gravity dam and a bridge box girder.