Influence of crack orientation on compressive behaviour affected by alkali–silica reaction under multi-axial restraints: a quantitative study using image analysis

The impact of anisotropic cracking on concrete mechanically degraded by alkali–silica reaction (ASR) under multi-axial restraint conditions was quantitatively explored. An experimental framework was established to observe and correlate the expansion, compressive behaviour and crack patterns from different directions across specimens under free expansion, uniaxial restraint and biaxial restraint. Anisotropic expansion was induced using a newly fabricated fixture and clear cracking anisotropy based on anisotropic restraint directions was revealed through image analysis. Correlating the compressive behaviour with the crack orientation distribution revealed that specimens with a higher proportion of cracks orthogonal to the compressive loading direction exhibited lower compressive strength and elastic modulus despite similar volumetric expansions. This finding highlights the inadequacy of evaluating ASR-induced degradation in restrained concrete based solely on volumetric expansion or parallel cracks to the compressive loading direction, emphasising the need to consider the negative impact of orthogonal cracks in ASR modelling. The methodology and findings of this study establish a foundation for accurately assessing ASR damage in concrete structures under complex restraints.