Aggregate Interlock and Shear Friction Behaviour of ASR Affected Concrete

Aggregate interlock is a critical shear resistance mechanism for the shear design of reinforced concrete structures. This mechanism relies upon shear transfer through cracks and depends on the bearing and the friction between aggregates and cement paste. The effectiveness of aggregate interlock mechanism is affected by the resistance of the cement paste and aggregates, as well as the crack opening and the structural restraints (e.g., presence of steel reinforcement and supports). The effect of alkali-silica reaction (ASR) on aggregate interlock is a complex phenomenon that impacts aggregate interlock. On the one hand, ASR may cause distress within the aggregates and reduces bond and friction between aggregate and the cement paste, reducing aggregate interlock capacity. On the other hand, enhanced confinement and compressive stress transferred across the crack interface caused by structural restraints and ASR concrete expansion may increase aggregate interlock capacity. To adequately consider these controlling and competing mechanisms, this paper examines the shear friction behaviour measured by push off tests and carried out on ASR affected concrete specimens (ASR-induced expansion up to about 0.12%). Results are compared with the predictions of various existing analytical models including those in design codes fib-model code 2010, ACI-318 and CSA A23.3.