Influence of aggregate fracture on shear transfer through cracks in reinforced concrete

Design methods for shear in reinforced concrete structures typically rely upon shear transfer through cracks, which depends upon the crack opening and sliding displacements and the roughness of the crack surfaces. The effectiveness of shear transfer through aggregate interlock is commonly believed to be reduced if the coarse aggregate fractures at cracks, as is frequently the case in high-strength and lightweight aggregate concretes. This paper describes two sets of push-off tests that were carried out to investigate the effect of aggregate fracture on shear transfer through cracks. Marine dredged gravel was used in one set of specimens and limestone in the other. The cracks typically passed around the gravel aggregate but through the limestone aggregate. The experimental results are compared with the predictions of various existing analytical models including those in design codes MC90, Eurocode 2 and ACI-318. The paper also examines the contribution of aggregate interlock to the shear strength of a parallel set of reinforced concrete beams, tested by the authors, which used the same types of aggregate as the push-off specimens.