The influence of mortar-aggregate bond strength on the behaviour of concrete in uniaxial compression

Modification of aggregate surfaces by ball mill treatment with various grades of abrasive grit allowed concretes to be prepared which differed only in the surface texture of the coarse aggregate. Due to the dependence of mortar-aggregate bond strength on the texture of the aggregate surface, an assessment could thus be made of its influence on the behaviour of concrete in compression. Substantial changes in the stress and longitudinal strain at ultimate load were observed. These appeared to be caused mainly by the retardation of initial bond failure at Initiation Stress due to the increased bond strength of the rougher aggregates. The occurrence of mortar-aggregate columns and cone-like deposits of mortar at the “poles” of aggregate particles was observed in failed concrete specimens and failure of the mortar-aggregate bond in both tension and compression-shear was confirmed.