Effect of Aggregate Size on Shear Behavior of Lightweight Concrete Continuous Slender Beams

Abstract

Twelve continuous slender beams were tested to ascertain the effect of the maximum aggregate size on the shear behavior of concrete beams. The typical characteristics of the failure surface along the inclined cracks of the beams tested were compared according to the maximum aggregate size and the type of concrete by using a microphotograph. The test results showed that the shear strength of lightweight concrete (LWC) continuous beams increased with the maximum aggregate size, though the increasing rate was lower than that of normalweight concrete (NWC) continuous beams. The microphotograph showed that the inclined crack of mortar beams with an aggregate size of 4 mm (0.16 in.) had a near-linear shape and a smooth failure surface, whereas that of the concrete beams was emboss-shaped with a failure plane partially formed along the pastes around the aggregate particles, regardless of the type of concrete. These characteristics of the failure plane contributed to the enhancement of the shear strength of LWC beams, though the shear force transferred by the aggregate interlock was much lower than that in NWC beams. The increasing rate of shear strength of LWC beams against aggregate size is similar to that predicted from the simplified compression field theory or the empirical formulas proposed by Bazant and Sun. The modification factor for shear strength of LWC specified in ACI 318-08 and EC2 is unconservative in the continuous beams tested, showing an increase of the unconservatism with the maximum aggregate size.