Experimental Study on Effect of Coarse Aggregate Volume Fraction on Mode i and Mode II Fracture Behavior of Concrete

Abstract

This paper utilizes double-K fracture criterion to investigate the effect of aggregate volume fraction on the Mode I and II fracture behaviors of concrete experimentally. Wedge splitting tests and Mode II fracture tests for non-notched specimens were carried out simultaneously for 60 specimens which were prepared with coarse aggregate in different volume fractions of 19%, 25%, 31% and 37%. It was found from the experimental results that as the volume fraction of coarse aggregate increases from 19% to 37%, both the Mode I and II fracture toughness increase and the crack trajectory becomes more tortuous. Based on the double-K fracture criterion, the ratio of KIIC/KIC is herein clarified as KIIC/KiniIC and KIIC/KunIC . It is found that the values of KIIC/KiniIC and KIIC/KunIC are not constants for concrete, instead, they are logarithmically related to the aggregate volume fraction. With the increase of the coarse aggregate volume fraction from 19% to 37%, the values of KIIC/Kini IC decrease sharply from 18.9 to 6.29, whereas the values of KIIC/Kun IC increase from 2.15 to 2.84. Finally, from the maximum distance between adjacent aggregates in concrete, a general formulation was proposed and verified by the published data and our tests to reasonably estimate Mode I and II fracture toughness with different volume fractions of coarse aggregate.