Brittleness index of cementitious composites

Series of direct tension tests were conducted to observe the softening response of different types of cementitious composites, namely, mortar, plain concrete, high strength concrete, normal fibrous concrete, and high strength fibrous concrete. The types of fibers used are straight and hooked end steel fibers with volume fraction of 0.5, 1.0, 1.5, and 2.0%. The strength of the matrix varied from 24 MPa to 83 MPa. Two types of direct tension specimen, a dog bone and an end-tapered specimen, were developed for monitoring the post-peak response of brittle composites like concrete. All tests were done in an MTS testing machine under closed-loop strain control. The complete load-displacement curve, both ascending and descending branches, of each test was closely monitored and recorded. A simple generalized stress-displacement relationship is proposed. A single variable named 'brittleness index' is introduced and use to model the softening response of different types of cementitious composites. The predicted responses agree closely with the experimental results.