Resilient properties and fatigue damage in stabilized recycled aggregate base course material

A stabilized fiber-reinforced base course material composed largely of recycled concrete aggregate with small amounts of portland cement and fly ash was subjected to repeated flexural loading to evaluate its resilient properties and progressive accumulation of fatigue damage. Cyclic load-deformation data were recorded continuously during the entire fatigue life until fracture to determine (a) the magnitude and variation of cumulative plastic strain and dynamic elastic modulus as a function of the number of loading cycles, (b) a range for the resilient modulus, and (c) the effect of fiber inclusions on the dynamic material properties and rate of damage accumulation. The extent of fatigue damage was calculated as a fatigue damage index, which is based on the cumulative energy dissipated (absorbed) during cyclic loading. All beam specimens used in this experimental program contained (by weight) 4 percent cement, 4 percent fly ash, and 92 percent recycled aggregate; the fiber-reinforced specimens contained an additional 4 percent (by weight) hooked-end steel fibers. Results show that the resilient modulus in flexure varies between about 2.75 GPa (400,000 lbf/in².) and 10.4 GPa (1.5 million lbf/in.²) and the degradation of the dynamic elastic modulus does not exceed 25 percent of the initial modulus. Miner's Rule of linear summation of damage is applicable to unreinforced material but not to fiber-reinforced material. In general, a modest amount of reinforcing fibers was very effective in retarding the rate of fatigue damage accumulation in this lean cementitious composite.