Flexural capacity of full-depth and two-lift concrete slabs with recycled aggregates

Full-depth and two-lift concrete slabs were cast with fractionated reclaimed asphalt pavement and recycled concrete aggregate as partial and full replacements of the coarse aggregate in a ternary blend concrete containing cement, slag, and fly ash. These large-scale slabs were monotonically loaded at the edge to quantify the effect of recycled aggregates on the slab's flexural capacity. Although the introduction of these recycled aggregates into the concrete reduced the compressive, split tensile, and flexural strengths as well as the elastic modulus of the concrete relative to virgin aggregate concrete, fracture testing demonstrated that recycled concrete aggregate can have fracture properties statistically similar to those of virgin aggregate concrete. Testing of the flexural capacity of the slabs revealed that concrete with recycled aggregates had peak loads at failure similar to or greater than those of virgin aggregate concrete despite a significant difference in beam flexural strength. The calculated tensile stress in the slab at flexural failure was underpredicted by the beam flexural strength by a factor of 1.5 Tor virgin aggregate concrete and 1.9 to 2.7 for concrete with recycled aggregates; these findings demonstrate that the beam flexural strength results are not always reliable predictors of slab capacity, especially with recycled aggregates. Because of lower beam flexural strengths with recycled aggregates, pavement engineers should compare the fracture properties of concrete containing recycled aggregate with those of typical virgin aggregate concrete before deciding whether to increase the required concrete slab thickness.