Flexural Capacity of Full-Depth and Two-Lift Concrete Slabs with Recycled Aggregates

Abstract

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 for 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.

Steel furnace slag aggregate expansion and hardened concrete properties

“…These findings agree with other studies, which indicated that K Ic and total fracture energy (G F ) can be increased with concrete containing SFS coarse aggregates [20,92]. Despite the reduction in split tensile strength, based on these fracture properties, the flexural slab capacity of concrete with SFS aggregates should be comparable to conventional paving concrete [93].…”

Bonding in cementitious materials with asphalt-coated particles: Part I – The interfacial transition zone

“…Reclaimed asphalt pavement (RAP) has traditionally been used as recycled aggregate in new asphalt pavements, but has also been identified and studied as an aggregate source for concrete [1][2][3][4][5][6][7]. Field demonstration projects have proved the viability of RAP as a virgin aggregate replacement in concrete pavements [8][9][10][11][12][13].…”

Two-lift concrete paving for sustainable pavements

“…Second, the lower strengths achieved when such recycled materials are used in the bottom lift still meets concrete paving specifications. In the context of the feasibility of two-lift pavement with RCA and FRAP, (Brand et al, 2014) showed although the mechanical properties of concrete cylinders and beams with FRAP and RCA materials were negatively affected compared to the control specimens, the concrete slabs demonstrated superior flexural performance.…”

“…One primary concern with recycled materials is the long-term durability performance, which is a function of the replacement level, water-to-cementitious-material ratio, concrete age, and moisture (Yehia et al, 2015). Even though recycled aggregate concrete typically results in lower mechanical properties (Brand et al, 2014), lower abrasion and ingress resistance (Thomas et al, 2013), and lower fresh concrete properties (Qasrawi and Marie, 2013), it can generally be produced to meet standard aggregate quality and grading requirements if adequate replacement level, proper care, and process control are taken into account. The incorporation of RCA, RAP, and/or FRAP into twolift concrete pavement provides economic, environmental, and sustainability advantages, and offers practical solutions.…”