Time-dependent behaviour of composite steel-concrete slabs prepared with recycled coarse aggregate

Abstract

The purpose of this research is to investigate the influence of recycled coarse aggregate (RCA) on the long-term behaviour of composite steel-concrete slabs. Several types of tests were conducted to fulfil the research, including material tests on recycled aggregate concrete (RAC), non-uniform shrinkage tests on small-scale slabs, and long-term tests on full-scale slabs. In the materials tests, the influence of service time of RCA and mixing methods on the mechanical properties of RAC were first investigated. The model to predict the RAC elastic modulus was developed accounting for the influence of residual mortar content. The shrinkage tests were then conducted on RAC using RCA obtained from parent concrete having different service time and compressive strengths. The models to predict the autogenous and drying shrinkage behaviour of RAC were developed accounting for the combined effects of parent concrete quality and residual mortar content. In the shrinkage tests on the small-scale slabs, the relative humidity (RH) and strain distributions through the thickness of seventeen slabs were monitored over time. Test parameters consisted of RCA replacement ratios, slab depths and sealing conditions of the slab surfaces. The mechanism of non-uniform shrinkage in composite slabs was revealed by the measured RH distributions through the thickness of slabs. In the long-term tests on the full-scale slabs, seven slabs were prepared and measured, including three steel-bars truss slabs and four composite slabs. A nonlinear finite element model was developed to account for the time-dependent behaviour of composite slabs to include the effects of non-uniform shrinkage, creep and concrete cracking. Based on the experimental investigations and numerical simulations, a design approach to be used for routine design of RAC composite slabs was proposed and validated.