Long-term Response Of Recycled Aggregate Concrete Simply Supported Composite Slabs

The excessive consumption of natural aggregates and the accumulation of constructional waste have been raising concerns of an environmental epidemic.The use of recycled aggregate concrete made of recycled coarse aggregates and recycled fine aggregates from construction and demolition waste is considered one of the potential solutions to mitigate this outbreak.Previous research studies always showed a negative influence of recycled coarse and fine aggregates on the mechanical and long-term behaviour of concrete suggesting that its use in structural members has to be limited.However,due to its moderate load carrying and serviceability requirements,a composite steel-concrete slab is considered one of the most viable options to implement the use of recycled aggregate concrete.The presence of a steel profile at the bottom of composite steel-concrete slabs has several advantages which will make the use of such slabs favourable.Nevertheless,the shrinkage behaviour of such slabs is negatively influenced by the steel deck due to the non-uniform moisture egression between the top and bottom of the slab.A shrinkage gradient caused by the non-uniform moisture egression is created along the cross section of the slab and this effect is normally referred to as the nonuniform shrinkage of steel-concrete composite slabs.The research work of this thesis aims to quantify the long-term behaviour properties of recycled aggregate concrete simply supported steel-concrete composite slabs accounting for the effect of non-uniform shrinkage.The simulation of the long-term behaviour of composite concrete-steel slabs is carried out using a finite element model written as a MATLAB code by Wang Qinghe.In order to account for the long-term effects(shrinkage and creep)of recycled aggregate concrete on the quantified long-term properties,several models proposed particularly to account for these effects are used in the finite element model.A stress strain relationship to account for the effect of concrete tension stiffening is also proposed and the validity of the model to account for the effect of non-uniform shrinkage with the proposed stress strain relationship is confirmed against experimental results available from the literature.A parametric study considering the influential parameters on concrete shrinkage is performed aiming to understand the effect of the non-uniform shrinkage on the long-term behaviour of steel-concrete composite slabs made with full contribution of recycled coarse and fine aggregates.The results of the parametric study show a significantly large influence of non-uniform shrinkage on the total mid-span deflection of the slab and the stress of the steel deck increasing them by 6-8 times and 20%-70% respectively.Based on the results of this parametric study,several equations will be proposed to account for the effect of non-uniform shrinkage on the long-term properties of of recycled aggregate concrete simply supported steel-concrete composite slabs.In order to understand the difference between the influence of recycled coarse and fine aggregates,a second parametric study is performed considering different contributions of recycled coarse and fine aggregates.The results of this parametric study show that the influence of recycled fine aggregates is always greater than the influence of recycled coarse aggregates by 25%-65%.Based on the conclusions from the performed parametric analysis,a large-scale third parametric analysis is performed and the results are used to establish models capable of predicting the total mid-span deflection and the total stress at the top and bottom of the steel deck accounting for the effect of non-uniform shrinkage.