Abstract
The use of crushed concrete aggregate (CCA), formerly referred to as recycled concrete aggregate (RCA) is increasing, particularly with a recent push towards sustainable sourcing of materials. Further research is required to understand the effect of coarse CCA on the mechanical properties and durability performance of structural concrete. The electrical resistivity, water absorption by capillary action and SEM analysis of CEM I and CEM III/A concretes were investigated to determine the effects on concrete microstructure and water ingress, together with compliance of characteristic (fc,cube) and target mean compressive strengths. The results show that for the three coarse CCA sources tested, the inclusion of coarse CCA generally has a detrimental effect on the microstructure and water ingress of structural concrete. These can be largely overcome through the incorporation of GGBS to produce CEM III/A concretes, allowing higher proportions of coarse CCA to be incorporated. We conclude that the GGBS and coarse CCA content be limited to 50% and 60% respectively, as this reduces the risk of a significant reduction of compressive cube strength and durability performance. The findings suggest that sustainable structural CEM III/A concrete can be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive and significant outcome for the wider implementation of coarse CCA into structural concrete applications.
Highlights
Crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA) have become increasingly popular to replace virgin aggregates since the 1980’s, with a more recent push towards sustainable sourcing of materials [28,66]
The magnitude of difference in the measured results between CEM I and CEM III/A concretes has shown that up to 100% coarse CCA, irrespective of the CCA sources adopted in this study, can be incorporated into structural CEM III/A concrete and have a better durability performance than that of control CEM I concrete, which is higher than the previously reported values of 25–50% [46,60,68,39,44] and a positive finding for the wider implementation of coarse CCA to produce sustainable structural concrete [29,30]
The results show that the inclusion of coarse CCA generally has a detrimental effect on the microstructure and water ingress of structural concrete
Summary
Crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA) have become increasingly popular to replace virgin aggregates since the 1980’s, with a more recent push towards sustainable sourcing of materials [28,66]. The British standards state that ‘these aggregates may be used in other exposure classes provided it has been demonstrated that the resulting concrete is suitable for the intended environment’, which is ambiguous as no performance criteria or limits are included to determine suitability [19,20]. This highlights the importance of further research of coarse CCA, to understand the effects on the mechanical and durability properties, if a more robust framework for coarse CCA is to become a possibility.
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