Abstract
The increasing use of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA), has led to research into the effects of coarse CCA in higher value structural applications. Concerns exist regarding the effect on chloride ion ingress which ultimately can cause deterioration of reinforced concrete. This concern is reflected in existing European and British concrete design standards as limitations prevent their use in environments where chlorides may be present. The rapid chloride migration coefficient and rate of accelerated corrosion of structural CEM I and CEM III/A CCA concretes was measured to determine the effect on chloride ion ingress. Three sources of coarse CCA were evaluated; results show that coarse CCA generally had a detrimental effect on the chloride ion ingress of structural concrete. However, these effects can be mitigated by the inclusion of GGBS to produce structural CEM III/A concretes, thus allowing higher proportions of coarse CCA. It is recommended that the GGBS and coarse CCA content be limited to 50% and 60% respectively as this reduces the risk of a significant detrimental effect on chloride ion ingress. The results also suggest that the limitations in existing European and British standards are conservative and sustainable structural CEM III/A concrete with the inclusion of coarse CCA could 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 outcome for the wider implementation of coarse CCA into structural concrete applications.
Highlights
The utilisation of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA) is increasing annually, with the increased recent interest into the more sustainable sourcing and procurement of materials [52,23,64]
The findings in this paper suggest that up to 100% coarse CCA in structural CEM III/A concretes could be incorporated without increasing the risk of a detrimental effect on chloride ion ingress when compared to the control CEM I concrete P < 0.081 – 28 days; P < 0.002 – 91 days)
The results show that the inclusion of coarse CCA generally has a detrimental effect on the chloride ion ingress of structural concrete when an electrical field is applied
Summary
The utilisation of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA) is increasing annually, with the increased recent interest into the more sustainable sourcing and procurement of materials [52,23,64]. One particular area of uncertainty is the effect of CCA on the longevity of reinforced concrete structures exposed to aggressive chloride environments during their service life [16,17,13]. The ability of chloride ions to penetrate the concrete cover is a key factor in the service life of a reinforced concrete structure. Absorption by capillary suction and diffusion are the dominant mechanisms that occur in aggressive chloride environments, relating to the transport of liquids and ions by surface tension effects in the capillaries of porous materials and concentration gradients respectively. Chloride induced corrosion is an electrochemical process and occurs when chloride ions penetrate the concrete cover and react with the passive protective film at the surface of the reinforcing steel, resulting in its depassivation [35,42]. A crack width greater than 0.3 mm can be detrimental to the durability of reinforced concrete for the majority of environmental exposure classes, and can be indicative of a failure of the protective concrete cover [22,21,57,12]
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