Abstract
Chloride-induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability, but most previous research projects and case studies have focused on concretes without cracks or not subjected to any structural load. Although it has been recognised that structural cracks do influence the chloride transport and chloride induced corrosion in reinforced concrete structures, there is little published work on the influence of micro-cracks due to service loads on these properties. Therefore the effect of micro-cracks caused by loading on chloride transport into concrete was studied. Four different stress levels (0%, 25%, 50% and 75% of the stress at ultimate load – fu) were applied to 100mm diameter concrete discs and chloride migration was measured using a bespoke test setup based on the NT BUILD 492 test. The effects of replacing Portland cement CEMI by ground granulated blast-furnace slag (GGBS), pulverised fuel ash (PFA) and silica fume (SF) on chloride transport in concrete under sustained loading were studied. The results have indicated that chloride migration coefficients changed little when the stress level was below 50% of the fu; however, it is desirable to keep concrete stress less than 25% fu if this is practical. The effect of removing the load on the change of chloride migration coefficient was also studied. A recovery of around 50% of the increased chloride migration coefficient was found in the case of concretes subjected to 75% of the fu when the load was removed.
Highlights
Chloride-induced corrosion of steel in reinforced concrete structures is one of the most serious problems affecting their service life and if unattended it can put the infrastructure at risk and endanger people’s lives
An understanding of the processes of chloride transport in concrete is very important for engineers attempting to predict the service life of reinforced concrete structures and numerous studies dealing with this topic can be found in the literature [1,2,3,4,5,6,7,8,9]
As concrete structures exposed to chloride environments are manufactured with cementitious materials containing mineral additives, the effect of such cementitious materials on micro-cracking under sustained loading and its consequential influence on chloride transport were part of the research reported in this paper
Summary
Chloride-induced corrosion of steel in reinforced concrete structures is one of the most serious problems affecting their service life and if unattended it can put the infrastructure at risk and endanger people’s lives. On the basis of a field survey of 57 bridges in Kansas, USA, Lindquist et al [31] have indicated that the chloride concentration at a depth of 76 mm from the location of a surface crack can exceed the corrosion threshold amount within the first year Another survey of 219 marine structures along the Norwegian coastline has shown that the signs of corrosion could be seen as early as 5–10 years, which means that the time for corrosion initiation was even earlier [32]. As concrete structures exposed to chloride environments are manufactured with cementitious materials containing mineral additives, the effect of such cementitious materials on micro-cracking under sustained loading and its consequential influence on chloride transport were part of the research reported in this paper
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