Field survey on durability of reinforced-concrete building using concrete with ground granulated blast furnace slag more than 60 % under natural condition for approximately 60 years

This paper reports the carbonation and rebar corrosion of existing reinforced-concrete buildings using concrete with more than 60 % ground granulated blast furnace slag (GGBFS) content under natural conditions for approximately 60 years and compares the results with those of ordinary Portland cement concrete. Survey results indicate that the rebar corrosion of concrete at low relative humidity is mild, although carbonation progressed significantly regardless of the binder type. This indicates that both carbonation and moisture contribute to rebar corrosion. A relative humidity of approximately 80 % and a rebar with a thin cover thickness significantly affected the corrosion in concrete structures. Meanwhile, the progress of concrete carbonation was not significant under a high moisture content with a relative humidity of 80 % or more, which prevented CO2 ingress from the outer zone. Overall, the GGBFS concrete structure with a sufficient cover thickness exhibited sound conditions. However, carbonation rendered the GGBFS more porous. Although carbonation-induced rebar corrosion is not a problem, the effect of carbonation-induced coarsening of the pore structure in the GGBFS system on the durability and structural performance of concrete members should be verified in the future.