Bond of tension bars in underwater concrete: effect of bar diameter and cover

Abstract

This research project is undertaken to assess the effect of washout loss on the drop in bond properties of reinforcing steel bars embedded in underwater concrete (UWC). Special emphasis was placed to evaluate bond using the same concrete mixtures that were subjected to washout. Testing was realized using the beam-end specimen method, and parameters evaluated included level of washout loss, bar diameter, and concrete cover. Test results showed that bond between steel and UWC is affected by the level of washout loss, which in turn is directly influenced by the mixture composition. Similarly to bond in concrete cast and consolidated above water, the ultimate UWC bond strength increases for smaller bar diameters and higher confinement reflected by increased concrete covers. UWC mixtures with increased washout losses exhibited higher drops in compressive, tensile, and bond strengths, as compared to concrete cast above water. Two boxes depending on the level of washout loss, i.e. from 4.2 to 6.9 % and from 8.8 to 10.8 %, have been proposed to predict the extent of bond decrease in UWC mixtures.