Effect of curing, finishing and loading rate on the bond strength of fiber reinforced SCC layer with normal concrete by pull-off method

The main factor in integrated performance of repair overlay and substrate concrete is the bonding between them. The accurate measurement of bonding is dependent to factors such as strength and surface characteristics of substrate concrete, loading mechanism and curing condition of overlay. In this research, 8 mix designs are considered. For assessment of strength level and surface quality of substrate, two concrete grades in the ranges of 20-30 and 40-50 MPa, and also two surface conditions including simple finishing and ribbed finishing were considered. Repair overlays were considered from three different strength grades of self-compacting concretes contained 0.5% and 1% of steel fibers. After fabrication, for curing, three different conditions of curing in open air, curing in warm water, and standard curing were deemed. Compressive strength, flexural strength and splitting tensile strength tests were performed on samples, and Pull-Off method were used for evaluation of bonding strength. The results indicated that the impact of substrate strength on bonding is more significant than overlay strength, and also the effect of curing condition was more salient than finishing quality. The bonding strength of overlays contained 0.5% of steel fibers and with strength grades of C50, C60 and C70 cured in warm water were 105%, 108% and 104%, respectively, higher than same samples cured in open air.