Effects of water-cement ratio, curing age, silica fume, polymer admixtures, steel surface treatments, and corrosion on bond between concrete and steel reinforcing bars

The bond between concrete and steel reinforcing bars was evaluated by electromechanical pull-out testing that involved measuring the shear bond strength and contact electrical resistivity of each sample. The bond strength was increased by steel reinforcing bar surface treatment (acetone, water, ozone, or sandblasting, with ozone treatment being the most effective and acetone treatment being the least effective), adding silica fume and polymer to the concrete, an increase in the water-cement ratio of concrete (particularly from 0.45 to 0.50), and a decrease in the curing age (particularly from 14 to 7 days). The origins of these effects are reinforcing bar cleansing for acetone treatment (accompanied by a decrease in contact resistivity), reinforcing bar surface oxide film formation for water and ozone treatments (accompanied by increases in contact resistivity), reinforcing bar surface roughening for sandblasting, polymer interface layer formation for the addition of polymer (accompanied by an increase in contact resistivity for the addition of latex, but not for the addition of methyl-cellulose), a decreased interfacial void content (accompanied by a decrease in contact resitivity) for an increase in the water-cement ratio (due to an increase in fluidity) and for a decrease in the curing age (due to a decrease in shrinkage), and an increase in the matrix modulus for the addition of silica fume. Corrosion initially caused the bond strength to increase while the contact resistivity increased, but further corrosion caused the bond strength to decrease while the contact resistivity continued to increase.