Title: Effects of Water-Cement Ratio, Curing Age, Silica Fume, Polymer Admixtures, Steel Surface Treatments and Corrosion on the Bond between Concrete and Steel Reinforcing Bar

Author(s): Xuli Fu and D. D. L. Chung

Publication: Materials Journal

Volume: 95

Issue: 6

Appears on pages(s): 725-734

Keywords: abrasive blasting; bond; cement; concrete; curing age;plastics; polymers and resins

DOI: 10.14359/417

Date: 11/1/1998

Abstract:
The bond between concrete and steel reinforcing bar was evaluated by electromechanical pull-out testing, which involved measuring the shear bond strength and contact electrical resistivity of each sample. The bond strength was increased by steel rebar surface treatment (acetone, water, ozone or sand blasting, with ozone being most effective and acetone being least effective), silica fume and polymer addition to concrete, increase in water/cement ratio of concrete (particularly from 0.45 to 0.50), and decrease in curing age (particularly from 14 to 7 days). The origins of these effects are rebar cleansing for acetone treatment (accompanied by contact resistivity decrease), rebar surface oxide film formation for water and ozone treatments (accompanied by contact resistivity increases), rebar surface roughening for sand blasting, polymer interface layer formation for polymer addition (accompanied by contact resistivity increase for latex addition, but not for methylcellulose addition), decreased interfacial void content (accompanied by contact resistivity decrease) for water/cement ratio increase (due to fluidity increase) and for curing age decrease (due to shrinkage decrease), and increased matrix modulus for silica fume addition. 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.