Title: Nondestructive Bond Strength Testing by Contact Electrical Resistivity Measurement
Author(s): Xuli Fu and Il. Il. L. Chung
Publication: Symposium Paper
Appears on pages(s): 295-318
Keywords: bond (concrete to reinforcement); carbon; cements; concretes;
electrical resistance; fibers; reinforcing steels
The contact electrical resistivity was found to correlate with the shear bond strength between steel rebar and concrete, between stainless steel fiber and cement paste, and between carbon fiber and cement paste. For the bond between steel rebar and concrete and that between stainless steel fiber (untreated or acetone washed) and cement paste, the contact resistivity increased linearly with increasing bond strength, due to an interfacial phase of high volume resistivity that helped the bonding. For the bond between stainless steel fiber (acid washed) and cement paste and that between carbon fiber (untreated) and cement paste, the contact resistivity decreased with increasing bond strength, due to the bond degradation by interfacial voids, which were high in volume resistivity. The acid washing of the stainless steel fiber decreased the contact resistivity, but had little effect on the bond strength. The high volume resistivity interfacial phase that enhanced the bonding between the untreated or acetone washed stainless steel fiber and cement paste apparently required for its formation the oxide layer on the stainless steel surface. The removal of the oxide layer by acid washing eliminated this phase, thus decreasing the contact resistivity and causing the contact resistivity to decrease with increasing bond strength. For a given interface at a given curing age, the correlation between bond strength and contact resistivity allows the bond strength to be nondestructively measured via contact resistivity measurement.