Bond of steel reinforcement with microwave cured concrete repair mortars

Abstract

This paper investigates the effect of microwave curing on the bond strength of steel reinforcement in concrete repair. Pull-out tests on plain mild steel reinforcement bars embedded in four repair materials in 100 mm cube specimens were performed to determine the interfacial bond strength. The porosity and pore structure of the matrix at the steel interface, which influence the bond strength, were also determined. Test results show that microwave curing significantly reduces the bond strength of plain steel reinforcement. The reduction relative to normally cured (20°C, 60% RH) specimens is between 21 and 40% with low density repair materials and about 10% for normal density cementitious mortars. The corresponding compressive strength of the matrix also recorded similar reduction and microwave curing resulted in increased porosity at the interface transition zone of the steel reinforcement.A unique relationship exists between bond strength and both compressive strength and porosity of all matrix materials. Microwave curing reduced shrinkage but despite the wide variation in the shrinkage of the repair mortars, its effect on the bond strength was small. The paper provides clear correlations between the three parameters (compressive strength, bond strength and porosity), which are common to both the microwave and conventionally cured mortars. Therefore, bond-compressive strength relationships used in the design of reinforced concrete structures will be also valid for microwave cured elements.

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

“…This research investigation reports the relationship between test results of internal and surface temperatures monitored on specimens of concrete repair mortars. The authors have previously reported on the parameters of microwave curing which affect the strength and other properties of concrete repair materials [20] including bond between a repair patch and both the substrate concrete and the steel reinforcement [21,22]. However, the interaction between microwave curing and hydration temperatures at early age can have significant effect on the properties and long term deterioration processes in concrete repair patches [23].…”