Bond between microwave cured repair and concrete substrate

Abstract

The bond strength between a concrete substrate and repair patch is critical to its durability. This paper investigates the effect of microwave curing the freshly applied repair, for 45 min at 132 Watts, on the 28 day bond strength between substrate concrete and different commercial repair materials. The repairs were applied at different ambient temperatures of 20, 10, 2 and -5°C. Tensile split tests on repaired cube specimens were performed to determine the interfacial bond strength. The ability of microwave curing to prevent the detrimental effects of freezing at early age on the bond and compressive strength of repair patches is investigated. Experimental results show that microwave curing prevents loss of long term (28 day) repair/substrate bond strength of repair materials applied at freezing temperatures (-5°C), relative to the repairs applied at higher temperatures (2-20°C), except one lightweight repair formulation. In comparison, the control samples (non-microwave cured) of repairs applied at -5°C suffered severe loss of bond strength and compressive strength due to early age freezing. In addition, no adverse effects on the bond strength and a small reduction of 6.75% in the 28 day compressive strength are observed in the early age microwave cured repairs applied at ambient temperatures of 2-20°C. The repair/substrate bond strength is independent of the compressive strength of the repair material at all temperatures of repair application. Microwave curing can accelerate the concrete repair process and facilitate construction activity in cold weather.

Hydration and Microwave Curing Temperature Interactions of Repair Mortars

“…This impact is likely to be more significant when microwave curing is used under normal ambient temperatures than under cold weather conditions. Recent research has shown much greater benefit of microwave curing in cold weather conditions [21].…”

“…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].…”

Bond of steel reinforcement with microwave cured concrete repair mortars

“…It deals with the bond of plain steel reinforcement embedded in different concrete repair materials. Another aspect of bond strength which is of critical importance for the efficient performance of concrete repair is the interfacial bond between the substrate concrete and patch repair, which has been reported elsewhere [16].…”

“…The reduction is due to loss of free water in the form of vapour and it depends on the mix proportions, cement replacement materials and admixtures used in the proprietary repair formulations. Shrinkage is a detrimental property of repair materials and a major cause of patch repair failure in service life often due to bond failure at the repair interface [16]. Manufactures often use shrinkage reducing admixtures or expansive cement as shrinkage compensators in repair materials.…”