Improving the bonding performance of new and old cement pastes by high-temperature treatment on the surface of old cement pastes

Abstract

In concrete structure repair projects, patch repair is one of the most commonly used methods. However, the bonding interface is often the weakest part of the overall repaired structure, and its performance affects the safety of the entire structure. In this study, different groups of cement specimens with similar exposed surface were prepared by splitting the cement paste samples with water–cement ratio of 0.4 and 0.2 into two halves from the middle point. The exposed/split surfaces were then activated in an oven at 600 °C, 700 °C and 800 °C (heating time 30 min and holding time 5 min) respectively, and the new cement pastes were poured on the treated surface of the old cement paste samples after the treated samples were cooled down to room temperature. The interface bonding strengths of different groups of samples were tested through a three-point bending test, and the interface microstructure and composition were analyzed through micro indentation, scanning electron microscopy, and X-ray diffraction tests. Among them, the interface bonding effect was the best with treatment temperature of 800 °C with an increase of more than 80 %. With this activation method, the old base cement can undergo rehydration reaction with the water in newly covered cement paste, thereby improving the bonding performance of the interface. However, high temperature can also cause microcracks on the surface of the old cement block, and it is necessary to control the activation temperature to achieve the required performance improvement. Combining mechanical tests, interface microstructure tests, and mechanism analysis, this study proposed and verified a method to improve the bonding interface strength between new and old cement pastes by high-temperature treatment on the surface of the old cement paste. Engineering applications were also discussed and explored.