Application of recycled ceramic aggregate as internal curing material in high performance concrete

High-performance concrete (HPC) has been increasingly used in modern engineering structures because of its superior material properties compared to ordinary concrete. One of the most critical issues in the application of HPC is serious early cracking, which is often encountered in the structures that involve mass concrete. Internal curing is a method that introduces water storage material into HPC to maintain the humidity inside the material so as to reduce the risk of early cracking. Recycled ceramic aggregate (RCA) is a porous material, which is promising to be employed as an internal curing material for HPC. RCA can usually be obtained from various sources. At present, the investigation of internal curing efficiency of different types of RCA in HPC is lacking, and the impact of RCA on the exothermic reaction and permeability of HPC has not been reported in literature. In addition, the study on the effect of temperature on the internal curing efficiency of RCA is currently not available. Therefore, it is of great significance to perform a systematic study on the internal curing of HPC using RCA. In this study, a comprehensive investigation of the application of RCA as internal curing material in HPC is performed with the consideration of. Three different types of RCA are selected, which include waste household ceramic, wall tile and floor tile. To explore the effects of the physical properties and chemical compositions of the three ceramic materials on internal curing efficiency, microscopic tests are firstly performed. The internal curing efficiency of the three types of RCA in HPC under ambient curing condition is then evaluated through mechanical testing and autogenous shrinkage test. The test results show that RCA, especially wall tiles, are very effective in reducing the autogenous shrinkage of HPC while maintaining a satisfactory level of mechanical properties. The effect of three different types of RCA on the exothermic reaction in HPC is then investigated for the first time to reveal the role of RCA in regulating the hydration heat output and permeability of HPC. To understand the ability of RCA to store and release water and the influence of RCA on the internal microcracking of HPC, the porosities and the pore distributions of the three types of RCA are investigated through microscopic tests. The internal structure of HPC with different types of RCA is also analysed based on computed tomography (CT) results. After that, the hydration heat test is performed to measure the maximum temperature and the time of peak temperature obtained during the exothermic process. Finally, chloride ion permeation experiment is performed to further investigate the effect of RCA on the permeability of HPC. It is found that RCA can reduce the temperature during exothermic reaction and prolong the cement hydration process. However, the permeability of HPC is increased due to the porosity of RCA and the weak bond between the glazed surface of RCA and the cementitious material.  In addition, the effect of temperature on the curing efficiency of RCA is investigated in this study. As the increase of curing temperature could accelerate the cement hydration rate, more hydration products are produced at an early stage, resulting in a denser microstructure of HPC. However, the effect of temperature on the microstructure of HPC with RCA added has not been investigated to date. Therefore, this study aims to explore the influence of curing temperature on the microstructure and pore distribution of HPC with RCA as an internal curing material. The mechanical properties and autogenous shrinkage of HPC at different ages and curing temperatures are tested. It is found that lower curing temperature and higher RCA substitution rate could better control the autogenous shrinkage of HPC. While the specimens with a lower RCA substitution rate at lower curing temperature could obtain better mechanical properties. In general, an appropriate amount of RCA with higher porosity at room temperature can improve the mechanical properties of HPC, reduce the early autogenous shrinkage of the material and lower the exothermic temperature inside HPC. An increase in the amount of RCA would reduce the mechanical properties and increase the permeability of HPC, but it could further reduce the early autogenous shrinkage and the hydration heat output. When the curing temperature is high, the mechanical properties of HPC decrease significantly, and more significant autogenous shrinkage can be observed. The higher the amount of RCA substitution at high temperatures, the lower the mechanical properties of HPC. However, the autogenous shrinkage of HPC decreases significantly at higher replacement amounts. The outcomes of this thesis will provide a reliable guidance on the testing and application of RCA as an internal curing material in HPC.