Effects of calcined clay on properties of mortar and concrete

The replacement of cement with cement replacing materials to improve the performance of different properties of concrete is the modern solution to increasing applications of concrete in construction. At present, the use of fly ash as a cement replacing material is common, however as there are only two sources of fly ash in Thailand, the low availability and logistics of using fly ash are limited and costly. A practical solution is to find an alternative cement replacing material to compensate for the demand for fly ash and enhance the properties of concrete. In Thailand, the abundant availability of kaolinite clay throughout the country has led to the development of calcined clay (CC) as an alternative cement replacing material. As calcined clay is a new material in Thailand, very little research has been conducted and there are no guidelines or standards for the use of calcined clay in concrete. This research aims to study the performances and effects of calcined clay on the properties of pastes, mortars, and concrete. As calcined clay is a new material, studies from the basic properties of the material to the effects of the use of calcined clay in combination with other types of binders for rational application of calcined clay were focused on. Basic properties such as setting times, water requirement, slump, strength activity index, and compressive strength were primarily investigated for pastes, mortars, and concrete, while basic properties of the calcined clay such as chemical compositions, mineral compositions, particle shape, particle size distribution, specific gravity and Blaine fineness were also performed. Durability and other properties such as autogenous shrinkage, total shrinkage, abrasion resistance, carbonation resistance, and semi-adiabatic temperature rise were also investigated for potential applications. Microstructural and mineralogical investigations were conducted to clarify the results. Mae Moh fly ash (FA) and BLCP fly ash (FAR) were used in this study as a comparison in binary binder system and used in combination with limestone powder (LP) and calcined clay (CC), in ternary and quaternary binder systems. Total replacement of cement with calcined clay by weight of total binder was varied from 0 to 45% to find the appropriate maximum replacement while maintaining satisfactory performance. Different combinations of CCLP and CCFA in different binder ratios (CC:LP and CC:FA) of 1:1, 1:2, and 2:1 were studied for the ternary binder system. Combinations of CCLP+FA with different binder ratios of (CC:LP:FA) at 1:1:1 and 2:1:1 were investigated for the quaternary binder system. The results of varying different amounts of replacement rates showed that a total replacement rate of 45% is possible with calcined clay, performing decently in strength activity index, compressive strength, and temperature rise. However, the use of CC in combination with LP and FA in ternary and quaternary binder systems showed exceptional performances. The use of CC leads to acceleration of setting times, high water requirement, low initial slump, high slump loss, and low strength development in the long term while CCLP showed minor improvements compared to CC-only. The combination of CCFA and CCLP+FA showed significant improvements in results compared to CC-only and CCLP mixtures.