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A comprehensive study is presented on the effects of pulverised fly ash (PFA) and ground granulated blast furnace slag (GGBS) on early-age engineering properties of Portland cement (PC) systems. It has been found that partially replacing PC by PFA or GGBS resulted in longer setting times but better workability with PFA exhibiting more prominent effect than GGBS. As the replacement level increased, the setting of both PFA and GGBS pastes further delayed but workability of concrete was enhanced. PFA concretes exhibited consistently lower compression and splitting tensile strengths than PC ones. As the replacement level increased, strengths decreased. At the replacement level up to 30% by mass, GGBS concrete exhibited higher splitting tensile strength than PC concrete. However, as the replacement level further increased, it developed lower strength than PC concrete up to 21 days. Then, it managed to gain higher splitting tensile strength than PC concrete at the replacement levels up to 70% by mass at 28 days. Both PFA and GGBS can reduce drying shrinkage and the reduction effects became more significant as replacement level increased with GGBS performing better than PFA. Adding fibres into PFA concrete increased its splitting tensile strength and further reduced its drying shrinkage.

A new experimental method by utilizing elliptical rings to replace circular rings recommended by ASTM and AASHTO was explored for assessing cracking potential of concrete and other cement-based materials under restrained condition. A series of thin and thick elliptical concrete rings were tested alongside circular ones until cracking. Cracking age, position, and propagation were carefully examined. It is found that thin elliptical rings with appropriate geometry can initiate cracks quicker than circular ones, which is desirable for accelerating the ring test. However, thick elliptical rings seem not to exhibit a desirable geometry effect of accelerating ring test compared with circular ones. There were multiple visible cracks that occurred in an elliptical ring and some cracks were initiated but did not propagate through the ring wall. In comparison, there was only one crack in the circular rings. Finally, the features of multiple cracks in restrained elliptical rings were examined and their impact on interpreting elliptical ring test results was elaborated.