Discusses the properties of pulverized fuel ash (PFA) concrete both in its fresh and hardened states, with emphasis on aspects which are relevant to warmer localities such as Hong Kong. Sufficient research evidence, including surveys of existing structures, have been reviewed to conclude that PFA, when used correctly and properly, has the potential to enhance the performance of good concrete. Analyses the contribution of PFA in the enhanced performance of concrete. Cautions that much of the enhanced performance depends on the microstructure of the concrete, which in turn depends significantly on a proper mix design, with or without PFA. Proposes that water reduction is a desirable property of PFA. However, considers it possible to accommodate PFA characteristics in the mix design and by the use of plasticizer to produce good quality PFA concrete. Briefly discusses the characteristics of Hong Kong locally produced PFA.

The effects of heating temperature, cooling method, re-curing time and water-to-cement ratio (w/c) on the natural restoration of mechanical properties of concrete exposed to high temperature were experimentally studied. The fire-damaged concrete specimens were re-cured in ambient conditions after they had been rapidly cooled in water and naturally cooled in air. Below 500°C, the natural restoration of the compressive strength of water-cooled concrete was more evident than that of air-cooled concrete. The natural restoration of the compressive strength of air-cooled concrete with low w/c ratio was more obvious than that of concrete with high w/c ratio. After being subjected to 500°C and re-cured for 3 months, the splitting tensile strength decreased to below 26% of the initial value. The splitting tensile strength of water-cooled concrete recovered more evidently than that of the air-cooled concrete. The restoration of elastic modulus was mainly affected by the heating temperature and cooling method. The elastic modulus of water-cooled concrete which had been subjected to 200, 300 and 400°C was obviously restored after being naturally re-cured for 3 months. The effects of w/c on the tensile strength and elastic modulus were not significant.