This paper addresses kinetics and strength build-up of pozzolanic reactions in 2-inch-cubes of biomass, coal fly ash/Ca(OH)2 (CH) and sand mortar. A comprehensive experimental design of six biomass/coal fly ashes, three temperatures, three mass ratios of fly ash/CH and six test dates of up to 1 year was set up. The results show that the compressive strength of biomass fly ash samples exceeds that of coal ash samples by factors of 2-3 and rivals that of pure cement ones. Further investigations indicate that except CH reaction extent, other factors, such as fly ash type, mixing ratio of fly ash with CH and curing temperature, all have significant effects of compressive strength build up of fly ash samples.

In this paper experimental evaluation on the effect of high volume fly ash as partial replacement of cement on fracture toughness of cement mortar are presented. The fly ash replacement level was 50%, 60% and 70% by weight of cement. Three-point bend notch beams were used to measure the fracture toughness of mortar. Results show that the use of 50% fly ash as partial replacement of cement reduces the fracture toughness values between 38% and 58% compared to that without fly ash. Reduction of compressive strength and Young’s modulus in mortar containing 50% fly ash as partial replacement of cement compared to that without fly ash is also observed in this study. The use of 60% and 70% fly ash as partial replacement of cement is found to have negligible effect on the reduction of fracture toughness of cement mortar. Long term effects of high volume fly ash (50% cement replacement) on fracture toughness, compressive strength and Young’s modulus of cement mortar are also evaluated in this study. Tests were conducted at 28, 56 and 91 days and at 5, 7, 10 and 12 months. Results show that the rate of increase of fracture toughness of cement mortar containing 50% fly ash with time is very slow. Compressive strength and Young’s modulus also increase with time.

Alkali-silica reaction known as ASR is series of complex reactions between alkali hydroxides in pore solution and active forms of silica. The product is alkali-silica gel that absorbs water and swells and causes cracks within the fabric of concrete. Using pozzolans as preventative method is very useful to protect against ASR. Zeolite, a new mineral admixture seems to be very efficient in controlling this reaction. In this paper, the effect of replacing portland cement with zeolite coming from Semnan, Iran, and fly ash has been investigated. Results show that zeolite and fly ash can reduce the potential of ASR. By taking economic considerations into account, using zeolite seems is an efficient alternative to be used in concrete for controlling ASR in Iran.

The production of lightweight aggregates entails heating a silica-rich raw material, which is usually shale, clay or slate to about 1150°C. This heat treatment appears to activate the surface of the expanded aggregates so as to produce pozzolanic properties that reduce expansion due to alkali-aggregate reaction. When these heat-treated aggregates are incorporated into a concrete mixture, beneficial effects result that enhance the properties of the concrete. These effects are similar to, but of a significant lower magnitude, than when a pozzolan such as fly ash or silica fume is added to a concrete mixture. This is to be expected because expanded shale, clay and slate that have been ground to a fineness somewhat greater than that of portland cement have been supplied to the concrete industry as a pozzolan for some time. Also, it has been shown in micrographs that the vesicular nature of lightweight aggregates provides a space for any reactants that might form to precipitate without causing expansion.

Silica fume (SF) and high reactivity metakaolin (HRM) are two highly reactive pozzolans that offer excellent potential for use in high-performance concrete since concrete mixtures containing them demonstrate superior performance in terms of strength, and durability. High-performance concrete applications, such as pavements and bridge decks, are also required to demonstrate superior performance against early age shrinkage cracking. This paper describes a comparative study of the effects of SF and HRM on the early age stress development and cracking in restrained mortar mixtures due to shrinkage. The restrained ring test was used to assess early age residual stress development in mortar ring specimens. In addition, free shrinkage strains and splitting tensile strength measurements were performed to assess the cracking potential. It was found that the addition of SF and HRM increased the shrinkage level in the mixtures which resulted in increases in residual tensile stress development due to restraint. In addition, their addition in the mixtures increased the cracking potential and resulted in early cracking in the ring specimens.