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.

This investigation experimentally documents mitigation of alkali-silica-reaction (ASR) expansion through partial replacement of cement with coal-biomass cofired fly ash. ASTM C 227 and 441 guide the experimental techniques. Biomass and Class F fly ash reduce ASR expansion within 0.1% at the 6 month with 35% replacement ratio, although biomass fly ash has much higher available Na2Oequiv (by ASTM C 33). Further analysis of pore solution by high pressure extrusion illustrates that biomass fly ash mixes have similar alkali metal concentrations to Class C mixes, but biomass fly ash is at least equal or much better than Class C in mitigating ASR expansion; this implied that biomass fly ash may absorb alkalis from the pore solution and may form non-expansive products instead of the expansive alkali silica gel.

This paper presents a long-term concrete shrinkage test on self-consolidating concrete (SCC) conducted at The University of Hong Kong. In this study, one normal concrete mixture with only portland cement and five SCC mixtures incorporating fly ash or both fly ash and silica fume were produced and tested for their shrinkage characteristics in the form of prismatic specimens. Fiber-optic sensors, which give stable and reliable measurements, were embedded into the prismatic concrete specimens to measure shrinkage strains. Compared with the normal concrete mixture, the autogenous shrinkage of the SCC mixtures included in this study is larger while the one-year drying shrinkage is smaller. Besides, lowering the water/cementitious materials ratio of a SCC mixture would increase its autogenous shrinkage but reduce its one-year shrinkage. Experimental results also reveal that replacement of cement by fly ash would reduce both autogenous and one-year shrinkage strains of SCC whereas replacement of cement by silica fume would increase both. Lastly, the shrinkage half-time of SCC is found to be longer than that of the normal concrete.

The purpose of the research program was to investigate how the addition of new-generation wastes produced in the coal-fired power plant, fluidized-bed type installations, impact mechanical properties and chemical durability of cements. Tests were made on cements derived from two portland cement clinkers containing widely different amounts of C3A. With addition of the fluidized-bed material from the brown and black coal combustion systems blended portland cements were made. The properties of these blended cements were compared with those of the reference portland cements. The composition of all cements was adjusted to achieve the maximum permissible amount of SO3 i. e. 3.5%. Three different curing procedures were used for mortar specimens: normal temperature and humidity conditions, low pressure steam curing, and autoclaving. Durability to sulfate attack was studied using two methods: one method involved monitoring of linear dimensions of 20 x 20 x 160 mm mortar prisms cured under different conditions and exposed to aqueous solutions of Na2SO4 and MgSO4, with 16±0.5 g/l concentration of SO42- anions. The other method involved investigation of changes of mechanical properties of 25x25x100 mm mortar prisms cured under different conditions and subjected to prolonged sulfate exposure. The strength of samples was measured after different times of exposure in sulfate. Five percent aqueous solutions of Na2SO4 and MgSO4 were used for sulfate immersion test. Compressive and flexural strength tests were measured after 90, 180, 365, and 730 days of exposure. SEM and EDS techniques were used for microstructure studies.

The purpose of this study was to examine the effect of a Class F fly ash on mechanical and durability properties of concrete. The fly ash used in this study, from a Mexican source, was characterized by chemical and mineralogical analysis, and by its pozzolanic activity. Concrete mixtures were prepared with 20, 25, and 30% fly ash by mass of total cementitious material. Concrete specimens were cast and tested to determine the durability of fly ash concrete; the tests used included water, rapid chloride permeability tests (RCPT), migration test, acid resistance and abrasion resistance tests. Also the compressive strength was determined. Mortar specimens were used to evaluate sulfate resistance and alkali-silica reaction. The results of this study confirmed that the Mexican Class F fly ash was suitable in improving the durability characteristics of concrete when used at 25% or higher dosage of cement replacement.