A study of high-volume fly ash concrete

High-volume fly ash concrete has typically 50–60% fly ash as a cement replacement and is favorable for use in some structures. It has not been widely accepted because of the lack of understanding of the structural behavior and mechanism of this type of concrete. The study presented in this thesis aims to establish a quantitative understanding of the hydration process and interfacial bond strength development of high-volume fly ash concrete. It also attempts to clarify the dependence of the strength, durability and compressive behavior of this type of concrete on the characteristics of the cement matrix and matrix-aggregate interfaces. Both experimental and numerical results are presented.; The hydration process of high-volume fly ash pastes is first addressed. The degree of hydration of the fly ash was determined using a selective dissolution procedure. The results indicate that high-volume fly ash pastes are highly heterogeneous, with more than 80% of the fly ash remaining unreacted after 90 days of curing.; The effect of high-volume fly ash on the microstructure characteristics of the cement matrix-aggregate interfaces is then noted. The interfacial porosity was studied by comparing the measured and calculated porosities for mortar and concrete. The improvement in the interfacial zone microstructure is found to be more important for the chloride resistance of concrete than other microstructure characteristics such as total porosity and average pore size.; It is found that fly ash replacement at levels of 15% and 25% substantially increases the matrix-aggregate interfacial bond strength and fracture energy. For high-volume fly ash concrete (45 to 55%), initially the interfacial bonding is weaker, but in the long-term the bonding is stronger than Portland cement specimens.; An investigation into the compressive stress-strain behavior of normal and high-volume fly ash concrete is also presented, which has not been undertaken by other researchers to date. The interfacial bond strength affected the shape of the stress-strain curve insignificantly. An increase in the interfacial bond strength increases in the compressive strength of concrete, but limited to an interface-to-matrix strength ratio of 2/3. The effects of the characteristics of the cement matrix and interfaces on the concrete compressive behavior are therefore clarified. (Abstract shortened by UMI.)...