Cement-stabilized fly ash base courses

A model for pozzolanic reaction of fly ash recently developed by Fraay and Bijen pointed out that the reactivity of fly ash is influenced greatly bij the pH value of the pore water. A ph of at least 13 is required to initiate fly ash pozzolanic reaction in a Portland cement environment. Pore water extraction measurements showed that the pH of cement-stabilized fly ash often has a substantially lower value. In this high-volume fly ash application the effect of the acidity of fly ash is much greater than in ordinary concrete with cement replaced bij fly ash up to 30%. By addition of NaOH and/or sodium silicate to the mixing water, the pH value can be increased above the 'threshold' value. Tests were carried out with different types of class-F fly ashes and with different NaOH concentrations in the mixing water.