Packing effect and pozzolanic reaction of fly ash in mortar

This research is to study the effect of particle size of fly ash on packing effect and pozzolanic reaction of mortar when 20% of fly ash is used to replace Portland cement type I. Both effects can be determined by using fly ash and insoluble material which have almost the same particle size to replace Portland cement type I. Normally, the compressive strength of fly ash mortar is contributed from hydration reaction, packing effect, and pozzolanic reaction. For mortar mixed with insoluble material, the compressive strength is due to hydration reaction and packing effect. Thus, compressive strength due to pozzolanic reaction can be determined from the difference in compressive strength between fly ash mortar and insoluble material mortar. The results show that the strength activity index of fly ash mortar depends on the median particle size of fly ash and curing ages of mortar samples. At early ages, the strength activity index of fly ash mortar due to packing effect is higher than that due to pozzolanic reaction. At the ages of 3 to 90 days, the difference in strength activity index due to packing effect of fly ashes with median particle size of 2.7 and 160 μm is almost constant about 22% of the strength of standard mortar (STD). The differences in strength activity index due to pozzolanic reaction of fly ashes with median particle size of 2.7 and 160 μm are 3%, 20%, and 27%, respectively, at the ages of 3, 28, and 90 days.