EFFECT OF FINENESSES OF FLY ASH AND RICE HUSK ASH ON COMPRESSIVE STRENGTH AND EXPANSION OF MORTAR IN ACCELERATED MORTAR BAR METHOD

Abstract

This research studied compressive strength and expansion of mortar containing
fly ash and rice husk ash. Both fly ash and rice husk ash were ground until the
particles were retained on a sieve No. 325 were 35±2, 25±2, 15±2, and 5±2%
by weight. Then, they were used to replace Portland cement type I at 20% by
weight of binder to cast mortars and the flow of mortars was controlled at
110±5% by adjusting the mixing water. Compressive strengths of mortars were
determined at the ages of 7, 14, 28, 60 and 90 days. The expansion of mortar
in accelerated mortar bar method was investigated by immersing mortar bars
in 1N sodium hydroxide (NaOH) solution at the temperature of 80°C for 28
days. The non-reactive aggregate was used as a fine aggregate in order to study
the effect of pozolanic materials on expansion of mortar in accelerated mortar
bar method. The results showed that the high fineness of rice husk ash and fly
ash was more effective in increasing the compressive strength and less
expansion than the low fineness of rice husk ash and fly ash. Moreover,
mortars containing ground fly ash and ground rice husk ash could produce
higher compressive strength than control mortar at the age of 60 days or more.
However, both ground and unground rice husk ash may not suitable to be
used as a pozzolan for controlling the ASR expansion potential.