Abstract:
This paper summarises the research work on determining suitability of rice husk ash
(RHA) to partially replace cement in manufacturing cellular masonry blocks. The particle size distribution
and chemical composition of RHA were measured for samples taken at different temperatures. In this
research, mixtures have been prepared in combinations of four binder-sand ratios namely 1:3, 1:4, 1:5 and
1:6, three water-binder ratios namely 0.4, 0.5 and 0.6 and five levels of cement replacement with RHA
namely percentages of 0, 5, 10, 15 and 20 by weight. One hundred and twenty cubes were cast
(4x3x5x2=120) and tested for compressive strength at 7 and 28 days. Based on the compressive strength
values, 1:5 binder-sand ratio was chosen as the appropriate mix proportion to cast cellular masonry blocks
for different water-binder ratios namely 0.5 and 0.6 as per SLS 855Part 1:1989.
RHA was blended with cement in percentages of 0, 5, 10, 15 and 20 by weight in producing cellular
masonry blocks of size 390 x 190 x 200 mm. These were tested for water absorption in addition to
compressive strength. The compressive strengths of cellular masonry blocks at 7, 14 and 28 days for 1:5
binder-sand ratio, water-binder ratio 0.5 and 5 per cent cement replaced with RHA were 2.05 N/mm2, 2.24
N/mm2 and 3.37 N/mm2 respectively. Likewise the values for 1:6 binder-sand ratio for water-binder ratio
0.5 and 5 per cent cement replaced with RHA were 1.6 N/mm2, 2.18 N/mm2 and 3.24 N/mm2 respectively.
The minimum compressive strength as per SLS 855 Part I: 1989 is 1.2 N/mm2. The water absorption rates
for water-binder ratios 0.5 and 0.6 are 9.8 and 10.5 respectively, which are within limits; the allowable
limit is 10-15% as per BS EN 1996-1-1. The study concludes that 15 per cent cement replacement level is
permissible.
