Abstract:
Rice husk ash (RHA), one of the cement replacing materials, exhibit high pozzolanic
characteristics when properly produced under controlled conditions. There are many works
that have been reported till today on use of RHA, especially, with concrete containing natural
stone aggregate. However, very few information is available on RHA containing brick
aggregate concrete. For this, eight concrete samples with target strength of 34 MPa were
prepared varying RHA content from 0% to 15% from both natural stone and crushed clay
brick aggregate concrete. Strength, permeability in the form of depth of water penetration,
shrinkage tests were conducted on the concrete samples prepared. It was found that strength
of concrete for containing both brick and stone aggregate increase up to 5% of cement
replaced by RHA. For further replacement, strength starts to decrease. For 15% of cement
replaced by RHA, strength is lower than concrete containing 0% RHA. For all the cases,
strength of brick aggregate concrete was found to be higher than stone aggregate concrete.
Depth of penetration test on cube samples for both natural stone and crushed clay brick
aggregate concrete show that permeability coefficient of concrete containing 5% of cement
replaced by RHA is similar to that of concrete with 0% of cement replaced by RHA.
However, coefficient of permeability increases by about 10% for both stone and brick
aggregate concrete when RHA content is increased up to 10%. For 15% of cement replaced
by RHA, depth of penetration is, again, found to decrease by about 3%. For all cases,
coefficient of permeability of brick aggregate concrete is much higher than that of stone
aggregate concrete. Cement replacement by RHA up to 10% show decreases in drying
shrinkage for both natural stone and brick aggregate concrete. However, further increase in
RHA content shows a corresponding increase in drying shrinkage value. However, for this 34
MPa concrete, which is on the higher side of normal strength concrete, there is little
difference in drying shrinkage between natural stone and crushed clay brick aggregate
concrete. From analysis of these properties, it can be concluded that up to 5% of cement may
be replaced by RHA without compromising any of the strength and durability properties of
concrete. Up to 10% of cement replaced by RHA, properties of concrete degrade by a little
margin; however, strength and other durability properties still remain within acceptable
range. Further increase i.e. 15% of cement replaced by RHA, durability and strength
properties of concrete worsen by considerable amount. Therefore, brick aggregate concrete
may contain up to 10% of cement replaced by RHA considering strength and durability
properties like permeability and shrinkage.
