"A Study on the Mechanical Properties of Light Weight Concrete by Replacing Course Aggregate with (Pumice) and Cement with (Fly Ash)"

Light weight concrete has become more popular in recent years owing to the tremendous
advantages it offers over the conventional concrete. Even Light concrete but at the same time strong
enough to be used for the structural purpose. Lightweight concrete has been successfully used since
the ancient Roman times and it has gained its popularity due to its lower density and superior thermal
insulation properties. Compared with Normal weight concrete, Lightweight concrete can significantly
reduce the dead load of structural elements, which makes it especially attractive in multi-storey
buildings. The most important characteristic of light weight concrete beside its light weight is its low
thermal conductivity. This property improves with decreasing density. The adaptation of certain class
of light weight concretes gives an outlet for industrial wastes and dismantled wastes which would
otherwise create problems for disposal.
The conventional mix has been designed for M25 grade concrete. Coarse aggregate replaced with
Pumice aggregate in volume percentages of 25% and 33.33% further Cement replaced with the Fly
ash in weight percentages of 15%, 20%, 25%, 30% for study in the present investigation. The
properties like Compressive strength, Split tensile strength, Flexural strength and Youngs’ modulus of
above combinations were studied and compared with conventional design mix concrete.
It is observed that there is retardation in Compressive strength, Split tensile strength, Flexural
strength and Young’s’ modulus for the light weight aggregate replaced concrete when compared to
the concrete made with normal aggregate. For these light weight aggregate concrete mixes when
‘cement’ was replaced by ‘fly ash’ it is noticed that there is a marginal improvement in the properties
studied. For 25% replaced light weight aggregate when cement was replaced by 15%, 20%,25% and
30%fly ash, the maximum gain in compressive strength of 18.71% at 28 days is observed for 20%
replacement of fly ash. Similarly the gain in split tensile strength, flexural strength and Youngs’
modulus of 16.66%, 29.51% and 10.15% is observed at 20% replacement of fly ash respectively. For
33.33% replaced light weight aggregate when cement was replaced by 15%,20%,25% and 30% fly
ash, the maximum gain in compressive strength of 26.3 % is observed for 20% replacement of fly ash.
Similarly the gain in split tensile strength, flexural tensile strength and Youngs’ modulus of
19.23%,26% and 3.33% is observed at 20% replacement of fly ash respectively Hence we can infer
that 20% replacement of cement by fly ash is optimum proportion among the proportions tested for
the properties studied in the present investigation.