3.6. Sustainability performance
3.6.1. Cost efficiency
In order to characterize the sustainability of the POFA-blended
OPSC in terms of its cost effectiveness, the compressive strengthmaterial
cost ratio was determined. The cost of materials was
based on the cost assumption reported by Kanadasan and Razak
(2015). The material cost of POFA (RM 0.02/kg) and OPS (RM
0.20/kg) was determined from the purchase price of the materials
from local palm oil mill. Although the material cost price of POFA is
lower compared to cement and the increased replacement level
would lead to cost reduction of the concrete, it should be noted that
the use of POFA at different cement replacement levels could affect
the compressive strength of the concrete. Therefore, the cost efficiency of the POFA-blended OPSC was determined and shown in
Fig. 8.
A higher cost efficiency indicates the better cost effectiveness of
the concrete mixture. As observed from Fig. 8, POFA replacement
levels between 10 and 20% gave improved cost efficiency compared
to the plain OPSC without POFA. At low replacement level of 5%,
although there was little reduction in the material cost, the
strength decrease had a more overriding effect and hence the mix
M5 had lower cost efficiency compared to the control mix M0. On
the other hand, when the POFA replacement level was increased to
10e20%, besides the greater material cost reduction, as discussed previously, the pozzolanic reaction by the ground POFA could also
improve the strength of the concrete, and hence, the mixes containing
10e20% POFA were more cost effective than the control
concrete. Further increase of the POFA replacement level to 25%,
however, resulted in overall decrease in the cost effectiveness due
to the significant reduction in the compressive strength of the
concrete. A comparison of the material cost required to produce
OPSC containing SCM was also done and shown in Table 7.
From Table 7, it was noticed that the OPSC produced in recent
times is more cost efficient compared to the mix design used in the
past. This could be attributed to the use of SP to facilitate workability
without compromising compressive strength by addition of
water as well as the use of higher cement content instead of costly
SCM such as silica fume. When compared to OPSC in more recent
times, the mix M10 had similar cost efficiency as that reported by Shafigh et al. (2013) whereas the use of lower-cost manufactured
sand (M-sand) led to significant improvement in the cost efficiency
in the OPSC mixes by Mo et al. (2015a) and Foong et al. (2015). It
should be noted that while the cost of cement was higher in the mix
M10 due to the higher cement content used, the lower SP content
used in this study resulted in greater overall cost efficiency of the
mix.