Energy saving is also an important issue in sustainability. According
to the Hong Kong Electrical and Mechanical Services Department's
(ESMD) 2013 annual report of energy end use break
down, in the year 2011 space air conditioning accounted for about
23% and 26% of total annual electricity consumption in residential
buildings and commercial buildings, respectively (Electrical and
Mechanical Services Department, 2013), which indicates that
building materials with better thermal insulation properties have a
promising future. Previous research works proved that by using
lightweight aggregate (expanded perlite) in concrete mixes, the
thermal conductivity can be lowered to about 0.13 W/mK (Sengul
et al., 2011). Demirboga and Kan (2012) prepared lightweight
aggregate concrete with a modified waste expanded polystyrene
(MEPS) to replace natural aggregates, the thermal conductivity of
the concrete was reduced to 0.600 W/mK. Akça
€
ozoglu et al. (2013)
used recycled waste PET lightweight aggregate (WPLA) to produce
concrete with improved thermal insulation property, and the result
indicated that by replacing natural aggregate with WPLWat 60% by
volume, the fresh concrete density was reduced gradually to
1530 kg/m
3
compared with 2240 kg/m
3
of the control mix, while
the thermal conductivity value was reduced from 0.9353 W/mK to
0.3924 W/mK. Another commonly used aggregate to improve
concrete insulation properties is rubber aggregate. Mohammed
et al. (2012) prepared hollow concrete blocks of dimension
390 mm 190 mm 190 mm with 10%e50% crumb rubber
incorporation, and the thermal insulation properties tests indicated
that 50% rubber aggregate incorporation resulted in a reduction of
concrete thermal conductivity from around 1.0 W/mK to nearly
0.6 W/mK. However, they also pointed out that the use of high
volume rubber aggregate resulted in significant strength losses, as
the concrete compressive strength was reduced from more than
12 MPa to less than 2 MPa due to the rubber aggregate
incorporation.