Page 189 - New Trends in Eco efficient and Recycled Concrete

Recycling of waste glass in construction materials 161

compacting concrete (SCC), which could be placed and compacted under its own
weight with little or no vibration effort. The experimental results showed that par-
tial replacement of river sand and coarse aggregates by GC increased the slump
flow, blocking ratio and air content of the SCC mixes. While the mechanical prop-
erties (compressive strength, tensile splitting strength and static modulus of elastic-
ity) of the SCC decreased with increased recycled glass content. However, the
increasing content of GC was helpful to increase the resistance to chloride ion pene-
tration and decrease the drying shrinkage of SCC. In terms of ASR tests, the high
content of GC in mortar bars caused large expansion due to the ASR of GC; how-
ever, the expansion could be effectively suppressed by the incorporation of fly ash
in the concrete specimens.
Discarded cathode ray tube (CRT) waste is also a major environmental concern
in Hong Kong. Ling and Poon (2012) and Zhao et al. (2013a) recycled the CRT
funnel glass as a potential material for the production of heavyweight/high-density
concrete. Although the inclusion of recycled CRT glass resulted in reductions in the
compressive and splitting tensile strengths, it considerably improved the fresh prop-
erties and the drying shrinkage of the concrete. Another issue of concern is that the
CRT glass is a hazardous waste due to its high content of lead oxide. Therefore,
Ling and Poon (2012) treated the CRT glass with nitric acid to remove lead and the
results showed that lead and barium leaching levels of the concrete prepared with
treated CRT glass were below permissible limits. This indicates that using treated
CRT glass as 100% substitution of fine aggregate for making heavyweight concrete
is feasible.
When waste glass is to be used as aggregates in concrete, the resistance to fire is
a concern because the glass will melt when exposed to high temperatures. As shown
in earlier works (Ling et al., 2012; Ling and Poon, 2013), the replacement of natural
aggregates by recycled GC decreased the residual strength of the concrete when the

exposure temperature was below 600 C; however, after exposure to 800 C, the ben-
eficial effect of incorporating GC in concrete on the water sorptivity and elastic
modulus were shown, which was related to the transition of RG from solid to liquid
at high temperature. The melted GC in the concrete may fill the internal cracks and
improve the pore structure and resistance to water penetration in the concrete
matrix after re-solidification when the concrete cools down to room temperature
(Ling et al., 2012).

6.6 Current and potential applications of waste glass in
construction industries

In Hong Kong, one main application of recovered glass containers is for the produc-
tion of concrete paving blocks with 25% of aggregates being replaced by GC. Such
paving blocks have been widely used in Hong Kong for paving pedestrian walk-
ways since 2010 with satisfactory results. The Hong Kong Government has also
explored the feasibility of increasing the content of GC (up to 50%) in paving