Page 183 - New Trends in Eco efficient and Recycled Concrete

Recycling of waste glass in construction materials 155

angular grain shapes of the glass aggregates impeding the flow of the cement paste.
Furthermore, additional cement paste was needed to coat the irregular glass aggre-
gates resulting in less available cement paste for fluidity. On the contrary, some
investigators (Zhao et al., 2013b; Ling et al., 2011; Terro, 2006) reported that the
replacement of natural aggregates by waste glass led to an improvement of work-
ability due to the non-absorbent nature of glass. Moreover, severe bleeding and seg-
regation occurred when 100% fine aggregates were replaced by recycled glass
aggregates (Taha and Nounu, 2008b). According to the study of de Castro and de
Brito (2013), the different impacts of glass aggregates on workability may be highly
dependent on the particle size of the aggregates replaced.
In terms of mechanical properties, increasing the content of glass aggregates was
reported to decrease the compressive, flexural (Wang, 2009; Topc¸u and Canbaz,
2004) and splitting tensile strengths (Mardani-Aghabaglou et al., 2015; Ling and
Poon, 2012) of concrete. The reduction of strengths was also observed in the case
of cement mortars prepared with a high content of glass aggregates (Ling et al.,
2011; Tan and Du, 2013). The possible reason for this was thought to be the pres-
ence of micro-cracks in the glass aggregates during the crushing process and the
smooth surface of waste glass, which resulted in weaker bond strength between the
glass surface and the cement paste.
With respect to the durability of glass cement based materials, the inclusion of
glass aggregates effectively improved the surface resistivity and sulphate attack and
improvement increased with the amount of sand replacement (Wang, 2009). The
chloride ion penetrability and drying shrinkage of concrete decreased when the
glass aggregate content increased (Kou and Poon, 2009). However, because of the
presence of a high amount of amorphous silica in waste glass, it cannot be used as
aggregates without taking the alkali silica-reaction (ASR) problem into account.
Preventive actions have been undertaken to mitigate the detrimental ASR expansion
by incorporating fly ash (Kou and Poon, 2009; Lam et al., 2007), metakaolin (Lam
et al., 2007; Taha and Nounu, 2009), ground blast-furnace slag (Taha and Nounu,
2009; Ling and Poon, 2014a), silica fume (Shayan and Xu, 2004; Du and Tan,
2013), glass powder (GP) (Taha and Nounu, 2009; Idir et al., 2010), steel fibre (Du
and Tan, 2013) or lithium nitrate (Taha and Nounu, 2008a).

6.3 Application of waste glass in cement mortar

Glass presents several advantages as a packaging material, such as its chemical
inertness, low permeability and high intrinsic strength (Bourhis, 2008). For these
reasons, a novel channel for recycling mixed glass is to reuse it as a replacement of
natural aggregates in architectural mortars. A typical glass-based architectural mor-
tar produced with white cement for decorative application is shown in Fig. 6.2. The
aesthetic appearance takes advantages of the appealing colours of the waste glass
cullet (GC) which is used to fully replace natural fine aggregates (e.g., river sand).
However, the ASR between the reactive GC and the alkaline pore solution of the