Page 188 - New Trends in Eco efficient and Recycled Concrete

160 New Trends in Eco-efficient and Recycled Concrete

0.14 (A) 0% GC 0 (B) 0% GC
55% GC
55% GC
55% GC+10% GP 55% GC+10% GP
0.12 –200
ASR expansion (%) 0.08 Standard limit Drying shrinkage (*10 –6 ) –400
0.10
–600
0.06
0.04
0.02 –800
–1000
0.00
–1200
0 7 14 21 0 7 14 21 28
Age (days) Age (days)
Figure 6.6 The effect of maximum content of glass cullet on the ASR and shrinkage of
paving blocks. (A) ASR expansion (80 C 1 M NaOH solution); (B) Drying shrinkage (25 C

and 50% humidity). ASR, Alkali silica-reaction.
absorption of pedestrian blocks should not exceed 6.0%. The water absorption value
of paving blocks with GC were less than 6.0%.
Although the 14-day expansion values did not exceed the deleterious limit, the
potential deterioration at longer ages as a result of ASR still need to be taken into
consideration (see Fig. 6.6A). Therefore, 10% of cement was replaced by GP in
order to mitigate the ASR expansion for the paving blocks. The experimental
results showed that the inclusion of GP could significantly suppress expansion and
the GP-blended paving blocks had comparable expansion values to the paving
blocks without GC. The reason for the effectiveness in reducing the ASR expansion
may be due to the fact that GP consumed more alkalis and free calcium hydroxide
in solution to form a sodium-calcium-silicate hydrate gel, leading to lower expan-
sion around the reactive aggregates (Shi et al., 2004). Another explanation was pro-
posed by Ichikawa (2009) who stated that the rate of ASR was highly controlled by
the particle size of reactive aggregate and that a grain size less than 50 μm (large
specific surface area) would preferentially react with alkali hydroxide to prevent
the formation of expansive pressure. On the basis of this size effect, the introduc-
tion of GP with small particle size is, thus expected to suppress ASR. Fig. 6.6B
shows the effect of GC on the drying shrinkage of paving blocks. When 55% of GC
was introduced to replace the fine aggregates in the paving blocks, the drying
shrinkage could be reduced effectively. The drying shrinkage values of the blocks
produced with the maximum content of GC and 10% GP were about half of those
of blocks without GC.

6.5 Application of waste glass in OPC concrete

Due to the non-absorbent nature of the GC, Kou and Poon (2009) made an attempt
to investigate the feasibility of using recycled glass in the production of self-