Civil Engineering Reference
In-Depth Information
Table 3.8
10 % crushing value of CDW aggregate and normal aggregate
Reference
10 % crushing value (kN)
CDW aggregate
Normal aggregate
Poon et al. (
2009
)
117.0
159.0
Rao et al. (
2011
)
120.5
231.3
Tam and Tam (
2007
)
61-155.6
189.4
Poon et al. (
2004a
)
NC: 101.9; HPC: 123.8
159.7
Poon et al. (
2009
)
72, 88
-
Limbachiya et al. (
2000
)
160
289
NC CDW aggregate prepared from normal concrete
HPC CDW aggregate prepared from high performance concrete
The crushing value of CDW aggregate is also higher than that of normal
aggregate. Limbachiya et al. (
2000
) reported a crushing value of 20 % for
CDW aggregate with size 10-14 mm compared to a crushing value of 14 % for
natural aggregate of similar size. A similar trend is observed by several researchers
(Sagoe-Crentsil et al.
2001
; Xiao et al.
2005
). Like other parameters of CDW
aggregate, the crushing value of CDW aggregate also varies depending on the
crushing technique. Li et al. (
2009
) found a crushing value of 27 % for CDW
aggregate crushed using a jaw crusher, and a crushing value of 23 % when an
impact crusher is used after crushing CDW aggregate with a jaw crusher.
The toughness of the aggregate is determined using the aggregate impact value.
Aggregate with high toughness exhibits a low impact value. An acceptable limit of
this value is between 25 and 45 %. In general, 25 % is specified for heavy-duty
concrete elements, 35 % for sub-base applications and 30 % for other low-grade
applications (Tam and Tam
2007
). The impact value of CDW aggregate is higher
than that of normal coarse aggregate (Table
3.9
). According to Rao et al. (
2011
),
this is due to the separation and crushing of adhered mortars in CDW aggregate
during testing.
3.5.5 Particle Shape and Texture
The surface of CDW aggregate is rough and porous due to the presence of mortar
adhered (Rao et al.
2007
; Domingo et al.
2010
). According to Topçu (
1997
), the
shape of CDW aggregate is angular because of debris. Limbachiya et al. (
2000
) used
a CDW aggregate, which was found to be coarser, porous and rougher but equi-
dimensional to that of natural gravel. Poon et al. (
2004a
) reported a CDW aggregate,
which is more inhomogeneous, porous, less dense and weaker than crushed granite.
From the optical and scanning electron microscopy (SEM) studies of CDW
aggregate, Malhotra (
1976
) concluded that the particles of CDW aggregate tended
to be more angular than those of natural aggregate (NA). According to Zaharieva
