Civil Engineering Reference
In-Depth Information
Fig. 3.10 Mercury intrusion porosity of CDW aggregate (Poon et al.
2004a
,
b
). a Cumulative
pore size distribution; b differential pore size distribution
3.5.3 Porosity
As the CDW aggregate has higher water absorption capacity than the normal
aggregate, therefore it has higher water accessible porosity than normal aggregate.
Poon et al. (
2004a
) evaluated the mercury intrusion porosity of natural coarse
aggregate (NA), CDW aggregate prepared from normal concrete (NC) and CDW
aggregate prepared from high-performance concrete (HPC), which are presented in
Fig.
3.10
. The authors reported that the porosities of NA, NC and HPC were 1.60,
16.81 and 7.86 %, respectively. According to the authors, the higher porosity of
CDW aggregates is attributed to the adhered cement paste. The pores in the NC
aggregate mainly distributed between 0.01 and 1 mm, whereas the majority of
pores in the HPC aggregate located in the region of less than 0.1 mm (Fig.
3.10
b).
The finer pore size distribution of the recycled HPC was due to the use of poz-
zolanic admixtures, which substantially improved the microstructure of the cement
paste and the paste-aggregate interfacial transition zone (ITZ) (Poon et al.
2004a
).
3.5.4 Mechanical Properties of CDW Aggregate
3.5.4.1 Los Angeles Abrasion
The aggregate abrasion value is defined as the percentage loss in weight by
abrasion, so that a high value denotes low resistance to abrasion (Neville
1981
).
Several tests are performed to evaluate the aggregates' abrasion value. Of these,
the Los Angeles abrasion test is more commonly used all over the world and
therefore the abrasion values obtained from this test reported in various references
are considered in this section. According to ASTM C-33, ''Standard specification
for concrete aggregates,'' the Los Angeles abrasion value should be less than 50 %
for aggregate used to produce concrete, and should be less than 40 % for aggregate
used to make roads.
