Aggregates should meet requirements of ASTM D448 and

Aggregates
grading used in porous concrete are normally either single size coarse
aggregate or grading between 19-9.5 mm. rounded and crushed aggregates, both
normal and lightweight, have been used to make porous concrete. The aggregate
used should meet requirements of ASTM D448 and C33/C33/M. Fine aggregate
content is limited in porous concrete mixtures because it tends to compromise
the connectedness of the pore system. The addition of fine aggregate may
increase compressive strength and density but correspondingly reduce the flow
rate of water through the porous concrete mass.

Aggregate quality in porous concrete is equally important as
in conventional concrete. Flaky or elongated particles should be avoided. The narrow-grade
coarse aggregate should be hard and clean, and free of coatings such as dust or
clay, or other absorbed chemicals that might detrimentally affect the
paste/aggregate bond or cement hydration. Aggregate sources with a service
record of acceptable performance are preferable. In the absence of a source
with an acceptable service record, a combination of tests could be conducted to
provide a basis for assessing the suitability of a candidate aggregate for
incorporation into a porous concrete mixture. Unit weights of aggregates should
be determined in accordance with ASTM C29/C29M (Neptune
and Putman 2010). In general, as the Cu of
the aggregate increased that is, the gradation became less uniform or single
sized and well-graded, the strength increases, whereas the porosity and
permeability decreases.

The
compressive, split-tensile, and flexural strengths are inversely related to
permeability. As the permeability increased, the strength properties of porous
concrete mixtures decreased. The compressive, split-tensile, and flexural
strengths increased with the Cu to points, after which a decrease in
strength was observed. This is consistent with the literature; as the aggregate
size decreases, the binding area increases and results in an improvement of the
strength (Yang and Jiang 2003).

 

Nguyen
et al. 2013 studied the use of sea shell by products in partial replacement of
aggregates in porous concrete both as an environment friendly building material
and a potential component. (W.T. Kuo et al 2013) demonstrated Washed municipal
solid waste incinerator bottom ash (MSWIBA) of maximum size 12.5 mm was used as
a substitute for natural aggregate and results shows that there is no
significant difference in connected porosities, compressive strength and
permeability coefficient.

 

Gaedicke
et al. 2014 studied three different types of coarse aggregate namely pea
gravel, limestone and a blend of RCAB of maximum size 9.5mm.

The
use of waste material such as recycle aggregate in porous concrete further
increases its environmental benefits by reducing the amount of materials
extracted from quarries and riverbeds. Li and Rizvi et al

.

(F.
Tittarelli et al. 2014). Evaluated no-fines concretes with
compressive strength ranging from 7 to 30 MPa by changing the w/c
from
0.41 to 0.34 and the a/c ratio from 8 to 4.

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