Aggregates partial replacement of aggregates in pervious concrete

Aggregates
grading used in pervious 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 pervious concrete. The aggregate
used should meet requirements of ASTM D448 and C33/C33/M. Fine aggregate
content is limited in pervious 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 pervious concrete mass.

Aggregate quality in pervious 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 pervious 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 pervious 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).

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Nguyen et al. 2013 studied the use of sea shell by products
in partial replacement of aggregates in pervious 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 pervious concrete further
increases its environmental benefits by reducing the amount of materials extracted
from quarries and riverbeds (Li and Rizvi et al. 2010).

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