Page 112 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

However, up about 20% by mass of aggregate,
the shrinkage of RCA, RA and the equivalent
natural aggregate concrete can assumed to be
16
comparable. Furthermore, there are very few
examples of RA concrete with shrinkage levels that
fall outside the upper limit of 0.075% permitted for
aggregates in BS EN 12620. In addition, it should be
noted that some tests have shown RA concretes to
have lower shrinkage than equivalent RCA and NA
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concretes.

There is limited research on the effect of recycled
aggregate concrete on creep. However, as creep
may be related to the elastic modulus of the
aggregate, and in turn the elastic modulus of
concrete, in general, results suggests that creep
is higher in recycled aggregate concrete than DURABILITY
23
equivalent natural aggregate concrete. The process of water absorption in recycled and
natural aggregate concretes is similar and in
24
Table 1. Comparison of engineering and general obeys the same laws. Therefore, since
durability performance of natural aggregate recycled aggregates contain particles with higher
(NA) and RCA concretes at equal w/c ratio porosity and higher water absorption properties
and equal strength
(e.g. old mortar, brick, masonry) than most natural
Property Concrete type
aggregates, recycled aggregate concrete tends
RCA, % Coarse
NA to be less resistant to most permeation-based
30 100 100
(equal exposure conditions than equivalent natural
strength)
aggregate concrete at the same w/c ratio. However,
28-day compressive 41.5 40.5 37.0 41.0 there is some evidence that when these properties
strength, N/mm 2
Flexural strength, 4.9 4.8 4.6 4.9 are compared in concretes of the same strength
N/mm 2 (made with the same cements), performance
Elastic modulus, 27.5 28.0 25.5 27.0 differences between recycled aggregate and
kN/mm 2
natural aggregate concrete are minimal (Table
Drying shrinkage, % 0.057 0.057 0.063 0.064
6
1). All the same, the most practical way to ensure
Initial surface 29 31 47 35
2
absorption, ml/m /s resistance of recycled aggregate concrete to
Air permeability, m 2 2.7 3.8 14.3 6.6 permeation-based deterioration is to use an
x 10 -17
appropriate blended cement to reduce the porosity
Carbonation depth, 13.5 13.5 16.5 13.5 of the paste and to bind aggressive agents. 25,26 In
mm
this respect Dhir and Henderson have carried out
Chloride diffusion, 1.16 1.17 -- 1.05
2
cm /s x 10 -6 a detailed study to demonstrate how coarse fly
Abrasion depth, ashes can be used with considerable advantage
mm 0.61 0.65 1.02 0.72
with recycled and secondary aggregates. 27
Freeze/thaw 97 98 96 97
durability factor, %

The Indian Concrete Journal | November 2018 113