Page 119 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

recycled aggregate must meet the requirements Angeles coefficient). As a result RA quality would
listed in Table 6 in addition to some rather tight be related to concrete performance across the
41
requirements on composition. JIS A 5023 has whole range of potential RA quality, independent
also been introduced as a standard for recycled of composition and source. The concept being
concrete using low-quality recycled aggregate that good quality RA (conforming to, say, class A)
(L), as permitted for use in backfilling, filling and will be suitable for high performance applications,
levelling concrete. An additional requirement is meeting the relevant standards and specifications,
that recycled aggregate L be used with blended whilst lower classes will be more appropriate
cements as a measure against alkali-silica reactivity. for lower value applications (Figure 6). Given
JIS A 5022 will provide requirements for a “normal” this approach, material that would currently be
recycled aggregate. classified as RA under BS 8500-2 (and therefore not
specified for use) can be classified and considered
for relevant applications. This should lead to
The concept being adopted in Japan has some
similarities with the approach to the use of recycled greater confidence in specifying and using RA and
aggregates proposed by Dhir and Paine below. 16,17 help to remove the main barrier that is preventing
However, the JIS reliance on some aspects of the uptake of RA in concrete.
composition, particularly with respect to recycled A major research project was carried out by
aggregate H, means that it is subject to many of Dhir Paine, commissioned by Waste Resource
the practical problems associated with the CEN Action Programme (WRAP), major aggregate
method.
producers and other stakeholders to investigate
the effect of the individual characteristics of RA
PROPOSED PERFORMANCE RELATED on the performance of concrete using various
APPROACH proportions of Ru, Rc and Rb. The research
16
As a result of the classification in BS 8500-2, only produced general guidance supporting the wider
RCA is permitted for use in concrete up to strength use of recycled aggregates in concrete as well as
class of C40/50 and durability classes X0, XC1-4, grouping aggregate particle composition into
DC1 and XF1.8 RA being restricted to concrete up three classes of recycled aggregate suitable for
to strength class C16/20 and durability classes X0 different applications, as given below.
and DC-1 (in other words unreinforced concrete
in a completely dry environment or buried in • Class A - recycled aggregates for use in a
non-aggressive soil). This means that material wide range of concrete including marine
containing 95% crushed concrete is permitted for environments;
use in a wide sphere of concrete activity, whilst
similar material containing 94% crushed concrete
is not. Clearly, this does not provide a sustainable
solution to the CDEW problem.

However, in line with the earlier discussed
implications of appropriate use of aggregates
in concrete, it is the effect of a given RA on the
performance of concrete that is most important. This
is not necessarily dependant on the composition,
and therefore, a more logical approach will be
to relate limits on allowable RA on performance-
based properties (i.e. strength), or for practicality,
on performance-related characteristics (e.g. Los

120 The Indian Concrete Journal | November 2018