Page 115 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

Materials Decree which is likely to be the basis a new project starts. The main alternative to
for revisions to Essential Requirement 3 (ER3). 35,36 using recycled aggregates is, of course, natural
A further study using EA NEN 7345 method has aggregate and these are still relatively low cost
shown that concrete made with aggregates at the materials. However, in a purely economic balance,
very extreme of composition (e.g. using incinerator the cost of processing to recycled aggregates in the
bottom ash aggregate) still satisfies the BMD. UK is becoming less than that of disposing of the
A similar leaching study on foamed recycled demolition waste and purchasing new aggregates,
aggregate concrete using the EA NEN 7345 due to increases in landfill tax and the newly
method has also demonstrated that there was no introduced aggregate levy. If recycled aggregates
significant difference in Cd, Cu, Pb and Zn leaching have to be transported a significant distance from
between foamed concrete containing RA and other the place of production to the place of use, then
37
aggregates. both the cost and environmental benefits may
become more questionable.
Table 2. Ratio between calculated emissions
2
of RDS, I (mg/m ) for unbound recycled A project, in consultation with all the main
b
aggregates and natural aggregates (100
mm deep layer) and the permitted release stakeholders, has developed strategies for
in BMD (I b,max ). I / I b,max ratios greater than recycling demolition arisings under a given set of
b
1.0 reflect that the BMD was not met. 34 circumstances, by establishing best practicable
Aggregate I /I b,max ratio environmental options (BPEOs) specific to those
b
circumstances. In particular it has developed
38
Cd Cu Pb Zn Cr (VI)
methodologies for carrying out environmental life-
Natural gravel 0.74 0.32 0.01 7.15 0.02 cycle analysis of each stage involved in processing
and handling construction and demolition wastes
Limestone 0.06 0.12 0.01 0.21 0.04
for recycling, developed methodologies for
Granite 0.34 0.50 0.09 0.66 0.01 environmental life-cycle analysis of the alternative
solutions using primary materials, and developed
Coarse RA 1 0.16 0.19 0.08 0.48 0.04
a procedure for assessing environmental impact of
Coarse RA 2 0.72 0.09 0.00 0.24 0.02 available recycling strategies for a given scenario,
such that the most environmentally benign can be
Fine RA 1 0.63 0.10 0.21 0.18 0.03 selected.
Fine RA 2 0.49 0.11 0.13 1.35 0.02
CURRENT PRACTICE
Gravel RCA 1.04 0.93 0.10 4.57 0.03
Recycled aggregate production
Limestone RCA 0.35 0.22 0.01 1.15 0.01
Recycling of CDEW can take place either at the site
from which the material is sourced using mobile
ECONOMICS AND BEST PRACTICABLE
OPTIONS crushers, or as is increasingly the case in Europe, the
material may be transported to a central recycling
Besides the technical issues relating to use
facility (sometimes referred to as an urban quarry)
of recycled aggregates in concrete, there is a
where large stockpiles may be accumulated. Mobile
practical problem of availability at the right time
crushers whilst often more economical in that they
and in the right place. Thus, a concrete supplier
avoid transporting CDEW away from site, are rarely
may not always have the materials at hand when
sophisticated enough to remove all impurities.

116 The Indian Concrete Journal | November 2018