Page 110 - ICJ Jan 2023

TECHNICAL PAPER COLLECTOR’S EDITION

2002, to concentrate on RA (recycled aggregate STRENGTH AND DEFORMATION
containing lower quantities of crushed concrete). CHARACTERISTICS
Indeed, the introduction of specialised centres for All researchers report a loss in compressive
recycling in Europe and Japan, have led to greater strength when RCA is used as a direct replacement
availability and requirements for use of this more of natural aggregate at the same w/c ratio. Values
mixed material. differ but losses in strength of up to 15% when
RCA is used as the sole aggregate compared to a
The first major project in the UK was carried out comparable natural aggregate are not uncommon.
by Dhir et al in 1996 and recognised for the very However, most researchers also report that a certain
first time that the simplest route for using RCA proportion of coarse RCA can be added to natural
in concrete would be through the designated aggregate without any effect on performance.
concrete mixes, where the concrete producer alone Dhir et al., who were the first to note this effect,
is responsible for ensuring and demonstrating suggested that the cut off point was around 30%
6
that the concrete has achieved the specified by mass of coarse RCA. However, a conservative
6,7
performance. The project studied the use of value of 20% by mass was later adopted in BS 8500-
8
RCA in concrete mixes with strength ranging from 2. Generally speaking the performance of RCA
C8/10 to C35/45, representing approximately 60% concrete is largely unaffected by the quality of the
of the total UK market at that time, and developed a original crushed concrete. 6
number of significant findings that have pioneered
research in this area. The main findings from this The reason for the loss in strength is usually
and later research are reviewed in the following associated with: (i) the weaker interfacial transition
sections. zone between aggregate and mortar, due to the

The Indian Concrete Journal | November 2018 111