Page 9 - ICJ-August-2020

point of view

SuStainable and

durable - with

recycled concrete

aggregate? Chris Goodier,
Wayne dodds

The responsible sourcing of materials and the potential to concrete is still used as general fill, sub-base material, or at
reduce waste and increase sustainability is an increasingly best in low grade concretes, as the quality requirements for
important topic of debate in the global construction industry. aggregates in these applications are lower than for structural
as part of this, innovative recent research from Loughborough concrete.
University in the UK has challenged common industry
perceptions regarding the use of recycled concrete aggregate The increasing quantities of construction and demolition waste
(rCa) in new structural concrete, and brought into question the (C&dW) produced annually ultimately provides an opportunity
existing limitations currently imposed by the international design for rCa to be utilised in a wider variety of applications including
standards . structural concrete. increased use of rCa is also particularly
[3]
beneficial for countries to help reduce import costs and maintain
The research analysed the effects of rCa, also referred to aggregate demand for large construction projects.
as crushed concrete aggregates (CCa), on the durability
performance of structural concrete and hence their suitability for The majority of C&DW arisings are either crushed on-site for
increased use in the civil engineering and infrastructure sectors. use on site, or are left unprocessed and removed offsite and
More than 1,400 concrete specimens were cast and tested as most likely taken to recycling plants for further processing and
part of an extensive laboratory programme across 100 different treatment before being sold on. The sustainability benefits
mix designs. of using rCa is soon diminished when the material has to
be transported long distances due to the energy required,
The findings have provided authoritative peer-reviewed therefore utilisation in applications close to the source is very
evidence that sustainable structural concrete can be a viable much preferred.
option for future responsibly sourced infrastructure projects,
which highlights the requirement and need for a new and 2. Specification of RCA in structural concrete
more robust framework for the efficient re-use and recycling of
concrete. Both coarse and fine RCA can be incorporated into structural
concrete applications. There is some debate however, over the
The next step is for the findings of this research to be acceptable replacement quantity without affecting performance
implemented in real-scale 'trial' structures or structural elements, characteristics. The Usa accepts that 10% inclusion is suitable
and consequently monitored to determine the effect on long- for most concrete applications, whereas some countries in
term durability. europe state that up to 20% is acceptable. european standards
for concrete production allow up to 30% replacement in certain
1. History environmental situations.

reinforced concrete is the most commonly used construction Bs en 12620:2013, aggregates for Concrete, states that a Type
material globally. With the increasing specification of concrete a coarse aggregate (>95% concrete product; 4/20mm), from a
worldwide there is an obvious increased pressure on quarrying known source, may be incorporated into structural concrete up
to meet the demand for natural aggregates. recycled concrete to 30% replacement by mass in low risk exposure classes only,
aggregates (rCa) have become increasingly popular in the UK, including: XC1-4, XF1, XA1 and XD1. BS 8500-1:2015+A1:2016
europe and elsewhere to replace natural/virgin aggregates and BS 8500-2:2015 permits the inclusion of coarse RCA up
since the 1980’s, in particularly more recently with an increasing to 20% replacement by mass, in concrete up to strength class
drive towards the more sustainable and responsible sourcing C40/50, except when the structure is to be exposed to chlorides.
of materials. Unfortunately, a significant proportion of crushed it also states that ‘these aggregates may be used in other

The IndIan ConCreTe Journal | augusT 2020 7
*Corresponding author : Chris Goodier, email : C.i.Goodier@lboro.ac.uk