Page 10 - ICJ-August-2020

point of view

exposure classes provided it has been demonstrated that the
resulting concrete is suitable for the intended environment’,
which is ambiguous as no performance criteria or limits are
included to determine suitability. This highlights the importance
of research into the effects of rCa on the mechanical and
durability properties, if a more robust framework and guidance
for coarse rCa is to become a reality. Work is however
underway, on a revision of eurocode 2 which will allow provision
for RCA, as well as the fib Model Code 2020.

3. Effect of coarse RCA on concrete properties
Figure 1: Section of RCA source concrete for petrographic analysis [3]
The effect of RCA on long-term durability performance is
under researched, particularly in relation to water and chloride
ion ingress. The majority of published research on the effect 4. Detrimental effects
of coarse rCa on concrete durability has focused on rapid The research showed that the inclusion of coarse rCa generally
migration and water absorption test methods to determine has a detrimental effect on the microstructure and water ingress
acceptable levels of replacement of na. The general consensus of structural concrete. These detrimental effects, however, can
is that 25-30% coarse RCA can be successfully incorporated be largely overcome through the use of GGBs to produce CeM
without detrimentally affecting the transport properties of iii/a concretes, allowing a higher proportions of coarse rCa to
concrete. The detrimental effect is generally attributed to the be used. GGBs however has a detrimental effect on strength
increased water absorption of the coarse rCa, in particular from development at early ages, hence replacement of GGBs and
the hardened cement paste .
[1]
coarse rCa should be limited to 50% and 30% respectively in
recent published research has shown that rCa content of even cases where compliance with the 28 day characteristic strength is
20% to 40% replacement for CeM i and CeM iii/a concretes of particular importance. if this criterion can be relaxed and the
respectively, have a significant detrimental effect on durability mechanical performance of CeM iii/a concretes tested at later
performance [1; 2] . The inclusion of sCMs (supplementary ages for conformity, then higher quantities of coarse rCa may
cementitious materials) however, considerably improve the be implemented up to 60% to produce a sustainable structural
resistance of concrete to water and chloride ion ingress. For concrete.
example, the CeM iii/a structural concrete incorporating 60%
coarse rCa in this research outperformed the control CeM i CeM iii/a concretes produced with up to 100% coarse rCa,
concrete for all the durability test methods adopted. irrespective of rCa source, have been shown to outperform
control CeM i concrete with na in durability performance tests.
The findings of this research clearly demonstrated that more if the cover depth of CeM iii/a concretes can be increased,
sustainable structural concrete, produced with up to 50% and similar to that of CeM i concretes, then the risk of potential
60% GGBs and rCa respectively, can be a viable option for durability performance issues could be further reduced.
future more responsibly sourced infrastructure projects - a
positive outcome for the wider implementation of coarse The findings of this study have highlighted that sustainable
rCa. replacement levels of this magnitude can relate to structural CeM iii/a concrete can be a viable option for future
significant savings in terms of cost and environmental impact responsibly sourced projects, provided that a reliable and
(Co 2 reduction). The addition of sCMs such as GGBs can also consistent source of rCa can be obtained. This is a positive
contribute to the ‘green’ credentials of the concrete . outcome for the wider implementation of coarse rCa into
[5]
structural concrete applications. The authors have also
The research was the first of its kind to provide a detailed previously published results on the incorporation of fine crushed
analysis and understanding, using petrographic techniques concrete aggregate on the durability of structural concrete , as
[6]
(Figure 1), of all the recycled materials incorporated into well as other durability properties [1; 2; 4; 5] .
the concrete . a good correlation was observed between
[3]
the properties of the original constituents and the durability 5. The case for segregation
performance and compressive strength of the resultant
structural concrete, highlighting the benefit of segregating good There are potentially significant benefits of segregating good
quality structural concrete from other demolition arisings and quality reinforced concrete sources on demolition sites to
the importance of additional testing to characterise materials. better predict potential impacts on durability performance

8 The IndIan ConCreTe Journal | augusT 2020