Page 529 - New Trends in Eco efficient and Recycled Concrete

Sequestration of carbon dioxide 16

by RCAs and enhancement of
properties of RAC by accelerated

carbonation

Dongxing Xuan and Chi Sun Poon
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic
University, Kowloon, Hong Kong

16.1 Introduction

Nowadays, concrete is very ubiquitous and its annual global production is approxi-
mately 2.0 tonnes per capita (Hasanbeigi et al., 2012). There is, thus, a great concern
on its impact on the global environmental carbon footprint, where the production of
its essential binding agent, cement, is highly energy-and-emissions intensive. It
accounts for about 5% 8% of current anthropogenic carbon dioxide (CO 2 )emissions
(Gordon et al., 2014). Meanwhile, the construction industry has recently been devel-
oping rapidly in many developing countries, such as China, where large amounts of
construction and demolition waste (CDW) are being generated. With accelerated
industrialisation and urbanisation, these regions would suffer from depletion in natu-
ral mineral resources and shortages of waste disposal sites. Consequently, recycling
and reuse of CDW are certainly necessary from the perspective of environmental pro-
tection and effective utilisation of secondary resources.
In many countries, reusing recycled concrete aggregates (RCAs) produced by
crushing old concrete debris as a renewable resource in lieu of virgin materials is
already being promoted (Safiuddin et al., 2013). However, the reuse of RCAs still
has limitations and their applications are often limited to low-level civil engineering
works like road sub-bases and non-structural concrete products. The reuse of RCAs
in structural concrete is still limited. This is mainly because when compared with
natural aggregates (NAs), RCAs have lower density, higher water absorption, high-
er porosity and poorer mechanical properties, which would have adverse impacts on
the new concrete produced with RCAs, resulting in lower strength and modulus and
poorer durability (Akbarnezhad et al., 2011).
To effectively facilitate the recycling and reuse of RCAs in new concrete, a
number of studies had attempted to improve the quality of RCAs and the perfor-
mance of recycled aggregate concrete (RAC) (Quattrone et al., 2014; Tam et al.,
2005; Ryu, 2002; Kong et al., 2010; Tam et al., 2007; Katz, 2004; Nagataki et al.,
2004; Kou and Poon, 2010; Tsujino et al., 2007; Shayan and Xu, 2003). Based on
New Trends in Eco-efficient and Recycled Concrete. DOI: https://doi.org/10.1016/B978-0-08-102480-5.00016-6
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