Using Recycled Concrete Aggregates in New Zealand
Ready-Mix Concrete Production
Wentao Zhang
1
and Jason M. Ingham, M.ASCE
2
Abstract: Motivations for adopting recycled concrete as an aggregate source include the preservation of natural resources, effective
utilization of a growing waste stream, and financial and energy savings. Although current New Zealand practices include some use of
crushed concrete in road construction, use of recycled concrete aggregate RCA in low specification concrete is currently infrequent and
the use of recycled concrete as an aggregate source in structural concrete applications is rare. To make such recycling feasible, the
properties of RCA must be related to the properties of new concrete that utilizes the recycled aggregates. In response to this need, a study
was undertaken to investigate the feasibility of using RCA as a viable alternative to natural aggregate NA in the production of concrete
manufactured in a conventional New Zealand ready mix concrete plant. Aggregate properties and hardened and fresh concrete properties
of RCA concrete were studied and compared with the associated properties derived from NA concrete. Results indicated that RCA is a
viable alternative to NA in the production of concrete. Furthermore, it was confirmed that the properties of RCA dictate the hardened
properties of the reconstituted concrete and that RCA from certain strength placements limited the resulting possible strengths of concrete
produced from it.
DOI: 10.1061/ASCEMT.1943-5533.0000044
CE Database subject headings: Recycling; Concrete; Sustainable development; Aggregates; New Zealand.
Author keywords: Recycled concrete; RCA; Sustainability; Recycled concrete aggregate.
Introduction
Currently there is a lack of research on the performance of New
Zealand recycled concrete aggregates RCA when the character-
istics of the original concrete used in its production are known,
and the general consensus within the New Zealand concrete in-
dustry is that recycled concrete can only be used in low-end,
nonstructural applications Park 2001. Transit New Zealand, the
national transport agency in New Zealand, allows some use of
RCA in pavement base courses but there are no standards for the
prescription and widespread use of RCA in New Zealand Transit
New Zealand 2006. Consequently, even though current New
Zealand practices include some use of crushed concrete in road
construction, use of RCA in low specification concrete is infre-
quent and the use of recycled concrete in structural applications is
rare Cement and Concrete Association of New Zealand
CCANZ 2007.
Numerous European demonstration projects have shown that
RCA can be used in high strength applications Limbachiya et al.
2000, and reuse of concrete debris to produce new concrete is
now practiced worldwide, with particularly extensive and stan-
dardized implementation in Japan and Europe Hansen 1992.
Typically, experimental investigations have preceded the develop-
ment of industry standards, such as the RILEM committee that
conducted research commencing in the 1960s and developed in-
dustry recommendations in the 1970s RILEM 1994. Conse-
quently, the study reported here was undertaken to address
practical issues associated with determining the properties and
behavior of New Zealand RCA, specifically pertaining to the pro-
duction of 20–60 MPa concrete, with a view to facilitating the
implementation of RCA in New Zealand ready mix concrete
plant.
Review of Past Research
In ordinary fresh concrete, due to the presence of a water film on
the aggregates, an interfacial transition zone ITZ is created be-
tween aggregate and cement paste where the w/c ratio may be
significantly higher than that of the cement paste. The ITZ is
widely regarded as the “weakest link” in concrete Alexander
1996; Jia et al. 1986; Keru and Jianhua 1988; Li et al. 2001;
Popovics 1987, inhibiting the achievement of composite action
in natural aggregate NA concrete. Obviously, the structure of
RCA concrete is more complicated than NA concrete Mehta and
Aitcin 1990, with NA concrete consisting of only one ITZ, being
the interface between the NA and the surrounding cement paste,
whereas RCA concrete has two ITZ, located between the aggre-
gate and old adhered mortar, and between the old adhered mortar
and the new cement paste Ryu 2002. The strength of RCA con-
crete is usually dictated by the weaker of these two ITZs. The
presence of adhered mortar generally degrades the quality of
RCA and negatively influences the fresh and hardened properties
1
Civil Engineer, Humes Pipeline Systems, Level 3, Wright Stephen-
son House, 585 Great South Rd., Penrose, Auckland, New Zealand cor-
responding author. E-mail: wentao.zhang@humes.co.nz
2
Associate Professor, Dept. of Civil and Environmental Engineering,
Univ. of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail:
j.ingham@auckland.ac.nz
Note. This manuscript was submitted on May 20, 2009; approved on
August 28, 2009; published online on April 15, 2010. Discussion period
open until October 1, 2010; separate discussions must be submitted for
individual papers. This paper is part of the Journal of Materials in Civil
Engineering, Vol. 22, No. 5, May 1, 2010. ©ASCE, ISSN 0899-1561/
2010/5-443–450/$25.00.
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / MAY 2010 / 443