Page 293 - New Trends in Eco efficient and Recycled Concrete

Comparative studies of the life 10

cycle analysis between
conventional and recycled

aggregate concrete

Sne ˇ zana Marinkovi ´ c and Vedran Carevi ´ c
Faculty of Civil Engineering, University of Belgrade, Belgrade, Serbia

10.1 Introduction

Recycled aggregate concrete (RAC) is an alternative to using natural aggregate
(NA) in concrete. Recycled concrete aggregate (RCA) are aggregates obtained by
recycling clean concrete waste where content of other building waste must be very
low below few per cent. For instance, British standard BS 8500-2 (BSI, 2006)
defines RCA as recycled aggregate with maximum masonry/fines content of 5%,
maximum lightweight material/asphalt content of 0.5% and maximum other foreign
materials content of 1%. The replacement of NA with RCA can be total (100%) or
partial (,100%). However, the use of fine RCA below 2 mm is uncommon because
of the high water demand of fine material smaller than 150 μm, which lowers the
strength and increases the concrete shrinkage significantly. This high water absorp-
tion and high cohesion of fine RCA also makes the concrete quality control very
difficult. Therefore, some standards and specifications forbid the use of fine RCA
in RAC for structural use (DAfStb, 2004; BSI, 2006).
RCA are produced in stationary recycling plants similar to those used for natural,
crushed aggregate production. Processing usually includes two-stage crushing (pri-
marily with jaw crushers and secondarily with impact crushers), removing the con-
taminants and screening. After primary crushing, the residual reinforcement is
removed by large electro-magnets. All types of contaminants, such as dirt, plaster,
gypsum and other building waste, must be carefully removed by water cleaning or
air sifting. RCA can also be processed in mobile recycling plants. These are typi-
cally used for demolition sites with large amounts of homogenous waste which will
be reused on site (e.g., rebuilding of roads and highways, large industrial facilities).
In mobile recycling plants, processing is limited to one-stage crushing, magnetic
separation and screening.
Recycling of demolished concrete into aggregate is environmentally beneficial
by preserving NA resources, by waste reduction and by preserving landfill space.
However, the recycling process itself and eventual higher cement-demand in struc-
tural concrete made with RCA result in new environmental burdens (Weil et al.,
New Trends in Eco-efficient and Recycled Concrete. DOI: https://doi.org/10.1016/B978-0-08-102480-5.00010-5
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