Page 248 - New Trends in Eco efficient and Recycled Concrete

216 New Trends in Eco-efficient and Recycled Concrete

and some regions are experiencing limitations regarding the supply of natural
aggregates. In 2014, the United Nations Environment Programme (UNEP, 2014)
warned for the actual depletion risk that a continued trend in the consumption of
aggregates could cause.
Nowadays, globalisation has made cross border purchase of natural aggregates
common practice. In fact, in some instances, financial advantages could be achieved
from transporting them from neighbouring countries instead of nationally. Although
the shortage problem could be solved, this practice adds a new environmental bur-
den to the manufacture of concrete since emissions due to transport have to be
included.
Besides the resource depletion, the magnitude of the extracted volumes is bound
to cause other relevant environmental impacts (Sonak et al., 2006). Sand and gravel
extraction affect the biodiversity of flora and fauna due to impacts on terrestrial,
fluvial and coastal ecosystems and generate changes in the landscape. Mineral min-
ing has negative visual impacts due to the incurred differences compared to the nat-
ural surrounding landscape. Nonetheless, usually national policies restrict the zones
liable for extraction and impose corrective measures after the cease of the activity
in order to restore the natural environment. Moreover, the mining operations are
responsible for dust and noise generation that could be detrimental for the human
health and potential groundwater contamination (hydrocarbons, suspended and
dissolved solids) due to the cleaning activities (Krausmannetal.,2011;Querol
et al., 2001).
Different impacts should be accounted for with regard to the production of
rounded and crushed aggregates. The former are the result of weathering and ero-
sion and require a bare minimum processing once collected from the sea or river
bed. Crushed aggregates are extracted from quarries and require a more intensive
mechanical process. Commonly, sand is obtained from open-pit mines or dredged
from underwater deposits, whereas gravel production requires more energy con-
sumption as it could include operations of blasting, drilling and crushing.
Nevertheless, the mechanical processes required for the production of natural aggre-
gates have a reduced contribution, around 15%, in the total CO 2 emission produced
in the manufacture of concrete, mainly due to the required operations of mining and
processing (Flower and Sanjayan, 2007). The aggregates also have a contribution in
the CO 2 emissions of the concrete sector, ranging between 0.004 and 0.008 kg per
kilogram of alluvial and crushed natural aggregate respectively (FIB, 2012), mainly
due to the required energy. In any case, according to Reid et al. (2009), life cycle
inventory (LCI) for mining activities are heavily influenced by the local conditions
of the quarry and processing plant and, thus, industrial data should be employed in
the LCA to improve the results.

9.2.1.5 Water
Concrete manufacturing and the production of its raw materials (cement, sand and
gravel) involve large amounts of water. The production of cement requires almost
4 L/t (Zabalza Bribia ´n et al., 2011), but this industry also requires water for cooling