Page 340 - New Trends in Eco efficient and Recycled Concrete

Equivalent functional unit in recycled aggregate concrete 297

clarify the meaning of ‘a given compressive strength at 28 days’, since: there are
many standards worldwide to test this characteristic of concrete; the compressive
strength can be tested in concrete cylinders or cubes; and f ctm (direct tensile
strength) or f ck (characteristic value) can be considered. In terms of durability,
chloride ion penetration and carbonation resistances are the most common charac-
teristics considered, depending on the on-site exposure conditions of concrete.
Again, standardised tests should be selected in order to have a consistent approach
for the characterisation and comparison of functionally equivalent alternatives for
a given use.

11.3 Relative performance of recycled aggregates
concrete versus conventional concrete

11.3.1 Recycled aggregates
As concrete production keeps on increasing worldwide, so does the use and con-
sumption of abiotic resources, such as aggregates. To corroborate this statement,
the worldwide aggregates demand will raise from 45.9 to 66.3 Gt in a time span of
10 years (e.g., 2012 22) (Freedonia, 2012). Another clear indicator of the use and
growth of concrete is related to cement production, that will increase from 2.77 Gt
in 2007 (USGS, 2008) to between 3.8 and 4.6 Gt in 2050 (IEA, 2010). Considering
these indicators, it is imperative that new solutions arise to replace NAs in concrete
production.
Among the possible solutions for this increased aggregate demand, replacing
NAs with RAs of industrial by-products seems a logic and environmentally attrac-
tive solution: not only does it help to solve the problem of abiotic depletion, but
also it can assist in the topic of industrial waste disposal, which often carries severe
environmental problems (Samuelson, 2009). The main source of these RAs is con-
struction and demolition waste (CDW), but other possible ones include mining
industry waste, plastics wastes, coal ashes, tyre rubber, slags, industrial sludges,
among others (de Brito and Saikia, 2013). Considering their nature and composi-
tion, it is common to define both CDW and mining wastes as mineral wastes, set-
ting them apart from the rest, in terms of potential use as RAs.
CDWs corresponded, in 2012, to about 33% (821 Mt) of all wastes produced in
the European Union, followed by mining industry wastes, which corresponded to
29% (734 Mt). Overall, mineral wastes add up to 62% of the total waste production,
emphasising the importance that by-products could have in any future solutions for
a greener concrete. CDW comprises a wide range of materials, different chemical
and mineralogical compositions, as well as different hazard levels. These differ-
ences are typically used to define smaller categories of CDW, which class materials
by their recycling potential. As an example, the European Union (EU Commission,
2016) established nine CDW sub-groups, ranging from ‘17 01—concrete, bricks, tiles
and ceramics’, the most suitable materials for recycling, to ‘17 09—Other CDWs’,