Page 26 - New Trends in Eco efficient and Recycled Concrete

Construction and demolition waste 3

A different combination of these processes can be seen in different plants; the
implementation or removal of those steps depends on the quality of the input CDW.
If the original CDW has high quality, lower quantity of treatments may be applied
to obtain adequate RA. In this way, if selected concrete blocks with lower contami-
nation content are used as input CDW, it is possible that, apart from the crushing
and screening stages, only an additional electromagnetic separation would be
required to produce high-quality recycled concrete aggregates (RCAs). On the other
hand, in the case of low-quality CDW with different types of components, a greater
complexity of treatments would be required to obtain suitable RA, including pre-
screening, air separation and manual separation. Under these circumstances, a
mixed RA (MRA) would be expected to result from this process.

1.2.1 Treatment processes for construction and demolition
waste

The appropriate treatment varies according to the original CDW that is delivered to
the recycling plant. If it is mostly comprised of concrete blocks, it is fairly easy to
obtain good-quality RCA with a reduced number of treatment steps and, thus, at
lower cost. Fig. 1.2 presents an example of a simple treatment scheme for the pro-
duction of RCA from selected concrete blocks. After an initial pre-screening stage
to eliminate possible contaminants, the material’s size is usually reduced with a jaw
crusher. Afterwards, an electromagnet is used to extract ferrous metals from the

Concrete

Pre-screening

Particles
< 4 mm Jaw
crusher

Electromagnetic
separation
Screening
Scrap steel

Fine RCA Coarse RCA
Figure 1.2 Basic treatment process of a concrete-based CDW batch. CDW, Construction and
demolition waste.