Civil Engineering Reference
In-Depth Information
3.6 Concluding Remarks
Using CDW as an aggregate in the preparation of new concrete has been the
subject of investigation for a long time. In general, the quality of CDW aggregate
is poorer than that of natural aggregate, which restricts its use in various con-
struction applications. Information gathered from this review can be summarised
as follows:
1. The production process of CDW aggregate affects its quality and composition.
Further processing and higher quality source concrete result in better quality
aggregates;
2. Depending on its source, CDW aggregates may contain only natural aggre-
gates with adhered mortar or several types of contaminants such as bitumen
mixtures, plastics, bricks and tiles in minor amounts along with natural
aggregate and adhered mortar contents;
3. Almost all properties of CDW aggregate are dependent on its mortar content.
The adhered mortar may be present as lumps embedded with varying pro-
portions of smaller natural aggregates or on the surface of the natural
aggregate present in CDW aggregate or as a binder to two or more natural
aggregate particles;
4. Several methods are proposed to determine adhered mortar content in CDW
aggregates
and
also
several
beneficiation
techniques
can
be
applied
to
decrease mortar content in CDW aggregate;
5. All types of densities along with bulk density of CDW aggregate are lower
than those of natural aggregates, due to the existence of porous and less dense
cement paste/mortar in the CDW aggregates;
6. As adhered mortar in CDW aggregate is porous by nature, it can absorb high
amounts of water. Thus the porosity and water absorption capacity of CDW
aggregate is very high compared to that of natural aggregate. The variation of
water absorption capacity in various CDW aggregates reported in various
references is due to the variation of cement paste content in this aggregate as
well as the content of other components such as crushed clay brick and tiles.
The higher water absorption capacity of CDW aggregate substantially dete-
riorates the workability of resulting concrete, which finally affects the various
properties of concrete;
7. Additional water is necessary to compensate for the extra absorption of the
CDW aggregates during preparation of concrete mix. Several methods are
adopted to improve the performance of CDW aggregate during concrete
mixing;
8. CDW aggregate has a lower Los Angeles abrasion value than that of natural
aggregate because of the presence of adhered mortar. However, this value for
the majority of the CDW aggregate reported in the literature meets the various
standard requirements for concrete and road constructions. The toughness of
CDW aggregate is also lower than that of natural aggregate;
