2.     LITERATURE
REVIEW

2.1.        
 INTRODUCTION

 Concrete, which is one of the most used
materials for construction is very important in the growth of the
infrastructural and industrial segment of any nation, but it has been claimed
that concrete is not an environmentally-friendly material due to its
destructive resource consuming nature and the possibly severe environmental
impact after its use. Concrete, nevertheless, remains the major construction
material being used in the world. These factors also contribute to the price
increase of aggregates in developed and developing countries. As a result of
this, researchers in the built environment are continually investigating
alternative construction materials that can be used as a partial or total
replacement for the conventional materials. Studies have shown that Recycled
aggregate concrete (RAC) has the ability to be an effective replacement for
natural aggregate concrete (NAC) (Avikal, 2014; Rahul et al, 2015; Yasir et al,
2016)

The use of
recycled concrete as an aggregate for concrete mixes helps in reducing the
depletion of natural resources, obeying of environmental laws and the disposal
of concrete waste at landfill sites.  In
order to study closely and in brief related studies in the field of RAC using
metakaolin based materials as composite filler this literature review was
carried out. This chapter gives an insight into various studies conducted by researchers
as well as the relevant materials used in the production of RAC.

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2.2.        
 RECYCLED
AGGREGATE CONCRETE

Concrete is the footing of
much of modern infrastructure and much of its physical development. “Concrete”
comes from roman roots and it is gotten from the Latin word concretus meaning
to grow together. It is a composite material produced using coarse and fine
aggregates which are bounded together with the mixture of cement or
cementitious materials with water. Chemical admixtures could be added to the mix
to provide special properties to the concrete mix. RAC is produced by replacing
the natural aggregates (NA) in the concrete mix with recycled aggregate (RA)
from C&D waste. Using recycled concrete as aggregate fulfills the three
basic principles of sustainability performance, environmental stewardship and
cost-effectiveness (Minnesota Department of Transportation 2017).

Some of the structures that
have been produced with the use of RAC includes the South Seas apartment
building in Greenpoint Cape Town shown below, The London Olympic 2012 Stadium which
used 30% Recycled concrete in its construction and The Nalawala Hall Fairfield
City Council’s Sustainability Hub incorporates the world’s first concrete
load-bearing foundation slab which is 95 per cent recycled (Avikal, 2014).

 

Plate 1: South Seas apartment
building in Greenpoint Cape Town

 

2.2.1.          
 MATERIALS

Recycled aggregate concrete is composed of six
main ingredients:

1.     
Cement

2.     
Pozzolans / supplementary cementitious
admixtures

3.     
Natural aggregate

4.     
Recycled aggregate

5.     
Water and

6.     
Chemical admixtures.

The first five ingredients are of necessity and
must be in every concrete mix, while the chemical admixture is used to add
special properties to the fresh or hardened concrete and is not always needed.

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