Recycling is the act of processing the used material for use in creating new product.
The usage of natural
aggregate is getting more and more intense with the advanced development in infrastructure area. In
order to reduce the usage of natural aggregate, recycled aggregate can be used as the replacement
materials. Recycled aggregate are comprised of crushed, graded inorganic particles processed from the
materials that have been used in the constructions and demolition debris. These materials are generally
from Buildings, roads, bridges, and sometimes even from catastrophes, such as wars and earthquakes.
There are many advantages through using the recycled aggregate such as Environmental Gain, Cost, Job
Opportunities, Sustainability, Market is wide and many more ( N.Sivakumar 2014). Use of recycled
aggregate in concrete can be useful for environmental protection. Recycled aggregates are the materials
for the future. The application of recycled aggregate has been started in a large number of construction
projects of many European, American, Russian and Asian countries (Sonawane, Sunil and Pimplikar
2007). Urbanization growth rate in India is very high due to industrialization. Growth rate of India is
reaching 9% of GDP. Rapid infrastructure development requires a large quantity of construction
materials, land requirements & the site. For large construction, concrete is preferred as it has longer life,
low maintenance cost & better performance. For achieving GDP rate, smaller structures are demolished
& new towers are constructed. Protection of environment is a basic factor which is directly connected
with the survival of the human race. Parameters like environmental consciousness, protection of natural
resources, sustainable development, play an important role in modern requirements of construction
works. Due to modernization, demolished materials are dumped on land & not used for any purpose.
Such situations affect the fertility of land. As per report of Hindu online of March 2007, India generates
23.75 million tons demolition waste annually. As per report of Central Pollution Control Board (CPCB)
Delhi, in India, 48million tons solid waste is produced out of which 14.5 million ton waste is produced
from the construction waste sector, out of which only 3%waste is used for embankment.(Magdum
2007)It is not surprising that alternatives are being sought out. One solution that solves both problems
simultaneously is recycling of concrete waste. Through a process that usually involves multistage
crushing, eliminating impurities and sieving, a new aggregate produced called recycled concrete
aggregate (RCA). When this new aggregate is used to make concrete, with complete or partial
replacement of natural aggregate, this concrete is called recycled aggregate concrete (RAC).Recycled
concrete aggregate and recycled aggregate concrete have been studied for several decades. At the
material level, practically all important characteristics of RCA and RAC have been studied, from short-
term and long-term mechanical properties to durability. The main characteristic that distinguishes RCA
from natural aggregate is the certain quantity of cement paste that remains attached to the aggregates
after crushing. This residual cement paste is the reason for higher water absorption of RCA compared
with natural aggregates, especially in the case of fine RCA. (Tošic´, Marinkovic´ and Ignjatovic 2016).
Using recycled aggregates crushed from demolished concrete to produce new concrete can reduce the
consumption of natural sources and save the landfill spaces. This kind of sustainable material is
commonly referred to as recycled aggregate concrete (RAC). (Gengand Wang 2016). S. Muthukumar
(2010), observed that concrete suitability and adaptability will change with respect to the environment,
the concrete must be such that it can conserve resources, protect the environment, economize and lead
to proper utilization of energy. To achieve this, major emphasis must be laid on the use of wastes and by-
products in cement and concrete used for new constructions. The utilization of recycled aggregate is
particularly very promising as 75 per cent of concrete is made of aggregates. The use of recycled
aggregates from construction and demolition wastes is showing prospective application in construction
as alternative to primary (natural) aggregates. Research on the usage of waste construction materials is
very important since the materials waste is gradually increasing with the increase of population and
increasing of urban development. The reasons that many investigations and analysis had been made on
recycled aggregate are because recycled aggregate is easy to obtain and the cost is cheaper than virgin
aggregate. The increasing and unsustainable consumption of natural resources, as well as the excessive
production of construction and demolition waste (CDW), has been a cause of great concern for the
environment and economy. In order to reverse this trend, there have been several efforts to promote the
ecological efficiency in the construction industry, one of them being the reutilization of CDW in new
construction. By doing so, besides decreasing the amount of waste mass sent to landfills and the
extraction of natural resources, more value will also be added to these materials, thus opening new
market opportunities (Coelho and Brito, 2013).Research on this subject started with basic observations
on the effects of using recycled concrete aggregates (RCA) on the compressive strength of concrete
(Buck, 1999;Frondistou-Yannas, 1998), as well as its economic feasibility (Frondistou-Yannas and
Itoh,2000). Since then, research on recycled aggregate concrete (RAC) has become progressively
complex, introducing several new variables, in which the durability-related performance has also been
considered. These more recent studies have generally shown a decline of the mechanical and durability-
related performance, when compared to that of natural aggregate concrete (NAC), with similar
characteristics (mix design, curing conditions, strength class,etc.Very large quantities of construction and
demolition wastes are generated yearly, only a small fraction is recycled. Among these wastes, concrete
is one of the most abundant. It can be crushed in order to produce new aggregates, called Recycled
Concrete Aggregates (RCA).RCA are composed of two phases: Natural Aggregates (NA) used for the
manufacture of the original concrete and hardened cement paste adhering to the natural aggregates.
Now, these recycled aggregates are essentially used in backfills for the construction of new roads. But
they could also be used for the manufacture of new concretes. These new concretes can be produced by
replacing different fractions of natural aggregates by RCA. (Rui´Vasco, Britoand Ravindra 2016). Topcu et
al. (2004) investigated that the recycling waste concrete aggregates in concrete production raises the
problem of workability. In particular, concrete with more than 50%waste concrete aggregates
experiences more workability problem.Figure 1.1: Recycled Aggregate
1.9 Justification of problem
Traditionally, the application of recycled aggregate is used as landfill. Nowadays, theapplications of
recycled aggregate in construction areas are wide. The applications aredifferent from country to
country.The main source of raw material for recycling of concrete waste comes from demolition of
concrete structures. The quality and purity of the raw material affect the quality of recycling products
and ultimately commercial acceptance of concrete recycling products, the process of manufacturing
concrete recycling products is relatively simple. BCSJ (2001).
Recycled aggregate can be used for construction of precast and cast in situ gutters and kerbs. It also Cost
saving: - There are no detrimental effects on concrete and it is expected that the i n c r e a s e i n t h e
c o s t o f c e m e n t c o u l d b e o f f s e t b y t h e l o w e r c o s t o f R e c y c l e d C o n c r e t e Aggregate
(RCA). ( Magdum 2007).Porosity of RAC are responsible gaps for the lower strength compared to NAC.
1.10 Statement of problem
Although aggregate has been used extensively in civil engineering construction in recent time. However
significant deficiency in its applicability in low mechanical and
durability properties compared to normal (natural) aggregate concrete. There is need to carry anoptimal
mix design that would reduce the porosity responsible for lower strength of Reincorporation of other
cementations materials such as metakaolin or microsilica would reduce the void or porosity.
1.11Project Aim/Objectives
The aim of this study is to develop high strength concrete made with recycled aggregate
using the rational mix design method. This would be achieve using the following objectives
1. To develop a mix design method to achieve high strength of 80N/mm using RCA.
2 To evaluate the compressive strength at different replacement level of cement with
metakaolin.
To determine the optimum replacement of RCA with natural aggregate.
