Development Of High Strength Concrete From Recycled Aggregate Concrete

INTRODUCTION
1.9 Background of Study
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). (Geng
and 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 byproducts 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, Brito
and 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
1.10 Justification of problem
Traditionally, the application of recycled aggregate is used as landfill. Nowadays, the
applications of recycled aggregate in construction areas are wide. The applications are
different 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
increase in the cost of cement could be offset by the lower cost of Recycled Concrete
Aggregate (RCA). ( Magdum 2007).
Porosity of RAC are responsible gaps for the lower strength compared to NAC.
1.11 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 an
optimal mix design that would reduce the porosity responsible for lower strength of RAC
Incorporation of other cementations materials such as metakaolin or microsilica would
reduce the void or porosity.

1.12 Project 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
 To develop a mix design method to achieve high strength of 80N/mm2
using RCA.
 To evaluate the compressive strength at different replacement level of cement with
metakaolin.
 To determine the optimum replacement of RCA with natural aggregate.
 To measure the tensile strength at different replacement level.

1.13 Methodology
Experimental method is used due to its versatility.
To establish a comparative basis control specimen of concrete made with natural
aggregate (granite) were prepared with RAC recycled aggregate concrete.
In order to obtain the optimum replacement level natural aggregate is replaced with RCA
in the following percentage 10%, 20%, 30% and 40%. To reduce the porosity or voids in
RAC , metakaolin was used to replace Portland cement by 5%, 10%, 15%.
36 cubes and cylinder specimens are made for compressive strength test and Tensile
strength equivalent samples are also made for the control specimen.
The specimens are tested subject to the variables of testing ages of 7, 14 and 28days
respectively.

1.6 Scope of the work
The scope of this project was to investigate the possibility of using low cost recycled coarse
aggregates as an alternative material to coarse aggregate in high strength structural concrete.
The study covers 7, 14 and 28 days casting and curing of cubes 100 x 100 x 100 dimension,
comprising of 36 concrete cubes and cylinder in different mixes, were made for compressive
strength test and tensile strength test involving recycled aggregate and natural aggregate. The
physical and mechanical properties, water absorption, compressive strength and tensile
strength are measured at various ages.

1.7 Delimitation of the work
This work is limited to the physical and mechanical properties, water absorption,
compression and durability aspects such as exposure of RAC to aggressive agents are not
considered.

1.8 Significance of Study
This study provides a design guideline on the application of recycled aggregate in the
production of high strength. The application of RA in construction could be achieve twofold
advantage.
 Reduction of environmental hazards
 Cheaper and economic advantages.

1.9 Layout of Project
This paper is organized into five (5) chapters followed by bibliography, references and
appendices. Each of the chapter is further divided into sections and subsections for clarity of
purpose and presentation. Brief overview of the contents of each chapter are as follows;
• Chapter 1 presents the introduction to the work with highlights on the background of study,
justification of problem, statement of problem, aims and objectives of the study, methodology,
scope of the work, delimitation of the work, significance of the study and layout of project.
• Chapter 2 provides a review of relevant literature, overview of recycling process, as well as
comparison of recycled aggregate and natural aggregate. This chapter also discussed the
previous investigation and testing done with recycled aggregate.
• Chapter 3 includes the preliminary design and information on the recycled aggregate testing,
sieve analysis and design of the concrete mix.
• Chapter 4 discusses the results and analysis of all experimental results obtained from the
testing procedures.
• Chapter 5 contains the conclusions of the research and recommendations on further work.