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International Journal of Science, Technology, Engineering and Management - A VTU Publication
One of the primary issues facing our current society is environmental conservation. The reduction of energy consumption and natural resources are some of the key elements in this regard and simultaneous utilization of waste materials being generated. Hence, considerable attention is given on these topics under sustainable development.
Concrete being the most vital and commonly used material
in the construction industry has been used from many
decades, meaning that a tremendous quantity is utilized and
also have to continue using it. The concrete uses up large
quantities of natural resources and creates an impact on
environment because of the debris created by the demolition
waste, which is being generally discarded in landfills. The
primary components of concrete being cement, water, coarse
and fine aggregates with the major fraction being the coarse
aggregates i.e., nearly 65% of the concrete is made up of
coarse aggregates. The production of aggregates that are
naturally occurring resources requires mining from the
quarries resulting in the depletion of resources at a rapid
pace.
The primary attention being on the preservation of
ecosystem and management of natural resources along with
the issue of waste disposal in particular the demolition
rubble has become a major concern for planning engineers
and environmentalists, resulting in attempts to replace
natural materials with the waste generated from demolition
of different structures. Researchers have proposed an
adequate treatment and reuse of concrete as an aggregate of
new construction. In order to make this possible, a
considerable amount of scientific studies were carried out
globally, primarily engaged in the handing of demolished
concrete and its mix design along with mechanical properties
and enhancement of durability aspects.
16 IJESM – VTU, 2021, Vol. 3, Issue. 1, pp. 15- 24 Dr. N. Suresh et. al.
While RCA are increasingly being used to render new
concrete in Western region and some of the far eastern
countries such as Japan and Korea, whereas there is a fairly
little understanding of the prospective use of these
aggregates in India. In addition, next to China India is the
world's largest cement user, implying that India is also one
of the primary consumers of concrete products such as fine
aggregates and coarse aggregates. Since aggregate resources
are not inexhaustible, information on the possible use of
RCA in the concrete manufacturing in India is essential.
The limitations of recycled concrete include higher creep,
larger drying shrinkage and greater chloride ion diffusion in
comparison with traditional concrete. This weakness shall be
negated by adding a definite volume of Fly ash to the
concrete, since Fly ash is expected to reduce the penetration
of concrete thereby reducing the creep, shrinkage and
chloride ion penetration [22].
It is clearly established that fire damage can cause explosive
spalling with the loss of strength due to spalling action of
some concretes under fire inhibits their usage in structures
requiring enhanced fire resistance. As a solution from the
literatures, the use of polypropylene fibres tends to be an
important step in reducing spalling of concrete. In addition,
the melting of polypropylene fibres provides an alternative
route that has been created, thereby releasing the internal
vapour pressure at higher temperatures [23]. The rationale
behind the experimental study is to assess the performance
of various mixes consisting of Recycled aggregates, Fly ash
and polypropylene fibers subjected to sustained higher
temperatures to produce concrete mixes, which comprises
more of sustainable materials without compromising the
performance.
The present investigation is to study the mechanical properties of RAC like flexural strength, compressive and split tensile strengths of mixes for different percentages of RCA, along with fly ash and 0.5% polypropylene fibers at sustained elevated temperatures of 200
0C, 400
0C and 600
0C
for 2 hours of duration.
1.1 LITERATURE REVIEW
Increased proportions of recycled aggregates in concrete can reduce the efficiency of masonry mortars, which cannot be compensated easily, but the majority of recycled aggregate mortars for descriptive applications has shown similar performances to traditional mortars and comply with the guidelines of European standards [1].
The applications of RAC have drawn global attention owing
to its socio, ecological and economic benefits in the future.
Out of several reasons, one important reason for utilizing
RAC in buildings is the resistance to spalling and improved
post-fire residual properties. With the inclusion of steel
fibers, the development of cracks gets postponed and
confines the crack opening in RAC thereby considerably
enhancing the fracture toughness and fracture energy of
RAC at elevated temperatures [2].
The fresh and rheological properties of SCC (Self-Compacting Concrete) with RCA both as fine and coarse aggregates reveals that Self Compacting qualities of concrete improves significantly with the levels of replacement
percentages of recycled coarse and fine aggregates included in the mixes for testing [3]. Also the structural behavior of elements casted using coarse aggregates of crushed recycled concrete from redundant components of the precast concrete industry had little influence on young’s modulus of elasticity [4].
The feasibility and quality of RCA obtained from crushed blocks of concrete obtained from demolished buildings had shown that RCA offers lower resistance to freezing / thawing than natural aggregates, but the degradation measured by Micro-Deval index, water absorption and porosity is less important [5]. Further, the properties of High Performance Concrete declines with the reduction in quality of RCA obtained from lower to higher grades of concrete [6].
RCA can be a potential answer for sustainability
developments since its residual performance was more often
comparable but slightly lower than the reference mixes
considered. In addition, the existence of impurities of non-
cementitious particles speeds up the damages on concrete at
higher temperatures [7].
The Mixed usage of Recycled Aggregates (MRA) as fine or
coarse aggregates fraction and the amount of usage of
cement showed decrease in permeability and strength of
concretes produced from sulphate resistant cement with the
increase in amount of MRA [8].
Studies were carried out on the concrete consisting of RCA
and insulation type of aggregates. A Recycled Aggregate
Thermal Insulation Concrete (RATIC) was created to lessen
the impact on environment with the improvement in
efficiency of the buildings. The study confirmed that beyond
400oC the residual compressive strength of concrete at
elevated temperatures reduces considerably and modulus of
elasticity deteriorates earlier than strength. Based on the
investigation, equations are developed for predicting
ultimate strain, peak strain, elastic modulus and residual
strength of RATIC after the exposure to higher temperatures
along with the compressive stress-strain relationship [9].
The inclusion of RCA in Hot-Mix Asphalt (HMA) can be a
means for encouraging sustainability in construction.
Presently, various investigators have evaluated the utilisation
of RCA in hot-mix asphalt. The results showed that HMA
with Recycled coarse aggregates covered with bitumen
emulsion displayed similar mechanical properties compared
to regular concrete mixes [10].
The Durability aspects of SCC prepared with RCA as full or
partial substitution for Natural Coarse Aggregates (NCA)
along with partial replacement of mineral admixtures for
cement were examined. The results showed that with the
usage of Metakaolin (MK) or Silica Fume (SF) at 10% by
weight of cement compensates for the lowering of durability
properties with 50% replacement of RCA, with Meta Kaolin
being more efficient than Silica Fume. At 100% replacement
of RCA for NCA, the mentioned pozzolans were inefficient
in balancing the loss of durability properties [11].
Shi Cong Kou et al had studied the influence of Fly ash as
Replacement for Cement on the Properties of RAC. The
study deals with the deficiency in the utilisation of recycled
aggregates by scientifically proving the results of including
Performance of recycled aggregate concrete along with polypropyle
Class F Fly ash on concrete properties. The outcome
indicated that the realistic way to develop a greater
percentage of RAC in concrete used for structures is by
including 25–35% Fly ash, so that the drawbacks persuading
with the usage of RA in concrete could be reduced [22].
Salah R et al. investigated on the Residual Mechanical
properties of RAC after subjecting the specimens
temperatures. The authors conducted an investigation where
six types of mixes was developed with combinations for
coarse aggregates produced from crushed limestone
aggregates, Recycled Concrete Aggregates (RCA) and river
gravel. The results indicated that for complete or partial
replacement of RCA for natural aggregates shows better
performance at elevated temperatures and are
to regular concrete. Further, no disintegration of concrete
specimens was observed in RCA concrete at elevated
temperature of nearly 750°C. The residual mechanical
properties show variations among the concrete mixtures with
various percentages of replacement for RCA [24].
1.2. Concrete at Sustained Elevated Temperature
Concrete when subjected to elevated temperature undergo
several transformations. Since aggregate occupies nearly 70
percent of volume in concrete, the behavior
elevated temperatures is largely affected by
aggregates used in concrete. The characteristics of
aggregates such as thermal expansion, thermal conductivity
and chemical stability plays a vital part in studying the
performance of concrete at elevated temperature.
1.3. Materials & Mix Proportions
Cement, Natural Coarse aggregates, Fine aggregates, Fly
ash, Water and Recycled coarse aggregates are used in
casting of specimens.
Cement: The cement used is Ordinary Portland cement
(OPC) of 53 grade which confirms to IS 12269:1987 with
the following properties - Specific gravity
fineness-2%, Standard consistency-27.75%, Initial setting
time and final setting time of 118 minutes and 255 minutes
respectively
Fine aggregates: Zone II Manufactured sand conforming to
IS 383- 1970, having a density of 1612 Kg/ m
gravity of 2.63 is used
Coarse aggregates: Crushed granite which are locally
available conforming to IS 383- 1970, with a Specific
gravity of 2.65 and passing through 20 mm sieve were used
as coarse aggregates.
Mineral admixture: Class F Fly ash is used which conforms
to IS 3812:2003 (part-1) with specific gravity of 2.01 and
18% standard consistency.
Polypropylene Fibers: Recron3S fibers of type CTP 2024
of Reliance make with length of 12 mm, melting point of
160-165OC with Specific gravity 0.90.
Water: Regular tap water that is free from salts and
impurities is used.
Performance of recycled aggregate concrete along with polypropylene fibers at sustained elevated temperature IJESM
on concrete properties. The outcome
indicated that the realistic way to develop a greater
n concrete used for structures is by
, so that the drawbacks persuading
with the usage of RA in concrete could be reduced [22].
Salah R et al. investigated on the Residual Mechanical
properties of RAC after subjecting the specimens to higher
temperatures. The authors conducted an investigation where
six types of mixes was developed with combinations for
coarse aggregates produced from crushed limestone
aggregates, Recycled Concrete Aggregates (RCA) and river
ated that for complete or partial
replacement of RCA for natural aggregates shows better
performance at elevated temperatures and are nearly similar
no disintegration of concrete
specimens was observed in RCA concrete at elevated
temperature of nearly 750°C. The residual mechanical
properties show variations among the concrete mixtures with
various percentages of replacement for RCA [24].
e at Sustained Elevated Temperature
Concrete when subjected to elevated temperature undergo
several transformations. Since aggregate occupies nearly 70
behavior of concrete at
elevated temperatures is largely affected by the type of
aggregates used in concrete. The characteristics of
aggregates such as thermal expansion, thermal conductivity
and chemical stability plays a vital part in studying the
performance of concrete at elevated temperature.
Cement, Natural Coarse aggregates, Fine aggregates, Fly
ash, Water and Recycled coarse aggregates are used in
: The cement used is Ordinary Portland cement
(OPC) of 53 grade which confirms to IS 12269:1987 with
Specific gravity-3.14, percentage
27.75%, Initial setting
time and final setting time of 118 minutes and 255 minutes
: Zone II Manufactured sand conforming to
ing a density of 1612 Kg/ m3 and specific
: Crushed granite which are locally
1970, with a Specific
gravity of 2.65 and passing through 20 mm sieve were used
: Class F Fly ash is used which conforms
1) with specific gravity of 2.01 and
: Recron3S fibers of type CTP 2024
of Reliance make with length of 12 mm, melting point of
water that is free from salts and
Recycled Coarse Aggregates (
a) The waste concrete cubes and
in the laboratory are collected and transported to the
crushing yard.
b) The samples were fed and crushed by mechanical crushers
c) The crushed samples are segregated into the respective
sizes of 4.75mm, 12.5mm, 20mm down etc.
d) The different sizes of aggregates are dumped
and transported
e) Since the crushing machine used for RCA is same as that
of NCA, the RCA obtained will be of similar in size of
that of NCA
IJESM - VTU, 2021, Vol. 3, Issue.1 17
ggregates (RCA)
The waste concrete cubes and cylinders, which were tested
are collected and transported to the
The samples were fed and crushed by mechanical crushers
The crushed samples are segregated into the respective
sizes of 4.75mm, 12.5mm, 20mm down etc.
The different sizes of aggregates are dumped separately
Since the crushing machine used for RCA is same as that
of NCA, the RCA obtained will be of similar in size of
16 IJESM – VTU, 2021, Vol. 3, Issue. 1, pp. 15
Fig1. Different Stages of Production of RCA
*Details of Corresponding Author: AddressDepartment of Civil Engineering, The National Institute of EngineeringMysore; Phone No.-9986590409; E-mail – [email protected]
18 5- 24
Different Stages of Production of RCA
Address:-Assistant Professor, Department of Civil Engineering, The National Institute of Engineering,