Influence of recycled aggregate on flexural behaviour of reinforced
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Department of Civil Engineering, University College of Engineering, Osmania University, Hyderabad, India
ABSTRACT: Conservation of natural resources and protection of environment is the key to sustainable
development. Construction engineers and the researchers have to share this critical responsibility. Research is
in progress to explore new civil engineering materials which can contribute to the sustainable development.
The research work on flexural behaviour of recycled aggregate concrete beams presented here is one such
attempt to establish performance of recycle aggregate concrete (RAC) as structural grade concrete. In the
present paper, two grade of RAC, viz., M25 and M30 and two types of sections namely, under reinforced and
balanced sections were considered for studying flexural behaviour (ultimate load, ultimate moment,
deflections, strains, moment-curvature relations and crack pattern) of beam specimens. For comparative study,
corresponding type of natural aggregate concrete (NAC) beam specimens were investigated for flexural
behaviour. In all 8 beams of RAC and 8 beams of NAC were tested for flexure under two point loading. The
investigations indicated encouraging results for RAC beams in all respects, thus, pointing to recycled
aggregate as potential alternative source of aggregate of the 21st Century.
1 INTRODUCTION balance and to ensure sustainable development,
there is an urgent need to restrict the use of natural
Continued growths in population, demand for resources. This means, the engineers and scientists
better quality of life and evolutionary have to explore the possibility of finding
industrialisation have resulted in rapid alternative materials or to adopt recycling
urbanization. Obviously, this explosion into an technology. While alternative to the cement in
urban way of life will demand enormous resources terms of fly ash and other pozzolanic materials
and supply of construction material required to were evolved for use in concrete, the alternative
build the infrastructure at a rapid pace. Civil materials to natural aggregate are being explored.
engineering structures such as housing, water This research work is a step forward to explore a
supply, transportation, sanitation etc, form a major popular alternative to the natural aggregate for use
component of the infrastructure development in concrete. The present work is an attempt to
supporting life in these metropolis and big cities. provide solution to the problems and concerns
Concrete is a predominant construction material raised by the environmentalist and contribute to
required for it and obviously, constituents of the sustainable development.
concrete, namely, cement and aggregates are in
high demand. This is evident from the fact that the
construction industry consumes 10 billion tonnes 2 NEED FOR THE PRESENT WORK
of concrete annually. Correspondingly, the
quantity of cement and aggregate requirement Enormous growth in construction industry and
would be in the range of 1.5 billion tonnes and 10 consequent to that, the growing demand for natural
billion tonnes respectively. aggregates is compounded by (i) considerable
The huge demand for cement and aggregates is decline in the availability of good quality natural
obviously alarming in view of growing concern aggregate in the vicinity of construction site, and
expressed by environmentalist on excessive (ii) stringent anti pollution and environmental
tapping of natural resources. Conservation of regulation for conservation of natural resources.
natural resources has become a key word and civil Simultaneously, there has been enormous increase
engineering materials are no exception to this in the quantities of demolished concrete, the
reality. Further, in order to maintain ecological disposal of which posed a serious problem due to
shortage of dumping sites and steep rise in construction engineer with a right solution for
dumping cost. The reports indicate that the proportioning recycled aggregate concrete
quantity of concrete discarded every year has especially suitable to Indian conditions.
reached the staggering figure of about 100 million A comprehensive literature review reveals
tonnes in the United States, and European significant work in the field, but most of the
Economic Communities; and 25 million tonnes in research work is on basic properties of recycled
Japan, France, and United Kingdom. It is estimated aggregate and recycled aggregate concrete. No
that these quantities of discarded material will research work is reported on performance of
increase nearly three fold by 2010 A.D. reinforced recycled aggregate concrete (RRAC)
The solution to the above problem is found in structural elements in flexure. As a matter fact,
adopting the recycling technology. Recycling not structural elements subjected to flexure are
only solves the waste disposal problem but also predominant component of a structural system.
reduces the cost and conserves the non- renewable Thus, structural performance of RRAC flexural
natural resources. Thus, attempts were made by elements needs to be investigated. The present
researchers to investigate the properties of recycled work is an attempt to initilise research
coarse aggregate (hereafter referred as recycled investigation on the vital aspect of flexural
aggregate) and study the performance of concrete behaviour of RRAC beam elements.
made out of recycled aggregate. BCSJ 1978, Buck,
A.D 1977, Hansen & Narud 1983, Hasaba,et.al.
1981, Ravindrarajah & Tam 1985, Frondistou- 3 OBJECTIVES
Yannas 1977, Malhotra 1976, Mukai 1979,
Gerardu & Hendrick 1985, Rasheeduzzafar & a) To evaluate the load carrying capacity and
Khan 1984, Ravande Kishore & Bairagi 1990 are moment carrying capacity of RRAC beam
among the notable researchers who have carried elements.
out research work on characteristics of recycled b) To examine the load-deflection and load-strain
aggregate and short term and long term behaviour characteristics of RRAC beam elements.
of recycled aggregate concrete. All of them have c) To study the moment curvature relationship for
indicated that, attached cement mortar of recycled RRAC beam elements.
aggregate particles is the main reasons for its
modified characteristics. A common observation is
the higher water absorption accompanied by lower 4 EXPERIMENTAL PROGRAMME
specific gravity values for recycled aggregate.
Further, the workability of recycled aggregate The experimental programme was carried out in
concrete is found to be lower in view of higher three phases as indicated below.
water demand of recycled aggregate due to the Phase 1: Evaluation of physical properties of
porous nature of adhered cement mortar on its natural aggregate and recycled aggregate.
surface. However, researchers have observed that a Phase 2: Concrete mixture proportioning and
properly proportioned fresh recycled aggregate preparation of test specimens.
concrete is cohesive. As regards to properties of Phase 3: Flexural testing of specimens.
hardened recycled aggregate concrete, 5 to 10
percent drop in compressive strength and 10 to 30 4.1 Phase 1
percent drop in modulus of elasticity is reported by
the investigators. However, reports on the The physical properties of natural fine aggregate
performance of recycled aggregate concrete in (NFA), natural coarse aggregate (NCA), recycled
indirect tension and flexure are contradicting with, coarse aggregate (RCA) and recycled fine
some reporting on par strength, while others aggregate (RFA) are evaluated to account them in
indicating 10 to 15 percent lower values. High the mixture proportioning. Important physical
values of creep and shrinkage strains are other properties such as specific gravity, water
common observation reported by various absorption, etc. were investigated by performing
investigators. A notable research work in this field tests as per procedure given in Indian standard
of research is on development of comprehensive specifications [IS 2386 1970]. The results of these
mix design chart and guidelines exclusively for tests are presented in Table 1.
recycled aggregate concrete by Ravande Kishore in
1994.This development has provided the
Table 1. Physical properties of aggregates comparative study, eight natural aggregate
concrete (NAC) beams of same type were also
NCA RCA NFA RFA
Property cast. The details of the types of beam viz., beam
notation, and reinforcement details are presented in
Sp. gravity 2.60 2.32 2.63 2.45 Table 3. The typical beam reinforcement and
Fineness loading details are shown in Figure 1.
6.73 6.64 2.88 2.78
kg/m3 Table 3. Reinforcement details for beam specimens
a) Loose 1387 1234 1550 1440 Beam Main reinf. & Reinf. No. of
b) Comp. 1534 1420 1694 1582 notation stps. (%) beams
Water M25 NU 2 nos. - 10 , 0.90 2
0.70 4.50 0.50 1.1
absorption, % 2 nos. - 8
Attached 6 @ 110mm c/c
cement - 33.0 - - M25 RU 2 nos - 10 , 0.90 2
mortar, % 2 nos. - 8
6 @ 110mm c/c
M25 NB 4 nos. - 10 1.10 2
4.2 Phase 2 6 @ 110mm c/c
M25 RB 4 nos. -10 1.10 2
Two grades of concrete viz. M25 and M30 were
6 @ 110mm c/c
considered for the investigation. The mixture
M30 NU 4 nos.- 10 1.10 2
proportions were worked out as per the guidelines
given in Indian standard specifications [IS 10262 6 @ 110mm c/c
1982]. Twenty eight days compressive strength of M30 RU 4 nos.- 10 1.10 2
normal portland cement was taken in to account in 6 @ 110mm c/c
design of concrete mixtures. For design of recycled M30 NB 2 nos.- 12 , 1.34 2
aggregate concrete (RAC) mixtures, RK method of 2 nos. -10
mixture proportioning [Ravande Kishore 1994] 6 @ 110mm c/c
was used. Fifty percent of natural fine aggregate M30 RB 2 nos.- 12 , 1.34 2
was replaced by recycled fine aggregate (RFA). 2 nos.- 10
The details of concrete mixtures of each grade are 6 @ 110mm c/c
given in Table 2. N-natural, R-recycled, U-under reinforced,
Table 2. Mix proportions of concrete
Materials Grade of concrete
NAC RAC NAC RAC
Cement, 385 396 429 443
FA, 574 334 545 303
kg/m + +
CA, 1190 1114 1183 1125
Water, 188 202 189 202
W/C 0.49 0.51 0.44 0.45
* RCA + RFA Figure 1. Typical beam reinforcement and
Eight recycled aggregate concrete (RAC) beams
were cast to study the flexural behaviour. For
Standard procedure was adopted in preparation 5 DISCUSSIONS
of beam moulds, placing of reinforcement and
moulding of beam specimens. While, natural 5.1 Properties of recycled aggregate
aggregate concrete mixing was done as usual, the
mixing of recycled aggregate concrete required Important physical properties of both natural
necessary care about presoaking of aggregate aggregate and recycled aggregate are presented in
before mixing and other measures as suggested in Table 1. The test results indicate that recycled
guidelines on mixing of RAC [Ravande Kishore aggregate exhibited lower specific gravity and
1994]. Workability tests in terms of slump and higher water absorption, when compared with
compaction factor were carried out to ensure corresponding values of natural aggregate. While,
desired workability. Three standard cubes were fineness modulus of recycled aggregate is more or
cast for each grade of concrete along with less same as that of natural aggregate, bulk density
moulding of beam specimens to evaluate of recycled aggregate is found to be on lower side.
compressive strength of concrete. The demoulding This significant change in specific gravity and
was done after 24 hours and the specimens were water absorption values in case of recycled
cured by conventional method for 28 days. aggregate has bearing on the properties of RAC.
This is obviously discussed in detail in the
4.3 Phase 3
5.2 Flexural behaviour of recycled aggregate
Two point transverse load test was performed on concrete
beams specimens to evaluate their flexural
behaviour. After curing, the specimens were given 5.2.1Ultimate Load
a white wash and identification number. The white Ultimate load for each of the four types of M25
wash was given to enable the detection of cracks grade beam specimens and four types of M30
during testing at various stages of loading. A steel grade beam specimens (RAC and NAC) are shown
frame with inner dimensions of 600x200x350mm in Table 4.The test results show that RAC type
with bolts at top and bottom to hold dial gauges beams failed at relatively lesser loads in both cases
was fixed to the beams to measure strains over a i.e. under reinforced section and balanced section.
200mm gauge length. Three dial gauges were fixed The percentage reduction of ultimate load is in the
at the top and one-third span sections. The beam range of 5.6% to 7.0% for under reinforced section
deflections were measured by means of three dial and 2.7% to 2.9% for balanced section. It may be
gauges set below the beam at mid span and one- noticed that, again balanced section indicated
third span sections. The dial gauges used has a slightly better performance when compared with
least count of 0.01mm. The beams were tested on a under reinforced section. As shown, the range of
universal testing machine (2000kN capacity) under ultimate load for M25 grade RAC concrete is
two point loading at one-third point of span as 118kN to 133 kN and for M30 grade NAC, it is
indicated in Figure 1. 132 kN to 142 kN. Thus, RAC beams exhibited
Dial gauge readings were recorded for every almost on par performance in terms of load
incremental load of 5.0 kN distributed equally over carrying capacity.
two points. Strains, both in compression and
tension zone, and deflections were monitored 5.2.2 Ultimate moment
during the test at various stages of loading. Cracks The values of ultimate moment carrying capacity
at various stages of loading were observed and of four types of M25 grade beams and four types
marked on beam specimens. The test results of M30 grade beams (RAC and NAC) are
recorded pertaining to load Vs deflection, load Vs presented in Table 4. As indicated in Table 4, the
strain are presented in graphical forms in Figures range of ultimate moment carrying capacity of
2-3. Further, moment curvature relationship are M25 grade RAC beams is 25.6 kNm to 28.8 kNm
also plotted and shown in Figure 4. Ultimate load and for M30 grade RAC beam, it is 28.6 kNm to
carrying capacity and ultimate moment carrying 30.8 kNm. Theses values are on lower side by
capacity (theoretical & experimental) of various 5.5% to 3.0% for M25 grade concrete beams and
types of beams (RAC & NAC) are also recorded 7.1 to 2.5% for M30 grade concrete beams when
and presented in Table 4. compared to corresponding values for NAC.
Further, it may be noted that balanced section
beams of all types exhibited slightly better NAC and RAC under reinforced beams of M25
performance with lower percentage reduction in grade concrete indicate almost same deflections up
ultimate moment carrying capacity of beams. to a load of 80 kN. The same trend is observed for
A comparison of theoretical and experimental M30 grade under reinforced beams. As regards to
values of ultimate moment carrying capacity of balanced section beams of both NAC and RAC
beams presented in Table 4 show that all types of types, the deflection were almost same up to a load
beams exhibited satisfactory performance. The of 120kN for M25 and M30 grade concrete.
experimental values are found to be 26.7% to However, it may be noticed that, in general, RAC
48.9% more than the theoretical values. Even RAC beams indicated 2.2 to 15.6% higher deflection at
beam exhibited 26.7% to 42.6% higher the same load when compared with corresponding
experimental values compared to corresponding values for NAC beams. Another significant
theoretical values. This clearly indicate that observation is that balanced sections beam of all
structural performance of RAC beams is more than types indicated relatively higher stiffness. This is
satisfactory and hence recycled aggregate may be obvious from the fact that, the maximum deflection
encouraged as alternative aggregate in place of of 16mm is observed at 118 kN at mid span section
natural aggregate. for M25 grade RAC under reinforced beam. The
corresponding deflection for balanced section
5.2.3 Load Vs deflection beam of same grade and type of concrete is
Load verses Deflection curves for beams namely 7.0mm. Like wise, for M30 grade RAC under
(i) M25 NU & M25 RU, (ii) M25 NB & M25 RB, reinforced beam, the mid span deflection is found
(iii) M30 NU & M30 RU, and (iv) M30 NB & to 17.8mm at 132 kN. The corresponding
M30 RB are presented in Figure 2 (a to d). It may deflection for balanced section of same grade and
be noted that, load Vs deflection curves of natural type of concrete is 10.3 mm.
aggregate concrete (NAC) and recycled aggregate Although, RAC beam specimens indicated
concrete (RAC) beam specimen of a particular higher deflection, compared to NAC beam
grade are plotted in one figure to bring out specimens, the deflections are within acceptable
comparative behaviour of NAC and RAC beams. limits. All the load Vs deflection curve reflect this
For both M25 and M30 grades of concrete, the fact at 50% of the failure load. Thus, performance
load Vs deflection profile of NAC & RAC beams of RAC beam specimens in terms of deflection
is identical. Further, it can be observed that, both criteria is quite encouraging.
Table 4. Ultimate load and ultimate moment of various types of beam specimens
Beam Ultimate Percentage Exp. Percentage Theo. Percentage
notation load, reduction of ultimate reduction of ultimate increase over
kN load over moment, moment over moment, theoretical
NAC, kN-m NAC, % kN-m moment, %
M25 NU 125 5.60 27.10 5.50 18.20 48.9
M25 RU 118 25.60 40.6
M25 NB 137 2.90 29.70 3..03 20.20 47.0
M25 RB 133 28.80 42.6
M30 NU 142 7.00 30.80 7.14 20.70 48.8
M30 RU 132 28.60 38.2
M30 NB 146 2.70 31.60 2.53 24.30 30.0
M30 RB 142 30.80 26.7
5.2.4 Load Vs strains 5.2.5 Moment – curvature relationship
Mean values of strain measured at mid span Moment curvature relationship for both M25 and
section are shown in Figure 3 (a to h) for each of M30 grades of RAC under reinforced and balanced
the four types of M25 grade beams and M30 grade beam sections are presented along with the
beams (RAC and NAC ). All the four types of corresponding moment curvature relationship for
RAC beams indicated relatively higher strain when NAC beam specimens in Figure 4 (a to d),
compared with corresponding NAC beams. (M25NU & M25RU, M25NB & M25RB, M30NU
Similarly, beams with balanced section have lesser & M30RU, and M30NB & M30RB respectively).
strains when compared with corresponding under The figures clearly depict that both RAC and NAC
reinforced sections. Although, the figures indicate beams follow the same trend. However, it may be
the strain differential up to 29% for the range of noticed that for the same value of moment, curves
maximum load of 120 to 145 kN, there is hardly for RAC beam specimen indicate higher curvature
any difference in strain values at 50% of the up to 31% indicating less ductility for RAC beams.
maximum load for each of the beam specimens. It Further, moment curvature relationship depict that
may be noted that, strain differential increase as curvature tends to be almost same as beam
the magnitude of load applied increase. Thus, RAC approach its ultimate moment carrying capacity,
beam specimens exhibit satisfactory performance with NAC beams having up to 10% higher ultimate
in terms of strains. moment value. Thus, the moment curvature
relationships for RAC beam specimens are
comparable with that of NAC beam specimens.
NU 100 NB
0 10 20 30 0 5 10 15
Deflection, mm Deflection, mm
(a) M25 NU and M25 RU (b) M25 NB and M25 RB
RU 60 RB
0 10 20 30 0 10 20 30
Deflection, mm Deflection, mm
(c) M30 NU and M30 RU (d) M30NB and M30 RB
Figure 2. Load-deflection curves at mid span section for various types of beam
Strain 103 Strain 103
(a) M25 RU (b) M25 NU
Strain 103 ³ Strain
(c) M25 RB (d) M25 NB
Strain 103 Strain 103
(e) M30 RU (f) M30 NU
Strain 103 Strain 103
(g) M30 RB (h) M30 NB
Figure 3. Variation of strain with load at mid span section
NU 20 NB
15 RU RB
0 10 20 30 40 0 10 20 30 40
Curvature, x104 Curvature, x104
(a) M25 NU and M25 RU (b) M25 NB and M25 RB
20 Moment, kN-m NB
0 10 20 30 40 0 10 20 30 40
Curvature, x104 Curvature, x104
(c) M30 NU and M30 RU (d) M30 NB and M30RB
Figure 4. Moment-curvature relationships at mid span section for various types of beam
5.2.6 Crack width 5.2.7 Influence of recycled aggregate on flexural
The cracks width were measured by conventional behaviour
means and it was found that the crack width were Although, flexural behaviour of RAC beams is
in the range of 0.25 to 1.3 mm. Since crack width relatively inferior when compared with NAC
for different cracks were varying in each of RAC beams, their performance level is comparable.
and NAC beams, no specific conclusion can be However, the main reason for relatively inferior
drawn about either RAC or NAC beam cracking flexural behaviour of RAC beams can be attributed
relatively wider. Further, the pattern of crack to the attached mortar component of recycled
development was found to be identical in all types aggregate. Weak bond between old mortar and the
of beam specimens. It may therefore be said that, virgin aggregate together with porous nature of
structural performance of RAC beams in terms of attached mortar component may have caused
cracking is at par with NAC beams. detrimental effect in respect of structural
behaviour. Relatively inferior but acceptable level
of performance in flexure at greatest advantage of Buck,A.D. 1977. Recycled concrete as sources of
attaining sustainable development is certainly a aggregate, ACI Journal, May: 212-219.
positive feature of this research investigation. Frondistou – Yanaas.S. 1977. Waste concrete as
aggregate for new concrete, ACI Journal,
6 CONCLUSIONS Gerardu, J.J.A. & Hendricks C.F. 1985. Recycling
of road pavement material in the Netherlands,
A maximum of 7.0% reduction in ultimate Rijkswaterstaat Communications, No.38, the
load and ultimate moment is observed for Hugue.
RAC beam specimens. Further, the Hansen,T.C. & Narud, 1983. Strength of recycled
experimental values of ultimate moment for aggregate concrete made from crushed concrete
RAC beams are 26.7% to 42.6% higher than coarse aggregate, Concrete International
the theoretical values. Design and Construction ,Vol.5, No.1:79-83.
Up to 15.6% higher deflections are observed Hasaba, S., et.al. 1981. Drying shrinkage and
for RAC beam specimens. durability of concrete made of recycled
No significant change in strain values are concrete, Trans, of the Japan Concrete Institute,
noted at 50% of ultimate load for any type Vol.3:55-60.
of RAC beam specimens. However, up to a IS 383, 1970. Indian standard specification for
29% more strain is noted for RAC beam coarse and fine aggregate from natural sources
specimen at ultimate load. for concrete, Bureau of Indian Standards, New
Moment curvature relationship of RAC beams Delhi.
follow same trend as that of NAC beams IS 10262, 1982. Recommended guidelines for
with almost same curvature at ultimate concrete mix design, Bureau of Indian
moment values. Standards, New Delhi.
No significant change in development of crack Malhotra,V.M. 1976. Use of recycled concrete as
and crack width is noted for RAC beam new aggregate, Report 76-18, Canada Centre
specimens. for Mineral and Energy Technology, Ottawa,
Mukai,T., et.al. 1979. Study on reuse of waste
7 CLOSING REMARKS concrete for aggregate of concrete, Seminar on
Energy and Resources Conservation in
The discussions and conclusions presented above Concrete Technology, Japan-U.S.Co-operative
favour the use recycled aggregate as alternative Science Programme, Sanfrancisco.
material in place of natural aggregate. The Rasheeduzzafar, & Khan,A. 1984. Recycled
increasing environmental awareness together with concrete –a Source of new aggregate, Cement
earnest need of conserving natural resources and Aggregate (ASTM),6, No.1:17-27.
certainly encourage the use of recycled aggregate Ravande Kishore, & Bairagi,N.K. 1990. Mix
for making concrete. Recycled aggregate concrete design procedure for recycled aggregate
is indeed a construction material of 21st Century for concrete, Construction and Building Materials,
sustainable development. Vol.4, No.4, December: 188-193.
Ravande Kishore, 1994. Some studies on recycled
aggregate concrete, Ph.D thesis submitted to
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