Durability of Recycled Aggregate Concrete with Conventional and Equivalent Mortar Volume Method: A Review

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 09 Issue: 07 | July 2022 www.irjet.net p-ISSN: 2395-0072
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Durability of Recycled Aggregate Concrete with Conventional and
Equivalent Mortar Volume Method: A Review
Nazneen Nazeer1, Praveen Mathew2
1P G Student, Dept. of Civil Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India
2Professor, Dept. of Civil Engineering, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India
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Abstract - Recycling construction wastes to prepare
structural concrete is an effective measure to solve the dual
problems of resource shortage and environmental pollution.
RA is an alternative and reliable source for replacement of
naturalaggregates. The concrete structures in service always
subject tothe coupled effect of multiple environmental factors
such as chloride attack, carbonation, water penetration and
aggressive agent penetration etc., which accelerates the
deterioration of durability. Durability resistance of recycled
aggregate concrete with diverse substitution rates using
conventional mix proportion compared with equivalent
mortar volume method under different factors are reviewed
in this paper. Durability resistance of RAC with conventional
and equivalent mortar volume mix method results from
several research are consolidated in this review paper.
Key Words: Chloride attack, Durability, RAC (Recycled
Aggregate Concrete), RCA (Recycled Coarse Aggregate),
Carbonation, EMV (Equivalent Mortar Volume).
1. INTRODUCTION
In the new context of a circular economy where the
environmental aspect is highlighted, the exploitation of
natural resources and generation of waste must be reduced.
The recycling of the old concretes can contribute to reduce
the extraction of the natural resources and to reduce the
waste deposit areas. For the resources conservation,
cleaner production and sustainable development, RAC is
considered as an ideal alternative to the traditional
concrete. Therefore, exploring the feasibility of RAC used as
structure concrete to expand the application range and
improve utilization rate of C&DWs is significant. Durability
is one of the main topic of concern while using recycled
aggregates in concrete constructions. The concrete
structures in service always subject to the coupled effect of
multiple environmental factors such as chloride attack,
sulphate attack, carbonation, and aggressive agent
penetration etc., which accelerates the deterioration of
durability. The properties related to the durability are
usually the risks of steel reinforcement corrosion
(carbonation, chloride penetration, air/water permeability,
porosity).
2. RECYCLED AGGREGATE
British standard BS 8500-2 (BSI, 2006) defines RCA as
recycled aggregate with maximum masonry/fines content
of 5%, maximum lightweight material/asphalt content of
0.5% and maximum other foreign materials content of
1%. Recycling of demolished concrete into aggregate is
environmentally beneficial by preserving natural
resources, by waste reduction and by preserving landfill
space. The properties of recycled aggregate mainly
depends on the properties of its parent aggregate
concrete and also on the quantity and quality of cement
mortar, which is attached to the grains of recycled
aggregate and on recycling methods.
Fig -1: Recycled aggregate of size range 12.5mm and
20mm
From practical experience, Mirjana shown that the bulk
density of recycled aggregate was on the average by 10%
lower compared to the bulk density of natural aggregates
[2]. The researchers from the University of Hong Kong
recommend that the amount of recycled aggregate in
structural concrete should range from 20% to 30%, in
order to ensure that the maximum water absorption of
aggregate used is less than 5%. [3]The water absorption
value of the classically recycled coarse aggregate ranges
within the interval from 3.5% to 10%, and for the fine
aggregate, within the range of 5.5% to 13% from the
results of Marinković [3].

3.PROPERTIES OF RECYCLED AGGREGATE
CONCRETE
From studies of Sherif Yehia, concrete made with RA
showed less durability due to high pore volume which
led to high permeability and water absorption. High
water absorption isdue to cement paste adhered on the
aggregate surface [9]. More water is needed for RAC to
achieve similar workability to that of NAC due to higher
absorption capacity of recycled aggregate, due to the
presence of impurities and attached cement hydrates. As
the RA content increases in the mix, the workability
reduces especially at lower w/c ratio [10]. Malesev
experiments showed that for 50 to 100% replacement of
virgin aggregates with the recycled aggregate decreases
the compressive strength by 5 to 25 % and a reduction
of up to 10% in split tensile strength was observedwhen
virgin aggregate was substituted with recycled
aggregate, also flexural strength reduction was observed
to be 10% that of RAC [11]. Specific gravity and bulk
density are relatively low for recycled aggregates when
compared to fresh granite aggregate. This is mainly due
to the high water absorption of the RA, as mortar has
higher porosity than aggregates and as the size of recycled
aggregate increases, achieved strength increases [12].
4. MIX DESIGN METHODS
4.1 Conventional method
In studies made by Emmanuel, the conventional
methods include the absolute volume approach
according to the American Concrete Institute (ACI)
standard or the Department of Environment (DoE)
concrete mix design method given by the British
specification [13]. A percentage ofnatural aggregates are
replaced with recycled aggregates in this method without
quantitatively considering the attached old mortar on the
recycled aggregate. Conventional methods require more
cement content compared to that proportioned using the
EMV mix design method [13]. Here RCA is treated as a
homogenous material as that of natural aggregate.
4.1 Equivalent mortar volume method
RCA is considered as a two-phase material comprising
residual mortar and original virgin aggregate. In the
proposedmethod, the RCA concrete mix is proportioned
to have the same TM volume as a companion concrete
mix made entirely with fresh NAs, with the companion
mix made with the same type of coarse aggregate as that
in RCA. The salient feature of the proposed mix design
method is the treatment of RM in RCA as part of the TM
content of RCA concrete.
Fig -2: Recycled aggregates containing attached
mortar
Fig -3: Recycled aggregates devoid of attached mortar
aftertreatment
Concrete proportioned based on this concept is shown to
havethe same or superior fresh and hardened properties
compared to equivalent conventional concrete with the
same amount of mortar [14]. Steps in determination of
equivalent mortar volume mix method involves:
Determination of companion concrete mix proportions
made with natural aggregate. That is the determination
of required RCA and fresh natural aggregate proportions
in companion RCA concrete mix. Determination of
required water, cement, and fine aggregate proportions
and minimum replacement ratio in RCA concrete mix.
Maximum residual mortar content in RCA concrete mix
made with 100% RCA through an equation given by G.
Fathifazl and through an experiment the residual
mortar content of recycled aggregate can be measured.
5.DURABILITY FACTORS
5.1 Chloride attack
. All RCA-concrete examples made from mixtures
proportioned using the EMV approach were found to
have apparent chloride diffusion coefficients of the same
order of magnitude as specimens made from
traditional structural-

grade concrete. In fact, RCA-concrete specimens without
additional cementitious ingredients and proportioned
using the EMV approach had apparent chloride diffusion
coefficients that were lower than those of specimens
prepared of mixture and proportioned using the
traditional method. The resistance
with substitution rate.
to chloride penetration of RCA-concrete specimens made
of mixtures proportioned by the EMV method was
improved by the addition of supplementary cementitious
materials (fly ash or bfs) as partial replacement for
ordinary portland cement. . In comparison to the
reduction brought about by the inclusion of fly ash, the
addition of bfs decreased the apparent diffusion
coefficient of RCA-concrete mixes created using the EMV
method by 120–200 percent. According to Abdelgadir
Abbas'analysis, using the EMV approach in combination
withadditional cementitious elements results in concrete
that is highly resistant to chloride penetration. [6]
Concrete's resistance to chloride corrosion was
evaluated. At four separate F-T cycles, the total passed
charge with regard to theRAC was calculated (0, 100, 200
and 300 cycles). It demonstrated a substantial link
between the overall charge passing amount, the RCA
substitution level, and the number ofF-T cycles. According
to ASTM C1202 (2012), the ability of chloride to
penetrate is low for total passed charges between 1000
and 2000, moderate for charges between 2000 and 4000,
and high for charges beyond 4000 coulombs. As shown
determinants of how long recycled concrete will last in a
challenging environment. Therefore, concrete and RCA
modification procedures might be taken into
consideration in order to increase the RAC's durability
and utilisation rate. [1] This condition is caused by the
old mortar's high porosity andmicrocracks, which cause
a high permeability for chloride ions. The F-T cycles
make this damage worse. The resistivity of recycled
aggregate concrete to chloride ion penetration was still
lower than that of regular aggregate concrete after ten
years of outdoor exposure. Fly ash greatly increased the
concrete mixture's resistance to chloride ion penetration
[16].
5.2 Freeze thaw cycles
According to the ASTM C 666-97 protocol, rapid freezing
and thawing in water was used for the freeze-and-thaw
experiments [15]. For a maximum of 300 cycles, the
relative dynamic modulus of the test prisms was
measured in order totrack the freeze-and-thaw damage.
By taking an accurate transverse frequency reading of
the specimens, one can calculate the relative dynamic
modulus. The durability factor served as a
representation of how well concrete performed in
freeze-and-thaw conditions. A strong resistance to
freeze- and-thaw action can be observed in RCA-
concrete mixes proportioned by the traditional mix
design method (100 percent RCA content) or by the EMV
method (63.5 percent and 74.3 percent RCA content for
RCA-concrete made with RCA- MO and RCA-VA,
respectively).
in
Fig. 4, the results revealed that, with the exception of
RAC- 25, all RAC had a high level of permeability after
300 F-T cycles. The ancient mortar's excessive porosity
and microcracks on the RCA surface are the cause of the
high chloride ion permeability. More chloride ions can
enter the RAC specimens because there are more holes
and microcracks that have created and connected flow
channels. In addition tosulphoaluminate cement, fly ash
and silica fume are mineral admixtures that can increase
the durability of concrete. The quality of RCA and the
type of concrete used are the main
Fig -4: The variation trend of chloride diffusion
coefficient
Fig -5: Compressive strength of recycled conventional
concrete (conventional mix method)
However, the EMV approach provides concrete with
greater resilience to freeze-and-thaw action than RCA-
concrete proportioned by conventional mix design
method [6] becauselower total mortar content in RCA-
concrete can be attained using this method. More
chloride ions can enter the RAC specimens thanks to a

5.3 Carbonation
content had a high resistance to carbonation. The
carbonationcoefficient for mixes created using the EMV
approach, however, was lower or equivalent to that of
mixes created using the conventional method for
specimens containing fly ash [6]. Concrete's carbonation
coefficient improved as recycled aggregate and fly ash
contents increased [16]. If all other parameters are equal,
larger carbonation depths result from the assimilation of
increasing amounts of RA. Concrete made entirely of
coarse RCA has the potential to carbonate at up to twice
the rate of similar NAC mixes. Regarding the RA type
effect on carbonation, it was discovered that RMA create
deeper carbonation depths than RCA for a given
replacement level. In an MRA blend, the depth of
carbonation in the final concrete increases as the RMA
content increases. Since concrete porosity and
carbonation are intimately related, it follows that adding
more porous RA will make concrete morepermeable and
so allow for deeper carbonation. An efficient way to
improve mechanical performance and decrease
carbonation in RAC mixes is to lower the w/c ratio with
the use of water lowering admixtures. It was also
determined that controlling the quality and quantity of
RA in the mix is preferred because these factors have a
stronger impact on this characteristic than reducing the
w/c ratio by adding water- reducing admixtures.
rise in F-T cycles, more holes and microcracks, and
the formation of interconnected flow pathways.
A setup based on advice from RILEM was used to conduct
a carbonation test. The carbonation depths of RCA-
concrete, both with and without additional cementitious
ingredients, are within the range anticipated for ordinary
structural-grade concrete. The least amount of
carbonation was found in RCA- concrete specimens
without additional cementitious ingredients, followed by
examples with fly ash. The reserve alkalinity of the
concrete's binder is the primary factor impacting the
carbonation of RCA-concrete, according to specimens
created with concrete proportioned using the EMV
method. It was discovered that specimens with a high
cement
Fig -6: Carbonated depth of concrete cured in different
environments (adapted from Amorim et al.)
The use of mineral additions as cement replacement
causes greater carbonation depths than those of mixes
without them.This happens because the Ca(OH)2 content
decreases thus lowering the pH of concrete.
Nevertheless, irrespective of the presence of RCA, the
difference in carbonation depth is similar over time to
that of the corresponding NAC, with or without any
mineral additions [17].
5.4 Water penetration
Test was performed by introducing the specimens into a
device in which they were submitted to a water pressure
equal to 500 kPa for a period of 72 hr, after that
specimen is cut in half in order to determine the water
penetration depth. Each mix class result of the water
permeability test was obtained from the average of three
different specimens. The results for every ACI mix,
compared to their correspondent EMV ones, show
higher water penetration. There also seems to be an
improvement when comparing the specimens by type of
RCA. In the majority of the cases, the use of the novel
method improves the concrete behavior on this specific
property when comparing it to the conventional RAC
and, when using small replacement amounts of RCA, the
EMV method achieves similar values to those of a
conventional concrete. These behaviors can be explained
by the concrete mixes characteristics as it has been
mentioned before, which are certainly closer to those of
a NAC than to a conventionally designed RAC [15]. ACI
based mixes proportioned by the EMV method, in both
0.45 and 0.6 w/c ratios, show better behavior in the
capillary absorption and water penetration properties
than the RAC prepared with conventional methods.

6. CONCLUSIONS
EMV method proved to be the most efficient method of
mix proportioning rather than the conventional
replacement of aggregate method. Reducing the total
mortar content in concrete was the main reason to
achieve better results in strength and durability. Also the
physical features of recycledaggregate like rough texture
and angular nature contributes to strength
characteristics of recycled concrete. Adjustments in mix
proportioning helped to achieve more durable mix.
Studies relating to durability issues regarding recycled
aggregate concrete are still going on worldwide.
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