Freeze–Thaw Resistance and Drying Shrinkage of Recycled Aggregate Concrete Proportioned by the Modified Equivalent Mortar Volume Method
International Journal of Concrete Structures and Materials
DOI 10.1007/s40069
1976-0485
Freeze-Thaw Resistance and Drying Shrinkage of Recycled Aggregate Concrete Proportioned by the Modified Equivalent Mortar Volume Method
Sungchul Yang
Hwalwoong Lee
To evaluate the effect of the mix proportioning method on drying shrinkage and freeze-and-thaw resistance of recycled concrete aggregate (RCA) concrete, two series of concrete mixes were made using the modified equivalent mortar volume (EMV) method and the conventional ACI method. In this study, different sources of RCAs were manufactured from on-site plants on air bases and at a commercial recycling plant. Keeping the total mortar at the same level, concrete mixes were proportioned by the modified EMV method, using different scale factors: S = 1 (with RCA substitution of 23%), S = 2 (with RCA substitution of 47%), and S = 3 (with RCA substitution of 73%). It was assumed that the residual mortar volume in the RCA concrete was represented in the sum of the volume of mortar and the volume of aggregate, in variance to the scale factors. Test results showed that the modified EMV method for all the mixes yielded the drying shrinkage property of the RCA concrete comparable to that of the companion concrete with natural coarse aggregate. On the other hand, it was observed in the freeze-and-thaw test that the modified EMV method could be marginally applied to the limited condition with S = 2.
recycled concrete aggregate; drying shrinkage; freeze-and-thaw; mix design
1. Introduction
Due to environmental regulations, difficulty in quality
control, and decrease in strength properties, the use of
recycled concrete aggregate (RCA) has been mostly limited
to nonstructural applications, especially in pavement layers
despite its economical and eco-friendly benefits
(Ministry of
Land, Transportation and Maritime Affairs 2009; Ministry of
Environment 2014; Kang et al. 2014; Yang et al. 2014;
Fathifazl 2008; Fathifazl et al. 2009)
. In particular, if RCA
concrete is proportioned according to the conventional
American Concrete Institute (ACI) method, it would be
difficult to enhance its properties such as the modulus of
elasticity, drying shrinkage, and freeze-and-thaw resistance
(Fathifazl 2008; Fathifazl et al. 2009; Abbas et al. 2009)
.
In the case of a military airfield on a base in Seoul, South
Korea, its runway was paved with good quality concrete
materials that has lasted around 30–40 years. Engineers
predict
(Yang et al. 2014)
that a half of all the airport
runaways in South Korea will undergo surface
reconstruction within 5–10 years. A few air bases have already been
under reconstruction, and the RCAs produced on-site on air
bases have been used only for the sub-base materials,
regardless of the potentially good RCA quality that the air
bases can produce. It is noticeable that the RCA recycled on
the air base normally contains fewer impurities than other
structures and at most contains some asphalt and rubber from
the patching and joint sealing areas.
In addition to the factors already mentioned that limit
RCA concrete use, there is also a security regulation and
financial conflict between the air base and recycling plant
owners. Regarding the regulation, it would be unavoidable
to take out the old paving concrete waste to an external
recycling plant and bring the standard grade RCA back to
the air base reconstruction site after recycling due to the
strict RCA quality requirement. The Korean standard (KS)
specifications require a specific gravity of 2.5 and water
absorption of less than 3% of the RCA for structural and
paving concrete use
(Ministry of Land, Infrastructure and
Transportation 2009; Korea Expressway Corporation 2011;
Incheon International Airport Corporation 2012)
. In
actuality, 4–6 steps of additional crushing processes are being
carried out at the recycling plant in order to satisfy the KS
specifications (see Fig. 4), resulting in a loss of time and
money
(Kang et al. 2014)
.
An innovative method to solve this problem has been
introduced by
Fathifazl (2008)
,
Fathifazl et al. (2009)
and
Abbas et al. (2009)
. They undertook an extensive literature
review and summarized the mechanical and durability
properties of RCA concrete
(Fathifazl 2008)
. The concrete
properties using the conventional RCA method are mainly
affected by the volume of the residual mortar (RM) attached
to the RCA. It was pointed out in 17 studies
(Fathifazl 2008)
that the elastic modulus of RCA concrete decreased by
0–45%, compared to that of the companion natural aggregate
concrete. Other researchers also confirmed that RCA
concretes had lower elastic modulus than normal aggregate one
(Tavakoli and Soroushian 1996; Eguchi et al. 2007; Padmini
et al. 2009; Limbachiya et al. 2012; McNeil and Kang 2013;
Wardeh et al. 2015)
. This means that the elastic modulus of
RCA concrete is a function of that of the mortar and also has
a proportional relationship with the volume of the mortar
(Fathifazl 2008)
. It was also mentioned in 11 studies
(Fathifazl 2008)
that the drying shrinkage of the RCA
concrete exhibited a 6–111% increase, compared to that of the
conventional mix concrete. Other studies also showed that
RCA concrete had higher drying shrinkages than normal
aggregate one
(Eguchi et al. 2007; Limbachiya et al. 2012;
Sagoe-Crentsil et al. 2001)
. This is due to the fact that the
drying shrinkage is proportional to the volume of the mortar.
Consequently, Fathifazl, et al. came up with the equivalent
mortar volume (EMV) method, treating the residual mortar
as part of the total mortar content of the RCA concrete, (i.e.
residual plus fresh mortar) and demonstrating that the elastic
modulus does not decrease and that the drying shrinkage
does not increase.
In essence, airport pavements require very delicate riding
smoothness, and this is greatly related to the low slump of
the paving surface. The low slump, often under 50 mm
(Korea Expressway Corporation 2011; Incheon International
Airport Corporation 2012)
, can be achieved for paving due
to the compaction of the concrete mix. A paving concrete
mix is therefore typically proportioned with a marginal
amount (usually less than 700 kg/m3) of fine aggregates. It
was pointed out in the previous study
(Yang and Lee 2017b;
Kim et al. 2016)
that the nature of the EMV mix proportions
leads to a far smaller amount of fine aggregates, in some case
less than 600 kg/m3, creating a harsh mix. It may have a
smooth finish if the slip form paver forcibly vibrates more
than 10,000 times per minute, but normally there will be a
range of shortage in the amount of sand or fresh mortar.
Therefore, the modified EMV mix proportioning method has
been proposed
(Yang and Lee 2017a, b; Kim et al. 2016)
,
assuming that a certain volume fraction of the residual
mortar may be mathematically treated as original virgin
aggregate, while the other fraction as a part of the total
mortar.
This study aims to assess the effect of different mix
proportioning methods (the conventional ACI method versus
the modified EMV method) on the drying shrinkage and
freeze-and-thaw resistance of concrete. The modified EMV
method and the conventional method were used for
comparison. Several RCAs were produced from the on-site
plants on air bases and at a commercial recycling plant in
South Korea. To verify the applicability of the modified
EMV method, especially for the drying shrinkage and
freeze-and-thaw of RCA concrete, two series of mixes were
made using the modified EMV mix design, along with the
original EMV and the conventional mix design, with various
types and sources of coarse RCA.
2. Modified Equivalent Mortar Volume
Method
The EMV mix design was originally proposed by
Fathifazl
(2008)
. It was ensured in the EMV concept that the total
volume of natural aggregate in recycled concrete aggregate
(RCA) concrete is equal to the volume of natural aggregate
in the conventional concrete with the same specified
properties
(Fathifazl 2008; Fathifazl et al. 2009; Abbas et al.
2009)
. Thus, the new fresh mortar volume in the RCA
concrete (RAC) mix is required to be reduced as much as the
residual mortar content (RMC). The RMC was obtained
using the following equation:
RMC ¼ ðWRCA
WOVAÞ=WRCA
100
ð1Þ
where WRCA is the initial oven-dry weight of the RCA
samples before the test and WOVA is the final oven-dry
weight of the original virgin aggregate (OVA) after complete
removal of the residual mortar (RM). However, it was noted
earlier that in the typical paving concrete mix the EMV
concept leads to too little mortar content. It was also
previously mentioned that the lack of fillers causes slump loss
and a detrimental shape due to too much reduction in the
amount of cement, water, and sand
(Yang and Lee 2017b)
.
Therefore, it was assumed in the modified EMV model
(Yang and Lee 2017b)
that the RM attached to RCA works
as aggregate in fresh concrete, and works as mortar after it is
hardened. Considering this treatment, the RM volume in
RAC was represented as the sum of the volume fraction of
mortar VRRMACa and the other volume faction of aggregate
VRRMACb, as follows:
VRRMAC ¼ VRRMACa þ VRRMACb
where
VRRMACa ¼ VRRCAAC
1
1
RMC
where the oven-dry weight of NA in NAC mix is represented
as WONDA:CNA.
The oven-dry weight of RCA in RAC mix WORDAC:RCA and
oven-dry weight of NA in RAC mix WORDAC:NA can be
determined as follows:
where the volume of RCA in RAC mix VRRCAAC is represented
by rearranging Eq. (4),
WORDACRCA ¼ VRRCAAC
WORDACNA ¼ VNRAAC
moBrytarminulttihpelycinogmptahneioqnuaNnAtitCiesbyofthteheVNRMiAnCgredients of the
VNAC ratio, the
corresponding quantities of water, cement, anMd fine aggregate in
RCA concrete can be calculated as follows:
ð5Þ
ð6Þ
ð7Þ
ð8Þ
ð9Þ
ð10Þ
ð11Þ
ð12Þ
ð13Þ
where the weights of water and cement are represented as
WwRAC and W RAC, respectively, and the oven-dry weight of
c
fine aggregate as WORDACFA. A sample mix proportioning can
be found in Ref.
(Yang and Lee 2017b)
.
3. Experimental Details
3.1 Materials
3.1.1 Cement
A type I Portland cement was used in this study. The
specific gravity of cement used in the mixture design was
3.15 and the specific surface area was 3200 cm2/g. Chemical
admixture used for this study were a solution of air
entraining and water reducing agent.
3.1.2 Recycled Concrete Aggregate
This experimental study used recycled aggregates
produced from three different sources in South Korea (see
Fig. 1). The Sa-Cheon (SC) aggregate that is represented as
‘C’ in Table 1 (and from there on) is a maximum size of
25 mm RCA. It was crushed further again in the Dae-Gil
(DG) recycling plant after initially demolishing and crushing
the old runway concrete pavement at the SC air base
reconstruction site. Secondly, the DG aggregate that is
represented as ‘D’ is a maximum size of 25 mm RCA, and
produced from unidentified sources of construction and
demolition waste (CDW) at the DG recycling plant. The
CDW consists of recycled aggregates with various
impurities such as brick, glass, and asphalt. Lastly, the SN
aggregate, which is represented as ‘A’ aggregate, is a maximum
size of 40 mm RCA, and manufactured from the old runway
concrete pavement at the SN air base reconstruction site.
Figure 2a shows a picture of the RCA production facilities
installed on the SN air base. For reasons of cost, dry process
crushing facilities are typically adopted. Figure 3a represents
a schematic diagram of production processes at the on-site
recycling plant. Note that only two to three stages of
crushing processes are undertaken. Figure 2b is a picture of
the RCA manufacturing facilities at the DG recycling plant.
Figure 3b represents a schematic diagram of production
processes at the recycling plant. It should be noted that a wet
type of process facilities with multiple crushing stages is
often operated in order to satisfy the high quality
requirement of the RCA standards. Weimann and M u¨ller (2004)
reported that the mechanical impact of the material from the
Water absorption
(%)
5.37
wet treatment increased finer grains in the total mass of the
treated material. This increase was mainly due to abrasion of
the adherent residual mortar
(Weimann and M u¨ller 2004)
.
Material properties and production sources of the RCAs
are recorded in Table 1. From a polarization microscope test
for the three test samples, the minerals that constitute the
original virgin aggregates were found to be tuff, hornfels,
and shale for the ‘C’ RCA, with andesite, hornfels, and
quartz porphyry for the ‘D’ RCA, and quartzite,
orthoquartzite, and mica-gneiss for the ‘A’ RCA
(Lee 2014)
.
According to the quality control requirements
(Ministry of
Land, Infrastructure and Transportation 2009)
, the RCA
contained less than 0.5% wood and less than 1% foreign
materials by weight. The properties of the RCAs were tested
according to the KS methods
(KS F 2007a, b)
, and are given
in Table 1. All three RCAs have failed to meet the required
KS standards on structural concrete in terms of the specific
gravity of 2.5 and the water absorption of 3.0%.
The RMC value of ‘A’ RCA only was determined by the
same method suggested by
Abbas et al. (2008)
Two samples
were used to determine the RMC values in individual size
fractions. After drying the samples for 24 h at 105 C, the
oven dried samples were immersed for 24 h in a 26% by
weight sodium sulfate solution. While still immersed in the
sodium sulfate solution, the RCA samples were subjected to
five cycles of freezing and thawing, i.e., 16 h at -17 C and
8 h at 80 C. After the last freeze-and-thaw cycle, the
solution was drained from the sample, and the aggregate was
washed with water over a No. 4 sieve. The washed aggregate
was then placed in an oven for 24 h at 105 C and its
ovendried weight was measured.
3.1.3 Fine Aggregates and Natural Aggregates
Two similar fine aggregates were used in this experiment
(See Table 2). Fine aggregate 1 is natural sand with the
specific gravity of 2.62 and the water absorption of 0.58%
and was used in mix series 1. Fine aggregate 2 has the
specific gravity of 2.55 and the water absorption of 0.95%
and was used in mix series 2. For coarse aggregate, natural
crushed granite aggregate was used. The specific gravity was
2.64 and the water absorption was 0.77%.
3.2 Mix Design
Two series of mixes were designed for typical road-paving
concretes (see Table 3). A control concrete with 35 MPa of
compressive strength was used. The first series of mixes
were designed for a highway-paving concrete with a
maximum aggregate size of 25 mm, while the second series of
mixes were designed for an airport-paving concrete with a
maximum aggregate size of 40 mm. The target air content
for all mix designs was a minimum of 4.0%. Due to the low
slump requirement for the paving concrete, all mixes were
determined to have a slump value under 50 mm.
The mix design identification in Table 3 can be explained as
follows. There are three different sets of terms. The first, 1 and
2 denote test series number. The second term C designates the
conventional mix method, while E is the EMV mix method.
The third indicates the type of coarse aggregates; N implies
natural coarse aggregate, while C and A are the RCAs
produced at the on-site recycling plant of the SC and SN air bases,
respectively, and D is the RCA produced from the DG
recycling plant. The numbers following the third, 1, 2, and 3
denote the RCA replacement levels and are related to the
S values applied in Eq. (3). For example, the 2E-A2 denotes
the EMV mix design in the second test series substituted with
the ‘A’ RCA, but proportioned with S = 2 in Eq. (3).
The first series of mixes were designed to confirm how the
conventional method with the RCA leads to decreased
durability properties such as drying shrinkage and the
freezeand-thaw resistance, compared to the corresponding concrete
mix containing natural aggregate. The second series of
mixes were then designed to apply the modified EMV
approach with scale factors, S = 1 (the original EMV mix
proportion), S = 2, 3, aiming to have the equivalent
durability properties, in comparison with the companion mixes
along with the conventional proportioning design.
3.3 Mixing Process for Making the Concrete
Specimens
A volume capacity of 60L concrete pan mixer was used in
the laboratory. Before the addition of water and the
admixture solution, the admixture in the mixing water was
thoroughly dispersed. Coarse aggregate and fine aggregate were
then added, giving the mixture a few turns. Cement was
subsequently added and the mixer was started for about 90 s.
Finally water was added while the mixer was running and
the concrete was mixed for another 120 s.
3.4 Fresh and Hardened Concrete Properties
Testing
The performance of the concrete mixtures was determined
by testing the fresh and hardened concrete properties.
Immediately after batching, the fresh concrete properties
such as air content (summarized in Table 3) and slump were
tested. The hardened concrete properties tests performed in
this study included compressive strength and modulus of
elasticity. Specimens were cast in plastic molds with the
specified consolidation method
(ASTM 2012)
, that is,
rodding and external vibration, and removed 24 h later. All
specimens were moist-cured at around 20 ± 2 C from the
time of molding until the moment of the test. Both
compressive strength and modulus of elasticity tests for mix
series 1 were performed in the 100 mm 9 200 mm cylinder,
where the tests for mix series 2 were done in the
150 mm 9 300 mm for mix series 2. Two different
cylinders were used for mix series 1 and 2 due to their different
maximum aggregate sizes of 25 and 32 mm, respectively.
Limbachiya et al. 2012; Sagoe-Crentsil et al. 2001; Lee et al.
2013), freeze–thaw test
(Abbas et al. 2009; Ballim 2000; Lee
et al. 2013)
, and creep
(Fathifazl 2008; Smadi et al. 1989)
and drying shrinkage tests
(Fathifazl 2008; Sagoe-Crentsil
et al. 2001; Smadi et al. 1989; Lee et al. 2013)
. Under the
assumption that chloride penetration and carbonation
properties may be better observed from the freeze–thaw test,
while drying shrinkage may demonstrate a similar trend to
creep behavior, freeze–thaw and drying shrinkage tests were
conducted in this paper to study durability of RCA concrete.
3.5.1 Drying Shrinkage
Drying shrinkage experiments were performed using a dial
gauge as one of the methods suggested by KS F 2424 2015),
which is equivalent to ASTM C 157-08. The size of each
experimental specimen was 100 9 100 9 400 mm. The
drying shrinkage was measured by the dial gauge with an
accuracy of up to 1/1000 mm. The specimens were kept
inside a temperature-and-humidity controlled chamber
(20 C and 60% of RH). The dial gauge was then installed
on top of the specimen to measure the change in the length
of the specimen. Figure 4 shows a schematic diagram and
experimental specimens with the dial gauges installed.
Figure 5a shows the change in the temperature and relative
humidity inside the chamber for mix series 1 and Fig. 5b for
mix series 2.
3.5.2 Freezing and thawing
The freeze-and-thaw tests were carried out by Procedure A
with rapid freezing and thawing in water specified in KS F
2456 (2013), which is equivalent to ASTM C 666-03. The
freeze-and-thaw tests were conducted on
100 9 100 9 400 mm prisms by monitoring the relative
dynamic moduli at every 50 cycles over a maximum of 300
cycles. The nominal freeze-and-thaw cycle of this test
consists of repeated changes in the temperature between 4 ± 2
and -18 ± 2 C within the range of 2–5 h.
The relative dynamic modulus is determined by measuring
the transverse frequency of the specimens as shown in
Fig. 6. The specimen under consideration was vibrated in
(a)
(b)
the middle, and the frequency was picked up at the end of
the specimen by an accelerometer and was recorded. The
relative dynamic modulus, Pc, is calculated based on the
following:
Pc ¼
n12
n2
100
ð14Þ
where Pc (%) is the relative dynamic modulus of elasticity
after c cycles of freezing-and-thawing, n1 is the initial
fundamental transverse frequency, and n is the fundamental
transverse frequency after c cycles of freezing-and-thawing.
4. Test Results
Previous studies
(Yang and Lee 2017a, b; Kim et al. 2016)
have shown that the use of the modified EMV mix
proportioning method originally would not result in low elastic
modulus of RCA concrete mixes. This section reports the
test results obtained from the drying shrinkage test and the
freeze–thaw test.
4.1 Drying Shrinkage
Figure 7 illustrates the effect of aggregate sources on the
drying shrinkage of mix series 1, based on the conventional
ACI mix design. The drying shrinkage was measured for
585 days. During days 350–400 of the experiment, the
shrinkage strain increased and then decreased repeatedly,
showing a ‘hump.’ This was considered to be caused by the
dramatic change in the RH, as previously seen in Fig. 5a.
From the age of 20 days, the drying shrinkage difference
between different mixes began to appear gradually. A similar
difference tendency occurred right after the age of 100 days.
At the last measurement at the age of 585 days, the
shrinkage strain of the control specimen, 1C-N was 736 lm/
m, and that of the plant RCA concrete mix 1C-C was
796 lm/m, indicating about an 8% increase. On the other
hand, the shrinkage strain of the airbase RCA concrete mix
1C-D was 954 lm/m, indicating a 30% increase in
Fig. 8 Effect of mix proportioning method on the drying
shrinkage for mix series 2.
comparison to the control mix. This is mainly due to the
higher unit volume of total mortar in the RCA concrete
mixes proportioned by the conventional method, compared
to the companion control mix. It was also observed that the
air base RCA concrete mix resulted in a worse shrinkage
strain, regardless of the similar specific gravity and water
absorption when compared to the plant RCA (see Table 2).
As mentioned previously, shale particles were found from
the air base RCA. This can be explained by the research
result of
Schuster and McLaughlin (1961)
,
Bentur and
Grinberg (1982)
,
Smadi et al. (1989)
,
Ballim (2000)
,
Lee
et al. (2013)
and
Meddah (2015)
in that increasing shale
content in concrete has a significant effect in increasing both
shrinkage and creep strain.
Figure 8 illustrates the effect of the mix proportioning
method on the drying shrinkage result of mix series 2
following 105 days. The RCA concrete shrinkage of the
conventional method was compared to that of the modified
EMV method. A constant difference tendency was observed
after the age of about 40 days. At the last measurement at
105 days, the shrinkage strain of the control mix, 2C-N,
made with natural aggregate, was 722 lm/m, while that of
the 2C-A mix, based on the conventional mix design with
the RCA substitution of 47%, increased by 13% to 816 lm/
m. On the other hand, the 2E-A1 (S = 1), 2E-A2 (S = 2),
2E-A3 (S = 3) mixes proportioned by the modified EMV
mix design, had shrinkage strains of 530, 660, and 700 lm/
m, indicating a 27, 9, and 3% decrease, respectively,
compared to the control specimen. This decrease is mainly
affected by the equivalent total volume in the RCA concrete
mixes proportioned by the modified EMV method. All the
results of 2E-A1, 2E-A2 and 2E-A3 confirm that the drying
shrinkage problem of the RCA concrete can be overcome
using the modified EMV mix design, contrary to the
conventional mix proportioning method.
4.2 Freeze-and-Thaw
The relative dynamic moduli were calculated using
Eq. (14). Figure 9 illustrates the effect of aggregate sources
on the freeze-and-thaw resistance of mix series 1 based on
the conventional ACI mix design. Test results showed that
the control mix 1C-N and the airbase RCA concrete mix
1CC had a gradual and similar decrease tendency with the
Fig. 9 Effect of aggregate sources on the freeze–thaw
resistance for mix series 1.
freeze-and-thaw cycles, while the plant RCA concrete mix
1C-D rapidly dropped to under 70% at the 300th cycle.
At the 100th cycle, the relative dynamic modules of 1C-N,
1C-C, and 1C-D were 93.9, 91.8, and 81.1%, respectively.
However in the case of 1C-D, the relative dynamic modulus
was 74.4% after the 200th cycle, not meeting the
requirement of 80% by the KS concrete structure specification
(Ministry of Land, Infrastructure and Transportation 2009)
.
Generally, the conventional mix design method results in a
lower freeze-and-thaw resistance against RCA concrete
(Fathifazl 2008; Abbas et al. 2009)
. Also worth noting is that
the plant RCA concrete mix resulted in the worst
freeze-andthaw resistance, regardless of the similar specific gravity and
water absorption in comparison to the air base RCA. It may
ascribe to be caused by more impurities with unidentified
sources contained in the plant RCA. Finally, the relative
dynamic modulus of 1C-N, 1C-C, and 1C-D at the 300th
cycle were measured as 92.5, 89.8, and 68.9%, respectively.
It was shown in Fig. 9 that the 1C-N and the 1C-C resulted
in over almost 90% of the relative dynamic modulus even
after the 300th cycle.
Figure 10 illustrates the effect of the mix proportioning
method on the freeze-and-thaw resistance for mix series 2.
Compared to mix series 1, it appears that all the test data in
mix series 2 showed a gradual decrease tendency with the
freeze-and-thaw cycles but satisfied the KS requirement of
80%, although the 2C-A mix and the 2E-A3 mix appeared to
diverge more.
At the 300th cycle, the relative dynamic modulus of 2C-A
mix, based on the conventional mix design with the RCA
substitution of 47% was 88.5%, indicating an 8% decrease
compared to the control mix 2C-N with the relative dynamic
modulus of 95.3%. On the contrary, both 2E-A1 (S = 1) and
2E-A2 (S = 2) mixes proportioned by the modified EMV
method with the RCA content of 47 and 73% resulted in the
relative dynamic modulus of 95.0 and 93.6%, respectively,
being only 0.4 and 2% lower than that of the control mix.
Meanwhile if one compares the effect of the mix
proportioning method between the conventional mix (2C-A) and
the modified EMV mix (2E-A2, S = 2) with the same RCA
substitution, it will be clearly seen in Fig. 10 that the relative
dynamic modulus of the modified EMV mix exhibits a 5.1%
stronger resistance than that of the conventional mix. This is
ascribed to a lower total mortar volume that was
incorporated in the modified EMV method. However, in the case of
2E-A3, using the modified EMV mix design with the RCA
substitution of 73% (S = 3), while the relative dynamic
modulus was 82.2% and a reduction of 6.3% was observed
in comparison to 2C-A, based on the conventional mix
design with the RCA substitution of 47%, too much of a
reduction in water, cement, and sand in 61, 112 kg, and
23 kg per m3, respectively, from the 2E-A3 mix affects the
freeze-and-thaw result in comparison to the 2C-A mix.
5. Conclusions
Drying shrinkage and freeze-and-thaw resistance of RCA
concrete have been tested to evaluate the effect of the mix
proportioning method, i.e., the modified EMV method and
the conventional ACI method. From the results of this study,
the following conclusions can be drawn.
(1) Test results showed that the RCA concrete mixes, with
the RCA substitution of 23% (S = 1), 47% (S = 2),
and 73% (S = 3), proportioned by the modified EMV
method, exhibited a 27, 9, and 3% decrease,
respectively, in the drying shrinkage at 585 days in
comparison to the companion natural aggregate concrete mix.
On the other hand, the RCA concrete mix with a
substitution of 47%, proportioned by the conventional
method, indicated a 13% increase. Thus, the
application of the modified EMV method resulted in RCA
concrete with lower drying shrinkage, compared to the
RCA concrete proportioned with the conventional
method.
(2) The RCA concrete mixes, with a substitution of 23%
(S = 1) and 47% (S = 2), proportioned by the EMV
method, had strong resistance against the
freeze-andthaw action, being only less than 2% lower than the
companion mix, while the RCA concrete mix with a
substitution of 47%, proportioned by the conventional
method, was 8% higher than the companion mix.
Conversely, in the RCA concrete mix with a
substitution of 73% (S = 3), proportioned by the modified
EMV method, a reduction of 6% in freeze-and-thaw
resistance was observed in comparison to the RCA mix
with a substitution of 47%, proportioned by the
conventional method. This was ascribed to too much
reduction of the water, cement, and sand in comparison
to the conventional mix.
(3) Test results showed that the modified EMV method
yielded a drying shrinkage property of the RCA
concrete comparable to that of the companion concrete
with natural coarse aggregate. On the other hand, it was
observed in the freeze-and-thaw test that the modified
EMV method could be marginally applied to the
limited condition with S = 2 (with RCA substitution of
47%).
Acknowledgements
This work was supported by the National Research
Foundation of the 2017 Korea Grant funded by the Korean
Government from the project titled ‘‘Structural Performance
of Reinforced Concrete Members made with Revised
E q u i v a l e n t Vo l u m e M i x P r o p o r t i o n i n g M e t h o d
(2016R1A2B4007932).’’
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