ARIYACHANDRA, 2020

Prévia do material em texto

Contents lists available at ScienceDirect
Cement and Concrete Research
journal homepage: www.elsevier.com/locate/cemconres
Effect of NO2 sequestered recycled concrete aggregate (NRCA) on
mechanical and durability performance of concrete
Erandi Ariyachandraa, Sulapha Peethamparana,⁎, Shrish Patelb, Alexander Orlovb
a Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY, United States of America
bDepartment of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY, United States of America
A R T I C L E I N F O
Keywords:
NO2 sequestered recycled concrete aggregate
(NRCA)
Recycled concrete aggregate (RCA)
Chloride binding
Chloride-induced corrosion
Polarization resistance measurements
A B S T R A C T
The utilization of recycled concrete as an adsorbent to sequester NO2 without additives or catalysts is an in-
novative, cost-effective, and sustainable approach to capture NO2 from targeted industrial facilities. This paper
presents the mechanical and durability performance of ordinary portland cement (OPC) concrete containing NO2
sequestered recycled concrete aggregate (NRCA). NRCA was used as a partial replacement for natural fine ag-
gregate at 20% and 40% rates by volume. The incorporation of NRCA in concrete resulted in increased com-
pressive strength, decreased water-permeable porosity, and reduced chloride ion migration. Moreover, test
mixtures comprising 40% NRCA showed a significant chloride binding capacity compared to control concrete
mixtures. Furthermore, high replacement rates of NRCA noticeably enhanced the resistance to chloride-induced
corrosion of steel in concrete or at least was on par with the performance of a commercially available calcium
nitrite-based corrosion inhibitor.
1. Introduction
Nitrogen oxides (NOx) are toxic gaseous compounds, mainly refer-
ring to two distinct chemical compositions: nitrogen dioxide (NO2) and
nitric oxide (NO) [1]. Between these oxides, NO2 is more toxic and a
precursor to ground-level ozone, formed by light-induced reactions
between volatile organic matter and NOx [1,2]. Not only do these
noxious NOx gasses pose a threat to health, but they also contribute to
the formation of acid rain, atmospheric particles, eutrophication, and
various other toxic substances instigating critical environmental issues
[3,4]. A great deal of research has been conducted on the photocatalytic
abatement of NOx pollutants using cementitious materials with ad-
ditives such as TiO2 and ZnO2 [4–8]. However, these approaches are
typically expensive and can be rather cumbersome due to the necessity
of continual inspection of the catalysts for deactivation and poisoning
[2,9,10]. On the other hand, utilization of adsorbents to capture NOx
can be reasonably economical and feasible, eliminating the use of
overly complicated setup or control procedures [2]. For e.g., previous
studies incorporated activated charcoal (one of the most extensively
used adsorbents for both gas/liquid pollutants) to enhance the NOx
removal efficacy in hardened cement pastes and concrete [1,11].
A recent innovative approach developed by some of this study's
authors, utilized recycled concrete as an adsorbent to capture the pri-
mary air pollutant, NO2, without additives or catalysts [2]. In this
previous study, it was concluded that the principal mechanism re-
sponsible for NO2 sequestration by demolished concrete is the chemical
neutralization between NO2 and surface alkaline hydrated products,
such as calcium hydroxide (CH). A thermodynamically feasible reaction
with −437 kJ/mol Gibbs Energy that explains the mechanism of NO2
uptake in cement-based materials can be described as follows
[2,11,12].
Ca OH + NO Ca NO + Ca NO + H O2 4 2( ) ( ) ( )2 2 3 2 2 2 2 (1)
Moreover, Ca (NO2)2 can be further decomposed into Ca(NO3)2 as
follows [13].
Ca NO + H O Ca NO + NO + Ca OH3 2 4 2( ) ( ) ( )2 2 2 3 2 2 (2)
The surface alkalinity of concrete typically declines over time due to
the reaction between CH and atmospheric CO2 to form calcium car-
bonate. Thus, old, demolished concrete generally exhibits a lower NO2
removal capacity than young concrete, owing to the decreased amount
of CH available to react with NO2 as given in the chemical Eq. (1). A
recent study showed that a 12-year-old concrete sequestered 60% of
NO2 compared to 100% sequestration capacity achieved by a 28 days
old control concrete [2]. However, since the degree of carbonation in
concrete relies upon several other factors such as the ratio of water to
cementitious materials, permeability, and the presence of mineral ad-
mixtures [14], recycled concrete derived from a parent concrete source
https://doi.org/10.1016/j.cemconres.2020.106210
Received 10 September 2019; Received in revised form 4 July 2020; Accepted 21 August 2020
⁎ Corresponding author.
E-mail address: speetham@clarkson.edu (S. Peethamparan).
Cement and Concrete Research 137 (2020) 106210
Available online 29 August 2020
0008-8846/ © 2020 Elsevier Ltd. All rights reserved.
T
http://www.sciencedirect.com/science/journal/00088846
https://www.elsevier.com/locate/cemconres
https://doi.org/10.1016/j.cemconres.2020.106210
https://doi.org/10.1016/j.cemconres.2020.106210
mailto:speetham@clarkson.edu
https://doi.org/10.1016/j.cemconres.2020.106210
http://crossmark.crossref.org/dialog/?doi=10.1016/j.cemconres.2020.106210&domain=pdf
can possibly enhance the NO2 removal capacity. In addition to the
mechanism presented in chemical Eq. (1), hydrated cement products
such as calcium silicate hydrates (C-S-H) (with Ca/Si = 1.7) are also
capable of adsorbing NO2 [11]. Moreover, alkaline-earth metal oxides
such as CaO, MgO, and BaO [15], as well as some barium aluminates
[16,17] and calcium aluminates [15,18] are known to sequester NO2.
Nicolas et al. [15] observed that NO2 sequestration into mortar pre-
pared with iron-lean, white calcium aluminate cement (Fe2O3 = 0.1%,
Al2O3 = 71%) was higher than that of iron-rich dark calcium aluminate
cement (Fe2O3 = 17%, Al2O3 = 42%). On the other hand, as reported
by Krou et al. [11], OPC and pure clinker phases such as tricalcium
silicate (C3S) and dicalcium silicate (C2S) had lower NO2 adsorption
capacities than hydrated components, CH and C-S-H. These prior stu-
dies demonstrate that NO2 can interact with numerous hydrated and
unhydrated cementitious components as well as cement-based mate-
rials with different chemical compositions. Hence, demolished con-
crete–a material with a wide range of variability in parent concrete
properties–is an excellent adsorbent for removal of toxic NO2 without
additives or catalysts. Demolished concrete that is currently being
landfilled on a massive scale can be recycled in a sustainable way as an
adsorbent to remove NO2 from flue gas from nearby industrial facilities.
Even though recent studies have been focused on improving the
efficiency of NO2 removal by cementitious materials, none of these
investigations have studied the fate of NO2 sequestered cement-based
materials (NSCM) in real-world concrete applications. The presence of
Ca(NO2)2 and Ca(NO3)2 (as described in the chemical equations in (1)
and (2)) makes NSCM an excellent constituent for concrete; Ca(NO2)2
and Ca(NO3)2 based chemical compounds are widely used as multi-
functional concrete admixtures [19] since they can function in many
ways such as inhibitors against chloride-induced corrosion of steel, set
accelerators, anti-freezes, and as self-healing agents in numerous con-
crete applications [12,20–25]. To the best of our knowledge, there are
three types of NSCM produced to date: (i) TiO2/ ZnO2 doped NSCM, (ii)
NSCM comprising activated charcoal, and (iii) NRCA (as studied by the
authors). NRCA is of interest because of limitations with the use of the
first two types of NSCM. The use of TiO2 doped NSCM as a component
in concrete can be expensive due to the poor dispersibility and/or oc-
clusion of TiO2 in cement hydrates [26–28]; this can increase the re-
quired load of TiO2 toproduce sufficient amounts of Ca(NO2)2 and Ca
(NO3)2 in TiO2 doped NSCM. Furthermore, the use of NSCM with ac-
tivated charcoal can immobilize other constituent chemical compounds
in concrete such as surface-active air-entraining admixtures [29] due to
the high adsorption capacity of activated charcoal. In contrast, the use
of NRCA as a constituent in concrete provides a new paradigm of
turning solid waste material into a useful product.
The objective of this study is to evaluate the effect of NRCA on the
Fig. 1. Experimental set up used for NO2 sequestration (not to scale).
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
2
mechanical and durability performance of OPC concrete when in-
corporated as a component in new concrete. NRCA was introduced in
fresh OPC concrete mixtures as fine aggregate to replace 20% and 40%
of natural sand by volume. The influence of NRCA on concrete com-
pressive strength, porosity, rapid chloride permeability, long-term
chloride diffusion coefficients, and resistance to chloride-induced cor-
rosion was investigated in this study.
2. Materials and methods
2.1. Materials
Concrete test specimens were prepared using type I ordinary port-
land cement (OPC), meeting the specifications of ASTM C150. The
coarse aggregate was a quarried crushed limestone. The nominal
maximum size, the dry rodded unit weight, and the specific gravity (in
saturated-surface dry condition) were 12.5 mm, 1591 kg/m3, and 2.65,
respectively. Both natural sand and recycled concrete aggregate (RCA)
were used as fine aggregates. The natural fine aggregate was quartz
sand with a specific gravity of 2.65, fineness modulus of 2.81, and
moisture absorption of 0.9%. RCA was derived from a 2-year-old con-
crete block with an average compressive strength of 28 MPa. A portable
mini rock-crusher was used to crush old concrete blocks; then, the
crushed concrete was sieved to obtain particles ranging from 0.60 mm
to 1.18 mm. This specific particle size range was selected to maximize
the NO2 uptake onto crushed concrete surfaces based on preliminary
analyses. The specific gravity (in saturated-surface dry condition) and
the moisture absorption of RCA were 2.41 and 6.73%, respectively.
2.1.1. Preparation of NRCA
NRCA was produced by subjecting RCA to NO2 using the experi-
mental set up shown in Fig. 1; the details are presented in a previous
study published elsewhere [2]. In this previous study, crushed demol-
ished concrete was used to sequester NO2 on a small-scale using 1.5 g
samples. The NO2 concentration used at the column inlet was only 180-
190 ppb. In the present study, we used a larger sample size of 500 g to
produce NRCA in order to utilize it as a fine aggregate in new concrete.
This is the first study to sequester NO2 using a crushed cementitious
material (RCA) on a large scale; many related studies used small sam-
ples (typically a few grams) subjected to short NO2 exposure periods
(typically < 24 h) with catalysts and adsorbents [1,8,11,30]. Hence,
the following modifications were made to the aforementioned experi-
mental set up to produce a total of about 10 kg of NRCA.
The flow reactor consisted of a quartz tube connected to synthetic
air and NO2 cylinders (1000 ppm NO2 balanced in N2) through mass
flow controllers (MFC). The synthetic air was humidified by being
passed through a gas bubbler, then mixed with dry air to achieve the
target relative humidity (RH) of 50%. The ratio of humidified and dry
air was determined based on data provided by a Vaisala HMP50 hu-
midity probe positioned downstream. Our preliminary investigations
revealed that the uptake of NO2 by fresh concrete under low humidity
conditions (at 0% RH) was only about 5-10% of the uptake at 50% RH.
The increased adsorption at higher RH can be mainly attributed to the
formation of multiple water layers on the surface of calcium hydroxide,
resulting in increased NO2 gas dissolution [31,32]. Since the RH of
waste gas exhaust from cement kilns is around 50% [33] and as we
propose the removal of NO2 from cement kiln effluent gas, we kept an
RH of 50%. An adsorption column measuring ϕ 65 mm × 290 mm was
used for NO2 sequestration. This column was loaded with 500 g samples
of RCA and exposed to a mixture of 250 sccm (standard cubic cen-
timeters per minute) of NO2 and 250 sccm of humidified synthetic air
for two weeks at room temperature. Before exposing RCA to the hu-
midified NO2 mixture, RCA samples were maintained at the air-dried
condition with a moisture content of 0.86%. To minimize the NO2
concentration gradient along the adsorption column (i.e., from inlet to
outlet), we periodically homogenized the RCA sample by rotating the
adsorption column twice per day to thoroughly mix the contents inside.
After the completion of the adsorption experiment, the NO2 sequestered
RCA sample was removed from the adsorption column, thoroughly
mixed, and placed in a sealed container until using it for the prepara-
tion of test specimens. The NO2 concentration was continuously mon-
itored at the outlet by an Enerac 500 NOx analyzer. During the two-
week exposure period, the 500 g RCA sample completely adsorbed the
whole NO2 from the cylinder (volume = 144 ft3); the NO2 concentra-
tion at the inlet was 500 ± 5 ppm whereas that at the outlet indicated
a zero-ppm reading throughout. Hence, the 2-year-old RCA sample
achieved a 100% NO2 removal capacity; it could have probably ad-
sorbed more NO2 if the sample had been exposed for longer than two
weeks. However, due to resource and time constraints, the above ex-
perimental conditions were implemented to optimize the amount of
NRCA produced in a shorter time frame.
2.1.2. Soluble nitrite/nitrate contents in NRCA
It is essential to determine whether NRCA can provide soluble ni-
trites/nitrates comparable to nitrite/nitrate-based admixtures when
incorporated as a fine aggregate in new concrete mixtures. Assuming
that NO2 predominantly reacts with CH phase in RCA to produce Ca
(NO2)2 and Ca(NO3)2 as given in the chemical equation in (1), it is
possible to estimate the nitrite/nitrate ion contents if the total amount
of adsorbed NO2 is known. According to the experimental conditions
used for the NO2 sequestration (as described in Section 2.1.1), a sample
of 500 g of NRCA completely adsorbed one cylinder of (V = 144 ft3) of
1000 ppm NO2 gas at room temperature (T = 23 °C) and atmospheric
pressure (P = 1 atm) during the two-week conditioning period. As-
suming that NO2 complies with the ideal gas law, PV = nRT, the
amount of adsorbed NO2 was calculated as 0.34 mol per 1 kg of NRCA.
Thus, as per the chemical Eq. (1), both nitrite and nitrate contents in
1 kg of NRCA should be equivalent to 0.17 mol. Furthermore, if n
amount of Ca(NO2)2 had been decomposed into Ca(NO3)2 as per the
chemical reaction (2), the final nitrite and nitrate ion contents per kg of
NRCA would be (0.17–2n) and (0.17–2n/3) moles, respectively.
Nevertheless, these calculations provide only an approximate estimate
of the nitrite/nitrate contents in NRCA. On the other hand, even though
the reaction between NO2 and CH is well known, reaction mechanisms
between NO2 and other unhydrated (such as tricalcium aluminate–C3A)
and hydrated products (such as C-S-H and aluminum containing pha-
ses–AFm/AFt) remain elusive.
To that end, an ion analysis was performed to precisely estimate the
amount of nitrites and nitrates present in NRCA. A 10 g sample of NRCA
was soaked in 100 ml of ultrapure water (Milli-Q water) in a 250 ml
beaker at room temperature. A 7-day soaking period was selected based
on the trial runs performed for different test durations (1, 7, and
14 days) to extract as many nitrite/nitrate ions as possible. After
soaking for one week, the beaker with the sample was placed on a
magnetic stirrer, and the contents were vigorously agitated for 5 min.
The beaker was then placed in an ultrasonic water-bath for 5 min, after
which it was again agitated for an additional 5 min on the magnetic
stirrer. After theNRCA particles had settled, the supernatant solution
was vacuum filtered through Whatman (no. three) filter paper into a
250 ml filter flask. The filter paper was then rinsed with approximately
50 ml increments of ultrapure water, and the total volume was made up
to 250 ml. The recovered leachate was diluted as necessary and ana-
lyzed for nitrites and nitrates by ion chromatography.
2.2. Concrete mixture proportioning, casting, and curing
A total of eight concrete mixtures were prepared with a water to
cement ratio (w/c) of 0.5, as presented in Table 1. Two control mixtures
(R0 and R0-CI) with a compressive strength of 30 MPa were prepared
without RCA. RCA and NRCA were employed in the remaining concrete
mixtures to replace natural sand at 20% and 40% levels by volume. A
commercially available calcium-nitrite based corrosion inhibitor,
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
3
abbreviated as (CI), was also used in three concrete mixtures (R0-CI,
R20-CI, and R40-CI) for comparison purposes. In these mixtures, the
mixing water was reduced by 0.84 kg per liter of CI according to the
manufacturer's recommendations [34]. To ensure a uniform mixture
without segregation, natural sand, RCA, and NRCA were maintained in
an over-saturated condition by limiting their surface moisture content
to 3–4% [35,36] for at least 24 h. Prior to mixing, the surface moisture
present in all fine aggregates was determined as per ASTM C70, and the
mixing water was adjusted accordingly. All concrete mixtures were
prepared using a Hobart laboratory mixer and moisture-cured as per
ASTM C192.
2.3. Compressive strength, porosity, and rapid chloride permeability
measurements
The compressive strength of concrete was evaluated using
ϕ50.8 mm × 101.6 mm test cylinders at 7, 28, and 90 days according to
ASTM C39. The water-permeable porosity was determined as per ASTM
C642 after 28 days of curing. Both short-term and long-term (described
in Section 2.5) tests were carried out to assess the chloride penetrability
of the concrete mixtures. After 28 days, the rapid chloride permeability
test (RCPT) was performed following the ASTM C1202 specifications.
2.4. Long-term chloride diffusion
The long-term chloride diffusion was evaluated by the Nord test
[37] using test specimens with dimensions ϕ101.6 mm × 101.6 mm.
Following a 90-day exposure period to 16.5% NaCl solution, concrete
powder samples were ground off in layers (precision ± 0.01 mm) par-
allel to the exposed surface using a drilling machine (Grizzly G0704-
Mill/Drill). Concrete powder samples of 5 g each were used for de-
termining both free and total chloride according to ASTM C1218 and
C1152, respectively. Potentiometric titrations were performed using the
Metrohm 848 Titrino plus automatic titrator with a silver/chloride
sensitive electrode and 0.05 N silver nitrate (AgNO3) titrant. The de-
tection level was 0.001% Cl−and the measurement accuracy was ± 5%
of the indicated reading. The apparent chloride diffusion coefficients
were estimated by nonlinear curve fitting of the chloride concentration
gradient to Eq. (3), where C(x,t) is the chloride concentration (% by
mass of concrete) at a depth of x (m) below the exposed surface at time t
(s). Cs and Ci denote surface and initial chloride concentrations (% by
mass of concrete), respectively. Da refers to the apparent chloride dif-
fusion coefficient in m2/s.
=C(x, t) C (C C ). erf x
4 D ts s i a (3)
2.5. Electrochemical tests
Lollipop concrete test specimens of ϕ50.8 mm × 101.6 mm with a
9.5 mm embedded rebar were used for corrosion tests, as illustrated in
Fig. 2 (a). Three replicate specimens were used to test each concrete
mixture. Prior to casting concrete, rebars were sandblasted and cleaned
with hexane to remove the mill scale. One end of the rebar was drilled
and tapped to provide an electrical connection through a stainless-steel
screw. An exposure length of 60.3 mm steel simulating a concrete cover
depth of 20.7 mm was defined to be the region of interest where cor-
rosion was allowed to occur and was in direct contact with concrete
during casting. Elsewhere, rebar was coated with two-part epoxy,
tightly wrapped with electroplater's tape, and covered with a polyolefin
heat shrink tube to prevent electrical and physical contact with the
concrete. The ends of the polyolefin tube were pinch closed and sealed
with two-part epoxy. The prepared rebar was centrally located in each
cylindrical mold while casting and compacting. The molds were then
secured with a centrally holed lid, enabling the rebar to align precisely
at the center. After moisture-curing for 28 days, the top and bottom
faces of the lollipop test specimens were coated in two-part epoxy to
allow chloride diffusion only through the radial direction. The condi-
tioned test specimens were then submerged in a high-concentrate ex-
posure solution of 16.5% NaCl at 23 ± 2 °C to accelerate the corrosion
process. Specimens were stored in polypropylene plastic tanks, and a
constant solution level was maintained (approximately 30 mm below
the top, the epoxy-coated face of the cylindrical lollipop specimen, as
shown in Fig. 2 (a)) throughout the test period. In this way, the working
electrode (i.e., exposed area of the embedded rebar inside concrete) had
access to oxygen through the top radial surface of the concrete to
promote the cathodic reaction (oxygen reduction) while it was being
adequately exposed to the saline solution through the bottom radial
concrete surface to initiate the chloride-induced corrosion. All elec-
trochemical tests were commenced after one week of exposure to 16.5%
saline solution, and regular measurements were taken on a monthly
basis up to a 16-month test duration. A conventional three-electrode
system was used to determine the electrochemical parameters, as por-
trayed in Fig. 2 (b). The electrochemical cell comprised a saturated
calomel electrode (SCE) reference and a counter electrode made of a
3.2 mm thick hollow stainless-steel cylinder measuring
ϕ76.2 mm × 101.6 mm, which was placed around the lollipop test
specimen. The embedded rebar in the test specimen served as the
working electrode with an effective exposure area of 1793.7 mm2. The
electrolyte was a 16.5% NaCl solution. All the electrochemical tests
were performed using an electrochemical workstation PARSTAT MC-
1000 Multichannel Potentiostat (Princeton Applied Research).
The corrosion potential (Ecorr) was determined by the open-circuit
measurement of the potential difference between working and re-
ference electrodes. In a typical electrochemical test session, Ecorr was
initially measured for 15 min to ensure quasi-steady-state conditions
during which the Ecorr did not deviate by > 1 mV as confirmed by trial
tests. The corrosion probability criterion specified in ASTM C 876 and
RILEM recommendations [38] was used to interpret Ecorr;
Ecorr > −126 mV (vs. SCE) indicates 90% probability of no corrosion,
Ecorr in the range of −126 to −276 mV (vs. SCE) denotes that the
corrosion state is uncertain, and Ecorr < −276 mV (vs. SCE) in-
dicates > 90% probability of corrosion. Once the open-circuit potential
Table 1
Concrete mixture proportions in SSD condition.
Mixture ID Description OPC (kg/m3) CI (l/m3) Water (kg/m3) Coarse Agg. (kg/m3) Fine Aggregates (kg/m3)
Natural RCA NRCA
R0 Control 433 0 217 882 733 0 0
R0-CI Control with CI 433 20 200 882 733 0 0
R20 RCA at 20% 433 0 217 882 586 133 0
R40 RCA at 40% 433 0 217 882 440 266 0
R20-CI RCA at 20% with CI 433 20 200 882 586 133 0
R40-CI RCA at 40% with CI 433 20 200 882 440 266 0
N20 NRCA at 20% 433 0 217 882 586 0 133
N40 NRCA at 40% 433 0 217 882 440 0 266
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
4
http://www.astm.org/Standards/C%20876
(Eocp) reached a steady-state, the test specimens were polarized using a
forward scan from Eocp -30 mV to Eocp + 30 mV at a scanning rate of
0.1 mV/s. The linear polarization resistance (Rp) was evaluated as the
ratioof the applied potential (E) to resulting current density (i) at i = 0
in E vs. i plot. Since the lollipop test specimens were fully saturated in
saline solution during measurements, the ohmic drop was un-
compensated, assuming that the concrete resistance was negligible
[39,40].
3. Results and discussion
3.1. Soluble nitrite/nitrate contents in NRCA
The amounts of water-soluble nitrite and nitrate ions in NRCA were
0.13 and 0.16 mol per kg of NRCA, respectively, as determined by the
ion analysis. This confirmed the presence of nitrites/nitrates in NRCA,
and the molar ratio of nitrite: nitrate ions was 1:1.3. Test results from
the ion analysis can be used to evaluate the amount of nitrites/nitrites
present in the NRCA containing concrete mixtures (N20 and N40). This,
in turn, permits the comparison of the nitrites/nitrates in NRCA mix-
tures with CI containing mixtures (R0-CI, R20-CI, R40-CI) to assess the
influence of NRCA on properties of concrete with respect to a com-
mercially available Ca(NO2)2 based multi-functional admixture. It
should be noted that the CI dosages used in R0-CI, R20-CI, and R40-CI
mixtures were similar and so are the nitrite contents, as per the man-
ufacturer's recommendations, 20 l of CI (specific gravity = 1.3, con-
centration = 30% w/w) were added per 1m3 of concrete. In contrast,
the nitrite/nitrate contents in N20 and N40 mixtures varied depending
on the replacement level of NRCA in each mixture. N20 and N40 test
mixtures contained 133 and 266 kg of NRCA, respectively, per 1m3 of
concrete. Table 2 compares the molar concentration of nitrite/nitrate
contents as well as the weight percentages (by weight of cement, 433 kg
of OPC was used per 1m3 of concrete). The percent weight of nitrites in
NRCA containing mixtures was significantly lower than that of CI
containing mixtures. The total percent weights of nitrite and nitrates in
N20 and N40 mixtures were 62% and 23% lower, respectively, com-
pared to the concrete mixtures with CI admixture (R0-CI, R20-CI, and
R40-CI). The maximum replacement rate of NRCA was limited to 40%
in this study since the mechanical and durability properties of concrete
can be significantly affected by the use of a higher percentage of fine
RCA [41–43]. On the other hand, it should be noted that both Ca(NO2)2
and Ca(NO3)2 based admixtures are used in relatively low dosages for
corrosion inhibition purposes; solutions with 25–30% solids (w/w) are
typically used at 2–4% by weight of cement [44]. The replacement rate
of NRCA can be adjusted, if needed, to optimize the mechanical and
durability performance of NRCA containing concrete.
3.2. Compressive strength, porosity, and rapid chloride permeability
The compressive strength evolution of the test concrete mixtures is
depicted in Fig. 3 (a). The water-permeable porosity and rapid chloride
permeability of the test mixtures evaluated at 28 days are presented in
Fig. 3 (b) and (c), respectively. Notably, the utilization of NRCA im-
proved the later age strength of OPC concrete, unlike the conventional,
unmodified RCA (R20 and R40). Both the 28 and 90-day strength of
N20 and N40 mixtures were higher than those of the R0, R20, and R40
control mixtures, as shown in Fig. 3(a). This favorable influence of
NRCA on concrete strength is significant because the use of RCA typi-
cally reduces the strength of an OPC concrete due to the weaker tran-
sitional zone formed between the micro-cracked old adhered mortar on
RCA and the new paste matrix [45–47]. As expected, the R40 mixture
showed the lowest strength at each curing period since the strength
reductions in RCA containing mixtures became more pronounced as the
replacement level was increased.
On the other hand, the addition of CI increased the compressive
Fig. 2. Schematic of (a) lollipop corrosion test specimen and (b) three-electrode electrochemical cell.
Table 2
Comparison of nitrite/nitrate contents in test concrete mixtures.
Concrete
Mixture
Molar concentration (moles/1m3
of concrete)
Weight % (by weight of
cement)
Nitrite Nitrate Nitrite Nitrate
R0-CI, R20-CI,
R40-CI
118 Negligible⁎ 1.25 Negligible⁎
N20 17 21 0.18 0.30
N40 34 42 0.36 0.60
⁎ As per the manufacturer's specifications [34].
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
5
strength of concrete mixtures with and without RCA. Test mixtures with
CI achieved the highest 7-day strength compared to other concrete
mixtures in the order of R0-CI > R20-CI > R40-CI, indicating at least
21% increases over their corresponding control mixtures without CI
(R0, R20, and R40). This is expected because Ca(NO2)2 based ad-
mixtures are well known to accelerate the cement hydration reaction
resulting in enhanced early age strengths in concrete [20,21,48]. N20
and N40 mixtures also gained higher 7-day strengths compared to RCA
containing control mixtures (R20 and R40, respectively), but the cor-
responding strength increases were relatively lower than in R20-CI and
R40-CI mixtures, respectively. The use of CI improved the later age
strength of concrete, consistent with previous research findings
[23,49]. Most importantly, although N20 and N40 mixtures had com-
paratively lower early age strengths, they quickly gained strength at 28
and 90 days, reaching almost comparable values to R20-CI and R40-CI
mixtures, respectively.
As portrayed in Fig. 3 (b), the 28-day water-permeable porosities of
the test concrete mixtures ranged from 14.70% to 17.06%, with R0
being the least porous mixture (with no recycled aggregates). Notably,
the porosity of concrete with NRCA was relatively lower than mixtures
with RCA. Accompanying reductions in the N20 mix were 7% and 3%
over R20 and R20-CI mixtures, respectively, whereas that in the N40
mix was 11% and 12% over R40 and R40-CI mixtures, respectively.
Moreover, N20 and N40 showed merely 1% and 3% increases in water-
permeable porosity over the R0 control mix. In contrast, the porosity of
concrete significantly increased with the use of RCA as expected, re-
gardless of the addition of CI admixture. The maximum increase with
20% RCA was 9% (in R20) and that with 40% RCA was 16% (in R40-CI)
compared to the R0 control mixture. The addition of RCA has a pro-
portional effect on porosity; i.e., the higher the RCA replacement rate,
the higher the porosity. This is mainly due to the intrinsic porosity of
the adhered mortar in RCA with abundant microcracks [41,45]. Despite
these facts, the porosity of concrete was not significantly influenced by
the NRCA replacement level.
The improved compressive strength in NRCA containing mixtures
can be mainly attributed to reduced porosity since the strength and
Fig. 3. (a) Compressive strength evolution (b) Water permeable porosity at 28 days (c) Rapid chloride permeability at 28 days.
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
6
porosity of cement-based materials typically show an inverse correla-
tion [50]. However, even though the addition of CI resulted in en-
hanced strengths, it did not influence the porosity of test concrete
mixtures; previous research findings also show that the addition of Ca
(NO2)2 or Ca(NO3)2 has little or no effect on the porosity of concrete
[23,51] Hence, Justness et al. [51] ascribed the increased strength in
concrete with Ca(NO3)2 to the development of a denser aggregate/paste
interface and relatively smaller CH crystals. In addition, other studies
[20,52] concluded that the enhanced strength of concrete in the pre-
sence of Ca(NO2)2 /Ca(NO3)2 is due to the formation of nitrite/nitrate-
containing double salts (predominantly NO2-AFm/NO3-AFm [53]);
they can form an initial skeleton structure which can function as micro-
reinforcement for C-S-H causing higher strengths [20].
A recent study [54] showed that the addition of Ca(NO3)2 caused a
10% reduction in total porosity in a carbonated mortar, contrary to
previous studies [23,51] on uncarbonated cementitious materials. Ni-
trates can readily convert monocarboaluminates (CO3-AFm) incarbo-
nated-systems to NO3-AFm by releasing carbonates; in the presence of
CH, liberated carbonates can be precipitated as calcite (CaCO3) crystals
[24,53] reducing porosity. Moreover, nitrates can also displace sulfates
from monosulfoaluminates (SO4-AFm). Consequently, SO4-AFm rapidly
decays while the amount of crystalline ettringite (SO4-AFt) increases.
This, in turn, leads to a dense matrix and, thereby a refined pore
structure owing to the better space-filling property of ettringite [53].
All these data suggest that the presence of nitrates (released from
NRCA) in combination with a carbonated material (in the form
NRCA)–that is typically rich in CO3-AFm/SO4-AFm phases–could be the
main reason behind the reduced porosity in NRCA containing concrete
mixtures. However, as the NRCA–OPC combined system is much more
complicated than the cement-based systems examined in the aforesaid
previous studies, further investigations are needed to understand the
reaction mechanisms between NRCA and a new OPC matrix.
As shown in Fig. 3(c), the chloride ion penetrability of all test
mixtures was “moderate” except for the R40-CI mix, which had “high”
chloride permeability according to ASTM C1202. The mixtures with
NRCA had lower chloride permeability than control RCA mixtures.
Moreover, the total charge passed in N40 and N20 were similar. Even
though the NRCA volume in N40 was double compared to N20, the
water-permeable porosity of N40 was merely 2% higher than N20, and
this, in turn, resulted in similar chloride penetrability. As expected,
chloride permeability of mixtures with RCA significantly increased as
the RCA replacement level increased, consistent with the previous ex-
perimental results [55–60]. This is primarily due to the interconnected
pore network in adhered residual mortar in recycled aggregates that
Fig. 4. (a) Total chlorides profiles (b) Free chloride profiles (c) Bound chlorides profiles, and (d) Percent chloride binding capacities of test concrete mixtures.
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
7
allows chloride ions to easily diffuse through the concrete [55,61]. The
addition of CI admixture interfered with RCPT test results in R0-CI,
R20-CI, and R40-CI mixtures, due to the presence of soluble nitrite ions,
causing much higher coulomb values than the corresponding control
mixtures R0, R20, and R40, respectively. This was anticipated because
RCPT is indicative of the electrical conductivity of concrete, rather than
a direct measure of chloride permeability; the addition of Ca(NO2)2
based admixtures increases the electrical conductivity of concrete
[62,63], and this can produce misleading RCPT results. However, such
interference in RCPT results was not found in mixtures containing
NRCA, and their reduced RCPT values can be attributed to the presence
of significantly lower nitrite ions in N20 and N40 containing mixtures
compared to concrete with CI, as shown by the ion analysis in Table 2.
In fact, N20 and N40 mixtures had only 14% and 29% of the nitrites
present in R20-CI, and R40-CI mixtures, respectively. As a result,
compared to R20-CI and R40-CI mixtures, both N20 and N40 mixtures
had lower RCPT values. Moreover, the water-permeable porosity
(Fig. 3(b)) of both N20 and N40 mixtures was lower than the corre-
sponding control mixtures, R20 and R40; water-permeable porosity of
N20 was 7% lower than R20, and N40 showed 11% reduced porosity
compared to R40. Thus, even though N20 and N40 contained nitrites,
the RCPT values in these mixtures were lower than the RCPT values in
R20 and R40, possibly due to the reduced porosity in concrete with
NRCA which appears to be the dominant factor due to the low amount
of nitrites.
3.3. Long-term chloride diffusion and chloride binding
Fig. 4 (a) and (b) present the best-fit curves based on Fick's second
law (in the form of Eq. (3)) for total and free chlorides, respectively, of
the test mixtures subjected to long-term bulk chloride diffusion. Table 3
summarizes the apparent chloride diffusion coefficients (Da-total and Da-
free) and surface chloride contents (Cs-total and Cs-free) estimated by non-
linear regression analysis. Both free and total chloride profiles indicated
a similar trend with respect to the type of concrete. In all test mixtures,
significant chloride contents were detected up to about 25 mm in depth
beyond which the ion concentrations were lower than 0.1% by mass of
concrete. The apparent diffusion coefficients ranged from 7.36 to
13.84 × 10−12 m2/s consistent with previous experimental findings
[64–66]. The percent weights of surface chlorides differed from 0.80 to
1.28%. The use of NRCA decreased the apparent diffusion coefficients
in concrete as opposed to the control mixtures with RCA. Both Da-free
and Da-total in N20 decreased by ⁓10% compared to R20, and those in
N40 were reduced by > 43% over R40. Moreover, N40 resulted in al-
most comparable chloride diffusion coefficients compared to the con-
trol mix, R0; in fact, Da-free in N40 was 2% lower than in the R0 control
mix. Importantly, the resistance to chloride diffusivity of N40 concrete
was higher than the N20 mix; N40 showed 11% and 4% lower Da-free
and Da-total, respectively than the N20 mix. Hence, the 40% rate of
NRCA favorably affected the long-term chloride ion diffusion, although
the short-term chloride permeabilities of N20 and N40 were similar.
The enhanced resistance to long-term chloride diffusion in concrete
with NRCA can be mainly attributed to its reduced porosity. In contrast,
R0-CI had ⁓40% higher diffusion coefficients than control R0. More-
over, the addition of CI also increased the chloride diffusivity in R40-CI
compared to the corresponding control mixture R40 (without CI). Even
though several studies observed little or no effect of CI on the long-term
chloride diffusion [23,49,67], Reou and Ann [68] reported a similar
trend to the present study; chloride diffusion coefficients, as well as the
surface chloride levels in OPC concrete, increased as the CI dosage in-
creased. This could have occurred due to the increased ionic con-
centration in the pore solution caused by highly soluble nitrite ions (in
contrast to the nitrate ions in mixtures with NRCA). The increased ionic
concentration can increase the chloride ion diffusivity. Chloride mi-
gration in concrete is influenced by the pore structure and the inter-
action between ions and the pore walls [69]. Thus, the addition of
calcium-nitrite based corrosion inhibiting admixture (CI) can influence
the chloride diffusivity of concrete as it introduces more ions (i.e., Ca2+
and NO2− ions) and hence increases the ionic concentration in the pore
fluid. Such variations in the pore solution chemistry considerably alter
the electrical conductivity of concrete [62]. The presence of CI sig-
nificantly increases the electrical conductivity of concrete; ASTM C
1202 also states that the addition of CI interferes with the rapid
chloride permeability test (RCPT) results, mainly because RCPT is in-
dicative of the electrical conductivity of concrete, rather than a direct
measure of concrete permeability [62,70]. However, a previous related
study [68] showed that both electrical conductivity and chloride dif-
fusion in concrete increased as the CI dosage increased; it was presumed
that the presence of CI was more conductive for ionic/electronic (i.e.,
chloride ions) transport in concrete [68]. Thus, it is clear that the ad-
dition of CI can possibly increase the chloride ion migration in concrete.
Our results from both RCPT and the long-term diffusion tests support
these findings.
In addition to the long-term chloride ion ingress, the effect of NRCA
on chloride binding ability of concrete was assessed by comparing
bound chloride profiles, as well as chloride binding capacities of test
concrete mixtures. Binding of chlorides inevitably enhances the re-
sistance to chloride-induced steel corrosion since it reduces the free
chloride content in pore water that is readily availablefor initiation of
corrosion when present at sufficient levels [71,72]. When cement-based
materials are exposed to chloride ions, chlorides can exist either in the
pore solution as free chlorides or bound to the cement matrix; the total
chloride measurement includes both free and bound chlorides. Chlor-
ides can be chemisorbed to C-S-H [73,74] and chemically bound to the
interlayer anion site of the AFm phase (preferably over other anions
such as sulfates, carbonates, hydroxides, nitrites, and nitrates [53])
forming 3CaO.Al2O3.CaCl2.10H2O (or Cl-AFm - Friedel's salt) and/or a
solid solution between SO4-AFm and Cl-AFm (i.e., 3CaO.A-
l2O3.0.5(CaSO4)0.5(CaCl2).11H2O or Kuzels's salt) [75,76]. The AFm
exhibits much larger specific chloride binding capacity and binds
chlorides more strongly than C-S-H [53]. Moreover, Cl-AFm itself is
capable of physically adsorbing chlorides on its surface [77].
Table 3
Test results of long-term bulk chloride diffusion by Nord test.
Mixture ID Apparent diffusion coefficient
(m2/s × 10−12)
Sum of squared errors Coefficient of determination (R2) Surface Cl % by mass of concrete
Free Total Free Total Free Total Free Total
R0 7.54 7.81 0.0087 0.0058 0.9932 0.9960 0.892 0.950
R0-CI 10.66 11.18 0.0028 0.0044 0.9941 0.9917 0.838 0.890
R20 9.03 9.35 0.0017 0.0024 0.9978 0.9971 0.828 0.871
R40 11.23 11.29 0.0038 0.0041 0.9950 0.9953 0.852 0.913
R20-CI 9.11 9.58 0.0042 0.0061 0.9960 0.9946 1.038 1.085
R40-CI 13.75 13.84 0.0140 0.0166 0.9883 0.9875 1.073 1.142
N20 8.25 8.30 0.0015 0.0029 0.9981 0.9966 0.966 1.022
N40 7.36 7.95 0.0055 0.0094 0.9958 0.9935 1.220 1.283
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
8
http://www.astm.org/Standards/C%201202
http://www.astm.org/Standards/C%201202
Fig. 4 (c) depicts the bound chloride profiles of the test concrete
mixtures that were obtained by subtracting the free chloride con-
centrations from the respective total chloride concentrations at each
depth from the exposed surface. All concrete mixtures contained com-
paratively higher bound chloride contents within the outer layers
compared to the inner layers. This could be due to the increased for-
mation of Friedel's and Kuzel's salts in the outer layers. As is evident
from Fig. 4 (c), most importantly, the bound chlorides in the N40
mixture were relatively higher than all other mixtures within the first
20 mm; in fact, N40 had the lowest Da-free among all mixtures indicating
the presence of a low amount of free chlorides in the cement matrix. All
CI containing mixtures with and without RCA also showed compara-
tively higher bound chloride contents than R0. In contrast, N20 and R0
had almost similar bound chloride profiles, whereas the content of
bound chloride in R20 within the first 15 mm was lower than the R0
mix.
Apart from the bound chloride profiles, we studied the relationship
between total and free chlorides determined from the long-term
chloride diffusion test to assess the chloride binding capacity of con-
crete as employed in several previous studies [78–81]. In cementitious
materials, total chlorides (Ct) are linearly correlated with free chlorides
(Cf) [82]. Hence, Ct can be expressed by using the expression Ct = αCf,
where α is a constant. The computed values of α by regression analyses
for R0, R0-CI, R20, R40, R20-CI, R40-CI, N20, N40 test concrete mix-
tures were 1.0589, 1.0622, 1.0638, 1.0686, 1.0654, 1.0719, 1.0667,
and 1.0743, respectively. The percentage chloride binding capacity
(Pcb), with respect to the total chlorides in concrete, was then computed
as Pcb = [(Ct - Cf)/Ct] × 100 [79,83] as presented in Fig. 4 (d). Pcb
ranged from 5.56 to 6.92%, with the highest value corresponded to the
N40 mix. Pcb increased as the replacement level of RCA or NRCA in-
creased; the addition of 20% RCA or NRCA improved the binding ca-
pacity by ~10% over the control mix R0, whereas it was further in-
creased more than ~20% in N40 and R40-CI mixtures. This can be
mainly attributed to the increased availability of hydrated products
such as C-S-H and AFm that exist in the residual old mortar layer in
recycled concrete. Chloride diffusion data of the present study suggest
that the incorporation of RCA yielded two contradicting effects on the
chloride transport of concrete. Both chloride permeability and chloride
binding capacity of concrete were improved as the RCA replacement
rate increased, and this corroborates the previous findings [84]. How-
ever, contrary to the conventional RCA containing mixtures, a 40%
replacement level of NRCA enhanced the resistance to chloride ion
ingress as well the chloride binding capacity of concrete compared to a
20% rate. Most importantly, both N20 and N40 mixtures improved the
chloride binding ability of concrete by 4 and 8% than control R20 and
R40 mixtures, respectively. Hence, the underlying mechanisms of the
NRCA in binding chloride ions in concrete seem to be distinct from that
of the conventional RCA.
3.4. Electrochemical tests
Fig. 5 (a) presents the evolution of corrosion potential (Ecorr) of the
lollipop test specimens exposed to 16.5% NaCl solution for a 16-month
test duration. Typically, less negative Ecorr values correspond to higher
corrosion resistance, whereas more negative corrosion potentials in-
dicate higher susceptibility to corrosion. Accordingly, the horizontal
dashed lines in Fig. 5(a) represent the threshold values corresponding
to each corrosion probability criterion as specified by ASTM C 876.
Corrosion initiation is indicated by a drastic drop in Ecorr, which dis-
tinguishes between the passive and active states. As is evident from
Fig. 5 (a), during the first few months, Ecorr of most of the test mixtures
followed a progressive evolution towards more noble potentials sig-
nifying an improved corrosion resistivity. This observation is consistent
with the previous findings [85–87], which can be mainly related to
changes in the chemical composition of the passive layer on steel
caused by the modified pore solution chemistry in concrete due to the
chloride ion ingress. Even though the formation of the passive film in an
alkaline medium like concrete is a spontaneous reaction [71,72,88],
this protective layer continues to grow (aging) until it reaches a steady-
state [89,90]. During this aging, the presence of chlorides in pore so-
lution is found to enhance the passivity of steel primarily due to an
enrichment in ferric oxides in the passive film until sufficient chlorides
are penetrated through concrete leading to a complete depassivation
[85–87]. Most notably, after the initial progression of Ecorr to more
positive potentials, both NRCA and CI containing test specimens
reached a stabilized phase by delaying the onset of corrosion, whereas
Ecorr of the control mixtures R0, R20, and R40 immediately declined
towards more negative values. This implies that NRCA is as efficient as
the commercially available CI corrosion inhibitor in improving the
concrete's resistance against chloride-induced corrosion of steel. The
N40 mix exhibited a very similar trend to that of control mixture R0-CI
in terms of Ecorr. Noticeably, the N40 mix delayed the initiation of
corrosion of steel in concrete by remaining in the passive state up to ten
months, similar to other CI containing mixtures, R0-CI, and R20-CI.
Both N40 and N20 mixtures indicated considerably higher corrosion
resistance compared to R0, in which corrosion was initiated after seven
months. Moreover, the higher replacement rate of NRCA (N40 over N20
mix) offered better protection against chloride-induced corrosion than
conventional RCA mixtures with or without CI. As expected, R40 had
the lowest resistance to chloride-induced corrosion, indicating the most
negative Ecorr values with 90% probability of corrosion during the 16-
month test period. Corrosion initiation was detected in R40 and R20
mixtures after five and six months, respectively. Similarly, the corrosion
potential of R40-CI dropped after nine months showing higher sus-
ceptibilityto chloride-induced corrosion than R20-CI. The favorable
influence of NRCA on corrosion resistance of concrete was further ob-
served during the corrosion propagation stage as well. After 11 months,
beyond which all the test specimens had been transformed from passive
to the active state of corrosion, the N40 mix still exhibited open-circuit
potentials similar to the R0-CI control mixture. N20 also showed rela-
tively higher resistance to corrosion in comparison to the conventional
R20 mix after corrosion initiation.
Fig. 5(b) depicts the evolution of polarization resistance (Rp) of test
concrete specimens. Rp is directly correlated with the resistance against
corrosion in reinforced concrete; the higher the Rp, the better the cor-
rosion resistance of concrete. A drastic drop in Rp typically denotes the
onset of corrosion. Rp of test specimens ranged from 406 to 18 kΩ cm2
during the 16-month test duration. Similarly to the behavior of Ecorr, a
steady increase in Rp was also detected in all concrete specimens during
the initial phase of the chloride exposure, possibly due to a change in
the passive film chemical composition, as discussed above. Subse-
quently, both NRCA and CI containing mixtures displayed relatively
stable Rp values, prior to reaching the active state of corrosion. On the
contrary, Rp values of the control mixtures without CI or NRCA was
dropped drastically without reaching a steady state. On par with Ecorr
test results, the N40 mixture exhibited higher Rp values similar to
mixtures with CI, especially R0-CI. Moreover, Rp in N20 was higher
than R0, R20, and R40 mixtures. As expected, the R40 mixture in-
dicated the lowest Rp values followed by R20 and R0 mixtures, re-
spectively. The corrosion initiation depicted by Ecorr results was ana-
logous to the evolution of Rp except in N40, R0-CI, and R20-CI
specimens after eight months. Even though the Rp of these three mix-
tures indicated a rapid decline after eight months, the corresponding
Ecorr values were relatively stable up to 10 months. Such contradictory
results have also been reported in previous studies as well [91–94]. The
corrosion potentials determined by the open-circuit measurements
(Eocp) provide only a qualitative comparison of the corrosion activity,
which cannot be relied on alone for a precise evaluation of the corro-
sion rates [91]. LPR measurements, however, provide strong evidence
for the corrosion activity in combination with the Stern-Geary coeffi-
cients that can be obtained by Tafel plots. Details of such electro-
chemical test results of the NRCA–OPC system will be published in a
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
9
http://www.astm.org/Standards/C%20876
separate article in the future. As is evident from Fig. 5 (b), following the
initiation of corrosion, the N40 mix continued to indicate relatively
higher Rp values, especially compared to R40 as well as R40-CI. This
implies that NRCA at 40% rate is capable of reducing the rate of cor-
rosion as opposed to the conventional RCA containing mixtures since Rp
and corrosion rate are inversely correlated [38,95].
Electrochemical test results of the present study suggest that not
only is NRCA efficient in delaying the onset of corrosion but also is
effective in reducing the corrosion rate once the chloride-induced cor-
rosion has been instigated. Likely reasons behind the enhanced corro-
sion resistance in concrete with NRCA are: (i) the presence of both
anodic inhibitors–Ca(NO2)2 and Ca(NO3)2, (ii) higher resistance to
long-term chloride diffusion caused by decreased porosity and (iii) in-
creased chloride binding capacity. Free nitrite/nitrate ions (in pore
solution) can mitigate steel corrosion by competing with the detri-
mental chlorides to rapidly oxidize ferrous ions to form a stable passive
film of ferric ions [12,19,96,97]. As discussed in Section 3.3, as the
chlorides displace the bound nitrites/nitrates in concrete with NRCA
(from NO2-AFm and NO3-AFm), liberated nitrites/nitrates can also be
available in the pore solution as free ions. The efficacy of these free
nitrites/nitrates in inhibiting corrosion essentially depends on their
concentrations relative to the free chlorides in the pore solution; molar
ratios of Cl/NO2− < 0.2 to 0.25 and Cl/NO3− < 0.25 have been re-
ported to provide sufficient protection against corrosion [19,98]. Si-
milar corrosion protection exhibited by the N40 mix (containing much
lower nitrite + nitrate amounts) compared to the mixtures with CI can
be explained using these Cl/NO2− and Cl/NO3− ratios; the decreased
amount of diffused chlorides as well as the low content of free chlorides
(caused by the higher ability to bind chloride) eventually reduces the
Cl/NO2− and Cl/NO3− ratios in the N40 mixture.
It has been widely accepted that the concept of chloride threshold
level (CTL) plays a major role in initiating corrosion of steel in concrete
[99]. The CTL is defined as the content of chlorides at the steel depth
that is necessary to sustain local passive film breakdown and hence
initiate the corrosion process [100]. The presence of anodic inhibiting
nitrite/nitrate-based admixtures increases CTL for steel corrosion in
concrete [12,68,101] primarily due to the formation of a stable passive
layer (ferric oxide film) and thereby inhibiting the reaction between
chloride and ferrous that can lead to pitting corrosion [12]. Likewise, in
the present study, concrete mixtures with RCA + CI had significantly
higher corrosion resistance compared to the control RCA mixtures. As
per long-term chloride diffusion results, both R20-CI and R40-CI had
increased chloride permeabilities compared to R20 and R40 mixtures,
respectively. However, the corrosion resistance of both R20-CI and R40-
CI was significantly greater than the RCA containing control mixtures in
terms of Ecorr and Rp. This implies that the addition of CI had increased
the CTL of the RCA + CI system compared to the control RCA mixtures
and consequently delayed the onset of corrosion as well as reduced the
rate of corrosion after initiation. Similar to R20-CI and R40-CI mixtures,
the addition of NRCA could possibly have increased the CTL of N20 and
N40 due to the presence of nitrites/nitrates resulting in enhanced re-
sistance against chloride-induced corrosion. Since the long-term
chloride permeability of NRCA incorporated mixtures (N20 and N40)
was comparatively lower than the control mixtures, it was difficult to
deduce the exact role of NRCA incorporated concrete on the CTL within
the scope of the present study.
The results of the present study show that the incorporation of
NRCA can significantly enhance the resistance to chloride-induced steel
corrosion in concrete compared to the conventional RCA. Between the
two replacement percentages evaluated, the 40% NRCA containing
concrete provided better protection mainly due to its relatively high
nitrite/nitrate contents reducing Cl/NO2− and Cl/NO3− ratios lower
than the aforesaid critical values. Therefore, a 40% replacement rate is
recommended over 20% of NRCA for enhanced corrosion resistance.
Consequently, higher rates than 40% of NRCA may provide even better
protection against corrosion, but further studies are needed to de-
termine the optimal rate of NRCA in mitigating chloride-induced cor-
rosion that would also enhance the strength and permeability char-
acteristics of concrete.
4. Conclusions
The influence of NRCA on compressive strength, porosity, rapid
chloride permeability, and long-term chloride diffusion coefficients was
evaluated. The efficacy of NRCA as a corrosion inhibitor for OPC con-
crete was also assessed in comparison with a commercially available Ca
(NO2)2 based corrosion inhibiting admixture. The main conclusions that
can be drawn from the present study are summarized below.
■ The two-year-old recycled concrete sequestered a significant
amount of NO2 either as nitrate or nitrite-based compound.
■ The addition of NRCA increased the compressive strength, de-creased the porosity, and reduced both short-term and long-term
chloride ion penetrability of concrete.
■ The NRCA was found to be an effective corrosion inhibitor due to its
ability to provide soluble nitrites/nitrates similarly to a
Fig. 5. Evolution of (a) corrosion potential and (b) polarization resistance.
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
10
commercially available Ca(NO2)2/Ca(NO3)2 based corrosion in-
hibiting admixture.
■ NRCA containing concrete exhibited better chloride binding capa-
city.
■ 40% of the natural fine aggregate can be replaced with the NRCA
without compromising the mechanical and durability properties of
concrete.
Future studies will be conducted to explore the mechanisms behind
the enhanced properties of NRCA integrated OPC concrete.
CRediT authorship contribution statement
Erandi Ariyachandra, Investigation, Visualization, Writing- Original
draft preparation
Sulapha Peethamparan, Conceptualization, Methodology, Writing-
Reviewing and Editing, Project administration
Shrish Patel, Investigation
Alexander Orlov, Conceptualization, Methodology, Project admin-
istration
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgment
The authors gratefully acknowledge financial support from The
National Science Foundation (NSF), USA, through CMMI-Award
#1538013. Any opinions, findings, and conclusions or recommenda-
tions expressed in this article are those of the authors and do not ne-
cessarily reflect the views of the NSF.
References
[1] M. Horgnies, I. Dubois-Brugger, E.M. Gartner, NOx de-pollution by hardened
concrete and the influence of activated charcoal additions, Cem. Concr. Res. 42
(2012) 1348–1355, https://doi.org/10.1016/j.cemconres.2012.06.007.
[2] G. Ramakrishnan, A. Orlov, Development of novel inexpensive adsorbents from
waste concrete to mitigate NOx emissions, Build. Environ. 72 (2014) 28–33,
https://doi.org/10.1016/j.buildenv.2013.10.016.
[3] O. US EPA, Basic Information about NO2, US EPA, 2016, https://www.epa.gov/
no2-pollution/basic-information-about-no2 , Accessed date: 9 August 2018.
[4] C.S. Poon, E. Cheung, NO removal efficiency of photocatalytic paving blocks
prepared with recycled materials, Constr. Build. Mater. 21 (2007) 1746–1753,
https://doi.org/10.1016/j.conbuildmat.2006.05.018.
[5] D. Seo, T.S. Yun, NOx removal rate of photocatalytic cementitious materials with
TiO2 in wet condition, Build. Environ. 112 (2017) 233–240, https://doi.org/10.
1016/j.buildenv.2016.11.037.
[6] M.-Z. Guo, J. Chen, M. Xia, T. Wang, C.S. Poon, Pathways of conversion of ni-
trogen oxides by nano TiO2 incorporated in cement-based materials, Build.
Environ. 144 (2018) 412–418, https://doi.org/10.1016/j.buildenv.2018.08.056.
[7] M. Pérez-Nicolás, I. Navarro-Blasco, J.M. Fernández, J.I. Alvarez, Atmospheric
NOx removal: study of cement mortars with iron- and vanadium-doped TiO2 as
visible light–sensitive photocatalysts, Constr. Build. Mater. 149 (2017) 257–271,
https://doi.org/10.1016/j.conbuildmat.2017.05.132.
[8] Q. Jin, E.M. Saad, W. Zhang, Y. Tang, K.E. Kurtis, Quantification of NOx uptake in
plain and TiO2-doped cementitious materials, Cem. Concr. Res. 122 (2019)
251–256, https://doi.org/10.1016/j.cemconres.2019.05.010.
[9] EPA-452/F-03-032, Air Pollution Control Technology Fact Sheet: Selective
Catalytic Reduction (SCR), (2003).
[10] EPA-452/F-03-031, Air Pollution Control Technology Fact Sheet: Selective Non-
Catalytic Reduction (SNCR), (2003).
[11] N.J. Krou, I. Batonneau-Gener, T. Belin, S. Mignard, M. Horgnies, I. Dubois-
Brugger, Mechanisms of NOx entrapment into hydrated cement paste containing
activated carbon — influences of the temperature and carbonation, Cem. Concr.
Res. 53 (2013) 51–58, https://doi.org/10.1016/j.cemconres.2013.06.006.
[12] J.M. Gaidis, Chemistry of corrosion inhibitors, Cem. Concr. Compos. 26 (2004)
181–189, https://doi.org/10.1016/S0958-9465(03)00037-4.
[13] M. Bausach Mercader, Reactivity of Acid Gas Pollutants With Ca(OH)2 at Low
Temperature in the Presence of Water Vapour, Universitat de Barcelona, 2005,
http://diposit.ub.edu/dspace/handle/2445/35400 , Accessed date: 29 October
2018.
[14] P. Sulapha, S.F. Wong, T.H. Wee, S. Swaddiwudhipong, Carbonation of concrete
containing mineral admixtures, J. Mater. Civ. Eng. 15 (2003) 134–143, https://
doi.org/10.1061/(ASCE)0899-1561(2003)15:2(134).
[15] M. Pérez-Nicolás, J. Balbuena, M. Cruz-Yusta, L. Sánchez, I. Navarro-Blasco,
J.M. Fernández, J.I. Alvarez, Photocatalytic NOx abatement by calcium aluminate
cements modified with TiO2: improved NO2 conversion, Cem. Concr. Res. 70
(2015) 67–76, https://doi.org/10.1016/j.cemconres.2015.01.011.
[16] S. Hodjati, K. Vaezzadeh, C. Petit, V. Pitchon, A. Kiennemann, NOx sorption–de-
sorption study: application to diesel and lean-burn exhaust gas (selective NOx
recirculation technique), Catal. Today 59 (2000) 323–334, https://doi.org/10.
1016/S0920-5861(00)00298-4.
[17] S. Hodjati, P. Bernhardt, C. Petit, V. Pitchon, A. Kiennemann, Removal of NOx:
part I. Sorption/desorption processes on barium aluminate, Appl. Catal. B Environ.
19 (1998) 209–219, https://doi.org/10.1016/S0926-3373(98)00077-0.
[18] A.N. Proto, R. Cucciniello, F.G. y Rossi, O. Motta, Ca-based Adsorbents for NOx
Measurement in Atmospheric Environments Surrounding Monumental and
Archeological Sites, (2013).
[19] H. Justnes, Calcium nitrate as a multi-functional concrete admixture, Concrete. 44
(2010) 34–36.
[20] V.S. Ramachandran, Concrete admixtures handbook, Properties, Science and
Technology, 2nd ed., William Andrew, 1996.
[21] H. Justnes, E.C. Nygaard, Technical calcium nitrate as set accelerator for cement at
low temperatures, Cem. Concr. Res. 25 (1995) 1766–1774, https://doi.org/10.
1016/0008-8846(95)00172-7.
[22] M. Ormellese, M. Berra, F. Bolzoni, T. Pastore, Corrosion inhibitors for chlorides
induced corrosion in reinforced concrete structures, Cem. Concr. Res. 36 (2006)
536–547, https://doi.org/10.1016/j.cemconres.2005.11.007.
[23] K.Y. Ann, H.S. Jung, H.S. Kim, S.S. Kim, H.Y. Moon, Effect of calcium nitrite-based
corrosion inhibitor in preventing corrosion of embedded steel in concrete, Cem.
Concr. Res. 36 (2006) 530–535, https://doi.org/10.1016/j.cemconres.2005.09.
003.
[24] Gabriel A. Arce, Marwa M. Hassan, Louay N. Mohammad, Tyson Rupnow,
Characterization of self-healing processes induced by calcium nitrate micro-
capsules in cement mortar, J. Mater. Civ. Eng. 29 (2017) 04016189, , https://doi.
org/10.1061/(ASCE)MT.1943-5533.0001717.
[25] J. Milla, M.M. Hassan, T. Rupnow, W.H. Daly, Measuring the crack-repair effi-
ciency of steel fiber reinforced concrete beams with microencapsulated calcium
nitrate, Constr. Build. Mater. 201 (2019) 526–538, https://doi.org/10.1016/j.
conbuildmat.2018.12.193.
[26] L. Yang, A. Hakki, L. Zheng, M.R. Jones, F. Wang, D.E. Macphee, Photocatalytic
concrete for NOx abatement: supported TiO2 efficiencies and impacts, Cem.
Concr. Res. 116 (2019) 57–64, https://doi.org/10.1016/j.cemconres.2018.11.
002.
[27] D.E. Macphee, A. Folli, Photocatalytic concretes — the interface between photo-
catalysis and cement chemistry, Cem. Concr. Res. 85 (2016) 48–54, https://doi.
org/10.1016/j.cemconres.2016.03.007.
[28] A. Folli, C. Pade, T.B. Hansen, T. De Marco, D.E. Macphee, TiO2 photocatalysis in
cementitious systems: insights into self-cleaning and depollution chemistry, Cem.
Concr. Res. 42 (2012) 539–548, https://doi.org/10.1016/j.cemconres.2011.12.
001.
[29] M. Mahoutian, A.S. Lubell, V.S. Bindiganavile, Effect of powdered activated
carbon on the air void characteristics of concrete containing fly ash, Constr. Build.
Mater. 80 (2015) 84–91, https://doi.org/10.1016/j.conbuildmat.2015.01.019.
[30] M.-Z. Guo, C.S. Poon, Superior photocatalytic NOx removal of cementitious ma-
terials prepared with white cement over ordinaryPortland cement and the un-
derlying mechanisms, Cem. Concr. Compos. 90 (2018) 42–49, https://doi.org/10.
1016/j.cemconcomp.2018.03.020.
[31] J. Gao, Enhancement mechanism of SO2 on NO2 removal by calcium hydroxide at
low temperature, 2011 Int. Conf. Comput. Distrib. Control Intell. Environ. Monit,
2011, pp. 2077–2081, , https://doi.org/10.1109/CDCIEM.2011.577.
[32] X. Zhang, H. Tong, H. Zhang, C. Chen, Nitrogen oxides absorption on calcium
hydroxide at low temperature, Ind. Eng. Chem. Res. 47 (2008) 3827–3833,
https://doi.org/10.1021/ie070660d.
[33] S.N. Irungu, P. Muchiri, J.B. Byiringiro, The generation of power from a cement
kiln waste gases: a case study of a plant in Kenya, Energy Sci. Eng. 5 (2017) 90–99,
https://doi.org/10.1002/ese3.153.
[34] Sika®-CNI, Corrosion Inhibiting Admixture, Product Data Sheet, (2014).
[35] ASTM C192 / C192M-16a, Standard Practice for Making and Curing Concrete Test
Specimens in the Laboratory, (2016).
[36] G. Andreu, E. Miren, Experimental analysis of properties of high performance
recycled aggregate concrete, Constr. Build. Mater. 52 (2014) 227–235, https://
doi.org/10.1016/j.conbuildmat.2013.11.054.
[37] NTBuild 443, Concrete, hardened: accelerated chloride penetration, Nordtest,
(1995) (n.d.).
[38] B. Elsener, C. Andrade, J. Gulikers, R. Polder, M. Raupach, Half-cell potential
measurements—potential mapping on reinforced concrete structures, Mater.
Struct. 36 (2003) 461–471, https://doi.org/10.1007/BF02481526.
[39] O. Oueslati, J. Duchesne, The effect of SCMs on the corrosion of rebar embedded in
mortars subjected to an acetic acid attack, Cem. Concr. Res. 42 (2012) 467–475,
https://doi.org/10.1016/j.cemconres.2011.11.013.
[40] V. Bouteiller, C. Cremona, V. Baroghel-Bouny, A. Maloula, Corrosion initiation of
reinforced concretes based on Portland or GGBS cements: chloride contents and
electrochemical characterizations versus time, Cem. Concr. Res. 42 (2012)
1456–1467, https://doi.org/10.1016/j.cemconres.2012.07.004.
[41] S.-C. Kou, C.-S. Poon, Properties of concrete prepared with crushed fine stone,
E. Ariyachandra, et al. Cement and Concrete Research 137 (2020) 106210
11
https://doi.org/10.1016/j.cemconres.2012.06.007
https://doi.org/10.1016/j.buildenv.2013.10.016
https://www.epa.gov/no2-pollution/basic-information-about-no2
https://www.epa.gov/no2-pollution/basic-information-about-no2
https://doi.org/10.1016/j.conbuildmat.2006.05.018
https://doi.org/10.1016/j.buildenv.2016.11.037
https://doi.org/10.1016/j.buildenv.2016.11.037
https://doi.org/10.1016/j.buildenv.2018.08.056
https://doi.org/10.1016/j.conbuildmat.2017.05.132
https://doi.org/10.1016/j.cemconres.2019.05.010
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0045
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0045
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0050
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0050
https://doi.org/10.1016/j.cemconres.2013.06.006
https://doi.org/10.1016/S0958-9465(03)00037-4
http://diposit.ub.edu/dspace/handle/2445/35400
https://doi.org/10.1061/(ASCE)0899-1561(2003)15:2(134)
https://doi.org/10.1061/(ASCE)0899-1561(2003)15:2(134)
https://doi.org/10.1016/j.cemconres.2015.01.011
https://doi.org/10.1016/S0920-5861(00)00298-4
https://doi.org/10.1016/S0920-5861(00)00298-4
https://doi.org/10.1016/S0926-3373(98)00077-0
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0090
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0090
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0090
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0095
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0095
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0100
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0100
https://doi.org/10.1016/0008-8846(95)00172-7
https://doi.org/10.1016/0008-8846(95)00172-7
https://doi.org/10.1016/j.cemconres.2005.11.007
https://doi.org/10.1016/j.cemconres.2005.09.003
https://doi.org/10.1016/j.cemconres.2005.09.003
https://doi.org/10.1061/(ASCE)MT.1943-5533.0001717
https://doi.org/10.1061/(ASCE)MT.1943-5533.0001717
https://doi.org/10.1016/j.conbuildmat.2018.12.193
https://doi.org/10.1016/j.conbuildmat.2018.12.193
https://doi.org/10.1016/j.cemconres.2018.11.002
https://doi.org/10.1016/j.cemconres.2018.11.002
https://doi.org/10.1016/j.cemconres.2016.03.007
https://doi.org/10.1016/j.cemconres.2016.03.007
https://doi.org/10.1016/j.cemconres.2011.12.001
https://doi.org/10.1016/j.cemconres.2011.12.001
https://doi.org/10.1016/j.conbuildmat.2015.01.019
https://doi.org/10.1016/j.cemconcomp.2018.03.020
https://doi.org/10.1016/j.cemconcomp.2018.03.020
https://doi.org/10.1109/CDCIEM.2011.577
https://doi.org/10.1021/ie070660d
https://doi.org/10.1002/ese3.153
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0170
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0175
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0175
https://doi.org/10.1016/j.conbuildmat.2013.11.054
https://doi.org/10.1016/j.conbuildmat.2013.11.054
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0185
http://refhub.elsevier.com/S0008-8846(19)31210-4/rf0185
https://doi.org/10.1007/BF02481526
https://doi.org/10.1016/j.cemconres.2011.11.013
https://doi.org/10.1016/j.cemconres.2012.07.004
furnace bottom ash and fine recycled aggregate as fine aggregates, Constr. Build.
Mater. 23 (2009) 2877–2886, https://doi.org/10.1016/j.conbuildmat.2009.02.
009.
[42] F. Cartuxo, J. de Brito, L. Evangelista, J.R. Jiménez, E.F. Ledesma, Rheological
behaviour of concrete made with fine recycled concrete aggregates – influence of
the superplasticizer, Constr. Build. Mater. 89 (2015) 36–47, https://doi.org/10.
1016/j.conbuildmat.2015.03.119.
[43] D. Carro-López, B. González-Fonteboa, J. de Brito, F. Martínez-Abella, I. González-
Taboada, P. Silva, Study of the rheology of self-compacting concrete with fine
recycled concrete aggregates, Constr. Build. Mater. 96 (2015) 491–501, https://
doi.org/10.1016/j.conbuildmat.2015.08.091.
[44] N.P. Mailvaganam, M.R. Rixom, D.P. Manson, C. Gonzales, M.R. Rixom,
D.P. Manson, C. Gonzales, Chemical Admixtures for Concrete, CRC Press, 1999,
https://doi.org/10.4324/9780203017241.
[45] C.S. Poon, Z.H. Shui, L. Lam, Effect of microstructure of ITZ on compressive
strength of concrete prepared with recycled aggregates, Constr. Build. Mater. 18
(2004) 461–468, https://doi.org/10.1016/j.conbuildmat.2004.03.005.
[46] I.F. Sáez del Bosque, W. Zhu, T. Howind, A. Matías, M.I. Sánchez de Rojas,
C. Medina, Properties of interfacial transition zones (ITZs) in concrete containing
recycled mixed aggregate, Cem. Concr. Compos. 81 (2017) 25–34, https://doi.
org/10.1016/j.cemconcomp.2017.04.011.
[47] H. Zhang, Y. Zhao, Integrated interface parameters of recycled aggregate concrete,
Constr. Build. Mater. 101 (2015) 861–877, https://doi.org/10.1016/j.
conbuildmat.2015.10.084.
[48] O.S.B. Al-Amoudi, M. Maslehuddin, A.N. Lashari, A.A. Almusallam, Effectiveness
of corrosion inhibitors in contaminated concrete, Cem. Concr. Compos. 25 (2003)
439–449, https://doi.org/10.1016/S0958-9465(02)00084-7.
[49] N.S. Berke, M.C. Hicks, Predicting long-term durability of steel reinforced concrete
with calcium nitrite corrosion inhibitor, Cem. Concr. Compos. 26 (2004) 191–198,
https://doi.org/10.1016/S0958-9465(03)00038-6.
[50] A.M. Neville, Properties of Concrete, Longman London, 1995.
[51] H. Justnes, A. Thys, F. Vanparijs, D. Van Gemert, Porosity and diffusivity of
concrete with long-term compressive strength increase due to addition of the set
accelerator calcium nitrate, 9th Int. Conf. Durab. Build. Mater. Compon, 2002, pp.
1–10.
[52] M.R. Rixom, N.P. Mailvaganam, Chemical Admixtures for Concrete, CRC Press,
London, UNITED KINGDOM, 1999http://ebookcentral.proquest.com/lib/
clarkson-ebooks/detail.action?docID=3059185 , Accessed date: 14 August 2019.
[53] M. Balonis, The Influence of Inorganic Chemical Accelerators and Corrosion
Inhibitors on the Mineralogy of Hydrated Portland Cement Systems, Ph.D
University of Aberdeen, 2010, http://digitool.abdn.ac.uk:80/webclient/
DeliveryManager?pid=153269, Accessed date: 14 August 2019.
[54] M. Stefanoni, U. Angst, B. Elsener, Influence of calcium nitrate and sodium hy-
droxide on carbonation-induced steel corrosion in concrete, CORROSION 75
(2019) 737–744, https://doi.org/10.5006/3085.
[55] R. Neves, A. Silva, J. de Brito, R.V. Silva, Statistical modelling of the resistance to
chloride penetration in concrete with recycled aggregates, Constr. Build. Mater.
182 (2018) 550–560, https://doi.org/10.1016/j.conbuildmat.2018.06.125.
[56] C. Faella, C. Lima, E. Martinelli, M. Pepe, R. Realfonzo, Mechanical and durability
performance of sustainable structural concretes: an experimental study, Cem.
Concr. Compos. 71 (2016) 85–96, https://doi.org/10.1016/j.cemconcomp.2016.
05.009.
[57] K. Kapoor, S.P. Singh, B. Singh, Durability of self-compacting concrete made with
recycled concrete aggregates and mineral admixtures, Constr. Build. Mater. 128
(2016) 67–76, https://doi.org/10.1016/j.conbuildmat.2016.10.026.
[58] M. Bravo, J. de Brito, J. Pontes, L. Evangelista, Durability performance of concrete
with recycled aggregates from construction and demolition waste plants, Constr.
Build. Mater. 77 (2015) 357–369, https://doi.org/10.1016/j.conbuildmat.2014.
12.103.
[59] S.-C. Kou, C.-S. Poon, H.-W. Wan, Properties of concrete prepared with low-grade
recycled aggregates, Constr. Build. Mater. 36 (2012) 881–889, https://doi.org/10.
1016/j.conbuildmat.2012.06.060.
[60] J. Thomas, N.N. Thaickavil, P.M. Wilson, Strength and durability of concrete
containing recycled concrete aggregates, J. Build. Eng. 19 (2018) 349–365,
https://doi.org/10.1016/j.jobe.2018.05.007.
[61] G. Dimitriou, P. Savva, M.F. Petrou, Enhancing mechanical and durability prop-
erties of recycled aggregate concrete, Constr. Build. Mater. 158 (2018) 228–235,
https://doi.org/10.1016/j.conbuildmat.2017.09.137.
[62] E. Vivas, A.J. Boyd, H. Iii, H. R, M. Bergin, Permeability of concrete — comparison
of conductivity and diffusion methods, https://trid.trb.org/view/813789, (2007) ,
Accessed date: 27 July 2018.
[63] J. Xu, Y. Song, Y. Zhao, L. Jiang, Y. Mei, P. Chen, Chloride removal and corrosion
inhibitions of nitrate, nitrite-intercalated MgAl layered double hydroxides on steel
in saturated calcium hydroxide solution, Appl. Clay Sci. 163 (2018) 129–136,
https://doi.org/10.1016/j.clay.2018.07.023.
[64] R.J. Thomas, E. Ariyachandra, D. Lezama, S. Peethamparan, Comparison of
chloride permeability methods for alkali-activated concrete, Constr. Build. Mater.
165 (2018) 104–111, https://doi.org/10.1016/j.conbuildmat.2018.01.016.
[65] M.S. Jung, K.B. Kim, S.A. Lee, K.Y. Ann, Risk of chloride-induced corrosion of steel
in SF concrete exposed to a chloride-bearing environment, Constr. Build. Mater.
166 (2018) 413–422, https://doi.org/10.1016/j.conbuildmat.2018.01.168.
[66] A. Dousti, R. Rashetnia, B. Ahmadi, M. Shekarchi, Influence of exposure tem-
perature on chloride diffusion in concretes incorporating silica fume or natural
zeolite, Constr. Build. Mater. 49 (2013) 393–399, https://doi.org/10.1016/j.
conbuildmat.2013.08.086.
[67] A. Królikowski, J. Kuziak, Impedance study on calcium nitrite as a penetrating
corrosion inhibitor for steel in concrete, Electrochim. Acta 56 (2011) 7845–7853,
https://doi.org/10.1016/j.electacta.2011.01.069.
[68] J.S. Reou, K.Y. Ann, The electrochemical assessment of corrosion inhibition effect
of calcium nitrite in blended concretes, Mater. Chem. Phys. 109 (2008) 526–533,
https://doi.org/10.1016/j.matchemphys.2007.12.030.
[69] G.K. Glass, N.R. Buenfeld, Chloride-induced corrosion of steel in concrete, Prog.
Struct. Eng. Mater. 2 (2000) 448–458, https://doi.org/10.1002/pse.54.
[70] ASTM C1202-17a, Standard Test Method for Electrical Indication of Concrete’s
Ability to Resist Chloride Ion Penetration, ASTM International, West
Conshohocken, PA, 2017 (n.d.).
[71] M.F. Montemor, A.M.P. Simões, M.G.S. Ferreira, Chloride-induced corrosion on
reinforcing steel: from the fundamentals to the monitoring techniques, Cem.
Concr. Compos. 25 (2003) 491–502, https://doi.org/10.1016/S0958-9465(02)
00089-6.
[72] A. Michel, M. Otieno, H. Stang, M.R. Geiker, Propagation of steel corrosion in
concrete: experimental and numerical investigations, Cem. Concr. Compos. 70
(2016) 171–182, https://doi.org/10.1016/j.cemconcomp.2016.04.007.
[73] P. Gégout, E. Revertégat, G. Moine, Action of chloride ions on hydrated cement
pastes: influence of the cement type and long time effect of the concentration of
chlorides, Cem. Concr. Res. 22 (1992) 451–457, https://doi.org/10.1016/0008-
8846(92)90088-D.
[74] J.J. Beaudoin, V.S. Ramachandran, R.F. Feldman, Interaction of chloride and C-S-
H, Cem. Concr. Res. 20 (1990) 875–883, https://doi.org/10.1016/0008-8846(90)
90049-4.
[75] F.P. Glasser, A. Kindness, S.A. Stronach, Stability and solubility relationships in
AFm phases: part I. chloride, sulfate and hydroxide, Cem. Concr. Res. 29 (1999)
861–866, https://doi.org/10.1016/S0008-8846(99)00055-1.
[76] U.A. Birnin-Yauri, F.P. Glasser, Friedel’s salt, Ca2Al(OH)6(Cl,OH)·2H2O: its solid
solutions and their role in chloride binding, Cem. Concr. Res. 28 (1998)
1713–1723, https://doi.org/10.1016/S0008-8846(98)00162-8.
[77] Y. Elakneswaran, T. Nawa, K. Kurumisawa, Electrokinetic potential of hydrated
cement in relation to adsorption of chlorides, Cem. Concr. Res. 39 (2009)
340–344, https://doi.org/10.1016/j.cemconres.2009.01.006.
[78] J. Liu, Q. Qiu, X. Chen, F. Xing, N. Han, Y. He, Y. Ma, Understanding the interacted
mechanism between carbonation and chloride aerosol attack in ordinary Portland
cement concrete, Cem. Concr. Res. 95 (2017) 217–225, https://doi.org/10.1016/j.
cemconres.2017.02.032.
[79] A. Noushini, A. Castel, J. Aldred, A. Rawal, Chloride diffusion resistance and
chloride binding capacity of fly ash-based geopolymer concrete, Cem. Concr.
Compos. 105 (2020) 103290, , https://doi.org/10.1016/j.cemconcomp.2019.04.
006.
[80] J. Zuquan, Z. Xia, Z. Tiejun, L. Jianqing, Chloride ions transportation behavior and
binding capacity of concrete exposed to different marine corrosion zones, Constr.
Build. Mater. 177 (2018) 170–183, https://doi.org/10.1016/j.conbuildmat.2018.
05.120.
[81] Y. Wang, C. Liu, Y. Tan, Y. Wang, Q. Li, Chloride binding capacity of green con-
crete mixed with fly ash or coal gangue in the marine environment, Constr. Build.
Mater. 242 (2020) 118006, , https://doi.org/10.1016/j.conbuildmat.2020.
118006.
[82] T.U. Mohammed, H. Hamada, Relationship between free chloride and total
chloride contents in concrete, Cem. Concr. Res. 33 (2003) 1487–1490, https://doi.
org/10.1016/S0008-8846(03)00065-6.
[83] T. Cheewaket, C. Jaturapitakkul, W. Chalee, Long term performance of chloride
binding capacity in fly ash concrete in a marine environment, Constr. Build. Mater.
24 (2010) 1352–1357, https://doi.org/10.1016/j.conbuildmat.2009.12.039.
[84] Villagrán-Zaccardi Yury Andrés, Zega Claudio Javier, Maio Ángel Antonio Di,
Chloride penetration and binding in recycled concrete, J. Mater. Civ. Eng. 20
(2008) 449–455, https://doi.org/10.1061/(ASCE)0899-1561(2008)20:6(449).
[85] M.C. Alonso, F.J. Luna, M. Criado, Corrosion behavior of duplex stainless steel
reinforcement in ternary binder concrete exposed to natural chloride penetration,
Constr. Build. Mater. 199 (2019) 385–395, https://doi.org/10.1016/j.
conbuildmat.2018.12.036.
[86] H. Mahmoud, M. Sánchez, M.C. Alonso, Ageing of the spontaneous passive state of
2304 duplex stainless steel in high-alkaline conditions with the presence of
chloride, J. Solid State Electrochem. 19 (2015) 2961–2972, https://doi.org/10.
1007/s10008-015-2908-6.
[87] L. Li, A.A. Sagues, Chloride corrosion threshold of reinforcing steel in alkaline
solutions—open-circuit immersion tests, Corros. Houst. 57 (2001) 19.
[88] C.L. Page, K.W.J. Treadaway, Aspects of the electrochemistry of steel in concrete,
Nature 297 (1982) 109–115, https://doi.org/10.1038/297109a0.
[89] Z. Ai, J. Jiang, W. Sun, X. Jiang, B. Yu, K. Wang, Z. Zhang, D. Song, H. Ma,
J. Zhang, Enhanced passivation