1. INTRODUCTION
⌅LC3 technology is the promising approach in reduction of CO2 emissions. As the population growth is increasing rapidly, there is an
outmost necessity of increasing the infrastructure, where cement clinker
plays a pivot role in the process of construction (11. Schmidt, W.; Alexander, M.; John, V. (2018) Education for sustainable use of cement based materials. Cem. Concr. Res. 114, 103-114. https://doi.org/10.1016/j.cemconres.2017.08.009.
, 22. Scrivener, K.; Martirena, F.; Bishnoi, S.; Maity, S. (2018) Calcined clay limestone cements (LC3). Cem. Concr. Res. 114, 49-56. https://doi.org/10.1016/j.cemconres.2017.08.017.
). An amount of about 5%-8% CO2 emissions throughout the World was observing every year, where most of it is from the production of cement (33.
Hanein, T.; Thienel, K.C.; Zunino, F.; Marsh, A.; Maier, M.; Wang, B.;
Canut, M.; Juenger, M.C.; Ben Haha, M.; Avet, F.; Parashar, A. (2022)
Clay calcination technology: state-of-the-art review by the RILEM TC
282-CCL. Mater. Struct. 55 [3], 1-29. https://doi.org/10.1617/s11527-021-01807-6.
, 44.
Pillai, R.G.; Gettu, R.; Santhanam, M.; Rengaraju, S.; Dhandapani, Y.;
Rathnarajan, S.; Basavaraj, A.S. (2019) Service life and life cycle
assessment of reinforced concrete systems with limestone calcined clay
cement (LC3). Cem. Concr. Res. 118, 111-119. https://doi.org/10.1016/j.cemconres.2018.11.019.
).
As of now all the developing countries were increased their
infrastructure facilities, ultimately there would be more utilization of
clinker and thus inviting more quantity of CO2 emissions (5-75.
Berriel, S.S.; Favier, A.; Domínguez, E.R.; Machado, I.S.; Heierli, U.;
Scrivener, K.; Hernández, F.M.; Habert, G. (2016) Assessing the
environmental and economic potential of Limestone Calcined Clay Cement
in Cuba. J. Clean. Prod. 124, 361-369. https://doi.org/10.1016/j.jclepro.2016.02.125.
6.
Sharma, M.; Bishnoi, S.; Martirena, F.; Scrivener, K. (2021) Limestone
calcined clay cement and concrete: A state-of-the-art review. Cem. Concr. Res. 149, 106564. https://doi.org/10.1016/j.cemconres.2021.106564.
7.
Vizcaíno-Andrés, L. M.; Sánchez-Berriel, S.; Damas-Carrera, S.;
Pérez-Hernández, A.; Scrivener, K. L.; Martirena-Hernández, J. F. (2015)
Industrial trial to produce a low clinker, low carbon cement. Mater. Construcc. 65 [317], e045. http://doi.org/10.3989/mc.2015.00614.
).
There is an urgent need to decrease these emissions by adopting to
sustainable technologies, where it can reduce the anthropogenic
emissions to save the environment. By using various ACM’s (Alternative
cementitious materials) like flyash, GGBS etc.., can decrease the
production of cement and global warming up to certain levels only (8-108.
Díaz, Y.C.; Berriel, S.S.; Heierli, U.; Favier, A.R.; Machado, I.R.S.;
Scrivener, K.L.; Hernández, J.F.M.; Habert, G. (2017) Limestone calcined
clay cement as a low-carbon solution to meet expanding cement demand in
emerging economies. Dev. Eng. 2, 82-91. https://doi.org/10.1016/j.deveng.2017.06.001.
9.
Bishnoi, S.; Maity, S.; Mallik, A.; Joseph, S.; Krishnan, S. (2014)
Pilot scale manufacture of limestone calcined clay cement: the Indian
experience. Indian Concr J. 77 [7], 22-28. https://www.researchgate.net/publication/316474228.
10.
Yu, J.; Wu, H.L.; Mishra, D.K.; Li, G.; Leung, C.K.; (2020) Compressive
strength and environmental impact of sustainable blended cement with
high-dosage Limestone and Calcined Clay (LC2).J. Clean. Prod. 278, 123616. https://doi.org/10.1016/j.jclepro.2020.123616.
).
Hence there is a need to find out the alternative to cementitious
materials which should be economical feasible, technically viable and at
the same time the replacement of clinker should be more.
The
utilization of ternary blended cements, which incorporate limestone and
blast furnace slag in an appropriate combination, offers a promising
approach to enhance the mechanical properties of concrete while
maintaining its sustainability. This combination of limestone and slag
exhibits a complementary effect, where limestone contributes to
early-age strength, and slag enhances strength at later stages of
concrete curing. Researchers have also developed models to predict the
strength of concrete incorporating ternary cements, emphasizing the
necessity of a minimum of 7 days of wet curing for achieving
satisfactory mechanical properties (1111.
Menéndez, G.; Bonavetti, V.L.; Irassar, E.F. (2006) Ternary blended
cement concrete. Part I: early age properties and mechanical strength. Mater. Construcc. 56 [284], 55-67. https://doi.org/10.3989/mc.2006.v56.i284.18.
, 1212.
Molina, F.L.; Fernández, Á.; Alonso, M.C. (2018) The influence of
curing and aging on chloride transport through ternary blended cement
concrete. Mater. Construcc. 68 [332], 4. https://doi.org/10.3989/mc.2018.11917.
).
To optimize the composition of concrete utilizing ternary composite
cements, multicriteria optimization techniques have been employed. These
techniques focus on jointly optimizing the absorption capacity and
compressive strength of concrete produced with Portland cement,
limestone, and/or granulated blast furnace slag. Through this approach,
researchers aim to find the most suitable proportions of each
constituent material, thereby maximizing the desired properties of the
concrete.
Furthermore, studies indicate that the adoption of
ternary cements can contribute to a reduction in the consumption of
non-renewable resources and energy during cement production, leading to
decreased CO2 emissions. This eco-friendly approach, however,
does not compromise the performance of the resulting concrete. The
integration of limestone and slag in ternary blended cements offers a
sustainable solution for improving concrete’s mechanical properties
while minimizing the environmental impact of the construction industry (13-1513. Menéndez, G.; Bonavetti, V.L.; Irassar, E.F.; (2007) Ternary blend cements concrete. Part II: Transport mechanism. Mater. Construcc. 57 [285], 31-43. https://doi.org/10.3989/mc.2007.v57.i285.37.
14.
Menéndez, G.; Bonavetti, V.L.; Irassar, E.F. (2007) Concretes with
ternary composite cements. Part III: multicriteria optimization. Mater. Construcc. 57 [286], 19-28. https://doi.org/10.3989/mc.2007.v57.i286.44.
15.
Alonso, M.C.; García-Calvo, J.L.; Lothenbach, B. (2016) Influence of
the synergy between mineral additions and Portland cement in the
physical-mechanical properties of ternary binders. Mater. Construcc. 66 [324], e097. https://doi.org/10.3989/mc.2016.10815.
).
An emerging technology, known as LC3 (Limestone, Calcined Clay, Cement), offers a promising solution to decrease CO2 emissions in cement production by up to 40%. LC3 is a triple blended cement that allows for the replacement of cement
clinker with a percentage of 50% or more. The composition typically
consists of 15% limestone (L), 30% calcined clay (CM), 5% gypsum (G),
and 50% clinker. LC3 technology utilizes abundant calcined
clays, which have a higher replacement capacity compared to other
alternative cementitious materials (ACMs). LC3 is a
low-carbon cementitious material aimed at reducing carbon dioxide
emissions compared to traditional cement. It involves the incorporation
of calcined clay as a partial replacement for clinker, the main
component of cement. The manufacturing process of LC3 entails
lower temperatures compared to the production of traditional cement
clinker. The calcination of the clay component in LC3 occurs
at temperatures ranging from 700 to 850 °C. In this process, appropriate
proportions of limestone, clay, and gypsum (or other additives) are
mixed, ground, and subjected to calcination at the aforementioned
temperatures. The lower temperature requirement during calcination
contributes to the reduction of the carbon footprint associated with LC3 in comparison to traditional cement. Following calcination, the
resulting material is finely ground and combined with clinker. The
proportion of clinker in LC3 can vary, but it typically
amounts to around 50%. The inclusion of clinker is necessary to achieve
the desired cementitious properties in LC3 (16-1816.
Scrivener, K.; Avet, F.; Maraghechi, H.; Zunino, F.; Ston, J.;
Hanpongpun, W.; Favier, A. (2018) Impacting factors and properties of
limestone calcined clay cements (LC3).Green Mater.7 [1], 3-14. https://doi.org/10.1680/jgrma.18.00029.
17.
Ivanović, M.M.; Kljajević, L.M.; Nenadović, M.; Bundaleski, N.;
Vukanac, I.; Todorović, B.Ž.; Nenadović, S.S. (2018) Physicochemical and
radiological characterization of kaolin and its polymerization
products. Mater. Construcc. 68 [330], e155. https://doi.org/10.3989/mc.2018.00517.
18.
Krishnan, S.; Emmanuel, A.C.; Bishnoi, S. (2019) Hydration and phase
assemblage of ternary cements with calcined clay and limestone. Constr. Build. Mater. 222, 64-72. https://doi.org/10.1016/j.conbuildmat.2019.06.123
).
Based on research work done by various authors on LC3 based mortars and concerts, it was concluded that the both mechanical
as well as durability properties are performed satisfactorily when
compared to other alternative binders (1919.
Ferreiro, S.; Canut, M.M.C.; Lund, J.; Herfort, D. (2019) Influence of
fineness of raw clay and calcination temperature on the performance of
calcined clay-limestone blended cements. Appl. Clay Sci. 169, 81-90. https://doi.org/10.1016/j.clay.2018.12.021.
, 2020.
Emmanuel, A.C; Bishnoi, S. (2023) Effect of curing temperature and
clinker content on hydration and strength development of calcined clay
blends. Adv. Cem. Res. 35 [1], 12-25. https://doi.org/10.1680/jadcr.21.00197.
).
As the workability of low carbon concrete is known to be less when
compared to CC which can be improved by addition of superplasticizers.
LC3 has good durability aspects with respect to sulphate
attack, reinforcement protection and many other factors. Besides it has
numerous advantages, due to the availability of clay material in the
local areas which could greatly reduce the charges of transportation and
the requirements of high kiln temperatures are eliminated to a large
extent, which helps to reduce the thermal energy up to 20-30%. As there
are many challenges faced by common ACM’s around the globe, LC3 becomes a better alternative due its low-cost nature (2121.
Dhandapani, Y.; Sakthivel, T.; Santhanam, M.; Gettu, R.; Pillai, R.G.
(2018) Mechanical properties and durability performance of concretes
with limestone calcined clay cement (LC3). Cem. Concr. Res. 107, 136-151. https://doi.org/10.1016/j.cemconres.2018.02.005.
, 2222.
Shah, V.; Parashar, A.; Mishra, G.; Medepalli, S.; Krishnan, S.;
Bishnoi, S. (2020) Influence of cement replacement by limestone calcined
clay pozzolan on the engineering properties of mortar and concrete. Adv. Cem. Res. 32 [3], 101-111. https://doi.org/10.1680/jadcr.18.00073.
). LC3 could be a modern technology which proves to be a sustainable material,
to get the optimum results and more durability than other types of
alternatives to the cement. In LC3 technology, due to the
presence of reactive aluminates in calcined clay and carbonates in
limestone involves in chemical reaction with the help of pozzolanic
action in CM and filling effect of L creates a synergetic effect of all
the constituents namely (limestone, calcined clay, and clinker) (2323.
Ez-Zaki, H.; Marangu, J.M.; Bellotto, M.; Dalconi, M.C.; Artioli, G.;
Valentini, L. (2021) A fresh view on limestone calcined clay cement (LC3) pastes. Mat. 14 [11], 3037. https://doi.org/10.3390/ma14113037.
, 2424.
Avet, F.; Scrivener, K. (2018) Investigation of the calcined kaolinite
content on the hydration of Limestone Calcined Clay Cement (LC3). Cem. Concr. Res. 107, 124-135. https://doi.org/10.1016/j.cemconres.2018.02.016.
). The pore size of LC3, gets reduced continuously with increase in curing period mainly due to
dense binder matrix which leads to dropout in the inter connecting of
pores. At early age of hydration LC3 system attained lower
pore size and reduced threshold size at microlevel, due to better
hydration property and there is a shift in the narrow pore space (2525.
Zunino, F.; Scrivener, K. (2021) The reaction between metakaolin and
limestone and its effect in porosity refinement and mechanical
properties. Cem. Concr. Res. 140, 106307. https://doi.org/10.1016/j.cemconres.2020.106307.
).
The refinement of pore structure in LC3 asset to create monocarboaluminate and hemicarboaluminate phases which
contribute to continuous development in microstructure. Higher fineness
in the calcined clay and clinker helps in the improvement of engineered
properties and plays a pivot role in creating submicronic particles
which reacts faster and provide surface for carboaluminate phases in the
binder matrix. Further, large quantity of clinker can be replaced with
LC3, which helps to create dense microstructure at inner binder matrix to enhance mechanical and durability properties (2626.
Dhandapani, Y.; Santhanam, M. (2017) Assessment of pore structure
evolution in the limestone calcined clay cementitious system and its
implications for performance. Cem. Con. Com. 84, 36-47. https://doi.org/10.1016/j.cemconcomp.2017.08.012.
). Present study was focused to identify the efficiency of LC3 at low water-binder ratio over other types of binders in terms of
hardened and durability characteristics of the resulting blending.
2. RESEARCH METHODOLOGY
⌅Present study focuses on evaluating the performance of LC3-based
high-performance concrete with 50% clinker replacement. Previous
studies have primarily explored low and medium-grade concretes using
different binder mixes. From a comprehensive literature review, it has
been observed that a combination of 30% calcined clay (CM), 15%
limestone (L), 5% gypsum (G), and 50% clinker has shown positive
outcomes in enhancing concrete properties (1111.
Menéndez, G.; Bonavetti, V.L.; Irassar, E.F. (2006) Ternary blended
cement concrete. Part I: early age properties and mechanical strength. Mater. Construcc. 56 [284], 55-67. https://doi.org/10.3989/mc.2006.v56.i284.18.
). To develop high-performance concrete with 50% clinker replacement, experimental investigations on LC3 concrete are required. The study examines the strength and durability
characteristics of two concrete mixes: Mix A, a high-strength concrete
with a target strength of 70 MPa, and Mix B, a standard strength
concrete with a target strength of 40 MPa. The obtained results are then
compared with equivalent mixes of conventional cement (CC) and
pozzolana cement (PC) based concretes.
3. EXPERIMENTAL INVESTIGATION
⌅3.1. Materials utilized
⌅Conventional cement -OPC-53 grade (CC) satisfying to IS 269 (2727.
Indian Standard, I.S. 269 (2015) Specification of requirements of
ordinary Portland cement. Bureau of Indian Standards, New Delhi, India.
[Google Scholar]
) and Portland pozzolana cement (PC) satisfying to IS 269 (2727.
Indian Standard, I.S. 269 (2015) Specification of requirements of
ordinary Portland cement. Bureau of Indian Standards, New Delhi, India.
[Google Scholar]
) was used as binders in the present investigation and low carbon cement (LC3)
procured from TARA, New Delhi, India is used as an alternative binder
to CC and PC with consists of Clinker: CM: L: G is 50:30:15:5. Physical
properties of all three binders i.e., CC, PC and LC3 are determined and tabulated in the Table 1. Gravel (CA) of 20 mm well graded satisfying the IS: 383 (2828.
IS 383, 2016. Coarse and fine aggregate for concrete-specification.
Bur. Indian Standards, New Delhi, India. [Google Scholar]
) and fine aggregate (FA) conforming to zone-II as per IS: 383 (2828.
IS 383, 2016. Coarse and fine aggregate for concrete-specification.
Bur. Indian Standards, New Delhi, India. [Google Scholar]
) was used as filling materials and the properties are shown in the Table 2. Poly carboxylic ether-based super plasticizer (SP) with brand name chryso optima-354 confirming to ASTM C494 (2929. ASTM, 2019. ASTM C494/C494M − 19: Standard specification for chemical admixtures for concrete. West Conshohocken, PA, USA. https://doi.org/10.1520/C0494_C0494M-19E01.
)
was used for better workability. Silica fume (SF) procured from apex
chemicals was added in Mix A-70 MPa concrete (8 % by weight of binder)
to attain required target strength at end of 28 days curing.
| No | TEST | CC | PC | LC3 |
|---|---|---|---|---|
| 1 | Consistency (%) | 31 | 33 | 35 |
| 2 | IST (min) | 56 | 48 | 37 |
| 3 | FST (min) | 430 | 470 | 360 |
| 4 | Specific gravity (SG) | 3.12 | 2.93 | 2.98 |
| 5 | Fineness (F) | 3% | 6% | 5% |
| 6 | Mortar cube strength at 28 days | 56.62 | 48.54 | 52.32 |
| No | Material properties | Gravel (10 &20 mm) | FA |
|---|---|---|---|
| 1 | Bulk Density (g/cc) | 1.64 | 1.76 |
| 2 | Specific gravity (SG) | 2.75 | 2.67 |
| 3 | Fineness Modulus (FM) | 7.75 | 2.76 |
| 4 | Void ratio (V) | 0.98 | 0.89 |
| 5 | Bulk Porosity (P) % as per IS 2386-Part III | 38 | 43 |
3.2. Concrete mix details
⌅Concrete mix proportions were designed as per IS 10262 (3030.
Indian standards guidelines for design and development of different
types of concrete mixes, IS 10262:2019. Bureau of Indian Standards, New
Delhi. [Google Scholar]
) and finalized based on
laboratory trail tests carried on large number of specimens by
considering a common binder content (370 kg/m3 and 500 kg/m3)
and water-cement ratios (0.46 and 0.34). Further, coarse aggregates
consist of 10 mm and 20 mm aggregates in the ratio of 45:55 respectively
is used in the mixes to obtain good packing density and Silica fumes
were added in Mix A-70 MPa grade concrete for achieving required target
strength and SP was also added to bring out the target slump of about
100 mm in the trial mixes. Final mix proportions are fixed based on the
28 days compressive strength results and the details of the mixes are
shown in Table 3.
Nomenclature for the Mixes A and B are given as OPC-70 which indicates
that Mix A with strength 70 MPa and the binder is CC similarly other
mixes also named according to strength of mix and type of binder.
| No | Strength of Concrete in MPa | Mix ID | Cement | FA (Zone-II) | Gravel (10 & 20 mm) | Water | SF | SP Dosage (% by weight of binder) |
|---|---|---|---|---|---|---|---|---|
| 1 | Mix A-70 | OPC-70 | 500 | 575 | 1295 | 160 | 40 | 1.85 |
| PPC-70 | 500 | 575 | 1295 | 160 | 40 | 1.65 | ||
| LC3 -70 | 500 | 575 | 1295 | 160 | 40 | 2.40 | ||
| 2 | Mix B-40 | CC-40 | 370 | 729 | 1098 | 155.4 | - | 0.85 |
| PC-40 | 370 | 729 | 1098 | 155.4 | - | 0.70 | ||
| LC3 -40 | 370 | 729 | 1098 | 155.4 | - | 1.20 |
3.3. Tests on Matured Concrete
⌅3.3.1. Mechanical properties
⌅Compressive
Strength (CS) of Concrete cubes of size100 mm x 100 mm were cast and
tested at the end of 7 D, 14 D, 28 D, 56 D and 90 D as per IS 516 (3131.
Bureau of Indian Standards, Is 516 (Part-1 Sec-I) - 2021, Hardened
Concrete —Methods of Test, Part 1: Testing of Strength of Hardened
Concrete, Section 1: Compressive, Flexural and Split Tensile Strength,
New Delhi. [Google Scholar]
). Split tensile strength
test (SPT) was performed on cylindrical specimens of size 75 mm radius
and 300 mm length according to IS 516 (3131.
Bureau of Indian Standards, Is 516 (Part-1 Sec-I) - 2021, Hardened
Concrete —Methods of Test, Part 1: Testing of Strength of Hardened
Concrete, Section 1: Compressive, Flexural and Split Tensile Strength,
New Delhi. [Google Scholar]
), at the end of 28 days
curing period. Flexural strength test (FST) was also conducted on prisms
of size 100 mm x 100 mm x 500 mm as per IS 516 (3131.
Bureau of Indian Standards, Is 516 (Part-1 Sec-I) - 2021, Hardened
Concrete —Methods of Test, Part 1: Testing of Strength of Hardened
Concrete, Section 1: Compressive, Flexural and Split Tensile Strength,
New Delhi. [Google Scholar]
). All the strength tests were carried on a 3000 kN compression testing machine with adjustable loading frame.
3.3.2. Resistivity of concrete
⌅The resistivity of concrete was determined using the Weener 4-probe resistivity meter ASTM G57 (3232.
Testing, A.S. 2020. Standard test method for field measurement of soil
resistivity using the wenner four-electrode method. American Society for
Testing and Materials, ASTM G 57-20,(2020) Annual Book of ASTM
Standards, 3. https://doi.org/10.1520/G0057-20.
).
This involved measuring the potential difference between two inner
probes while measuring the current flow in the two outer probes. The
surface of cylindrical specimens with a radius of 50 mm and a height of
200 mm was contacted under surface moisture conditions, and measurements
were recorded at three different locations. The resistivity of the
concrete was calculated using an empirical formula given by an Equation [1].
Where
I=Current
V=Voltage
a=inner distance between probes in cm
3.3.3. Defiance to chloride ion entry
⌅The defiance to chloride entry was determined using rapid chloride permeability test (RCPT) according to ASTM C 1202 (3333. ASTM, C. 2022. Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration. C1202 − 22. https://doi.org/10.1520/C1202-22E01.
),
to get a qualitative analysis of chloride ion ingress into concrete. An
average of three specimens (size 50 mm thick and 50 mm radius) was
chosen for each mix. The RCPT gives the total charge passed on a soaked
concrete sample which indicates the resistance against chloride entry.
3.3.4. Accelerated corrosion permeability test (ACPT)
⌅Accelerated
corrosion test was performed to know the corrosion resistance of
embedded steel in concrete under harsh environment conditions. Concrete
samples of size 100 mm (ϕ) and 200 mm length by inserting 10 mm diameter
steel bar were cast and tested at the required time period as per ASTM
C876 (3434.
ASTM International, 2022. ASTM C876-22b Standard test method for
corrosion potentials of uncoated reinforcing steel in concrete. https://doi.org/10.1520/C0876-22B.
).
3.3.5. Sorptivity test
⌅Sorptivity
is determined by calculating the rate of flow of water into the voids
of concrete by capillary suction according to ASTM C1585 (3535.
American Society for Testing and Materials (ASTM) (2013) Standard test
method for measurement of rate of absorption of water by
hydraulic-cement concretes, ASTM C1585-13, ASTM International, West
Conshohocken, Pennsylvania. https://doi.org/10.1520/C1585-13.
).
The concrete specimens are tested after completion of required curing
period and the cylindrical samples of size like RCPT were considered and
samples are placed in contact with water up to a level of 5 mm from
bottom. To evaluate the penetration of moisture, mass of each specimen
is recorded at frequent interval of time and thesorptivity coefficient
is calculated based on the Equation [2]:
Where
∆W=quantity of water absorbed in (g)
i=Water absorption coefficient = ∆w/(A x d)
A=cross-section area of specimen contacts with moist (mm2)
t=time (min)
S=the sorptivity coefficient of the specimen (mm/min0.5)
3.3.6. Porosity test
⌅Porosity
is the amount of air void between concrete medium. The porosity of
concrete is defined as the ratio of the volume of void gap in a unit
matter to the total volume of matter. The porosity of concrete is
determined by oven drying method after 28 days of specified curing. The
standard specimens of size 100mm diameter disc with a thickness of 50mm
were cast and tested as per ASTM C642 (3636. ASTM C642-21, A. 2021. Standard test method for density, absorption, and voids in hardened concrete. ASTM International. https://doi.org/10.1520/C0642-21.
). The porosity (Φ) of concrete is determined by using relation:
Where
p is the porosity (mass 100%)
Wssd is the sample mass in soaked surface dry (SSD) condition
Wd is the sample dry mass
Ww is the mass of the soaked specimen.
4. RESULTS AND DISCUSSIONS
⌅4.1. Strength results
⌅4.1.1. Compressive strength results
⌅Figure 1 in the study illustrates the compressive strength (CS) development of various concrete mixes, including Mix A-70 and Mix B-40 with LC3, and their correlation with conventional cement (CC) and pozzolana cement (PC) concretes. The results reveal that LC3-based concrete specimens exhibit higher compressive strength at all ages compared to CC and PC concretes in the high-strength concrete. This suggests that LC3 has a positive impact on strength enhancement. On the other hand, PC concrete exhibits lower strength at early ages (up to 28 days) regardless of the concrete grade. However, due to its pozzolanic action, it improves its CS value at later ages (56 days and 90 days) compared to CC concrete. The presence of silica fumes in LC3-based concrete, especially in higher grade concrete, contributes to its early-age strength development. This is a significant advantage in terms of strength achievement. Additionally, Mix B-40, the standard strength concrete, demonstrates similar behavior in strength attainment regardless of the binder used. Both LC3 and PC-based concretes achieve better strength results at later ages (56 days and 90 days) compared to OPC (ordinary Portland cement)-based concrete. This finding highlights the potential of LC3 and PC as alternatives to cement binders in terms of strength aspects.
The strength advancement in LC3-based
concrete, for both higher grade and standard grade, can be attributed
to the presence of rich alumina in calcined clay. This alumina reacts
with the calcium carbonate in limestone to form silica-carbide phases at
the microlevel (1818.
Krishnan, S.; Emmanuel, A.C.; Bishnoi, S. (2019) Hydration and phase
assemblage of ternary cements with calcined clay and limestone. Constr. Build. Mater. 222, 64-72. https://doi.org/10.1016/j.conbuildmat.2019.06.123
, 2222.
Shah, V.; Parashar, A.; Mishra, G.; Medepalli, S.; Krishnan, S.;
Bishnoi, S. (2020) Influence of cement replacement by limestone calcined
clay pozzolan on the engineering properties of mortar and concrete. Adv. Cem. Res. 32 [3], 101-111. https://doi.org/10.1680/jadcr.18.00073.
).
This reaction contributes to improved strength properties. In contrast,
CC-based concrete exhibits lower strength results at later ages (56
days and 90 days) due to the absence of pozzolanic reactivity phases at
the microlevel. The use of alternative cementitious materials (ACMs)
like LC3 can enhance the strength properties at later ages,
providing a promising approach for reducing cement manufacturing.
Overall, the benefits of LC3-based concrete include higher
early-age strength, better strength development in higher grade and
standard grade concretes, and the potential to reduce reliance on
conventional cement, thereby contributing to the reduction of carbon
emissions associated with cement production.
By analyzing the error bars, a notable trend emerges, the standard deviation of strength values at 7 days is higher compared to that at 28 days. However, in the case of 40 MPa concrete, this deviation is considerably lower than in the 70 MPa concrete. Despite the deviation, both concrete mixes achieve the required strength at 28 days, regardless of the binder used. Furthermore, there is a slight deviation observed at 90 days strength due to the improved strength in LC3-based concrete when compared to CC-based concretes. This discrepancy indicates the pozzolanic activity present in PC and LC3-based concretes. In summary, the comparison shows that the standard deviation of strength values is higher at 7 days but decreases at 28 days. The 40 MPa concrete exhibits lower deviation than the 70 MPa concrete. At 90 days, a slight deviation is observed due to the enhanced strength of LC3-based concrete compared to CC-based concretes. This difference signifies the presence of pozzolanic activity in PC and LC3-based concretes.
4.1.2. Split tensile strength and flexural strength results
⌅ Figure 2 and 3 shows the results of SPT and FST for Mix A-70 and Mix B-40 with various
types of binders. From SPT values, it was plainly noticed that all
types of concrete are attain similar results irrespective type of binder
and strength of mix. However, LC3 based concretes contribute
higher SPT value that that of CC and PC concretes, only marginal
differences are observed at end of 28 days testing. Figure 3 depicts the results for FS for Mix A-70 and Mix B-40 with different binder. From results it was observed that in case of FS, LC3 concrete shown better result than that of CC and PC concretes. Further studies should be carried to known efficiency of LC3 binder at later ages in terms of improvement in SPT and FS results. The attribution of strength in LC3 concrete is due to the formation of carboaluminate phases at inter
facial transition zone, which allows for the alternative binary
reactions in blended cements (1010.
Yu, J.; Wu, H.L.; Mishra, D.K.; Li, G.; Leung, C.K.; (2020) Compressive
strength and environmental impact of sustainable blended cement with
high-dosage Limestone and Calcined Clay (LC2).J. Clean. Prod. 278, 123616. https://doi.org/10.1016/j.jclepro.2020.123616.
).
4.2. Durability results
⌅4.2.1. Surface resistivity test results
⌅Surface resistivity provides valuable insights into the interconnectedness of pores within the concrete medium and serves as an immediate indicator of concrete quality in terms of its resistance to ionic ingress. Table 4 illustrates the corrosion rate corresponding to different electrical resistivity values. Figure 4 and 5 present the electrical resistivity of Mix A-70 and Mix B-40 concrete specimens with various binders at different curing ages (7 days, 14 days, and 28 days).
| Corrosion Rate as per (ASTM G57-06) | Very High | High | Moderate | Low |
|---|---|---|---|---|
| Electrical Resistivity (kΩ-cm) | < 5 | 05 to 10 | 10 to 20 | >20 |
The
results indicate that Mix A-70 MPa concrete exhibits higher resistance
compared to the 40 MPa concrete. This is attributed to the lower
water-binder ratio and the incorporation of silica fumes, which
contribute to improved resistivity. Conversely, LC3 concrete
consistently demonstrates higher resistivity values throughout the
curing stages, regardless of the concrete strength. The increase in
resistivity during the early stages of low carbon concrete is attributed
to the refinement of pore structure within the concrete system. In
contrast, PC-based concretes exhibit low corrosion rates during later
stages, particularly after 14 days of curing, and show enhanced
resistivity at 28 days due to extended pozzolanic reaction with
prolonged curing time. CC-based concretes, however, exhibit moderate
susceptibility to corrosion during the initial curing stages and
demonstrate minimal changes in resistivity with extended curing time.
Notably, in Mix A-70, CC-based concrete with silica fumes displays
better resistivity at 28 days of curing compared to Mix B-40. Overall,
LC3-based concrete demonstrates higher surface resistance
primarily due to the development of a dense microstructure within the
binder matrix. Additionally, PPC-based concretes exhibit significant
improvements in resistivity with prolonged curing periods (2020.
Emmanuel, A.C; Bishnoi, S. (2023) Effect of curing temperature and
clinker content on hydration and strength development of calcined clay
blends. Adv. Cem. Res. 35 [1], 12-25. https://doi.org/10.1680/jadcr.21.00197.
).
4.2.2. Defiance to chloride ion entry
⌅RCPT (Rapid Chloride Permeability Test) measures the quantity of chloride ion penetration into the concrete structure by determining the amount of charge passed in coulombs. Lower charge passed indicates higher resistance to chloride ion ingress. Figure 6 illustrates the experimental results of RCPT for Mix A-70 and Mix B-40 with different binders after a 28-day curing period.
The results indicate that LC3-based
specimens exhibit a lower amount of total charge passed, indicating a
significant contribution to resistance against chloride ingress in the
concrete, particularly during the early stages of curing, regardless of
the concrete grade. Moreover, PC-based specimens show improved
performance compared to CC-based specimens. Fly ash-based concretes
demonstrate enhanced quality only after 28 days of curing, whereas LC3 concrete exhibits better resistance to chloride ingress during the
early stages, which is a positive outcome for the utilization of
alternative binders in terms of enhancing durability at an early age of
the concrete. Furthermore, CC-based Mix A-70 concrete with the addition
of silica fume displays very low chloride ion permeability. Similarly,
LC3 concrete in the same mix exhibits negligible chloride ion
ingress. The primary reason for this resistance is the faster
reactivity potential of calcined clay, which aids in the creation of a
refined pore structure and a dense cement matrix at the microlevel.
This, in turn, prevents the entry of fluid medium into the concrete,
contributing to improved resistance to chloride ingress (2121.
Dhandapani, Y.; Sakthivel, T.; Santhanam, M.; Gettu, R.; Pillai, R.G.
(2018) Mechanical properties and durability performance of concretes
with limestone calcined clay cement (LC3). Cem. Concr. Res. 107, 136-151. https://doi.org/10.1016/j.cemconres.2018.02.005.
).
4.2.3. Accelerated corrosion permeability test results
⌅Impressed voltage technique was used to identify the susceptibility of concrete to corrosion environment. Resistance of concrete will be higher, when less amount of current is passed through a specimen and the post depassivation cracking time should be higher for the same specimen. Table 5 & Figure 7 shows the final critical corrosion current (CCR) in mA and post depassivation cracking time (PDCT) in hrs, results for Mix A-70 and Mix B-40 with different binders. From results it is found that the lower corrosion current (mA) was recorded for LC3 based concrete specimens when corelated to CC and PC based concrete specimens. On the other hand, the post depassivation cracking time is also higher for LC3 based concrete specimen, which indicates the strong resistance towards corrosion in harsh environments. Whereas PC based specimens are competitive and on par with LC3 specimens, this could be because of pozzolanic reaction at inner phases of concrete. However, CC based specimens reported higher critical corrosion current (mA) value irrespective of strength concrete and the cracking period is less, which indicates that the resistance to corrosion was not significant when corelated to LC3 and PC based concretes.
| Type of Binder | Mix A-70 | Mix B-40 | ||
|---|---|---|---|---|
| CCR (mA) | PDCT (hrs) | CCR (mA) | PDCT (hrs) | |
| OPC | 16.8 | 282 | 30.4 | 218 |
| PPC | 13.7 | 334 | 25.6 | 243 |
| LC 3 | 10.8 | 368 | 22.4 | 268 |
High
strength concrete i.e., Mix A-70 specimens has shown improved
resistance to corrosion when compared to standard concrete i.e., Mix
B-40 irrespective of type of binder, which is mainly due to the lower
water-binder ratio which creates dense pore structure at inter facial
transition zone of concrete phases and effect of silica fume helps in
evolution of secondary C-S-H gel. However, the post depassivation
cracking time was less in CC based concrete specimens, this indicates
early failure after the process of initial crack. Better resistance to
failure due to lower corrosion rate and delay in the initial crack was
observed in LC3 based concrete, which is a positive indication for attaining better durability. LC3 is one of the best alternatives for replacing cement up to maximum
extent without compromising the strength and durability aspects, because
clinker phases in OPC will undergo maximum reaction at early stages
whereas, LC3 develop sifted pore structure at starting stage
of hydration process. In addition to this due to the availability of
rich aluminates in calcined clay’s helps to create more binding at inner
transition zone when compared to other types of binders (22. Scrivener, K.; Martirena, F.; Bishnoi, S.; Maity, S. (2018) Calcined clay limestone cements (LC3). Cem. Concr. Res. 114, 49-56. https://doi.org/10.1016/j.cemconres.2017.08.017.
, 44.
Pillai, R.G.; Gettu, R.; Santhanam, M.; Rengaraju, S.; Dhandapani, Y.;
Rathnarajan, S.; Basavaraj, A.S. (2019) Service life and life cycle
assessment of reinforced concrete systems with limestone calcined clay
cement (LC3). Cem. Concr. Res. 118, 111-119. https://doi.org/10.1016/j.cemconres.2018.11.019.
).
4.2.4. Sorptivity test results
⌅Absorption
rate in concrete is determined based on the moisture ingress through
capillary action which is termed as sorptivity. The sorptivity
coefficient was determined from the descend of the linear relation
between cumulative water absorption (i) and square root of time (√t).
Higher the sorptivity values, higher was the porosity which represents
lower durability. Figure 8 depict the plots of cumulative water absorption (i) vs time0.5 (√t) and Figure 9 shows the sorptivity coefficient values for different mixes. From Figure 8,
it is clearly observed the absorption of water is more in case of Mix
B-40 specimens when compared to Mix A-70 specimens. However, CC based
concrete reported high water absorption in both mixes when compared to
the PC and LC3 based concretes. Due to supplement of ACM’s
the binary pozzolanic and high packing density attains lower water
absorption rate in PPC and LC3 based concretes. From Figure 9, it can be concluded that LC3 based concrete attains lower sorptivity coefficient value when relates
to other binders. However, PC based concrete reported minimal and on par
with the LC3 based concrete, as the supplementary
cementitious materials act as pore refinement in the inner phases of
concrete which will form binder matrix at capillary pores. Although CC
based concrete performed well in case of Mix A-70 but not up to level of
LC3 based concrete. The main reason for having improved
performance, in terms of strength, low permeability, high electrical
resistivity, high resistance towards chloride ingress, low critical
current and prolonged cracking period in LC3 based concrete
is due to the presence of fibrillar-like pore structure which further
helps in reducing threshold size and critical pore size at the
microlevel (1818.
Krishnan, S.; Emmanuel, A.C.; Bishnoi, S. (2019) Hydration and phase
assemblage of ternary cements with calcined clay and limestone. Constr. Build. Mater. 222, 64-72. https://doi.org/10.1016/j.conbuildmat.2019.06.123
, 2020.
Emmanuel, A.C; Bishnoi, S. (2023) Effect of curing temperature and
clinker content on hydration and strength development of calcined clay
blends. Adv. Cem. Res. 35 [1], 12-25. https://doi.org/10.1680/jadcr.21.00197.
).
4.2.5. Porosity test results
⌅The porosity (mass %) was determined based on oven drying method for Mix A-70 and Mix B-40 with three binders. Form Table 6 it is clearly identified that Mix A-70, LC3 based concrete undergone less porosity (mass %) when corelated to CC and PC concretes. However, PC based specimens exhibit similar trend that of LC3 based specimens, this is mainly due to the ternary action of binders which creates a dense cement matrix at inner phases of concrete. On other hand CC based concrete reported higher porosity value in Mix A-70, but in case of Mix B-40 CC based concrete has shown similar porosity (mass %) when compared to PC and LC3 based concretes.
| Type of binder | Porosity (mass %) | |
|---|---|---|
| Mix A-70 | Mix B-40 | |
| OPC | 6.61 ± 0.3 | 8.81 ± 0.2 |
| PPC | 4.98 ± 0.2 | 8.26 ± 0.4 |
| LC 3 | 4.27 ± 0.4 | 8.15 ± 0.5 |
Figure 10 shows the strength verses porosity relationship for different mixes
with the 28D-compressive strength values and 28D-Porosity values for the
two mixes of different binders. The strength vs porosity relationship
obtained from experimental investigation was compared with the various
models in the literature on cement-based materials (3737. Kumar, R.; Bhattacharjee, B. (2003) Porosity, pore size distribution and in situ strength of concrete. Cem. Concr. Res. 33 [1], 155-164. https://doi.org/10.1016/S0008-8846(02)00942-0.
) and this experimentally obtained strength-porosity values are compared with models of Balshin (3838.
Balshin, M.Y. (1949) Relation of mechanical properties of powder metals
and their porosity and the ultimate properties of porous-metal ceramic
materials. Dokl. Askd. Nauk SSSR, 67 [5], 831-834. [Google Scholar].
), Ryskovitch (3939. Hasselman DPH. (1969) Griffith flaws and the effect of porosity on tensile strength of brittle ceramics, Jou. Ame. Cer. Soc. 52[8], 457-457.
), Hasselman (4040. Rossignolo, J.A. (2009) Interfacial interactions in concretes with silica fume and SBR latex. Con. Bui. Mat. 23 [2], 817-821. https://doi.org/10.1016/j.conbuildmat.2008.03.005.
) and Schiller (4141. Ryshkevitch R. (1953) Compression strength of porous sintered alumina and zirconia. J. Am. Ceram. Soc. 36 [2], 65-68. https://doi.org/10.1111/j.1151-2916.1953.tb12837.x.
). The values of the parameters σ0 in models of Hasselman, Balshin and Ryskovitch correlate to the
strength of non-pervious material and are extrapolated to the strength
of samples at zero porosity. The proposed strength at zero porosity (σ0)
from Balshin, Ryskovitch and Hasselman are 87.40, 90.19 and 83.28 MPa.
It was clearly observed that the experimental data fitted well linearly
with all equations. Based on porosity results it is found that the
samples with more porosity values exhibits low CS value and lower
porosity values exhibit high CS value. The main reason that LC3 based concrete performed well in all aspects of durability properties
is due to the early reduction of inter connecting pore space by the
mechanism of ternary binding system. The resistivity of LC3 based concrete was significantly higher than that of CC and PC concretes
which is mainly due to refinement of pore structure (pore space
reduces) and also presence of highly reactive aluminate phases in
calcined clay, which allows to develop dense microstructure (66.
Sharma, M.; Bishnoi, S.; Martirena, F.; Scrivener, K. (2021) Limestone
calcined clay cement and concrete: A state-of-the-art review. Cem. Concr. Res. 149, 106564. https://doi.org/10.1016/j.cemconres.2021.106564.
, 1818.
Krishnan, S.; Emmanuel, A.C.; Bishnoi, S. (2019) Hydration and phase
assemblage of ternary cements with calcined clay and limestone. Constr. Build. Mater. 222, 64-72. https://doi.org/10.1016/j.conbuildmat.2019.06.123
).
5. CONCLUSIONS
⌅Based on experimental studies carried on two mixes (70 MPa and 40 MPa) with various types of binders (i.e., LC3, CC and PC), the following conclusions can be drawn:
-
LC3 concrete exhibited superior early-stage strength development compared to CC and PC concrete. However, at 90 days of curing, LC3 concrete (Mix A-70) achieved a 10% higher compressive strength (CS) value compared to CC concrete, while Mix B-40 specimens showed an 18% higher CS value.
-
In terms of resistivity, LC3 concrete specimens demonstrated 70% higher resistivity values at all curing stages, regardless of the concrete strength, when compared to CC concrete specimens. On the other hand, CC-based concretes exhibited moderate susceptibility to corrosion during the initial stages of curing and showed minimal changes in resistivity with extended curing time.
-
LC3-based specimens (Mix A-70) exhibited excellent resistance against chloride ion ingress during the early stages of curing, irrespective of the type of binder and concrete strength. Additionally, Mix B-40 specimens displayed a 40% higher resistance compared to CC specimens.
-
In conclusion, LC3-based concrete has demonstrated enhanced durability compared to normal concrete. The inclusion of LC3 has resulted in several beneficial outcomes. Concrete (Mix A-70) with LC3 exhibited a 55% higher resistance to moisture ingress compared to CC concrete. Similarly, Mix B-40 displayed a 40% increase in resistance and achieved lower porosity values when compared to CC and PC concretes.
-
The comprehensive studies conducted indicate that LC3 concrete exhibits superior performance in terms of hardened and durability aspects. It has shown high strength, low permeability, high electrical resistivity, increased resistance to chloride ingress, and a low critical current. These findings highlight the favorable attributes of LC3 concrete, suggesting its potential as a viable alternative to CC and PC concretes.
-
Overall, the incorporation of LC3 in concrete formulations holds promise for improving the performance and durability of concrete structures.