Mechanical and durability investigation of fiber effect in finer concrete with various admixtures

ABSTRACT

Waste recycling and reuse from the industries are effective way to maintain and enhance the sustainable environment. To investigate the optimal percentage of replacement of cement with industrial waste materials such as Alccofine and calcined clay and the addition of polypropylene fibre as an additive to concrete are the novelty of the present study. The use of polypropylene fibre in concrete is to improve its structural performance and sustainability. Polypropylene fibre was chosen for its excellent tensile strength, chemical resistance, low cost and cementitious material compatibility and also very good in decreasing cracks, enhancing durability. The study followed 15% and 30% replacement of Alccofine and calcined clay for cement and with 2% of fiber were added to enhance the mechanical and durability properties of M40. The study found that, 15% of replacement is optimal percentage of Alccofine and calcined to increase the mechanical properties such as 19.38% of compressive strength, 15.24% of bending strength and 14% of tensile strength. The microstructural studies confirmed that the increase in strength and durability of the concrete is due to the thinness of the Alccofine material and its ability to fill voids.

Keywords:
Alccofine; Calcined clay; Concrete and polypropylene fibers

1. INTRODUCTION

In developing countries, rapid industrialization and technological advancements have established concrete as one of the most essential construction materials [¹]. All over the world around million to billion tons of cement, fine aggregate, coarse aggregate, and water are being used per year for various infrastructure and construction projects. Cement production produces large amounts of CO₂, and cement is one of the most used materials in construction. There are two aspects of cement production that lead to CO₂ emissions. The first is the chemical reaction involved in production and the second source is the combustion of fossil fuels [²]. As the water content is required in large quantities, the hydration process leads to porosity in the concrete which is the most important aspect of the cementitious material and it is difficult to characterize the behavior of the porosity as the range of the scale is large from nm (nanometer)-cm (centimeter). Efforts to improve the performance of concrete over the past few years have shown that cement replacement materials and mineral and chemical additives can improve the strength and durability properties of concrete [³, ⁴, ⁵]. Cement, on the other hand, is taken as one of the important binding material which helps in binding all the materials used for the production of concrete together and helps in hardening the energy consumption during the production of cement is high and therefore the inclusion of fly ash improves the workability of concrete [⁶, ⁷]. Coral aggregate can also be used as a substitute in previous studies as it is lightweight, but it is not suitable for making concrete with high tensile strength or for using concrete structures in the terrestrial atmosphere. For structural applications, studies were conducted on concrete mixtures containing two types of calcined clay pozzolans obtained from Mancranso and Thanoso. The Mancranso specimen is marked as type I and Thanoso is also marked as type II [⁸]. Calcined clay is highly reactive towards pozzolanic materials, it helps to improve the microstructural pores of the structure at an early stage. Alccofine boosts early strength through rapid pozzolanic reaction, while calcined clay refines long term durability. Polypropylene fiber was chosen for its corrosion resistance, crack control with concrete. This is observed with an increase in the proportion of alccofine, which increases the resistance to chlorides and contributes to an increase in the sedimentation fluidity of concrete [⁹]. This project considers the possibility of using pond ash as a partial replacement for fine aggregates and using alcophene as a partial replacement for cement, which has the least environmental impact. As reported in the research [¹⁰, ¹¹], 20% replacement of fine aggregate with pond material and 10% replacement of cement with alcohol maximizes the strength of concrete and has superior durability properties compared to conventional concrete and other mixtures. Due to the high degree of hydration of CSH and Portlandite, the use of calcined clay and Alccofine can help increase the filling efficiency of the system to increase its strength. The use of Alcofin showed an increase in intensity compared to the corresponding reference beam [¹², ¹³]. The addition of Alccofine increases its self-compression properties such as fillability, throughput and segregation resistance [¹⁴, ¹⁵]. Alcofin is a recycled product based on a high content of reactive glass obtained from a controlled granulation process [¹⁶]. Experimental Study on High-Performance Concrete by Using Alccofine and Fly Ash – Hard Concrete Properties” which provided promising results [¹⁷]. Steel reinforcement is also widely used to increase the tensile strength of the concrete, but reinforcement may suffer due to the corrosion caused by the moisture and the carbon present in the atmosphere which leads to carbonation and ultimately failure of the structure [¹⁸]. Environmental pollution leads to chloride salts and sulphate attack when the concrete is in an exposed condition [¹⁹]. Different kind of sulphates present in the environment includes magnesium sulphate, sodium sulphate, calcium sulphate, ammonium sulphate in the solutions, which may result in affecting the concrete’s integrity.

Polypropylene fibre reinforced concrete (PFRC) is concrete mixed with randomly placed polypropylene fibre, which is short in length and mainly used to enhance the reinforcement property of the concrete internally. Polypropylene fibre is a lightweight synthetic fibre [²⁰, ²¹]. Compared to conventional concrete, it reduces cracks due to heat and shrinkage and increases strength. It was observed that polypropylene fibers did not have a significant effect on compression (or) bending strength, but bending toughness and impact strength showed increased values. Even at 2%, polypropylene fibre content increases the compressive strength to 28 N/mm² was observed [²², ²³, ²⁴]. One of the important principles for incorporating the fibre in the concrete is to reduce cracking and deformation by increasing the matrix of the fibre and the flexural, tensile, compressive strength as well as durability, workability, impact resistance of concrete [²⁵, ²⁶, ²⁷, ²⁸]. Fibers can affect the facets of uniaxial compressive behavior, including shear and tensile strains [²⁹, ³⁰]. The compressive and split tensile strengths of concrete samples made with different fiber percentages varied in the range of 0%, 0.5%, 1%, 1.5% and 2.0% [³¹]. The addition of polypropylene fibers does not significantly affect the direct tensile crack resistance [³²]. Adding water to fiber reinforced concrete to improve workability may reduce compressive strength [³³]. Increasing the fiber content and increasing the cement content further reduces the strength [³⁴]. The use of polypropylene fibres increases the resistance to shrinkage as well as its toughness in concrete along with its impact loading [³⁵, ³⁶].

The presence of altcoin powder and calcined clay in concrete increases the geopolymer concrete’s mechanical and durability properties. Alccofine powder accelerates the polymerization process, fills the voids in the concrete, and increases the compressive strength of geopolymer concrete [³⁷]. DANGI et al. [³⁸] predicted the strength characteristics of concrete using nanomaterials combined with alccofine and fly ash replacement for cement in M30 concrete grade. The study used 10% arccosine, 20% fly ash, and nano-silica (1 to 5%) replacement for cement and found that the presence of nano-silica, alccofine increases the density of concrete and reduces the pores percentage, which increases the strength of the concrete. NAVEEN KUMAR et al. [³⁹] carried out a detailed investigation to improve the alkaline resistance properties of concrete using alccofine and metakaolin powder. The study found that using alccofine and metakaolin in concrete increases the supplementary cementation system and reduces greenhouse gas emissions.

Based on the detailed literature studies, the combined use of alccofine and calcined clay for cement replacement in high-strength concrete needs more research to establish the usage of industrial waste. The optimal replacement percentage of alccofine and calcined varies with concrete application based on the use and environmental conditions. The novelty of the present study is to identify the optimal replacement percentage of industrial waste in high-strength concrete and evaluate the integrated properties, such as mechanical and durability properties of concrete with varying ages. In the present study, a detailed investigation aims to prove the effective use of alccofine and calcined clay in high-strength concrete. This paper presents the report on the experimental study on concrete with varying percentages of arccosine and calcined clay as partial replacement of cement and the mechanical strength of M40 grade blended cement concrete with polypropylene fiber as reinforcement.

2. MATERIAL AND METHODS

2.1. Materials

Concrete is generally made with cement, coarse aggregate and fine aggregate. In this research, the alccofine and calcined clay are added to the replacement of cement and polypropylene fibre is added as an additive to the concrete. The material properties have been carried out using Indian standards. Common Portland cement (OPC) grade 53 conforming to the IS 122692013 standard [⁴⁰] was used for this operation. The properties of coarse aggregates were established by performing several basic tests according to IS2386 (Part III) 1963, such as specific gravity, impact test, absorbency, sieve analysis, etc. Throughout the study, basic tests were performed to determine some physical properties such as specific gravity, water content and particle size factor as fine aggregates in concrete mixtures. Alccofine is a patented mineral supplement based on calcium silicate. The controlled granulation process provides a unique particle size distribution. The hydration process is enhanced due to its hydrodynamic potential and pozzolanic reactivity. The addition of Alccofin improves the packing density of the paste component. The specific gravity of alcohol is 2.86 and the degree of grinding is 12,000 cm²/g. Limestone calcined clay cement (LC3) is a low-carbon cement developed by the Lausanne Federal Polytechnic School. Rural Development Activities and Central University of Las Villas (Cuba). Cement can reduce manufacturing-related carbon dioxide (CO2) emissions by up to 30% compared to conventional Portland cement. In 2014, the calcined clay project received a CHF 4 million funding for research and development from the Swiss Development and Cooperation Agency (SDC).

2.2. Mix proportions

Mixture proportions of concrete grade M40 are compiled for cubes, cylinders and beams, and materials are also calculated for these samples. The composition of the mixture can be expressed as the ratio of cement: sand: aggregate. Calculation of concrete mixtures involves various steps to determine the optimal composition and required calculations according to the IS 456:2000 [⁴¹] standard. The physical properties of the alccofine are mean particle size of the materials is 4.25 µm, fineness is 11570 cm²/gm, specific gravity is 2.875 and bulk density is 642 kg/m³. Calcined clay properties are specific gravity of 2.65, bulk density is 345 kg/m³. Based on the literature studies, 5 to 30% of alccofine and calcined clay has been replaced by cement in high strength concrete. The optimal percentage were varying from 10 to 30% for alccofine and 15 to 35% for calcined clay in previous studies. In order to identify the optimal percentage, the study followed 15% and 30% of alccofine (15% increase in each trial mix), 15% and 30% of calcined clay (15% increase in each trial mix) has been used (Table S1). The Mix ratio 1:1.508:1.85. The cement content is 520 kg/m³, coarse aggregate 960.284 kg/m³, fine aggregate 784.252 kg/m³, water 208 l/m³. The specific percentage of replacement levels were calculated in order to increase the cementitious properties of the concrete, density, mechanical behavior and durability of the concrete.

2.3. Experimental procedure

It uses a cubic mold measuring 150 × 150 × 150 mm and a cylindrical mold 300 mm high and 150 mm in diameter, carefully cleaned with a dry cloth and oiled before pouring. After measuring the weight of cement, fine aggregate, and coarse aggregate by weight, they were mixed on a waterproofing platform under standard conditions. Water was added gradually until all ingredients were properly mixed to form a homogeneous mixture. Then fresh concrete was poured into the mold and compacted with a standard rammer. The compressive strength of all mixtures was measured on a cube sample measuring 150 mm (length) × 150 mm (width) × 150 mm (depth). According to IS 516-1959 standards for compressive, tensile and flexural strength tests, the concrete strength test method [¹², ⁴²], the specimen was completely immersed in a water bath for 7 and 28 days and then cured. The bending strength of all mixtures was measured using a beam. Sample size 700 mm (length) × 150 mm (width) × 150 mm (depth). For the test method for concrete strength [⁴²], the specimens were tested according to IS 516-1959 standards, for compressive, tensile, and flexural strength tests after being fully immersed in a water tank and cured for 28 days. For testing, we used the centroid loading method.

Bending strength, also known as modulus of elasticity, is a brittle material mechanical parameter is defined as a material that can withstand deformation under load. Bending strength is the highest stress applied to a material at the moment it breaks. A sample of 100 mm × 100 mm × 500 mm was used for this test. Samples were tested on universal testing machines. Note the load at which the control sample will eventually fail. Bending strength is calculated using the formula: Bending strength = 𝑝𝑙/𝑏𝑑2 (MPa) where P = maximum load (N), l = length between supports (mm), d = specimen depth (mm), and b = specimen width (mm). The tensile strength upon separation of all mixtures was measured on a cylindrical sample measuring 300 mm (length) × 150 mm (diameter). For the method of testing the tensile strength of concrete in splitting, the specimens were tested after being fully immersed in a water tank and cured for 28 days according to IS 5816:1999 – Method of Test for Splitting Tensile Strength of Concrete. New Delhi: BIS, 1999. In the direct method, it is difficult to accurately hold the specimen in the testing machine without stress concentration, and it is difficult to apply a uniaxial tensile load without eccentricity. Because concrete has weak tensile forces, even small load eccentricities cause combined bending and axial forces, and concrete fractures at apparent tensile stresses rather than tensile forces. The absorbance value is used to calculate the weight change due to water absorption in the pores. It is used to determine the amount of water absorbed, considering the cube’s initial weight (W1) and final weight (W2) after drying, after which the absorption rate is calculated. An acid resistance test was performed on cubes measuring 150 × 150 × 150 mm stored for 28 days. After 28 days, the hardened cubes were removed and left to dry for 24 hours before being weighed in hydrochloric acid (HCl) medium.

2.4. Microstructural studies

After the 28-day compressive strength test, the sample was finely ground and passed through a 90 μm sieve, and the sample was used for SEM and XRD tests. X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of crystalline materials and can provide information on unit cell dimensions. The test material is ground finely and homogenized and the average bulk composition is determined.

3. RESULT AND DISCUSSION

3.1. Basic test

Table 1 compares the initial setting times of cement slurries with different calcined clay (CC) and Alccofine (AF) ratios. As the content of calcined clay (CC) and Alccofine (AF) increases, the setting time also increases proportionally. Initial setting time when the needle penetration depth of the Vicat device reached 45 mm. This indicates a gradual decrease in penetration depth. As a result, the curing time of OPC with various CC and AF ratios is 24 hours, which is much longer than all other mixed pastes. This is due to the presence of large amounts of calcined clay (CC) and Alccofine (AF) with cement, which is itself a retardant.

Table 1
Physical properties of materials.

MIX COMBINATION	INITIAL SETTING TIME (MINS)	FINAL SETTING TIME (MINS)
OPC	45	320
15% CC	155	350
30% CC	230	510
15% AF	295	660
30% AF	350	780
OPC + 2% PF	85	300
15% CC + 2% PF	125	330
30% CC + 2% PF	190	480
15% AF + 2% PF	240	570
30% AF + 2% PF	315	750

3.2. Chemical composition of materials

The chemical composition of the cementitious materials is shown in Table 2. When comparing the proportions of CaO and SiO₂, the availability of CaO is very high in cement while SiO₂ in the calcined clay (CC) content is very high, which makes us, understand a possible fact that the formation of CSH will be more in the calcined clay (CC) blended concrete. Also, it can be inferred from the results, that the finer AF doesn’t really affect the chemical combination and it has only reduced the particle size. Next to the CSH structure another crystalline structure that increases the strength of concrete is mullite, the composition indicates that the amount of Al₂O₃ is also high in calcined clay (CC) and Alccofine (AF), thus it is expected for the formation of more mullite in concrete.

Table 2
Comparison of chemical composition.

COMPOSITION	SiO2	Al2O3	Fe2O3	CaO	MgO	K2O	Na2O	SO3	LOI
OPC	21.41	5.54	4.47	62.32	1.23	0	0	2.83	1.05
Calcined Clay	55.9	23.70	6.84	3.12	1.64	1.35	1.06	0.69	2.37
Alccofine	37.31	23.53	6.46	1.59	6.58	1.37	1.04	0.7	2.14

3.3. Workability results

The workability test values of OPC substituted with different ratio mixtures of calcined clay (CC) and Alccofine (AF) are compared with Table 3. Because the amount of water required to achieve consistency when adopting Alccofine (AF) as a substitute increases as the calcined clay (CC) content of cement paste increases. Material, water requirements are very low compared to mixed calcined clay (CC) paste. This water requirement may be due to the unburned carbon content of the calcined clay (CC), which requires more water to reach consistency. Grinding of GGBS reduces the particle size and improves the properties of Alccofine (AF), increasing the consistency of the mixed composite paste, reducing water demand.

Table 3
Workability of blended concrete.

MIX COMBINATION	SLUMP IN mm	COMPACTION FACTOR
OPC	25	0.86
15% CC	30	0.85
30% CC	25	0.84
15% AF	35	0.86
30% AF	30	0.86
OPC + 2% PF	35	0.85
15% CC + 2% PF	30	0.87
30% CC + 2% PF	25	0.86
15% AF + 2% PF	45	0.89
30% AF + 2% PF	35	0.88

3.4. Compression strength of concrete

The results of compressive strength were presented in Figures 1 and 2, the test has carried out conforming to IS516-1959 to obtain compressive strength of concrete at the age of 7, 14 and 28 days. From the results, compressive strength is 33.45 MPa at 14 days and 44.96 MPa at 28 days for 15% replacement of cement with Alccofine which is the optimum content on comparison with 30% replacement. 30% compared to replacement. The replacement levels of 15% and 30% were selected based on previous studies which reported that cementitious replacements in this range often provide balance between strength development and durability. The 15% replacement was specifically chosen to evaluate the optimal dosage for strength enhancement without compromising workability or early-age strength, while 30% was included to investigate the upper limit of replacement where the pozzolanic benefits might begin to plateau or decline due to dilution of cementitious content. This comparative approach helps identify the most effective dosage for maximizing compressive strength and microstructural performance. Due to the high pozzolanic properties of alccofine and its ability to fill voids, the compressive strength of concrete is greatly improved, whereas the compressive strength decreases with higher alccofine content [⁴²]. By using 15° as a cement substitute, the compressive strength of concrete was increased to 31.21 MPa and 43.07 MPa, which showed higher compressive strength than conventional concrete and 30% SS-cement substitute concrete, assuming voids Filling of the smallest clay particles Force increases the compressive strength of concrete. Each group tests three concrete samples, and the compressive strength is calculated according to the average value [⁴³].

Figure 1
Compressive strength of blended CC with cement concrete.

Figure 2
Compressive strength of blended AF with cement concrete.

The addition of 2% of polypropylene fibre increases the compressive strength of concrete while replacing the cement with Alccofine (AF) and calcined clay (CC). The optimum percentage of replacement of alccofine for cement was found to be 15% which provided the compressive strength of 36.5 MPa and 47.93 MPa which is around 8 MPa greater than that of the conventional concrete for 14 and 28 days respectively. The calcined clay (CC) replacement was also optimized at 15% where the compressive strength for 14 and 28 days were found to be 35.26 MPa and 45.64 MPa which is around 7 MPa greater than that of conventional concrete with 2% addition of polypropylene fibre which suggests that the inclusion of fibre in the concrete matrix increases the compressive strength of the concrete.

3.5. Split tensile of concrete

The results of cleaving tensile strength are shown in Figures 3 and 4, respectively. Tests were performed to determine the tensile strength of concrete after 14 and 28 days according to IS5161959. As a result, when alccofine was replaced with 15% cement, the tensile strength was 2.7 MPa after 14 days and 4.17 MPa after 28 days. Due to the high pozzolanic properties of Alccofine and its ability to fill voids, the tensile strength of concrete is greatly improved. By using 15° as a substitute for cement, the tensile strengths of 2.4 MPa and 3.89 MPa, which are higher than the compressive strength of conventional concrete, and the tensile strength of concrete in which SS was substituted for cement by 30% were improved. It suggests that the ability of the smallest clay particles to fill the voids increases the compressive strength of concrete [⁴⁴].

Figure 3
Split tensile strength of blended CC with cement concrete.

Figure 4
Split tensile strength of blended AF with cement concrete.

(1) $$\text{ftc = 2F/πA = 0}\text{.637 F/A}$$

The shear strength results are shown in Figures 3 and 4, respectively. Tests were performed to determine the tensile strength of concrete after 14 and 28 days according to IS5161959. As a result, when the alccofine was changed to 15°, the tensile strength of was 2.7 MPa after 14 days and 4.17 MPa after 28 days. Due to the high pozzolanic properties of Alccofine and its ability to fill voids, the tensile strength of concrete is greatly increased. When 15° was used as a cement substitute, the tensile strengths of 2.4 MPa and 3.89 MPa, which were higher than the compressive strength of general concrete, and the tensile strength of concrete in which Silica sand (SS) was replaced with cement were improved by 30%. This suggests that the ability of small clay particles to fill the voids increases the compressive strength of concrete [⁴⁵].

3.6. Flexural strength test of concrete

The bending strength results are shown in Figures 1, 5 and 6. According to IS5161959, the flexural strength of concrete at 14 days and 28 days was obtained. As a result, when 15% of alccofine was replaced with cement, the tensile strength at splitting was 4.8 MPa after 14 days and 5.5 MPa after 28 days. Due to the high pozzolanic properties of Alccofine and its ability to fill voids, the flexural strength of concrete is greatly improved [⁴⁶]. The use of 15% calcined clay (CC) as a replacement for cement increased in flexural strength of concrete to 4.3 MPa and 4.9 MPa which is greater than the flexural strength attained by the conventional concrete as well as concrete with 30% replacement of calcined clay (CC) for cement suggesting that the pore filling ability of the minute clay particles increases the flexural strength of the concrete [⁴⁷].

Figure 5
Flexural strength of blended CC with cement concrete.

Figure 6
Flexural strength of blended AF with cement concrete.

The addition of 2% of polypropylene fibre increases the flexural strength of concrete while replacing the cement with alccofine and calcined clay. The optimum percentage of replacement of alccofine for cement was found to be 15% which provided the flexural strength of 4.8 MPa and 5.7 MPa which is around 0.5 MPa greater than that of the conventional concrete for 14 and 28 days respectively. The calcined clay (CC) replacement was also optimized at 15% where the flexural strength for 14 and 28 days were found to be 4.4 MPa and 5.2 MPa which is around 0.3 MPa greater than that of conventional concrete with 2% addition of polypropylene fibre which suggests that the inclusion of fibre in the concrete matrix increases the flexural strength of the concrete.

3.7. Water absorption test

Water is used for moisture absorption testing. The test procedure is the same as the chloride resistance test. The mass loss and strength loss of the sample under the influence of water were measured. The absorption test results are shown in Figures 7 and 8. A conditional absorption test was performed on concrete aged 28 days. After 28 days, the absorption rate is 1.00%.

Figure 7
Percentage of water absorption of blended CC with cement concrete.

Figure 8
Percentage of water absorption of blended AF with cement concrete.

3.8. Acid resistance test

The Concrete mixes of OPC with different replaced of calcined clay (CC) and Alccofine (AF) at various percentages were analysed the acid resistance and shown in Figures 9 and 10 respectively. The cubes were to be immersed in HCl solution for 28 days. The concentration is to be maintained throughout this period. After 28 days the specimens were taken from the acid solution [⁴⁸]. The surface of the specimen has cleaned, and weights were measured. The specimen was tested in the compression testing machine under a uniform rate of loading 140 kg/cm² as per IS 516 [⁴⁹]. The loss of mass and loss of strength of specimen due to hydrochloric acid Attack was determined.

Figure 9
Percentage of water absorption of blended CC with cement concrete.

Figure 10
Percentage of water absorption of blended AF with cement concrete.

The results of the acid resistance test were presented in Figures 11 and 12. The test has carried out conforming to obtain acid resistance of concrete at the age of 28 days. The replacement of 30% of calcined clay (CC) and Alccofine (AF) reported the lease percentage of weight loss in 120 days which was around 7.3% and 6.4% which is lesser compared to 9.15% of conventional concrete. The inclusion of polypropylene fiber in concrete significantly reduced the percentage weight reduction of concrete by around 0.07% from the above-said values suggesting that 30% replacement of cement with calcined clay (CC) and Alccofine (AF) respectively provided the most desirable results. This significant improvement in the acid resistance of concrete is because of the high pozzolanic nature of the Alccofine and calcined clay and its void filling ability [⁵⁰].

Figure 11
Compressive strength of blended CC with cement concrete with acid curing.

Figure 12
Compressive strength of blended AF with cement concrete with acid curing.

3.9. Micro structural study results

In addition to mechanical properties of concrete such as compressive strength and tensile strength, it is very important to recognize changes in the microstructure of concrete because major changes occur only in the binder. SEM images of concrete and calcined clay (CC), Alccofine (AF) mixtures are shown in Figure 13. SEM images at 5-micron magnification are compared at 28 days of age for the optimal mixture [⁵¹, ⁵²]. The SEM images of calcined clay (CC) and Alccofine (AF) show the size change of AF particles, CC particles are round and AF particles are very irregular and relatively very small [⁵³]. The comparison between the calcined clay (CC) and Alccofine (AF) concrete shows that in the OPC concrete there is a lot of un-hydrated SiO₂ in the structure, which is identified from the spherical structure in the SEM images, while the Alccofine (AF) concrete shows no sign of un-hydrated compounds which shows the pulverization increases the reactivity between the water and cementitious products which resulted in very compact structural formation [⁵⁴].

Figure 13
SEM images of blended concrete at the age of 28 days.

In addition, AF concrete has a very dense structure compared to conventional concrete samples, indicating the effectiveness of the filler and the formation of more hydration products in the concrete. Comparing the images of AF and concrete, the needle-like structure of concrete is clearly visible, and it can be seen that ettringite is formed due to small particles [⁵⁵, ⁵⁶, ⁵⁷, ⁵⁸]. It also shows the increase in concrete strength due to the addition of Alccofine (AF). For concrete with calcined clay (CC) and Alccofine (AF) additives, the element content range does not change significantly with the addition of fine particles, as can be seen in the SEM plot [⁵⁹, ⁶⁰, ⁶¹, ⁶²].

X-ray diffraction patterns for various calcined clay (CC) percentages are shown in Figure 14. This indicates that most of the peaks are related to the presence of quartz and mullite in the feed, which also extends to a higher intensity for calcined clay (CC) when comparing the peaks at the 26.6 peak, which is attributed to the quartz. Also, for OPC there is a small peak for Fe₂O₃ at 33.25. Aside from these changes, there is little change in the diffraction patterns obtained from the Alccofine (AF) and OPC samples. on Figure 15 shows the XRD spectra of OPC concrete samples with different Alccofine (AF) ratios. Peaks in the 2θ range between 18° and 70° were assigned to appropriate crystalline compounds for which most of the peaks were present in the spectrum. The main peaks in the spectrum are quartz, calcium silicate hydrate (CSH), calcite, aragonite, vaterite, portlandite (Ca(OH)₂, calcium aluminum hydrate (C₄AH₁₃), mullite, hematite, ettringite and calcium, the main peaks 26.6 and 27.9 of the zincate (CaZn₂(OH)₆·2H₂O) OPC concrete sample are for quartz and CSH, respectively, indicating that quartz and CSH in the concrete are necessary compounds for strength improvement. More specifically, V represent the presence of calcium carbonate (CaCO₃), M represent the presence of combination of calcium magnesium and silicate (Merwinite), Q represent the presence of quartz [⁶³, ⁶⁴].

Figure 14
XRD pattern of blended CC with cement concrete at age of 28 days.

Figure 15
XRD pattern of blended AF with cement concrete at the age of 28 days.

When comparing the peaks of OPC and calcined clay (CC) blended concrete, the major peak shows a variation in terms of counts which indicates the more available C-S-H compound in 15% calcined clay (CC) blended concrete. This caused the strength of concrete to get increased when compared to the conventional concrete itself. Also, for AF blended concrete the elongation of the major peak is huge while comparing the other blends. The major peaks for the OPC + AF blended concrete are assigned to C-S-H. this indicates that there is a huge availability of reactive Si and Ca from fly ash and cement necessary for the formation of CSH in the concrete. When analyzing the spectrum of concrete samples with AF shown the availability of ettringite in some of its peaks, thus the SEM imaging and XRD spectrum of concrete samples confirm the presence of Ettringite in concrete. The formation of ettringite is attributed to the availability of sulphate in the concrete. At 28-day compressive strength increased with 15% replacement primarily due to the enhanced pozzolanic reaction. The reactive silica and alumina in the additive reacted with Ca(OH)₂ (a by-product of cement hydration) to form additional calcium silicate hydrate (C-S-H) gel, which is responsible for strength development. Furthermore, the formation of ettringite during the early hydration stages helped refine the pore structure. If the additive contained thermally treated clay, the presence of mullite contributed to long-term strength and thermal stability due to its crystalline, rigid structure. Along with ettringite, there is an availability of CaZn₂(OH)₆·2H₂O in peaks at 32.092, this confirms with the findings of [⁶⁵, ⁶⁶, ⁶⁷, ⁶⁸].

4. CONCLUSION

In order to reduce the greenhouse gas emission, utilization of waste products from industries, enhance the mechanical and durability properties of high strength concrete, the present study used alccofine and calcined clay materials. As from the above done experimental studies and microstructure characterization, the following conclusions were drawn,

• The use of calcined clay (CC) in concrete increases the formation of CSH by 15%, while the use of Alccofine (AF) does not affect the chemical composition of the materials.

• The replacement of calcined clay (CC) for cement increases the water requirement due to the presence of unburnt carbon, while the use of Alccofine (AF) as a replacement reduces the water requirement since the particles are finer due to the pulverization of GGBS.

• The study found that, 15% of replacement is optimal percentage of Alccofine (AF) and calcined clay (CC) to increase the mechanical properties such as 19.38% of compressive strength.

• The flexural strength of concrete reaches 5.5 MPa with 15% AF and 5.7 MPa with 15% Alccofine (AF) and 2% PF because of the high pozzolanic nature of Alccofine.

• Comparatively, 30% of Alccofine (AF) replaced concrete absorb less amount of water than other trail mixes. The study found that, increasing percentage of Alccofine (AF) in concrete reduce the water absorption capacity of concrete.

• Microstructure analysis suggested that the binding between the particles due to the addition of alccofine and calcined clay increased which was evident from the SEM and XRD studies, which is proven, by the increase in the compressive strength.

Based on the present study results, usage of Alccofine and calcined clay materials are more significant to reduce the greenhouse gas emission and to strengthen the mechanical and durability property of M40 concrete.

SUPPLEMENTARY MATERIAL

The following online material is available for this article

Table S1: Trail mix for all combinations.

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Publication Dates

• Publication in this collection
  05 Sept 2025
• Date of issue
  2025

History

• Received
  10 Mar 2025
• Accepted
  30 July 2025