Introduction

Concrete is one of the most widely used construction materials across the globe, while Ordinary Portland cement (OPC)is one of the most used binding agents in concrete production. The production of cement requires the use of raw materials and energy, which leads to increased emissions of CO21. The cement industry contributes between 5 and 8% to global carbon dioxide emissions2,3. Cement production generates large amounts of solid and liquid wastes that lead to the extensive use of energy and raw materials in the production process3. Furthermore, the process of cement manufacturing not only increases the cost but also has negative impacts on the environment. Under such situations, it is essential to reduce the emission of carbon dioxide (CO2) during cement production and consequently reduce energy costs, while also ensuring safety and sustainability4.

In recent decades, agricultural development has significantly increased, generating substantial volumes of waste materials. Proper management of waste disposal emerges as a significant concern, given that most of the garbage is deposited in landfills, resulting in a reduction of usable land space and environmental pollution. Several different byproducts, such as blast furnace slag, silica fume, and coal fly ash have been employed as cementitious materials, leading to enhanced concrete performance5,6,7,8,9,10. Sugarcane is the predominant crop produced globally for sugar production. Statistics indicate that the total area of land dedicated to sugar cultivation worldwide is approximately 31.3 million hectares. The leading countries in the production of sugarcane, Brazil ranks first with 36% production, India with 17%, Thailand with 8%, China with 7%, and Pakistan with 4% respectively11.

SCBA (Sugarcane bagasse), commonly utilized as an energy source in the sugar production industries, is also utilized as a primary resource in the paper-making industry. The pozzolana formed by this ash is acquired through the burning of the residual substance left after extracting the juice from sugar cane. The pozzolanic characteristics are primarily influenced by the source, calcination method, and the maximum temperature reached during burning. Due to the high carbon content above 15% and small particle size, SCBA can have high pozzolanic activity and improve strength when used as a hydraulic binder12. Based on the literature review, several authors have noted an increase in the compressive strengths of concrete after 7 days and 28 days with the incorporation of 10% of SCBA as cement replacement13,14. Concrete with 10% SCBA increases the mechanical properties of concrete and reduces the workability of the concrete while it increases the water absorption capability as the content of bagasse ash increases15. Some of the unique characteristics of concrete produced with SCBA as cement replacement were enhanced early-age concrete strength, low permeability to water, and high resistance to absorption and diffusion of chlorine, reported by Amin et al.16 and Ganesan et al.17. The use of polypropylene (PP) fibers in concrete helps mainly increase the mechanical properties and reduce micro-cracking, as well as concrete permeability and its resistance to acid penetration.

Ternary blends improve the properties of fresh and hardened concrete, decrease concrete’s negative impact, and increase its durability18. Some of the potential blends incorporated in concrete include slag, fly ash, GGBS, and silica fume and these have superior workability, improved specific gravity, and better environmental benefits when compared to other materials19. It reduces the demand for raw materials by recycling and reusing industrial waste20. Thus, it is necessary to maintain a proper proportion to achieve a significant performance.

According to prior studies, it is evident that incorporating further cementing materials into the primary concrete blend improves the product’s performance, making up for the absence of specific cementitious characteristics21,22. The combination of greater than one SCM has drawn interest for its potential to enhance the cement properties. Research on the ternary blends which include OPC with these additives indicate that the ternary blends prove to be cheaper and have less impact on the environment than binary blends. Several previous investigations show that ternary blends decrease the cement content while increasing the functionality of concrete for the intended purposes. Ternary methods and their combinations indicate that the use of multiple blends would remove the undesirable effects of binary blends23. Ternary blend systems provide good environmental performance, efficiency, and better mechanical properties compared to single constituent replacement24,25.

The purpose of this investigation is to evaluate the feasibility of including SCBA with other blended cementitious materials in the manufacturing of environmentally friendly concrete products, considering the ongoing worldwide challenge of mitigating the negative impact of building development on the environment. Ultimately, through different ternary blends of concrete, the study will seek to increase the efficiency of concrete, improve durability, and, at the same time, consider the effects of cement on the environment. The findings of this research will evaluate the efficiency of SCBA in enhancing the cementitious material and mechanical properties of concrete and aid in determining the overall sustainability of concrete as a substitute for usual materials. It will also examine how these blends are useful in efforts towards improved waste management as well as the efficient utilization of resources. It is believed that the results will provide practical recommendations on how to use SCBA in cementitious compositions while contributing to the achievement of global sustainability targets and meeting the problems of waste disposal and carbon emissions. Thus, the study is aimed at contributing to further improvement of environmentally friendly construction approaches and fostering the shift towards more sustainable construction practices.

Novelty

This research explores the effects of adding bagasse ash, metakaolin and polypropylene (PP) fibres simultaneously in the production of concrete. It provides a new method for modifying the properties of concrete for better performance as well as durability. Although research work done individually has reported consequences when these additives are used, to date there is a scarcity of information on their synergistic effects in the above-stated proportion26,27,28. This research adds to the growing knowledge of these composites’ interaction and their effects on the possibilities of further enhancement of the ratio of the composites in the ternary system. Hence, this research seeks to contribute to enhancing knowledge on proportional control of these composites and their properties such as strength and durability. This study provides the foundation for subsequent research that focuses on further improvements in the performance and implementation of these composite materials in the context of sustainable construction.

It is a new approach for the application and proportioning of Sugarcane Bagasse Ash (SBA), metakaolin, and polypropylene fiber in a ternary blended concrete system with a view of establishing their interactive impact on mechanical and durability characteristics. Compared with other works that have focused only on these materials individually, the present work analyzes the composite behaviour of these materials and how the variation of a particular characteristic of concrete affects this pattern of combination. The findings reveal potential enhancements in concrete durability, reduction of deterioration effects, and possibilities for future study to develop cost-effective and sustainable construction materials.

Rationale behind selection

The reason for the use of 5% sugarcane bagasse ash (SCBA), 1–1.5% polypropylene fibers, and 15% metakaolin is based on the recommendation of the proven results as per the previous studies for maximizing concrete mechanical and durability characteristics. This investigation revealed that 5% SCBA has increased the pozzolanic activity of silica, which involves the reaction of silica with calcium hydroxide to expand the formation of of calcium silicate hydrate (C-S-H), increasing the strength and decreasing porosity. Furthermore, it is also reported that the usage of 5–10% SCBA provides a good relationship between mechanical properties and the workability of concrete29,30.

The use of 5% polypropylene fiber is reported to help prevent crack formation, increase the tensile strength, and maintain homogeneity in the concrete structure. Furthermore 1–2% fiber content appears to offer the most effective crack resistance combined with increased toughness without negative effects on the mix31,32,33.

The 15% metakaolin dosage is adopted based on its high pozzolanic reactivity and physical effects, such as accelerating the degree of hydration, improving the microstructure of the hardened cement paste, and improving the early age strength. The addition of metakaolin in quantity varying within 10–20% enhances the durability of concrete and reduces the permeability. The selection of 15% is the most appropriate for this parameter, as indicated in the previous research paper34,35.

These dosages are selected based on literature data to enhance the performance of concrete and, thus, increase such characteristics as strength, durability, and crack resistance while maintaining suitable workability of concrete. As earlier research has established that each of the above materials independently enhances mechanical strength and durability, this research is unique in that it seeks to find out the synergistic effects of these materials when combined. The study aims to maximize the contribution of both forms to enhance the performance of the concrete through integration.

Methodology

Materials

OPC and aggregates

The study utilized the ‘Askari’ OPC brand, which meets with ASTM C150 standards. The cement used had a fineness of 2671 cm2/g, the sand had a fineness modulus of 2.93, and the coarse aggregate fulfilled both local availability and ASTM standards (ASTM C33). Metakaolin and bagasse ash were selected because of their benefits in improving the properties of concrete. The specific gravity of course and fine aggregate are 2.62 and 2.51 respectively. Figure 1 displays the sieve analysis results for the fine aggregate, while Fig. 2 presents the sieve analysis results for the coarse aggregate. The chemical composition of OPC, fly ash, and metakaolin are mentioned in Table 1.

Fig. 1
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Sieve analysis of fine aggregate.

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Fig. 2
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Sieve analysis of coarse aggregate.

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Table 1 Properties of SCBA, OPC, and metakaolin.
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Sugar cane bagasse ash

Sugarcane bagasse ash, which is produced from sugarcane in Pakistan’s Sakhakot-Malakand region, is used as an SCM in building materials. The physical and chemical characteristics of OPC and SCBA are listed in Table 2.

Table 2 Properties of SCBA and OPC.
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SCBA processing

Bagasse ash is burned at 600–800 °C, producing ash rich in silica, making it a good substitute for cement. The high silica content of bagasse ash makes it a promising material for pozzolanic growth. However, grinding it to cement size greatly improves its reactivity in cement mixes36,37,38.

The standard method ASTM C618 is the standard method for determining the percentage of fineness of Bagasse Ash. The apparatus Blaine air-permeability, in line with the ASTM standard C204 method, was used for measuring the surface area of the ash generated by crushing SCBA for specific durations (ASTM,2011). The specific surface area of SCBA was closest to that of cement at 2618.8 cm2/g after 45 min of grinding, SCBA that had been ground for 45 min was employed as a cementitious additive in concrete.

Sugarcane bagasse ash’s physical and chemical properties as reported in previous research investigations are presented in Table 3, respectively and these properties of bagasse ash are subject to impact from multiple aspects, including but not limited to the conditions under which it is grown, the process of calcination and cooling, the conditions and methods employed during grinding, and the approach used for its collection39.

Table 3 Sugar cane baggas ash (SCBA) physical properties.
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Polypropylene fiber (PPF)

In this research polypropylene (PP) fibers, sourced from Sika Pakistan (Pvt.) Limited, were used. The reason for choosing Polypropylene (PP) fiber as a variable in the study is due to its frequent utilization in construction projects and extensive accessibility in the market. The physical parameters of polypropylene (PP) fibers are presented in Table 4. Figure 3 shows the PP fiber used in this research.

Table 4 Physical properties of polypropylene fiber.
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Fig. 3
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Polypropylene fiber.

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Experimental program

The assessment of the compressive strength was carried out by ASTM C-39. In total, nine cylinders were set up for one mixture; three cylinders were investigated at each of the stated times of 14, 28, and 90 days. The measurement of tensile strength is done as per the criteria mentioned in ASTM C-496. ASTM standard procedures are utilized for the evaluation of concrete characteristics, including compressive strength (ASTM C39), tensile strength (ASTM C496), sorptivity (ASTM C1585), absorption (ASTM C642), and acid attack resistance (ASTM C1898). The acid utilized in this research is H2SO4. Table 5 shows the details of the specimens.

Table 5 Specimens detail.
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Composition of mixes

The ACI Mix design procedure is applied to achieve the target strength (27 MPa) of the control mix. The concrete mix included (0.5%, 1%, and 1.5%) polypropylene fiber49 and 15% metakaolin50 were used to increase strength and durability. These percentages were based on previous research, this study addressed how its mutual combination affects the behavior of new composite concrete.

In the mix design, the proportions of materials utilized per cubic meter of concrete contained 1088 kg of coarse aggregate with a particle size of 20 mm, 645 kg of fine aggregate with a particle size of 2 mm, and a total OPC content of 430 kg. The water-to-binder (w/b) ratio was 0.5. A decrease in the water-to-binder ratio results in increased compressive strength and decreased permeability, while just ensuring adequate workability for optimal placement. This balance guarantees optimal performance and increased durability of the concrete. By controlling the OPC (Ordinary Portland Cement) content, the mixture can be optimized for individual purposes, maintaining sufficient strength while minimizing expenses.

A total of 9 mixes were prepared with different compositions. The 9 mixes can be categorized into two primary groups. Group 1(Mix-I) consists of four sub-mixes, with the first mix in this group acting as the control reference. The mixture has various proportions of polypropylene (PP) fiber, specifically 0.5%, 1%, and 1.5%, in addition to 5% bagasse ash. Group 2(Mix-II) incorporates 15% metakaolin as a ternary additive. Each subgroup is assigned a distinct nomenclature, such as BA0-PP0, where BA represents bagasse ash and PP denotes polypropylene fiber. Similarly, in group 2, the designations MK-15 are used to indicate 15% metakaolin, respectively. The composition of all mixes is shown in Table 6 for a compressive strength of 27 MPa.

Table 6 Constituents of each blend.
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Results and discussion

Compressive strength

Figure 4 graphically shows the compressive strength of the control mix and all mixes containing different percentages (0.5%, 1%, and 1.5%) of PP fiber along with 5% bagasse ash. The mixes containing 15% metakaolin of concrete exhibited higher performance compared to plain cement concrete, indicating the enhanced pozzolanic nature of the material and the crack detention capability of polypropylene (PP) fibers. After 7 days, the mix with bagasse ash showed 3% higher compressive strength than normal concrete mix. The mix (BA5-PP15) achieved the highest compressive strength improvement of 7% after 7 days of curing, the increase in the compressive strength has been due to the pozzolanic activity of bagasse ash which has imparted strength to the concrete matrix as well as due to crack controlling property of PP fibers which minimizes micro-cracking. The strength with 15% metakaolin composites increased by 7%, 8.2%, and 9.1% with PP fiber at 0.5%, 1%, and 1.5% respectively. The improved strength can be attributed to the strong bridging action of PP fiber and the pozzolanic properties of metakaolin. Bagasse ash with 0.5%, 1%, and 1.5% PP fiber showed 5%, 6.3%, and 8.1% higher compressive strength than control (BA0-PP0) after 28 days of curing while with the addition of 15% metakaolin, the strength further increases, 13%, 17.1% and 13.5% for the same PP fiber percentages respectively. Metakaolin enhances the pozzolanic activities of concrete by reacting with the calcium hydroxide found in concrete to form an additional calcium silicate hydrate (C-S-H) gel. This gel improves the concrete matrix by increasing the density, and bonding and hence a great improvement in the compressive strength.

The effectiveness of bagasse ash is dependent upon the reactive silica content and the aluminum concentration, which can be influenced by several parameters including treatment regimen, grinding technique, and sample collecting method51. The reason for enhancing the strength of concrete is attributed to the silica content, which then undergoes a reaction with Ca(OH)2 to produce C-S-H gel52. Many factors influence the effectiveness of employing bagasse ash to reduce the stress and increase the strength, these include particle size, the chemical composition of the bagasse ash, grinding, and packing density12,53. The chemical constituents affect the hydration process and setting time, which in turn enhances the reactivity and strength of pozzolanic materials. These effects are impacted by the reduction in particle size and the level of grinding. Enhancing workability is achieved by increasing the packing density value, which in turn ensures a low porosity of the produced concrete. The enhancement in compressive strength can be attributed to the chemical reaction between bagasse ash and calcium hydroxide, resulting in the creation of a calcium silicate hydrate (CSH) gel54.

Fig. 4
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Compressive strength tested at 7 days, 28 days, and 90 days.

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Tensile strength

Figure 5 shows that the addition of polypropylene fiber percentages (0.5%, 1%, and 1.5%) enhanced strength after 7 days by 4%, 10.2%, and 13%, respectively. This improvement is associated with the capability of the fibers to span the cracks and spread the tensile stresses across the cementitious matrix. After 7 days, the mix containing bagasse ash showed 4% higher tensile strength than normal concrete mix. The mix (BA5-PP15) achieved the highest tensile strength improvement of 7.4% after 7 days. The strength with 15% metakaolin composites increased by 10.2%, 11.4%, and 13% with PP fiber addition at 0.5%, 1%, and 1.5% respectively. The improved strength is attributed to the pozzolanic properties of metakaolin and the high bridging action and tensile strength provided by PP fiber. Bagasse ash with 0.5%, 1%, and 1.5% PP fiber showed 14%, 17%, and 18.5% higher tensile strength than BA0-PP0 after curing of 28 days while with the addition of 15% metakaolin, the strength further increased, by 29%, 31.2% and 33% for the same PP fiber percentages respectively. The concrete’s highest tensile strength is achieved with 5% SCBA due to its pozzolanic reaction with hardened calcium hydroxide, forming a new C-S-H gel to increase the concrete matrix density. Moreover, the fine particles of SCBA also settle in the voids hence decreasing the porosity of the structure. This increases the interaction between cement and aggregates, providing better tensile strength.

Fig. 5
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Tensile strength at 7, 28 and 90 days.

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Bagasse ash improves the compressive strength of concrete by three distinct mechanisms: Initially, it has a chemical interaction with calcium hydroxide, leading to the creation of compounds that adhere, therefore enhancing the density of the concrete and enhancing its strength55. Additionally, it decreases the ratio of water to binder, enhancing the process of cement hydration and resulting in a higher density of concrete, thus increasing its strength. Ultimately, it fills gaps between aggregate particles, raising the density of packing and the distribution of stress, hence further improving tensile strength56. PP fibers spread uniformly through the concrete matrix as per SEM analysis shown in Fig. 8, binding to the cement mortar or surrounding coarse particles. The orientation of these fibers helps in crack control by holding the matrix of concrete resulting in the added capability of reinforced concrete to face bending forces as per the findings by Rashid57.

The same trend was observed regarding the tensile strength of concrete at 28 days of the curing period. A percentage of 5–25% of the SCBA was used in the substitution of cement. However, 30% of cement can be replaced by SCBA17,58. The use of a 5% SCBA mixture showed the highest tensile strength which was 33% and 40% higher than the reference mix at 28 and 90 days, respectively. However, the 30% SCBA had a lower split tensile strength as compared to the reference mix59.

Density

The amount utilized to express how much mass is present in each volume can be referred to as the density of concrete. This component also plays a significant role in assessing other aspects of concrete, such as the lattice parameters associated with the C-S-H phase in hydrated cement, porosity, durability, and strength60. The incorporation of bagasse ash into construction enhances the density of concrete using the presence of small particles that fill the voids within the concrete matrix. This decrease in permeability enhances the strength of concrete by reducing its susceptibility to water, chemical degradation, and other environmental factors. The presence of polypropylene fibers in concrete serves to inhibit acid penetration and cracking by creating a framework that bridges micro-cracks and enhances aggregate density. The inclusion of fiber reinforcement in the concrete matrix serves to mitigate the formation and advancement of cracks, therefore creating pathways for acid infiltration and subsequent enhancement of its acid resistance.

The finding of density is given in Fig. 6, the density of all 9 mixes was seen to be slightly lower when compared to the density of control concrete. The findings show that the incorporation of 5% SCBA led to a decrease in density from 2291 kg/m3 to 2287 kg/m3 for the BA0-PP0 mixture. Similarly, the inclusion of 0.5%, 1%, and 1.5% PP fiber along with 5% bagasse ash showed further reduction of density to 2265 kg/m3, 2263 kg/m3 respectively. On the other hand, with the use of 15% metakaolin, the density is found to be increased from 2291 kg/m3 to 2397 kg/m3 but the incorporation of PP fiber at the same percentages showed a decrease in density to 2395 kg/m3, 2378 kg/m3 and 2361 kg/m3 respectively. The use of polypropylene (PP) fibers at concentrations of 0.5%, 1%, and 1.5% has been shown to decrease micro-cracking and enhance the durability of concrete by increasing durability against mechanical stress. While using PP fiber, leads to improved crack management, reduced permeability, and overall improved resistance to adverse environmental conditions. Thus, enhancing the durability of concrete.

Fig. 6
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Variation in density.

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Similar findings revealed that the density exhibited a poor relationship with the rising percentage of SCBA. Depending on particle size and dosage, SCBA and metakaolin can affect concrete density through reactions and filler effects. Mix proportions or particle size distribution may be optimized to satisfy density and performance requirements. According to Memon et al.61, SCBA has lower specific gravity as compared to cement which may be the reason for the reduction in its value. Similarly, several studies also show the same trend which is the decrease in density of concrete with the increase in bagasse ash content. This has been explained based on the reduction of the specific weight of bagasse ash relative to cement with the gradual increase in cement content62,63.

Water absorption

Utilizing bagasse ash with polypropylene fibers can influence the water absorption of concrete13. The Pozzolans can react chemically with calcium hydroxide in water to produce more binding materials since concrete has a lesser porosity. When bagasse ash is added to concrete, it decreases the product’s size and capillary activity. This leads to a reduction in water absorption because the sizes and interaction levels of the capillary holes in the concrete matrix have declined. At optimal rates of addition, bagasse ash fills the space between the cement particles and the aggregates more closely. This action results in a consequent reduction in the overall porosity64.

The findings after 28 days of curing period are shown in Fig. 7, which demonstrates that the inclusion of bagasse ash has a decreasing effect on water absorption. Additionally, the incorporation of PP fiber further reduces porosity, resulting in decreased absorption. The use of 15% metakaolin also led to a decrease in water absorption. The control sample (BA0-PP0) has the highest reported absorption, measuring 6.4% while the absorption for 1.5% PP fiber and 5% bagasse ash is 6.1%. Furthermore, in the case of 15% metakaolin, the absorption is 5.9% which reduces to 5.6% with the incorporation of 1.5% PP fiber. Similarly, from the 90 days values in Fig. 7, it is clear, that the absorption for the control mix measures 4.2% while the absorption for 1.5% PP fiber and 5% bagasse ash is 3.6%. Furthermore, in the case of 15% metakaolin, the absorption is 3.5% which reduces to 3.1% with the incorporation of 1.5% PP fiber.

Fig. 7
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Water absorption variations at 7, 28 and 90 days.

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Similar results reported that the concrete specimens blended with SCBA exhibited a significant reduction in water penetration after the curing period of 28 and 56 days13,65.

Acid resistance

Bagasse ash is a high variant of silica that can react chemically with calcium hydroxide, which is a fragile component in concrete. As C-S-H gel develops in excess the amount of calcium hydroxide that is available to be attacked by the acids is reduced due to this reaction. Since the reduction of permeability was observed as a positive impact of the use of bagasse ash, it is possible that the incorporation of this material improved the strength and durability of concrete which in turn decreased the chances of acid infiltration66. On the other hand, Polypropylene fibers are used in concrete to control and as a preventive measure for cracking which is affected by various factors such as chemical decay. This means that a decrease in the number of cracks happens to be related to a reduction in the number of paths available for the penetration of acid. Methods to increase concrete resistance to physiological stress resulting from chemical attack. It should be noted that the modification of materials with a high risk of cracking due to acidity can be recommended for introducing a high fiber content67,68,69.

The analysis (shown in Fig. 8) of this research regarding the strength loss in 5% H2SO470,71 solution for two different periods of 1-month and 3-month exposure is shown which revealed that bagasse ash incorporation with the different percentages of PP fiber shows better performance (less loss in compressive strength) when exposed in an acidic environment. This may be due to the decrease of porosity caused by the impermeable nature of PP fiber, resulting in increased strength and reduced mass loss. Furthermore, the use of 15% metakaolin has demonstrated better results compared to the control concrete. The findings of the quantitative study indicate that the combination of 5% bagasse ash, 15% metakaolin, and 1.5% PP fiber provided the most beneficial results compared to the other mixes. It is important to highlight that sulfuric acid absorbs CH within pastes of cement, leading to the formation of a substance called calcium sulfate, which are materials that expand. The expansion of such substances into a hardened concrete lead to the deterioration of composite materials, and decalcification of C–S–H due to acid exposure leads to a reduction in strength, Water combines with cement’s calcium silicate components, notably C3S and C2S, to generate calcium silicate hydrate gel72,73.

Fig. 8
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Result of acid attack after one and three months.

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Sorptivity

The phenomenon of capillary action in concrete concerns the capacity of concrete to absorb water or other liquids into its micropores and capillaries because of its porous nature. The incorporation of SCBA as a cementitious concrete filler has been found to enhance the microstructure. The substance effectively occupies the spaces among the cement elements resulting in a reduction in the dimensions of the pores inside the concrete. A small pore size restricts the capacity for water to be transported through capillary action74. Polypropylene fibers indirectly contribute to reducing long-term pore activity inside the concrete, considering that the concrete itself remains in an adequate condition. Polypropylene fibers can, in specific cases, migrate upwards during the finishing process, therefore facilitating the formation of a surface that provides improved resistance to corrosion. The implementation of this technique has the potential to mitigate vibrations experienced on the surface of concrete and minimize the access of water into the concrete structure.

The findings presented in Fig. 9 confirmed that the incorporation of polypropylene fiber at different concentrations (0.5%, 1%, and 1.5%) in combination with 5% bagasse ash has exhibited a significant improvement in the concrete durability of and a reduction in capillary action. This enhancement is attributed to the enhancement of microstructure packing density and the reduction of sorptivity. The incorporation of 15% metakaolin results in a significant enhancement in the pore structure, hence reducing the sorptivity. The BA5-PP0-MK15 mixtures have demonstrated a reduction in sorptivity of 38%, as compared to the control mixture (BA5-PP0). The use of 15% metakaolin in concrete enhances the pore structure by filling up the small and large pores in the concrete. This leads to a stronger concrete matrix and lower porosity, hence increasing the durability of the concrete. The BA5-PP0-MK15 mixtures have demonstrated a reduction in sorptivity of 28%, as compared to the control mixture (BA5-PP0). This improvement is attributed to the interaction of metakaolin and polypropylene fibers that led to the development of a more effective microstructure of the concrete and the decrease in its water absorption rates.

Fig. 9
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Results of sorptivity at 7, 28 and 90 days.

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Similar findings reported that the sorptivity of concrete that includes bagasse ash decreases as the amount of replacement increases and decreases over time throughout the curing phase. The utilization of 20% bagasse ash in concrete resulted in a decrease of 19% and 48% in sorptivity values after 28 days and 90 days of curing, respectively. However, when using 30% bagasse ash, a slight increase in value was noted17. The use of SCMs (Supplementary Cementitious Materials), such as SCBA, in concrete, has the potential to yield notable reductions in both chloride diffusion and chloride permeability13. Moreover, it is also mentioned that this decrease in permeability is due to the smaller size of the bagasse ash particles75. However, some investigations revealed that the use of superplasticizer influences the properties of bagasse ash in concrete76.

Microstructure of bagasse ash in concrete

Previous literature review on the topic of bagasse ash’s effects on concrete’s mechanical characteristics, even though this study didn’t conduct experiments to examine its microstructure. Bagasse ash, according to previous research, is composed of particles in various forms, including needle-shaped, prismatic, tubular, and spherical ones. It is these particles that give the concrete its durability and mechanical strength29. These needle-shaped and tubular particles increase the interfacial bond between the cement matrix and other particles and increase the load transfer between the particles, hence improving the composite strength as described in some prior works77. Some of the properties that optimize concrete include prismatic and irregular particles, which contribute to increased density by occupying the gaps in the mix and increasing the interlocking, hence minimizing porosity and maximizing strength30. Spherical particles perform the functions described in the literature as essential additives that enhance the workability and packing of the mix. This enables them to interlock within the spaces of larger particles, thus leading to a dense matrix and decreased water-cement ratio, hence increasing the compressive strength of the product78.

Moreover, the presence of agglomerated particles, as described in the literature, may go a long way in filling up microvoids, hence decreasing porosity levels as well as increasing density. Higher density of concrete is reflected in lower porosity and increased durability and strength—a conclusion that can be drawn from numerous studies79. The literature further supports that bagasse ash enhances the physical and chemical characteristics of concrete because of its high silica content. During cement hydration, this silica reacts with calcium hydroxide and produces more C-S-H and, due to the shapes of the particulate matter in the ash, a denser, less porous, and mechanically stronger matrix is created77. Thus, while this paper does not originally analyze the microstructure of bagasse ash, based on characteristics mentioned in prior literature, it can be assumed that the addition of bagasse ash to concrete improves the microstructure and increases both strength and durability30,77,79. The EDS and SEM analyses are shown in Figs. 10 and 11, respectively.

Fig. 10
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Micrographs of bagasse ash examined by EDS X-ray spectroscopy80 .

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Fig. 11
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Bagasse ash SEM at different magnifications80.

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The combination of bagasse ash and polypropylene fibers together gives a complementary improvement to the microstructure of the concrete. The presence of bagasse ash as a filler and pozzolanic material gives an enhanced density of the matrix and reduced porosity, while the incorporation of polypropylene fibers aims at bridging the cracks, thus making the material more ductile. This interaction results in enhanced load transfer across the matrix, thereby avoiding the formation of weak areas and brittle failure. Furthermore, the fibers control the microcrack, whereas bagasse ash enhances the fiber-matrix interface, improving the resistance of the developed composite32.

Polypropylene fibers spread uniformly through the concrete matrix, as shown in Fig. 12 by the SEM analysis, binding to the cement mortar or surrounding coarse particles. The orientation of these fibres helps in crack control by holding the concrete matrix, resulting in reinforced concrete’s added capability to face bending forces, as per the findings by57.

Fig. 12
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Dispersion PP fiber in cement matrix57.

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Analysis of cost

This research explores the substitution of OPC with Bagasse ash, a byproduct derived from the sugar-producing industry. Cement serves as the primary binding material of concrete, constituting the costliest element and thus exerting significant influence over the entire expenses associated with concrete construction. In contrast, bagasse ash represents a waste material that costs solely transportation and processing expenses. The anticipated outcome of this replacement is a substantial reduction in costs. The prices of the materials are shown in Table 7. Concrete costs are analyzed by comparing the prices of “control” concrete and “concrete containing bagasse ash” for concrete of a unit cubic meter. The results are shown in the Table 8.

Table 7 Materials prices.
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The results suggest that incorporating bagasse ash into the concrete mixture provides a more economically viable alternative when compared to the control concrete. The incorporation of a blended mixture BA5-PP0-MK15, which consists of bagasse ash and metakaolin, leads to a cost reduction of 12.2% when compared to the BA0-PP0-CON mixture, which contains cement. This cost reduction pertains specifically to the production of one cubic meter of concrete. The entirety of the cost analysis is presented in the local currency, specifically the Pakistani rupee.

Table 8 Cement (replaced with bagasse ash) analysis of cost for one cubic meter.
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Conclusion

  • The present investigation reveals that the addition of 5% bagasse ash and 0. 5%, 1%, and 1. 5% polypropylene fibers improves the compressive and tensile strength besides reducing the permeability of concrete.

  • The density of concrete slightly decreases from 2291 kg/m2 to 2287 kg/m2 with the partial replacement of cement by 5% SCBA and PP fibers but increases to 2397 kg/m2 by using 15% metakaolin owing to the difference in filler characteristics and specific gravity.

  • The addition of bagasse ash, metakaolin, and polypropylene fibers may also decrease water absorption and porosity, thereby enhancing the durability and protection of concrete against adverse conditions.

  • Incorporating bagasse ash, metakaolin, and polypropylene fibers improves concrete microstructure by decreasing the pore area and capillary activity, improving durability. This modified mix also offers cost advantages (12.2% cheaper per cubic meter) compared with normal concrete.

Bagasse ash can be used as a substitute for cement, and it has been found to increase the strength and durability of concrete. This utilization of waste provides economic advantages as well. When combined with PP fibers and metakaolin, it enhances the sustainability and performance of concrete. Further research is recommended to understand how to optimize mixed mortar and the durability of structures using this combination.