Development of Sustainable Concrete from Hypo Sludge Combined with Basalt Fibre and Latex

: Cement production is a major source of carbon dioxide pollution. An environmentally friendly concrete needs to be developed in order to overcome the adverse environmental impacts of cement production and the continuing depletion of natural resources. Paper waste (hypo sludge) from the paper industry is becoming a challenge due to its extensive area requirements for disposal and continually increasing adverse environmental effects. To reduce paper waste and pollution, it might be beneﬁcial to use it as hypo sludge in concrete mixes. In the present investigation, hypo sludge was used as a partial replacement in varied proportions (5, 10, 15, 20, 25, and 30%) of cement in concrete of M30 grade to be assessed. Styrene–butadiene rubber (SBR) latex and basalt ﬁbre (BF) were added to hypo sludge concrete to improve its durability and post-cracking behaviour. From the test results, the optimum dosage of hypo sludge, basalt ﬁbre, and SBR latex was found to be 15%, 0.3%, and 10%, respectively. From the mechanical properties testing compared with the control concrete, latex-added hypo sludge basalt ﬁbre showed an increase in compressive strength by 17.08%, ﬂexural strength by 14.55% and tensile strength by 14.29%. Microstructural results showed that SBR latex created greater consistency in the interaction of the concrete stages. Results of the tests indicate that the performance of the concrete in terms of its strength was improved by partially replacing the cement in the concrete with hypo sludge.


Introduction
Raw materials are in high demand due to the recent significant development in construction activities.Cement is a key component in the construction sector, and its manufacturing process emits CO 2 , which pollutes the environment.Waste disposal and environmental protection from polluting industrial sectors are major concerns around the world.Several industrial waste materials can be reused in construction activities to generate sustainable concrete, lowering construction costs and trash disposal that harms the environment.The pulp and paper industry is one of the most energy-intensive polluters of the environment.India's overall paper production accounts for approximately 4% of global total paper output, with an estimated production of more than 20 tonnes by 2020 [1].Paper manufacturing uses a lot of energy and water, and produces a high concentration of chemical-based effluent; solid waste is formed throughout the paper industry's manufacturing process [2,3].The landfilling of solid waste from the paper industry has an environmental impact due to harmful chemical compounds flowing into the ground.Sludge disposal has become a major issue; as a result, several studies have led to the utilization of waste sludge in construction applications.Industrial wastes such as glass powder [4,5], eggshell powder [6], fly ash [7], and rice husk ash [8] were used to partially replace cement in concrete, which may reduce CO 2 emissions.
Waste paper sludge is one such promising industrial by-product of the paper industry.As a result, paper sludge can be recycled and reused in a variety of construction applications.Because of its pozzolanic qualities, hypo sludge is utilized as a supplemental cementitious ingredient in concrete [9,10].Extensive research has been conducted on the incorporation of sludge obtained from the paper industry for various uses such as brick manufacture [11] and clay ceramics [12].At the age of 28 days, replacing 5-10% of the cement in the mortar with paper sludge enhanced the compressive strength [9].Flexural strength of the beam was enhanced by 8.91% and 11.08%, respectively, when 10% hypo sludge and 20% fly ash were used [13].Based on a study of past studies on fundamental qualities, 10% partial replacement of cement by hypo sludge increased compressive and split tensile strength.An increase in the percentage of hypo sludge resulted in increased water absorption due to higher fibrous material, creating an increase in chloride ion penetration and hence decreased durability [14].Hypo sludge has numerous applications in road construction and hydrophobic concrete [15,16].Despite the fact that the addition of paper mill wastes to concrete has the benefits of cost savings and sustainable concrete manufacturing, little research has been conducted on the performance of concrete with the use of hypo sludge.As a result, the current study was carried out to assess the various properties of concrete including hypo sludge.
Styrene-butadiene rubber (SBR) latex has been used in concrete and mortar for its improved bonding capability, flexibility, impermeability, and toughness.The mechanical properties of mortars containing SBR latex were examined [17].The inclusion of SBR latex enhances the workability, compressive strength, and flexural strength of pervious concrete, as well as the split tensile strength [18].The addition of latex to concrete enhanced water permeability resistance due to the creation of a latex layer on the concrete [19] and reduced water absorption in concrete [20].The incorporation of styrene-butadiene rubber (SBR) latex into light-weight aggregate concrete reduced the water content of the concrete, and it was discovered that latex reduces the penetration of chloride ions [21].In general, fibres were introduced to improve the strength and post-cracking behaviour of concrete.Basalt fibre (BF) has recently emerged as a viable alternative to steel and polypropylene fibre [22].BF is a type of mineral fibre derived from basalt rock that has superior tensile properties, fire resistance, good interfacial shear strength, a high modulus of elasticity, and acceptable chemical resistance.The mechanical and durability properties of BF utilized as reinforcement, chopped fibres in concrete, have been examined in the cementitious matrix.The addition of basalt fibres resulted in a marginal increase in compressive strength [23].Numerous studies have shown that adding basalt fibres to concrete improves its flexural strength, split tensile strength, energy absorption, and toughness [24].The use of basalt fibres improved the crack resistance of concrete [25].
Despite the fact that many research studies indicate that hypo sludge has pozzolanic properties, there is still scepticism about using it as a supplementary cementitious material in concrete because there was no significant improvement in strength and it also exhibited reduced durability properties due to a high rate of water absorption due to its higher fibrous content.According to previous research investigations, adding basalt fibres to concrete improves mechanical qualities by altering the cracking mechanism, consequently enhancing the strength of the concrete and post-peak behaviour.According to previous research, the use of SBR latex in concrete results in a dense microstructure due to the production of a latex film that is well dispersed in the cement matrix and fills the micro cracks and holes of the concrete.There is also a considerable reduction in the size of calcium hydroxide crystals, indicating a solid microstructure and enhanced resistance to water permeability.The transition zone in latex-modified concrete lacks fully formed crystals of calcium hydroxide near the aggregate, indicating a less porous zone [26], and so contributing to improved strength and durability.
To overcome the limits of hypo sludge, basalt fibres were used to improve the strength and post-cracking behaviour of hypo-sludge-based concrete, and SBR latex was added to improve the strength and reduce water absorption.As a result, the current study intends to investigate the effect of basalt fibres and SBR latex on the mechanical, durability, and micro-structural aspects of hypo-sludge-based concrete.This research will be beneficial in minimizing landfill waste from the paper sector and utilizing the trash to produce sustainable concrete.

Materials
Ordinary Portland cement (OPC) of grade 53 [27] was utilized.In accordance with the specifications, Zone II river sand with specific gravity 2.54 and fineness modulus 2.83, and coarse aggregate with specific gravity 2.66, water absorption 0.5%, and bulk density of 1578 kg/m 3 were used for the control mix [28].Polycarboxylate-based super plasticizer adhering [29] was employed to improve workability.Hypo sludge was collected from Coimbatore, Tamil Nadu, India, and used as supplementary cementitious material.It had a specific gravity of 2.69. Figure 1 shows the process of powdered hypo sludge.Table 1 shows the chemical composition of powdered hypo sludge.The raw material used in the current study is shown in Figure 2. Figure 3 shows the particle size distribution of cement and hypo sludge.The chopped basalt microfibers were used in the current study.Tables 2 and 3 show the characteristics of basalt fibre and SBR latex, respectively.
density of 1578 kg/m 3 were used for the control mix [28].Polycarboxylate-based sup plasticizer adhering [29] was employed to improve workability.Hypo sludge was co lected from Coimbatore, Tamil Nadu, India, and used as supplementary cementitiou material.It had a specific gravity of 2.69. Figure 1 shows the process of powdered hyp sludge.Table 1 shows the chemical composition of powdered hypo sludge.The raw m terial used in the current study is shown in Figure 2. Figure 3 shows the particle siz distribution of cement and hypo sludge.The chopped basalt microfibers were used in th current study.Tables 2 and 3 show the characteristics of basalt fibre and SBR latex, r spectively.

Preliminary Investigations
The specimens cast for testing is shown in Figure 4. Preliminary compressive strength and water absorption tests were performed on 150 mm cube specimens containing 0%, 5%, 10%, 15%, 20%, 25%, and 30% hypo sludge as a cement replacement material in order to optimize the proportion of hypo sludge, and the results are presented in Figure 5.For a similar proportion of hypo sludge replacement, basalt fibres were integrated with 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% for evaluating the optimum dosage of fibre content in hypo sludge concrete, and the compressive strength results for various mixes are presented in Figure 6.According to Figure 5, the mix with 15% substitution by hypo sludge gave the highest compressive, split tensile and flexural strength.It could be attributed to hypo sludge filling significant interstices in the control concrete.However, over 15% hypo sludge concentration had a negative impact on concrete strength due to the formation of big pores due to the porous character of hypo sludge.Previous studies found similar outcomes [30].Based on the mechanical strength results of trial mixtures including 5% to 30% hypo sludge as cement replacement material, 15% hypo sludge concrete mix were chosen as the optimal combination for further research.Because of the high cellulose fibre content in the sludge matrix, the rate of water absorption increased with the addition of hypo sludge.The maximum compressive strength was achieved when 0.3% basalt fibres were introduced to the hypo sludge concrete.Despite the fact that the 0.3% basalt fibre addition without hypo sludge demonstrated the highest compressive strength, the mix with 0.3% basalt fibres and optimum 15% hypo sludge replacement for cement that demonstrated comparable compressive strength was chosen as the mix that requires further investigation.

Preliminary Investigations
The specimens cast for testing is shown in Figure 4. Preliminary compressive strength and water absorption tests were performed on 150 mm cube specimens containing 0%, 5%, 10%, 15%, 20%, 25%, and 30% hypo sludge as a cement replacement material in order to optimize the proportion of hypo sludge, and the results are presented in Figure 5.For a similar proportion of hypo sludge replacement, basalt fibres were integrated with 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% for evaluating the optimum dosage of fibre content in hypo sludge concrete, and the compressive strength results for various mixes are presented in Figure 6.According to Figure 5, the mix with 15% substitution by hypo sludge gave the highest compressive, split tensile and flexural strength.It could be attributed to hypo sludge filling significant interstices in the control concrete.However, over 15% hypo sludge concentration had a negative impact on concrete strength due to the formation of big pores due to the porous character of hypo sludge.Previous studies found similar outcomes [30].Based on the mechanical strength results of trial mixtures including 5% to 30% hypo sludge as cement replacement material, 15% hypo sludge concrete mix were chosen as the optimal combination for further research.Because of the high cellulose fibre content in the sludge matrix, the rate of water absorption increased with the addition of hypo sludge.The maximum compressive strength was achieved when 0.3% basalt fibres were introduced to the hypo sludge concrete.Despite the fact that the 0.3% basalt fibre addition without hypo sludge demonstrated the highest compressive strength, the mix with 0.3% basalt fibres and optimum 15% hypo sludge replacement for cement that demonstrated comparable compressive strength was chosen as the mix that requires further investigation.SBR latex was added in an optimized proportion of hypo sludge at 5%, 10%, 15%, and 20% by weight of cement to reduce water absorption and improve the durability qualities of sludge-based concrete, and the results are presented in Figure 7.The use of Hypo Sludge(%) 0% fiber 0.1% fiber 0.2% fiber 0.3% fiber 0.4% fiber 0.5% fiber    SBR latex was added in an optimized proportion of hypo sludge at 5%, 10%, 15%, and 20% by weight of cement to reduce water absorption and improve the durability qualities of sludge-based concrete, and the results are presented in Figure 7.The use of Hypo Sludge(%) 0% fiber 0.1% fiber 0.2% fiber 0.3% fiber 0.4% fiber 0.5% fiber    SBR latex was added in an optimized proportion of hypo sludge at 5%, 10%, 15%, and 20% by weight of cement to reduce water absorption and improve the durability qualities of sludge-based concrete, and the results are presented in Figure 7.The use of Hypo Sludge(%) 0% fiber 0.1% fiber 0.2% fiber 0.3% fiber 0.4% fiber 0.5% fiber SBR latex was added in an optimized proportion of hypo sludge at 5%, 10%, 15%, and 20% by weight of cement to reduce water absorption and improve the durability qualities of sludge-based concrete, and the results are presented in Figure 7.The use of up to 10% SBR latex boosted compressive strength while decreasing water absorption.Because SBR latex generates a polymer film that is evenly distributed throughout the cement matrix, a thick network that is interlaced in the cement matrix is formed [26].Though SBR latex improved compressive strength, the inclusion of a large amount of hypo sludge causes agglomeration and the production of larger voids in the concrete.As a result, 10% SBR latex by weight of cement was chosen as the optimal blend for further research.
Sustainability 2023, 15, x FOR PEER REVIEW up to 10% SBR latex boosted compressive strength while decreasing water abso Because SBR latex generates a polymer film that is evenly distributed througho cement matrix, a thick network that is interlaced in the cement matrix is forme Though SBR latex improved compressive strength, the inclusion of a large amo hypo sludge causes agglomeration and the production of larger voids in the concr a result, 10% SBR latex by weight of cement was chosen as the optimal blend for research.

Mix Proportions and Testing Methods
To investigate the mechanical and durability features of concrete, a set of different mixes was selected based on preliminary test results for further investiga the current major study, a concrete grade of M30 was used, and the mix was m accordance with [31].A consistent water-to-cement ratio of 0.45 was used to arriv mix proportion.The first group included a control mix (CC) with no additional ma a mix HSC (15% HS), a mix BFC (0.3% BF), and a mix HSBFC (15% HS + 0.3% B following group comprised of all of the preceding mixes with the addition of SBR 10% by weight of cement and was designated as LMHSC, LMBFC, and LMHSBF mix proportions of all the concrete mix are presented in Table 4.

Mix Proportions and Testing Methods
To investigate the mechanical and durability features of concrete, a set of seven different mixes was selected based on preliminary test results for further investigation.
In the current major study, a concrete grade of M30 was used, and the mix was made in accordance with [31].A consistent water-to-cement ratio of 0.45 was used to arrive at the mix proportion.The first group included a control mix (CC) with no additional materials, a mix HSC (15% HS), a mix BFC (0.3% BF), and a mix HSBFC (15% HS + 0.3% BF).The following group comprised of all of the preceding mixes with the addition of SBR latex at 10% by weight of cement and was designated as LMHSC, LMBFC, and LMHSBFC.The mix proportions of all the concrete mix are presented in Table 4.

Mechanical Testing
The compressive strength of concrete is the most important factor in determining its overall quality.Tests for compressive strength and flexural strength on 150 mm × 150 mm × 150 mm cubes and 100 mm × 100 mm × 500 mm prisms were performed in accordance with the Indian standard [32].Split tensile strength tests were performed on a 300 mm × 150 mm cylinder specimen as per code [33].At 7 days and 28 days, the concrete's compressive, flexural, and split tensile strengths were evaluated.

Durability Testing
After 28 days of curing, cube specimens of 100 mm × 100 mm × 100 mm were subjected to a water absorption test [34].The sorptivity of 100 mm cube specimens was tested in accordance with code [35].Sorptivity is a test that measures the capillary flow of water in concrete specimens.After casting the specimens, a cure time of 28 days was permitted.In order to prevent water from leaking through the sides of the test specimens, they were heated at 100 • C for 24 h before being cooled to room temperature and coated with a non-absorbent coating.The concrete cylinder is weighed and submerged in water.Limits for evaluating concrete quality in a quick chloride penetration test are provided in Table 5.After filling two clear plastic cells with a concrete disc specimen that had been wet with water, a 50 V electrical potential was applied across the specimen.Copper mesh electrodes were attached to the concrete disc's outer edges, and leak-proof seals were made using a rubber gasket and an appropriate sealant.Both cells were filled, but one with a NaCl solution of 3% and the other with a NaOH solution of 0.3 M. Current flow was monitored every 30 min after the copper mesh electrodes were connected to an external DC power supply providing 50 V.

Microstructural Testing
The characteristics of concrete are greatly influenced by the microstructure of hardened concrete.Cementitious composite materials morphology is examined using scanning electron microscope (SEM) visuals.

Mechanical Properties 4.1.1. Compressive Strength
Figure 8 displays the testing results for the compressive strength of eight mixtures at days 7 and 28.At the age of 7 days, the compressive strength of the mix HSC decreases, but at 28 days, it is 10.26% greater than the control concrete.For the combination HSC, the maximum strength loss after 7 days is 4.29%.Due to the high water demand features of hypo sludge, its presence had the impact of lowering compressive strength at an early age.During the early curing phase, a second cementing reaction takes place, which boosts compressive strength relative to the control concrete [37].In 7 and 28 days, the increase in strength for the mix BFC was 8.76% and 18.81%.The addition of basalt fibres to the concrete matrix results in increased strength.The strength data show that BF has a beneficial impact on compressive strength at a young age while hypo sludge has a negative impact.In contrast to the control concrete, the hypo sludge and BF mixture showed an increase in strength at both ages.The addition of BF in hypo sludge concrete showed an increase of 1.88% and 16.28% at 7 days and 28 days, respectively.The early-age strength for the mix LMHSC was raised to 3.75% from −4.29% for the mix HSC.For the combination HSC and LMHSC, the compressive strength at 28 days was enhanced by 10.26% and 14.73%, respectively.It demonstrates that compressive strength increases with the addition of SBR latex.Due to improved consistency in the interaction between the stages of concrete, the addition of latex to the mix demonstrated a considerable improvement in strength.Previous research showed comparable outcomes for the addition of latex and silica fume [38].When compared with the control concrete, the LMBFC mix compressive strength increased by a maximum of 18.77% and 24.94% at 7 and 28 days, respectively.When compared with the control concrete, the strength of the mix LMHSBFC significantly increased at 7 and 28 days, by 8.02% and 17.08%, respectively.The combination of latex and BF with hypo sludge improves the compressive strength of the concrete.

Flexural Strength
Figure 9 depicts the flexural strength of various mixtures.At 7 days, the flexural strength of the mix HSC decreased to 4.02% and increased to 6.67% at 28 days.The reason for the decrease in strength at this early stage is due to the slow hydration reaction of hypo sludge.At 7 days and 28 days, the flexural strength of the BFC mixture increased by 11.46% and 12.38%, respectively.BF has the greatest impact on flexural strength and enhances the concrete bending performance.Observations of a comparable increase in strength were reported by previous research [23].LMBFC attained the greatest increase in strength, with an increase of 17.65% at 7 days and 20% at 28 days.In general, the addition of latex to concrete increased its flexural strength as a result of enhanced interaction between the aggregate's transition zone and cement paste.Identical results were reported by previous research [21].In comparison with the control concrete mix, the strength of the LMHSBFC mix increases by 14.55% and 15.24% at 7 and 28 days, respectively.For the combination HSC and LMHSC, the compressive strength at 28 days was enhanced by 10.26% and 14.73%, respectively.It demonstrates that compressive strength increases with the addition of SBR latex.Due to improved consistency in the interaction between the stages of concrete, the addition of latex to the mix demonstrated a considerable improvement in strength.Previous research showed comparable outcomes for the addition of latex and silica fume [38].When compared with the control concrete, the LMBFC mix compressive strength increased by a maximum of 18.77% and 24.94% at 7 and 28 days, respectively.When compared with the control concrete, the strength of the mix LMHSBFC significantly increased at 7 and 28 days, by 8.02% and 17.08%, respectively.The combination of latex and BF with hypo sludge improves the compressive strength of the concrete.

Flexural Strength
Figure 9 depicts the flexural strength of various mixtures.At 7 days, the flexural strength of the mix HSC decreased to 4.02% and increased to 6.67% at 28 days.The reason for the decrease in strength at this early stage is due to the slow hydration reaction of hypo sludge.At 7 days and 28 days, the flexural strength of the BFC mixture increased by 11.46% and 12.38%, respectively.BF has the greatest impact on flexural strength and enhances the concrete bending performance.Observations of a comparable increase in strength were reported by previous research [23].LMBFC attained the greatest increase in strength, with an increase of 17.65% at 7 days and 20% at 28 days.In general, the addition of latex to concrete increased its flexural strength as a result of enhanced interaction between the aggregate's transition zone and cement paste.Identical results were reported by previous research [21].In comparison with the control concrete mix, the strength of the LMHSBFC mix increases by 14.55% and 15.24% at 7 and 28 days, respectively.

Split Tensile Strength
The split tensile strength for various mixes is shown in Figure 10.It is observed that the HSC mix reduced the early-age strength by 4.76% and increased the 28-day strength by 3.57%.A significant positive effect on the tensile strength was achieved using BF with increased strength of 14.29% and 16.07% at 7 and 28 days compared with the control concrete.Previous investigations [23,39] have reported that there is a significant increase in split tensile strength with the addition of fibres.Basalt fibres in the concrete matrix controlled the development of cracks.There is a marginal increase in tensile strength of 10.42% for the mix LMHSC at 28 days.Latex helps in binding the internal microstructure of the concrete, thereby reducing the thickness of ITZ.Compared with the control concrete, the mix LMHSBFC showed a significant increase in split tensile strength of 14.29% and 18.45% at 7 and 28 days, respectively.

Split Tensile Strength
The split tensile strength for various mixes is shown in Figure 10.It is observed that the HSC mix reduced the early-age strength by 4.76% and increased the 28-day strength by 3.57%.A significant positive effect on the tensile strength was achieved using BF with increased strength of 14.29% and 16.07% at 7 and 28 days compared with the control concrete.Previous investigations [23,39] have reported that there is a significant increase in split tensile strength with the addition of fibres.Basalt fibres in the concrete matrix controlled the development of cracks.There is a marginal increase in tensile strength of 10.42% for the mix LMHSC at 28 days.Latex helps in binding the internal microstructure of the concrete, thereby reducing the thickness of ITZ.Compared with the control concrete, the mix LMHSBFC showed a significant increase in split tensile strength of 14.29% and 18.45% at 7 and 28 days, respectively.

Water Properties
A structure's endurance is mostly determined by the concrete's porosity.The rate of water absorption provides sufficient information about the pore structure of concrete.The water absorption results of the various combinations are shown in Figure 11.Results demonstrate that the mix HSC absorbed more water than the control concrete mix, which is consistent with the finding of other studies [40].The elevated rate of water absorption  The split tensile strength for various mixes is shown in Figure 10.It is observed that the HSC mix reduced the early-age strength by 4.76% and increased the 28-day strength by 3.57%.A significant positive effect on the tensile strength was achieved using BF with increased strength of 14.29% and 16.07% at 7 and 28 days compared with the control concrete.Previous investigations [23,39] have reported that there is a significant increase in split tensile strength with the addition of fibres.Basalt fibres in the concrete matrix controlled the development of cracks.There is a marginal increase in tensile strength of 10.42% for the mix LMHSC at 28 days.Latex helps in binding the internal microstructure of the concrete, thereby reducing the thickness of ITZ.Compared with the control concrete, the mix LMHSBFC showed a significant increase in split tensile strength of 14.29% and 18.45% at 7 and 28 days, respectively.

Water Properties
A structure's endurance is mostly determined by the concrete's porosity.The rate of water absorption provides sufficient information about the pore structure of concrete.The water absorption results of the various combinations are shown in Figure 11.Results demonstrate that the mix HSC absorbed more water than the control concrete mix, which is consistent with the finding of other studies [40].The elevated rate of water absorption

Durability Properties 4.2.1. Water Properties
A structure's endurance is mostly determined by the concrete's porosity.The rate of water absorption provides sufficient information about the pore structure of concrete.The water absorption results of the various combinations are shown in Figure 11.Results demonstrate that the mix HSC absorbed more water than the control concrete mix, which is consistent with the finding of other studies [40].The elevated rate of water absorption was noticed as a result of the hypo sludge matrix's dominant high cellulose fibre content, whose incorporation rendered the concrete more porous.When compared with the control concrete, basalt fibre incorporation did not significantly reduce water absorption [41].All SBR latex-added mixes had lower water absorption than the control concrete.According to research, matrix-aggregate interfacial transition zone (ITZ) thickness has decreased and a polymer film layer has formed over the matrix materials, which has caused a decrease in the absorption of water [42].As the pores are filled with SBR latex, the total porosity of the concrete is lowered and the entry of water is decreased [26].Among other mixes, the LMBFC mix had the lowest water absorption value (2.1%).However, compared with the control concrete, the LMHSBFC mix has less water intrusion because pores are filled with fibres and latex, which also results in less water absorption.
creased and a polymer film layer has formed over the matrix materials, which has caused a decrease in the absorption of water [42].As the pores are filled with SBR latex, the total porosity of the concrete is lowered and the entry of water is decreased [26].Among other mixes, the LMBFC mix had the lowest water absorption value (2.1%).However, compared with the control concrete, the LMHSBFC mix has less water intrusion because pores are filled with fibres and latex, which also results in less water absorption.

Rapid Chloride Ion Penetration Test
The results of the chloride ion penetration of the M30 grade concrete mix containing hypo sludge, basalt fibres, and SBR latex are shown in Figure 12.When hypo sludge replaced the cement, the amount of ion penetration increased.Compared with the control mix, the HSC mix penetration value increased by 6.43%.As a result of the high cellulose fibre content, it shows that the addition of hypo sludge enhanced the porosity in the concrete and decreased its resistance to chloride ion penetration.The addition of latex to sludge-based concrete resulted in a 21.64% drop in penetration value.The mixture containing latex had charge passage in the range of 1000-2000 coulombs, indicating low chloride ion permeability.SBR increases the microstructure of the matrix and improves its resistance to chloride ion penetration [42,43].Water permeability is reduced by polymer chemical reactions and the creation of a film layer over cement and aggregate matrix particles.All mixtures without the addition of latex had a total charge in the range of 2000 to 4000 coulombs, indicating a moderate permeability to chloride ions.

Rapid Chloride Ion Penetration Test
The results of the chloride ion penetration of the M30 grade concrete mix containing hypo sludge, basalt fibres, and SBR latex are shown in Figure 12.When hypo sludge replaced the cement, the amount of ion penetration increased.Compared with the control mix, the HSC mix penetration value increased by 6.43%.As a result of the high cellulose fibre content, it shows that the addition of hypo sludge enhanced the porosity in the concrete and decreased its resistance to chloride ion penetration.The addition of latex to sludge-based concrete resulted in a 21.64% drop in penetration value.The mixture containing latex had charge passage in the range of 1000-2000 coulombs, indicating low chloride ion permeability.SBR increases the microstructure of the matrix and improves its resistance to chloride ion penetration [42,43].Water permeability is reduced by polymer chemical reactions and the creation of a film layer over cement and aggregate matrix particles.All mixtures without the addition of latex had a total charge in the range of 2000 to 4000 coulombs, indicating a moderate permeability to chloride ions.

Correlation between Compressive Strength and Durability Properties
The pore structure of cement paste affects both permeability and water absorption, and liquid transfers from the surface to the interior.As a result, it was observed that surface water absorption has a significant impact on the permeability.Figure 13 represents the correlation existing between the hardened compressive strength and sorptivity with an R 2 of 0.896.There is a decrease in linearity with an increase in the compressive strength of the concrete produced using hypo sludge, basalt fibres, and SBR latex.In RCPT investigations also a similar trend of decreasing linearity with the regression co-

Correlation between Compressive Strength and Durability Properties
The pore structure of cement paste affects both permeability and water absorption, and liquid transfers from the surface to the interior.As a result, it was observed that surface water absorption has a significant impact on the permeability.Figure 13 represents the correlation existing between the hardened compressive strength and sorptivity with an R 2 of 0.896.There is a decrease in linearity with an increase in the compressive strength of the concrete produced using hypo sludge, basalt fibres, and SBR latex.In RCPT investigations also a similar trend of decreasing linearity with the regression coefficient value of 0.821 was observed.Moreover, there exists a good relationship between the strength of hardened concrete and durability characteristics.From Figure 13, it was inferred that there is a significant drop in sorptivity value with the addition of latex.Addition of latex tends to reduce the voids in the cementitious matrix thereby creating a dense microstructure throughout the cement matrix, which leads to the increase in the strength and reduces the water absorption of sludge-based concrete compared with the control concrete.
and liquid transfers from the surface to the interior.As a result, it was ob surface water absorption has a significant impact on the permeability.Figur sents the correlation existing between the hardened compressive strength and with an R 2 of 0.896.There is a decrease in linearity with an increase in the c strength of the concrete produced using hypo sludge, basalt fibres, and SB RCPT investigations also a similar trend of decreasing linearity with the reg efficient value of 0.821 was observed.Moreover, there exists a good relationsh the strength of hardened concrete and durability characteristics.From Figur inferred that there is a significant drop in sorptivity value with the addition o dition of latex tends to reduce the voids in the cementitious matrix thereby dense microstructure throughout the cement matrix, which leads to the incr strength and reduces the water absorption of sludge-based concrete compar control concrete.

SEM Analysis
Scanning electron microscopy pictures may efficiently assess the mor cementitious composite structures [44].The SEM images for various comb 10,000× magnifications are shown in Figure 14a-d

Microstructural Studies SEM Analysis
Scanning electron microscopy pictures may efficiently assess the morphology of cementitious composite structures [44].The SEM images for various combinations at 10,000× magnifications are shown in Figure 14a-d.The morphology of cement hydration in concrete was examined from the photographs.The SEM picture for the control concrete (CC) specimen in Figure 14a shows that there are noticeable voids and extensive interstices in the concrete as a result of improper phase interaction in the concrete.This suggests that the lack of a mineral additive meant the concrete was not completely packed.The SEM image for the concrete combined with hypo sludge and latex (LMHSC) is shown in Figure 14b.The figure shows that sludge increased the consistency of the concrete; however, in some locations, hypo sludge agglomerates and produces tiny gaps in the concrete.The latex reduced the system's porosity by filling the cracks by creating a thin film layer over the matrix's components [45,46].The SEM visuals of the concrete with basalt fibre and latex (LMBFC) are shown in Figure 14c.Due to the joining of the fibres, the microstructure imaging showed that the sample is tightly packed and of acceptable consistency.The SEM picture for the concrete mixed with basalt fibre, hypo sludge, and latex (LMHSBFC) is shown in Figure 14d.Compared with other mixes, LMHSBFC provided better interaction between the components of concrete.The features of the matrix-aggregate ITZ are improved in latex-concrete, resulting in a decrease in porosity and the production of calcium hydroxide.In general, it has been found that mixes containing SBR latex created concrete that was significantly stronger and more durable with lower permeability than mixes without SBR.These mixes also produced more consistent results in the interaction between the phases of the concrete.latex (LMHSBFC) is shown in Figure 14d.Compared with other mixes, LMHSBFC provided better interaction between the components of concrete.The features of the matrixaggregate ITZ are improved in latex-concrete, resulting in a decrease in porosity and the production of calcium hydroxide.In general, it has been found that mixes containing SBR latex created concrete that was significantly stronger and more durable with lower permeability than mixes without SBR.These mixes also produced more consistent results in the interaction between the phases of the concrete.

Conclusions
The purpose of this research is to develop an approach to produce environmentally friendly concrete that makes use of hypo sludge as a partial replacement for cement, and it is accomplished by overcoming the limitations of the method by incorporating basalt fibres and SBR latex into the mix.Evaluations are made of mechanical, durability, and microstructural characteristics.The test results have led to the following conclusions:

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The waste from paper industry can be used as partial replacement for cement for making ecofriendly sustainable concrete and it will reduce the emission of CO 2 and landfill problems.Utilising the waste material can reduce the amount of cement used in concrete construction.

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In comparison to the control concrete, the addition of hypo sludge at 15% for replacement of cement with 0.3% BF and 10% SBR latex significantly increased compressive strength by 17.08%, and the LMHSBFC mix significantly increased flexural strength by 14.55% at 28 days.

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Compared with the control concrete, the mix LMHSBFC significantly increased split tensile strength by 14.29%.In order to increase the splitting tensile strength of concrete, hypo sludge containing basalt fibres and SBR latex was used.In the LMBFC mix, the greatest improvement in tensile strength of 20.95% was noted.

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The mechanical qualities of hypo sludge concrete significantly improved with the addition of basalt fibres and SBR latex.

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In comparison with control concrete, the mix LMHSBFC exhibits decreased water absorption, permeability, and chloride ion penetration, as well as better concrete durability.

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Micro-structural research showed that adding hypo sludge to the concrete enhanced its interfacial interactions.Due to the creation of a film layer by SBR latex in the cement matrix and a decrease in the ITZ of the concrete, the mix LMHSBFC demonstrated a homogeneous and denser microstructure when compared with the control concrete.

Figure 5 .
Figure 5. Optimized test results for hypo sludge concrete.

Figure 5 .
Figure 5. Optimized test results for hypo sludge concrete.

Figure 5 .
Figure 5. Optimized test results for hypo sludge concrete.

Figure 5 .
Figure 5. Optimized test results for hypo sludge concrete.

Figure 7 .
Figure 7. Compressive strength and water absorption of HSC with SBR latex.

Figure 7 .
Figure 7. Compressive strength and water absorption of HSC with SBR latex.

Figure 10 .
Figure 10.Test results for split tensile strength.

Figure 10 .
Figure 10.Test results for split tensile strength.

Figure 10 .
Figure 10.Test results for split tensile strength.

Figure 11 .
Figure 11.Water absorption test results at initial and saturated condition.

Figure 12 .
Figure 12.RCPT values for all mixes at 28 days.

Figure 12 .
Figure 12.RCPT values for all mixes at 28 days.

Table 1 .
Chemical composition of hypo sludge.

Table 2 .
Properties of basalt fibre.

Table 3 .
Properties of SBR latex.

Table 2 .
Properties of basalt fibre.

Table 3 .
Properties of SBR latex.

Table 4 .
Mix proportions for 1 m 3 of concrete.

Table 4 .
Mix proportions for 1 m 3 of concrete.
Water absorption test results at initial and saturated condition.