Performance of High-Strength Concrete with the Effects of Seashell Powder as Binder Replacement and Waste Glass Powder as Fine Aggregate

: Seashell powder (SSP) is a waste from aquatic life that is generally available near the coastal region. Due to its high calcium content, SSP can be utilized as a supplementary cementitious binder. SSP can be used as a sustainable binder to replace ordinary Portland cement (OPC) and signiﬁcantly reduce the carbon footprint. The present study investigates the effects of SSP and waste glass powder (WGP) on the fresh, mechanical, and microstructure properties of high-strength concrete (HSC). The SSP utilized in this research was varied, with 5%, 10%, and 15% cement replacement levels. The impact of WGP was also observed with two replacement levels, 5% and 10%, replacing natural sand. The slump ﬂow of all the HSC mixes varied between 700 and 785 mm. A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days. The split tensile strength values of all the HSC mixes were found in a range from 5.45 to 10.56 MPa. The modulus of elasticity values of all the HSC mixes were found to lie between 40.2 and 46.8 GPa. The lowest water absorption was observed in the mix containing 5% SSP. The SEM image of the HSC with increased SSP showed that it was denser and had fewer unreacted particles. XRD and EDS showed the presence of various gels, such as calcium silicate hydrates (CSHs), ettringite, calcium hydroxide (CH), and calcium carbonate (CC). The predicted equations for its split tensile strength, ﬂexural strength, modulus of elasticity, and water absorption were also carried out in the present research.


Introduction
Due to rapid developments in high-rise buildings and infrastructure advancements across the globe, there are numerous applications of HSC in the construction industry [1][2][3][4].Significant changes have taken place in the properties of concrete and its constituents in the past 50 years.Concrete is a useful material that can easily be mixed to meet a variety of special needs and molded to essentially any shape.At present, concrete is in high demand, especially in developing countries.This demand can be met by generating costeffective concrete by using its substitutes to enhance certain qualities and reduce its impact on the environment.The early deterioration of normal concrete structures in aggressive environments has led to the need for HSC.Harmful substances such as chloride, sulphate ions, and carbon dioxide in water and also in oxygen, which penetrate into the concrete, are liable to cause reductions in concrete strength.This problem can be solved by incorporating mineral admixtures as partial replacements for cement.Improvements in the density of the pore structure check the ingress of harmful materials into the concrete, thereby improving its strength and durability.
Compared with normal-strength concrete, HSC possesses very high strength.HSC has very low permeability, with increased resistance to corrosion in severe environments.An experiment conducted using cementitious materials showed that they have less permeability than normal concrete.The permeability of HSC with cementitious materials is 100 times higher than that of normal conventional concrete [5][6][7][8].In civil engineering, HSC has a wide range of applications because of its increased strength.It is used in bridges to reduce the number of beams needed to support the slab.It is highly recommended in hydropower structures due to its performance in handling the high speed of water and huge amounts of silt.The early strength gain of HSC, its low permeability, and its improved abrasion resistance are the key points which have led to HSC being used in highway pavements.As HSC can be applied for service quickly, it is also used to repair damaged pavement.HSC is further used in protections from high-density radiation, bulk concrete projects, noise and vibration damping of offshore platforms, tall structures, and tunnels.Due to reductions in the dead load, vibration, deflection, and maintenance of concrete, HSC is used in high-rise buildings.Compared with normal concrete structures, fiber-reinforced HSC acts as a repair material due to its high mechanical performance.Prefabricated HSC sleepers are used in modern high-speed railway tracks for their higher stability [9,10].
With advancements in technology, there is a need for concrete of higher strength.HSC is one such class of concrete that has been formulated in recent decades owing to its exceptional properties of strength.It is widely used around the world as its performance over normal concrete is "innovative, enhanced, and upgraded".The addition of pozzolana can increase the compressive strength to 150 MPa, which is very significant in HSC production.Obtaining HSC involves more consideration of the proper design in terms of mixing, assembling, placing, and curing the concrete.The design of a suitable concrete mixture plays an important role for determining the type of HSC materials and structures used.The stability of concrete structures depends mostly on the durability of concrete itself.HSC, with its dense microstructure and very low permeability, has more durability than ordinary concrete.The deterioration of concrete under high temperatures could be reduced to an extent by incorporating steel fiber [11][12][13][14][15].
The blended binders generally include OPC, silica fume (SF), slag, fly ash (FA), etc.Recent studies also tend towards using various alternative binders such as agricultural wastes, clay, ferrochrome slag, C&D wastes, etc. Calcined limestone clay cement and ferrochrome slag aggregates have been found to be ecofriendly binders with improved mechanical performance [16][17][18][19][20][21][22][23][24].The present study focuses on an alternative binder material, SSP.Waste seashells comprise another possible waste material readily available to use as a binder.Oyster, mussel, scallop, periwinkle, and cockle shells are among the various waste seashells obtainable [25].The State of World Fisheries and Aquaculture 2020 reported that 26,000 tons of seashells and bones are produced each year.Most of this proportion of seashell debris comprises oyster, clam, scallop, and mussel shells, with just a tiny proportion being reused for other applications such as fertilization and crafts [26].Due to the limited availability of seashell powder that may be utilized as a binder and the issues of soil solidification and economic matters, reuses are minimal.Furthermore, there are challenges with waste seashells being dumped illegally into open waters and reclaimed land.If seashells remain untreated over an extended period, they can emit foul odors due to the breakdown of the leftover muscles in the shells or the microbial decomposition of salts into gases such as H 2 S, NH 3 , and ammonia products.The biodegradation of seashells can significantly impact the quality of life of those living nearby and cause environmental contamination.The current study utilizes waste SSP, which reduces OPC use.The bare-minimum use of OPC can reduce greenhouse gas and CO 2 emissions, achieving sustainability goals [27][28][29].
In addition, WGP is another material used to replace fine aggregate.Glass is a popular material that can be found practically anywhere and in various shapes, including in food jars, decorative items, laboratory equipment, cold drink urns, tubes, lights, and monitors.India produces thousands of tons of regulated glass trash from residential, institutional, and industrial activity.It is nearly 100 percent recyclable, but with the current collection and recycling network, only 45 percent of glass is recycled.The usage of WGP reduces the consumption of natural sand and quartz sand [30][31][32][33][34]. WGP has a significant effect on concrete's setting and flow properties.WGP content in concrete reduces its flow and setting.However, the mechanical properties of concrete are decreased slightly compared with concrete without WGP.Nanosized glass waste with FA in cement showed good engineering properties along with minimizing environmental hazards [35][36][37][38][39].
Various studies have tried to utilize many supplementary cementitious materials.The mechanical properties of HSC, such as compressive strength, split tensile strength, flexural strength, modulus of elasticity, and water absorption, with the effect on waste binders, have been studied.Yang Zhang et al. (2020) investigated utilizing concrete as a material for the durability and reinforcement of deteriorated conventional concrete structures due to its excellent characteristics, such as superior compressive strength, high tensile capacity, and extremely low permeability [40].Ye Shi et al. (2019) have aimed to prove that concrete with high strength is used to reduce the harmful effects of building materials on the environment and post-maintenance compared with standard concrete.A study of HSC presented a series of comprehensive methods, including the optimization design of the binder system, the utilization of nanoparticles and chemical activators, and heat curing to prepare HSC with relatively lower environmental impact [41].
Xie et al. (2018) studied shrinkage's impact in concrete.Three unique practices to reduce the effect of shrinkage were investigated: reducing the powder content, chemical admixture, and using crushed ice to partly substitute mixing water [42].Sarcomas et al. ( 2018) have studied the effects of constituent materials on the microstructure and mechanical properties of concrete.An attempt was made to study the rheological properties of concrete using a squeezing flow test [43].Suleyman et al. ( 2017) have concentrated on producing high-strength concrete by using pumice aggregate to gain an advantage in transportation due to its low weight.Brass-coated steel fibers and polycarboxylate-based superplasticizers were utilized with OPC and silica fumes [44].Hiremath and Yaragal (2017) have studied the effects of standard, steam (hot water bath), autoclave, and combined (steam and standard) curing regimes on the early strength development of HSC.HSC studies have revealed that steam curing was found to have the highest strength among the four different curing regimes.Seashell and mussel shell powders were used to replace OPC in the range of 5%-20%.Replacement with seashell binders increased the mechanical and microstructure properties but adversely reduced the setting and flow characteristics.The influence of curing days on the enhancement of mechanical properties at the early phases is considerably more critical than the impact of the later curing days [45][46][47][48][49][50][51].The details in the literature have displayed various studies of curing regimes, materials used, methods, and different studied mechanical properties.The literature mentioned above indicates that limited research has been conducted on SSP and WGP utilization.
The current study aims to find the optimum percentages of SSP as a binder replacement and WGP as a fine aggregate replacement in HSC.This investigation focuses on the effect of SSP, which varied with 5%, 10%, and 15% cement replacement levels.In addition, the impact of WGP was observed with two replacement levels, 5% and 10%, replacing natural sand.The report also includes the fresh properties of HSC such as slump flow, T500, and T700.This research also considers mechanical properties such as the compressive strength, split tensile strength, flexural strength, modulus of elasticity, and water absorption of HSC with SSP and WGP.The microstructure of HSC was also studied using SEM, EDS, and XRD.The present investigation also includes the predicted equations for split tensile strength, flexural strength, modulus of elasticity, and water absorption.

Binders
Concrete is considered to be a two-phase material, consisting of the paste or cement phase and solid or aggregate phase.The overall properties of concrete are influenced by both the properties and qualities of paste phase as compared with those of aggregate phase.The properties, such as strength, elastic properties, permeability, durability, and change in volume of concrete, are highly influenced by the concrete's paste structure.Figure 1 shows the different binder materials used in the present study.

Binders
Concrete is considered to be a two-phase material, consisting of the paste or cement phase and solid or aggregate phase.The overall properties of concrete are influenced by both the properties and qualities of paste phase as compared with those of aggregate phase.The properties, such as strength, elastic properties, permeability, durability, and change in volume of concrete, are highly influenced by the concrete's paste structure.1. Ramco brand of OPC was procured from a local supplier.The specific gravity and surface area of OPC 53 were 3.10 and 240 m 2 /kg, respectively.The chemical and physical properties of OPC 53 grade are tabulated in Tables 2 and 3. PSD and SEM images of OPC 53 grade are shown in Figures 2 and 3a.   1. Ramco brand of OPC was procured from a local supplier.The specific gravity and surface area of OPC 53 were 3.10 and 240 m 2 /kg, respectively.The chemical and physical properties of OPC 53 grade are tabulated in Tables 2 and 3. PSD and SEM images of OPC 53 grade are shown in Figures 2 and 3a.

Silica Fume
SF is also known as microsilica, produced from silicon metal and other ferrosilicon alloys.In the present study, SF was used in HSC owing to its high reactivity and fineness.SF fulfilled the criteria as per ASTM C 1240.The specific gravity and surface area of SF were 2.35 and 23,500 m 2 /kg, respectively.The chemical and physical properties of SF are presented in Tables 2 and 3. SF was procured from Astra Chemical Limited, Chennai, India.PSD and SEM images of SF are shown in Figures 2 and 3b.

Class C Fly Ash
Class C FA was collected from an RTPS, Raichur, India.Class C FA satisfied the chemical composition requirement criteria as per clause of ASTM C618.The specific gravity and surface area of FA were 2.65 and 446 m 2 /kg, respectively.The chemical and physical properties of Class C FA are presented in Tables 2 and 3. PSD and SEM images of Class C FA are shown in Figures 2 and 3c.

Seashell Powder
SSP is a composite binder containing more than 90% calcium carbonate by its weight.SSP is produced by grinding the oyster shells found in the marine ecosystem and calcining them at 600 to 700 • C. The chemical and physical properties of SSP are presented in Tables 2  and 3, respectively.Calcium-rich SSP has shown promising results in a few studies.PSD and SEM images of SSP are shown in Figures 2 and 3d.

Natural Sand
Natural sand was procured from a local supplier.The sand used in the mix was made to pass through a 2.36 mm IS sieve, and its water absorption was found to be less than 2% with specific gravity of 2.61.

Waste Glass Powder
WGP left over after cutting glasses was collected from local glass manufacture shops.WGP materials cannot be reused because of the high cost of recycling.WGP was grounded to below 150 microns and was used as a partial replacement for cement and fine aggregate.XRD of WGP and SSP is shown in Figure 4. WGP was in amorphous phase and SSP was in crystalline phase with CaO as the major peak as compared with Ca(OH) 2 and CaCO 3 .

Natural Sand
Natural sand was procured from a local supplier.The san to pass through a 2.36 mm IS sieve, and its water absorption w with specific gravity of 2.61.

Waste Glass Powder
WGP left over after cutting glasses was collected from lo WGP materials cannot be reused because of the high cost of re to below 150 microns and was used as a partial replacement fo XRD of WGP and SSP is shown in Figure 4. WGP was in am in crystalline phase with CaO as the major peak as compared

Chemical Admixture
Polycarboxylate-ether-based (PCBE) superplasticizer Mapei Dynamon 550 was used for its high workability and to achieve high mechanical properties of HSC.The use of PCBE reduced the w/c ratio to 0.20 for a dosage of less than 2%.

Steel Fibers
The steel fibers used were 12.5 mm long and 0.45 mm in diameter, and the fibers were in a crimped shape.The density of steel fibers was 7850 kg/m 3 and the fibers were corrosion-free.The characteristics of steel fibers are tabulated in Table 4.

Mix Proportions
Mixes of concrete with high strength published by various authors were referred to and adopted in the present work [13,51].HSC mixes were then developed using a trial-and-error procedure.Mix proportions were achieved based on trial and error, and the number of materials used to prepare the various mixes of HSC is tabulated in Table 5. C90SSP0 and C80SSP0 are referred to as reference mixes; details are given in Table 5.The effect of SSP in HSC was studied with 5%, 10%, and 15% cement replacement levels.The impact of WGP was also examined with replacement of natural sand in two groups at 5% and 10%.The total binder content of 1000 kg/m 3 was constant throughout all mixes.The w/c ratio of 0.2 was kept constant in the present study.PCBE superplasticizer was fixed at 2% binder content throughout the blends.In addition, steel fibers used were observed at 3% of the total volume in all mixes.Various mechanical properties of seven different HSC mixes were studied.

Test Methods
A slump flow test was conducted on fresh HSC mixes to obtain a good combination as per IS:1199-1959.HSC's compressive strength was tested as per IS:516-1959 at 7, 28, and 56 days of water curing period.HSC cylinders were cast to test the splitting tensile strength of concrete specimens as per IS:5816-1999.HSC cylinders were tested after water curing for 28 and 56 days.The flexural strength of beams of size 100 × 100 × 500 mm (B × H × L), cast as per IS:516-1959, was tested at 28 and 56 days of water curing.Water absorption test was conducted on HSC samples as per codal provisions of BS 1881 .SEM-EDS and XRD were performed for microstructure properties of HSC using EVO MA18 with Oxford EDS (X-act) and Rigaku Miniflex 600.

Effects of SSP and WGP on Slump Flow of HSC
The slump flow of all the HSC mixes varied from 700 to 785 mm.The slump flow time for the HSC to reach a diameter of 500 mm for all the mixes was less than 8 s, and the time needed to achieve a flow diameter of 700 mm for all mixes ranged between 20 and 25 s.The slump flow values, T500 and T700, agreed with European guidelines and are plotted in Figure 5.The C65SSP15 mix displayed the lowest slump flow value and T500, which were 738 mm and 8 sec, respectively, which may have been due to an increase in the surface area of the binder.The increased surface area led to more water being utilized by the seashell powder, significantly reducing the slump flow and slump time.Similar observations were also noted in previously published outcomes [48,49].In addition, the increase in waste glass powder reduces the slump flow and slump time, which can be seen in the mixes C75SSP5GP5 and C75SSP5GP10.

Effects of SSP and WGP on Compressive Strength of HSC Mixes
The compressive strength of various HSC mixes at 7, 28, and 56 days of underwater curing was examined, as shown in Figure 6.The HSC specimens were tested after being removed from the water and patted dry.A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days.
The C75SSP5 and C75SSP5GP5 mixes showed higher strength than all five other mixes because of their additional hydrated products and higher particle packing.The C80SSP0 mix showed a slower hydration process because of its 10% FA content.The C70SSP10 and C65SSP15 mixes indicated a loss of strength as the SSP percentage increased from 5% to 15% due to the increase in CSH gel, which can be seen in the XRD and SEM images.C75SSP5GP10 showed a more significant reduction in strength than C75SSP5GP5 because its WGP content was increased from 5% to 10%.A mix containing 5% SSP and 5% GP exhibited the maximum compressive strength of the C75SSP5 and C75SSP5GP5 mixes, indicating optimum SSP and WGP.The C75SSP5 mix was also steam cured for three days at 90 °C, and compressive strength was achieved at about 154 MPa.With the inclusion of SSP, it can be noted that the compressive strength improved quickly in the early curing days; later, the compressive strength was enhanced more slowly.It can be observed that the impact of the curing days on the enhancement in compressive strength was considerably more noticeable in the early curing days compared with the later curing days, and these outcomes are in good agreement with the results displayed.Comparable results have been observed in previous findings [52][53][54].

Effects of SSP and WGP on Compressive Strength of HSC Mixes
The compressive strength of various HSC mixes at 7, 28, and 56 days of underwater curing was examined, as shown in Figure 6.The HSC specimens were tested after being removed from the water and patted dry.A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days.

Effects of SSP and WGP on Compressive Strength of HSC Mixes
The compressive strength of various HSC mixes at 7, 28, and 56 days of underwater curing was examined, as shown in Figure 6.The HSC specimens were tested after being removed from the water and patted dry.A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days.
The C75SSP5 and C75SSP5GP5 mixes showed higher strength than all five other mixes because of their additional hydrated products and higher particle packing.The C80SSP0 mix showed a slower hydration process because of its 10% FA content.The C70SSP10 and C65SSP15 mixes indicated a loss of strength as the SSP percentage increased from 5% to 15% due to the increase in CSH gel, which can be seen in the XRD and SEM images.C75SSP5GP10 showed a more significant reduction in strength than C75SSP5GP5 because its WGP content was increased from 5% to 10%.A mix containing 5% SSP and 5% GP exhibited the maximum compressive strength of the C75SSP5 and C75SSP5GP5 mixes, indicating optimum SSP and WGP.The C75SSP5 mix was also steam cured for three days at 90 °C, and compressive strength was achieved at about 154 MPa.With the inclusion of SSP, it can be noted that the compressive strength improved quickly in the early curing days; later, the compressive strength was enhanced more slowly.It can be observed that the impact of the curing days on the enhancement in compressive strength was considerably more noticeable in the early curing days compared with the later curing days, and these outcomes are in good agreement with the results displayed.Comparable results have been observed in previous findings [52][53][54].

Effects of SSP and WGP on Split Tensile Strength
The split tensile strength values of all HSC mixes were in the range of 5.45-10.56MPa, as shown in Figure 7. HSC mixes showed higher strength due to the presence of 3% of the total volume of steel fibers.The C75SSP5 and C70SSP10 mixes revealed 23% and 18.37% T 700 (sec) The C75SSP5 and C75SSP5GP5 mixes showed higher strength than all five other mixes because of their additional hydrated products and higher particle packing.The C80SSP0 mix showed a slower hydration process because of its 10% FA content.The C70SSP10 and C65SSP15 mixes indicated a loss of strength as the SSP percentage increased from 5% to 15% due to the increase in CSH gel, which can be seen in the XRD and SEM images.C75SSP5GP10 showed a more significant reduction in strength than C75SSP5GP5 because its WGP content was increased from 5% to 10%.A mix containing 5% SSP and 5% GP exhibited the maximum compressive strength of the C75SSP5 and C75SSP5GP5 mixes, indicating optimum SSP and WGP.The C75SSP5 mix was also steam cured for three days at 90 • C, and compressive strength was achieved at about 154 MPa.With the inclusion of SSP, it can be noted that the compressive strength improved quickly in the early curing days; later, the compressive strength was enhanced more slowly.It can be observed that the impact of the curing days on the enhancement in compressive strength was considerably more noticeable in the early curing days compared with the later curing days, and these outcomes are in good agreement with the results displayed.Comparable results have been observed in previous findings [52][53][54].

Effects of SSP and WGP on Split Tensile Strength
The split tensile strength values of all HSC mixes were in the range of 5.45-10.56MPa, as shown in Figure 7. HSC mixes showed higher strength due to the presence of 3% of the total volume of steel fibers.The C75SSP5 and C70SSP10 mixes revealed 23% and 18.37% respective increases in splitting tensile strength compared with the C90SSP0 blend, due to the strong influence of SSP reactivity and enhanced interlocking of particles with aggregates.C75SSP5GP5 indicated a 13.8% increase in splitting tensile strength compared with the C90SSP0 mix.The compressive strength results were also similar in terms of split tensile strength values.Previously published studies of HSC mixes have shown similar outcomes [55,56].

Effects of SSP and WGP on Modulus of Elasticity
The modulus of elasticity values of all HSC mixes were found to vary from 40.2 to 46.8 Gpa, as shown in Figure 8.The HSC mixes showed a higher modulus of elasticity due to the steel fibers.The highest modulus of elasticity value was that of the C75SSP5 mix at 46.8 GPa, and the C65SSP15 mix displayed the lowest modulus of elasticity value of 40.2 GPa.The C75SSP5 mix revealed a 4.7% increase in its modulus of elasticity compared with the C90SSP0 mix, owing to the rise in paste stiffness with 5% SSP.C75SSP5GP5 also indicated a 1.76% increase in its modulus of elasticity, because it contained 5% more WGP than the C90SSP0 mix.It can be observed that the compressive strength and split tensile strength results also indicate similar trends in terms of modulus of elasticity values.Other recent investigations of HSC mixes have yielded similar results [57][58][59].

Effects of SSP and WGP on Modulus of Elasticity
The modulus of elasticity values of all HSC mixes were found to vary from 40.2 to 46.8 Gpa, as shown in Figure 8.The HSC mixes showed a higher modulus of elasticity due to the steel fibers.The highest modulus of elasticity value was that of the C75SSP5 mix at 46.8 GPa, and the C65SSP15 mix displayed the lowest modulus of elasticity value of 40.2 GPa.The C75SSP5 mix revealed a 4.7% increase in its modulus of elasticity compared with the C90SSP0 mix, owing to the rise in paste stiffness with 5% SSP.C75SSP5GP5 also indicated a 1.76% increase in its modulus of elasticity, because it contained 5% more WGP than the C90SSP0 mix.It can be observed that the compressive strength and split tensile strength results also indicate similar trends in terms of modulus of elasticity values.Other recent investigations of HSC mixes have yielded similar results [57][58][59].

Effects of SSP and WGP on Modulus of Elasticity
The modulus of elasticity values of all HSC mixes were found to vary from 40.2 to 46.8 Gpa, as shown in Figure 8.The HSC mixes showed a higher modulus of elasticity due to the steel fibers.The highest modulus of elasticity value was that of the C75SSP5 mix at 46.8 GPa, and the C65SSP15 mix displayed the lowest modulus of elasticity value of 40.2 GPa.The C75SSP5 mix revealed a 4.7% increase in its modulus of elasticity compared with the C90SSP0 mix, owing to the rise in paste stiffness with 5% SSP.C75SSP5GP5 also indicated a 1.76% increase in its modulus of elasticity, because it contained 5% more WGP than the C90SSP0 mix.It can be observed that the compressive strength and split tensile strength results also indicate similar trends in terms of modulus of elasticity values.Other recent investigations of HSC mixes have yielded similar results [57][58][59].

Effects of SSP and WGP on Water Absorption
The water absorption of all of the HSC mixes, performed at 28 days, is demonstrated in Figure 9.The water absorption reduced with increasing SSP in the mixes, and the lowest water absorption was observed in the HSC mix with 5% SSP.A combination of SSP and WGP, i.e., the C90SSP0 combination, had a water absorption value of 3.3%.The C80SSP0, C75SSP5, C70SSP10, C65SSP15, C75SSP5GP5, and C75SSP5GP10 mixes had water absorption values of 3.8, 2.9, 3.1, 3.6, 3, and 3.1%, respectively.As the percentage of SSP increased, the water absorption of the HSC mixes decreased, owing to the denser paste and lower porosity.The WGP slightly affected water absorption, which may be due to having unreacted particles and higher porosity than the C75SSP5 mix.The correlation between the water absorption and compressive strength of all of the HSC mixes was Y = 7.80 − 0.047 × X, where Y is water absorption and X is compressive strength with an R2 value of 0.78.The latest studies on HSC mixes have revealed similar findings [60,61].

Effects of SSP and WGP on Water Absorption
The water absorption of all of the HSC mixes, performed at 28 days, is in Figure 9.The water absorption reduced with increasing SSP in the mixes, water absorption was observed in the HSC mix with 5% SSP.A combinat WGP, i.e., the C90SSP0 combination, had a water absorption value of 3.3% C75SSP5, C70SSP10, C65SSP15, C75SSP5GP5, and C75SSP5GP10 mixes had tion values of 3.8, 2.9, 3.1, 3.6, 3, and 3.1%, respectively.As the percentage of the water absorption of the HSC mixes decreased, owing to the denser pa porosity.The WGP slightly affected water absorption, which may be due t acted particles and higher porosity than the C75SSP5 mix.The correlatio water absorption and compressive strength of all of the HSC mixes w 0.047 × , where Y is water absorption and X is compressive strength wi of 0.78.The latest studies on HSC mixes have revealed similar findings [60

Effect of SSP in HSC Mixes Using Scanning Electron Microscope (SEM) Im
SEM analysis of the C90SSP0 mix (reference mix) is shown in Figure SEM micrograph of the C90SSP0 blend, it can be observed that the format occurred all over the mixture in a hydrated cement paste, and that led to compressive strength with the curing time.The presence of calcium and th CaCO3 are visible in the mix, and these are the primary sources for stren C90SSP0 mix was less dense, and there was no visible ettringite formation nation.
SEM analysis of the C80SSP0 mix is displayed in Figure 10b.The micro showed a decreased formation of CSH gel, which led to a slower hydration ing 10% FA to the mix slowed the hydration process.The decrease in CSH the presence of unreacted particles.Due to ITZ formation between the pa gregate, visible cracks were found in the mix.
SEM microscopic analysis of the C75SSP5 mix is displayed in Figure images show a comparatively denser mixture, and maximum hydration w 56 days.Replacement with SSP as a binder has a considerable effect on t properties of HSC, which can be noted from the increased CSH gel form

Effect of SSP in HSC Mixes Using Scanning Electron Microscope (SEM) Images
SEM analysis of the C90SSP0 mix (reference mix) is shown in Figure 10a.From the SEM micrograph of the C90SSP0 blend, it can be observed that the formation of CSH gel occurred all over the mixture in a hydrated cement paste, and that led to an increase in compressive strength with the curing time.The presence of calcium and the formation of CaCO 3 are visible in the mix, and these are the primary sources for strength gain.The C90SSP0 mix was less dense, and there was no visible ettringite formation in the combination.
SEM analysis of the C80SSP0 mix is displayed in Figure 10b.The micrographic study showed a decreased formation of CSH gel, which led to a slower hydration process.Adding 10% FA to the mix slowed the hydration process.The decrease in CSH gel was due to the presence of unreacted particles.Due to ITZ formation between the paste and the aggregate, visible cracks were found in the mix.
SEM microscopic analysis of the C75SSP5 mix is displayed in Figure 10c.The SEM images show a comparatively denser mixture, and maximum hydration was achieved at 56 days.Replacement with SSP as a binder has a considerable effect on the mechanical properties of HSC, which can be noted from the increased CSH gel formation in a hydrated paste.Nonetheless, in the C75SSP5 mix, many unreacted particles can be observed in an inactivated state; these could be further activated using heat or steam curing.Calcite formation in the combination was high, leading to strength gain.Ca and CaCO 3 increases can be seen in the mix; these are the crucial triggers for strength gain.
non-hydrated elements in the mixture resulted in a loss of strength.
SEM microscopic analysis of the C65SSP15 mix is illustrated in Figure 10e.An increase in SSP led to a further decrease in CSH development due to the unreacted phase of supplementary particles.An improper bond was found between aggregate and binder particles.The CSH gel formation was inadequate, which led to a further reduction in strength.The reaction between silica content and portlandite in the mix was stopped after 28 days, which was also a possible reason for the low strength [6,12,39].

Effect of SSP on Energy-dispersive X-ray Spectroscopy (EDS)
EDS analyses of the C90SSP0, C80SSP0, C75SSP5, C70SSP10, and C65SSP15 mixes are shown in Figure 11.EDS analysis demonstrated the presence of Ca, Si, Na, and traces of other elements in all of the HSC mixes.The Ca content in the OPC-SSP blend increased in the binders' system with an increase in SSP, which remained unreacted in the HSC mix.A substantial increment in compressive strength was found with the addition of SSP in the HSC mix.The C65SSP15 mix showed more CSH gel formation, but it was still unreacted.C75SSP5 displayed a chemically stable state compared with C70SSP10 and C65SSP15.The Ca/Si ratios of the C90SSP0, C80SSP0, C75SSP5, C70SSP10, and C65SSP15 mixes were 4.88, 4.01, 3.66, 2.45, and 2.82, respectively.According to the EDS results analysis, the development of CSH gel was prominent, and there was also the existence of CASH gel.The addition of SSP to the binder system resulted in additional CSH gel development due to the rise in calcium content.The Ca/Si ratios in the SSP-based paste decreased while the Si/Al ratios increased, contributing to the mechanical properties of the HSC mixes [56,57].Fewer peaks of CSH formations were obtained in the XRD analysis, as shown in Figure 12.SEM microscopic analysis of the C70SSP10 mix is shown in Figure 10d.An increase in SSP density improved the mix density; however, ITZ development caused cracks in the mix.Increased SSP had a negative effect on the mix's mechanical performance.Increased non-hydrated elements in the mixture resulted in a loss of strength.
SEM microscopic analysis of the C65SSP15 mix is illustrated in Figure 10e.An increase in SSP led to a further decrease in CSH development due to the unreacted phase of supplementary particles.An improper bond was found between aggregate and binder particles.The CSH gel formation was inadequate, which led to a further reduction in strength.The reaction between silica content and portlandite in the mix was stopped after 28 days, which was also a possible reason for the low strength [6,12,39].

Effect of SSP on Energy-Dispersive X-ray Spectroscopy (EDS)
EDS analyses of the C90SSP0, C80SSP0, C75SSP5, C70SSP10, and C65SSP15 mixes are shown in Figure 11.EDS analysis demonstrated the presence of Ca, Si, Na, and traces of other elements in all of the HSC mixes.The Ca content in the OPC-SSP blend increased in the binders' system with an increase in SSP, which remained unreacted in the HSC mix.A substantial increment in compressive strength was found with the addition of SSP in the HSC mix.The C65SSP15 mix showed more CSH gel formation, but it was still unreacted.C75SSP5 displayed a chemically stable state compared with C70SSP10 and C65SSP15.The Ca/Si ratios of the C90SSP0, C80SSP0, C75SSP5, C70SSP10, and C65SSP15 mixes were 4.88, 4.01, 3.66, 2.45, and 2.82, respectively.According to the EDS results analysis, the development of CSH gel was prominent, and there was also the existence of CASH gel.The addition of SSP to the binder system resulted in additional CSH gel development due to the rise in calcium content.The Ca/Si ratios in the SSP-based paste decreased while the Si/Al ratios increased, contributing to the mechanical properties of the HSC mixes [56,57].Fewer peaks of CSH formations were obtained in the XRD analysis, as shown in Figure 12. approach increased the effectiveness of OPC, SSP, SF, and FA, resulting in a more compact binder system that greatly improved the HSC's mechanical properties.The identified peaks were Q-quartz (ICDD-01-072-0646), C-calcium silicate hydrate (ICDD-01-083-1550), E-ettringite (ICDD-01-072-0646), T-tobermorite (COD 01000046), and CH-calcium hydroxide (ICDD-01-072-0156).The XRD results are in good agreement with the SEM and EDS results.

Split Tensile Strength Versus Compressive Strength
The relationship between the split tensile strength and compressive strength of HSC at 28 days was analyzed and compared with the IS code, the ACI code, and the outcomes of Singh et al. (2022) [61], as shown in Figure 13a.The proposed equation of  = 0.34 × ^(0.68)with an R 2 value of 0.88 was obtained using nonlinear regression analysis, where X is compressive strength (MPa) and Y is split tensile strength (MPa).

X-ray Diffraction (XRD)
XRD analyses of the C90SSP0, C80SSP0, C75SSP5, C70SSP10, and C65SSP15 mixes are displayed in Figure 12.The HSC mix with C75SSP5 samples exhibited higher CSH peaks than those with C70SSP10 and C65SSP15.The reaction of the SSP binder pastes indicated the new semicrystalline intensities developing in various compounds.There were few impurities from the OPC 53, SF, and FA binders in their crystalline intensities all over the binder hydration process.Since SSP is slightly more reactive compared with OPC and FA, the HSC mixes experienced complete or incomplete hydration, observing a decreased CSH peak.Ettringite was also observed with SSP and without SSP.Although SSP is more reactive than OPC and FA, the quaternary mixtures underwent a full or partial hydration process, as evidenced by the lower peak intensity of CSH.As the quantity of SSP in the quaternary mixes improved, the peak intensity of CSH increased dramatically.Since a greater SSP percentage resulted in a higher cement matrix, which added a considerable number of gels to the paste, higher SSP content resulted in more hydrates.Secondary hydrates, on the other hand, had a major impact on CH development.The cross-bonding approach increased the effectiveness of OPC, SSP, SF, and FA, resulting in a more compact binder system that greatly improved the HSC's mechanical properties.The identified peaks were Q-quartz (ICDD-01-072-0646), C-calcium silicate hydrate (ICDD-01-083-1550), E-ettringite (ICDD-01-072-0646), T-tobermorite (COD 01000046), and CH-calcium hydroxide (ICDD-01-072-0156).The XRD results are in good agreement with the SEM and EDS results.

Split Tensile Strength Versus Compressive Strength
The relationship between the split tensile strength and compressive strength of HSC at 28 days was analyzed and compared with the IS code, the ACI code, and the outcomes of Singh et al. (2022) [61], as shown in Figure 13a.The proposed equation of Y = 0.34 × Xˆ(0.68) with an R 2 value of 0.88 was obtained using nonlinear regression analysis, where X is compressive strength (MPa) and Y is split tensile strength (MPa).

Modulus of Elasticity Versus Compressive Strength
The relationship between the modulus of elasticity and compressive strength of HSC at 28 days was analyzed and compared with the IS code and the ACI code, as shown in Figure 13b.The predicted equation of  = 4.85 × ^(0.48)with an R 2 value of 0.92 was obtained using nonlinear regression analysis, where X is compressive strength (MPa) and Y is the modulus of elasticity (GPa).

Conclusions
The experimental results of the effects of SSP and WGP on the fresh, mechanical, and microstructure properties of HSC are discussed below.Based on the experimental outcome, the following conclusions have been drawn:

•
Seashell powder can be used as a binder that reduces OPC consumption significantly.The increase in SSP in binders decreased the slump flow, T500, and T700, and as per the fresh properties requirement, the optimum percentage of SSP that can be used in HSC is 5%.

•
WGP can also be utilized as fine aggregate that substantially reduces the consumption of natural sand.The increment of WGP as a fine aggregate reduced the flow properties, and the optimum percentage replacement of 5% WGP may be utilized in HSC.

•
A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days.The impact of increased SSP within binders enhanced compressive strength significantly, but 5% SSP and 5% WGP exhibited better compressive strength.In addition, the C75SSP5 mix was steam cured for three days at 90 ℃, and compressive strength was achieved at about 154 MPa.Similar observations were made regarding split tensile strength and the modulus of elasticity.

•
SEM microscope images of HSC with SSP exhibited dense and compact structures.However, a small number of unreacted particles were still present; reacting with heat or steam-curing regimes can compact HSC further.

•
EDS analysis of HSC with SSP displayed the presence of various gels such as CSH, CASH, CH, and CC, which contribute to HSC's mechanical properties.The Ca/Si ratios in the SSP-based paste decreased while the Si/Al ratios increased, contributing to the mechanical properties of the HSC mixes.

•
XRD analysis of HSC with SSP showed the presence of quartz, CSH, and ettringite.The cross-bonding approach increased the effectiveness of OPC, SSP, SF, and FA,

Modulus of Elasticity Versus Compressive Strength
The relationship between the modulus of elasticity and compressive strength of HSC at 28 days was analyzed and compared with the IS code and the ACI code, as shown in Figure 13b.The predicted equation of Y = 4.85 × Xˆ(0.48) with an R 2 value of 0.92 was obtained using nonlinear regression analysis, where X is compressive strength (MPa) and Y is the modulus of elasticity (GPa).

Conclusions
The experimental results of the effects of SSP and WGP on the fresh, mechanical, and microstructure properties of HSC are discussed below.Based on the experimental outcome, the following conclusions have been drawn:

•
Seashell powder can be used as a binder that reduces OPC consumption significantly.The increase in SSP in binders decreased the slump flow, T500, and T700, and as per the fresh properties requirement, the optimum percentage of SSP that can be used in HSC is 5%.

•
WGP can also be utilized as fine aggregate that substantially reduces the consumption of natural sand.The increment of WGP as a fine aggregate reduced the flow properties, and the optimum percentage replacement of 5% WGP may be utilized in HSC.

•
A maximum compressive strength of 112.91 MPa was found for the C75SSP5 mix at 56 days.The impact of increased SSP within binders enhanced compressive strength significantly, but 5% SSP and 5% WGP exhibited better compressive strength.In addition, the C75SSP5 mix was steam cured for three days at 90 °C, and compressive strength was achieved at about 154 MPa.Similar observations were made regarding split tensile strength and the modulus of elasticity.

•
SEM microscope images of HSC with SSP exhibited dense and compact structures.However, a small number of unreacted particles were still present; reacting with heat or steam-curing regimes can compact HSC further.

•
EDS analysis of HSC with SSP displayed the presence of various gels such as CSH, CASH, CH, and CC, which contribute to HSC's mechanical properties.The Ca/Si ratios in the SSP-based paste decreased while the Si/Al ratios increased, contributing to the mechanical properties of the HSC mixes.

•
XRD analysis of HSC with SSP showed the presence of quartz, CSH, and ettringite.The cross-bonding approach increased the effectiveness of OPC, SSP, SF, and FA, resulting in a more compact binder system that significantly improved the HSC's mechanical properties.
Figure 1 shows the different binder materials used in the present study.

Figure 1 .
Figure 1. Materials used to develop HSC: (a) OPC 53; (b) Class C FA; (c) SF; (d) SSP; (e) WGP; (f) steel fibers.2.1.1.OPC OPC 53 grade conforming to IS 12269 was utilized in binder systems in the present work.The compressive strength of cement mortar as per IS 4031 should not be less than 53 MPa at 28 days.The obtained test results of OPC 53 grade are tabulated in Table 1.Ramco brand of OPC was procured from a local supplier.The specific gravity and surface area of OPC 53 were 3.10 and 240 m 2 /kg, respectively.The chemical and physical properties of OPC 53 grade are tabulated in Tables 2 and 3. PSD and SEM images of OPC 53 grade are shown in Figures 2 and 3a.

Figure 1 .
Figure 1. Materials used to develop HSC: (a) OPC 53; (b) Class C FA; (c) SF; (d) SSP; (e) WGP; (f) steel fibers.2.1.1.OPC OPC 53 grade conforming to IS 12269 was utilized in binder systems in the present work.The compressive strength of cement mortar as per IS 4031 should not be less than 53 MPa at 28 days.The obtained test results of OPC 53 grade are tabulated in Table 1.Ramco brand of OPC was procured from a local supplier.The specific gravity and surface area of OPC 53 were 3.10 and 240 m 2 /kg, respectively.The chemical and physical properties of OPC 53 grade are tabulated in Tables 2 and 3. PSD and SEM images of OPC 53 grade are shown in Figures 2 and 3a.

Figure 2 .
Figure 2. Particle size distribution of powder binder materials.

J
. Compos.Sci.2023, 7, x FOR PEER REVIEW 10 of 18 respective increases in splitting tensile strength compared with the C90SSP0 blend, due to the strong influence of SSP reactivity and enhanced interlocking of particles with aggregates.C75SSP5GP5 indicated a 13.8% increase in splitting tensile strength compared with the C90SSP0 mix.The compressive strength results were also similar in terms of split tensile strength values.Previously published studies of HSC mixes have shown similar outcomes[55,56].

Figure 8 .
Figure 8. Modulus of elasticity values of HSC mixes at 28 days.

J
. Compos.Sci.2023, 7, x FOR PEER REVIEW 10 of 18 respective increases in splitting tensile strength compared with the C90SSP0 blend, due to the strong influence of SSP reactivity and enhanced interlocking of particles with aggregates.C75SSP5GP5 indicated a 13.8% increase in splitting tensile strength compared with the C90SSP0 mix.The compressive strength results were also similar in terms of split tensile strength values.Previously published studies of HSC mixes have shown similar outcomes[55,56].

Figure 8 .
Figure 8. Modulus of elasticity values of HSC mixes at 28 days.

Figure 8 .
Figure 8. Modulus of elasticity values of HSC mixes at 28 days.

Figure 9 .
Figure 9. Water absorption of RPC combined at 28 days.

Figure 9 .
Figure 9. Water absorption of RPC combined at 28 days.

Figure 13 .
Figure 13.Relationships between mechanical properties of HSC: (a) relationship between split tensile strength and compressive strength at 28 days; (b) relationship between modulus of elasticity and compressive strength at 28 days.

Figure 13 .
Figure 13.Relationships between mechanical properties of HSC: (a) relationship between split tensile strength and compressive strength at 28 days; (b) relationship between modulus of elasticity and compressive strength at 28 days.

Table 1 .
Test results of OPC 53 grade.

Table 1 .
Test results of OPC 53 grade.

Table 2 .
Physical properties of powder materials.

Table 3 .
Chemical properties of powder materials.

Table 3 .
Chemical properties of powder materials.

Table 4 .
Characteristics of steel fibers.

Table 5 .
Mix proportions for HSC.