Potential use of silane-modified oyster shell powder in hydrophobic concrete

This article describes the laboratory-scale manufacture of hydrophobically modified oyster shell powder (mOSP) via a silane coupling agent and used as cement substitutes at 0% to 2.5%. Hydrophobic chemicals have been used in concrete to minimise capillary action by researchers. Although hydrophobic fillers improve concrete’s water repellency, replacing fine particles with them in higher proportions has a negative effect. We can use hydrophobically modified fillers in smaller amounts to replace cement while maintaining its critical properties. When mOSP is added in various quantities to binary and ternary mixes with natural zeolite, concrete hydration, mechanical strength, and durability are examined. At a 1.5% replacement ratio, mOSP improved concrete characteristics and durability. With free water and the hydrophobic modified nOSP, concrete mixes were consistently more workable. A gliding effect on the cementitious matrix caused by the surface roughness and hydrophobicity of the developed silane-coated nOSP increases the slump value. The 28-day compressive strength of concrete containing modified nOSP ranged from 39 to 42 MPa without zeolite and 43 to 46 MPa with it. Compressive strength increased more when 10% natural zeolite (NZ) was added with different amounts of mOSP. The RCPT values of the concrete series without zeolite dropped until 1% mOSP replacement (mOSCII), while the 1.5% mix (mOSZIII) had the lowest value. The angularly modified nOSP aggregates interlocked, improving the migration coefficient of mOSP concrete.


Introduction
Environmental sustainability is currently an essential component of the construction industry, and nearly every modern structure is constructed with sustainable building materials in mind (Han et al 2022).Civil engineers utilize locally sourced materials that have minimal ecological impact in order to minimize cement consumption.This practice is also prevalent for the advancement of society (Liao et al 2023).As the cement industry is a significant contributor to global warming, efforts have been made to reduce the escalating demand for cement production through the use of cement substitutes and supplementary cementitious materials (Liao et al 2022, Seifu et al 2022, Fode et al 2023, Navarrete et al 2023).Nevertheless, the utilization of SCMs has encountered major challenges related to transportation and limited availability in the area (Vejmelková et al 2015, Shekarchi et al 2023).Furthermore, an essential characteristic of a concrete material is its exceptional resistance to physical and chemical degradation that occurs with age (Islam et al 2022).Moreover, the fundamental property of the concrete's integral component should not be compromised when novel materials are utilized.Degradation of concrete, particularly at later ages, is a concern; therefore, materials must be used selectively following a comprehensive experimental analysis to ensure the long-term safety of the structure (Glasser et al 2008, Gao et al 2023).Even though many researchers have tried to incorporate bio-based materials into concrete (Kawaai et al 2022, Benmahiddine et al 2024), fewer people have reported on the durability of such structures, particularly as they age (Yin et al 2021, Wu et al 2023).The pore structure of concrete elements has a significant impact on their durability (Lv et al 2021).To mitigate the degradation of concrete components, additives are utilized to prevent moisture and other harmful substances from penetrating the pore spaces (Ahdal et al 2022, Kazemian and Shafei 2022).Therefore, it is critical to ensure that cavities are effectively plugged with fillers in order to improve the strength and durability of concrete structures and ensure their satisfactory performance (Liao et al 2022, Maglad et al 2023, Martínez-García et al 2024).The gradation of concrete ingredients and particle packing density of aggregates also influence the durability of concrete, which is primarily determined by its moisture transport mechanism (She et al 2020, Basha et al 2022).The primary determinant of concrete durability is water migration and permeation; this property can be enhanced by reducing the concrete's water absorption (Zhao et al 2020, Kong et al 2022).The decrease in water ingress serves as an indicator of the concrete's resistance to deteriorating mechanisms, including chemical attack and corrosion (Eziefula et al 2018, Song et al 2022, Hamada et al 2023).
Diverse types of additives have been utilized in previous investigations that acted as a physical barrier, protective coatings in the form of metallic and polymeric surface coating techniques to protect concrete from degrading environments (Dorado et al 2023, Liu andShi 2024, Shohide 2024).An estimated 20 million metric tonnes of additives as fillers (calcium carbonate, aluminium trihydrate, talc, kaolin, mica, and reinforcing fibres included) are produced annually for the global construction industry (Xia et al 2023, Zhao et al 2023).In addition to improving mechanical properties (specifically, flexural rigidity) filler is also used to enhance durability, which is arguably the most important characteristic of any building material (Suwannasingha et al 2022).Additionally, fillers may undergo surface modification using coupling agents to improve the interface with the matrix, or alternatively, with other agents designed to enhance the filler dispersion within the matrix and enhance the workability and durability of the concrete system (Xiong et al 2006, Pan et al 2022).Although organosilane surface modifiers are relatively costly, they have the potential to significantly strengthen the bond between filler and polymer, thereby improving performance and cost-effectiveness across a broad spectrum of applications (Ren et al 2023).Organosilanes, which are multifunctional substances containing reactive groups, exhibit strong adhesion to both the filler surface and the cement matrix (Khandelwal and Rhee 2021).This property facilitates the formation of an efficient interface between the filler and matrix (Cong et al 2021).There is a wide range of commercial products that incorporate reactive groups, the functionality of which can be modified by modifying the cement matrix, mostly with an alkoxy silane as the reactive group (Sudbrink et al 2017).A number of additional organic and inorganic coatings demonstrated enhanced resistance through their ability to enclose the surface and impede the ingress of hazardous substances (Sakr andBassuoni 2021, Luo et al 2022).In conjunction with the use of suitable additives, the surface coating of concrete can safeguard it against hazardous substances by preventing the ingress of moisture and enhancing its resistance to chemicals and physical deterioration (Elnaggar et al 2019, Wong et al 2020).However, the prohibitively high cost of commercial coatings also prevents the application of polymeric substances to the surface of concrete.
Some studies utilized a mineral admixture-magnesium potassium phosphate cement slurry characterized by a pre-coating and pre-curing of RCA surfaces.These surface treatments are simple to administer on-site, saving building time (Wang et al 2024).On untreated and treated recycled aggregate concrete, the optimized ball mill method using silica fume and basalt fiber resulted in improved concrete durability (Çakır and Dilbas 2021).Treated concrete results are slightly worse than untreated untreated.Concrete becomes hydrophobic when superhydrophobic oyster shell powder is applied.Concrete water repellency and corrosion resistance is achieved using superhydrophobic oyster shell powder (Song et al 2022).The support vector regression could be used to predict the recycled aggregate concrete frost durability in a cold region based on a durability agent cold climate value.Ant Lion, Grey Wolf, and Henry Gas Solubility Optimization were used to find the optimal values.While these methods could help to predict concrete frost difficulty in cold regions, the best method was the combination of Henry Gas Solubility Optimization with support vector regression (Esmaeili-Falak and Sarkhani Benemaran 2024).Thermally treated oyster shell powder can increase polymer bioactivity.Improved mechanical bioactive behaviour bio composites rendering treated shells potential polymer additives and antibacterial agents (Tsou et al 2019).A research work involved testing of discarded oyster shell powder and industrial blast furnace slag (BFS) as replacements for cement to make concrete sustainable (Han et al 2022).OSP and BFS are found to degrade mortar working performance, compressive strength, and cumulative heat of hydration.The use of expanded vermiculite as the carrier of microbial self-healing agents in concrete (Su and Jin 2022).Microbial self-healing agents were incorporated in wrapped vermiculite, which led to a substantial increase in the ability of the concrete to self-repair.The highest compatibility was observed in vermiculite that had been wrapped, with the treatment having no effect on apparent density or mechanical characteristics of the concrete mix.Some researchers goes deeper into the variety and extratenacity of microorganisms responsible for the curing part of the concrete as well as their habitat (Zhang et al 2024).When inorganic minerals were used to adjust the crack zone's chemical level in marine concrete, the addition ratio was improved in the activity of mineralized microorganisms.The research not only presents a promising outlook for the curing of fractures in marine concrete but also confirms the impact of bimetallic hydroxide in improving the habitat and improvement of the breeding conditions of microorganisms (Fu et al 2022).
In the present study, an economically viable, environmentally sustainable, and long-lasting infill coated with a hydrophobic agent is utilized as an effort to rectify the aforementioned issues.An attempt is made to establish a correlation between the durability properties and mechanical behaviour of concrete that incorporates a surfacemodified OSP as an infill.From a sustainability standpoint, the incorporation of organic additives, such as biocalcareous substances, can serve the dual purpose of reducing water absorption and improving the adhesion between concrete components.Induced by microbes, calcite precipitation served additional purposes, such as pore plugging and surface modification.Concrete alteration with hydrophobic additives has proven to be a highly successful approach for enhancing the material's durability and strength.Various researchers have employed a variety of hydrophobic additives in concrete to reduce the capillary action of the concrete.Although the water repellency of concrete is greatly enhanced by adding hydrophobic fillers, the usage of these additives as replacements for fine aggregates at higher proportions had a detrimental effect.Therefore, we can employ hydrophobically modified fillers as a substitute for cement in smaller amounts, while still achieving the essential characteristics.This study is highly significant as it aims to tackle the problem of concrete durability by utilizing nano-modified OSP, a sustainable and environmentally friendly material, for the manufacturing of concrete.In this study, a novel approach to research is offered that aims to make use of naturally occurring sea shell powder (oyster shell) as a filler and hydrophobic additive in order to improve the qualities of concrete in both normal and bad conditions.Because there are so few studies that have been conducted on the manufacturing and utilisation of natural materials as hydrophobic agents in concrete, the research work that has been done is considered to be innovative because it aims to determine the influence that hydrophobically modified OSP has on the properties of concrete.

Materials
Based on the technical specifications of IS 12269-1987, the primary binder material that is utilized is Portland cement (Grade 53).The oyster shells are collected from nearby seashore region, Tuticorin in Tamil Nadu is used for the present study whereas the natural zeolite powder is chosen as a pozzolanic admixture.The fine aggregates utilized throughout this investigation are river sand, which is in accordance with International Standard 383:1970.In order to create coarse aggregate, we utilized aggregates that had a texture that was rough and an angular shape.The fineness modulus of these aggregates ranged from 6.1 to 20 millimeters.The XRF (X-ray fluorescence analysis) technique was adopted to find out the chemical compositions, and the results are found in table 1. Polycarboxylate superplasticizer, also known as Sika ViscoCrete, has a specific gravity of 1.08 and is utilized for the purpose of correcting the fluidity of concrete.Under the brand name Zycosil, the organosilanebased component is utilized in this investigation as a modifier and their technical specification is presented in table 2. Through the application of the fine ball grinding approach, the oyster shell powders are transformed into nanoform.It is a mechanical grinding process that reduces the particles to the nanoscale.In this method, oyster shell particles are subjected to high-energy ball milling.This ball milling entails placing the powders in a ball mill with the grinding media like stainless steel balls and then grinding them with severe mechanical forces produced by the collision of the grinding media with the powders.Due to multiple impacts and frictional connections, the oyster shell particles reduce to smaller sizes, which means the shell particles are smaller.Thus, the particle size is continuously reduced by milling until the nano range.Such decrease is achieved in parallel with the milling.The use of a fine ball for grinding allows for precise and better-controlled reduction of the particle size and, thus, better quality production of the nanostructured materials.They can be applied in different fields such as material science, environmental remediation, biotechnology among others noting that they exhibit increased properties.

Production of modified nOSP
Prior to milling, the oyster shells that had been cleaned were allowed to dry at room temperature for a period of twenty-four hours.The process of milling was carried out in two distinct stages, the dry milling stage came first and then the wet milling stage.In the first step of the process, thirty grammes of dried oyster shells were measured and then dry milled in a ball mill to produce oyster shell powder (OSP).There are fifty stainless steel balls with a diameter of ten millimetres, and there is a stainless-steel jar with an inner diameter of one hundred millimetres that is used for milling.
The oyster shells were milled in a clockwise direction for thirty minutes at a speed of 450 revolutions per minute.After going through the milling process, the shell powder was put through a sieving shaker using mechanical equipment.During the second stage, the OSP that had been collected was subjected to wet milling in order to produce nano oyster shell powder (nOSP).Consequently, thirty grammes of OSP were weighed and placed into the stainless-steel jar, which had a capacity of five hundred millilitres.At a ratio of one to twenty, Zycosil ought to be diluted with water that can be consumed.After that, 100 millilitres of water were added to the Zycosil that was based on organosilane, and the mixture was wet milled at 450 revolutions per minute for 258 min in a clockwise direction.The subsequent step involved the separation of mixtures of nOSP and solvent by means of the decantation technique, which involved the removal of the liquid layer that was devoid of any precipitate.In order to guarantee that the nano shell powders were free of any impurities, this process was carried out five times.In order to obtain a modified nOSP, the nOSP that was obtained through the process described above was dried in an oven at a temperature of 35 degrees Celsius for a period of 72 h. Figure 1 illustrates the process that is used to manufacture modified nano OSP.

Materials characterization
The PSD curves of the coated and unmodified OSP is presented in figure 2. It can be seen that the average particle size of the coated (shell powders) varied significantly and this is due to the layer of coating provided by the silane.The uniformity of the silane coating on the OSP was also evident from the controlled distribution of the OSP thus assuming the consistency of the properties of the coated OSP.The XRD patterns of the silane-modified oyster shell powder at various proportions are presented in figure 3. The crystallographic structure of the oyster shell powder was modified slightly due to the organo-silane molecules.The coating of the shell powder using silane did not produce any additional peaks but, however, modified the intensity of the calcite peaks of the OSP.The absence of any additional peaks indicates the non-crystalline structure of the coating material.The amorphous nature of the coating can also be visualised through the XRD patterns due to the absence of distinct peaks.It can also be seen that the broadening of peaks has occurred due to the coating of the OSP.Thus, it can be inferred that the interaction of the crystalline phases of the OSP has occurred with the SA due to the formation of nano-layer and multi-layer coatings on the surface of the OSP.It can also be concluded that the coating on the OSP was thick enough to cause crystalline interactions, as evident from the XRD.
The FTIR patterns of the OSP with the silane coating after being subjected to three cycles of water washing are presented in figure 4. The functional groups of the silane-coated OSP showed a strong characteristic peak of the aliphatic CH stretching alkyl bond around 2800 cm −1 , which is not visible in the uncoated OSP.The C-O stretching bond of the carboxylic acid was also visible in the silane-coated OSP pattern at around 1200 cm −1 , which is the characteristic functional group of the silane.Apart from silane peaks, the carbonate peaks of the OSP are also evident from the stretching C-O bonds around 1500 cm −1 , 1400 cm −1 , 1300 cm −1 , and 1000 cm −1 .The OH stretching vibrations of the OSP at around ~3300 cm −1 are clearly minimised in the coated OSP, which < 100 cps is a result of the decreased physically absorbed water molecules of the OSP, indicating an increase in the hydrophobicity of the coated OSP.It can also be seen that no other peaks were identified, indicating the absence of impurities and other trace elements in the OSP.The fingerprint region also showed the characteristic calcite peaks at 710-870 cm −1 , again confirming the non-appearance of new crystalline phases and no modification in the crystal structure.
A comparison of silane-treated and untreated OSP micrographs is presented in figure 5.It can be seen that the microstructure and surface morphology of the OSP exhibited a distinct and uniform surface texture due to the coating of the OSP by the silane functional molecules.The untreated OSP showed a micrograph that was compact, disordered, and brittle.The morphology of the treated samples underwent several structural alterations, like an increase in porosity.Because of the alterations introduced to the porous surface structure, the silane-coated OSP had some empty pores with irregular shapes.As a result of the silane functional molecules coating the OSP, the modified nOSP showed a distinct and homogeneous surface texture in terms of both microstructure and morphology.In addition, the silane-modified nOSP had reduced aggregation and better functional properties.Visualizing the improved smoothness and surface texture provides an insight into the extent to which the silane coating enhances the micro-level characteristics of the OSP for concrete applications.The silane modified nano OSP also showed better dispersion and less agglomeration and improved functional properties.The introduction of a silane molecule on the surface of the OSP also showed a distinctive silane coating (thin and uniform) with a greater degree of coverage.The visual understanding of the greater smoothness and surface texture gives an insight on the effectiveness of the silane coating in enhancing the micro level properties of the OSP for use in concrete applications.

Proportioning details of mix
The proportion of the developed concrete mixes is shown in table 3. The water to cement ratio was taken as 0.45 for all the mixes and the superplasticizer dosage was kept constant to determine the effect of nOSP on the workability of mixes with and without zeolite.The modifed nOSP concrete mixes was then prepared by substituting the cement by nano OSP at various dosages (0.5, 1, 1.5, 2%) by the weight of cement.In this study, the comparative effect is performed on the modified OSP developed with and without the presence of zeolite as an additional replacement by weight of cement.Natural zeolite was added 20% by weight of the cement in the modified nOSP replaced mixes (mOSZ-I, mOSZ-II, mOSZ-III and mOSZ-IV).In the first case, the cement and modified nOSP were mixed thoroughly in dry state in order to achieve homogeneity, whereas the mixing is done with cement, modified OSP and natural zeolite in the second case.The developed mixes after conducting the fresh state tests were then cast into respective moulds as per the testing's performed.These samples were left in the mould for 24 h after which they were demoulded and placed under water for curing up to 7, 28, 90 and 180 days respectively.After the respective days the specimens were then tested for compressive, chloride penetration, bulk chloride diffusion and chloride migration.

Experiments
Slump cone tests, as per IS 1199-1959, are used to ascertain whether concrete is workable.The visual representation of the specimens is provided in figure 6.A compressive testing machine is employed to calculate the strength property of 100 mm × 100 mm cubical concrete samples in compliance with the methods outlined in IS 516:2002.The RCPT test measures electric current through a cylindrical 100 mm × 50 mm specimen.For 6 h, the specimen's ends have a 60V DC potential difference.The cathode is 3% NaCl, and the anode is 0.3N NaOH.A potential difference ionizes the NaCl solution, causing chloride ions to migrate through the specimen.The electrical conductance of the cylindrical specimen is evaluated from the total charge passed through it using equation (1): where, Q Ch = Charge passed evaluated in Coulombs; I 0 = Current evaluated immediately after voltage is applied in amperes; I t = Current at t minutes after voltage is applied in amperes.To measure chloride penetration, this study followed NT Build 492, 1999.The idea behind this technique is that chloride ions are compelled to migrate into the specimens when an external electric potential is passed across them.The method outlined in ASTM C 1556 is followed when conducting the bulk diffusion test.The cylindrical specimens, which have been cured for 28 days and measure 100 mm in diameter and 75 mm in height, are subjected to the test.One side of the cylindrical specimens was left exposed to the chloride solution, which contained 3.5% NaCl, and the other sides were coated with epoxy resins.Applying a spray of freshly made 0.1M AgNO 3 to the surface of the cracked concrete yields the chloride penetration depth.A white precipitate of silver chloride forms on the surface of concrete when silver nitrate and chloride ions react.It is possible to ascertain the chloride penetration depth by measuring the depth to which the white precipitate forms.The diffusion coefficient can be determined from the level of penetration observations of chloride ions by employing the following equation (2):  while the WP model aggregates criteria by way of multiplication as given in equation (4), The Weighted Aggregated Sum Product Assessment methodology is a way to integrate preference values obtained by the application of the WS and WP models and is used to enhance existing decision-making mechanisms.WASPA combines the virtues of the WP and WS models by coordinating the following three steps -aggregation, normalisation, and ranking.

Workability measurement
The workability of the concrete mixes containing modified nOSP with and without zeolite is presented in figure 7. The results reported in tables 4(a) and (b) clearly showed higher slump value with nOSP additions and a reasonable decrease in the slump value as the zeolite is added into the mix.The least slump value is observed for the control concrete mix (CTM) whereas the modified nOSP mixes containing zeolite expressed lower slump comparably to the mixes without zeolite.
As expected, the increase in the slump value is a function of surface texture of the nOSP and hydrophobicity of the developed silane coated nOSP that produced a gliding effect on the cementitious matrix.It can also be  noted that no extra water was required to attain the required workability even with the addition of nano sized particles in the mix.Therefore, the quantity of water remained constant throughout the mixing and relatively less amount of water absorbed by the modified nOSP further influenced the strength increment.The availability of free water and the hydrophobic effect of the modified nOSP also indicated a consistent increase in the workability of the concrete mixes.

Mechanical strength
The values of the compressive strength of the concrete mixes measured at different ages is presented in figure 8.As from table 5(a) it can be seen, the 28 days compressive strength of concrete containing modified nOSP ranged between 39 MPa to 42 MPa in terms of no zeolite mixes whereas the zeolite included mixes ranged between 43 MPa to 46 MPa respectively.Also, the mix (mOSZ-III) with 20% and 1.5% modified nOSP showed compressive    zeolite admixture showed an appreciable increase in the compressive strength at 28 days and even at later ages.
The results show an increment in the 180 days compressive strength of 11.3%, 29.1% for 1% mOSP series without zeolite and 1.5% mOSP mixes with zeolite respectively, when compared to the control mix.According to the test results, the zeolite addition plays an important role in the compressive strength increment.Thus, it can be observed that the modified OSP effectively functioned as a filler enhancing the 28 days compressive strength whereas it provides lesser role in the later age strength.The utilization of zeolite on the other hand showed least influence on the early age strength whereas a significant positive effect is seen on the later age strength.This sequence is synergistically seen in the mixes containing modified nOSP and zeolite that showed better early age strength and later age compressive strength indicating the effectiveness of the proposed combinations.The essential factors that led to the improvement in the compressive strength can be summarized as follows: (1) Filler effect of nOSP (2) Hydrophobic effect of silane coating (3) Pozzolanic effect of zeolite Generally, the utilization of nano-sized fillers leads to an increment in the compressive strength up to 28 days and even after that.However, the effect of inert fillers becomes less significant as the age of concrete increases.This is confirmed through the fact that the incremental rate becomes almost negligible as the age progresses beyond 28 days.When the modified nOSP proportion in the concrete increases from 0.5 to 2% the increment in the compressive strength were observed to be 9.2%, 14%, 12.3%, 10.2% at 90 days and 5.8%, 11.3%, 8.7%, 7.4% at 180 days respectively in case of no zeolite substitution which is clearly evident from table 5(b).Likewise, the zeolite included modified nOSP mixes showed a strength increment of about 18.9%, 24.3%, 28.5%, 24.9% and 18.5%, 23.9%, 29.1%, 26.4% respectively at 90 and 180 days.And the compressive strength slightly decreases as the proportion of modified nOSP reaches 2% without zeolite.Thus, it can be obtained that 1% nOSP is the optimal concentration for obtaining maximum compressive strength in case of no zeolite concrete mixes whereas the optimum is considered as 1.5% nOSP for zeolite included concrete mixes.The strength development is pronounced in the mixes containing zeolite showing the influence of silicate and alumina molecules of the zeolite that formed gel like polymeric network formation.The inclusion of zeolite significantly enhanced the later ages strength of concrete at 90 and 180 days with an average increment rate of 24.1% and 24.5% respectively.As mentioned, the hydrophobic stabilization of the nOSP also played an important role in the strength increment in combination with zeolite functioning as a pore filling of the mesopores present in zeolite.

Chloride penetration
As the amount of mOSP in the concrete mixes increased, there was a significant reduction in the total charge that was transmitted through the modified OSP-substituted concrete mixes which is clearly evident from figure 9.The RCPT values of the concrete series that did not contain any zeolite decreased until 1% mOSP substitution (mOSCII), whereas the 1.5% mOSP mix (mOSZIII) had the lowest value.Beyond these substitutions with and without the presence of zeolite-substituted mixes, the RCPT values also experience a slight increase which can be evident from tables 6(a) and (b).The blocking effect that is caused by modified nOSP is responsible for the lower penetration that mOSZIII is able to hold in comparison to other concrete mixes.Because of their high electrical resistivity, aggregates do not contribute to the passage of ions through concrete.The hydration of ions through concrete occurs according to an electrolytic process that occurs through the cement paste.The ion migration process is significantly influenced by the conductivity of the ions as they move through the pore solution in the concrete.The process by which ions are able to pass through the concrete is influenced by the kind of ions that are dissolved in the pore solution.The electrolytic ions, which include Na+, K+, OH−, and Ca2+, are actively involved in the process of ions having the ability to penetrate.The presence of positively charged ions that originate from metal ions increases the rate at which ions are able to penetrate, which in turn improves the process of ionic migration.During RCPT, the presence of OH-ions in the pore solution causes a significant amount of ions to be transported.This is due to the fact that the OH ions serve as a supporting electrolyte for the chloride ions.The chloride ions, which are negatively charged, move in the direction of the pores that are present in the concrete until the pore contribution provides an adequate amount of resistance.The amount of OH-ions that are present in the pore solution is known to be determined by the type of mineral admixture that is added.Because of the pozzolanic action, the OH-ions are typically depleted.This occurs as a result of a decrease in the amount of OH-ions that are present in the pore solution.A reduction in the porosity of concrete occurs when the density of the concrete is increased.This results in an improvement in the resistivity against ionic migration, which in turn directly reduces the amount of charge that is able to pass through the concrete.A decrease in the chloride penetration of the concretes that have a higher percentage of modified nOSP replacement for fine aggregate is brought about by the incorporation of zeolite into the concrete.The incorporation of zeolite into the concrete material resulted in a reduction in the quantity of excessive free water content that was present in the concrete mixtures.It is possible that the separation of the materials that are present in the concrete could be reduced if there was a lower amount of free water present.In most cases, the increased interfacial area between the modified nOSP and the cement paste results in the formation of microvoids and pores, which in turn make it possible for chloride ions to move through the pores in the concrete.It is possible that the low water-binder ratio that was used in the concrete mixes was responsible for this decrease in porosity.This ratio reduced the  formation of voids, which in turn led to a decrease in the thickness of the concrete, which in turn led to an increase in its resistance to chloride penetration.In addition, the absence of free water reduces the formation of microchannels, which are capable of forming porous pathways through which chloride ions can pass.

Bulk diffusion
In figure 10, the chloride penetration depth of the modified nOSP-substituted concrete mixes is compared to the control concrete at various ages.In addition, the modified nOSP substitution performs an effective function as a pore-blocking agent, which helps to reduce the chloride penetration depth of the concrete mixes.The reduction in the number of pores in the concrete was brought about by the formation of highly water-stable reaction products, which were brought about by the addition of zeolite and modified nOSP to the concrete.Because of the zeolite's ability to block pores, the depth of chloride penetration in developed concrete was reduced as a result of the addition of zeolite.This was accomplished by rendering the pores difficult to access.As evident from tables 7(a) and (b), the beneficial role that modified nOSP plays in preventing the penetration of chloride ions is only effective up to a certain level of 1% and 1.5% with and without zeolite substitution respectively.As the substitution of modified nOSP increases beyond this certain percentage, there is a corresponding increase in the chloride penetration depth.This may be due to the fact that the substitution of modified nOSP causes bleeding beyond a certain percentage addition, which results in the formation of continuous water channels that form voids around the surface of the fine aggregates.As a result, it is possible to draw the conclusion that the substitution of modified nOSP for fine aggregate, even at higher percentage levels, results in a reduction in the chloride penetration depth of the concrete.This is because of the synergistic effect that they have with zeolite.Zeolite effectively reduces the chloride penetration depth of the mixes by occupying the pores through which chloride ions can diffuse, which provides a clear and concise explanation for the filler effect of zeolite.Aside from that, Because of the addition of zeolite, the cement paste undergoes the formation of additional reaction points, which ultimately results in the formation of hydration products that are extremely stable.Additionally, the modified nOSP and zeolite that were used to increase the density of the concrete contributed to the filling of the empty spaces that were present in the concrete.Therefore, it is possible to draw the conclusion that the porosity of the concrete is the primary factor that determines the structural properties of the concrete, specifically its strength and durability.The relative penetration depth decrement is an effect of the superfine zeolite that filled the pores in the concrete and strengthened the interfacial transition zones of the concrete, thereby minimizing the penetration depth caused by the chloride.In essence, the chloride penetration depth of the concrete is dependent on the efficiency of the filler.The contribution of modified nOSP is noteworthy, despite the fact that modified nOSP substitution has been shown to be ineffective in improving the penetration resistance of concrete at higher substitution levels that are considered to be normal.The angularity stability of modified nOSP reduce the expansion of the concrete, which in turn reduces the formation of cracks in the concrete.According to the findings of the particle size analysis, the interlocking behavior of zeolite with modified nOSP has resulted in an increase in penetration resistance.This improvement was achieved by increasing the particle packing capacity of zeolite, modified nOSP, and fine aggregates of varying sizes.

Chloride migration
Figure 11 illustrates the chloride migration coefficients of the modified nOSP concrete mixes with and without zeolite content.There is a possibility that the addition of zeolite, which contributes to the improved adhesion of the components of the concrete in both a physical and chemical sense, is responsible for the decrease in the migration coefficient of the developed concrete mixes when compared to the control concrete (CTM).The interlocking behaviour that was displayed by the angularly modified nOSP aggregates resulted in an improvement in the migration coefficient of the mOSP concrete.This improvement was achieved in conjunction with the high specific surface area.Additionally at higher replacement level, the increased fineness of the zeolite also resulted in an increase in the fineness of the binder phase, which ultimately led to an increase in the migration coefficient of the concrete as shown in table 8(a).In addition, the angular surface texture of the modified nOSP increases the cohesive property of the concrete by occupying the spaces within the fine aggregates, thereby adversely affecting the chloride migration into the concrete by transforming the concrete into a non-porous material.The loss of free water and the dehydration of the CH and CSH gels of the concrete, which results in an increase in porosity, may be the cause of the increased migration coefficients of the modified nOSP-replaced concrete specimens when their substitution level increased beyond 1% and 1.5% in case of no zeolite and with zeolite.The chloride ions are able to easily access these pores within the material.As a result of the addition of modified nOSP, which reduced the excessive amount of free water content in the concrete mixes, the migration coefficients of the modified nOSP-substituted concrete mixes were found to be lower than those of the control concrete at all ages.This results in a minimal amount of pores remaining in the hardened concrete because the reduced amount of free water reduces the amount of separation that occurs between the particles of the concrete.In light of this, it is possible to establish that the porosity of the concrete is directly proportional to the chloride migration coefficient of the concrete.As from table 8(b), it is clear that the concrete with a higher strength exhibited lower porosity values, which was accompanied by a corresponding decrease in the chloride migration coefficient, and vice versa.

SEM analysis
The SEM images in figure 12 clearly showed a better CSH gel formations indicating the non-interference with the hydration of cement paste.The zeolite additions further enhanced the formations of CASH and NASH gels.Thus, it shows a confirmation to the sequence of the compressive strength results.The slight decrement in the compressive strength of the concrete mixes with the addition of modified nOSP may be justified by the role played by the organo silane coating.The silane coating may sometimes result in the presence of unhydrated cement particles as evident from the SEM results.
The higher mechanical strength is due to the filling effect of nOSP and this filling effect can be visualized from the less amount of pores present in the SEM images.The quantification of voids/pores using image analysis technique clearly showed that the voids were plugged effectively by the nOSP.In contrast, very less amount of unreacted particles are found in the concrete mix with zeolite addition.Another possible reason for the reduction in compressive strength at later ages may be due to the formation of weak gels around the nOSP which was strengthened by the formation of Al rich gel due to the zeolite additions.This can be confirmed by the EDS analysis conducted on the concrete mixes with zeolite that showed lesser Ca/Si ratio, and greater Ca/Al ratio.

Multi-criteria evaluation
Tables 9(a) and (b) represents the aggregation of preference values from the performance evaluation of casted specimens on the four criteria, namely 28-day Compressive Strength, RCPT, RCMT, and Bulk Diffusion, obtains an aggregated preference matrix, conveying how generally desirable or undesirable each alternative was in each criterion.preference value is achieved through normalisation to ensure uniformity and objectivity in the evaluation of criteria differences and alternatives.Lastly, the options are ranked based on the performance difference by the normalised preference score.The lambda (λ) for the WASPA technique that has been done is set at the value of 0.5.This implies that the two aggregation approaches of additive and multiplicative approaches on the WASPA framework need to have equal relevance or balance as part of an integration.

Conclusions
The primary outcome of this study is a method for improving the durability of the concrete by modifying it in such a way that it becomes more hydrophobic and absorbs less water without sacrificing its mechanical strength.When compared to other types of modifications, this method of hydrophobic modification of concrete matrices using nanosized fillers offers an extra layer of protection against water diffusion through micropores.The study concludes that incorporating silane-modified nano OSP as a filler in cement concrete, particularly when combined with zeolite as a mineral admixture, yields promising results.The workability of the concrete improves with increasing percentages of modified nano-OSP, with zeolite further enhancing stability.The combination of zeolite and modified nano OSP leads to significant improvements in mechanical strength early on, as well as further improvements in hydration later on.Adding modified nano-OSP and zeolite also makes it harder for chloride to get through because it improves the rate at which the particles dissolve in water and makes the pores less connected, as shown by microstructural analysis.This study underscores the potential of utilizing modified nano-OSP and zeolite to enhance various properties of cement concrete, paving the way for more durable and sustainable construction materials.Further research should prioritize the examination of the long-term durability of hydrophically modified concrete.Future studies on creep, shrinkage, and freeze-thaw tests are reliable indicators of concrete durability, and additional investigation into the effects of implementing different treatment methods on the shell powders, which could be beneficial in creating hydrophobic concrete mixtures with enhanced properties, seems to be promising.Moreover, conducting research on the integration of sustainably treated hydrophobic shell powders into binary and ternary blended concrete mixes can yield significant benefits.

Figure 5 .
Figure 5. SEM images of unmodified and modified OSP.

Figure 7 .
Figure 7. Workability measurement of modified OSP-concrete at various time intervals.

Figure 8 .
Figure 8. Compressive strength behaviour of modified OSP concrete mixes at various ages.

Figure 9 .
Figure 9. RCPT test results of modified OSP concrete mixes at various ages.

Figure 10 .
Figure 10.Chloride penetration depth measurement of modified OSP concrete mixes at various ages.

Figure 11 .
Figure 11.Chloride migration coefficient of modified OSP concrete mixes at various ages.

Figure 12 .
Figure 12.(a) SEM image of control mix.(b) SEM image of modified nOSP without zeolite substitution.(c) SEM image of modified nOSP with zeolite substitution.

Table 1 .
Chemical composition of raw materials.

Table 3 .
Mix details of developed samples.

Table 4
. (a) Slump measurements.(b) Measured slump variation.and 180 days respectively.It shows that the use of modified snOSP has the potential to greatly improve the compressive strength of concrete without the need of any special admixtures/curing methods.Although an increment in the compressive strength was observed, the strength values could not demonstrate an appreciable increase at later ages.In contrast, the 28 days average compressive strength of the concrete is 40.9MPa for no zeolite mixes and 44.8 MPa for zeolite contained mixes which is 15.8% and 31.2%respectively, greater than the reference mix indicating a marginal improvement.This suggests that the later age strength of concrete containing nOSP has no significant position influence on strength.The series of concrete mixes containing

Table 7 .
(a) Chloride penetration depth measurements.(b) Percentage variation of chloride penetration depth.

Table 9
(c)shows the results of Weighted Aggregate Sum Product Assessment.The aggregated

Table 9 .
(a) Preference score from weighted sum model.(b) Preference score from weighted product model.(c) Preference score from WASPAS.