Influence of silane treated nano eggshell powder on mechanical and durability properties of concrete

In order to test concrete’s sustainability, this study substitutes nano eggshell powder (nESP) for cement in a silane-treated environment. The results showed that the silane-treated concrete mixtures outperformed the untreated ones in terms of performance. nESP was replaced by 5 to 20% with in cement of 5% along with constant replacement of 30% fly ash by weight of cement. It was found that partial cement substitution with nESP up to 10% produced a sample with greater strength than the control sample. The filling and reinforcing properties of the nESP and the pozzolanic effect of flyash after silane treatment produced favorable results when mechanical strength was evaluated. The increased electrical resistance with age may be caused by the increased hydration products and excess CSH gel formation induced by the pozzolanic action of the fly ash in concrete.


INTRODUCTION
Concrete and cement-based building materials are currently the most popular and adaptable building materials worldwide [24].However in challenging environments, water and toxic ions always find their way into concrete structures, causing corrosion and ultimately damaging the reinforced concrete structure and shortening its useful life [25].Reducing the use of energy, natural resources, and greenhouse gas emissions has become essential because it is anticipated that the amount of cement and concrete production will increase overtime [11].Fly ash has been thoroughly investigated as a cementfree option in the building industry for many years to produce structural concrete.The heating process and the early-age cracking potential of concrete have been discovered to make fly ash more workable and reduce the rate of hydration [1].An efficient way to increase compressive strength at a young age is to use enhanced fine fly ash in cement-based products.The cement-fly ash system features dilution, improved pozzolanic reaction, nucleation, and physical filling effects due to the inclusion of fine fly ash [32].Saha 2018 investigated how fly ash affected the quality of concrete's durability.In conclusion, concrete containing fly ash showed lower compression strength at young ages than conventional concrete, but the strength gradually increased as the curing of the concrete advanced.To increase the mechanical strength development of standard concrete, fly ash is utilized as a water reducer [23].The performance of concrete is enhanced in terms of density and strength by adding SiO2 and Al2O3 to the fly ash [8] .Continuous landfill expansion and significant environmental problems 1282 (2023) 012003 IOP Publishing doi:10.1088/1757-899X/1282/1/012003 2 are brought on by the disposal of waste products like eggshells.Due to its availability and chemical makeup, this solid waste has significant environmental impact when not adequately treated.
Researchers have sought to use waste materials as a replacement for cement to make the building sector more sustainable and at the same time reduce the waste that is produced [29].There are now two major groups of popular techniques for preventing moisture transport.The first is enhancing the concrete's compactness by adjusting the water-cement ratio, adding water reduction agents, and mixing in mineral admixtures [36].Khan et al. 2014 discovered that denser and less permeable concrete could be developed with the inclusion of fine particle sized mineral admixtures with greater surface area.Also the concrete fluidity can be reduced significantly due to the ultra-fine particles and helps to create a new way for maximum workability [6].Implementing polycarboxylate based admixtures into the concrete can enhance workability and the ability to counteract the side effects of nano-particles [7].The second strategy involves usage of coatings such as osmotic, surface-sealing and surface-enhanced to prevent water from coming into contact with concrete [20].Their primary method of protecting concrete is through the physical or chemical reaction of the coating, which creates a shield-like layer over the surface that can prevent dangerous chemicals from penetrating inside, increase durability and service life.Cement-based material's anti-permeability and anti-icing capabilities have been improved by super hydrophobic surfaces with more than 150° water contact angles and within 100 roll-off angles [5] [31].Materials from water infiltration for the anti-permeability performance were protected by excellent water repellency, allowing concrete to be more durable [17].Super hydrophobic surfaces can be applied to concrete in two ways: externally and internally.A hydrophobic coating was used to treat the surface [13].By treating Nano materials of TiO2 and SiO2 with perfluorodecyltriethoxysilane, created super hydrophobic coatings that they sprayed on the cement surface [11].To lessen the amount of ice depositing on the pavement, [2] developed a super hydrophobic coating using Nano-materials.In order to duplicate and transfer the micro-textured structure to the concrete surface, [11] [15] employed polydimethylsiloxaneas a template and created a uniform surface coating through the mechanism of spraying siloxane based compounds.However, the long evity of super Hydrophobic surfaces created using this technology frequently run into issues because the water proofing capacity of the coating degrades with time and peeling [16].Super hydrophobic particles were added to cement pastes to address internal concerns.[3] incorporated super hydrophobic Nano-particles to cement pastes to boost the hydrophilic nature of calcium silicate hydrate (C-S-H) gels and avoid excessive surface energy there by reducing the permeability.Scott et al.Mixed super hydrophobic admixtures with tailored cementitious composites increased the water-repellence and extend the service life of concrete [19].In [28] modified concrete using fluoro alkysilane during the hydration process and covered it with metal mesh to produce super-durable super hydrophobic concrete.The application of silanes, according to evidence from various studies, dramatically reduces water up take, which minimizes the entrance of chlorides and consequently lowers the risk of corrosion to the reinforcement [25].However, factors like surface flaws, cyclic wetting and drying, applicator expertise, surface preparation, application rates, and the immediate environment can all impact on how well they operate.Numerous techniques have been used to increase the permeability of concrete, including its compactness and is made possible by the employment of water-repellent admixtures, silane impregnation, isolation and super hydrophobic coatings [18][4].However, each of these techniques has drawbacks of its own.For instance, increasing the concrete compactness would not alter its hydrophilic properties, water continues to be absorbed by concrete.Integral hydrophobic additive significantly reduces the concrete strength [32].The surface barrier coating process is susceptible to failure due to cracking and peeling resulting in poor weather resilience [10].The surface silane impregnation technology is too expensive to be applied extensively in the building materials industry.Hydrophobic agents and potential fillers are the critical raw ingredients for super hydrophobic coatings [35].The super hydrophobic covering makes it harder for water to be absorbed.Therefore, the super hydrophobic coating technique is the best for lowering concrete permeability.The main barriers to the practical deployment of super hydrophobic coatings are their high cost, poor durability, and challenging manufacturing processes [14].Therefore, it is crucial to create super hydrophobic coatings for concrete surfaces that are in expensive, simple to prepare, and have the suitable durability.The current study aims to evaluate the effects of silane additive on concrete incorporating waste Nano egg shell particles as an integral addition and surface treatment of aggregate.The primary goal of the current study is to investigate the effects of eggshell powders at the Nano scale on the strength and durability behaviour of concrete under silane-treated and untreated circumstances.

MATERIALS
OPC53 grade is chosen as a primary binder and table1 represents their oxide composition.It was determined that the cement's physical characteristics met the standards outlined in IS: 12269-1987 for 53grade OPC.At a consistent weight ratio of 30%, Class F fly ash from Astraa Chemicals in Tamil Nadu was used as a substitute.The fine aggregate is naturally derived river sand and 10mm crushed stone as coarse aggregate is employed in this study.The physical properties and particle size distribution curves are listed in table 2 and figure 1 respectively.The data presented for cement, fly ash, river sand and aggregate are provided from their collected sources.Raw eggshells (ES) were gathered from nearby bakeries and eateries.They were cleaned with tap water to eliminate the organic debris and other surface dusts.After that, they were dried in an electric oven at 110 ± 50C for a day.The dried eggshells were heated to 800 0 C in an electric furnace it is then immediately crushed and milled to minimize their particle size.In order to lower the carbon content, the 150mm sieved shell powders are allowed to expose in the electric furnace at 800 0 C for 6 hours.The final Product nESP, contained particles with a diameter of 524nm and the XRD pattern is given in figure 2. After being sieved the Nano eggshell powders were stored in sealed containers and used.Sika superplasticizer (SP) was applied at constant ratio of 1% to support the concrete fluidity.Three different series of concrete mixtures and a control concrete mix with no replacement were made by making four mixes for each series with cement substitutions of 5%, 10%, 15%, and 20% nESP.Each mix undergoes three trial mixes upon which the average will be considered for obtaining the result and hence 12 mixes are casted for each series in addition to three trial mixes casted for reference mix.The fly ash replacement ratio is fixed as 30% for all the concrete mixes except the reference mix.
The water to binder ratio was 0.37, and the total binder content was 500 kg/m3.The first stage involved combining the solid components with coarse and fine particles for three minutes.After the mixed water was absorbed, the binder components such as cement, nESP were added deliberately and the mixture was mixed for five minutes.The second half of the leftover water and SP were added to the concrete mixture after it had been mixed for 5 minutes.Two different series are created to test the effects of silane surface treatment and integral silane addition on the characteristics of concrete.One contained reactive aggregates that had been silane-treated, while the other had silane agents in varying amounts.The silane-treated reactive aggregates and silane agent addition range from 0.5 to 2% by weight of cement represents each series as shown in Table 3.The concrete mixtures were pre-mixed with water and the liquid ingredient before adding the silane.

METHODOLOGY
According to IS: 7320:1974, the fresh state behaviour of created concrete mixtures was assessed using slump flow.According to IS:456:2000, compressive and flexural strength tests were employed on cubic and prismatic specimens of 100 mm and 160x40x40mm3 respectively.On cylindrical specimens measuring 100mm x 200mm, the split tensile strength test was conducted following IS: 5816-1959.
After that, the100 mm cube samples underwent a UPV test following IS: 13311 Part-1:1992.According to ASTM C 642, absorption research was carried out to determine the concretes' relative porosity permeable void space.The ability of concrete to withstand the flow of an electric current while being impacted by chloride ions is known as electrical resistivity, and measurements of electrical resistivity were made using the Wenner probe method over cylindrical   .The filling effect that the nESP demonstrated up to a certain threshold level, which sealed the interstitial holes in the concrete matrix thus functioning as an active bio-filter, may be used to explain the gain in compressive strength.However once nESP exceeded a 10% cement replacement rate, compressive strength values declined.Beyond the threshold addition level, a drop in compressive strength maybe caused by a rise in nESP, which took up spaces that could have been used to make concrete, weakening the crystal development of concrete.The pozzolanic character of fly ash makes it feasible for the calcium hydroxide (C-H) to react with the silica produced during the hydration of cement, resulting in the creation of calcium silicates responsible for the strength of the cement mix.By filling up the Voids already present, nESP served as filler, resulting in a more compact concrete mix and the creation of higher compressive strength.For nESP10 under the untreated, silane treated, and silane supplemented conditions, the rise in percentage was roughly 9%, 17%, and 13%, respectively at 28 days.When nESP is used with high cement content, calcium hydroxide and silica in the mixture are reduced due to the lower cement content.Because of this, there is not enough silica to react with C-H to create C-S-H gel, which leads to a shortage of compressive strength.Along with the pozzolanic flyash, then nESP also served as a filler by filling in the gaps in the internal structure of the concrete, which increased the materials density and compressive strength.The high CaCO3 concentration of eggshells, aids in the hydration of cement paste, nESP inclusion improves concrete compressive strength at all ages.CaCO3 combines with C3A from the cement during hydration creating a ucleation site or an enancedhydration process.Due to the fly ash content, the concrete hydrates more completely and forms more CSH gel, improving the internal micro structure and reducing voids and porosity.Beyond a 10% replacement rate, nESP raises the water demand, which raises the water-cement ratio and lowers the strength.The flexural results thus show that the nESP effectively improved the flexural strength of the concrete mixes due to their surface properties that increased the cohesion between the cement matrix and the filler surface there by improving the flexural strength of concrete.Generally, the flexural strength of concrete increases with the increase of nESP content up to a certain point.The optimal flexural strength attained for nESP10 is about 27.02% for silane treated concrete mixes whereas the silane addition showed 23.67% strength increment.The filling effect of nano eggshells can increase the flexural strength of concrete, so the flexural strength is higher than the control mix.The activation of Nano eggshell powder in combination with fly ash and their finer nature improved flexural performance of the concrete when compared to the reference mix.

Figure 5 Mechanical behaviour of developed concrete mixes
The improved split tensile strength of concrete up to 10% nESP is mainly due to the filling capacity of the Nano sized ESP.The fine nature of ESP and fly ash enhanced the interlocking mechanism between the cement and aggregates is more evident in the silane treated concrete mixes.The reduced splitting tensile strength beyond 10%may be due to the loss in the moisture of the concrete thereby increasing the pores in the concrete.The silane treated mixes showed enhanced tensile strength of 25.22MPa followed by silane added mixes proving that silanes super hydrophobic nature is more effective when treated rather than their integral addition.
As the substitution ratio of the nESP grew, ultrasonic velocities decreased which can be evident from figure 6.This decrease in UPV could be brought by the concrete specimens having pores.The increased capacity for absorption and the existence of micro pores in the egg shell powders also decreased the ultrasonic velocities.Due to the inside structure's numerous voids and pores, the quality of the concrete drastically decreased at10% of nESP.Pulse velocity was utilized to gauge the compressive strength of concrete inner cracks and voids that undermined the material's structural integrity decreased the pulse velocity.The increased UPV value of nESP-replaced concrete mixes compared to conventional concrete mix served as evidence of the beneficial effects of Nano eggshell powder.The porosity of the concrete mixes was reduced due to then ESP's enhanced specific surface and faster rate of hydration due to fly ash, which impacted the ultrasonic pulse velocity at all ages.The denser internal structure of the concrete caused due to combined action of fly ash and nESP enhanced the pulse velocity, which in turn represents the filling capacity of the nESP.The concrete composites' stiffness was increased by the nESP's high particle packing density, which led to the greatest improvement.The interaction between the surface of the bio-filler and the cement matrix, in particular, has a positive impact on flexural strength as a result of replacing shell powder.The UPV value evaluated at 28 days for the nESP10 mix at the untreated, silane treated, and silane supplemented conditions, respectively, improved by 6%, 11.7 %, and 9.6 % when compared to the reference concrete illustrating the good synergistic effect of cement and nano eggshell powder.The decrease in ultrasonic pulse velocity is due to the enhanced pore structure and micro cracking of the concrete with nESP and fly ash replacement.The residual ultrasonic pulse velocity significantly differed from the control mix's velocity due to nESP's interlocking behaviour.All of the nESP replaced concrete mixes showed improved ultra sound velocity than the control mix at all ages and were rated as having "good and medium" quality by IS 13311-1.The improvement in mechanical strength of the concrete mixes was further substantiated by the higher Ultra-sonic pulse velocities.The production of CSH mainly due to pozzolanic activity of fly ash, which can self-heal and close opened pores, may have increased, which

5.
. Ultrasound Pulse Velocity is another explanation for the increase in ultrasonic pulse velocity.The water absorption values of the nESP replaced at 7, 28, 90, and 180 days are shown in figure 7. The use of nano egg shell powder in combination with the fly ash reduced the water absorption up to 10% nESP due to their filling ability and hydrophobic inclination.However, it was shown that the water resistance qualities were reduced when compared to the reference mix after a nESP substitution of more than 10%.Increased Heterogeneity and voids is due nESP's inadequate dispersion in the concrete matrix.The 10% nESP that had been silane treated out performed all roughly by 32% among all specimens at 28days.This might be because of the tightly packed concrete structure that the nESP exhibits.Because there were less pores in the concrete, the water absorption values decreased.Additionally, the nESP's filling properties and pozzolanic nature of fly ash significantly lowered the water absorption values, which closed pores and permeable voids.The pores in the concrete's surface

Water absorption
were refined by the nESP's finer texture, which closed any porous voids.
The fly ash as binder replacement produced more secondary C-S-H gel while serving as excellent filler for the concrete mixture and adding additional calcium.As a result, the gel can fill up any gaps in the concrete, reducing water absorption rate.Compressive and flexural strengths demonstrate the importance of C-S-H gel as a main strength-producing reaction product of cement hydration.It also acts as a porosity reducer, producing dense concrete.Additionally, including nano-ESP in the concrete significantly contributed to the reduction of porosity, which raised the concrete's compressive strength.
Porosity studies from figure 8 shows that the specimen's porosity values reduced after the nESP substitution.However, for the specimens treated with nESP, especially at more significant proportions, the increases in the porosity values were minor.The porosity reduction of about 33.4%, 36.5%,36.9%,40.6% is attained for nESP10 mix at 7days, 28 days, 90 days and 180 days respectively.The leading causes of the reduction in porosity are the filling effect brought on by the replacement of cement with nESP and the decrease in the micro cavities is due to high specific surface area of the nESP.The nESP and fly ash reduces the number of accessible pores in the concrete by successfully bonding with the cement paste due to its spherical surface features.The pozzolanic activity of fly ash mainly encourages the development of C-S-H gel, which fills the pores in the concrete and reduces their volume.Nano particles with small particle sizes help to improve the microstructure of concrete by suffusing the pores in the cement paste and thereby improving the packing level.Nanoparticles further boost the strength of cement-based products by accelerating the hydration of cement, which leads to the creation of calcium-silica-hydrate a

Porosity
nd helps make concrete even denser.As the replacement level of the cement with nESP grew up to 10%, the electrical resistivity of the concrete mixtures increased as well.The improvement in electrical resistance at 7 days, 28 days, 90 days, 180 days for nESP10 mix is 27.8%, 32.3%, 37.1% and 45.1% respectively.Beyond this the resistivity levels considerably decreased but remained within the allowable range.The silane treatment produced concrete of typical quality, reducing the likelihood of corrosion even more.Due to the synergistic action of nESP and fly ash, the concrete mixes increased density and decreased porosity were the leading causes of this variation in electrical resistivity.The enhanced hydration products and additional CSH gel formation caused by the pozzolanic fly ash may be responsible for the increased electrical resistance with age.The decreasing porosity, tortuosity, and chemistry of the pore solution and pore network may have contributed to this inc

Electrical Resistivity
reased electrical resistance with ageing.
As observed from the results, the optimum replacement of 10% nESP exhibits better properties than other substitution levels.The percentage improvement over the tests conducted is presented in figure 10.It can be clearly observed that the improved behavior at 28 days proves that the developed concrete mix with 10% nESP holds their implementation for concrete works.The early age

Effect of optimum ESP substitution
improvement is also found to be satisfiable.1.The strength aspects of the developed concrete mixes yielded better results when the developed mixes were silane treated than the silane added mixes.The silane treated mixes exhibited an optimum improvement of about 17.4%, 27%, and 25.2% for compressive, flexural and split tensile strength at 28 days respectively.
2. By filling up the existing spaces, the nESP effectively served as filler up to a 10% substitution, which made the internal structure of the concrete more packed and promoted the formation of higher strength.Ultra sonic velocities also decreased due to the eggshell powders more tremendous potential for absorption and the existence of micro pores.The 28

Figure 1 Figure 2
Figure 1 Particle size distribution curves of raw materials test specimens employed for testing are presented in figure3.

Figure 3 Test specimens used in research 4 . RESULTS AND DISCUSSIONS 4 . 1
Figure 3 Test specimens used in research

Figure 4 Figure 5
Figure 4 Slump values of developed concrete mixes

Figure 6
Figure 6 UPV results showing the quality of developed concrete mixes

Figure 7 Figure 8 10 Figure 9
Figure 7 Water absorption of developed concrete mixes

Figure 9 Figure 10
Figure 9 Electrical resistivity of developed concrete mixes

Table 3 Mix details of developed concrete specimens
7.days UPV values were found to be maximum of about 11.7% for 10% nESP substitution as cement replacement in 1282 (2023) 012003 The filling capabilities of the nESP sealed pore sand permeable spaces, significantly lowering the water absorption values.The fly ash content created more secondary C-S-H gel in addition to being a excellent filler for the concrete mixture and adding additional calcium, which slows down the rate of water absorption.The optimum reduction in water absorption and porosity of about 32.2% and 36.5% is attained for 10% nESP at 28 days respectively.The enhanced hydration products and excess CSH gel formation brought on by the pozzolanic action may increase in electrical resistance with ageing.The improved resistance was provided by 10% nESP at 7 days, 28 days, 90 days, 180 days of about 27.8%, 32.3%, 37.1% and 45.1% respectively.