Development of red mud based sintered artificial aggregates with various industrial wastes

Red mud (RM) has drawn a lot of attention in the search for potential uses in the production of sintered artificial aggregate from industrial waste products. The main objective of the study is to produce an RM-based sintered artificial aggregate (SAA), with several blends (binary, ternary, and quaternary) using various industrial wastes. This study includes assessing the mechanical and physical properties of SAA as well as the sintering parameters in order to determine the appropriate material mix ratio. To achieve these objectives, a comprehensive experimental approach was adopted. A total of 35 different mixtures were formulated by incorporating various industrial wastes as binders and sintering additives. The green pellets were preheated at 105 °C for 24 h, and consecutively sintered at different temperatures, namely 700 °C, 900 °C, 1100 °C, and 1150 °C with a duration of 30 min. A compressive strength test was performed in order to find the mechanical property of SAA similarly water absorption and bulk density tests were conducted to find the physical properties of SAA. To characterize the SAA, scanning electron microscope analysis (SEM), X-ray diffraction (XRD) and energy dispersive x-ray analysis were conducted, and also data analysis was performed using Artificial Neural Network (ANN) tools, yielding accurate predictions. Successfully best compressive strength low water absorption SAA was produced. The best material weight mix ratio for the production of SAA was identified as (A18) RM: Fly Ash: Waste Glass Powder; 78:10:12. Out of all blends the ternary blend (A18) SAA exhibited impressive properties after 30 min of sintering at 1150 °C: high compressive strength of 22.92 MPa, water absorption of 4.26%, and bulk density of 1296.12 kg m−13. This was made possible by the high amount of Al2O3, SiO2, in the combination of fly ash, and waste glass powder with RM. SEM and XRD analysis also confirmed that the (A18) SAA achieved the best compressive strength, and low water absorption due to turning the surface and core area into a solid, reduced internal pores and formed quartz, and hematite phases. The findings of this study serve as a foundation for future work and pave the way for the development of sustainable construction materials.


Introduction
The continuous growth of the global population has created a constant demand for infrastructure and minerals.However, the construction of infrastructure and the manufacturing process of minerals has led to significant depletion of natural resources.Additionally, these processes generate substantial amounts of industrial waste, posing a major environmental challenge.The key issue lies in finding ways to minimize waste generated by manufacturing and quarrying operations, and instead, transform this waste into functional products.The construction industry, experiencing rapid expansion, is facing a shortage of essential ingredients, particularly traditional aggregate, which is crucial for concrete production, per year, nearly 48.3 billion tons of traditional aggregate being consumed globally (Bekkeri et al 2023, Vembu andAmmasi 2024).As a result, there is a pressing need to promote the use of sustainable materials and reduce the reliance on non-renewable resources on a global scale.This shift towards sustainable practices is essential to address the resource scarcity and environmental impact associated with conventional construction practices (Tian et al 2021).By encouraging the transformation of waste materials into functional products, the construction industry can contribute to a more circular economy.Instead of discarding waste, these materials can be repurposed and utilized in various construction applications, reducing the demand for virgin resources.This approach not only mitigates the negative environmental consequences of resource depletion but also offers economic benefits by reducing waste disposal costs and creating new market opportunities for recycled materials.Implementing sustainable practices in the construction industry involves embracing innovative techniques and technologies that promote resource efficiency, waste reduction, and the use of renewable or recycled materials.This can include incorporating alternative aggregates derived from industrial by-products, such as red mud (RM), fly ash (FA), ground granulated blast furnace slag (GGBS), waste glass powder (WGP), sewage sludge (SWS) and bentonite (BTN) etc.Since these are the discarded materials and cheaply available.Additionally, adopting construction methods that minimize material waste and promote efficient resource utilization, such as prefabrication and modular construction, can significantly reduce the environmental footprint of industrial waste.
RM is a byproduct generated during the extraction of alumina using the Bayer process, which is responsible for 90 per cent of global alumina production.Compared to other production methods, the Bayer process results in higher alkaline content in the RM.In India alone, approximately 9 million tons of RM are produced annually (Wang et al 2018, Ghosh andRansinchung 2022).Over the years, the commercialization of alumina production resulted in the generation of an astounding 120 million tons of RM annually (Sun et al 2021).It takes around 1 to 2 tons of RM to produce 1 ton of alumina (Pei et al 2021).The storage and disposal of RM present significant challenges.The bunds and dams in the storage area need extensive maintenance to contain the discharged bauxite residual slurry, and the seepage of alkaline solution poses a threat to groundwater (Jones et al 2012).The composition of RM in India varies depending on the type of ore used, typically containing 14%-29% Al 2 O 3 , 18%-54.8%Fe 2 O 3 , 6.2%-56% SiO 2 , 3.5%-50% TiO 2 , 0.8%-11.8%CaO, and 3.3%-9.0%(Samal et al 2013).Additionally, thermal power plants in India alone produce nearly 226 million tons of FA per year (Ghosh and Ransinchung 2022).On a global scale, an astonishing 1.6 to 2.0 billion tons of municipal solid waste (MSW) are produced annually (Tian et al 2021, Shao et al 2022, Sharma et al 2023).WGP is eco-friendly to use in construction materials (Manikandan and Vasugi 2021).
Recently, a large number of researchers have experimented extensively to create sintered artificial aggregate (SAA) as an alternative building material.SAA or ceramsite is an artificial aggregate, by turning leftover materials into an aggregate through the sintering process.Heavyweight or lightweight SAA was produced and used in conventional, light-weight and geopolymer concrete, depending on the application, except major structural element construction (Tuan et al 2013, Majhi et al 2021, Ozkan and Kabay 2022, Kumar Behera et al 2023, Thukkaram and Ammasi 2024).Similarly, RM-based SAA was produced and utilized in concrete (De Oliveira and Rossi 2012).since the SAA harmful chemical concentrations were far lower than the Chinese national threshold, it is likely that RM-based ceramsite cannot contribute to secondary pollution of the environment (Mi et al 2021, Song et al 2021).Hence RM is being used to produce high porosity bricks, ceramics and grouting materials (Kim et al 2019, Zhang et al 2020, Mi et al 2021, Sun et al 2021).For the production of SAA, the following materials were used in the literature with different blends, RM, FA, fuel ash, barium sulphate, sawdust, BTN, reservoir sediment, and WGP (Chiou and Chen 2013, Molineux et al 2016, Mi et al 2021, Pei et al 2021, Raghubanshi et al 2021).Heavyweight SAA was produced with a combination of barium sulfate, activated charcoal powder and RM at 1300 °C and achieved low water absorption of 0.9%, density of 4.1 g cm −3 (Raghubanshi et al 2021).With a gold tailing end, a 75% high porosity of RM brick was produced (Kim et al 2019).Lightweight aggregate (LWA) was developed with compressive strength of 10.77 MPa, water absorption of 1.46% and density 728.76 kg m −3 at 1080 °C by using RM and acid leaching tailings (Song et al 2021).RM which is high in calcium is a better raw material for making RM-based LWA than RM which is rich in iron (Sun et al 2021).Fineness of WGP effectively influenced the SAA density (Chiou and Chen 2013) Sodium ions concentration has been drastically decreased in RM-based ceramsite when compared to RM (Pei et al 2021).Low silicon RM is sufficient to produce light weight aggregate at 1200 °C, with addition of sintering additives (Liu, et al 2023).Low silicon RM ceramsite was produced with a combination of silica fume, BTN, and glass powder and the optimum ratio was obtained as 19.79:9.28:12wt% also stated water absorption and density effectively influenced by silica fume.On the other hand, glass powder negatively affected (Liu et al 2023).By using 50% RM replacement with clay, ceramic brick was produced at 950 °C and achieved greater strength than pure clay brick (Pérez-Villarejo et al 2012).In Rm based sintered products, hazardous elemental content was very low when sintered above 950 °C (Park andPark 2017, Scribot et al 2018).(Molineux et al 2016) reported, 44% RM with pulverized fuel ash (PFA) sintered LWA exhibits positive characteristic values and the pH 10.8 value has been decreased after sintering at 1200 °C to pH 8. Titanium oxide (TiO 2 ) , borax, and sewage sludge (SWS) were used as additives and binders respectively (Vasugi and Ramamurthy 2014, González-Corrochano et  The main objective of the study is to produce an RM-based sintered artificial aggregate (SAA), with several blends (binary, ternary, and quaternary) using various industrial waste materials such as FA, SWS, GGBS, BTN, WGP, and titanium oxide (TiO 2 ).This study includes assessing the mechanical, physical properties and characterizations of SAA as well as the sintering parameters in order to determine the appropriate material mix ratio.

Source materials
In this study, sustainable sintered artificial aggregates were developed using various industrial waste materials, including red mud (RM), fly ash (FA), sewage sludge (SWS), ground granulated blast furnace slag (GGBS), titanium oxide (TiO 2 ), bentonite (BTN), and waste glass powder (WGP).The main raw material, RM, was sourced from NALCO in Daman Jodi, India, while FA was collected from Ennore Thermal Power Station in Chennai, India.SWS was obtained from the wastewater treatment plant at Vellore Institute of Technology, Chennai, India, and GGBS from Jindal Southwest Steel Ltd. in Chennai, India.TiO 2 , BTN, and WGP were procured from Astrra Chemicals, also located in Chennai, India.In this study, FA, SWS, GGBS, and BTN were considered binders, while TiO 2 and WGP were examined as sintering additives.
The chemical composition of these materials, as listed in table 1, revealed that Al 2 O 3 and SiO 2 were crucial ingredients in the manufacturing of SAA.The chemical composition of these materials, as listed in table 1, out of all Al 2 O 3 , SiO 2 and Fe 2 O 3 were very crucial ingredients in the manufacturing of SAA.Based on the results from table 1, Al 2 O 3 -rich materials are FA, GGBS, RM, and BTN, whereas SiO 2 -rich materials are WGP, FA, BTN, GGBS, SWS, and Fe 2 O 3 -rich materials are RM, BTN.The loss on ignition of the raw materials was examined at 900 °C for a 2-hour sintering period.As per table 1, lower to higher order of loss on ignition results were as follows: GGBS, WGP, FA, RM, BTN, SWS.These findings provide valuable insights into the chemical composition and properties of the raw materials used in the production of sustainable SAA.

Experimental approach
Figure 1 depicts the step-by-step manufacturing and testing process for SAA.Initially, RM, SWS, and FA were subjected to a drying process at room temperature for three days, followed by 48 h of drying in an oven at 105 °C to reduce their high moisture content.During this stage, these materials were in solid form with sizes ranging from 20 to 50 mm, except for FA, which was pulverized to a 150-micron size.GGBS, TiO 2 , BTN, and WGP were received from a source in a size below 75 microns.As shown in figure 1, a disc pelletizer with a diameter of 455 mm and a depth of 90 mm was utilized to create pellets.The disc pelletizer's design system allowed for control of the disc pan speed and inclination.To prevent the diffusion of dust into the air, 0.05% water was added to the dry powder, ensuring homogeneous blending before being placed in the pelletizer disc.
During the pelletization process, water was uniformly sprinkled onto the powder to facilitate agglomeration through capillary action during gravitational rotation (Hwang et al 2012, Vasugi andRamamurthy 2014).The duration of the process ranged from 8 to 20 min, and the inclination of the pelletizer disc varied between 40-50°, depending on the specific mix.A total of 35 mixes (A1 to A35) were prepared, as indicated in table 2 for binary blend material combinations, table 3 for ternary blend material combinations, and table 4 for quaternary blend material combinations.After pelletization, the green pellets were initially dried at ambient temperature for 24 h.These green pellets were dried even more by using oven for an additional 24 h at 105 °C.After that, pellets bigger than 4.75 mm were separated by sieve and collected for additional processing.In a box muffle furnace, the collected pellets were first heated to the required temperature at a rate of 10 °C m −1 for 150 min.After that, they were sintered for 30 min at 700 °C, 900 °C, 1100 °C, and 1150 °C.At this point, the sintered SAA were collected and kept in an airtight cover once they had cooled.Mechanical and physical parameters, such as compressive strength, and bulk density, water absorption, were measured for the SAA.To the SAA, scanning electron microscope (SEM) analysis, X-ray diffraction (XRD) and energy dispersive x-ray (EDAX) analysis were conducted, and also data analysis was performed using Artificial Neural Network (ANN) tools, yielding accurate predictions.

Observations during pelletization
After conducting multiple trials, the optimal settings for the pelletizer disc were determined based on the material combination.The inclination of the disc was set between 50°to 60°, while the disc speed was fixed at 385 rpm.It was observed that at inclinations above 60°, pellets formed were smaller than 8 mm in size, whereas inclinations below 40°resulted in 60% of the powder remaining as sensitive pellets or in powdered form (Manjari et al 2023).The strategic placement of pelletizer disc vanes, as depicted in figure 1, played a crucial role in achieving the desired pellet form within a shorter duration.To prevent the diffusion of dust into the air, 0.05% water was added to the 500 grams of powder for all blends.
During pelletization, when using 100% RM, 14% water was required, and the process took approximately 15 min.For other cases, the water content and pelletization time were increased accordingly.The addition of FA, SWS, and BTN resulted in increased water demand, with SWS requiring the highest amount.It should be noted that excessive water sprinkling caused the pellets to become greasy, stick together, and lose their shape.In the pelletization process, the high plasticity of the BTN mixture caused the pellets to stick together and adhere to the pelletizer disc pan (Manikandan and Ramamurthy 2007).However, the addition of WGP, TiO 2 , and GGBS to the RM during pelletization yielded positive results.

Measurement of mechanical and physical properties
The compressive strength of SAA was assessed using a compression testing machine.Due to variations in spherical shape, the average compressive strength of 25 pellets was determined as the SAA compressive strength.The formula used to calculate the SAA compressive strength (S) in mega-pascals (MPa) is given by equation (1) (Yashima 1987, Li et

Results and discussions
Table 5 shows that the compressive strength of the SAA did not fulfil the even pinch test requirements for any of the three blends (binary, ternary, and quaternary) up to 900 °C.(Manikandan and Ramamurthy 2012, Mi et al 2021, Jia et al 2023).Furthermore, it was observed that at low temperatures, there was no liquid phase presented to bind the particles together.However, at medium temperatures, a liquid phase with surface tension emerged, resulting in a more cohesive SAA due to the filling of gaps and voids.

Compressive strength variation of SAA in binary blend
Figure 3 illustrates the impact of different FA (A1 to A10) levels on the compressive strength of SAA at various temperatures.As discussed earlier, the liquid phase began to form at 1100 °C, resulting in a compressive strength range of 0.65 MPa to 3.53 MPa.At a higher temperature of 1150 °C, the SAA compressive strength is enhanced with increasing FA levels up to 60%.However, beyond 60% FA replacement, the compressive strength of SAA decreased.A study by (Molineux et al 2016), reported that at 1200 °C, LWA comprising 44% RM replacement demonstrated favorable results with compressive strength of 8 MPa and water absorption of 6.26%.In the present investigation, it was observed that up to 60% FA replacement resulted in a slight improvement in compressive strength, reaching 9.42 MPa, though still weaker compared to lytag aggregate (Wasserman and Bentur 1997).The increase in Al 2 O 3 and SiO 2 levels corresponded to the rise in FA content.Higher levels of Al 2 O 3 and SiO 2 generally lead to higher melting temperatures and viscosity, as reported by (Kockal andOzturan 2011, Manjari et al 2023).Figure 4 illustrates the impact of various SWS (A11 to A13) levels on the compressive strength of Sintered Artificial Aggregate (SAA) at different temperatures.Surprisingly, no significant differences in compressive strength were observed at any SWS replacement level and temperature.However, it was noted that the main oxides Al 2 O 3 , SiO 2 , and flux components (Fe 2 O 3 , CaO, MgO, K 2 O, and Na 2 O) decreased when SWS partially substituted RM, which subsequently led to an increase in the required sintering temperature.According to the literature (Jia et al 2023), SWS-based lightweight aggregates typically require sintering temperatures between 1180 °C and 1250 °C.Notably, SWS contains an organic component that acts as a favourable sintering agent, contributing to the sintering process.However, in this particular study, the effect of SWS on the compressive strength of SAA at various temperatures did not show any significant results.
Figure 5 illustrates the impact of various WGP (A14 to A16) concentrations on the compressive strength of SAA at different temperatures.As the level of WGP increases, the compressive strength of SAA also increases when RM is substituted by different amounts of WGP.This rise in compressive strength can be attributed to the increased content of SiO 2 and CaO in conjunction with higher WGP concentrations, resulting in enhanced strength at lower temperatures.Previous research (Tuan et al 2013) reported that the highest compressive strength is achieved at 30% WGP replacement, followed by 50% replacement, and then 10% replacement.Other studies (Kockal and Ozturan 2011, Li et al 2021, Jia et al 2023) have also utilized WGP as a sintering agent due to its high concentration of main oxides and flux agents.As the temperature and glass powder content increase, a sufficient low-viscosity liquid phase is formed, leading to a reduction in internal pores and the absence of gas released in the LWA (Jia et al 2023).In this particular study, the highest compressive strength achieved by SAA was 15.22 MPa at 1150 °C when 20% WGP was used as a replacement.

Compressive strength variation of SAA in ternary blend
Figure 6 depicts the influence of different levels of WGP (A17 to A20) on the compressive strength of SAA at varying temperatures.As the WGP content increased from 8% to 20% in 4% increments, the compressive strength of SAA showed an increase from 10.67 MPa to 22.92 MPa.This enhancement in strength is attributed to the rise in Al 2 O 3 , SiO 2 , and flux components (Fe 2 O 3 , CaO, MgO, K 2 O, and Na 2 O) when RM, FA, and WGP were incorporated, leading to an increase in the glassy phase at elevated temperatures.According to (Jia et al 2023), the density and compressive strength of ceramsite exhibited a similar pattern, first increasing and then declining at 1200 °C with an increased WGP content, resulting in an amplified glassy phase.In the case of SAA, at 8% WGP replacement, a partial glassy phase with low viscosity formed.At 12% WGP replacement, sufficient glassy phase with moderate viscosity filled internal voids, resulting in densification and compressive strength of 22.92 MPa.However, beyond 12% WGP substitution, excessive glassy phase retention led to the trapping of released gas and the creation of internal voids, leading to a decrease in compressive strength.observation aligns with findings from (Liu et al 2018), where an enhancement in SiO 2 content led to a reduction in compressive strength, whereas an increase in Al 2 O 3 content resulted in improved compressive strength.In this study, the compressive strength of SAA increased from 6.18 MPa to 11.38 MPa as the WGP level was raised from 8% to 20%.However, this value is considerably lower than the compressive strength of 21.01 MPa achieved by the RM, FA, and BTN ceramsite (Mi et al 2021).
In   content contribute to better compressive strength at lower temperatures.Moreover, the compressive strength steadily increased from 6.51 MPa to 11.95 MPa as the WGP level was raised from 8% to 16% with a 4% difference, but it decreased at 20% WGP.The chemical composition of the RM, GGBS, and WGP mix is similar to that of the RM, BTN, and WGP mix, except for CaO and Fe 2 O 3 .As a result, at 1150 °C, the compressive strength of the SAA is nearly similar in both cases.
Figure 9 illustrates the impact of various WGP levels (A29 to A31) on the compressive strength of SAA at different temperatures.As the WGP content increases from 8% to 20%, the compressive strength of SAA also  increases significantly, ranging from 1.84 MPa to 7.32 MPa.This improvement in compressive strength is attributed to the increased presence of SiO 2 , Al 2 O 3 , and CaO components in the mix, as observed in (Tuan et al 2013), where the inclusion of GGBS up to 50% led to enhanced compressive strength.Compared to the binary blend SAA (A11 to A13), the ternary blend with WGP (A29 to A31) shows the highest compressive strength.The compressive strength of LWA, created using 90% of dry SWS and 10% of GP at an optimal temperature of 1180 °C, was reported as 7.10 MPa (Li et al 2021).The current results demonstrate the effectiveness of incorporating WGP in the mix to achieve higher compressive strength in SAA.

Compressive strength variation of SAA in quaternary blend
As mentioned in table 4, the quaternary blend (A33 to A35) involved combining RM, TiO 2 (2%), FA (10%), and varying amounts of WGP (ranging from 8% to 16%).At 1100 °C for 30 min, the compressive strength of SAA increased from 5.59 MPa to 8.27 MPa, as illustrated in figure 10.Subsequently, at 1150 °C, the SAA compressive strength further improved from 11.53 MPa to 13.56 MPa with increasing WGP content.According to a study conducted by (Wei et al 2020), the inclusion of 2% TiO 2 resulted in a substantial 44.9% increase in compressive strength at 1550 °C, demonstrating the effectiveness of TiO 2 as a good sintering agent.However, it is important to note that the compressive strength achieved in this blend was notably lower compared to the ternary blend A18 mix, as shown in the results.

Water absorption and bulk density
The best compressive strength SAA (A18) was taken into consideration for bulk density and water absorption analysis, because compressive strength is the primary factor in coarse aggregates as well as many SAA samples may not with-stand these tests.Table 6 shows the A18 SAA water absorption, and bulk density as 4.26% and 1296.12(kg/m 3 ) respectively.As per IS: 2386 (part 3)-1963 allowable limit, water absorption exceeds 2.26%, whereas bulk density is with-in the limit.

SEM analysis of SAA
Figure 11, shows surface and core SEM images of the strongest SAA from each ethnic group, along with mix ID, after sintering for 30 min at 1150 °C.Observing the A7 mix, the core appears more solid than the surface, exhibiting tiny pores.The A7 mix contains lower Al 2 O 3 , SiO 2 , and CaO compounds compared to the A18 mix, resulting in some unbonded regions on the surface, which contributes to lower compressive strength.Regarding the A16 mix, a combination of RM and WGP, its core has completely solidified with significant pore holes due to the higher content of WGP.At the same time, almost all surfaces, except for a small area, have been fully laminated with Al 2 O 3 and SiO 2 liquid.A study by (Lim et al 2020), indicated that a high content of glass powder leads to an enlargement of inner-side pores in SAA.The A18 mix in the ternary blend demonstrates a high level of compressive strength since both the surface and the core have completely solidified, reducing internal pores.This is achieved by increasing the flux oxides and decreasing the quantity of released gas when FA and WGP are added to the RM.The A24 and A27 mixes exhibit poor sintering and lamination quality in their surface and core portions due to the shortage of Al 2 O 3 , SiO 2 , and still high temperature is required.Although SEM images reveal some unburnt material in both the surface and the core area of the A32 mix, it still exhibits improved compressive strength compared to the binary blend (A11 to A13).However, it requires a higher temperature for complete solidification.Despite the addition of TiO 2 as an additive in the quaternary blend, the A35 SEM image indicates that both the surface and core areas of SAA were partially sintered.TiO 2 additive did not contribute in terms of enhancing the sintering.

EDAX and XRD analysis
In order to determine the elemental compounds and minerals, EDAX and XRD analyses were performed on the A18 mix SAA, due to exhibiting the best strength and bonding.EDAX was carried out on SAA at the designated location; figure 12, shows the elemental compounds that are present in SAA (A18).The elements discovered in this examination included oxygen, iron, aluminium, silica, titanium, calcium, and sodium.In a similar manner, XRD was used on a powder sample of SAA (A18) to determine the phase development; figure 13 shows the diffraction peaks, which are quartz (SiO 2 ) and hematite (Fe 2 O 3 ) at different sintering temperatures.In the nonsintered sample case, the intensity of quartz peaks was significantly higher than that of hematite.However, as the temperature increased, the hematite peaks exhibited a noticeable increase, meanwhile quartz peaks decreased due to glassy phase formation.This phenomenon endorsed the improvement of compressive strength of A18 SAA with temperature (Liu et al 2018).

3.7.
Compressive strength prediction of SAA using ANN An artificial neural network architecture, as depicted in figure 2, was employed to predict the compressive strength of sintered artificial aggregates in binary, ternary, and quaternary blends.The developed ANN model    7.The designed ANN architecture achieved an error of less than 10% between the real and predicted values.Table 7 presents the minimum and maximum percentages of prediction error for different sintering conditions: 0.00% and 8.33% at 700 °C for 30 min, 0.00% and 6.35% at 900 °C for 30 min, 0.00% and 8.33% at 1100 °C for 30 min, and 0.19% and 7.60% at 1150 °C for 30 min.These results demonstrate the accuracy and reliability of the ANN model in predicting the compressive strength of sintered artificial aggregate under various conditions.

Conclusions
The present study aimed to produce RM-based synthesized sintered artificial aggregate with various industrial waste materials and testing their strength, and characteristics to identify the best material mix ratio.Successfully best compressive strength low water absorption SAA was produced with the combination of RM, FA and WGP.The following conclusions were drawn from the outcomes: • Despite the use of sintering additives like WGP and TiO 2 and binders like FA, SWS, GGBS, and BTN when combined with RM, there were no appreciable changes in compressive strength up to 1100 °C due to the absence of glassy phase.
• Sewage sludge and TiO 2 had no detectable effect in terms of enhancing strength or reducing sintering temperature at these conditions.
• The best material mix ratio for the production of SAA was (A18) RM: FA: WGP; 78:10:12.Out of all blends the ternary blend A18 exhibited impressive properties after 30 min of sintering at 1150 °C: high compressive strength of 22.92 MPa, water absorption of 4.26%, and bulk density of 1296.12 kg m −13 .This was made possible by the high amount of Al 2 O 3 , SiO 2 and other flex oxides, in the combination of FA, WGP with RM.
• SEM analysis describes the surface and core area of (A18) SAA, which were completely burned, solidified and reduced internal pores after 30 min of sintering at 1150 °C.Hence SAA achieved the best compressive strength and low water absorption.XRD analysis described that the main minerals of the (A18) SAA were hematite and quartz.Hematite peaks increased along with the temperature increment; mean-while quartz peaks decreased due to glassy phase formation.This phenomenon endorsed the improvement of compressive strength of A18 SAA with temperature.
• The developed ANN model accurately predicted errors of less than 10% between the experimental and predicted values.This achievement was accomplished by employing the Levenberg-Marquardt algorithm and the feed-forward backpropagation approach.
al 2016, Wei et al 2020).The temperature and formation of the glassy phase in the process of SAA are mainly influenced by the oxide components Al 2 O 3 , SiO 2 , flex (Fe 2 O 3 , Cao, MgO, K 2 O and Na 2 O) (Chiou and Chen 2013, Molineux et al 2016, Mi et al 2021, Pei et al 2021, Manjari et al 2023).Glass phase forms when the sintering temperature rises to high and alumina encapsulate around the insoluble substance (Zou et al 2009).

Figure 1 .
Figure 1.SAA Step-by-step manufacturing and testing procedure.
al 2000, Mathew et al 2023) the compressive strength of the SAA (MPa), L is the peak load of the specimen (N) and d is the length between the top and bottom plates (mm).Water absorption and bulk density were carried out to best compressive strength of SAA as per the IS: 2386 (part 3)-1963.s = Note Standard error of SAA compressive strength n : Where σ = Sample standard deviation; x = Individual values in sample; μ = Samples average; n = Number of samples sets for training, (20%) 28 sets for testing, and (20%) 28 sets for validation purposes randomly allocated.The input parameters provided to the ANN model included RM, FA, SWS, TiO 2 , WGP, BTN, GGBS, temperature, and time.The output of the model was the compressive strengths of SAA for the binary, ternary, and quaternary blends, obtained based on the experimental data.The entered data was processed by the developed ANN model to make predictions of the compressive strength values.The accuracy of the ANN predictions was evaluated using the percentage of predicted error, calculated using equation (2) (Natrayan and Senthil Kumar 2020, Manikandan and Vasugi 2022).This error metric served as a measure of the ANN model performance in predicting the compressive strength values of SAA for different blends.

Figure 2 .
Figure 2. ANN architecture adopted in the study.
Figure 7 displays the effect of various WGP levels (A21 to A24) on the compressive strength of SAA at different temperatures.A comparison between the mixtures of RM, FA, and WGP, and RM, BTN, and WGP shows a reduction in the main oxide component Al 2 O 3 and flux components (Fe 2 O 3 , MgO, K 2 O, and Na 2 O).However, SiO 2 has only been partially neutralized, resulting in a decrease in compressive strength.This

Figure 3 .
Figure 3.Effect of different levels of FA on SAA compressive strength.

Figure 4 .
Figure 4. Effect of different levels of SWS on SAA compressive strength.
figure 8, the effect of various WGP levels (A25 to A28) on the compressive strength of SAA at different temperatures is illustrated.The inclusion of a significant amount of CaO in GGBS played a crucial role in achieving good compressive strength in the A25 to A28 mixes.The compressive strength ranged from 3.63 MPa to 7.31 MPa at 1100 °C, which outperformed other mixes in this study.This observation is consistent with previous studies (Kockal and Ozturan 2011, Mi et al 2021) that demonstrated how high CaO and other flux

Figure 5 .
Figure 5.Effect of different levels of WGP on SAA compressive strength.

Figure 6 .
Figure 6.Effect of varying WGP in the presence of 10% FA on SAA compressive strength.

Figure 7 .
Figure 7. Effect of different levels of WGP with 10% BNT on SAA compressive strength.

Figure 8 .
Figure 8.Effect of varying levels of WGP with 10% GGBS on SAA compressive strength.

Figure 9 .
Figure 9.Effect of different levels of WGP with 10% SWS on SAA compressive strength.

Figure 10 .
Figure 10.Effect of different levels of WGP on quaternary blend SAA compressive strength.

Figure 11 .
Figure 11.SEM images of SAA surface and core portion along with mix number.

Table 1 .
Chemical characteristics of the raw materials.

Table 5 .
SAA compressive strength (MPa) at various sintering temperatures and time intervals.

Table 6 .
SAA water absorption and density.
utilized 9 neurons in the input layer, representing parameters such as RM, FA, SWS, TiO 2 , WGP, BTN, GGBS, temperature, and time.Additionally, there were 12 neurons in a single hidden layer and one neuron in the output layer.The predicted values and corresponding error percentages are listed in table 7.