Ferrock cement and oxalic acid for enhanced concrete strength and durability against sulphate attack

Concrete is widely known for being plentiful, durable, and strong, but it can be damaged by different chemicals and environments, that can shorten its lifespan. Consequently, there is a growing interest among researchers to find more durable, stronger, and environmentally friendly cement alternatives. This study focuses on evaluating the workability, strength, durability properties, and morphological aspects of ferrock cement-based concrete, which involves substituting varying percentages of ferrock cement (0%, 5%, 10%, 15%, and 20%) for conventional cement. Ferrock, comprising Iron Powder, Fly Ash, Lime Powder, and glass powder offers pozzolanic potential as a sustainable cement substitute. Additionally, oxalic acid is introduced into the mixes to explore its role in catalyzing reactions between CO2 and water, thereby enhancing the concrete’s strength and durability. Compressive and flexural strength are analyzed after replacing the cement with ferrock, with and without oxalic acid, while durability is assessed through water absorption and resistance to sodium sulphate solution after 28 days of curing. Nine sets of mixes, all with a consistent water-cement ratio of 0.49, are investigated. Results indicate that concrete containing ferrock-based cement, particularly with oxalic acid, exhibits superior strength and enhanced resistance to sulphate attack. The addition of 5% and 10% ferrock with the integration of oxalic acid has 32.28% and 38.7% of compressive strength respectively, the same proportion has 0.2% and 0.1% of mass loss regarding resistance to sulphate attack. Notably, a 10% ferrock replacement with oxalic acid demonstrates the highest performance of concrete as determined by the multi-decision methods.


Introduction
Concrete is an indispensable element of infrastructure development, profoundly impacting the economic progress of nations globally.It stands as the most widely used man-made material and the second most consumed substance after water worldwide [1].Comprising fine and coarse aggregates bonded with cement and water, concrete solidifies over time.However, the growing demands on infrastructure due to population growth, urbanization, and industrialization have led to the depletion of natural resources [2].Moreover, the Sustainable development goals report underscores the challenges posed by multiple crises affecting global progress toward sustainability [3].Modern society places a great deal of emphasis on protecting the environment and waste produced in various industries.Some of the appropriate options for a large reduction in waste and environmental impact from the industries are reuse and recycling.This strategy might be advantageous for the building sector since it allows for the development of new projects.Ferrock cement-based concrete has specific applications such as concrete in buildings, bridges, structures in contact with seawater, and any conventional constructions [4].
The production of cement is highly energy-intensive, necessitating the utilization of supplementary cementitious materials from recycled and by-products for concrete production [5].This involves the use of supplementary cementitious materials, especially those derived from industrial operations, to substitute Portland cement, and recycled materials to replace natural resources.Pozzolanic waste materials are widely employed as supplementary cementitious materials in concrete production [6].Researchers are currently exploring various sustainable alternatives to traditional cement.One promising innovation in concrete technology is ferrock which was pioneered by David Stone [7,8].This addresses environmental concerns associated with cement production by utilizing recycled materials and minimizing carbon emissions.Ferrock offers potential benefits such as improved durability and reduced environmental impact compared to conventional concrete formulations.It is a binder material used as a partial or complete replacement for cement in concrete [9,10].Ferrock is a combination of iron dust, fly ash, metakaolin, and limestone powder with a major proportion of iron scraps from steel industries [11,12].
Iron dust, a byproduct of the iron industry, is combined with trace amounts of calcareous material, fly ash, and metakaolin to make this novel material, which would otherwise be disposed of in landfills [13,14].A major constituent of Ferrock is an iron powder obtained from the waste of steel industries, which is elongated and angular in shape with a large surface area, providing greater reactivity [15].Generally, it is a blend of iron powder, fly ash, lime powder, metakaolin, and recycled glass.All ingredients necessary for Ferrock production are conventional industrial materials except for iron powder [16] Iron oxide reacts with carbon dioxide and water to produce iron carbonate, which can enhance the environment by absorbing atmospheric carbon dioxide and improving the hardening process [10].Fly ash, a pozzolanic fine powder is a by-product from burning coal in electric generation power plants containing aluminous and siliceous material that forms cement in the presence of water.Another ingredient of Ferrock is limestone powder, which could reduce water demand, increase strength, and improve workability [10].Silica and alumina are used in purpose to facilitate iron dissolution and to improve material properties [17,18].
Limestone, due to its reactive nature, provides nucleation sites for clinker hydration products and reduces the heat of hydration.Ferrock contains waste glass, which can contribute to a reduction in heat conductivity and a decrease in the sorptivity of concrete.Oxalic acid, which is critical for Ferrock concrete, acts as a reaction modifier in glass-ionomer systems.It accelerates the setting reaction without affecting strength but is limited to low concentrations due to its relatively poor solubility in water [19].It accelerates polymerization but slows down alite and belite hydration.In addition, the unique quality of ferrock is that absorbs more CO 2 [20].The reactions are as follows [4]: And the net reaction is: Oxalic acid, which is relatively a weak organic acid having formula C 2 H 2 O 4 with a medium average pH value.It is broadly used as a cleaning agent to remove stains from different surfaces in addition to its use in ferrockbased concrete as a catalyst to increase the reaction .It acts as an accelerator for cement hydration reactions [21].This may also be helpful in the formation of a protective electrical double-layer film around the cement particle during the gel state [10].Oxalic acid serves multiple roles in Ferrock-based concrete.Oxalic acid accelerates the formation of FeCO 3 in Ferrock-based concrete primarily through its ability to facilitate the conversion of iron oxides into iron carbonate (FeCO 3 ) during the curing process.This reaction occurs due to the acidic nature of oxalic acid, which promotes the dissolution of iron oxides and subsequent precipitation of iron carbonate.In addition, oxalic acid acts as an accelerating chemical process for cement hydration [22].
Despite efforts to enhance sustainability in concrete production, significant environmental issues such as sulphate corrosion are among the most prevalent and harmful processes which affect concrete service life [23].Sulphate corrosion occurs when metals react with sulphurous compounds like hydrogen sulphide or sulphate ions, forming corrosive metal sulphides.This process is common in industries where sulphurous compounds are present.Solid sulphates do not damage concrete, but when in a solution state, they penetrate porous concrete and interact with hydrated cement products, leading to damage, especially magnesium sulphate, causing maximum harm [24].When magnesium sulphate penetrates concrete, it reacts with the calcium hydroxide present in the hydrated cement paste, forming expansive compounds such as calcium sulphate and magnesium hydroxide.These compounds exert pressure on the concrete matrix, leading to cracking, spalling, and deterioration of the structure.Furthermore, a magnesium sulphate attack can disrupt the concrete's pore structure, increasing its permeability and allowing more water and aggressive ions to penetrate, accelerating the corrosion of embedded reinforcement steel.Some chemicals in concrete cause a short life of concrete unless special precautions are followed.Chloride-induced in reinforced concrete has been reported as a major durability problem worldwide [25].Exposure to sulphates and carbonation are the main challenges of concrete [26].Previous researchers conducted a variety of studies on Ferrock as full and partial substitutions for cement.However, further studies on Ferrock concrete with oxalic acid are crucial for the durability of ferrock-based concrete, such as sulphate attack and water absorption.This study investigates Ferrock concrete with and without oxalic acid, primarily focusing on durability against sulphate attack and mechanical performance.Mechanical Strength such as the compressive and flexural strength of ferrock-based concrete with and without the addition of oxalic acid, providing insights into its structural performance; Durability aspects of ferrockbased concrete such as water absorption and sulphate attack resistance by subjecting specimens to submerged exposure in sodium sulphate solutions and utilizing the mass loss method to quantify deterioration; Microstructural Examination: Investigate the microstructure of ferrock-based concrete and conventional concrete using scanning electron microscopy, elaborating on any differences in their morphology; and Determination of appropriate combination using optimization approach by Topsis decision methods are investigated.

Materials
This experimental research aimed to assess the impact of partially substituting cement with Ferrock cement, allowing a maximum replacement rate of 20%.The mixture was created by adjusting the proportions of Ferrock cement while maintaining the other ingredients' constant.The ingredients were collected and prepared for each laboratory test on cement, fine, and coarse aggregate for the development of the specimen.Ordinary Portland cement with a specific gravity of 3.15, a brand of 42.5N was taken for concrete production.According to ASTM C33 [27], coarse aggregate consists of crushed stone with a particle size of 4.75 mm and above, and with the same standard, aggregates that are less than 4.75 mm and retained by 0.75 mm are designated as sand.A portion of the water used for mixing is used for the hydration of cement, and the right amount of water is needed to give the concrete its desired workability.
Ferrock is a binder material used as a partial or complete replacement for cement in concrete.It is measured based on its testing with different proportions of the raw materials.It is made up of iron powder, fly ash, limestone, and recycled glass to transform industrial waste products into new substances.The composition of ferrock was taken as 60% iron powder, 20% fly ash, 10% recycled glass, 8% limestone, and 2% oxalic acid.Iron powder is the waste product from steel mills during scrap steel processing from other industries through shot blasting.It is one of the metals in commercial use and is primarily composed of iron, carbon, and silicon, but may also contain traces of sulphur, manganese, and phosphorus.For this research, the powder is extracted from shavings of automotive brake disks done in torno houses.ASTM B214-16 [28] Standard Test Method for Sieve Analysis of Metal Powders specifies the use of a series of standard sieves for particle size analysis of iron powder which is used in passing 75 um sieve and retained on the pan was used as a powder which acts as a cement replacement agent.Figure 1 is the ferrock cement composed of iron powder, coal ash powder, limestone, and glass powder.
Based on this class F fly ash passing 75um sieve and retained on the pan was used as a powder which acts as a ferrock combination by 20% replacement agent.It is good in cold weathering resistance and non-shrink material.The sum of constituents such as SiO 2 , Al 2 O 3 , and Fe 2 O 3 of coal ash which is greater than 70% indicates that the sample fly ash is classified as an ASTM Class F fly ash.Limestone powder used in this research is prepared by grinding raw limestone collected from a cement Factory which takes 10% and acts as a replacement agent for ferrock.In addition to the above materials, 8% waste glass powder was used, which is produced from colorless bottles that are mostly known as soft drink bottles.

Experimental test and mix design
The detailed procedures for the characterization test of sands were also followed based on Astm, C. 117 [29].The process of sieving granular material through a succession of sieves with successively decreasing mesh sizes and weighing the quantity of material retained in each sieve as a percentage of the total mass is sieve analysis and used to determine the particle size distribution of granular material.Standard cast iron molds measuring 150 mm * 150 mm * 150 mm were utilized to prepare cubes for compressive strength, water absorption, and sulphate attack tests.Rectangular beam molds measuring 100 mm * 100 mm * 500 mm were employed solely for flexural strength tests.For each experiment, five sample specimens were molded and subsequently tested.The compressive strength test of cubes is an indication of their ability to resist compressive loads.A higher compressive strength indicates that the cubes are more capable of resisting compressive loads.The compressive strength of concrete cubes is typically measured at 7 and 28 days, followed using ASTM C39/C39-09 [30] of using an automatic compressive strength test machine.A compressive strength test is conducted by placing the cubes in the compression testing machine with a loading rate of 14 N mm −2 min −1 (0.23 load rate/second).Compressive load is applied slowly until the specimen fails, and the maximum load is attained.
The flexural strength of the beams is an indication of their ability to resist bending loads.A higher flexural strength indicates that the beams are more capable of resisting bending loads.Concrete specimens prepared according to ASTM C78/C78M-17 [31] dimensions undergo casting in suitable forms.Curing follows the guidelines of ASTM C31/C31M-17a.The flexural strength test employs ASTM C293 [32], utilizing a four-point loading system.The calculation of flexural strength involves the load at failure divided by the product of beam width and the square of beam depth.This study also examined the water absorption of normal and ferrockbased concrete at curing periods of 28 days to determine the water tightness of concrete.In the water absorption test, the samples were taken out of the curing water and dried at a temperature of 105 °C for 24 h, weighed, then immersed in water for 72 h, and weighed again, based on ASTM, C1585 [33].To investigate the sulphate attack, the mass loss method is employed [34].Concrete's chemical resistance is assessed by immersing specimens in acid or alkaline solutions, with weight changes indicating sulphate resistance.50mg/L Na2SO4 concentration was used in the experimental study.The specimens were weighed after initial curing in water for 28 days, then immersed in a 5% sodium solution for 28 days with a regularly renewed solution.
In this experimental investigation, the objective is to assess the influence of oxalic acid on Ferrock cement when employed as a partial replacement for traditional cement in concrete formulations.Two distinct types of Ferrock cement are prepared: one containing oxalic acid at a fixed concentration of 2%, and the other devoid of oxalic acid.To comprehensively evaluate the effects, concrete mixtures are formulated incorporating varying proportions of Ferrock cement (ranging from 0% to 20%) alongside a control group designed using the wellestablished ACI Method [35] for C-25 grade concrete.To ensure precision and accuracy in measurements, a mass-based batching approach is adopted for concrete ingredients, recognizing the variability in void spaces within granular materials.This approach enables the maintenance of consistent mixture proportions throughout the experiment.The concrete mixing process involves a systematic approach aimed at achieving homogeneity and uniformity in the mix.Using the electric cement mixer, coarse aggregates, sand, conventional cement, and Ferrock cement variants are blended in a dry state for two minutes.Subsequently, the predetermined quantity of water is introduced, and mixing continues for an additional four minutes to ensure thorough hydration and distribution of all constituents within the mixture.Table 1 shows about code designation and quantity of cement, ferrock aggregates, and water.
In table 1, M0 represents the control mix.The ferrock cement mixes are labeled FM5 to FM20, indicating the mixes that contain 5% to 20% ferrock cement without oxalic acid.Furthermore, FAM5, FAM10, FAM15, and FAM20 represent 5%, 10%, 15%, and 20% ferrock cement, respectively, with oxalic acid.The standardized testing procedures enable a comprehensive evaluation of the mechanical properties of the concrete mixtures under consideration.By adopting a rigorous and systematic approach devoid of subjective bias, the aim is to generate reliable data that will enable discernment of any discernible differences in the performance of concrete mixtures containing Ferrock cement with and without oxalic acid, thereby contributing to a deeper understanding of the material's behavior and potential applications in construction practice Following the casting process, concrete specimens were carefully extracted from the steel Molds after a curing period of 24 h.Subsequently, the specimens underwent curing procedures by ASTM C511 [36], which dictates standards for mixing rooms, moist cabinets, moist rooms, and water storage tanks utilized in concrete testing.To facilitate proper curing, the specimens were expeditiously transferred to metal tanks containing water at room temperature.Here, they were fully submerged underwater and left to cure for durations of 7 and 28 days, ensuring optimal development of strength and durability properties.Adhering to ASTM C511 [36] specifications, the test specimens were removed from the curing metal tank 24 h before testing including considering ambient conditions, ensuring consistency and reliability.

Fresh and mechanical properties of ferrock concrete
The study examined several key aspects including workability, compressive strength, flexural strength, durability, and morphological characteristics of concrete mixes incorporating ferrock-based cement as a partial substitute for conventional cement.The normal consistency of pastes, an indicator of workability, was evaluated to achieve a settling depth of 10 ± 1 mm within 30 s, typically falling within a water-cement ratio range of 26% to 33% by ASTM C187 [37].The control paste exhibited a normal consistency of 28%.Notably, Ferrock-based cement pastes showed equal or higher consistency compared to the control as replacement percentages increased from 5% to 20%.However, a gradual increase in normal consistency was observed beyond 10% replacement, reaching 29.5% at 20% replacement, attributed to the higher surface area of Ferrock cement.
Regarding compressive strength, specimens containing 5% and 10% Ferrock cement with oxalic acid exhibited superior strengths compared to the control mix on both the seventh and 28th days of curing.However, replacements of 15% and 20% with Ferrock cement containing oxalic acid experienced a decline in strength compared to the control mix.Similar trends were observed for replacements with Ferrock cement without oxalic acid.These findings are consistent with prior studies [4,10,18], suggesting better performance up to 12% replacement, while noting a decrease in strength beyond certain replacement percentages, likely due to the influence of excessive silica in pozzolans.Table 2 shows the mean value of compressive strength, and flexural strength after the 7th and 28th days of curing.The reduction in strength may be attributed to excessive silica in pozzolans converting into Si during hydration, leading to swelling silica-hydrated compounds, causing swelling, or cracking and reducing strength [38].However, [8] noted a decrease in compressive strength with 15% or more ferrock replacement, consistent with the present study.
The mean flexural strength of samples at 7 and 28 days, alongside the control concrete, has been examined.Noteworthy trends have emerged in ferrock concretes, where flexural strength was evaluated after 7 and 28 days of curing.Firstly, samples without oxalic acid displayed a consistent decrease in flexural strength compared to the control C-25 concrete (M0).This decrease was observed as the replacement percentage increased from 5% to 20%.Conversely, for samples incorporating oxalic acid, a positive impact on flexural strength development was noted at 5% and 10% replacement.However, at replacement percentages of 15% and 20%, the rate of flexural strength development decreased, indicating a diminishing effectiveness of oxalic acid beyond a certain replacement threshold.Overall, the analysis suggests that the flexural strength of the concrete increased up to 10% replacement with ferrock cement containing oxalic acid.However, beyond this threshold, a reduction trend was observed.Moreover, the data for 28 days of flexural strength revealed superior performance at 5% and 10% replacement.Nevertheless, as the replacement percentage exceeded 10%, a decline in flexural strength was observed.This decline can be attributed to the diminishing binding properties of cement and increased brittleness arising from the carbon content in iron powder from ferrock.

Durability of hardened concrete
Moisture penetration is one of the factors affecting the durability of concrete.Concrete is a porous material that can allow water to migrate through it, corroding steel reinforcement, and bringing in harmful chemicals, so it is a predominant factor to be determined to assess the quality of concrete.The water absorption capacity of concrete cubes was tested after 28 days of curing.The cubes were prepared from various mixing batches, each with a different percentage of cement replaced with ferrock cement containing oxalic acid-0%, 5%, 10%, 15%, and 20%.The water absorption values of the cubes varied, with the cubes containing oxalic acid reaching a maximum of 6.6% absorption.Without oxalic acid, this result showed a maximum of 7.9% for 20% ferrock cement replacement.In the first scenario, with ferrock cement containing oxalic acid, an increase in water absorption was observed as the percentage replacement increased from 10% to 20%.Similarly, in the second scenario, with ferrock concrete without oxalic acid, an increase in water absorption was noted as the percentage replacement increased from 0% to 20%.
The experimental results indicate that higher water absorption, implying more capillaries or greater porosity, leads to increased water absorption and reduced strength in concrete.The study's findings highlight the favorable performance of a 10% replacement of cement with ferrock containing oxalic acid compared to conventional concrete.Figure 2 shows the water absorption value of ferrock concrete with and without oxalic acid.This suggests that the addition of ferrock cement with oxalic acid at a 10% replacement level may lead to a reduction in water absorption and an improvement in concrete strength, potentially enhancing the material's durability.
Further research and analysis could elucidate the specific mechanisms by which ferrock cement with oxalic acid influences water absorption and strength, potentially paving the way for more resilient and durable concrete formulations.Varying mass losses were observed in concrete batches with 0% (M0), 5%, 10%, 15%, and 20% replacement of cement with ferrock.Lower mass loss percentages in the context of sulphate attack indicate better quality and resistance.It was found that ferrock cement containing oxalic acid exhibited superior sulphate resistance compared to mixes without oxalic acid and the control mix.The control C-25 concrete displayed a mass loss of 0.4%, while all ferrock cement concretes with oxalic acid demonstrated improved durability against Na 2 SO 4 attack, with mass losses ranging from 0.1% to 0.3%.
Notably, the 10% replacement with ferrock and oxalic acid showed the least mass loss (0.1%), signifying high hardened concrete density and superior durability.As the replacement of cement with ferrock and oxalic acid increased beyond 10%, durability against sulphate attack gradually decreased.However, replacements up to 20% still outperformed the control C-25 concrete.This suggests that the high hardened density of ferrock concrete effectively resists sodium sulphate attack when combined with oxalic acid.The graphical representation in figure 3 clearly delineates the impact of oxalic acid on sulphate attack resistance and the effect of ferrock percentage on resistance to sulphate attack.
These findings underscore the potential for improved sulphate resistance when using ferrock cement with oxalic acid, especially at a 10% replacement level, providing valuable insights for enhancing concrete durability in the face of sulphate exposure.
The analysis revealed that ferrock cement concrete without oxalic acid displayed relatively lower resistance to sulphate attack, with mass losses ranging from 0.2% to 0.4%.Interestingly, the 5% and 10% ferrock replacements with oxalic acid showed better resistance than the 20% replacement with ferrock cement and the control mix.The observed improvement against sulphate attack is attributed to the reduction of C 3 A in cement achieved by replacing cement with ferrock and reducing the water-cement ratio.This highlights the potential benefits of reducing C 3 A in cement and adjusting the water-cement ratio for enhancing sulphate resistance in concrete formulations.
C 3 A reacts with sulfate ions present in the environment to form calcium sulfoaluminate hydrates, which can cause expansion and cracking of concrete, leading to deterioration [39].Therefore, higher C 3 A content in cement can potentially increase the susceptibility of concrete to sulfate attack.

Morphological result of ferrock concrete
After 28 days of curing, concrete samples from both ferrock cement with and without oxalic acid were obtained from the middle of the specimens.These samples were then subjected to SEM image analysis at 10 kV by mounting small broken sections on brass stubs.The SEM images depicted that mineral admixtures, such as ferrock-containing oxalic acid-based additives, led to a reduction in pore areas and smaller crack widths compared to those without oxalic acid.This aligns with the broader understanding that mineral admixtures contribute to pore size refinement and the filling of capillary pores and crack spaces, thereby improving the overall microstructure of the cement paste [40].
As presented in figure 4, the absence of oxalic acid in the 10% Ferrock cement-based concrete revealed a higher number and longer length of microcracks and pores compared to Ferrock-containing oxalic acid samples, indicating the role of oxalic acid in reducing crack dimensions and enhancing the overall strength and durability of concrete.These findings show that oxalic acid plays a role in reducing crack dimensions and enhancing the overall strength and durability of concrete.SEM analysis presented in the study aligns with existing literature on the microstructural characteristics of cementitious materials.[41].The incorporation of oxalic acid in Ferrock-based concretes demonstrates positive effects on pore minimization, crack reduction, and overall matrix modifies their characteristics that contribute to improved concrete strength and durability.
Iron oxide particles from the ferrock are used for improvement due to their finer than cement particles.In the mix, the iron oxide particles can surround and fill the cement particles.It could help to provide greater reactivity.Oxalic acid is a weak acid that acts as an accelerator for cement hydration reactions.This may also be helpful in the formation of a protective electrical double-layer film around the cement particle during gel state which can be used for corrosion resistance.Ferrock concrete typically has a grayish or brownish color due to the presence of iron oxide and other mineral components.However, the addition of oxalic acid can used to clean and remove stains from concrete surfaces.Ferrock concrete without the addition of oxalic acid typically retains its natural grayish color.When oxalic acid is added to Ferrock concrete, it can have a bleaching effect, lighting the color of the concrete.

Ferrock concrete mix optimisation
TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) is a multi-criteria decision-making method used to determine the best alternative from a set of options.This is a decision analysis method to compare various alternatives based on multiple criteria, allowing decision-makers to select the most suitable option [42].The combination selection for the tool holder is conducted considering the aforementioned requirements.To ensure the combination of the specific mix from a large number of alternatives, multi-criteria decision-making (MCDM) methods have been used [43].The candidate materials combination was ranked by using these methods and the results obtained by each method were compared.There are various Multi-Criteria Decision Method (MCDM) techniques here using Technique for order performance by similarity to ideal solution (TOPSIS).There are simple but basic procedures.According to [44], the TOPSIS procedures are used here.
Create a matrix consisting of M alternatives and N criteria.This matrix is usually called an 'evaluation matrix'.(aij) M × N, Where, M is the material combination and N is the decision criteria for test results For this research, the options are taken from mix types of replacement of cement by ferrock with 0% (control mix), 5%, 10%, 15%, and 20% with and without oxalic acid.Therefore, there are totally nine options with four decision makers such as compressive strength, Flexural strength, sulphate attach resistance, and water absorption.Table 3 shows the options of alternatives and multi-decision criteria matrix.
Normalize matrix data: this is the first step for TOPSIS.Each metric j for each material combination and i is normalized to be in between 0 and 1, the higher its value the better the metric.
The second step is calculating the weighted normalized decision matrix data.It is important to note that each criterion should have its weight so that all of them would sum up to 1.The weights can be derived randomly.
There are basic steps involved in optimizing using it such as normalization, weighting, ideal and negativeideal Solutions, similarity Scores, and ranking.Notably, a 10% replacement of cement with ferrock containing oxalic acid stands out for its superior performance in terms of durability and strength.This suggests that incorporating ferrock, especially with oxalic acid, in concrete mixtures can not only enhance performance.After the weight estimation and normalization process, the following ranking order is estimated.After we assign a weight to each financial metric, we need to normalize those so that these sum up to 1. Then we need to multiply each normalized metric from step 2 by the corresponding normalized weight.Table 4 shows the process of normalization, whereas table 5 is a summary of optimization using the TOPSIS decision approach.
From the table, it is observed that 10% of ferrock concrete with oxalic acid is an appropriate mix for concrete production with a consideration of compressive strength, Flexural strength, sulphate attack resistance by mass loss, and water absorption.

Conclusion
The study highlights the promising potential of ferrock as a supplementary cementitious material in concrete applications, both with and without oxalic acid.Key findings include: • The concrete workability is decreased due to higher water demand with increasing ferrock content, notable enhancements in compressive strength were observed.• The superior compressive strength and flexural strength exhibited by concrete with 5 to 10% cement replacement with ferrock, especially when combined with oxalic acid, compared to the control mix after 28 days of curing and without oxalic acid.
• The study investigated water absorption and resistance to sulphate attack.Oxalic acid played a crucial role in reducing water absorption and mitigating mass loss during exposure to sodium sulphate, thereby demonstrating increased durability.
• Scanning electron microscopy provided valuable insights into the tangible effects of ferrock on the concrete matrix.The concrete containing 10% ferrock with oxalic acid exhibited a denser matrix, contributing to stronger and more durable concrete compared to both the control mix and without oxalic acid.
• Decision analysis, conducted using the Topsis method, allowed for the comparison of various alternatives based on multiple criteria.This facilitated decision-makers in selecting a 10% ferrock replacement with oxalic acid as the most suitable option and ranking all alternatives accordingly.
Overall, these findings underscore the potential benefits of incorporating ferrock into concrete mixes, especially when complemented with oxalic acid.

Figure 1 .
Figure 1.Ferrock powders are used for concrete production.

Figure 2 .
Figure 2. Water absorption of ferrock concrete with and without oxalic acid.

Figure 3 .
Figure 3. Mass loss in sulphate attack resistance.

Figure 4 .
Figure 4. SEM image of 10% Ferrock cement-based concrete with and without oxalic acid.

Table 1 .
Mix Code designation and quantity of ingredients (kg).

Table 2 .
Compressive and flexural strength of ferrock concrete.

Table 3 .
A summary result of Ferrock cement concrete.

Table 4 .
Normalized matrix result of Ferrock cement concrete.

Table 5 .
Summary of optimization using Topsis decision approach.