Comparative Study Using Wash Bottom Ash and Steel Slag by Replacement by Fine Aggregate

Comparative Study Using Wash Bottom Ash and Steel Slag by Replacement by Fine Aggregate

Kartik M. Choudhari, Prerna R. Awari, Manasi R. Balpande, Mansi D. Kathane, Chaitnya S.Bawane

Students, Civil Engineering, Kavikulguru Instistutes Of Technology And Sciences, Ramtek, Nagpur, Mh, India

Kavita S. Kene

Assitants Professors, Civil Engineering, Kavikulguru Instistutes Of Technology And Sciences, Ramtek, Nagpur, Mh, India

Abstract : The escalating global demand for natural aggregates and the environmental challenges associated with industrial waste disposal have driven the construction industry toward more sustainable practices. This review paper synthesizes current research on the integration of industrial by-productsspecifically steel slag (SS), coal bottom ash (CBA), and waste foundry sand (WFS)as partial or full replacements for fine aggregates in various concrete types, including Ordinary Portland Cement (OPC) , geopolymer , and ultra-high- performance concrete (UHPC).A critical analysis of the literature reveals that the mechanical performance of concrete containing these substitutes is generally comparable or even superior to conventional concrete at optimal replacement levels. For instance, studies indicate that a 30% replacement of sand with a combination of bottom ash and waste foundry sand can yield mechanical properties (compressive, flexural, and splitting tensile strength) equivalent to or exceeding control mixes. Similarly, the optimal replacement level for steel slag is typically reported between 30% and 60%, enhancing both strength and durability characteristics. In specialized applications, such as foamed concrete, crushed steel slag has proven feasible for both structural and non-structural purposes. Despite these benefits, the review identifies challenges such as increased water demand to maintain workability and the necessity for specific processing, such as washing bottom ash to reduce carbon content. The paper concludes that while industrial by-products offer a sustainable alternative to river sand, further research is required to standardize their use across diverse environmental conditions and specialized concrete applications.

IndexTerms Industrial by- product; Steel slag; Bottom ash; Sustainable concrete; Mechanical properties; Durability; Fine aggregates replacement

1. INTRODUCTION

   Concrete has emerged as the dominant construction material for the infrastructure needs of the 21st century due to its strength, longevity, and durability. However, the construction industry faces significant challenges, including the high consumption of natural resources, the depletion of natural aggregates (like river sand), and environmental pollution caused by CO2 emissions during cement production. To achieve sustainable development, it is essential to increase resource efficiency by reducing the use of raw energy and raw materials.

   In response, the engineering and scientific communities are exploring “green and recycled by-products” as supplementary materials in concrete. Substituting natural fine aggregates with industrial by-products offers technical, economic, and environmental advantages that are crucial for sustainability in the modern construction sector. Two prominent by-products currently being investigated are WASH Bottom Ash (WBA), a waste material from thermal power plants, and Steel Slag (SS), a byproduct of the steel manufacturing industry and manufacturing wastages of glass industry. Utilizing these materials not only addresses the “sand crisis” but also provides a solution for industrial waste disposal that would otherwise require vast landfill space.

   1. STEEL SLAG (SS)

      Steel slag is a solid, chemically complex industrial byproduct of steel manufacturing primarily composed of calcium, silicon, aluminum, and iron oxides. Global production is massive and rising and reaching up to 280 million tons annually and yet utilization rates remain low in many regions, leading to environmental concerns and land occupation from landfilling. To combat this, steel slag is increasingly recycled for cement production, road engineering, and soil improvement due to its high strength and alkaline properties. Furthermore, its porous structure makes it a promising material for wastewater treatment, where it effectively removes heavy metals through both physical and chemical adsorption.

   2. WASH BOTTOM ASH (WBA)

Washed Bottom Ash (WBA) is a refined industrial byproduct derived from the combustion of coal. While raw bottom ash contains high levels

of unburned carbon, chlorides, and heavy metals that limit its utility, the washing process which involves submersion, agitation, and drying transforms it into a high-quality construction resource. By removing these impurities, the material gains the chemical stability and physical durability necessary to meet strict engineering and environmental standards. Consequently, WBA serves as a sustainable, eco-friendly substitute for natural aggregates in concrete production, road base layers, and various civil engineering projects, effectively turning industrial waste into a valuable asset for the circular economy.

II CRITICAL REVIEW

This research paper investigates the technical and environmental feasibility of replacing natural sand in concrete with two industrial by- products: Wash bottom ash (BA) By testing various mixes with up to 60% replacement, the study found that a 30% replacement level yielded the highest mechanical strength and that levels up to 50% remained highly effective. Beyond strength, the experimental concrete demonstrated exceptional durability, showing “very low” chloride ion permeability and strong resistance to dicing salts. Microstructural analysis via SEM and XRD confirmed that these recycled materials do not negatively alter the cement’s hydration process, concluding the WBA is a sustainable, high-performance solution for the modern construction industry by Aggarwal et al. [1]

This research paper investigates the technical and environmental feasibility of utilizing coal bottom ash (BA) as a partial replacement for natural fine aggregates (sand) in concrete. Through experimental investigations of various concrete mixes with replacement levels ranging from 0% to 50%, the study found that while the inclusion of bottom ash initially decreases workability and density due to its higher water demand and lower specific gravity, the material’s pozzolanic action allows it to gain significant strength over time. Although the mechanical propertiesincluding compressive, splitting tensile, and flexural strengthremained lower than the control concrete in early stages, the strength gap narrowed considerably after 28 days. Notably, mixes with 30% and 40% bottom ash eventually achieved compressive strengths at 90 days that exceeded the 28-day strength of normal concrete. The researchers concluded that replacing up to 50% of natural sand with bottom ash is a viable and sustainable strategy for the construction industry, effectively repurposing industrial waste into a reliable building resource for various structural applications by Singh et al. [2]

This research paper investigates the technical and environmental feasibility of utilizing coal bottom ash (BA) as a partial replacement for natural fine aggregates (sand) in concrete. Through experimental investigations of various concrete mixes with replacement levels ranging from 0% to 50%, the study found that while the inclusion of bottom ash initially decreases workability anddensity due to its higher water demand and lower specific gravity, the material’s pozzolanic action allows it to gain significant strength over time. Although the mechanical propertiesincluding compressive, splitting tensile, and flexural strengthremained lower than the control concrete in early stages, the strength gap narrowed considerably after 28 days. Notably, mixes with 30% and 40% bottom ash eventually achieved compressive strengths at 90 days that exceeded the 28-day strength of normal concrete. The researchers concluded that replacing up to 50% of natural sand with bottom ash is a viable and sustainable strategy for the construction industry, effectively repurposing industrial waste into a reliable building resource for various structural applications by Olonade et al. [3]

The experimental results revealed that concrete containing up to 30% steel slag performed similarly to conventional concrete,

showing comparable stress-strain characteristics. While the inclusion of steel slag generally maintained the required strength standards, the researchers noted that the optimum replacement level was 30%, beyond which some properties began to deviate from the control mix. Ultimately, the paper concludes that steel slag is a technically feasible and eco-friendly alternative to natural aggregates, offering a way to reduce the depletion of natural resources while providing a productive use for industrial waste in the construction sector by Rajan et al. [4] This research paper provides a comprehensive review of the potential for utilizing Coal Bottom Ash (CBA) from Malaysian thermal power plants as a sustainable alternative to natural aggregates in the construction industry. As Malaysia shifts toward “greener” practices, the study addresses the environmental burden of CBA, which is currently produced in massive quantities and largely relegated to landfills by abubakar et al. [5]

The experimental study focused on concrete mixes with a constant water-to-cement ratio of 0.55, testing various replacement proportions to determine their impact on mechanical strength. The results indicate that WBA is a viable and sustainable alternative to natural aggregates, with the study identifying 30% replacement as the optimum level by Sami et al. [6]

This systematic review paper provides a critical evaluation of using Steel Slag (SS) as a sustainable alternative to natural river sand in concrete, addressing the global sand crisis and the environmental challenge of industrial waste disposal. The study synthesizes data on the fresh, mechanical, and durability properties of concrete containing steel slag, noting that while its angular

shape and rough texture can reduce workability often requiring the use of superplasticizers, the same characteristics enhance the mechanical interlocking within the concrete matrix. The review highlights that replacing sand with steel slag typically leads to improved compressive and tensile strengths, with many studies identifying an optimum replacement level between 30% and 50%. Furthermore, the paper examines durability aspects, finding that steel slag concrete often exhibits superior resistance to chloride penetration and abrasion compared to conventional mixes. However, the authors also caution about the potential for volumetric instability due to the presence of free lime and magnesia in certain types of slag, which can cause expansion if not properly treated. Ultimately, the paper concludes that steel slag is a high- potential, eco-friendly replacement for sand that can significantly enhance concrete performance while promoting a circular economy in the construction and steel industries by Tiong et al. [7]

This research article investigates the impact of replacing silica sand with steel slagan industrial by-producton the mechanical and environmental performance of Ultra-High-Performance Concrete (UHPC). The study evaluates various replacement levels (25%, 50%, 75%,

and 100%) and identifies a 50% replacement as the optimal threshold for maximizing performance. At this level, the UHPC achieved a peak compressive strength of 126 MPa (+13.5%), a flexural strength of 11.6 MPa (+20.8%), and a tensile strength of 7.2 MPa (+6.5%) compared to the reference mix. These improvements are primarily attributed to the pozzolanic reactivity of the steel slag, which reacts with calcium hydroxide to form additional calcium silicate hydrate (C-S-H), thereby densifying the cement matrix by Zadeh et al. [8]

Beyond the 50% replacement mark, however, the mechanical properties began to deteriorate. Scanning Electron Microscopy (SEM) analysis revealed that higher steel slag content led to a weakened bond between the cement matrix and the aggregates, as well as an accumulation of calcium hydroxide (CH) crystals that disrupted the material’s microstructural cohesion. Additionally, increasing the steel slag content consistently led to higher density and water absorption. Environmentally, the 50% replacement strategy offered significant benefits, including a 5.1% reduction in CO2 equivalent emissions. Ultimately, the study concludes that steel slag is a viable, cost-effective, and sustainable alternative to traditional silica sand in UHPC, provided the replacement is maintained at approximately 50% to ensure structural integrity by Bahmani et al. [9]

This research article presents a comparative study of the corrosion performance of sustainable Geopolymer Concrete (GPC) made with fly ash and 50% bottom ashagainst Ordinary Portland Concrete (OPC)1111. By utilizing industrial by-products and alkali activators instead of traditional cement, GPC addresses environmental concerns regarding $CO_{2}$ emissions and industrial waste management2222. The study highlights that GPC achieved a comparable 28-day compressive strength of 31.70 MPa (targeted at 35 MPa) relative to OPC, with evidence of a stronger binder-to-aggregate bond in the GPC specimensThe core findings, derived from accelerated corrosion tests using Half- Cell Potential (HCP) and Linear Polarization Resistance (LPR), demonstrate that GPC offers superior durability. Specifically, GPC exhibited a significantly lower corrosion rate (1020year) compared to OPC (4060year). While OPC specimens showed visible rust and longitudinal cracks after approximately 60 to 200 hours of exposure, GPC specimens remained free of cracks throughout the 300-hour test period. Furthermore, HCP analysis showed that GPC reached a 90% probability of corrosion much later (day 13) than OPC (day 7), indicating enhanced passivation and resistance to chloride-induced damage7. Ultimately, the study concludes that fly-ash and bottom-ash- based geopolymer concrete is a highly effective, sustainable alternative to conventional concrete for corrosion-prone environments by Morla et al. [10]

III.CONCLUSION AND RECOMMENDATION

The collective findings from the analyzed research indicate that industrial by-products like steel slag (SS), coal bottom ash (CBA), and waste foundry sand (WFS) are highly effective and sustainable partial replacements for natural fine aggregates in concrete. These materials not only address the growing scarcity of river sand but also provide significant technical advantages. Specifically, replacing sand with 30% to 50% steel slag in Ultra-High-Performance Concrete (UHPC) or foamed concrete can enhance compressive and flexural strength by densifying the cement matrix through pozzolanic reactions. Similarly, substituting natural sand with 30% washed bottom ash or a 30% combination of bottom ash and waste foundry sand provides optimal mechanical performance, achieving strengths comparable to or exceeding those of conventional concrete mixes. Furthermore, geopolymer concrete incorporating fly ash and bottom ash demonstrates superior durability, particularly in terms of corrosion resistance and chloride penetration, making it an ideal choice for harsh environmental conditions.Based on these results, it is recommended that the construction industry adopt these industrial by-products as standard supplmentary materials to promote “green” construction practices. For structural applications, a 30% replacement level is generally suggested as the ideal threshold to maximize strength without compromising workability or causing microstructural cohesion issues. It is also highly recommended to use washed or processed versions of these materials, such as washed bottom ash, to minimize carbon content and ensure consistent quality in the final concrete product. Future implementations should focus on optimizing mix designs for specific environmental exposures, leveraging the enhanced durability of geopolymer and slag-based concretes to extend the service life of infrastructure.

REFERENCES

1. Aggarwal, Y. and Siddique, R., 2014. Microstructure and properties of concrete using bottom ash and waste foundry sand as partial replacement of fine aggregates.

   Construction and Building Materials, 54, pp.210-223.

2. Singh, M. and Siddique, R., 2013. Effect of coal bottom ash as partial replacement of sand on properties of concrete. Resources, conservation and recycling, 72, pp.20-32.
3. Olonade, K.A., Kadiri, M.B. and Aderemi, P.O., 2015. Performance of steel slag as fine aggregate in structural concrete. Nigerian Journal of Technology, 34(3), pp.452-458.
4. Rajan, M.S., 2014. Study on strength properties of concrete by partially replacement of sand by steel slag. Int. J. Eng. Technol. Sci, 1(6), pp.96-99.
5. Abubakar, A.U. and Baharudin, K.S., 2012. Potential use of Malaysian thermal power plants coal bottom ash in construction. International Journal of Sustainable Construction Engineering and Technology, 3(2), pp.25-37.
6. Sani, M.S.H.M., Muftah, F. and Muda, Z., 2010. The properties of special concrete using washed bottom ash (WBA) as partial sand replacement. International Journal of Sustainable Construction Engineering and Technology, 1(2), pp.65-76.
7. Tiong, H.Y., Lim, S.K. and Lim, J.H., 2017. Strength properties of foamed concrete containing crushed steel slag as partial replacement of sand with specific gradation. In MATEC Web of Conferences (Vol. 103, p. 01012). EDP Sciences.
8. Zadeh, A.A., M. Puffer, S., Ahadisarkani, S. and Ahmadi, F., 2025. Steel Slag as Sand Replacement in Concrete: A Systematic Review of Fresh, Mechanical, and Durability Properties. Advances in Civil Engineering, 2025(1), p.3901578.
9. Bahmani, H., Mostafaei, H., Santos, P. and Fallah Chamasemani, N., 2024. Enhancing the mechanical properties of Ultra- High-Performance Concrete (UHPC) through silica sand replacement with steel slag. Buildings, 14(11), p.3520.
10. Morla, P., Gupta, R., Azarsa, P. and Sharma, A., 2021. Corrosion evaluation of geopolymer concrete made with fly ash and bottom ash. Sustainability, 13(1), p.398.