Optimizationof Fly Ash-Based Composite Cementitious Material Proportion Using Box-BehnkenResponse Surface Methodology

Abstract

To realize high-value synergisticutilization of the three major solid wastes from thermal power generation (flyash-FA, coal-fired slag-CS, desulfurizationgypsum-DG), a Box-Behnken response surface model was established with CS, DG,and cement as factors and FA as the matrix. Unlike existing research focusingon single or binary solid waste composites, this study systematically optimizedthe synergistic blending ratios of the three wastes without additionalactivation. The 7d/28d strength models showed significant statistical validity(R² = 0.9918/0.9979, p < 0.001). The optimal mixratio (CS 21.38%, DG 10.96%, cement 16.15%, FA 51.51%) achieved 7d strength of13.60 MPa and 28d strength of 19.07 MPa, with a model deviation rate below 2%.The statistical model results are deeply correlated with the mechanisms ofhydration and microstructural evolution: cement and DG drive early-stagehydration reactions to form rapid-strength products, while CS continuouslygenerates hydration gel through slow pozzolanic reactions to develop late-stagestrength. XRD/SEM analysis confirmed significant formation ofcalcium-aluminum-silicate hydrate (C-(A)-S-H), calcium hydroxide (CH), and ettringite (AFt), verifying full activationof pozzolanic substances in FA and CS. This study innovatively overcomesbottlenecks in the simultaneous high-value utilization of three thermal wastes,providing a scientific pathway for optimizing cementitious materials frommulti-source solid wastes.

Keywords

Responsesurface methodology / Fly ash / Coal-fired slag / Desulfurization gypsum / Composite cementitious material

Acknowledgments

Special thanks to Wu Z.J. and Xie X.Q. for their generous support of this research. We also extend our gratitude to our colleagues in the laboratory for their assistance and support.

Author Contributions

H.X.: Writing-original draft, Supervision, Conceptualization, Data curation. L.Z.: Writing—original draft, Investigation, Data curation. Z.Z. (Ziyu Zou): Writing—review & editing, Data curation. Z.Z. (Zecheng Zeng): review & editing, investigation. M.Z.: Investigation, Funding acquisition. Z.W.: Funding acquisition, Resources, Writing—review & editing, Project administration. X.X.: Writing—review & editing, Visualization.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The statement is required for all original articles which informs readers about the accessibility of research data linked to a paper and outlines the terms under which the data can be obtained.

Funding

This work was supported by the Yuelu Mountain Industrial Innovation Center Project in Changsha, China (2024YCII0104) and the Central Government Guidance Fund for Local Science and Technology Special Projects in China (2024ZYC022).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Bo L, Yang S, Liu Y, Zhang Z, Wang Y, Wang Y. Coal Mine Solid Waste Backfill Process in China: Current Status and Challenges. Sustainability 2023, 15, 13489. DOI: 10.3390/su151813489

[2] Falah M, MacKenzie KJD. Photocatalytic Nanocomposite Materials Based on Inorganic Polymers (Geopolymers): A Review. Catalysts 2020, 10, 1158. DOI: 10.3390/catal10101158

[3] Barbhuiya S, Das BB, Kapoor K, Das A, Katare V. Mechanical performance of bio-based materials in structural applications: A comprehensive review. Structures 2025, 75, 108726. DOI: 10.1016/j.istruc.2025.108726

[4] Li H, Zhang N, Yang J, Huang G, Lu M, Wang L. Chapter 17—Recycling of Textile and Fiber Wastes as Construction Materials. In Wastes to Low-Carbon Construction Materials; Wang L, Guo B, Ma B, Eds.; Woodhead Publishing: Cambridge, UK, 2025; pp. 521–560. Available online: https://www.sciencedirect.com/science/article/pii/B9780443273421000130 (accessed on 5 March 2026).

[5] Li H, Zhang N, Yang J, Wang L, Köberle T, Mechtcherine V. Synergistic reinforcement of recycled carbon fibers and biochar in high-performance, low-carbon cement composites: A sustainable pathway for construction materials. Cem. Concr. Compos. 2025, 162, 106148. DOI: 10.1016/j.cemconcomp.2025.106148

[6] Han X, Mu Z, Wang Z. Optimization control and economic evaluation of energy storage combined thermal power participating in frequency regulation based on multivariable fuzzy double-layer optimization. J. Energy Storage 2022, 56, 105927. DOI: 10.1016/j.est.2022.105927

[7] Wang P, Hu B, Tai N, Zhao L, Vafai K. Peak shaving auxiliary service analysis for the photovoltaic and concentrating solar power hybrid system under the planning-dispatch optimization framework. Energy Convers. Manag. 2023, 295, 117609. DOI: 10.1016/j.enconman.2023.117609

[8] Xu Z, Li C, Xiao B, Chen G. Development of slag-based filling cementitious materials and their application in ultrafine tailing sand filling. Constr. Build. Mater. 2024, 452, 138966. DOI: 10.1016/j.conbuildmat.2024.138966

[9] Ruan S, Liu L, Zhu M, Shao C, Xie L, Hou D. Application of desulfurization gypsum as activator for modified magnesium slag-fly ash cemented paste backfill material. Sci. Total Environ. 2023, 869, 161631. DOI: 10.1016/j.scitotenv.2023.161631

[10] Zhang P, Wu F, Gao Q, Zhang T, Wang Y, Qi X. Use of coal-fired slag in filling bodies with early strength for mining applications. J. Clean. Prod. 2023, 414, 137465. DOI: 10.1016/j.jclepro.2023.137465

[11] Zhang X, Zhang X, Shuai P, Su L, Cai G. Mechanical properties and microscopic characteristics of fly ash–slag composite backfill. Geomech. Geophys. Geo-Energy Geo-Resour. 2023, 9, 132. DOI: 10.1007/s40948-023-00664-7

[12] Chu F, Li C, Wu C, Wang Y. Research on the hydration process of solid waste–based cementitious materials and application in roadbase. Front Energy Res 2024, 11, 1348557. DOI: 10.3389/fenrg.2023.1348557

[13] Zhou J, Chen S, Das AK. Application of sludge as a sustainable material in building materials: A comprehensive review. J. Build. Eng. 2025, 111, 113434. DOI: 10.1016/j.jobe.2025.113434

[14] Das AK. Natural sea-based materials SBM-ECCs: Experimental, analytical, and machine learning approaches to early-age behavior and modulating factors. Appl. Soft Comput. 2026, 186, 114101. DOI: 10.1016/j.asoc.2025.114101

[15] Sahani K, Timsina AP, Tuladhar B, Sahani SK, Kumar Das A. Low cost upcycling of non-segregated plastic waste as building materials in Nepal: Experimental investigation and microstructural analysis. Constr. Build. Mater. 2025, 492, 142955. DOI: 10.1016/j.conbuildmat.2025.142955

[16] Das AK, Qi Y. High performance natural seawater coral sand ECC (HP-NSCS-ECC) in coastal conditions: Experimental characterization, microstructure, and sustainability. Constr. Build. Mater. 2025, 499, 143860. DOI: 10.1016/j.conbuildmat.2025.143860

[17] Das AK, Qiu J, Leung CKY, Yu J. A novel strategy to assess healing induced recovery of mechanical properties(HIRMP) of strain hardening/engineering cementitious composites(SHCCs/ECCs) in autogenous healing. Cem. Concr. Compos. 2023, 142, 105177. DOI: 10.1016/j.cemconcomp.2023.105177

[18] Das AK, Leung CKY. A strategy for in situ determination of self-healing state for strain hardening cementitious composites. Cem. Concr. Compos. 2020, 112, 103641. DOI: 10.1016/j.cemconcomp.2020.103641

[19] Li G, Zhou C, Ahmad W, Usanova KI, Karelina M, Mohamed AM, et al. Fly Ash Application as Supplementary Cementitious Material: A Review. Materials 2022, 15, 2664. DOI: 10.3390/ma15072664

[20] Ge Y, Liu X, Shui Z, Gao X, Zheng W, Zhu Z, et al. Design and Preparation Technology of Green Multiple Solid Waste Cementitious Materials. Materials 2024, 17, 1998. DOI: 10.3390/ma17091998

[21] Amsalu Fode T, Jande YAC, Kivevele T. Modelling and optimization of multiple replacement of supplementary cementitious materials for cement composite by response surface method. Clean. Eng. Technol. 2024, 19, 100735. DOI: 10.1016/j.clet.2024.100735

[22] Li Z, Lu D, Gao X. Multi-objective optimization of gap-graded cement paste blended with supplementary cementitious materials using response surface methodology. Constr. Build. Mater. 2020, 248, 118552. DOI: 10.1016/j.conbuildmat.2020.118552

[23] Wang K, Fu J, Wang J. The ratio optimization and hydration mechanism of multi source solid waste cementitious materials. Constr. Build. Mater. 2024, 411, 134267. DOI: 10.1016/j.conbuildmat.2023.134267

[24] An H, Wang L, Lv F, Fu R, Lu Y, Kong D. Multi-objective optimization of properties on polymer fiber-reinforced desulfurization gypsum-based composite cementitious materials. Constr. Build. Mater. 2023, 369, 130590. DOI: 10.1016/j.conbuildmat.2023.130590

[25] Das AK, Leung CKY, Barbhuiya S. Experimental investigation and machine learning-based modelling of shrinkage evolution due to natural sea sand on fiber reinforced cementitious composites. J. Sustain. Cem.-Based Mater. 2025, 14, 2145-2165. DOI: 10.1080/21650373.2025.2524763

[26] Das AK, Xiao J. Upcycling waste glass bottles as a binder within engineered cementitious composites (ECCs): Experimental investigation and environmental impact assessment. Clean. Mater. 2025, 16, 100311. DOI: 10.1016/j.clema.2025.100311

[27] Ogirigbo OR, Black L. Influence of slag composition and temperature on the hydration and microstructure of slag blended cements. Constr. Build. Mater. 2016, 126, 496-507. DOI: 10.1016/j.conbuildmat.2016.09.057

[28] Zheng W, Dong J, Wen J, Chang C, Li Y, Wang Q. Effect of desulphurization gypsum on hardening mechanism of the geopolymer produced with steel slag and granulated blast furnace slag. J. Mater. Cycles Waste Manag. 2025, 27, 159-169. DOI: 10.1007/s10163-024-02099-y

[29] Zhou Y, Xie L, Kong D, Peng D, Zheng T. Research on optimizing performance of desulfurization-gypsum-based composite cementitious materials based on response surface method. Constr. Build. Mater. 2022, 341, 127874. DOI: 10.1016/j.conbuildmat.2022.127874

[30] Aziz A, Stocker O, El Amrani El Hassani I-E, Laborier AP, Jacotot E, El Khadiri A, et al. Effect of blast-furnace slag on physicochemical properties of pozzolan-based geopolymers. Mater. Chem. Phys. 2021, 258, 123880. DOI: 10.1016/j.matchemphys.2020.123880

[31] Lee B, Kim G, Nam J, Lee K, Kim G, Lee S, et al. Influence of α-Calcium Sulfate Hemihydrate on Setting, Compressive Strength, and Shrinkage Strain of Cement Mortar. Materials 2019, 12, 163. DOI: 10.3390/ma12010163

[32] Poupelloz E, Gauffinet S, Nonat A. Study of nucleation and growth processes of ettringite in diluted conditions. Cem. Concr. Res. 2020, 127, 105915. DOI: 10.1016/j.cemconres.2019.105915

[33] Sevim O, Sengul CG. Comparison of the Influence of Silica-rich Supplementary Cementitious Materials on Cement Mortar Composites: Mechanical and Microstructural Assessment. Silicon 2021, 13, 1675-1690. DOI: 10.1007/s12633-021-01013-7

[34] Liu L, Tan J, Qiu H, Zhang J, Guo Y. Study on microstructural and mechanical properties of cementitious materials composed of fly ash and dacite powder. Front Mater 2024, 11, 1267197. DOI: 10.3389/fmats.2024.1267197