Use of Industrial Waste Materials in Sustainable Cement Manufacturing

Use of Industrial Waste Materials in Sustainable Cement Manufacturing
Abstract
Cement production is a major contributor to global carbon dioxide emissions, accounting for approximately 7–8% of anthropogenic CO₂ release. Simultaneously, industries such as metallurgy, power generation, chemical manufacturing, and mining generate billions of tonnes of industrial waste annually, most of which is landfilled or stockpiled. Utilizing industrial waste materials as supplementary cementitious materials (SCMs) to partially replace cement clinker represents a critical pathway for simultaneously mitigating the carbon footprint of the cement sector and addressing industrial waste disposal challenges. This report systematically reviews the mechanisms, performance characteristics, and engineering feasibility of typical industrial wastes—including fly ash, ground granulated blast furnace slag, red mud, carbide slag, and construction-derived powders—in cementitious systems. The findings demonstrate that many industrial wastes, after appropriate processing, possess significant pozzolanic activity or filler effects, capable of maintaining or even enhancing the mechanical properties and durability of cement-based materials at replacement levels of 15–50%, while reducing carbon emissions by 25–85%.
Keywords: Industrial waste; Supplementary cementitious materials; Sustainable cement; Circular economy; Pozzolanic activity; CO₂ reduction
1 Introduction
Cement is an indispensable binding material for modern infrastructure. However, its production process faces severe environmental challenges: both limestone decomposition and fuel combustion release substantial amounts of carbon dioxide, making the cement industry a key target for global industrial emission reduction. It is estimated that producing one tonne of ordinary Portland cement (OPC) emits approximately 0.8–1.0 tonnes of CO₂, with the global cement industry's annual emissions exceeding 2 billion tonnes. Meanwhile, industries such as metallurgy, power generation, and chemical manufacturing generate enormous quantities of by-products and residues that have long been regarded as environmental burdens, typically disposed of through stockpiling or landfilling.
Converting industrial waste into resources for cement production serves both as a waste management solution and a key strategy for emission reduction in the cement industry. The theoretical foundation of this pathway is "industrial symbiosis," wherein the waste of one industry becomes the raw material input for another, achieving maximum resource efficiency and minimum emissions at the system level. Within this framework, industrial by-products such as fly ash, slag, and red mud serve as supplementary cementitious materials (SCMs) to replace a portion of cement clinker, and have been extensively researched and applied globally.
This report aims to systematically review the current state of industrial waste utilization in sustainable cement manufacturing, focusing on material reaction mechanisms, the influence of replacement levels on performance, environmental benefits, and the bottlenecks and countermeasures for large-scale implementation.
2 Classification and Characteristics of Industrial Wastes
2.1 Fundamental Basis of Reactivity in Supplementary Cementitious Materials
The performance of industrial wastes as SCMs depends on their chemical composition, mineral phases, and physical morphology. Pozzolanic activity is the core functional mechanism of most SCMs: reactive silica and alumina in the material react with calcium hydroxide produced by cement hydration in an alkaline environment, generating additional C-S-H gel and aluminate hydrates, thereby contributing to strength and densifying the microstructure.
Reactivity is controlled by multiple factors. For glass-phase-dominated materials (such as slag and fly ash), the ratio of non-bridging oxygen to network formers is an important indicator describing the degree of glass depolymerization; higher network depolymerization correlates with greater reactivity. Calcium, as a network modifier, has the most significant influence on glass reactivity, while trace elements such as titanium and zirconium can significantly reduce glass dissolution rates even at low concentrations. Specific surface area is equally critical, though "reactive surface area" more accurately reflects the surface actually participating in reactions than total BET surface area.
Recent research has demonstrated that grinding process parameters—including grinding duration, mill filling, and classifier speed—exhibit clear dose-response relationships with performance evolution. Generally, longer grinding increases Blaine fineness and decreases median particle size (d50), enhancing dissolution and nucleation, advancing the main heat-release peak, and increasing total heat. However, excessive fineness increases water demand and paste viscosity, altering transport properties. The uniformity coefficient of the particle size distribution correlates positively with strength at all ages, as optimized PSD improves packing density and enhances multi-scale pore filling.
2.2 Major Types of Industrial Wastes
Fly Ash. A by-product of coal-fired power plants, primarily composed of glass microspheres with chemical composition dominated by SiO₂, Al₂O₃, and Fe₂O₃. Class F fly ash (low calcium) reacts relatively slowly, while Class C fly ash (high calcium) possesses self-cementing properties and reacts more rapidly. Morphologically, the spherical particles of fly ash improve concrete workability and provide micro-filler effects.
Ground Granulated Blast Furnace Slag (GGBFS). A by-product of the steel industry, formed by water quenching to create an amorphous structure with high calcium content and latent hydraulic properties. Slag reactivity is significantly higher than fly ash, making it one of the most mature SCMs currently in use. In cement-slag systems, slag both consumes calcium hydroxide and contributes to strength development through its latent hydraulic reaction.
Red Mud (Bauxite Residue). The primary by-product of alumina production. The EU alone generates over 7 million tonnes annually, yet less than 100,000 tonnes is recycled; most is landfilled because no large-scale sustainable reuse option currently exists. Red mud is rich in iron and alumina, with alkalinity presenting both challenges and opportunities for cementitious applications. The EU-funded ReActiv project has demonstrated that processed bauxite can substitute up to 30% of clinker, employing thermal activation, carbothermic vitrification, and reductive smelting processing routes. Life-cycle assessment estimated the 100-year global warming potential at 200 kg CO₂/t for co-calcined processed bauxite, 440 kg CO₂/t for vitrified, and 470 kg CO₂/t for smelted product.
Carbide Slag. A bulk solid waste from the acetylene chemical industry, primarily consisting of Ca(OH)₂ with content exceeding 80%. Its low cost makes it highly suitable as an alkaline activator and supplementary calcium source. The rapid dissolution of Ca(OH)₂ from carbide slag provides a sustained high-alkalinity environment, effectively disrupting the glassy network structure of other SCMs and promoting the dissolution of reactive silicon and aluminum components.
Construction and Demolition Waste Powders. Precast concrete block waste (PCBW) from rejected quality-control pieces and demolition activities represents a significant untapped resource. Research has shown that PCBW can be effectively used as SCM in replacements up to 20%, with the presence of mortar and adhered cement paste containing potentially un-hydrated cement particles that could become reactive after mechanical activation. Isothermal calorimetry results demonstrated that hydration of C₃S was monotonically enhanced with increasing PCBW replacement due to the filler effect.
Coal Gangue and Coal Waste. Coal mining and washing generate substantial solid waste. Thermally activated coal waste at 750°C reduces loss on ignition from 33% while retaining pozzolanic activity. However, the porous structure and irregular particle morphology of coal gangue cause significant water absorption, reducing workability—mitigated through synergistic blending with GGBFS.
3 Reaction Mechanisms and Synergistic Effects
3.1 Pozzolanic and Latent Hydraulic Reactions
The fundamental chemical mechanism underlying industrial waste utilization is the pozzolanic reaction: reactive SiO₂ and Al₂O₃ in the waste material react with Ca(OH)₂ (portlandite) liberated during cement hydration to form additional calcium silicate hydrate (C-S-H) and calcium aluminate hydrate phases. This reaction consumes portlandite, refines pore structure, and contributes to long-term strength development.
For latent hydraulic materials like GGBFS, the reaction is initiated by alkaline activation from the cement pore solution, but the material can subsequently sustain hydration through its own calcium content. The combination of GGBFS with pozzolanic materials creates complementary reaction pathways that enhance overall system performance.
3.2 Synergistic Effects in Ternary and Multi-Component Systems
Recent research has revealed significant synergistic effects when multiple industrial wastes are combined. A study on sugarcane bagasse ash (SCBA) and red mud (RM) demonstrated that while binary systems incorporating high dosages of solid waste underperformed—due to either low reactivity of raw SCBA or the inhibitory effect of RM on OPC hydration—ternary OPC-SCBA-RM systems achieved equivalent or slightly superior mechanical performance compared to plain cement. In these ternary systems, the early nucleation benefit from SCBA was suppressed by RM, yet SCBA contributed to later-age strength through continued pozzolanic reaction.
Similarly, the combination of coal gangue, carbide slag, and blast furnace slag in sulphoaluminate cement systems demonstrated that carbide slag provides the alkaline environment necessary to activate coal gangue's pozzolanic reactivity, while BFS enhances strength development and refines pore structure. The ternary system achieved excellent performance synergy and component compatibility, presenting a superior cost-performance ratio and lower carbon footprint.
3.3 Filler and Nucleation Effects
Beyond chemical reactivity, finely divided industrial wastes provide physical benefits through filler and nucleation effects. Higher specific surface area increases ionic supply and dissolution while furnishing more heterogeneous nucleation sites for C-S-H formation, thereby shortening the induction period and elevating the apparent reaction rate of silicate phases. Limestone surfaces often promote nucleation more strongly than quartz, suggesting that mineralogy modulates this effect.
Particle packing optimization through appropriate PSD selection improves paste density and reduces porosity. The filler effect is particularly significant in systems with high replacement levels, where the physical presence of fine particles compensates for reduced clinker content by providing additional nucleation sites and improving particle packing.