Search Results (508)

The growing demand for low-carbon cementitious materials has increased interest in natural zeolite as a supplementary cementitious material capable of reducing clinker consumption while modifying cement system performance. This study presents an integrated experimental evaluation of natural zeolite-modified cementitious materials by combining rheological behavior, hydration, compressive strength, density, scanning electron microscopy (SEM), and X-ray diffraction (XRD) within a single experimental framework. Natural zeolite was used as a partial replacement for cement at dosages of 5–12.5 wt.%. The results showed that zeolite significantly affected both fresh-state and hardened-state properties. Zeolite increased the rheological resistance of fresh mixtures, shifted the exothermic hydration peak from 12 h to 8–10 h, and reduced the maximum hydration temperature by approximately 8–12%. Among the investigated compositions, the mixture containing 7.5% zeolite exhibited the highest compressive strength (44.9 MPa at 28 days) together with increased hardened density, suggesting more efficient particle packing and matrix development than the reference mixture. SEM observations indicated a more uniform distribution of hydration products in mixtures containing moderate zeolite dosages, while XRD analysis confirmed changes in the crystalline phase assemblage associated with zeolite incorporation. The results demonstrate that moderate natural zeolite replacement, particularly at 7.5%, provides an effective balance between rheological behavior, hydration characteristics, mechanical performance, and microstructural development, highlighting its potential as a sustainable supplementary cementitious material for low-carbon cement-based composites. Full article

Magnesium–rich environments are frequently encountered in cementitious systems, including the use of high–Mg raw materials in clinker production, cement–clay interfaces relevant to nuclear waste disposal, and exposure of cement–based materials to seawater, where progressive decalcification can substantially alter the structure and durability of calcium aluminosilicate hydrate (C–A–S–H) phases. In this study, density functional theory (DFT) calculations were employed to investigate the combined effects of interlayer and intralayer partial decalcification, Mg²⁺ substitution, and reinforcement with epoxy– and hydroxyl–functionalized reduced graphene oxide (rGO) on the structural stability and elastic properties of alkali charge–balanced C–A–S–H under dry and hydrated conditions. Adsorption–energy calculations reveal thermodynamically favorable interactions between functionalized rGO and silicate hydrate species in the presence of Mg²⁺, with hydroxyl/rGO promoting stronger interfacial stabilization and epoxy/rGO preserving greater graphene lattice integrity. The results demonstrate that Mg²⁺ substitution together with rGO intercalation generally enhances the mechanical response of partially decalcified structures through structural densification and interfacial cohesion. Relative to dry systems, hydration further improves elastic performance, increasing Young’s modulus and bulk modulus by 1–11% and 4–19%, respectively, for interlayer decalcified nanocomposites, while intralayer configurations exhibit stronger but model–dependent enhancements of up to ≈22% and ≈33%. Compared with untreated systems, rGO–treated nan–composites exhibit enhanced stiffness, with Young’s modulus and bulk modulus increasing by up to ≈22% and ≈15%, respectively. Overall, these findings provide atomistic insights into stabilization mechanisms in partially decalcified alkali charge–balanced C–A–S–H systems and identify Mg²⁺–rGO incorporation as a promising strategy for mitigating decalcification–induced degradation in durable low–carbon cementitious nanocomposites. Full article

Accelerated carbonation of cement-based materials offers a promising route for CO₂ sequestration driven by waste heat co-emitted from cement and power plants; however, existing kinetic models typically describe the low-temperature gas–liquid–solid regime near 100 °C and the high-temperature gas–solid regime near 600 °C in isolation, limiting their applicability to plant-scale reactor design. This study proposes a unified dual-regime kinetic framework spanning 20–700 °C. The low-temperature branch couples Henry’s-law CO₂ solubility, a sigmoidal water-film stability function, and an Arrhenius ionic reaction term, whereas the high-temperature branch integrates shrinking-core surface reaction and product-layer diffusion with an attenuation term near the CaCO₃ decomposition onset. Seven parameters were calibrated by bounded least squares against a 51-point temperature dataset compiled from the author’s previously published carbonation experiments. The calibrated model reproduced the bimodal temperature dependence of the carbonation degree (R² = 0.62; RMSE = 0.083), with peaks near 100 °C and 640 °C, and predicted reactor volumes of order-of-magnitude 150–200 m³ for a 1 Mt/y cement plant under three waste-heat operating points. The framework bridges particle-scale kinetic and plant-scale design, and identifies mixing as the dominant operational sensitivity at the clinker-cooler condition. Full article

Cement clinker production is a thermal- and emissions-intensive process requiring high-temperature heat for drying, calcination, and sintering. This review provides a process-based assessment of refuse-derived fuel (RDF), solid recovered fuel (SRF), tire-derived fuel (TDF), and biomass as partial substitutes for coal and petcoke in modern dry-process cement kilns. The study synthesized the evidence from plant-scale trials, pilot and laboratory experiments, process modeling, computational fluid dynamics, emissions studies, life-cycle assessment (LCA), techno-economic analysis (TEA), and regional case studies to evaluate alternative fuels across fuel properties, kiln-zone suitability, process stability, clinker quality, emissions performance, and environmental outcomes. The review shows that stable co-processing generally requires fuels with net calorific values above 14 MJ kg⁻¹ and moisture contents below 15%, although TDF can provide 26–33 MJ kg⁻¹ and sustain high-energy kiln duty when sulfur, zinc, and steel residues are controlled. RDF, SRF, and biomass require pre-processing, homogenization, calibrated dosing, and continuous fuel-quality monitoring to limit incomplete burnout, deposit formation, volatile circulation, and clinker-quality variation. LCA studies show that 20% RDF thermal substitution can reduce global warming potential by about 3.3–4.2%, increasing to approximately 6.7% when avoided landfill methane credits are included. Modern abatement systems can maintain particulate matter at about 10–30 mg Nm⁻³ and PCDD/F below 0.1 ng TEQ Nm⁻³ under stable operation. The review concludes that alternative fuels are quality-dependent co-processing options whose mitigation role is complementary to clinker-factor reduction, energy-efficiency improvement, low-clinker binders, electrified heating, oxy-fuel calcination, and carbon capture. Full article

The development of sustainable grouting materials is essential for enhancing underground strata stability while reducing the environmental impact associated with ordinary Portland cement (OPC). This review summarizes previously published studies on alkali-activated grouting materials (AAGMs) prepared using fly ash (FA) and ground granulated blast furnace slag (GGBFS), activated by sodium hydroxide and sodium silicate solutions. A comprehensive literature-based analysis was conducted to evaluate both fresh and hardened properties, including fluidity, setting time, yield stress, compressive strength, and durability-related performance. Particular attention was given to the influence of FA-GGBFS proportions and activator composition on rheological behaviour, mechanical performance, and engineering applicability. The reviewed studies indicate that increasing GGBFS content significantly accelerates geo-polymerization and setting behaviour and enhances early-age strength development due to its higher calcium reactivity. In contrast, FA contributes to improved workability and flowability, attributed owing to its spherical particle morphology and slower reaction kinetics. The reviewed literature further suggests that balanced FA–GGBFS alkali-activated systems can provide a favourable combination of fluidity, injectability, setting behaviour, and mechanical performance, making them particularly suitable for underground grouting and rock mass reinforcement applications. Compared with conventional OPC-based grouts, AAGMs demonstrate superior mechanical performance together reduced environmental impact through the utilization of industrial by-products and reduced clinker consumption. However, several critical challenges still hinder the large-scale implementation of alkali-activated grouting materials in underground mining, particularly with respect to field-scale validation, shrinkage mitigation, safe handling of alkaline activators, and the current lack of standardized specifications and design guidelines for underground grouting applications. These findings provide a robust scientific basis for the design and application of eco-efficient grouting materials in deep underground mining environments and support the advancement of sustainable practices in underground engineering. Full article

Steel slag is a major high-temperature by-product of steelmaking. Stockpiling can cause persistent burdens. Cr(VI) leaching, particulate emissions, and land occupation are key concerns. Many treatment and utilization processes exist. Most studies still assess them one by one. This study compares five representative processes in a consistent life-cycle framework: hot slag splashing (HS), heat recovery (HR), molten slag reconstruction (MSR), mineral carbonation (MC), and cement co-processing (CP). This study applies ReCiPe 2016 and USEtox. This study reports midpoint impacts, endpoint damages, normalization, and sensitivity analysis. The endpoint results show that HS has the largest human-health damage (5.2 × 10⁻⁶ DALY·t⁻¹). The endpoint results show that HS also has the largest ecosystem damage (3.4 × 10⁻⁶ species·t⁻¹). The endpoint results show that CP and MC have the lowest human-health damages (0.5–0.7 × 10⁻⁶ DALY·t⁻¹). The endpoint results show that CP and MC provide net resource credits (−0.9 to −1.2 USD2013·t⁻¹). MSR reduces toxicity through high-temperature immobilization. MSR also increases resource damage (4.5 USD2013·t⁻¹) because the process requires high energy input. MC can achieve net-negative greenhouse-gas results when CO₂ fixation exceeds ~80%. CP shows stable benefits through clinker substitution. Sensitivity analysis identifies process-specific parameters as dominant drivers. The results support process selection and process improvement, and the results help limit burden shifting. Full article

This study investigated the feasibility of using hydroxyapatite (HAp) derived from pyrolyzed waste chicken bones as a sustainable cement replacement material for cement mortar. Commercial tricalcium phosphate (TCP), which belongs to the same calcium phosphate family but possesses distinct crystalline characteristics, was used as a comparative material. HAp and TCP were incorporated as partial cement replacements at 2, 5, 10, and 20% by weight, and the workability, compressive strength, flexural strength, microstructure, and CO₂ emission characteristics of the resulting mortars were evaluated. The results showed that low replacement ratios improved early-age strength owing to the micro-filler effect of fine calcium phosphate particles. In particular, the HAp mixtures exhibited superior long-term performance compared with the TCP mixtures, with the 2% HAp mixture achieving the highest compressive strength of 54.5 MPa at 56 days. Flexural strength results showed a similar trend, with HAp effectively suppressing microcrack propagation through improved matrix densification and interfacial bonding. However, replacement ratios exceeding 10% reduced mechanical performance due to cement dilution, increased porosity, and particle agglomeration. SEM observations confirmed that HAp replacement levels of 2–5% densified the mortar matrix, whereas excessive replacement caused localized agglomeration and microstructural defects. The carbon emission assessment indicated that pyrolysis reduced direct CO₂ emissions compared with incineration by immobilizing part of the carbon in solid char; however, laboratory-scale pyrolysis increased total emissions because of high electricity consumption. Nevertheless, process integration with cement clinker production could enable waste valorization and carbon reduction by utilizing existing high-temperature kiln systems. Overall, chicken bone-derived HAp–carbon composite demonstrated strong potential as an eco-friendly cement replacement material, with an optimal replacement ratio of 5% or less. Full article

The generation of slag from copper smelting is between 40 and 45 Mt per year. However, the utilisation of this material in large-scale applications remains limited. This study evaluates the combined use of copper slag as a fine natural aggregate substitute (50, 75, and 100%) and natural mordenite-type zeolite as a partial cement replacement (25, 40, and 55%) in the development of sustainable mortars. The samples were characterised using XRF, particle size distribution, and density analysis, and sixteen mixtures were produced. The consistency and water demand in fresh state, the flexural and compressive strength at 7 and 28 days, and the porosity measurements of the hardened mortars were analysed. The results demonstrate that zeolite significantly increases water demand, leading to higher porosity (27–34%) and reduced mechanical strength (14–31 MPa). Conversely, copper slag decreases the water-to-cement ratio and produces denser matrices with the lowest porosity values (8–13%), achieving compressive strengths at 28 days that are higher (53–58 MPa) than the reference mortar (50 MPa). In hybrid mixtures, slag partially mitigates the porosity increase induced by zeolite, revealing a favourable interaction between both materials. Mixtures containing 75–100% copper slag and 25% zeolite (MZ-8 and MZ-9) exhibited balanced porosity (18–21%) and mechanical performance (38–39 MPa), confirming their suitability for mortar applications. The findings demonstrate that the joint incorporation of copper slag and natural zeolite is a viable strategy for producing eco-efficient mortars while reducing clinker and natural aggregate consumption. Full article

Granulated blast furnace slag is a commonly used supplementary cementitious material in cement-based materials. The raw materials for ironmaking and the cooling process affect its composition, thereby influencing its reactivity. Three types of slag were selected and incorporated at replacement ratios of 15%, 30%, and 50% to investigate the influence of chemical composition on the activity index of slag at different ages and the mechanisms. The results indicate that in the early hydration stage, slag primarily plays a mechanical filling and dilution role (inert volumetric occupation without significant heterogeneous nucleation), while the pozzolanic effect dominates at later stages. Al₂O₃ in the slag is activated at early ages to form ettringite; at replacement ratios of 30%, C-A-S-H gel is also formed at later ages; when the replacement ratio reaches 50%, the significant reduction in cement clinker content leads to dropping in system alkalinity—corresponding to a 50% reduction in cement-derived Ca(OH)₂, the activation of Al₂O₃ in the slag is not significant at early ages. The effects of glass content, alkali content, specific surface area, CaO + MgO content, quality coefficient, and basicity coefficient on the reactivity become prominent at longer ages. No additional crystalline phases beyond those present in pure cement paste were detected in the cement paste after slag incorporation. This study provides a theoretical basis and data support for the high-value utilization of industrial solid waste in green building materials. Full article

Ion diffusion, the precipitation of hydration products, and interactions between different reactive particles are critical for optimizing the design of low-carbon cementitious systems. However, at the sub-micron scale, the complex spatial and chemical interactions among diverse components at an early age remain challenging to quantify. In this study, a machine learning-assisted BSE-EDS analytical method was applied to quantify both the phase assemblage and the spatial element features of cement–fly ash–slag ternary systems. The equidistant strip delineation of single-particle and rectangular inter-particle path methods were employed to quantify ionic diffusion gradients in the ternary systems. Single-particle strip analysis quantified the hydration front of clinker, slag and fly ash, while inter-particle analysis identified a persistent calcium-starvation zone at slag–fly ash interfaces. This region is characterized by exceptionally high Si/Ca ratios and a lower average atomic number and material density due to ionic diffusion limitations. These findings identify the slag–fly ash interface as the primary microstructural weak link, providing a robust methodology for capturing the chemical heterogeneities and optimizing the design of sustainable cementitious materials. Full article

Phosphogypsum (PG) is an industrial solid waste whose use in cementitious materials is limited by strength reduction at high dosages. This study evaluated a clinker-free multi-solid-waste binder containing 40 wt.% PG for cemented paste backfill using steel slag powder (SSP) and granulated blast-furnace slag (GBFS) as co-binders, with phosphate mine tailings and slime as aggregates. Uniaxial compressive strength (UCS), X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance were combined with image-based pore-structure sensitivity analysis to examine the relationships among hydration products, pore evolution, and strength development. The results showed that AFt and C–S–H-like gels were associated with pore refinement and strength gain. All mixtures reached UCS values above 0.5 MPa at 7 days and 1.0 MPa at 28 days. The A2 mixture achieved the highest 7-day UCS of 0.8 MPa, whereas A1 showed the highest 28-day UCS of 1.6 MPa. Porosity, pore probability entropy, and fractal dimension were negatively correlated with UCS, with pore probability entropy showing the highest sensitivity to 7-day strength. These findings support the use of high-PG clinker-free binders for targeted phosphate-mine backfill. Full article

The cement industry is one of the most energy- and emission-intensive sectors and plays a crucial role in achieving climate neutrality and sustainability objectives. This study examines waste management practices in cement production within the framework of the circular economy and low-carbon transition, with particular emphasis on Polish cement plants operating under EU environmental regulations. Particular attention is given to the use of waste as alternative fuels and secondary raw materials, as well as to the economic and environmental implications of EU climate policy instruments. The research methodology includes an analysis of key emission sources such as clinker production, fuel combustion, and raw material transport and an evaluation of technological and organizational measures aimed at improving energy efficiency and reducing emissions. The empirical analysis is based primarily on operational observations from selected Polish cement plants operating under EU ETS conditions and combines plant-level operational evidence with comparative sectoral data and scenario-based techno-economic assessments related to selected low-carbon technologies. The results suggest that increasing the use of waste-derived fuels and materials may contribute to emission reduction, lower reliance on non-renewable resources, and improved circularity in cement production systems operating under advanced regulatory conditions. Furthermore, the findings highlight the potential for synergies between environmental performance and economic competitiveness. The study underscores the importance of coherent regulatory frameworks and continued investment in low-emission and circular technologies to ensure the long-term sustainability and viability of the cement industry. Full article

This study evaluates the technical feasibility, environmental sustainability, and economic viability of producing sulfoaluminate cement (SW-SAC) by co-utilizing bauxite and industrial solid wastes—phosphogypsum, calcium carbide residue (CCR), and red mud—with the solid wastes accounting for approximately 75% of the raw meal. CCR replaces limestone as the primary CaO source, releasing H₂O instead of CO₂, while phosphogypsum supplies SO₃; the raw meal is directly calcined in a single step at 1300–1350 °C, 100–150 °C below that of ordinary Portland cement (OPC). Calcination temperature and holding time were optimized through phase analysis, microstructural observation, free lime (f-CaO) determination, and strength testing. SW-SAC meeting the 42.5 strength class was then prepared using phosphogypsum as a setting regulator and phosphorus slag or limestone powder as Supplementary materials. X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM) were used to examine hydration products and microstructural evolution. The optimized clinker was dominated by ye’elimite (${\mathrm{C}}_4{\mathrm{A}}_3\overline{\mathrm{S}}$) and belite (C₂S). Phosphorus slag favored the formation of gel-like products at later ages, whereas limestone powder promoted ettringite (AFt) stabilization and monocarboaluminate (Mc) formation. SW-SAC exhibited a lower carbon footprint than both Type P·I Portland cement and conventional SAC, and a lower production cost than conventional SAC. These results demonstrate a promising low-carbon route for high-value utilization of industrial solid wastes. Full article

This study investigates the reuse of mussel shell waste as a secondary raw material in bio-cement mortars designed for the additive manufacturing of artificial reefs for marine habitat restoration. The novelty of the research lies in combining a high recycled shell content (60 wt.%), low-clinker cement, and two 3D-printing techniques: Extruded Material Systems (EMS) and Powder-Based Systems (PBS). Mechanical performance was evaluated through flexural and compressive tests after 7, 28, and 91 days under both air and freshwater curing conditions, while environmental impacts were assessed through Life Cycle Assessment (LCA). The LCA evaluated both the environmental performance of shell-based mixtures compared with conventional materials and the impacts associated with the investigated fabrication techniques. The best-performing bio-mixtures achieved compressive strengths up to 46.01 MPa and flexural strengths up to 9.91 MPa after freshwater curing, demonstrating the suitability of shell-based mortars for submerged applications. LCA results showed reduced impacts in land use and mineral resource depletion compared with conventional mixtures, despite slightly higher energy and water demands associated with shell pre-treatment. The results demonstrate the technical and environmental feasibility of integrating aquaculture waste into sustainable 3D-printed marine restoration solutions. Full article

Rapid urbanization has increased the demand for building materials, depleting natural resources used in cement production and prompting the use of alternative and waste materials. This research verifies that eggshell powder waste can fully replace limestone in clinker synthesis. Five clinkers were produced using eggshell powder, aluminum sources (bentonite, zeolite, fly ash, and kaolinitic–illitic clay), Fe-slag, and quartz sand, with mechanical preprocessing (10–30 min) before sintering at 1300 °C. Experimental tests assessed the effects of mix design and mechanical activation on clinkerization, phase formation, temperature, and mechanical properties. XRD, FTIR, and SEM/EDS confirmed consistent phase compositions and primary cement minerals. Aluminum source raw materials contributed significantly to tricalcium aluminate and tetracalcium aluminoferrite formation. Eggshell and fly ash promoted tricalcium silicate and dicalcium silicate synthesis, enhancing cement strength at early and late ages. Longer mechanical pretreatments hindered clinkerization. Eggshell-based cements untreated or pretreated for 10 min are suitable for structural concrete; 20–30 min pretreatment is appropriate for low-demand or non-structural applications. The proposed methodology reduces clinker manufacturing temperature by about 100 °C from the typical range of 1400–1450 °C while maintaining mechanical properties comparable to ordinary Portland cement. Full article