The effect of metakaolin on the properties of MSWI fly ash-slag binder: Compressive strength and chloride ions immobilization.

Evaluation of alternative bed materials in fluidized bed incineration for ash recycling as supplementary cementitious material.

Achieving cleaner resource recovery by adding biochar into MSWI fly ash/coal fly ash-based cementitious materials: Immobilization capacity, hydration mechanism, and carbon sequestration potential

This study investigates the potential of Fe-bearing magnesium silicate glasses as alternative supplementary cementitious materials (SCMs) for reducing CO 2 emissions in Portland cement production, given the limited supply of traditional SCMs. The glass powders were synthesized using a low-temperature sol-gel process and ascorbic acid (AA) as a reducing agent. This route enables controlled partial reduction of Fe 3+ to Fe 3+ and stabilizes a fraction of the reduced species during heat treatment, without requiring strongly reducing gases (e.g., H 2 or CO). The reactivity of the glasses was evaluated through batch dissolution tests revealing significantly higher elemental solubility for the glasses synthesized with AA compared to those produced without additives. By combining dissolution experiments with 57 Fe Mössbauer spectroscopy and XPS, we establish a direct link between Fe redox state/coordination (Fe 2+ and tetrahedral vs. octahedral Fe 3+ ), silicate network depolymerization, and glass reactivity relevant for SCM use. The higher reactivity is particularly pronounced at low Fe concentrations, attributed to the reduction of Fe 3+ to Fe 2+ , which acts as a network modifier and enhances the solubility. While the solubility slightly decreases with higher Fe concentrations among AA-assisted glasses, it remains remarkably higher than in glasses synthesized without AA. This is attributed to a greater proportion of octahedral Fe 3+ , facilitated by chelation between AA and Fe. Tetrahedral Fe 3+ acts as a network former, whereas octahedral Fe 3+ acts as a network modifier that depolymerizes the silicate network and enhances elemental solubility. Overall, AA-assisted glasses with intermediate Fe contents (Fe/(Fe+Mg) = 7−15 mol%) exhibit the highest reactivity, attributable to their higher Fe 2+ fraction in the network, making them the most promising candidates for low-CO 2 cement applications. • Reactive Fe 2+ /Fe 3+ Mg-Si glasses are produced by a rapid AA-assisted sol-gel route. • AA alters Fe ion behavior and promotes glass depolymerization, enhancing reactivity. • Mössbauer and XPS link Fe speciation and Q n distributions to dissolution. • AA-optimized Fe-Mg-Si glasses reach 85% Si solubility, showing strong SCM potential.

Synchrotron X-ray techniques have been extensively applied to characterise the mineralogy of anhydrous cementitious materials, the hydration processes and products in cementitious systems, and the alterations induced by different environmental exposure conditions. However, with changes in cement compositions and performance requirements, and an increased focus on materials design for sustainability, there is now strong emphasis on the use of advanced analytical tools to bring fundamentally based, multi-scale, multi-modal, spatially-resolved and/or time-resolved understanding of the physico-chemical factors influencing cementitious materials in the fluid, hardening and cured states. Beamline-based analysis complements conventional laboratory techniques, bringing unique capabilities to develop high-level insights. Here we provide a critical overview of the application of synchrotron radiation-based techniques to cementitious materials, and the opportunities and research needs to unlock their full potential for their use in future cement materials research, including issues related to handling and processing the very large datasets that can be generated.

Ambient-cured one-part geopolymer systems from industrial by-products: A sustainable chemistry pathway for low-carbon cementitious materials

Synergistic effect of binary metakaolin–sugarcane bagasse ash blends as supplementary cementitious materials

The rising problem of plastic waste, coupled with a shortage of construction materials, has prompted research into the replacement of traditional aggregates with recycled plastic aggregates (rPA) in cementitious structures. However, the impact of the highly alkaline pore solution present in cement on the long-term stability and performance of rPA is still not fully understood. This research examined the alkaline stability of two types of commonly recycled plastics that increasingly serve as aggregate substitutes in concrete: polyethylene terephthalate (rPET) and high-density polyethylene (rHDPE) in two size ranges, when exposed to extremely alkaline conditions. The effects of exposure to simulated alkaline cement pore solutions on rPA stability were analysed by assessing alterations to polymer mass, surface features, functional groups, and crystallinity. Prolonged exposure (up to 75 days) to simulated cement pore solution significantly decreased the stability of rPA, while fine particle sizes underwent faster degradation, losing up to 40 % of weight. Recycled HDPE demonstrated greater alkali resistance than rPET, suggesting better suitability as an alternative aggregate in concrete, although factors like surface hydrophobicity should be considered. The amorphous regions of rPET surfaces proved more susceptible to hydroxyl reactions compared to crystalline regions, resulting in inferior stability of rPET compared to rHDPE, and therefore raises questions about the use of rPET as an alternative aggregate. Overall, this study elucidated the physical and chemical stability of recycled plastics in alkaline cementitious matrices, revealing how plastic type, intrinsic properties, particle size, and exposure duration govern their suitability as aggregate replacements.

Development of geopolymer with red mud, fly ash, calcium carbide slag, and phosphogypsum as a step toward low-carbon building materials.

Mineral surfaces in contact with aqueous solutions develop an electric double layer (EDL) through surface (de-)protonation reactions and adsorption of ions, diffusion, and electrostatic forces, resulting in a Stern- and a diffuse layer of ions. Most current models used for surface speciation calculations do not consider changes in surface chemistry caused by charge regulation effects, i.e. effects of interacting EDLs of surfaces in close proximity. Charge regulation modeling requires equilibrium calculation of every involved surface simultaneously, while also solving the Poisson-Boltzmann equation (PBE) to quantify electrostatic interaction. Since analytical solutions of the PBE for complex geometries do not exist it becomes necessary to solve such problems numerically. A Python code is presented that combines a general chemical speciation code, Three Plane Surface Complexation Model, and a Finite Element solution of the PBE on two-dimensional domains. The Finite Element PBE solver is benchmarked against analytical solutions and the speciation code is benchmarked against a PHREEQC model as well as an existing 1D charge regulation code. A test case involving charge regulation in a corner of two perpendicular surfaces is modeled. Charge regulation modeling on a nanoscale enables simulations of the electrostatic environment and surface chemistry in nano-confined systems and interactions of nanoparticles. This may also improve simulations of environmental and biological systems, cementitious materials and modeling of the electrostatic environment and sorption on nanoporous clay materials. Such information can be vital for the in depth understanding of natural and engineered barrier systems of nuclear waste repositories or other environmental scenarios.

Functional contribution and optimization of mix proportion of coal gangue, slag, and fly ash in the preparation of alkali-activated backfill materials.

This comprehensive review examines the application of fractal theory and technology in the study of cementitious materials, with a focus on cement and concrete. We begin by introducing the fundamental concepts of fractal geometry and the various fractal dimensions used to quantify material features. We then explore how fractal analysis has been applied to key aspects of cementitious materials, including pore structure, particle size distribution, fracture surfaces, and crack propagation. Each section highlights the methodologies employed, the insights gained, and the implications for material design and performance. Additionally, we discuss the use of fractal-based techniques in the non-destructive testing and monitoring of structures. Finally, we address the challenges and limitations of fractal approaches and propose future directions for research in this interdisciplinary field. Fractal theory can become a useful tool in the study of cementitious materials, aiding a deeper understanding of their physical properties and long-term durability, and guiding the design of more durable and efficient construction materials by giving engineers the required knowledge on the technology and its limitations.

Accelerated carbonation curing of cementitious materials: a systematic review of performance, limitations, and industrial feasibility

The limited high-temperature resistance of Ordinary Portland Cement (OPC) remains a critical challenge for fire-exposed and industrial concrete structures. Its performance deterioration above 500 °C is associated with dehydration and recrystallization of hydration products, leading to structural degradation of the cement matrix. To address this limitation, partial clinker replacement with fly ash combined with sodium water glass activation was proposed to enhance thermal stability. Physico-chemical analysis revealed the absence of portlandite and the formation of C-A-S-H and zeolite-like N–C–A–S–H phases in the fly ash-containing alkali-activated Portland cement. Upon heating, C-A-S-H phases sintered into stable high-temperature calcium aluminosilicate phases and zeolite-like phases underwent topotactic recrystallization into feldspathoid-type structures, preserving matrix integrity at high temperatures. The optimized composition region of cement system (fly ash—12.0–16.5 wt. %, density of water glass—1220–1240 kg/m3) was characterized by residual strength ≥ 50%, while compressive strength at 28 days was ≥80 MPa, exceeding the residual performance typically reported for conventional OPC systems under similar conditions (5–35%). The study was devoted to revealing the potential of low-emission Portland cements in high-temperature-resistant concretes through the utilization of fly ash. The mechanism that controls the compressive strength and temperature resistance of such cements has been demonstrated.

The greening of cement industry has become a necessity and obligation in many countries and the Global Green Cement market is projected to grow at a Compound Annual Growth Rate of 9.9% in the 2024-2032 period. The race for more sustainable concretes includes a number of key strategies, such as the substitution of cement/clinker with other cementitious materials. In the current research a CEMI (complying with EN197-1:2011) based industrial mix of self-compacting concrete (SCC) is modified with an experimental mix based on CEMII/B-M(P-W-L)42.5N conforming to EN 197-1:2011. The experimental mix presents a dual reduction in CO2 footprint, since not only it is formulated with CEMII, instead of CEMI, but it also contains 320 kg of CEMII/m 3 instead of 420 kg of CEMII/m 3 , by substituting the remaining mass of binder with emery powder. nanoparticles of silicon dioxide (nanosilica) and 12 mm polypropylene fibres were also added. The 7-day compressive strength reached 45 MPa and the 28-day strength reached 51 MPa, marginally lower than that of the industrial mix (60.3 MPa). The performance of nanosilica is discussed. Selected fresh properties in terms of density, slump-flow, air entrainment and strength testing, coupled with surface morphology observations with the use of stereo microscopy shed light into the potentials of such sustainable SCC mixes.

Soil improvement involves mechanical mixing of cementitious binders into natural soils. To reduce carbon dioxide emissions, considerable research efforts are made on supplementary cementitious materials to replace the use of cement. However, different laboratory mixing methods are used, and few studies have compared how these methods affects the strength and stiffness development. This paper presents comparative results of the wet and dry mixing methods, that is mixing a binder in slurry and in dry form, respectively. A natural soil was improved with mixtures of cement, ground-granulated blast-furnace slag, and paper sludge ash (PSA), designed and statistically analysed using a response surface methodology and hypothesis testing. Results showed insignificant differences at low final water to binder ratio (wbr). At higher wbr, the dry method with high PSA proportions yielded 2.4–4.4 times higher strengths than the wet method. The differences were attributed to varying binder dispersion, that is mixabilities and effects of low binder concentrations. The findings shows that the type of laboratory mixing method must be considered in soil improvement studies, particularly when using supplementary cementitious materials in low quantities.

The utilization of cement is one of the primary sources of carbon emissions in concrete, driving the search for sustainable alternative materials. Although extensive research has been conducted on the use of agricultural waste as supplementary cementitious materials (SCMs), the effects of coconut shell ash (CSA) and coir fiber (CF) on concrete properties have not been extensively investigated. This study systematically investigates the influence of CSA as a SCM (0–20%) and CF as a reinforcement material (0–0.32%) on the workability, density, compressive strength, flexural strength, splitting tensile strength, and failure modes of concrete, complemented by microstructural mechanism analysis. The cement and CSA were characterized using XRF, XRD, and SEM. The results indicate that the incorporation of both CSA and CF reduces the workability and density of concrete. For concrete with CSA only, the compressive strength decreases by up to 24.7% when the replacement level reaches 20%. However, concrete with 10% CSA still maintains 87.2% of the strength of ordinary concrete, which satisfies the C40 requirement. In contrast, CF incorporation alone improves the mechanical properties, with compressive strength, flexural strength, and splitting tensile strength reaching peak increases of 6.4%, 13.9%, and 7.5%, respectively, when the CF content is 0.24%. Incorporating 0.16% CF into 10% CSA concrete mitigates the strength reduction caused by CSA, achieving compressive, flexural, and splitting tensile strengths of 47.99 MPa, 5.63 MPa, and 3.99 MPa, respectively (95.7%, 98.3%, and 96.4% of the strengths of ordinary concrete). Microstructural analysis reveals that CSA deteriorates the interfacial transition zone (ITZ), while CF compensates for partial strength loss through the bridging effect, although its reinforcement efficiency is influenced by fiber dispersion and ITZ quality. This study provides a theoretical foundation and technical reference for the utilization of coconut shell waste in sustainable concrete.

The synthesis of cementitious binders incorporating industrial solid waste represents a strategic pathway toward achieving large-scale resource valorization. The synergistic utilization of binary and ternary solid waste systems has emerged as a prominent research field, leveraging the complementary physical and chemical attributes of diverse waste streams. This work systematically evaluates the synergistic effects within multi-component solid waste systems and analyzes their influence on the mechanical properties and hydration kinetics of cementitious matrices. Specifically, the underlying mechanisms of alkali-mediated structural evolution and sulfate-induced microstructural reinforcement are characterized to elucidate the collaborative interactions between different waste phases. Finally, the prevailing technical constraints in the application of multi-component wastes are identified, and strategic directions for future development are proposed. This study provides a vital theoretical framework for the high-volume and cost-effective utilization of industrial by-products as sustainable building materials, contributing to energy conservation and carbon footprint reduction within the construction industry.

Microbial-induced calcite precipitation (MICP) offers a sustainable strategy for extending the service life of concrete through autonomous crack healing, yet the high alkalinity of cementitious environments restricts microbial viability. In this study, more than 200 indigenous bacterial isolates collected from extreme environments across Iran were systematically screened for urease and carbonic anhydrase (CA) activities. A dual-enzyme activity index (EAI) was developed to quantitatively rank their calcification potential. Four robust spore-forming strains-Bacillus subtilis, Sporosarcina pasteurii, Bacillus sphaericus, and the environmental isolate E10.2-were identified as top candidates based on high EAI values, sporulation capacity, and survival at pH 13.5. These strains retained at least 70% of their enzymatic activity after alkaline exposure and precipitated up to 89% more CaCO3 than controls. When incorporated into mortar, bio-treated specimens reached strength levels slightly exceeding the uncracked control under the tested conditions (46.8MPa at 28days compared to 34.2MPa in cracked controls). Ultrasonic pulse velocity, SEM, and XRD analyses confirmed dense CaCO3 bridging within healed cracks. This study establishes a performance-based framework for selecting dual-enzyme-producing alkaliphilic bacteria for durable, self-healing concrete.

Under dual challenges of global infrastructure expansion and industrial solid waste management, alkali-activated polymers (AAP), as industrial solid-waste-based low-carbon cementitious materials, exhibit immense potential in grouting engineering applications. This review synthesizes current research progress through three critical dimensions: reaction mechanisms, performance characteristics, and grouting applications (grouting for reinforcement and water-blocking). The reaction mechanism universally comprises three stages: dissolution, depolymerization, and polycondensation. Key performance determinants include precursor composition (e.g., slag, fly ash, metakaolin) and alkaline activator properties (type, modulus, concentration). The multifunctional advantages of AAP are fundamentally governed by their microstructural evolution. Specifically, the rapid formation of highly cross-linked C-(A)-S-H and N-A-S-H gels directly contributes to rapid setting and high early strength development, with high-calcium precursors such as slag exhibiting faster strength gain than low-calcium systems, such as fly ash and metakaolin. Furthermore, the absence of vulnerable calcium hydroxide phases, combined with a densified, low-porosity aluminosilicate network, provides superior thermal stability, corrosion resistance, frost durability, and low permeability. Nevertheless, pronounced autogenous shrinkage and drying shrinkage, driven by mesopore moisture loss and the highly viscoelastic solid skeleton, remain primary constraints for field implementation. In grouting reinforcement, AAP can effectively enhance the strength and structural integrity of weak soils, such as soft clay, loess, and sulfate-rich saline soils. For grouting water-blocking, particularly in sodium-silicate-based binary systems, AAP achieves rapid gelation, superior washout resistance, and high anti-seepage pressure, proving optimal for groundwater inflow control. Future research must prioritize (i) standardized mix design protocols for performance consistency, (ii) advanced shrinkage mitigation strategies, (iii) systematic durability assessment under coupled environmental stressors (e.g., wet-dry cycling, chemical attack, thermal fatigue), and (iv) cross-disciplinary collaboration for industrial-scale validation.