To achieve zero net carbon dioxide (CO2) emissions by 2050, the search for new alternative materials to replace Portland clinker is urgent. Biomass fly ash (BFA) is one of the possible materials. Given the extremely high variability in the mineralogical, chemical and microstructural properties of these ashes, a large number of samples must be explored. This study presents a physicochemical characterisation of wood and paper BFA, offering guidelines for sample preparation and data analysis. Four BFAs were characterised using particle size analysis, specific gravity, Brunauer–Emmett–Teller (BET)-surface area analysis, total carbon analysis, scanning electron microscopy, X-ray fluorescence, thermogravimetric analysis and X-ray diffraction (XRD). The studied biomass ashes were found to contain more than 15 phases, with 30 wt.% of potentially reactive phases, including both crystalline and amorphous components. The chemical composition of the amorphous phase is estimated to lie between that of calcareous fly ash and blast-furnace slag. The correlation between the XRD amorphous hump position and the calcium oxide/(silicon dioxide + aluminium oxide) (CaO/(SiO2+Al2O3)) ratio of the amorphous phase is further refined within the calcareous fly ash domain.
This study systematically investigated the effect of gypsum, added after clinker firing during cement preparation, on the hydration behaviour and performance of belite calcium sulfoaluminate (BCSA) clinkers synthesised at a low temperature of 1150°C, with clinkers prepared at 1250°C evaluated for comparison. A series of analytical techniques including X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and compressive strength tests were performed. The results showed that the addition of gypsum accelerated the early hydration of BCSA clinkers. Increasing gypsum content promoted the formation of ettringite while inhibiting the hydration of belite and the precipitation of monosulfate and strätlingite. Clinkers produced at 1150°C exhibited greater hydration reactivity of ye’elimite than those prepared at 1250°C. The increased consumption of aluminium hydroxide indicated greater belite dissolution in clinkers synthesised at lower temperature. BCSA clinkers gained strength rapidly at early ages from fast ye’elimite hydration, while later strength depended on belite hydration. Higher gypsum content increased early-age strength but reduced strength at later ages. Clinkers fired at 1150°C exhibited higher strength than those prepared at 1250°C. It is noteworthy that low-temperature firing offers significant benefits in performance and environmental sustainability for BCSA clinker production.
The performance of a low-purity magnesium oxide (magnesia) source for the synthesis of magnesium silicate hydrate (M-S-H) cements was evaluated. Magnesia-rich precursors were produced from a raw magnesite containing significant levels of impurities (e.g. silicon dioxide, aluminium oxide and ferric oxide), which was ground and calcined at different temperatures (600, 650 and 700°C). The alternative precursors were initially characterised by their physical, chemical, mineralogical and hydration properties. Cement pastes were then prepared using the calcined magnesite samples and commercial silica fume and evaluated in terms of mechanical performance (after 3, 7, 28 and 56 days of curing) and microstructure (after 7 and 56 days of curing). The pastes produced with the most reactive samples (calcined at 650°C and 700°C) exhibited compressive strength equivalent to or higher than that of the control mixture (prepared using high-purity commercial magnesia with the same mix proportions). Microstructural characterisation further revealed structural similarities among the M-S-H phases formed in all samples after 56 days of curing. These findings demonstrate the feasibility of using low-value magnesia-rich precursors to produce M-S-H binders through appropriate grinding and/or calcination strategies. Moreover, this study encourages further research on the valorisation of magnesia-rich industrial wastes for the development of more eco-efficient cement-based composites.
The urgent need to mitigate the carbon dioxide footprint of cement production has driven the development of innovative blended cements. The focus of this study was a hybrid system integrating sulfoaluminate cement (SAC), ground granulated blast-furnace slag (GGBFS) and fly ash (FA), with desulfurisation gypsum (DG) as a functional addition to balance performance and sustainability. Life cycle assessment revealed that the optimised blended cement formulation achieved a 70% reduction in carbon dioxide emissions compared with conventional ordinary Portland cement, primarily attributed to 50% SAC replacement and reduced clinker dependency. The experimental results demonstrated that 4% DG incorporation enhanced the 28-day compressive strength and reduced the chloride diffusion coefficient, correlated with a refined pore structure and suppressed harmful phase transitions. Microstructural analysis confirmed that the DG modulated the hydration kinetics, which promoted continuous ettringite formation and reduced the pores of size > 50 nm by 17.7% at 28 days, thereby enhancing matrix densification. The synergy within the GGBFS-FA binary system under DG modulation established a viable pathway for sustainable cement design, addressing the goals of both reducing carbon dioxide emissions of construction materials and industrial waste valorisation.
In this study, the bond strength and failure mechanism evolution of ceramic tile adhesive () after water immersion are investigated, focusing on vinyl acetate ethylene () modification effects under dry and water curing conditions. By comparing VAE-modified to unmodified CTA, the various parameters were evaluated, including bond strength, cohesion, interfacial adhesion and dimensional variations. The results indicated that VAE-modified had higher bond strength than unmodified because boosted the degree of hydration at 7 days, and improved interfacial adhesion more than cohesion under 7 days of dry curing, inducing predominant cohesion failure. Following 2 days of water immersion, sharp declines in both properties (greater for interfacial adhesion) were caused, shifting the failure mode to interfacial adhesion failure (A-F) due to internal stresses from differential dimensional variations. After 21 days of water immersion, enhanced cement hydration contributed more to an improvement in cohesion, thereby increasing the occurrence of A-F. Subsequent re-drying for 48 h allowed the bond strength of VAE-modified to recover to 180% of its value post-immersion, benefiting from the water resistance of the polymer film.
In this study, tetraethoxysilane () was added into alkali-activated slag () to enhance water resistance. The products of hydrolysis and condensation were analysed and characterised. Meanwhile, the influences of on compressive strength, fluidity, setting time, pore structure, water absorption process, hydration products and water contact angle of were studied. The experimental results demonstrated that the presence of unhydrolysed slightly enhanced the fluidity and prolonged the setting time of . Additionally, while the incorporation of slightly reduced the formation of hydration products after 28 days, the nucleation and filling effects of the nano-silicon dioxide particles accelerated the long-term hydration process of . As a result, the compressive strength of the material improved by a maximum of 6.56% after 90 days. By optimising the pore structure and introducing hydrophobic groups into the AAS, the waterproof performance of TEOS-modified has been significantly enhanced. As a result, the water contact angle increased from 20.05 degrees to 64.05 degrees, and capillary water absorption was reduced by 1.79-13.52% with the addition of .
Coal gangue pervious concrete () is a building material that can address urban flooding and the heat island effect. It also provides a new approach for the treatment of coal gangue. However, the high fluidity of the slurry causes it to settle at the bottom of the CGPC, blocking a large number of pores and reducing the permeability coefficient, which limits its wide application. In this study, coal gangue was used as the aggregate, and hydroxypropyl methyl cellulose () and ultrafine fly ash () were added to explore the synergistic regulation effect of the two on the performance of . The results showed that reduced the fluidity of the slurry and significantly increased the permeability coefficient, but led to a decrease in the compressive strength of . When the replacement rate was 10%, the compressive strength of reached 21.7 MPa, the permeability coefficient was 3.1 mm/s, which was 70% higher than that of the control group, and the porosity was 22%. Microscopic analysis showed that slowed down the hydration rate of cement; the synergistic effect of and improved the structure of the interfacial transition zone and reduced micropores.
Ye'elimite containing sodium and iron (Ca(4-)xNa(2)xAl(5.6)Fe(0.4)(16) with x = 0.1) was synthesised using reagent-grade chemicals. Characterisation of the sample was performed using X-ray diffraction () and Rietveld analysis in combination with analytical scanning electron microscopy. A combination of energy-dispersive X-ray spectroscopy () and electron backscatter diffraction () was applied to characterise phases. A full documentation of how to obtain the pattern of ye'elimite is given. The obtained pattern quality of the ye'elimite was good and allowed indexing. Indexation using the Hough transformation and measuring angles between planes showed mostly a best fit with the orthorhombic structure of ye'elimite. This finding deviated from the analysis and is discussed using results from and dynamic pattern matching, a novel method for indexing patterns. The results of the EBSD-EDX mapping data revealed the mean chemical composition and crystal size of ye'elimite. The crystal size (average maximum Feret diameter of 2.6 & micro;m) was significantly smaller than the size of alite crystals in Portland cement clinker. Therefore, mapping data has to be recorded at a small step size (<0.2 & micro;m). Phase identification by EBSD-EDX analysis revealed that, besides the target ye'elimite phase, ferrite, sodium sulfate and a monocalcium aluminate phase (CaAl2O4) were also present.
Calcium sulfoaluminate belite cements have found widespread use in specialised applications but have not been applied broadly due to rapid setting times. Conventional set retarders such as citric and tartaric acids modify hydration kinetics, introducing ancillary effects that alkanolamines may avoid. This study examined the effects of three alkanolamines, triisopropanolamine (), triethanolamine () and diisopropanolamine (), on early hydration at 0.02% dosage; was also tested across a broader dosage range. Reaction kinetics and phase evolution were examined in pastes by calorimetry, thermogravimetric analysis () and in situ quantitative X-ray diffraction () for 72 h of hydration, along with setting time and amplitude-sweep rheometry. Calorimetry showed that and delayed and reduced the main cement hydration peak, while all alkanolamines delayed and enhanced the shoulder and secondary hydration peaks. In situ and suggested that alkanolamines decrease ettringite and alumina gel formation by 24 h and may lead to poorly crystallised ettringite that cannot be quantified by . Alkanolamine-containing samples demonstrated increased storage and loss moduli and extended linear viscoelastic ranges. A consistent grouping of similar behaviour emerged: control/TIPA versus TEA/DIPA, suggesting distinct mechanisms. Finally, among the alkanolamines, was the most effective, increasing the setting time by 18 min.
The large drying shrinkage of geopolymer seriously hinders its industrial production and application. In this study, mechanochemical processing was introduced into the one-part geopolymer to alleviate its drying shrinkage. The effects of ball-to-powder ratios, ball milling duration and steam time on the mechanical properties and drying shrinkage of one-part geopolymer were investigated. The drying shrinkage mitigation mechanism was explained by testing hydration products, pore structure and infrared spectroscopy. The results indicated that by extending the ball milling time and increasing the ball-to-powder ratios, the macropore volume and total porosity were significantly reduced, and the mechanical strength of the one-part geopolymer was enhanced (28 days compressive strength was about 22.2% higher than that of the simple mixed group). However, as the pore size distribution of the mortars becomes finer, drying shrinkage and mass loss exhibited the opposite trend. In addition, steam curing significantly enhanced the early compressive strength of one-part geopolymer mortar and simultaneously reduced the drying shrinkage rate (the drying shrinkage rate at 56 days was approximately 79.5% lower than that of the specimens without steam curing).
Supersulfated cement (), a low carbon dioxide binder utilising 80-90% ground granulated blast-furnace slag (), faces a critical challenge in balancing mechanical performance and carbon dioxide footprint reduction when incorporating basic oxygen furnace slag () - a steelmaking byproduct with underutilised potential. However, adding more than 10% to causes a significant reduction in strength, which limits both its broader application and its potential for further reducing carbon dioxide emissions. This study explores the synergistic effect of sodium lactate in BOFS-modified () to address this limitation. The results show that even a small addition of 0.5% sodium lactate significantly improves the 7-day and 28-day strength of . Hydration heat tests reveal that the combined use of and sodium lactate significantly inhibits early hydration, leading to a more porous initial microstructure. This porosity facilitates the dissolution of slag during the later stages of hydration. Furthermore, the chelating properties of lactate ions promote the dissolution of ions from both and BOFS, increasing the formation of ettringite and enhancing the hydration of . These findings demonstrate that the simultaneous use of sodium lactate and offers a significant improvement in both the performance and environmental benefits of SSC, making it a more viable option for sustainable cement production.
The properties of cement grout significantly deteriorate at high temperatures, making it unable to meet the demands for reinforcement in deep engineering projects. This study employed plastic polycarboxylic superplasticiser (PCS), ground granulated blast-furnace slag (GGBS), fly ash (FA) and silica fume (SF), using the orthogonal test design method, to improve the properties of cement at high temperatures. Laboratory tests, including viscosity, mechanical strength, stone rate and porosity, were carried out, and a comprehensive performance index was established to determine the optimal mix proportion. The results showed that the significantly reduced the viscosity, enhanced compressive strength and decreased porosity, but also decreased the stone rate. could reduce the viscosity, improve compressive strength and decrease the stone rate, but it increased porosity. and could improve the compressive strength and stone rate, but impaired the pore structure and increased its viscosity. The viscosity of the new grout at 80 degrees C was decreased by >90%, and the compressive strength improved by >180%, while the porosity was also slightly increased. The hydration of mineral admixtures generated calcium-poor calcium silicate hydrate gels and calcium aluminium silicate hydrate gels, which inhibited the decalcification effect of gels at high temperatures, while the morphology and size of the gels remained essentially unchanged.
To enhance the anti-washout performance of magnesium phosphate cement-based grouting materials (), this study investigates the incorporation of anionic polyacrylamide () as a functional additive. The effects of the water-to-binder ratio (0.20-0.30) and dosage (0-1.5 wt% of the combined mass of magnesia and phosphate) on the workability (fluidity, setting time and bleeding rate), mechanical properties (compressive strength, flexural strength and tensile bond strength) and microstructural characteristics of were systematically investigated. The results indicate that significantly reduces the bleeding rate of the slurry while extending the setting time. It also greatly enhances resistance to water-induced dispersion, with acceptable workability retained. When the content was 0.5 wt% and the water-to-binder ratio was 0.25, the suspension turbidity decreased by 66.3% compared to the control, while the fluidity remained at 250 mm and the setting time was 14 min. At this composition, the 3-day compressive strength, flexural strength, and tensile bond strength reached 21.25 MPa, 5.41 MPa and 2.71 MPa, respectively. Microstructural analysis revealed that retarded the hydration process, altered the crystal morphology and pore structure and facilitated the formation of K-struvite as a hydration product.
The efficient selection of clay deposits is critical for the widespread use of calcined clays as suitable supplementary cementitious material (SCM). The current initial assessment relies on chemical composition determined by X-ray fluorescence. However, the assumed direct correlation between elemental composition and mineral phase does not always hold true, especially for complex materials like clays. And, this approach often excludes promising non-kaolinite clays. Therefore, a simple minerology-based test is essential to improve the accuracy of initial screening for a large number of samples. This study proposes the use of the methylene blue (MB) test as a rapid and low-cost alternative for the initial assessment of clays. In this study, 38 natural samples were collected and characterised for chemical and mineralogical composition. The results demonstrate a good correlation between the MB test and X-ray diffraction analysis. The MB test effectively distinguishes clay from non-clay materials and also differentiates between clay mineral types. The simplicity, rapidity and low cost make this test a highly practical tool for preliminary screening of a large number of samples and enhances the efficiency of SCM selection.
The phase conversion of metastable products in calcium aluminate cement (CAC) at elevated temperatures can significantly affect its durability. This study systematically investigates the degradation and leaching behaviour of CAC-based materials in water environments at 20 degrees C and 60 degrees C. The compressive strength evolution of CAC mortars was tracked over 56 days. The underlying mechanisms were elucidated by analysing the phase composition, microstructure, and pore structure of CAC paste specimens, complemented by monitoring the chemistry of the exposure solution. Crucially, a depth-resolved, layer-by-layer analysis was conducted on larger specimens to reveal the leaching gradient. The results show that at 20 degrees C, the leaching behaviour is not pronounced; instead, ongoing hydration densifies the microstructure, leading to a continuous increase in compressive strength. Conversely, at 60 degrees C, the material undergoes rapid degradation. This is driven by a synergistic process involving the conversion of metastable hydrates to stable C3AH6 and gibbsite, and the accelerated dissolution of these products by the water environment, resulting in a porous microstructure and a severe loss of mechanical properties. The depth-resolved analysis provided direct evidence of these mechanisms, confirming that at 60 degrees C, degradation is a progressive process that attacks the material from the exterior.
The extremely short setting time and relatively poor rheology performance of belite-calcium sulfosilicate-sulfoaluminate cement (BTCSA) slurry hinder its large-scale cast-in-situ application. This study investigated the coupling effects of polycarboxylate superplasticiser (PCE) and calcium nitrite additions on the fluidity, setting times and compressive strengths of BTCSA. The hydration kinetics and microstructural evolution of BTCSA were characterised using isothermal conduction calorimetry, X-ray diffraction and scanning electron microscopy analysis. The results showed that the setting times were extended. The additions of PCE and calcium nitrite were more effective in enhancing the fluidity than using PCE alone. The optimal dosages were 0.4% PCE and 0.8% calcium nitrite. The initial setting time was 90 min, the final setting time was 113 min and the fluidity achieved 238 mm. The compressive strength reached 74.6 MPa in 3 days and 121.1 MPa in 60 days. The early-age hydration was delayed but the degree of hydration within 3 days of curing was enhanced. A denser microstructure with linear and columnar calcium sulfonate crystals was formed, and the early-age compressive strength was enhanced.
Calcium sulfoaluminate (CSA) cement and Portland cement (CSA-PC) can form blends with excellent performance. Adding cellulose ethers (CEs) can further adjust the macroscopic and microscopic properties of the blends. However, there are few studies on the effect of CEs on the performance of CSA-based blends. The results indicate that adding CE decreases the mechanical strength. CE delays the release of hydration heat of blends with high CSA cement content. Adding PC decreases the hydration heat of the blends. Meanwhile, adding 0.2-0.5% CE decreases the weight loss of ettringite and C-S-H gel in the blends with 85% and 70% CSA cement by about 1-2%, and decreases the content of chemically bound water by about 0.5-6%. The contents of the above hydration products and bound water decrease with the increase in PC content. In addition, as the CE content increases, the large capillary and macro pores significantly increase, resulting in an increase in cumulative pore volume and total porosity by about 0.08 ml/g and 10%, respectively. Furthermore, the cement mortars with high CE and CSA cement content have lower water capillary absorption. This study can provide theoretical guidance and a reference for the application of CSA-based repair materials in rapid repair and construction engineering.
The aim of this work was to produce a new type of limestone-based Portland cement (LPC) by minimising the amount of clinker (in the range 50-64%) in accordance with the European standard EN 197-5. Such cements are called CEM II/C-M. The new LPC produced, which meets the specific requirements of EN 197-1, was prepared by partially replacing clinker with 5-20% granite waste powder or brick waste powder (BWP) and adding a constant percentage of 20% limestone filler and 6% gypsum. The new LPC powder was evaluated for chemical characterisation, specific surface area and density. The consistency, setting times and soundness properties of the LPC paste were investigated. In addition, the compressive and flexural strengths, drying shrinkage and chemical resistance (hydrochloric acid and sulfuric acid) of mortars prepared with the new LPC were studied. The LPC materials produced with 5% or 10% BWP showed improved mechanical properties, drying shrinkage and durability compared with the reference systems. This study contributes to the development of new cements by minimising the clinker content. The new LPC prepared by substituting clinker with up to 10% BWP can be classified as 32.5R cement.
This study focuses on the origins of different strains in the cement pastes that condition the viscoelastic properties and the structural build-up/thixotropy. Owing to the complexity of demonstrating the contribution of the nucleation of hydrates during the induction period of cement hydration, different chemically inert mineral suspensions with different granular properties (fineness, shape and particle size) are tested. The effect of the solid volume fraction and time on the different strains is also investigated. The results reveal that all of the suspensions studied display a critical strain of the same order of magnitude, and this critical strain does not change over time in the case of cement pastes. So the critical strain cannot be associated only with the nucleation of hydrates (C–S–H bridges) at the contact points between particles, as reported in the literature. The nucleation and increase of hydration products just increase the surface contact between particles, resulting in rigidification of the particles network characterised by an increase of the storage modulus after the formation of a colloidal network.
This study pioneers a novel methodology to assess the feasibility of utilising industrial byproducts in calcium sulfoaluminate (CSA) cement systems through simulated alkaline environments, specifically employing phosphogypsum (PG) and electrolytic manganese residue (EMR) stabilisation by way of struvite precipitation. The stabilisation protocol comprised two phases. In the first phase, struvite synthesis was optimised using an EMR-to-PG mass ratio of 2:1, a solid-to-liquid ratio of 1:0.7, and pH 9.0 adjusted by magnesium oxide/magnesium sulfate supplementation, followed by 20 days of curing to achieve optimal precipitation. Subsequently, a calcium hydroxide solution-based simulation system replicating CSA hydration conditions (pH <10.5) was established to evaluate the long-term stability of stabilised/solidified (S/S) composites over equivalent 20-day periods. Fourier-transform infrared spectroscopy indicated that the characteristic absorbances of phosphate and nitrogen-hydrogen were markedly intensified after the 20-day S/S treatment and remained stable following alkali exposure. Compressive strength at 14 days (44.4 MPa) was comparable to the control, confirming that 10% cement replacement by the S/S composite does not reduce the later mechanical performance of CSA. These findings significantly advance the application of PG and EMR in CSA.
