Search Results (2,566)

The maturity method (ASTM C1074) predicts in situ concrete strength from a recorded temperature history but assumes a constant apparent activation energy, contradicting the experimental evidence that the activation energy falls as hydration shifts from kinetics control to diffusion control—an effect that differs between binder chemistries when supplementary cementitious materials (SCMs) are used. This study develops a physics-based maturity model in which the apparent activation energy varies linearly with temperature, Q(T) = Q₀ + β_Q(T − T_ref), coupling a variable-energy Arrhenius equivalent age to a hyperbolic strength–maturity relationship. The model was calibrated on 196 mean-strength observations (588 cube tests) from seven self-compacting concrete mixtures cured isothermally at 10, 20, 35 and 50 °C and tested at seven ages (1–90 days). All four SCM systems (fly ash, GGBS, silica fume and rice husk ash) returned a negative coefficient (−210 to −974), enclosing the temperature sensitivity implied by independent calorimetric measurements on Portland cement paste (≈−580 J/(mol·K)), whereas the ordinary Portland cement control returned a positive point estimate (+101) that is not statistically distinguishable from zero. The model achieved R² = 0.929 (RMSE = 4.74 MPa), outperforming the constant-energy ASTM C1074 baseline in both accuracy and the Akaike Information Criterion while eliminating its systematic bias at the temperature extremes. Five-fold cross-validation confirms the out-of-sample accuracy (R² = 0.901, RMSE = 5.59 MPa), and bootstrap analysis shows the negative coefficients of the fly ash, GGBS and rice husk ash systems to be statistically significant. External validation on 120 independent literature observations gave R² = 0.881. Full article

Fiber-reinforced high-water-resistance concrete backfill (FHWCB) is a rapid-setting cementitious backfill system used for underground support and backfilling, but its stability is strongly affected by mixture water content and fiber dispersion. This study investigated the fresh-state behavior, mechanical performance, acoustic emission (AE) fractal characteristics, b-value response, and energy evolution of FHWCB. Mixtures with water-to-cement ratios (w/c) of 1.0–1.8 and fiber volume fractions (Vf) of 0–0.5% were prepared and tested using fresh property measurements, unconfined compression, thermogravimetry, AE monitoring, correlation dimension analysis, b-value analysis, and strain energy partitioning. Increasing w/c improved flowability and delayed setting, but weakened the hydration skeleton and reduced early-age compressive strength by approximately 56–61%. Fiber reinforcement showed a non-monotonic effect: Vf = 0.3% increased compressive strength by approximately 16–26%, whereas excessive fiber addition reduced strength because of fiber clustering and weak local zones. AE amplitude sequences exhibited measurable fractal characteristics. A higher correlation dimension indicated distributed microdamage, while decreasing correlation dimension and b-value reflected the transition toward localized macrocrack growth. Energy analysis showed that the peak elastic strain energy density decreased from approximately 0.60 to 0.39 MJ/m³ as w/c increased. The proposed AE fractal–b-value–energy framework provides a quantitative basis for tracking damage progression and optimizing FHWCB for underground engineering. Full article

The fine powder fraction generated during concrete recycling is often regarded as a low-value by-product or used as a filler in cement-based materials. This study investigates recycled concrete powder (RCP) as the main component of pressed cement-free and low-cement mineral composites. The <0.14 mm fraction was obtained by crushing and sieving concrete waste. Cylindrical specimens were produced by semi-dry pressing at 20 MPa with a forming moisture content of 12–13% and cured under humid-air conditions. Four systems were studied: untreated RCP, thermally activated RCP, RCP with 2.5 wt.% Portland cement, and RCP with 5 wt.% Portland cement. Thermal activation was performed at 600 °C for 2 h. Compressive strength, bulk density, and water resistance coefficient were determined at 3, 7, and 28 days. At 28 days, compressive strength increased from 6.9 MPa for untreated RCP to 11.4 MPa for thermally activated RCP and 12.8 MPa for RCP with 5 wt.% cement, while the water resistance coefficient increased from 0.61 to 0.86. DTA/TGA analysis revealed thermal effects and mass-loss patterns consistent with the presence and evolution of hydrated and carbonate-containing phases. The results demonstrate that RCP can serve as a structure-forming component in pressed cement-free and low-cement materials. Full article

This article is a continuation of research conducted by the authors on the effects of fire on cementitious composites and presents findings of an investigation into cement mortars that incorporate monofilament (I) and multifilament (F) polypropylene fibres following exposure to temperatures between 100 and 600 °C. Research was undertaken to examine the effect of adding fibre on the mechanical performance, microstructural characteristics, and thermochemical degradation behaviour of the mortars under conditions representative of high-temperature exposure during fires in energy infrastructure facilities. The scope of the research comprises establishing the modulus of elasticity using dog-bone-shaped specimens, as well as flexural and compressive strength tests performed on prisms measuring 4 × 4 × 16 cm and on 10 × 10 × 10 cm cubes to determine the strength class of the mortars. Microstructural analyses complemented the mechanical testing, performed with the use of scanning electron microscopy (SEM); this made it possible to assess temperature-induced changes in the cement matrix. The results have demonstrated that polypropylene fibres had a significant influence on the degradation behaviour of mortars subjected to elevated temperatures, particularly those between 200 and 400 °C, where fibre melting promoted the formation of additional pore channels. This phenomenon promotes the dissipation of internal energy associated with boiling water vapour contained in the capillary pores, as well as water released during the dehydration of cement hydration products, thereby limiting rapid pressure build-up and reducing the risk of explosive spalling. Moreover, the observed microstructural changes were associated with progressive decomposition of C–S–H gels and other thermo-chemical processes occurring within the cement matrix. The results confirm that polypropylene fibres act as a passive mechanism for the dissipation of thermal and mechanical energy in cement mortars, which has a positive effect on their performance under high-temperature conditions. The study provides new experimental data of significance for the design of cement-based materials with enhanced resistance to thermal exposure in energy-sector facilities. Full article

The growing demand for CO₂ emission reduction and efficient waste management has created a need for the development of sustainable construction materials. This study presents a comparative investigation of geopolymer and cement-based composites modified with bio-based additives originating from two abundant and underutilized waste streams: apple-processing waste and biomass collected during lake restoration activities. Geopolymer and cement composites containing 5 and 10 wt.% apple-processing waste or 5 and 10 vol.% lake fibers were prepared, and their compressive strength, flexural strength, density, and thermal conductivity were experimentally evaluated. The results revealed substantial differences between the investigated binder systems. Apple-processing waste significantly deteriorated the mechanical performance of both materials, particularly in cement-based composites, where disturbances in cement hydration and loss of structural integrity were observed. Although geopolymer composites also exhibited reduced compressive strength after the incorporation of apple residues, their structural cohesion was maintained. In contrast, biomass fibers obtained from lake restoration demonstrated considerably better compatibility with the geopolymer matrix, limiting compressive strength reductions to approximately 13–16% while contributing to improved crack resistance and post-failure integrity. The incorporation of bio-based additives reduced composite density and decreased thermal conductivity, resulting in enhanced thermal insulation performance. The lowest thermal conductivity was obtained for the geopolymer containing 10 wt.% wet apple waste, reaching 0.4216 W/(m·K), compared with 0.7067 W/(m·K) for the reference geopolymer. The findings indicate that lake-restoration biomass represents a promising reinforcement for geopolymer-based construction materials, whereas fruit-processing residues require further pretreatment before practical application. Overall, the study highlights the superior compatibility of geopolymers with organic waste streams and demonstrates their potential as sustainable, non-structural construction materials supporting circular economy strategies, waste valorization, and environmental remediation efforts. Full article

Understanding chloride transport in fly ash cement pastes is essential for improving durability, yet the relationships between pore structure parameters and the apparent chloride diffusion coefficient remain insufficiently understood. This study investigates these relationships and assesses the relative associations of selected pore structure parameters with the apparent chloride diffusion coefficient within the present experimental dataset. Cement pastes with 0–70% fly ash were prepared at a water-to-binder ratio of 0.53 and cured for 90 days. The hydration phase assemblage was assessed by X-ray diffraction and thermogravimetric analysis, with particular attention to portlandite (CH), ettringite (AFt), and layered calcium aluminate hydrate (AFm) phases. Pore structure was characterized by nitrogen adsorption and mercury intrusion porosimetry. The apparent chloride diffusion coefficient was evaluated by fitting water-soluble chloride profiles obtained from bulk diffusion tests conducted for 30, 60, and 90 days. Fly ash significantly altered the CH content, AFm phase assemblage and pore structure. At fly ash replacement levels of 50–70%, capillary porosity increased from 20.77% at 50% fly ash to 30.31% at 70% fly ash, while the critical pore diameter increased from 47 nm to 75 nm, indicating substantial pore coarsening. At 90 days, the apparent chloride diffusion coefficient initially decreased from 6.3 × 10⁻¹² m²/s for pure cement to 5.7 × 10⁻¹² m²/s at 30% fly ash replacement and then increased to 10.1 × 10⁻¹² m²/s at 70% fly ash replacement. Among the investigated pore structure parameters, critical pore diameter showed the strongest association with the apparent chloride diffusion coefficient after 90 days of immersion (R² = 0.791). Full article

The cement industry accounts for approximately 7% of global anthropogenic CO₂ emissions, making clinker reduction, alternative binders, and carbon use and capture technologies essential mitigation strategies. However, decarbonization based on the replacement of clinkers with supplementary cementitious materials or alternative binders generally adjusts the materials’ physicochemical properties and reactivity. As these actions may have implications for durability and performance throughout the life cycle, this paper presents a systematic review, based on the Methodi Ordinatio approach, of studies published in the last decade in indexed databases that examine the relationship between low-emission cements, durability, and service life. Of 48 selected articles, most focused on quantifying CO₂ avoidance through clinker reduction, without comprehensively addressing the use phase. When present in the literature, durability is found in studies of chloride penetration and carbonation resistance. However, no integrative chain studies or long-term studies focused on the durability of less emissive cement-based materials were identified. Across the reviewed studies, durability was mainly associated with changes in pore structure, hydration products, transport properties, and matrix alkalinity. Fine and reactive additions may promote pore refinement and restrict the ingress of aggressive agents, whereas extensive clinker replacement and portlandite consumption may reduce the alkaline reserve and increase carbonation susceptibility. However, these relationships are strongly dependent on binder composition, replacement level, and curing conditions, and were rarely evaluated together over sufficiently long periods. Full article

Waste rock wool (WRW) has attracted increasing attention as a supplementary cementitious material (SCM) because of its mineral composition and its potential for reducing industrial waste. Although thermal treatment is commonly applied during WRW recycling, the practical necessity of additional low-temperature thermal treatment after mechanical activation remains unclear. This study evaluated the feasibility of mechanically activated WRW as an SCM by comparing materials with and without subsequent thermal treatment at 250 °C. Cement paste containing 15 wt.% WRW was prepared, and the effects of thermal treatment were evaluated through X-ray fluorescence (XRF), scanning electron microscopy (SEM), compressive strength testing, and thermogravimetric analysis (TGA). The XRF and SEM results revealed only negligible differences in chemical composition and particle morphology between the thermally treated and non-thermally treated WRW. Although both WRW mixtures exhibited lower early-age compressive strengths than the Plain mixture, comparable or higher long-term strengths were achieved. The TGA results also showed only minor differences in calcium hydroxide content and degree of hydration between the two WRW mixtures. Overall, additional low-temperature thermal treatment provided limited practical benefits beyond mechanical activation alone. These findings demonstrate that mechanically activated WRW without subsequent thermal treatment is a feasible supplementary cementitious material, offering a simplified and more energy-efficient recycling strategy for cementitious applications. Full article

This study quantitatively investigates the coupled effects of curing temperature and slurry density on the early-age acoustic maturation of ultra-low-density Hollow Glass Microsphere (HGM)-modified oil well cement systems, addressing the critical challenge of determining reliable sonic logging timing under lightweight cementing conditions. Longitudinal wave velocity evolution was systematically characterized across a broad thermo–density domain, revealing a consistent three-stage acoustic trajectory comprising percolation-driven acceleration, transition-controlled consolidation, and acoustic stabilization. The results demonstrate that curing temperature primarily regulates the kinetic rate of acoustic maturation through hydration activation, whereas slurry density modulates the initial structural configuration, HGM-induced acoustic impedance heterogeneity, and development of effective solid connectivity. A derivative-based dual-criterion approach was proposed to define the optimal sonic logging time based on intrinsic acoustic stabilization behavior rather than conventional empirical strength-based thresholds. Furthermore, a thermo–density coupled semi-empirical model incorporating Arrhenius-type thermal activation and density-dependent structural effects was developed, providing reliable prediction of sonic logging timing with clear physical interpretability. The model captures the nonlinear interaction between thermal activation and structural constraints, revealing that acoustic maturation is accelerated under elevated-temperature and higher-density conditions but substantially delayed under low-temperature and ultra-low-density scenarios. This study establishes a physics-informed temperature–density–acoustic coupling framework that links hydration-controlled structural evolution with sonic logging optimization, providing a rational basis for improving cement bond evaluation reliability and operational efficiency under challenging wellbore conditions. Full article

Boron-containing concrete is an important neutron-shielding material for nuclear engineering, but the addition of boron compounds may adversely affect cement hydration and mechanical properties. This study employed boric acid and boron carbide as boron-10 neutron-absorbing sources. Within the material system investigated, the comprehensive effects of boric acid, boron carbide, and their combined use on setting time, mechanical properties, and effective boron loading were compared. MAA-based mix design and the analytic hierarchy process (AHP) were then employed to screen candidate mix proportions. Based on particle packing optimization, a series of concrete mixtures were prepared to evaluate workability, setting time, mechanical strength, boron content, and hydration products. The results show that boric acid provides good boron dispersibility but strongly retards cement hydration, leading to prolonged setting time and reduced strength. Pretreatment with calcium hydroxide and the use of an early strength admixture can partly mitigate this negative effect; the final setting time of the boric acid-containing mixtures still reached as high as 34 h 11 min. Boron carbide exhibits better chemical stability and has less influence on cement hydration. When incorporated at 5–10%, boron carbide improves the balance between mechanical performance and neutron-shielding potential. In particular, the 10% boron carbide mixture achieved a 28-day compressive strength of 47.3 MPa and a splitting tensile strength of 4.21 MPa, compared with 55.5 MPa and 6.2 MPa, respectively, for the control mixture, while maintaining relatively high strength. An analytic hierarchy process was further applied to comprehensively evaluate compressive strength, splitting tensile strength, final setting time, and boron content. Furtherly, XRD results confirmed the different interaction mechanisms of boric acid and boron carbide in cementitious systems. The study provides a framework for developing boron-containing concrete with potential neutron-shielding applications. Full article

The combined use of ceramic waste powder (CWP) as a supplementary cementitious material and magnetized water (MW) as mixing water represents a promising strategy for producing sustainable concrete with reduced cement consumption while maintaining mechanical performance and durability. However, the synergistic effects of burnt ceramic waste powder (BCWP) and unburnt ceramic waste powder (UBCWP) combined with MW, particularly under aggressive environmental conditions, remain insufficiently investigated. This study evaluates the influence of BCWP and UBCWP, used as partial replacements for ordinary Portland cement (OPC) at replacement levels of 10%, 20%, and 30% by weight, together with conventional tap water (TW) and MW produced using a dual-field magnetic device (0.9 T and 1.5 T). A total of fourteen concrete mixtures were investigated through compressive strength tests at 7, 28, and 120 days; indirect tensile and flexural strength tests at 28 and 120 days; sulfate resistance after 120 days of MgSO₄ immersion; residual strength after thermal exposure at 200 °C; and microstructural characterization using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results indicate that increasing the CWP replacement level progressively reduced the mechanical properties of concrete; however, MW consistently mitigated these reductions by promoting cement hydration and producing a denser cementitious matrix. The mixture containing 20% BCWP with MW achieved a 120-day compressive strength comparable to that of the TW control, demonstrating that cement consumption can be reduced without compromising structural performance. Furthermore, MW mixtures exhibited significantly improved durability, with compressive strength losses of only 16–28% after sulfate attack compared with up to 42% for TW mixtures, and 1–13% after thermal exposure compared with up to 53% for TW mixtures. SEM and XRD analyses confirmed the development of denser microstructures with enhanced C–S–H gel formation in MW–CWP concretes. Overall, the findings demonstrate that the synergistic combination of ceramic waste powder and magnetized water provides an effective strategy for producing sustainable concrete with enhanced long-term mechanical performance, improved durability under aggressive environmental conditions, and reduced environmental impact. Full article

With the continuous expansion of grouting material applications, solid waste to prepare grouting materials can effectively mitigate the environmental issues caused by waste accumulation. In this work, an all-solid-waste grouting material (ASWGM) was prepared with silica fume, coal gangue, desulphurization gypsum, fly ash, steel slag and carbide slag. The impact of water–cement ratio (W/C), environmental temperature, silica fume content, and hydration time on the fluidity of grouting materials was systematically analyzed. The chemical substances of such ASWGM were investigated by performing XRD and Fourier transform infrared spectroscopy measurements, while its fluidity was comprehensively evaluated by conducting apparent viscosity, yield stress, fluidity, and thixotropy tests. Based on our analysis, the optimal silica fume content was determined to be 5%, and 20 °C identified as the optimal environmental temperature. Under the preferred performing combination within the tested scope, the yield stress of the materials was 126.4 Pa. The incorporation of silica fume would decrease the early strength of the materials. The strength greatly increased in the late phase as the hydration continued. The strength exceeded 50 MPa at 12 h and 80 MPa at 28 d. Not only can the use of all-solid waste effectively solve the environmental pollution caused by solid waste stacking and facilitate green development, but also obtain grouting materials with satisfying fluidity and mechanical properties through design optimization. The research results can serve as a reference for guiding engineering practice. Full article

Using ultrafine silicate cement as the cementitious material, and admixtures such as expansion agent, rapid-setting agent and water reducer as additives, a new type of composite grouting material with high early strength and high toughness was obtained by modification with nano-Al₂O₃ (NA). The influence of NA content on the mechanical properties, flowability, bleeding behavior, setting time, volume shrinkage, and microstructure was investigated for composite grouting materials. The results show that, as the NA content increases, the flowability of the paste decreases, the bleeding rate reduces, and the setting time increases first and then decreases. Appropriate NA can effectively improve the mechanical strength of the composite grouting material. Especially at the condition of 3% NA, the composite grouting material reached the highest early compressive strength and toughness. Compared with the control group, the compressive strength of the specimen increases by 39.54% and 6.83% respectively at 1 d and 21 d, and the flexural strength increased by 55.41% at 1 d. XRD, FTIR, SEM and hydration heat analysis confirm that the NA can promote the early hydration heat of ultrafine cement, and shorten the induction period. Moreover, more C-A-H gel products will be generated by consuming Ca(OH)₂ with active NA, leading to an improvement in the matrix compactness. Such an outstanding mechanical property can be mainly attributed to the triple coupling mechanism of the hydration regulation, microstructure and filling effect of superfine cement by nano-Al₂O₃ in combination with multi-component admixtures. Full article

This study investigates the damage evolution mechanism affecting the fracture-bearing performance of fly ash cement paste under low-temperature curing conditions. Pre-cut cement paste specimens with fly ash contents of 0%, 15%, and 25% were prepared and subjected to both standard curing and low-temperature curing at 5 °C for 28 days. Three-point bending tests combined with acoustic emission (AE) monitoring were conducted to analyze peak flexural load, AE ring count, cumulative energy, RA-AF crack classification, and b-value evolution. Additionally, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed to characterize micromorphology and relative changes in hydration product content. The results indicate that both fly ash incorporation and low-temperature curing significantly reduce the flexural bearing capacity of pre-notched specimens. Under low-temperature curing, the peak loads of LF15 and LF25 decrease by 34.83% and 47.19%, respectively, compared to LF0. At the same fly ash replacement level, all low-temperature-cured specimens exhibited lower peak loads than those cured under standard conditions. Overall AE activity was reduced in low-temperature-cured specimens, with crack propagation instability occurring at lower load levels. The addition of fly ash shifted the fracture mode toward a tensile-dominated type, whereas low-temperature curing increased the proportion of shear-type AE events. Fly ash incorporation increased the relative content of calcium silicate hydrate (C-S-H) gel and decreased that of calcium hydroxide (CH); however, this did not result in improved peak flexural load. This outcome is attributed to the insufficient reactivity of fly ash at low temperatures, leading to residual unreacted spherical particles, dilution of clinker, and inadequate interfacial bonding, which collectively weaken the continuous load-bearing skeleton of the matrix. This paper establishes a multi-scale interpretation of the damage mechanisms affecting the low-temperature fracture-bearing performance of fly ash cement paste by correlating macroscopic bearing response, AE damage evolution, crack types, and hydration product composition. Full article

Due to the fact that municipal sludge incineration generates a large amount of toxic sewage sludge ash (SSA), cement solidification is becoming an efficient harmless treatment method. However, the large amount of phosphorus in sludge ash can delay the setting time of cement pastes and lead to a decrease in its later strength. Moreover, as an important non-renewable resource, the recycling and utilization of phosphorus is also a current research hotspot. To this end, this paper proposes to remove phosphorus from incinerated sewage sludge ash (ISSA) by the acid washing process, and, in response to the problem of reduced volcanic ash activity in acid-washed sewage sludge ash (ASSA), calcium chloride (CaCl₂) is added as an activator to explore the optimal process and hydration mechanism for enhancing ASSA activity. This study removed phosphorus from calcined SSA (800 °C, 2 h) via acid washing (0.3 mol/L H₂SO₄, L/S = 10:1, 2 h) to obtain ASSA, and used CaCl₂ as an activator to improve its pozzolanic activity. Different CaCl₂ dosages (1–3%) were tested for paste setting time, 3/7/28 d compressive strength, and characterized by hydration heat, XRD, SEM, etc. Experimental results indicated that the synergistic addition of 2 wt.% CaCl₂ and 20 wt.% ASSA shortened the initial and final setting times by 38% and 23% to 142 min and 289 min, respectively. Meanwhile, the compressive strength at 28 days was improved by 24%, with a final strength value of 42 MPa. Microanalysis revealed abundant Friedel’s salt formation and a denser structure (fine mesopores 60%, coarse mesopores 26%), confirming CaCl₂ effectively activates ASSA for cement admixture use. Full article