Search Results (1,704)

This study evaluates the influence of different crushed gneiss contents on the mechanical, durability, environmental, and economic performance of sand–gravel/gneiss mixtures for sustainable road construction. Natural sand–gravel aggregate was blended with crushed gneiss at three proportions (10%, 30%, and 50% by mass). The experimental program included grain size analysis, compaction characteristics, California Bearing Ratio (CBR), deformation modulus, and freeze–thaw durability tests. Environmental performance was assessed using a cradle-to-site carbon footprint approach based on Life Cycle Assessment principles according to ISO 14040, ISO 14044, and ISO 14067, with the analysis focused on Global Warming Potential (GWP100), combined with a Total Cost of Ownership analysis. Increasing gneiss content improved mechanical performance, with CBR increasing from 45% to 95% and deformation modulus from 110 to 185 MPa. The 70/30 sand–gravel/gneiss mixture provided the most balanced performance among the investigated compositions, combining high bearing capacity, satisfactory freeze–thaw resistance, and favorable environmental and economic characteristics. Its carbon footprint was 3.90 kg CO₂ eq./t, with diesel consumption during aggregate handling identified as the dominant emission source (69%), followed by gneiss transportation (20%) and electricity consumption (12%). Higher gneiss contents and longer transport distances increased environmental impacts and production costs. The results indicate that selecting an appropriate aggregate composition and reducing transport-related emissions can support lower-carbon construction materials while maintaining required engineering performance. Full article

To promote the high-value utilization of industrial solid waste and enhance the durability of construction materials in cold regions, this study investigates an autoclaved aerated concrete (AAC) system prepared primarily with fly ash and oil shale residue, with a particular focus on its frost resistance. The physical and chemical properties of the raw materials were characterized using X-ray fluorescence (XRF) and X-ray diffraction (XRD) to optimize the pore structure and mineral composition. A systematic evaluation of 15 continuous freeze–thaw cycles was conducted, comprehensively analyzing the compressive strength retention, mass loss rate, and thermal conductivity. The experimental results indicate that a 50% replacement of fly ash with oil shale residue, combined with an optimized water-to-binder ratio (0.66), significantly improves the pore uniformity and skeleton stability of the AAC. The optimized mixture (YYY50W) achieved a compressive strength of 5.2 MPa and a low thermal conductivity of 0.1654 W/(m·K). After 15 freeze–thaw cycles, the mass loss was minimal (<3 g), and the compressive strength retention rate ($R$) reached 90.0%, demonstrating superior frost resistance. This study elucidates the microstructural mechanism by which oil shale residue promotes the formation of low-crystallinity tobermorite and C-S-H gels, providing potential experimental evidence for the utilization of industrial by-products in building materials for cold environments. Full article

The durability deterioration of concrete under the coupled action of freeze–thaw cycles and corrosive media is a critical technical challenge for engineering structures in cold regions and salt corrosive environments. This paper systematically reviews the research progress on the mechanical properties of concrete subjected to coupled freeze–thaw and corrosion effects. Starting from the mechanisms of freeze–thaw damage and corrosion damage, it analyzes the material degradation laws under individual factors and the synergistic failure mechanism of the coupled freeze–thaw–corrosion condition. The coupling effect is revealed: freeze–thaw-induced microcracks accelerate the penetration of corrosive media, while the expansion of corrosion products in turn aggravates freeze–thaw damage. Building on this, from the perspective of factors influencing concrete failure, this paper systematically summarizes the key factors governing concrete damage under single-factor and coupled-factor conditions as well as their nonlinear response characteristics. The review indicates that the damage degree under the coupled action is far greater than the simple superposition of damage caused by individual factors and presents complex patterns, including the concentration threshold effect, the time-sequence effect, and sensitivity to a low water–cement ratio. Existing reviews predominantly focus on qualitative descriptions of single-factor deterioration mechanisms, while systematic comparative analyses of threshold behaviors under multi-factor coupling and quantitative consolidation of mechanical degradation metrics remain limited. Furthermore, targeted durability design guidance tailored to cold saline environments is rarely summarized in the prior literature, which motivates the present comprehensive review. Although existing studies are relatively well-established for single damage mechanisms, further efforts are still needed to deepen the understanding of multi-factor interaction thresholds and dynamic evolution processes. The findings of this review can provide theoretical support and engineering reference for the durability design and service life prediction of concrete structures in cold regions and salt corrosive environments. The summarized threshold laws and quantitative mechanical degradation data can provide targeted parameter guidance for the durability design of hydraulic structures, bridge substructures, and port engineering in northwest saline soil, northern severe cold, and eastern coastal salt fog areas. Full article

Self-compacting concrete (SCC) shows considerable potential for infrastructure applications on the Qinghai–Tibet Plateau, which is characterized by a hypoxic environment. However, the quantitative effects of the volumetric water-to-powder ratio (V_W/V_P) on the freeze–thaw durability of SCC remain poorly understood, particularly when tuff powder is incorporated as a filler. This research explores the effects of V_W/V_P on the frost resistance of SCC incorporating tuff powder. Three SCC mixtures with V_W/V_P values of 1.0, 1.1, and 1.2 were prepared to systematically evaluate their mechanical performance and freeze–thaw durability. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were employed to characterize the microstructure of the corresponding hardened pastes. The findings indicate that both compressive and splitting tensile strengths decrease markedly as V_W/V_P rises. Under the same number of freeze–thaw cycles (FTCs), higher V_W/V_P gives rise to an increased mass loss rate and accelerated degradation of the relative dynamic elastic modulus (RDEM). Over the course of 250 FTCs, the RDEM decreased from 75.5% to 67.3%, accompanied by an increase in mass loss from 1.34% to 5.20%. Microstructural analyses reveal that the proportions of harmful pores (100–200 nm) and multi-harmful pores (>200 nm) increase as V_W/V_P rises, indicating that a reduced V_W/V_P enhances pore structure densification and the frost resistance of SCC. The forecasted trajectories of mass loss and RDEM derived from our established damage model are in close accordance with the measured laboratory data, confirming that lower V_W/V_P effectively prolongs the operational life of SCC under harsh freeze–thaw environments. Furthermore, an improved comprehensive performance evaluation considering mechanical performance, freeze–thaw resistance, cost, and environmental impact was proposed, demonstrating that SCC with lower V_W/V_P exhibits superior overall performance. Full article

To promote the high-value utilization of construction and industrial solid wastes, this study prepared an all-solid-waste-based flowable solidified soil (FSS) using soft clay and recycled fine aggregate (RFA) as the main constituents. The binder system comprised ground-granulated blast-furnace slag (GGBS), carbide slag (CS), and desulfurization gypsum (DG), while fly ash (FA) was incorporated to improve workability. The primary objective was to identify an appropriate RFA content for this FSS system through a combined evaluation of workability, mechanical performance, durability, and microstructural characteristics. The results showed that increasing the RFA content increased flowability and shortened the setting time. Unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) both increased initially and then decreased as the RFA content increased, and relatively favorable mechanical performance was observed at RFA contents of 40–60%. In the durability tests, the mixture containing 40% RFA exhibited the lowest mass loss and UCS loss after both wetting–drying and freeze–thaw cycles within the investigated range. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses suggested that a moderate RFA content was associated with the development of C-(A)-S-H-gel-related phases and ettringite (AFt), together with a denser and more continuous microstructure. The improved strength and durability at moderate RFA contents were therefore interpreted as the combined results of hydration-product development and the physical skeleton effect provided by RFA. By contrast, the performance decline at excessive RFA contents appeared to be related to a less favorable internal structure, as indicated by SEM observations. Overall, when workability, mechanical performance, durability, and microstructural observations are considered together, 40% RFA is recommended as the most suitable content for the material system and test conditions investigated in this study. These findings demonstrate the potential of RFA to regulate the performance of all-solid-waste-based FSS and to improve the resource efficiency of multiple solid-waste streams. Full article

Cold recycled mixtures with bitumen emulsion (CRME) serving in seasonally frozen regions are susceptible to mechanical deterioration under repeated freeze-thaw (F-T) cycles, which is primarily manifested as interfacial damage and crack propagation. However, the micro-mechanical processes associated with the transmission and dissipation of frost-heaving stresses induced by water-ice phase transition within the interfacial transition zone (ITZ) between reclaimed asphalt pavement (RAP) and asphalt mortar remain to be further characterized. In this study, a numerical simulation approach coupling frost heave effects with the phase transition of water-ice particles was developed based on X-ray computed tomography (CT) and the discrete element method (DEM), and the micro-mechanical parameters of the RAP-asphalt mortar ITZ were determined through laboratory experiments. Combined with acoustic emission (AE) monitoring, the damage evolution characteristics of cold recycled mixtures and the associated interfacial damage mechanisms under freeze-thaw action were systematically investigated. The results indicate that the optimal micro-parameters of the RAP-asphalt mortar ITZ can be taken as approximately 85% of those of virgin asphalt mortar. After 20 freeze-thaw cycles, the number of shear cracks and tensile cracks in ITZ on RAP surface reached 493 and 92, respectively, which were much higher than 11 and five on the surface of new aggregate. ITZ was the main control weak area of freeze-thaw damage. Compared with the unfrozen specimens, the minimum effective contact number of mortar decreased by 1.63%, 4.52% and 8.52% respectively after 5, 10 and 20 freeze-thaw cycles, and the total effective contact number decreased from 75,842 to 69,383. Freeze-thaw cycles significantly reduce the strain energy storage capacity of CRME: the maximum energy storage capacity of the adhesive spring decreased from 2.15 J in the non-freeze-thaw state to 1.28 J in 10 cycles (a decrease of 40.47%) and 1.16 J in 20 cycles (a decrease of 46.05%), and the damage mode changed from brittle fracture to interface-controlled energy dissipation. The proposed water-ice phase transition-based DEM framework provides a reliable numerical tool for investigating freeze-thaw damage mechanisms and supporting durability-oriented design of cold recycled pavement materials. Full article

Repeated freeze–thaw (F–T) action, together with dynamic disturbances, can progressively weaken rock masses in cold regions. However, how freezing temperature affects the relationship between microstructural evolution and dynamic strength decay remains insufficiently quantified. This study investigated yellow sandstone subjected to F–T cycles at freezing temperatures of 0, −3, −5, and −20 °C. CT-based 3D reconstruction and Split Hopkinson pressure bar (SHPB) tests were combined with grey relational analysis (GRA) to characterize pore-structure evolution, dynamic strength decay, and their relationship. The results indicated that lower freezing temperatures promoted increases in pore connectivity and structural complexity. After 60 F–T cycles at −20 °C, connected porosity increased from 11.15% to 18.67%, while the ratio of connected porosity to total porosity increased from 51.1% to 85.7%. At an impact pressure of 0.3 MPa, the dynamic strength after 60 cycles decreased by 9.51%, 20.9%, 38.1%, and 61.5% at 0, −3, −5, and −20 °C, respectively. Among the examined microstructural parameters, average throat length had the highest overall grey relational grade (0.821), suggesting that throat development is closely associated with dynamic strength decay. Lower freezing temperatures enhanced pore-ice expansion and unfrozen-water migration, promoting pore enlargement, throat extension, and crack connection. These results quantitatively link pore-network evolution to dynamic strength decay under different freezing temperatures, providing a microstructural basis for assessing the dynamic deterioration of sandstone in cold regions. Full article

Durability deterioration and interlayer bonding failure of ultra-thin overlays remain critical challenges under coupled environmental and mechanical actions. Although environmental damage to asphalt mixtures has been widely investigated, the relationship between pore-structure evolution and interlayer fatigue deterioration in polymer-composite-modified ultra-thin overlays incorporating styrene–butadiene–styrene (SBS) and micro carbon fiber (MCF) remains insufficiently understood. This study therefore extends existing research by clarifying this relationship under freeze–thaw cycling and water immersion. Three-point bending and direct shear fatigue tests were conducted to evaluate bending and interlayer shear fatigue performance, respectively, while nanoindentation and X-ray computed tomography (CT) were used to characterize micromechanical properties and three-dimensional pore-structure evolution. The results showed that five freeze–thaw cycles reduced the bending fatigue life by 75.3% and the interlayer shear fatigue life by 49.6%, while six days of water immersion reduced the interlayer shear fatigue life by 55.1%. Freeze–thaw cycling promoted open-pore and pore-throat development and increased total porosity by 23.9%, contributing to aggregate displacement and redistribution of the internal skeleton. In contrast, immersion increased the proportion of small and closed pores, while isolated pores concentrated near the interlayer weakened interlayer shear resistance. Although immersion caused greater reductions in hardness and modulus, freeze–thaw-induced pore development was associated with greater deterioration in bending fatigue performance. Furthermore, an adaptive-network-based fuzzy inference system (ANFIS) was developed to predict pore tortuosity from equivalent diameter, shape factor, and porosity, with testing errors ranging from 0.102 to 0.129 for untreated, freeze–thaw, and immersed specimens. An exponential relationship was further identified between tortuosity and the pore comprehensive effect index (PCEI), providing a quantitative approach for characterizing pore connectivity and evaluating environmental deterioration in polymer-composite-modified asphalt concrete. Full article

Water-retaining roller-compacted concrete (RCC) dams suffer severe deterioration under coupled moisture ingress and freeze–thaw (F-T) cycles. To elucidate the damage mechanisms, this study employed industrial X-ray computed tomography (CT) synchronized with uniaxial compression and acoustic emission (AE) monitoring. The cross-scale damage evolution of RCC was investigated under dry, water-saturated, 25, and 50 F-T cycle conditions. The results indicate the following: (1) Macroscopically, F-T damage causes linear peak stress attenuation, shifting the failure mode from brittle axial splitting to ductile oblique shear. (2) Mesoscopically, frost-heaving stress expands native mesopores (500–2500 μm), increasing their volume fraction from 8.45% to 14.86% and remodeling isolated voids into a 3D interconnected defect network. (3) Microscopically, GMM-based AE clustering reveals a fracture transition. Driven by moisture lubrication and defect propagation, global shear cracks surpass the 50% threshold at 25 cycles (53.5%), reaching 68.6% at 50 cycles. (4) For cross-scale mapping, calibrating the AE b-value via Aki’s method decouples pore-water signal attenuation. Its pre-peak characteristic (an initial decrease followed by a rebound) accurately maps microcracks unstably coalescing along interconnected pores to form macroscopic shear planes. This cross-scale mechanism provides a scientific paradigm for condition monitoring of massive concrete in cold regions. Full article

This study investigates the effects of low-volume steel microfibers (0–0.4 vol.%) and superplasticizer (SP) dosage (0.8 wt.% and 1.5 wt.%) on the mechanical and durability properties of self-compacting concrete (SCC) for railing structures, with a constant water-binder ratio of 0.28. Fresh (slump flow), mechanical (compressive strength up to 90 days, 28-day flexural strength), durability (drying shrinkage, freeze–thaw resistance after 200 cycles), and microstructural (mercury intrusion porosimetry) properties were evaluated. SP enhances flowability while steel fibers reduce it. All mixtures except that with 0.8% SP and 0.4% fibers meet the workability requirements of Chinese standard JGJ/T 283-2012 for SCC. Compressive and flexural strengths generally increase with fiber content but decrease when the SP dosage rises from 0.8% to 1.5%. Steel fibers effectively reduce drying shrinkage and improve freeze–thaw resistance, as indicated by higher relative dynamic elastic moduli and lower mass loss after 200 cycles. Microstructural analysis reveals that the higher SP dosage (1.5 wt.%) significantly increases porosity, which explains the observed higher shrinkage and lower strength. Considering mechanical properties, durability, and castability, the SCC mixture with 0.3 vol.% steel fibers and 0.8 wt.% SP is recommended for railing structure applications. Full article

Traditional cement-based foamed lightweight soils suffer from high construction costs, poor durability, and low solid waste utilization efficiency, which severely restrict their engineering application. A novel polyvinyl alcohol (PVA)-reinforced solid waste-based foamed lightweight soil is fabricated using Bayer red mud, mineral powder, and fly ash. To clarify the durability evolution mechanisms, systematic freeze–thaw cycling, long-term water immersion, and sodium sulfate erosion tests were conducted on PVA-reinforced solid waste-based, unreinforced solid waste-based, and pure cement-based specimens. The results demonstrate that the PVA-reinforced specimen achieves optimal freeze–thaw resistance with only 17.10% strength loss after 50 cycles, owing to the internal three-dimensional fiber network that restrains crack propagation and enhances matrix toughness. It also exhibits excellent long-term water immersion stability, with a mild strength increment of 4.04–10.33% after 120 days. In contrast, the CN exhibited a strength increase of 43.62%, attributed to its lower initial strength caused by incomplete hydration; however, its final strength remained between those of the other two groups. In sulfate environments, unreinforced solid waste-based specimens present superior corrosion resistance, while PVA fiber-induced interconnected pores slightly weaken sulfate erosion resistance. Microscopic analysis confirms that the generation of alunite and gypsum hydration products fundamentally causes performance discrepancies among different specimens. Different from previous studies focusing on single fiber modification or single solid waste partial replacement of cement, this study innovatively adopts a composite modification strategy of “multi-solid waste alkali-activated matrix + PVA fiber toughening”, and systematically reveals the durability evolution mechanism under multiple harsh environments. Full article

This study examined the effects of coating waste tire aggregates (WTAs) with pumice, perlite, or diatomite, combined with polypropylene (PP) fiber addition, on the fresh, mechanical, transport, and durability properties of one-part hybrid geopolymer composites. Sixteen mixtures were produced using a Taguchi L16 design with a binder system of fly ash, CEM II/B-S cement, and sodium metasilicate powder. Coating type, WTA ratio, and PP fiber content were the key performance factors. Pumice coating performed best overall by improving the interfacial transition zone: 28-day compressive strength reached 15.5 MPa and flexural strength 1.60 MPa, while porosity and capillary water absorption decreased significantly. Among the studied WTA levels, 10% WTA yielded the most positive direct responses in compressive strength, flexural strength, toughness, and capillary water absorption, whereas higher contents weakened matrix continuity. The effect of PP fiber was response-dependent: 0.5% fiber maximized compressive strength and durability-related responses, while 2% fiber gave the greatest flexural strength and toughness; no single dosage was universally optimal. The pumice-coated series was also the most stable under high temperature, freeze–thaw, MgSO₄, and H₂SO₄ exposure. Overall, waste tire aggregates can be technically incorporated into one-part hybrid geopolymer composites; a dedicated life-cycle assessment is nevertheless required to quantify the net environmental benefit. Full article

The transition to lower-clinker binders in heavy precast concrete is constrained by the need to combine rapid production cycles, high early-age strength, self-compacting performance, durability and measurable environmental benefits. The scientific gap addressed in this study is the limited integrated evidence comparing these criteria under conditions that are representative of industrial heavy precast production, particularly for CEM II/A-S 52.5 R and CEM II/B-V 42.5 R. Four concretes were assessed: CEM I 52.5 R, CEM II/A-S 52.5 R, CEM II/B-V 42.5 R, and a 50:50 CEM I/CEM II/B-V binder. The experimental programme included slump-flow, a plant-specific 600 mm flow-time indicator, compressive strength development, hardened density, water absorption, water penetration under pressure and freeze–thaw resistance. Environmental performance was evaluated using the manufacturers Environmental Product Declarations (EPDs) for the cement component within a cradle-to-gate boundary. All mixtures corresponded to at least strength class C50/60 at 28 days, while CEM I, CEM II/A-S and the 50:50 blend corresponded to C55/67. CEM II/A-S reduced water absorption from 5.49% to 4.29% and water penetration from approximately 61 to 23 mm relative to CEM I, but its freeze–thaw strength loss was 26.80% compared with 4.50% for CEM I. CEM II/B-V provided the lowest cement-related GWP, approximately 154 kg CO₂-eq/m³, about 25% below CEM I, whereas the 50:50 blend reduced this indicator by approximately 12% while achieving the highest 28-day compressive strength (approximately 78 MPa). The results show that cement selection for heavy precast concrete cannot be based on clinker content or strength alone. CEM II/A-S offered the most balanced technological and transport-property performance, whereas CEM II/B-V offered the greatest GWP reduction but requires consideration of its lower strength class and slower early-age development. Long-term durability and full life-cycle impacts remain to be verified. Full article

Previous studies have mainly examined sandstone freeze–thaw degradation under unloaded conditions, whereas the continuous influence of sustained stress on compressive and tensile properties remains unclear. To address this issue, water-saturated specimens were subjected to axial loads of 0–2 MPa and 0–10 freeze–thaw cycles, followed by uniaxial compression and Brazilian splitting tests. A two-variable exponential strength model and a load–freeze–thaw coupled discrete element model were established. Both strengths decreased with increasing freeze–thaw cycles. Under no load, after 10 cycles, the uniaxial compressive strength and tensile strength decreased by 27.85% and 36.67%, respectively, indicating higher freeze–thaw sensitivity of the tensile property. Loading mitigated strength loss: after 10 cycles, the two strengths of the 2 MPa group were 9.59% and 10.53% higher than those of the no-load group. The retention effect on compressive strength first increased and then decreased, whereas that on tensile strength increased with cycle number. The discrete element results showed that frost-heave cracks evolved from local initiation to connection and clustering, with tensile cracks dominating. Loading reduced tensile bond breakage and slowed crack accumulation and subsequent coalescence, linking the observed strength retention to the inhibition of mesoscopic tensile damage. Full article

Fine-aggregate source can alter both the load-bearing response and surface scaling of mortar under freezing and thawing, but these responses are often reduced to a single durability ranking. This study compared coal gangue sand mortar (CGM), river sand mortar (RSM), desert sand mortar (DSM), and standard sand mortar (StSM) after 0, 25, and 50 freeze–thaw cycles (FTCs). Compressive strength and mass loss were measured using three replicate specimens per quantitative condition, while post-compression fragments were examined by scanning electron microscopy (SEM). The primary integrative analysis was a parameter-free two-dimensional damage-trajectory map that retained absolute compressive strength and mass loss as separate measured axes; a weighted coupled index was retained only as an auxiliary sensitivity check. Before cycling, the compressive strengths of StSM, RSM, DSM, and CGM were $68.13\pm 0.48$, $53.90\pm 0.39$, $19.47\pm 0.33$, and $6.49\pm 0.07$ MPa, respectively. After 50 FTCs, StSM retained the highest absolute strength ($33.61\pm 0.39$ MPa) and the lowest mass loss ($0.21\pm 0.02\%$), whereas DSM retained $9.91\pm 0.19$ MPa and exhibited the highest mass loss ($17.46\pm 0.05\%$). The StSM trajectory moved primarily toward lower strength with negligible surface-material loss, while DSM moved toward both low residual strength and severe scaling. RSM showed substantial strength reduction followed by later-stage surface loss. CGM followed an atypical trajectory in which measured strength increased to $11.13\pm 0.13$ MPa while mass loss reached $9.67\pm 0.04\%$; because age-matched non-frozen controls were unavailable, this apparent gain cannot be separated from continued hydration and specimen-age effects. The SEM images suggested pores, interfacial discontinuities, cracking, and matrix loosening, although some defects may have been induced or widened by compression. The trajectory representation exposed distinct deterioration modes without arbitrary weighting, whereas the calculated ordering of CGM and RSM in the auxiliary index changed with weighting and normalization choices. The results support reporting absolute residual strength and surface loss jointly when screening alternative fine aggregates for cold-region mortar. Full article