Search Results (1,035)

The potential of clay as a replacement for Portland cement in the manufacture of injection cement–clay mortars (ICCMs) for soil stabilization is examined in this investigation. The objective of this study is to produce environmentally friendly injection-molded mortars for soil stabilization based on Portland cement (PC) and clay (C). Experimental ICCMs with C contents ranging from 0% to 50% without the addition of microsilica (MS) and ICCMs with C contents ranging from 0% to 50% and 2% MS were produced. The evaluation included the density, water segregation, and cone spread diameter of fresh ICCMs, alongside the density, flexural strength, and compressive strength of hardened ICCMs. The findings indicated that as C content rose from 0% to 50%, fresh mortars experienced a decrease in density, flowability, and water segregation. Hardened mortars exhibited reduced density, compressive strength, and flexural strength as C content increased. Modifying mortars with MS has a positive effect on their strength properties. The reduction in flexural and compressive strength for mortars with 50% C was 54.2% and 60.1%, respectively, while for similar mortars with 2% MS, the reduction in strength was 47.9% and 51.8%, respectively. ICCM soil stabilization compositions modified with MS are the most effective in comparison with similar compositions without MS and have a homogeneous structure with pores, microcracks, and hydration reaction product zones. The optimal ratios of raw components for the production of ICCMs for soil stabilization were determined: a water–solid ratio of 0.6, PC content from 90% to 50%, C content from 10% to 50%, and an MS content of 2% of the dry component weight. This research contributes to sustainable development by reducing CO₂ emissions per 1 m³ of mixture production by up to 47.8% and by using raw materials rationally. Full article

Concrete is the most used construction material, but its long-term performance depends on durability. Although fly ash has been used as a supplementary cementitious material, the effects of its mechanical activation on the concrete durability require further investigation. This study evaluated the influence of replacing 30% of cement with natural Class F fly ash (NFA) and ground fly ash (GFA) in concrete with a water-to-binder ratio (w/b) of 0.62, using a mixture without fly ash (WFA) as reference. Mechanical activation was performed by milling the fly ash, followed by characterization through particle size analysis and X-ray diffraction. Concrete durability was assessed using electrical resistivity, ultrasonic pulse velocity (UPV), water absorption, porosity, rapid chloride permeability (RCPT), carbonation resistance, and compressive strength tests. Mechanical milling reduced and transformed the ash morphology from spherical to amorphous, while quartz and mullite remained the main crystalline phases. Compared with CNFA, CGFA exhibited up to 101% higher electrical resistivity, 39.6% greater resistance to chloride penetration, 10.8% improved carbonation resistance, 0.4% lower water absorption, and a 5.38% reduction in porosity, although compressive strength decreased by more than 20%. These results demonstrate that mechanically activated fly ash is a viable alternative for enhancing the concrete durability performance exposed to aggressive environments. Full article

Cement-based grouting materials with a high water-to-cement ratio are susceptible to connected pore development, chloride ingress, and mechanical degradation in chloride-bearing groundwater and marine environments. To improve resistance to NaCl attack, this study compared an unmodified cement-based grouting material (NC) with a polyacrylate-emulsion-modified material (PA). Mechanical properties, surface wettability, pore structure, phase assemblage, thermal behavior, functional groups, and microstructure were investigated under different NaCl concentrations (0%, 5%, 10%, and 15%) and immersion durations (28 and 90 d). This study systematically evaluates the coupled evolution of mechanical strength retention, surface wettability, pore structure, chloride-bearing phases, and microstructure in a bulk PA-emulsion-modified high-water-to-cement-ratio grouting material under graded NaCl exposure. The results showed pronounced concentration- and time-dependent effects. Low NaCl concentrations were associated with continued hydration and reaction-product filling, whereas higher concentrations and prolonged exposure led to pore coarsening and strength loss. PA modification improved the mechanical stability of the material in NaCl environments. After 90 d of immersion in 15% NaCl, the compressive and flexural strengths of the PA group were 23.60% and 22.53% higher than those of the NC group, respectively, while the corresponding strength-retention ratios were higher by 9.06 and 10.40 percentage points. Contact-angle and MIP results showed that PA reduced surface wettability and mercury-accessible porosity. After 15% NaCl exposure, the contact angle of the PA group remained 72.5°, compared with 40.1° for the NC group, while the porosity decreased from 38.11% in the NC group to 30.98% in the PA group. XRD, TG-DTG, and FTIR analyses indicated the formation and evolution of Friedel’s salt or other chloride-bearing AFm phases after NaCl exposure. Combined with SEM observations, the results indicate that PA mitigates NaCl-induced deterioration through reduced surface wettability, refined pore structure, regulated chloride-bearing product distribution, and improved matrix integrity. Overall, the findings establish a coupled surface–pore–phase–microstructure framework for understanding the enhanced NaCl resistance of PA-modified cement-based grouting materials. Full article

Loess is highly water-sensitive and collapsible, and its conventional use as backfill in road and railway infrastructure may lead to settlement and deformation after wetting. Converting excavated loess into controlled low-strength material (CLSM) provides an alternative for backfilling; however, its engineering performance is strongly dependent on the water-to-solids ratio (W). In field construction, variations in the natural moisture content of loess cause the actual W to deviate from its design value, whereas conventional CLSM mix designs generally assume a fixed W, which may result in insufficient flowability or strength under actual field conditions. A Box–Behnken design was first employed to investigate the effects of the cement-to-soil ratio (C), water-to-solids ratio (W), and polycarboxylate superplasticizer content (P) on flowability (f), bleeding rate (Bᵥ), wet density (ρ), and 28-day compressive strength (qᵤ), based on which regression-based predictive models were developed. The sequential least squares programming (SLSQP) algorithm was then used to optimize mix proportions for backfilling behind abutments, culverts, and retaining walls and for subgrade backfilling. The optimization minimized the material cost per unit volume while requiring all performance indicators to satisfy the specified criteria under variations in W (ΔW = 0%, ±1%, ±2%, and ±3%). The results show that W is the dominant factor governing f, Bᵥ, and ρ, whereas C has the greatest influence on qᵤ. Increasing P markedly improves f but also increases Bᵥ. For backfilling behind abutments, culverts, and retaining walls, when the mean field soil moisture content is overestimated and the actual W is consequently lower than its design value, the mix optimized for ΔW = −3% satisfies the flowability criterion even when the measured flowability is up to 21.3 mm below the design value because of the lower actual soil moisture content. Conversely, when the mean field soil moisture content is underestimated and the actual W exceeds its design value, the mix optimized for ΔW = +3% satisfies the compressive-strength criterion even when the measured strength is up to 0.09 MPa below the design value because of the higher actual soil moisture content. Accounting for possible variations of up to ±3% in the water-to-solids ratio under field conditions, the optimal mix proportions are C13.14W37.64P0.069 for backfilling behind abutments, culverts, and retaining walls and C15.00W34.28P0.097 for subgrade backfilling. These findings provide a basis for the performance control and mix design of loess-based CLSM subjected to variations in the water-to-solids ratio. Full article

The 100 mV depolarization value cathodic protection (CP) criterion is widely used to protect the steel bars in atmospherically exposed concrete structures. The CP on the steel in concrete creates a secondary effect by increasing OH^- ions and decreasing Cl^- ions near the surface of the steel, against steel corrosion. In this phenomenon, there is a possibility that the CP criteria of 100 mV could be decreased due to the environmental changes caused by these secondary effects. In this study, the effects of different depolarization values of 25, 50, and 100 mV for the protection of steel bars in concrete specimens with different chloride ion concentrations were experimentally evaluated, and their effects on the corrosion rate of steel were investigated. The concrete had a water-to-cement ratio of 0.55 and a sand-to-total-aggregate ratio of 49%, and chloride was admixed as NaCl to give Cl⁻ contents of 2, 5 and 10 kg/m³, equivalent to 0.58%, 1.45%, and 2.90% by mass of cement. The steel bars were pre-corroded by an impressed current of 1.33 A/m² and were then protected for 250 days at 20 ± 2 °C and 60% relative humidity, the protection current being adjusted to hold average depolarization values of 21–37 mV, 57–63 mV, and 117–121 mV. After 250 days, the corrosion rate under CP was 0.18–0.95 mA/m², a reduction of 60–77% relative to the unprotected specimens, and raising the target depolarization from 25 mV to 100 mV improved that reduction by only 6–11 percentage points. The measured reduction factor of 2.5–4.3 is far below the factor of 50 predicted by the Tafel relationship for a 100 mV activation polarization, which is attributed to the partly passive state of the steel and to the non-activation components of the 24 h potential decay. Within the exposure conditions tested, a depolarization criterion below 100 mV therefore protected the steel as effectively as the conventional 100 mV criterion while requiring a markedly lower protection current density. 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 durability of marine concrete square piles is critically governed by chloride transport at the corners of piles, regions subject to multi-directional erosion and pronounced accumulation under cyclic wetting–drying conditions. In this study, we developed a two-dimensional coupled moisture–chloride convection–diffusion model for a quarter section of the corner of a square pile, incorporating the time-dependent surface chloride concentration and a nonlinear moisture diffusion coefficient. The governing equations were numerically solved using the unconditionally stable alternating direction implicit (ADI) finite-difference method, which effectively overcomes the instability issues inherent in long-term simulations of strongly coupled systems. Model predictions were validated against experimental data from the literature, showing good agreement. Parametric investigations revealed that (1) the effect of moisture–chloride coupling is significant, with a low initial degree of saturation intensifying capillary-driven convection and accelerating early-stage chloride ingress; (2) a higher water-to-cement ratio markedly increases pore connectivity, exacerbating chloride accumulation under bidirectional erosion; and (3) increasing the drying-to-wetting time ratio effectively reduces net chloride buildup by curtailing the total duration of immersion. These findings provide a theoretical foundation for durability design and service-life assessment regarding square pile foundations in marine tidal and splash zones. Full article

Marine concrete structures are subjected to multiple aggressive ions that react with hydration products, driving dynamic phase evolution and altering ion transport pathways. This study develops a multi-scale lattice diffusion–reaction coupled framework grounded in a microstructural evolution model, incorporating a simplified analytical correction for the electrical double layer (EDL) effect. Validation against Poisson–Boltzmann numerical solutions across a pore size range of 1.5–50 nm confirms that the mean relative errors for monovalent, divalent, and trivalent ions remain within 10%. The phase evolution of cement paste under single-ion attack was simulated, and its impact on ion transport performance under multi-ion coupled ingress was systematically investigated. Under multi-ion attack, solid phases exhibit a highly ordered spatial zonation. Chloride ions completely displace monosulfate, forming a Friedel’s salt-enriched zone. Meanwhile, directly penetrating external sulfate generates a pronounced surface ettringite peak, while sulfate released from monosulfate decomposition in the Friedel’s salt zone induces secondary ettringite precipitation deeper within the material, producing a characteristic double-step ettringite distribution. A cracking criterion based on the critical capillary pore filling fraction captures the transition from pore filling to microcracking, yielding a three-zone profile for the relative diffusion coefficient. At 500 days of exposure, crystallization-induced microcracking triggers a more than 7-fold increase in surface relative diffusivity ($w/c$ = 0.35). Furthermore, at 250 days, once cracking initiates, low water-to-cement ratio ($w/c$ = 0.3) matrices display a higher relative diffusivity amplification factor of approximately 9, compared to approximately 6 for high water-to-cement ratio ($w/c$ = 0.4) matrices. The established framework provides a quantitative tool for assessing the durability of concrete structures under complex chemical attack environments. 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 current reuse of blast furnace slag is limited, and the products made from it have low added value and minimal pricing potential. The primary objective of this research is to develop new eco-friendly 3D printing materials using blast furnace slag as the main raw material, simultaneously achieving combined optimization of color appearance and material performance, to increase the reutilization value of slag and address environmental problems caused by slag. Existing studies on slag-based 3D printing materials mainly focus on improving material performance, often neglecting the combined optimization of color and material performance. This study proposes a solution to create colored slag-based 3D printing materials, aiming to break the conventional view of slag waste as simply “black or gray.” This study optimized the particle size distribution of slag-based 3D printing materials using the Andreasen model. The CIELAB color difference formula was applied to reveal how color difference values varied under different mix ratios. Digital image analysis was conducted to evaluate the color characteristics of the specimens and the uniformity of the pigmentation. After 28 days of natural air curing, the color difference ΔE at various measurement points on each colored specimen remained below 3.0, indicating that iron oxide pigments exhibit satisfactory color stability within the slag matrix. To ensure high-quality 3D printing, this study examined the effect of water temperature on the curing time of colored slag-based 3D printing materials. Range analysis results showed that water temperature exerted the most significant influence on setting time (range = 255 s), substantially greater than that of pigment dosage (range = 15 s) and pigment type (range = 5 s). The Herschel–Bulkley constitutive model was used to calculate the flow index of the material. Printing tests confirmed that colored slag 3D printing materials are suitable for extrusion-based 3D printing. The 28-day compressive test results showed that the average fracture load of the three pigmented specimen groups ranged from 23.30 to 24.58 N. Cost analysis further indicated that the comprehensive material cost is approximately 467 RMB/ton, which is lower than that of commercially available colored cement, demonstrating favorable economic competitiveness. The development of colored materials for 3D printing based on blast furnace slag can expand their applications and market potential. It also improves material performance and market acceptance, and its cost advantage over commercial colored cement further enhances its viability for practical applications, promoting high-value recycling and reuse of slag waste. Full article

Silica aerogel–incorporated cementitious composites possess low density and thermal conductivity. Their thermal conductivity is influenced by the interplay of mix composition, pore structure, mineral admixtures, and environmental testing conditions. In this study, a literature-derived database containing 208 data records was established for thermal conductivity prediction. Eight variables were utilized as inputs: aerogel content, water-to-cement ratio (W/C), sand content, foam content, silica fume content, fly ash content, testing temperature, and testing relative humidity. Thermal conductivity was designated as the output. The models developed for this study included XGBoost, random forest (RF), support vector regression (SVR), and their counterparts optimized using particle swarm optimization (PSO), which were subsequently compared. Among the optimized models, PSO–SVR showed the most balanced predictive performance, with test-set R², RMSE, and MAE values of 0.9306, 0.1005, and 0.0658, respectively. SHAP analysis identified sand content as the most important variable, followed by W/C and aerogel content. Mechanistically, silica aerogel reduces effective thermal conductivity by introducing low-conductivity phases, weakening solid heat–transfer networks, increasing heat–flow tortuosity, and accumulating interfacial thermal resistance. This study provides a data–driven and interpretable approach for thermal conductivity prediction and low–conductivity mix design of silica aerogel–incorporated cementitious composites. Full article

The use of sugarcane molasses (SCM) as a sustainable stabilizing agent for geomaterials, particularly granular subbase soils, has recently attracted growing attention as an alternative to traditional stabilization methods employing cement, lime, or bitumen, which are often associated with high costs and environmental concerns. This study presents a mechanistic–experimental evaluation of SCM for stabilizing granular subbase materials at dosages of 2.5%, 5%, 7.5%, and 10% by weight of dry granular material. A comprehensive testing program was conducted, including compaction characteristics, California Bearing Ratio (CBR), resilient modulus (${\mathrm{M}}_{\mathrm{r}}$), permanent deformation under repeated loading, optical microscopy, and FTIR spectroscopy. In addition, multilayer elastic analysis using KENLAYER was performed to assess pavement structural performance in terms of critical strains and service life. The results showed that SCM significantly improved subbase performance within an optimum dosage range. The mixture containing 5% sugarcane molasses (5SCM) exhibited the highest overall performance, increasing CBR from approximately 26% to 34% and reducing accumulated permanent strain by approximately 45% compared with the control mixture. Optical microscopy and FTIR analyses supported the proposed stabilization mechanism, indicating improved particle contact at moderate SCM contents, whereas excessive SCM contents adversely affected performance due to lubrication and excessive particle-coating effects. Mechanistic analysis demonstrated that 5SCM improved pavement durability, increasing allowable load repetitions from 9.54 × 10⁵ to 1.14 × 10⁶ and extending pavement service life by approximately 20%. A durability–cost assessment further identified 5SCM as the most efficient dosage from both engineering and economic perspectives. Water immersion assessment indicated that SCM stabilization is suitable for pavement structures with effective drainage, whereas its application in continuously saturated or flood-prone environments is not recommended. Overall, SCM demonstrates strong potential as an environmentally sustainable stabilizer for granular subbase materials, with an optimum dosage of approximately 5% for enhancing both material performance and pavement durability. 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

The construction of adequate infrastructure in low-resource regions is frequently constrained by limited technical facilities, inadequate supply chains, and the absence of standardized quality control. This study presents a case study of the reinforced concrete foundation system of a multifunctional sports hall constructed in Cacine, Guinea-Bissau, where concrete production was carried out under severe logistical and technological constraints. Following construction, laboratory investigations were performed to evaluate the transported cement sample, locally available aggregates, and concrete specimens collected on site. Cement characterization included particle-size distribution, thermal analysis, and compressive strength testing, while the concrete was assessed through compressive strength and water absorption measurements. The aggregate grading complied with the relevant technical requirements and fell within the recommended grading envelope; however, the cement exhibited lower mechanical performance than expected from its declared class, although the non-standard specimen geometry does not permit formal conformity assessment. The concrete reached an average 28-day compressive strength of 12.9 MPa and exhibited relatively high water absorption, reflecting the combined influence of volumetric batching, high water demand, limited mixing efficiency, and the absence of chemical admixtures. Scenario analyses based on the Bolomey relationship indicated that improved control of the effective water-to-cement ratio could substantially enhance concrete performance. Although the study is limited by retrospective testing and a small number of specimens, it provides practical insight into the adaptation of concrete technology to resource-constrained environments and identifies key technological priorities for future infrastructure projects in Guinea-Bissau and similar regions. Full article

Intact deep sandstone cores are scarce, heterogeneous with poorly repeatable, limiting systematic laboratory studies of deep-rock mechanical behavior. This study selected dense sandstone recovered from 1050 m in the Pingdingshan mining area as the prototype system for the development of a targeted-sandstone-constrained screening strategy for simulated deep sandstone. The strategy integrates mineral-composition matching, orthogonal mixture design, mechanical testing, PCA-based comprehensive similarity evaluation, GMM classification, stress–strain curve comparison and fracture-morphology verification. Candidate materials were prepared using a cement–silica-fume matrix with quartz sand, K-feldspar, Na-feldspar, nanoclay and superplasticizer. Results show that the water–binder ratio dominated uniaxial compressive strength, tensile strength and elastic modulus, whereas superplasticizer and nanoclay had secondary effects. The PCA-based index assigned weights of 52.9%, 29.2% and 17.9% to uniaxial compressive strength, elastic modulus and brittleness index, respectively. Among the 25 mixtures sampled, S5 showed the highest mechanical similarity, with a simulation index of 71.65% and a stress–strain curve similarity of 0.958. GMM clustering identified S5 and S10 as the closest high-strength, high-stiffness and high-brittleness group, while S10 better reproduced natural crack geometry. These results indicate that the optimal simulated sandstone depends on the target response and provide a task-oriented route for reproducible simulated deep sandstone. Full article