Search Results (158)

Cement slurry is a staple grouting agent, yet its properties can weaken when exposed to heat. Studying grouting materials for use in high-temperature tunnels is therefore a matter of considerable importance. To enhance the applicability of cement-based slurry in high-temperature tunnels, multi-walled carbon nanotubes (MWCNTs), polycarboxylate ether superplasticizer (PCE), and hydroxypropyl methylcellulose (HPMC) were added to improve their performance at elevated temperatures. Various experimental methods were employed to investigate the properties of the modified slurry at different temperatures, including flowability, setting time, compressive strength, and dynamic water retention ratio. Additionally, X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM) were used to study the effects of temperature on hardened slurry. Experimental results indicate that the optimal MWCNTs content is 0.32%. At this content, the compressive strength of the hardened slurry after 28 days of curing at 80 °C increases by approximately 20%, reaching 26.4 MPa. PCE improves the fluidity of the slurry, while HPMC enhances its water dynamic water retention ratio. The optimal proportion was found to be 0.3% PCE and 0.2% HPMC. At this ratio, the fluidity of the slurry increased by about 8%, reaching approximately 17.7 cm; the dynamic water retention ratios of 0.8 m/s and 1.0 m/s improved by approximately 22% and 38%, respectively, achieving 35.8% and 18.1%. Furthermore, multi-walled carbon nanotubes significantly enhance the compressive strength of the hardened slurry primarily by suppressing the formation of ettringite during the later stages of hydration, as well as by providing nucleation sites, encapsulating hydration products, and bridging hydration product clusters within the microstructure. This investigation lays a theoretical groundwork for formulating and choosing grouting materials suited to high-temperature tunnel environments. Full article

To address the inherent conflict between fluidity and stability in high-concentration unclassified tailings slurries for blasthole stemming slurry (BSS), this study establishes an evaluation system based on “equal fluidity” to screen and optimize chemical admixtures suitable for high-concentration BSS. Three typical superplasticizers—polycarboxylate (PCE), naphthalene-based (NF), and melamine-based (MF)—were selected to systematically compare their effects on rheological parameters and bleeding performance under a controlled, consistent fluidity condition (16.0 ± 0.5 cm). The results indicate that the effectiveness of superplasticizers exhibits noticeably concentration dependence. While NF demonstrates the highest dispersion efficiency at low concentrations, PCE emerges as the sole effective admixture capable of maintaining the fluidity of high-concentration BSS (71% solid mass fraction), attributed to its robust steric hindrance effect. Rheological analysis reveals that the PCE-modified BSS exhibits a unique state characterized by “low yield stress and high differential viscosity,” which effectively decouples the contradiction between macroscopic flow and microscopic stability. Furthermore, the synergistic effect of high concentration and PCE constructs a kinetically stable suspension system, achieving “zero bleeding.” This study confirms that PCE is the optimal choice for preparing high-concentration pumpable BSS, providing a theoretical foundation for the design of deep-hole stemming materials in mining engineering. Full article

The present study investigates the development of non-autoclaved aerated concrete (NAAC) incorporating rice husk ash (RHA)-derived amorphous silica, polypropylene microfibers, and a polycarboxylate-based superplasticizer to improve mechanical performance and durability while maintaining low density and thermal conductivity. Experimental investigations included density, compressive strength, thermal conductivity, water absorption, X-ray diffraction (XRD), microstructural observations, and TG–DTA analysis. The developed compositions containing 5–7% RHA and 0.10–0.20% polypropylene microfibers achieved compressive strength values of 4.5–4.8 MPa at densities of 520–560 kg/m³, which are comparable to or higher than values commonly reported for non-autoclaved aerated concrete of similar density. Thermal conductivity decreased to 0.12–0.13 W/(m·K), while water absorption was reduced to 15–18%. XRD, microstructural, and TG–DTA analyses suggested enhanced hydration reactions and improved development of the cementitious matrix due to pozzolanic interaction between amorphous silica and calcium hydroxide. The incorporation of polypropylene microfibers was associated with improved structural homogeneity of the developed NAAC compositions, whereas the superplasticizer enhanced mixture homogeneity and pore stability. The results suggest that the combined use of agricultural waste-derived silica and fiber reinforcement provides an effective approach for producing sustainable and energy-efficient NAAC without autoclave curing. Full article

The addition of sulfoaluminate cement (SAC) to ultra-high-performance concrete (UHPC) enables sustainable high-speed construction due to the high 7-day strength without thermal curing. The fast hydration of SAC, however, endangers the admixture efficacy, which may compromise the structural integrity of the infrastructure components. This study investigates the effect of the physical form of polycarboxylate ether (PCE) superplasticizers on the performance of UHPC with the incorporation of SAC in ambient conditions. A paired experimental design of 32 mixtures compared liquid superplasticizers (LSPs) and powder superplasticizers (PSPs) in various binder compositions (OPC/SAC of 1/4–4/1) and water-to-binder ratios (0.18–0.21) at a constant dosage of admixtures of 1% except where w/b 0.18 (1.5% superplasticizers and 1% retarders were used). Findings indicate that LSPs enhance workability and compressive strength by 45% and 10.03%, respectively. The underlying mechanism is explained by comprehensive microstructural characterization through the use of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. SEM study showed a 23% decrease in porosity, and XRD patterns showed the increased formation of amorphous C-S-H gel for LSPs. The higher levels of Al³⁺ incorporated into the gel structure (C-A-S-H) of the liquid forms was also verified by FTIR spectra. Mechanically, the research reveals one of the kinetic mismatches, where the rate of SAC hydration is greater than the rate of powder dissolution, which leads to a failure to fully disperse and shear-controlled failures. LSPs, in contrast, make it possible to disperse particles immediately, so the matrices become more dense and shift to axial failure. These results provide practical guidelines to infrastructure engineers to use liquid superplasticizer in SAC-based systems in order to achieve sustainability and reliability in terms of performance in precast and fast-track construction projects. Full article

Improving the durability of reinforced concrete sleepers is essential for railway infrastructure exposed to dynamic loading, moisture, and repeated freeze–thaw action. This study proposes a material-level modification approach for heavy concrete for type 2 reinforced concrete sleepers based on the combined use of activated microsilica, a ferroalloy-production byproduct, electrolyzed mixing water, and a polycarboxylate superplasticizer. The novelty of the work lies in the preliminary electrochemical activation of microsilica in an alkaline medium and in the optimization of its joint use with KN-5 by means of second-order experimental design. The concrete was evaluated by compressive and bending strength tests, scanning electron microscopy (SEM), water-penetration testing, and freeze–thaw resistance testing. All modified mixtures outperformed the reference concrete. The highest 28-day compressive strength reached 67.0 MPa, while bending strength reached 7.26 MPa. SEM observations showed a denser and more homogeneous cement matrix with reduced capillary porosity and improved interfacial transition zones. Water resistance improved from W8 for the reference mixture to W10–W14 for the modified concretes. Most modified mixtures achieved a frost resistance grade of F500, and the composition containing 15% activated microsilica and 1.0% superplasticizer reached F550. The proposed approach is effective at the material level for producing heavy concrete with enhanced strength and durability characteristics for reinforced concrete sleeper applications. Full article

Driven by global carbon reduction targets, supersulfated cement has emerged as a promising low-carbon cementitious material. This study investigates the influence of a polycarboxylate superplasticizer (PCE) on the rheological behavior and early interfacial evolution of phosphogypsum-based supersulfated cement (PSSC). Rheological measurements, pore solution ion analysis, hydration heat analysis, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS) are employed to correlate early hydration processes with structural development. The results indicate that the incorporation of PCE significantly reduces the initial yield stress and moderates the structural build-up rate. At a PCE dosage of 0.3 wt.%, the initial static yield stress decreases from 1313 Pa to approximately 125 Pa, while the structural build-up index I_s,s reaches 10.19, indicating improved particle dispersion while maintaining progressive structural reconstruction during hydration. Phosphogypsum (PG) functions not only as a sulfate source but also as an active interfacial substrate that promotes the preferential nucleation of AFt on its surface. In the absence of PCE, continuous Ca–P-enriched layers form on PG particles, accompanied by localized AFt accumulation. After the incorporation of PCE, the primary crystalline phases remain unchanged; however, gypsum dissolution and AFt formation are delayed. Meanwhile, Ca–P enrichment shifts from continuous coverage to a more dispersed distribution, promoting the spatially separated growth of AFt crystals rather than dense localized aggregation. Overall, PCE influences the evolution of the structure and properties of the system by regulating early interfacial reactions and the spatial organization of hydration products. Full article

As a widely used building material, the performance of concrete has a far-reaching impact on the quality and durability of hydraulic engineering. Polycarboxylate superplasticizer (PCE) plays an increasingly important role in concrete engineering because of its unique high-efficiency water-reducing performance and the improvement effect on concrete performance. In this paper, the application and influence of polycarboxylate in concrete, including its chemical structure, action mechanism and application effect, are reviewed. It is found that polycarboxylate can greatly reduce the shrinkage of concrete and control its volume deformation. The objective of this review is to elucidate the mechanisms by which polyurethane-modified polycarboxylate (MPCE) reduces autogenous and drying shrinkage in concrete and to demonstrate its advantages over conventional PCE. On this basis, we focus on the core research object of MPCE and discuss in depth its effect on reducing the surface tension of concrete pore solution and the intrinsic mechanism of regulating volume deformation. The research clarifies the superior performance of MPCE over ordinary PCE in inhibiting autogenous shrinkage and drying shrinkage in concrete, which provides a targeted scientific basis for the practical application of MPCE in concrete volume deformation control. Full article

This study investigates the influence of the physical and chemical characteristics of three polycarboxylate ether (PCE) superplasticizers—differing in main-chain length, side-chain density, and dispersing-to-stabilizing polymer ratio (75:25, 50:50, and 25:75)—on the dispersion of calcined clays with varying metakaolinite contents (30.04–74.91 wt%) in synthetic cement pore solution (SCPS). Clays were characterized by XRF, XRD, TGA, FTIR, BET, Blaine fineness, and particle size distribution; PCEs were characterized by FTIR, ¹H NMR, GPC, and zeta potential. Dispersion was assessed via mini-slump tests for water demand, PCE dosage to achieve 260 ± 5 mm spread, and slump retention over 120 min, quantified by a normalized spread retention index (SR₁₂₀). Results revealed that clays with a higher metakaolinite content (58.45–74.91 wt%) and Blaine fineness (up to 13.116 m²/g) required two times higher PCE dosages and exhibited greater water demand due to enhanced surface reactivity and Ca²⁺/carboxylate affinity. Slump retention depended on PCE–clay compatibility: at a low metakaolinite content (30.04 wt%), all PCEs yielded SR₁₂₀ ≈ 1; at higher contents, dispersing-rich PCEs (e.g., 75:25 ratio) sustained superior retention (SR₁₂₀ > 1 in intermediate cases), while stabilizing-rich variants showed rapid loss. Zeta potential values remained close to zero due to the high ionic strength of the SCPS, indicating that electrostatic interactions play only a secondary role in the dispersion process, while steric effects govern the performance of the investigated PCEs. Overall, optimal PCE selection requires matching polymer architecture to clay reactivity for effective dispersion and fluidity retention in sustainable calcined clay systems. Full article

Gypsum (CaSO₄·2H₂O) crystallization is highly sensitive to the supersaturation pathway, which governs the balance between nucleation and crystal growth and ultimately controls growth morphology. In this study, gypsum was synthesized via two contrasting routes—diffusion-controlled crystallization and rapid precipitation—using identical reactant systems to enable a direct comparison of distinct kinetic regimes. A polycarboxylate-based superplasticizer was incorporated to investigate pathway-dependent additive effects. Time-resolved observations reveal that rapid precipitation is characterized by high nucleation density under steep supersaturation, whereas diffusion-controlled crystallization proceeds under gradually increasing supersaturation with restricted nucleation and sustained anisotropic growth. Powder X-ray diffraction confirms the formation of phase-pure gypsum under all conditions. Scanning electron microscopy shows that the presence of the superplasticizer reduces crystal number density and modifies crystal habit in both pathways, although the extent and manifestation of these effects depend strongly on the governing kinetic regime. Under diffusion-controlled conditions, the increasing superplasticizer dosage promotes the transition from elongated to more tabular morphologies, while rapid precipitation results in dense, intergrown aggregates under high supersaturation. Overall, the results demonstrate that the effectiveness of the superplasticizer is not intrinsic but depends on the crystallization pathway. These findings provide new insight into how supersaturation profiles mediate the interplay between additive interactions and growth processes, enabling improved control over gypsum crystal morphology. Full article

Concrete, as a widely used construction material, suffers from performance degradation due to chloride penetration and sulfate attack in harsh environments. Conventional performance-enhancing methods are costly and emit high levels of carbon dioxide. This study modified graphene oxide (GO) with polycarboxylate superplasticizer (PCE) alone or PCE synergized with a rubber viscosity reducer, optimized dispersion (50 °C water bath for 1 h), and prepared C50 modified concrete (500 kg/m³ cementitious materials, w/b = 0.33). GO contents were 0%, 0.001%, 0.003%, 0.005%; a group with 8% reduced cementitious materials (460 kg/m³) was also tested. Results showed PCE-viscosity reducer synergy better dispersed GO, improving concrete workability. GO accelerated cement hydration via nucleation, refining C-S-H gel and reducing porosity. At 0.005% GO, 56 d drying shrinkage dropped by 29.3% vs. the blank, and 56 d chloride penetration electric flux was 586 C, meeting 100-year service life. Sulfate resistance also improved with higher GO content. Even with 8% less cementitious materials, modified concrete outperformed the blank. This provides support for GO’s application in cement-based materials. Full article

This study investigated the effect of a polyurethane-modified polycarboxylate superplasticizer (P-PCE) on the volume deformation of hydraulic concrete. Macroscopically, the autogenous and drying shrinkage of concrete incorporating different types and dosages of PCEs were measured to analyze their influence. Microscopically, scanning electron microscopy (SEM) was employed to observe the hydration product morphology at 7 and 28 days. Low-field nuclear magnetic resonance (NMR) was utilized to quantify the pore structure, and a fractal dimension model was applied to correlate the microstructural characteristics with the macroscopic deformation. The results demonstrated that, compared to conventional PCEs, the laboratory-synthesized P-PCE (40% solid content) significantly reduced shrinkage and improved pore structure, thereby enhancing the volumetric stability of hydraulic concrete. The experimental results showed that, compared to ordinary PCE, P-PCE reduced the 60-day autogenous-shrinkage strain by 8.8% and the drying-shrinkage strain by 8.4%. Additionally, it decreased the total porosity by 19.46%, while also optimizing the pore structure distribution, thereby significantly improving the volume stability of hydraulic concrete. Full article

Conventional polycarboxylate superplasticizers (PCEs) suffer from uncontrollable adsorption, characterized by rapid initial uptake and limited subsequent release, which causes pronounced slump loss, particularly at elevated temperatures where hydration accelerates and dispersion efficiency declines. To overcome these limitations, we developed a series of chitosan-based upper critical solution temperature (UCST) responsive superplasticizers (Thermo-PCE_x, UCST = 40–42 °C) capable of temperature -adaptive dispersion during cement hydration. A vinyl-functionalized chitosan macromonomer (uCS-g-T₈) was synthesized by reacting cetyl polyoxyethylene glycidyl ether with chitosan, followed by methacrylate modification, and then copolymerized with acrylic acid and isopentenol polyoxyethylene ether to yield Thermo-PCE_x with tunable sugar-to-acid ratios. The polymers exhibited clear UCST-type phase-transition behavior in aqueous solution. When incorporated into cement paste, Thermo-PCE_x enabled continuous fluidity enhancement at 25 °C (<UCST), with increases of 43.6%, 52.9%, 62.3% and 63.6%, after 180 min for x = 0.5, 1, 1.5 and 2, respectively. Adjusting dosage and composition further regulated setting time, improved rheological stability, and enhanced mechanical strength. These findings demonstrate a viable pathway for designing bio-based, temperature-responsive superplasticizers with self-adaptive dispersibility for sustainable cement technologies. Full article

Rheology plays an important role in the 3D concrete printing technology, because it directly governs the flowability and shape retention of the material, impacting both the printing process and the final quality of the obtained structure. Local raw materials such as Portland cement, washed sand, and tap water were used for the preparation of 3D-printed concrete mixtures. The solid-state polycarboxylate ether with an anti-foaming agent was used as superplasticizer. The Portland cement was partially replaced (by volume) with a natural zeolite additive in amounts ranging from 0% to 9% in 3D-printed concrete mixtures. A rotational rheometer with coaxial cylinders was used in this research for the determination of rheological characteristics of prepared 3D-printed concrete mixtures. The Herschel–Buckley model was used to approximate experimental flow curves and assess rheological parameters such as yield stress, plastic viscosity, and shear-thinning/thickening index. The additional experiments and calculations, such as water bleeding test and evaluation of the carbon footprint of 3D-printed concrete mixtures, were performed in this work. The replacement of Portland cement with natural zeolite additive positively influenced rheological and stability-related properties of 3D-printed concrete mixtures. Natural zeolite additive consistently reduced water bleeding, enhanced yield stress under increasing shear rates, and lowered plastic viscosity, thereby improving flowability and mixture transportation during the 3D printing process. As the shear-thinning/thickening index remained stable (indicating non-thixotropic behavior in most cases), higher amounts of natural zeolite additive introduced slight thixotropy (especially under decreased shear rates). These changes contributed to better shape retention, layer stability, and the ability to print taller and narrower structures without collapse, making natural zeolite additive suitable for use in the optimized processes of 3D concrete printing. A significant decrease in total carbon footprint (from 3% to 19%) was observed in 3D-printed concrete mixtures with an increase in the mentioned amounts of natural zeolite additive, compared to the mixture without this additive. Full article

Balancing high fluidity and stability is a critical challenge in deep-shaft cemented paste backfill (CPB) with high-concentration tailings. This study investigates the synergistic regulation mechanism of a combined admixture system comprising hydroxypropyl methylcellulose (HPMC) thickener and polycarboxylate (PCE) or Melamine-Formaldehyde Resin (MFR) superplasticizers on CPB rheology, mechanical strength, and microstructure. Results indicate that HPMC significantly enhanced anti-segregation performance via intermolecular bridging, substantially increasing yield stress and plastic viscosity. Upon PCE introduction, the steric hindrance provided by its side chains effectively disrupted HPMC-induced flocs and released entrapped water. Consequently, yield stress and plastic viscosity were reduced by up to 22.1% and 64.3%, respectively, with PCE exhibiting markedly superior viscosity-reducing efficiency compared to MFR. Mechanical testing revealed that PCE co-addition did not compromise early-age strength but enhanced 3, 7, and 28-day unconfined compressive strength (UCS) by refining pore structures and promoting the uniform distribution of hydration products. Microstructural analysis unveiled a competitive adsorption mechanism: preferential PCE adsorption dispersed particle agglomerates, while non-adsorbed HPMC formed a viscoelastic network within the pore solution, constructing a stable “dispersion-suspension” microstructure. This work provides a theoretical basis for optimizing high-performance backfill formulations. Full article

The overlying rock in the weathering and oxidation zone has well-developed micro-fissures, making roadway roof control highly challenging. Ordinary cement slurry is hard to inject, failing to achieve effective reinforcement. By introducing admixtures like ultrafine fly ash and polyvinyl alcohol (PVA) to modify ultrafine cement, this paper developed a PVA-modified ultrafine cement-based grouting material (PVAM-UFCG). It systematically investigated the influences of various factors on the slurry’s setting time, fluidity, water separation rate, viscosity, and 28-day uniaxial compressive strength, determining the optimal mix ratio through comprehensive analysis. The results show that the water–cement ratio is the dominant factor affecting slurry viscosity, strength, and setting time; the polycarboxylate superplasticizer concentration has the most significant influence on fluidity and water separation rate; a 20% ultrafine fly ash replacement rate can optimize particle gradation and enhance long-term strength; and a 1.0% polyvinyl alcohol concentration can effectively control the water separation rate (≤5%) and improve slurry cohesiveness. Through range analysis and multi-indicator comprehensive evaluation based on the entropy weight method, the performance-balanced optimal mix ratio meeting the grouting requirements for the Weathering and Oxidation Zone was determined: a water–cement ratio of 0.6, an ultrafine fly ash replacement rate of 20%, a polyvinyl alcohol concentration of 1.0%, and a polycarboxylate superplasticizer concentration of 0.4%. This mix ratio material exhibits good permeability, stability, and appropriate reinforcement strength. The research results can provide a new material choice and theoretical basis for controlling the surrounding rock of roadways under similar geological conditions. Full article