Search Results (74)

The conservation of tuff- and coral rock-built architectural heritage structures (AHS) is challenging because access to original tuff and coral rock has become difficult and severely limited due to urbanization, land reclamation, the depletion of stone quarries, anti-mining and anti-quarrying legislation. An emerging approach to address this issue is to create compatible “replacement” rocks via geopolymerization, a process that is more sustainable and greener than the use of conventional cement and concrete. To explore the potential of geopolymers for AHS conservation strategies, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were implemented; 103 eligible articles were identified and classified into geopolymers for AHS (34 articles), tuff-built AHS (60 articles), and coral rock-built AHS (9 articles). Tuff substrates in AHSs appear in a variety of colors (yellowish-brown, grayish-cream, reddish-brown, pale greenish-gray and pink hues), densities (1.0–2.5 g/m³), and compressive strengths (3–100 MPa). Meanwhile, coral rock substrates in AHSs appear in whitish-cream color and are coarse-pored (1–5 MPa), fine-grained (8–15 MPa), and calcarenite (50–60 MPa). In terms of geopolymer formulation, metakaolin was reported as the most popular main precursor or admixture, while NaOH and Na₂SiO₃ were used simultaneously as alkaline activators. Aggregates used in geopolymer formulations depended on local availability, including quartz sand, river sand, crushed stones, carbonate stones, volcanic rock, volcanic sand, tuff, brick, ceramic tiles, and waste materials. Aesthetics, chemical composition, physical attributes, and mechanical properties have been identified as key criteria to ensure geopolymer compatibility for AHS conservation application. To date, geopolymers have been applied for AHS conservation as repair mortars, consolidants (i.e., grout and adhesives), and masonry strengthening (i.e., fiber-reinforced mortar). Finally, geopolymers formulated for AHS conservation have similar durability as the original substrate based on accelerated aging tests (i.e., salt mist, wet-dry, and freeze–thaw) and long-term outdoor exposure experiments. Full article

Industrial activities have caused heavy metals, such as cadmium (Cd), chromium (Cr), lead (Pb), and copper (Cu), to seriously threaten groundwater safety through seepage pathways. This study explored the formation of biofilms using microbe-induced calcium carbonate precipitation (MICP) technology to simultaneously reduce seepage in contaminated water and immobilize heavy metals. By optimizing the cementation fluid concentration and the intermittent grouting time, the optimal operating conditions for forming a biofilm were determined to be 1.5 mol/L cementation fluid and an intermittent time of 12 h, under which the stable infiltration rate of the sandy loam soil column can be reduced by more than 80%. We found that this biofilm can effectively inhibit the convective transport of Cd, Cr, Pb, and Cu, with the cumulative convective flux reduction rates reaching 56.25%, 56.25%, 54.54%, and 55.59%, respectively. SEM and XRD analysis indicate that the physical blockage of soil pores by calcium carbonate crystals is the dominant mechanism controlling infiltration flow, while the detection of new mineral phases, such as lead carbonate (PbCO₃), cadmium carbonate (CdCO₃), and basic copper carbonate (Cu₂(OH)₂CO₃) provides direct evidence for the chemical co-precipitation immobilization of heavy metals. This study demonstrates that MICP biofilm is a green and sustainable technology for in situ remediation of heavy metal pollution through physical–chemical synergistic effects, offering a promising alternative with a lower environmental footprint compared to conventional methods. Full article

Under dual challenges of global infrastructure expansion and industrial solid waste management, alkali-activated polymers (AAP), as industrial solid-waste-based low-carbon cementitious materials, exhibit immense potential in grouting engineering applications. This review synthesizes current research progress through three critical dimensions: reaction mechanisms, performance characteristics, and grouting applications (grouting for reinforcement and water-blocking). The reaction mechanism universally comprises three stages: dissolution, depolymerization, and polycondensation. Key performance determinants include precursor composition (e.g., slag, fly ash, metakaolin) and alkaline activator properties (type, modulus, concentration). The multifunctional advantages of AAP are fundamentally governed by their microstructural evolution. Specifically, the rapid formation of highly cross-linked C-(A)-S-H and N-A-S-H gels directly contributes to rapid setting and high early strength development, with high-calcium precursors such as slag exhibiting faster strength gain than low-calcium systems, such as fly ash and metakaolin. Furthermore, the absence of vulnerable calcium hydroxide phases, combined with a densified, low-porosity aluminosilicate network, provides superior thermal stability, corrosion resistance, frost durability, and low permeability. Nevertheless, pronounced autogenous shrinkage and drying shrinkage, driven by mesopore moisture loss and the highly viscoelastic solid skeleton, remain primary constraints for field implementation. In grouting reinforcement, AAP can effectively enhance the strength and structural integrity of weak soils, such as soft clay, loess, and sulfate-rich saline soils. For grouting water-blocking, particularly in sodium-silicate-based binary systems, AAP achieves rapid gelation, superior washout resistance, and high anti-seepage pressure, proving optimal for groundwater inflow control. Future research must prioritize (i) standardized mix design protocols for performance consistency, (ii) advanced shrinkage mitigation strategies, (iii) systematic durability assessment under coupled environmental stressors (e.g., wet–dry cycling, chemical attack, thermal fatigue), and (iv) cross-disciplinary collaboration for industrial-scale validation. Full article

The degradation of building foundations, underground structures, and historical fabrics in sulfate-laden environments poses a persistent threat to the durability and safety of the built environment. Developing effective, sustainable repair materials is of paramount importance. This study presents the development, systematic optimization, and performance validation of a novel micro-expansive grout designed for high durability in aggressive sulfate conditions. The grout formulation utilizes industrial by-product fly ash, quicklime, and site-compatible soils, emphasizing sustainability. Nine chemical admixtures were screened for sulfate resistance enhancement. Laboratory experiments rigorously characterized the effects of water-to-solid ratio and admixture dosage on fresh-state properties (fluidity, setting time) and hardened-state performance (volumetric stability). To resolve a multi-objective optimization problem balancing injectability, dimensional compatibility, and cost-effectiveness, an integrated multi-criteria decision-making (MCDM) framework combining FAHP, MII, CRITIC, and TOPSIS was employed. This data-driven methodology identified an optimal formulation incorporating 3% disodium hydrogen phosphate (DSP) at a 0.58 water-to-solid ratio. The optimized grout exhibited a flow value of 75 mm, ensuring excellent injectability within the target range (40–120 mm), and an expansion rate of 7.67%, which falls within the safe range (0%–10%) to ensure dimensional compatibility. Accelerated durability tests via cyclic immersion in sodium sulfate solution demonstrated the optimized grout’s exceptional resistance to sulfate attack, retaining approximately 88% of its compressive strength after 15 aggressive cycles. The balanced properties and validated durability indicate strong potential for this grout in demanding repair scenarios. One key example is the repair of fissures in earthen heritage structures, which requires extreme material compatibility and long-term performance. Full article

Overburden layers, composed of unconsolidated sediments, are widely distributed in construction, transportation, and water conservancy projects, but their inherent defects (e.g., developed pores, low strength) easily induce engineering disasters. Grouting is a core reinforcement technology, yet traditional design relying on empirical formulas and on-site trials suffers from high costs and low prediction accuracy. Numerical simulation has become a key bridge connecting grouting theory and practice. This study systematically reviews the numerical simulation of overburden grouting based on 82 core articles screened via the PRISMA framework. First, the theoretical system is clarified: core governing equations for seepage, stress, grout diffusion, and chemical fields, as well as their coupling mechanisms (e.g., HM coupling via effective stress principle), are sorted out, and the advantages/disadvantages of different equations are quantified. The material parameter characterization focuses on grout rheological models (Newtonian, power-law, Bingham) and overburden heterogeneity modeling. Second, numerical methods and engineering applications are analyzed: discrete (DEM) and continuous (FEM/FDM) methods, as well as their coupling modes, are compared; the simulation advantages (visualization of diffusion mechanisms, parameter controllability, low-cost risk prediction) are verified by typical cases. Third, current challenges and trends are identified: bottlenecks include the poor adaptability of models in heterogeneous strata, unbalanced accuracy–efficiency, insufficient rheological models for complex grouts, and theoretical limitations of multi-field coupling. Future directions involve AI-driven parameter optimization, cross-scale simulation, HPC-enhanced computing efficiency, and targeted models for environmentally friendly grouts. The study concludes that overburden grouting simulation has formed a complete “theory–parameter–method–application” system, evolving from a “theoretical tool” to the “core of engineering decision-making”. The core contradiction lies in the conflict between refinement requirements and technical limitations, and breakthroughs rely on the interdisciplinary integration of AI, multi-scale simulation, and HPC. This review provides a clear technical context for researchers and practical reference for engineering technicians. Full article

This study follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework, combining bibliometric mapping and mechanistic synthesis to provide a unified evidence-based review of cementitious grouts in ground support systems. The bibliometric layer quantifies global research activity, while the systematic synthesis interprets how material composition, pozzolanic chemistry, and rheology control grout performance and sustainability. This study presents a systematic review complemented by bibliometric analysis to synthesise global research trends and technical advances in grout design. A dataset of 1200 articles was screened, from which 101 journal papers met the inclusion and quality criteria and were analysed in detail. Co-occurrence mapping of author keywords was then used to identify research hotspots and collaborative structures. The bibliometric analysis revealed that Construction and Building Materials is the leading outlet. Co-authorship mapping highlighted strong international collaboration, with leading clusters centred on supplementary cementitious materials, rheology, and microstructural analysis. The technical review consolidates five interrelated themes: reinforcement mechanisms, cementitious grouts, chemical reactions and pozzolanic reactivity, fresh and hardened state properties, and microstructural development with rheological behaviour. Across these themes, supplementary cementitious materials and waste-derived binders have emerged as central to both performance enhancement and carbon reduction, while advanced experimental and modelling techniques have refined understanding of microstructural evolution and grout–rock–bolt interactions. Collectively, the findings underline that cementitious grouts are no longer passive fillers but engineered composites designed for mechanical efficiency, durability, and environmental responsibility. Key research gaps remain in the standardisation of rheological testing, long-term durability under complex field conditions, and integration of life-cycle assessment into grout development. Addressing these challenges will be critical for the design of next-generation grouts capable of meeting the dual imperatives of safety and sustainability in mining and civil engineering. Full article

Achieving sustainable pavement construction through high-content Reclaimed Asphalt Pavement (RAP) is a critical industry goal, but its implementation is frequently challenged by the reduced mechanical performance and durability inherent in such mixtures. This study evaluates the performance of semi-rigid pavements with RAP from 0% to 100%, a chemical rejuvenator, and four novel cementitious grout formulations (G1–G4). A comprehensive experimental program examined compressive strength, flexural strength, rutting resistance, fatigue life, and moisture sensitivity. Statistical analysis revealed that increasing RAP content significantly reduced all performance metrics. However, the primary innovation of this work lies in identifying strong interaction effects between key variables. The chemical rejuvenator effectively mitigated performance losses, with its benefits most pronounced at higher RAP contents (p ≤ 0.003). Among the Gi types, G3, containing a proprietary high-reactivity mineral additive, consistently achieved superior results; for instance, the R100-J-G3 regained over 70% strength of the virgin control mix (R0-NJ-G3). Notably, the interaction between RAP content and grout type (p ≤ 0.015) revealed that G3’s performance increased with RAP content, demonstrating its pivotal role in enabling technically viable 100% RAP mixtures. These findings underscore that the successful use of high-content RAP depends not just on individual components but on the optimized synergy between rejuvenator and grout selection, offering a validated pathway for technically viable pavements containing 100% RAP, reducing reliance on virgin materials and lowering environmental impact. Full article

The long-term stability of grout-reinforced fractured rock masses in acidic groundwater environments after tunnel fires is critical for the safe operation of underground engineering. In this study, grouting reinforcement tests were performed on fractured diorite specimens using a high-strength fast-anchoring agent (HSFAA), and their mechanical degradation and microstructural evolution mechanisms were investigated under coupled high-temperature (25–1000 °C) and acidic corrosion (pH = 2) conditions. Multi-scale characterization techniques, including uniaxial compression strength (UCS) tests, X-ray computed tomography (CT), scanning electron microscopy (SEM), three-dimensional (3D) topographic scanning, and X-ray diffraction (XRD), were employed systematically. The results indicated that the synergistic thermo-acid interaction accelerated mineral dissolution and induced structural reorganization, resulting in surface whitening of specimens and decomposition of HSFAA hydration products. Increasing the prefabricated fracture angles (0–60°) amplified stress concentration at the grout–rock interface, resulting in a reduction of up to 69.46% in the peak strength of the specimens subjected to acid corrosion at 1000 °C. Acidic corrosion suppressed brittle disintegration observed in the uncorroded specimens at lower temperature (25–600 °C) by promoting energy dissipation through non-uniform notch formation, thereby shifting the failure modes from shear-dominated to tensile-shear hybrid modes. Quantitative CT analysis revealed a 34.64% reduction in crack volume (V_ca) for 1000 °C acid-corroded specimens compared to the control specimens at 25 °C. This reduction was attributed to high-temperature-induced ductility, which transformed macroscale crack propagation into microscale coalescence. These findings provide critical insights for assessing the durability of grouting reinforcement in post-fire tunnel rehabilitation and predicting the long-term stability of underground structures in chemically aggressive environments. Full article

This study evaluates adhesive bolts (chemical anchors) bonded with epoxy and vinyl ester resins for surface and tunnel excavations in tropical mining environments under static and dynamic loading. Over 300 pull-out tests in concrete and hard rock examined the effects of bolt length, curing time, and substrate condition on load capacity, failure mode, and bond–slip response. Epoxy anchors exhibited higher bond strength, including under early-age and thermally active conditions, while vinyl ester showed improved ductility and post-peak behaviour in fractured rock. Numerical modelling with Rocscience RS2 (Phase 2) and Unwedge simulated excavation responses for bolt lengths of 190–250 mm and spacings of 0.5–2.0 m. Tensile failure dominated at wider spacings, whereas closely spaced anchors enhanced confinement and redistributed stresses. The combined experimental–numerical evidence quantifies chemical-anchor performance in complex subsurface settings and supports their use for early-age support and long-term stability. Findings motivate integration of resin-grouted bolts into modern support designs, particularly in seismically sensitive or hydrothermally variable mines. Full article

The rehabilitation of underground infrastructure requires cement grouts that combine high injectability into micro-cracks with superior mechanical strength and durability. Conventional grouts, however, are limited by excessive yield stress and the formation of weak crystalline phases. This study investigated sodium polyacrylate (PAAS) as a multi-functional modifier to address these limitations. Through a multi-scale approach combining rheological measurements, spectroscopic analysis (FTIR, LF-NMR), diffraction (XRD), and electron microscopy (SEM), we elucidated the synergistic modification mechanisms of PAAS. The results demonstrated that PAAS operated via two pathways: (i) chemically, its carboxyl groups chelated Ca²⁺ ions, suppressing Ca(OH)₂ crystallization and refining C-S-H gel; (ii) physically, it provided electrostatic and steric dispersion, dismantling flocculated networks to reduce yield stress by 80.3% and enhance fluidity by 30.7%. This drastically improved injectability was complemented by micro-structural optimization, where PAAS eliminated percolation pores (>1 μm) and promoted a homogeneous, dense matrix. Consequently, the mechanical properties were significantly enhanced, with a 0.04% PAAS dosage maximizing compressive strength (15.56 MPa, +26.2%) and a 0.06% dosage elevating flexural strength (5.74 MPa, +29.3%). This work establishes that low-dosage PAAS modification enables a unique combination of high fluidity, strength, and durability by leveraging synergistic chemical and physical mechanisms, providing a tailored, cost-effective solution for advanced grouting applications. Full article

This paper addresses the issues of insufficient expansion force, low early strength (1-day compressive strength < 1.5 MPa), and poor toughness (flexural strength < 0.8 MPa) in traditional chemical foamed cement used for road grouting repair. By combining single-factor gradient experiments with microscopic mechanism analysis, the study systematically investigates the performance modulation mechanisms of controlled-release foamed cement using additives such as heavy calcium powder (0–20%), calcium chloride (0.2–1.2%), latex powder (0.2–1.2%), and polypropylene fiber (0.2–0.8%). The study innovatively employs a titanium silicate coupling agent coating technique (with the coating agent amounting to 25% of the catalyst’s mass) to delay foaming by 40 s. Scanning electron microscopy (SEM) and pore structure analysis reveal the microscopic essence of material performance optimization. Full article

Traditional soil stabilization methods, including cement and chemical grouting, are energy-intensive and environmentally harmful. Microbial-induced carbonate precipitation (MICP) technology offers a sustainable alternative by utilizing microorganisms to precipitate calcium carbonate, binding soil particles to improve mechanical properties. However, the application of MICP technology in soil stabilization still faces certain challenges. First, the mineralization efficiency of microorganisms needs to be improved to optimize the uniformity and stability of carbonate precipitation, thereby enhancing the effectiveness of soil stabilization. Second, MICP-treated soil generally exhibits high fracture brittleness, which may limit its practical engineering applications. Therefore, improving microbial mineralization efficiency and enhancing the ductility and overall integrity of stabilized soil remain key issues that need to be addressed for the broader application of MICP technology. This study addresses these challenges by optimizing microbial culture conditions and incorporating polyethylene fiber reinforcement. The experiments utilized sandy soil and polyethylene fibers, with Bacillus pasteurii as the microbial strain. The overall experimental process included microbial cultivation, specimen solidification, and performance testing. Optimization experiments for microbial culture conditions indicated that the optimal urea concentration was 0.5 mol/L and the optimal pH was 9, significantly enhancing microbial growth and urease activity, thereby improving calcium carbonate production efficiency. Specimens with different fiber contents (0% to 1%) were prepared using a stepwise intermittent grouting technique to form cylindrical samples. Performance test results indicated that at a fiber content of 0.6%, the unconfined compressive strength (UCS) increased by 80%, while at a fiber content of 0.4%, the permeability coefficient reached its minimum value (5.83 × 10⁻⁵ cm/s). Furthermore, microscopic analyses, including X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS), revealed the synergistic effect between calcite precipitation and fiber reinforcement. The combined use of MICP and fiber reinforcement presents an eco-friendly and efficient strategy for soil stabilization, with significant potential for geotechnical engineering applications. Full article

Microbial-induced calcium carbonate precipitation is an efficient and environmentally friendly soil stabilization technology. To explore the mineralization performance of carbonate precipitation, this study selects three factors, including the type of cementing solution (TCS), the cementing solution concentration (CSC), and the ratio of bacteria to cementing solution (B/C ratio), to investigate their effects on microbial mineralization. This study reveals the influence of each factor on the amount and rate of carbonate precipitation and analyzes the changes in the characteristics of carbonate precipitation crystals, such as the crystal diameter. The experimental results show that (1) the mineralization effect of magnesium ions and calcium ions results in higher precipitation amounts and rates than copper ions, with less environmental pollution. The concentration of the grout solution is positively correlated with the precipitation amount and negatively correlated with the precipitation rate, while the B/C ratio shows the opposite trend. (2) The crystal diameter of CaCO₃ between crystals reduces as the B/C ratio decreases and the CSC increases. (3) The characteristics of MgCO₃ crystals are mainly affected by the CSC. Both excessively high and low concentrations lead to an increase in crystal diameter. (4) The characteristics of CuCO₃ crystals are relatively stable, with smaller crystal particles maintained at around 1 μm. This study can provide a reference for the reinforcement of different types of soils, offering optimal reinforcement solutions based on the required crystal size, carbonate generation amount, and generation rate. It reduces resource waste and unnecessary chemical use, providing a theoretical foundation for sustainable soil remediation and ecological construction. Full article

This study aims to identify the most suitable pre-reinforcement support measures to prevent TBM jamming when passing through the fractured zone of a gully fault. Given the high likelihood of jamming in such areas, the research focuses on selecting the most effective support system by considering factors such as surrounding rock stability, strata displacement, support structure stress, and cost-effectiveness. Theoretical analysis is employed to predict TBM jamming risks, based on design data, a 10 m gully unit and fractured rock mass were established at 75 m in the excavation direction with assigned parameters. Support effects of pipe curtains, grouting, anchors, and arch supports were analyzed under four conditions: chemical grouting, conduit installation, advanced pipe grouting, and double-layer pipe grouting. On-site verification reveals that TBM jamming occurs when the resisting torque on the cutter exceeds the maximum torque the cutter can generate. For the gully fault, pre-reinforcement measures are essential to stabilize the surrounding rock. Among the different methods, surface drilling reinforcement is the most effective. It significantly improves the surrounding rock’s stability, reducing the plastic zone’s depth by approximately 52.3% compared to the advanced pipe shed method. The axial force on the anchors decreases by 77.9–83.8%, arch stress is reduced by 68.9–90.8%, and tunnel deformation is minimized by 2.13–50.78%, all of which contribute to enhancing the safety of the initial support structure. On-site coring results, TBM boring parameters, and deformation monitoring data confirm that the surface drilling pre-reinforcement method outperforms the grouting pre-reinforcement for the pipe shed, ensuring the safe excavation of TBM in the gully fault conditions. These findings provide valuable insights for TBM tunnel construction in similar geological environments. Full article

This paper reports the results of a full-scale field test that was conducted to assess the performance of the use of wet-milling cement and chemical compound grouting in the same hole to reinforce a flexural fracture zone. Wet-milling cement and chemical compound grouting methods were used to treat a layer of the flexural fracture zone with a thickness of 19 m. The procedures of the cement–chemical compound grouting method were described in detail, and the results of the normal water pressure test, fatigue water pressure test, failure water pressure test, and shear wave velocity test suggested that the working effects in the epoxy testing area were better than those in the acrylic acid salt test area, which further indicated that the cement–chemical compound grouting method was feasible. In addition, the improvement mechanism of the cement–chemical compound grouting technology was studied; this method is beneficial for solving the problem of the reinforcement effect not being ideal in practical engineering and further improving the compactness of dam structures. Full article