Search Results (48)

This study presents a comprehensive analysis of self-healing concrete technologies, focusing on autogenous and autonomous self-healing methods, through a systematic literature review of peer-reviewed articles. The autogenous self-healing method relies on the natural hydration and carbonation processes of unhydrated cement particles, enhanced by additives such as fly ash, slag, and superabsorbent polymers. It is effective for small cracks (<200 μm), environmentally favorable, and cost-efficient, although it is limited by relatively slow healing rates and reduced performance over time. The autonomous self-healing method incorporates external agents, primarily bacteria like Bacillus cohnii and Bacillus sphaericus, encapsulated in protective carriers. These bacteria precipitate calcium carbonate (CaCO₃) upon activation, sealing cracks up to approximately 1240 μm. While generally more effective in terms of healing efficiency and durability, the autonomous self-healing method involves higher production costs. Life cycle assessment results indicate that the autonomous self-healing concrete can exhibit up to 85% higher environmental impact during the production phase than conventional concrete. However, during the production phase, the autogenous self-healing method shows about 32% higher CO₂ emissions than the autonomous method. Results from investigating the mechanisms, performance, repairability, environmental impacts, and economic aspects in this study demonstrate that bacterial concentration and nutrient type critically influence mechanical properties, with optimal strength gains at 10⁵ cells/mL. Both techniques reduce corrosion risk and extend service life, with the autonomous self-healing method displaying superior performance in harsh environments. However, the autogenous self-healing method is more feasible for large-scale applications due to lower costs and simpler implementation. The study concludes that method selection should align with project-specific durability, sustainability, and economic goals. Full article

Cementitious materials are naturally brittle, which makes them prone to cracking. This study effectively employs autogenous healing techniques using microcapsules to solve this issue. The goals were twofold: first, to microencapsulate isophorone diisocyanate (IPDI) as a catalyst-free healing agent; and second, to evaluate how these microcapsules improve the healing abilities of cementitious materials. Polyurethane (PU) prepolymer with an NCO content of 19.8% was successfully created. Using interfacial polymerization, smooth, spherical microcapsules of IPDI with an average diameter of 38 to 62 micrometers were produced. The elastic modulus of the microcapsules ranged from 0.23 to 0.18 GPa, while their hardness varied between 5.29 and 4.15 MPa. Over six months, the microcapsules showed a weight loss of 9.72% to 12.47%, depending on their size, under ambient conditions. Specimens containing 3% of fabricated microcapsules demonstrated the ability to seal cracks less than 100 µm wide by up to 70%. Specimens that incorporated 3% of their cement weight in IPDI microcapsules achieved an impressive 74% recovery rate in compressive strength. In contrast, control mortars without microcapsules showed a recovery rate of less than 50%. Analysis using Energy Dispersive Spectroscopy (EDS) revealed a significant presence of carbon in areas where the microcapsules had ruptured and the cracks had healed. This confirms the effectiveness of the healing process, consistent with established self-healing theories. The water tightness recovery trace showed a recovery rate of up to 61%. Additionally, the specimens containing microcapsules exhibited higher initial compressive strength than the control specimens. However, this also indicates that some microcapsules may have ruptured unintentionally during preparation and molding. Therefore, further research on the mechanical properties of microcapsules, especially their stiffness in cementitious composites, is necessary. Full article

This investigation examines the novel application of bacterial concrete as a sustainable substitute for traditional concrete within the construction sector, utilizing bibliometric analysis in conjunction with machine learning. The main aim of the study is to gain insights into the application and potential benefits of using bio-based concrete in the construction industry. A comprehensive search of all publications indexed in Scopus was carried out for the period spanning from 2020 to 14 March 2025, followed by meticulous screening and extraction of relevant documents. The dataset obtained from Scopus was processed in strict accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to uphold transparency and replicability throughout the systematic review process. A descriptive analysis was undertaken to evaluate publication trends over time. The research on bio-concrete combined with machine learning is highly concentrated in Asia, Europe, and the USA; in contrast, vast areas of Africa show no research output regarding self-healing concrete based on this data extraction. Various types of bacteria, including Bacillus species, are explored for their calcium carbonate precipitation capabilities in this review. Microbial-induced calcite precipitation process reduces carbon emissions associated with cement production and extends concrete lifespan by sealing cracks. Full article

To address the severe wear and galvanic corrosion of TC4/Mg three-dimensional interpenetrating composites caused by the potential difference and hardness disparity between the two phases, this work proposes a hybrid surface modification strategy combining plasma electrolytic oxidation (PEO) with a self-assembled monolayer (SAM) doped with multi-walled carbon nanotubes (MWCNTs). A PEO ceramic coating was first grown in situ on the composite surface, followed by sealing modification using MWCNTs-containing SAM. The microstructure, phase composition, tribological behavior and potentiodynamic polarization curves of the coatings were systematically evaluated. The results show that the PEO coating is mainly composed of Mg₂SiO₄, MgO, MgF₂ and TiO₂, exhibiting a typical porous structure. After the MWCNTs-doped SAM composite modification, the nano-fillers and the molecular layer synergistically seal the micropores and cracks, and the surface transforms into a continuous and dense layered morphology. Wear tests reveal that the composite coating reduces the friction coefficient to 0.195 and decreases the wear volume by 93.53% compared with the bare composite. The “micro-roller bearing” effect and debris adsorption of MWCNTs significantly improve the wear resistance, and the dominant wear mechanism changes from abrasive wear to three-body wear. Electrochemical measurements show that the corrosion current density of the composite coating decreases from 2 × 10⁻⁴ A·cm⁻² (bare composite) to 1.401 × 10⁻⁹ A·cm⁻², i.e., a reduction by five orders of magnitude, with a protection efficiency of 99.99%. This is attributed to the physical barrier effect of the PEO coating and the synergistic sealing of defects, as well as the blocking of electron transfer by MWCNTs/SAM. The multi-level protection system of “PEO + MWCNTs + SAM” constructed in this work achieves a synergistic improvement in both wear resistance and corrosion resistance of the TC4/Mg two-phase interpenetrating composite, and holds promise for further investigation as an osseointegration implant material. Full article

Deep geological disposal is widely recognized as the most reliable strategy for the long-term isolation of high-level radioactive waste (HLW). In granitic host rocks, fractures in the near-field represent the primary pathways for groundwater flow and potential radionuclide migration. The self-sealing capacity of carbonate-filled fractures, along with its long-term effectiveness, plays a critical role in maintaining the integrity of the multi-barrier system and ensuring repository safety. Near-field fractures undergo complex thermo–hydro–mechanical–chemical (THMC) coupled evolution driven by excavation-induced disturbances, decay heat, groundwater saturation, and ongoing water–rock interactions. Within the confined fracture spaces, carbonate minerals may persistently undergo precipitation–dissolution cycling and micro- to nanoscale structural reorganization, resulting in progressive reductions in fracture connectivity and hydraulic transmissivity. However, existing studies have largely focused on short-term sealing effects, with limited systematic understanding of the long-term safety functions. In this context, this study comprehensively investigates carbonate-induced self-sealing in granitic fractures within the near-field of a repository under realistic THMC-coupled conditions. We elucidate the micro- and nanoscale heterogeneous precipitation characteristics governed by non-classical nucleation pathways, reveal how dynamic precipitation–dissolution equilibria facilitate ongoing reductions in fracture transmissivity, and propose a multi-dimensional framework for long-term hydraulic, mechanical, and chemical performance assessment. Our findings demonstrate that carbonate self-sealing operates as a dynamic, reorganizing, and multi-mineral cooperative mechanism rather than a static, one-directional process. Its core safety function lies in the sustained suppression of fracture transmissivity. The mechanistic insights and evaluation framework proposed in this study provide a foundation for integrating natural carbonate self-sealing with engineered barrier system design, thereby improving fracture control, advancing long-term safety assessment, and optimizing the design of HLW deep geological repositories. Full article

Concrete infrastructure in coastal regions is prone to premature degradation due to crack formation under aggressive environmental exposure. Conventional repair methods remain costly and often ineffective. This study evaluates a biomineral self-healing system incorporating Paenibacillus polymyxa spores and calcium carbonate (CaCO₃) to improve the durability and mechanical performance of medium-strength concrete with a design compressive strength of 21 MPa, intended for vulnerable coastal housing. A full factorial experimental program was conducted using three bacterial concentrations (1.0%, 1.5%, 2.0% of mixing water volume) and three CaCO₃ dosages (3%, 5%, 7% as cement replacement). Specimens were pre-cracked under compressive loading, exposed to a simulated coastal environment, and monitored for 28 days. The optimal formulation (2% bacteria + 5% CaCO₃) yielded an 8.8% increase in compressive strength and a 24% increase in flexural strength compared with the control. Crack width reduction reached up to 0.23 mm (65.7%) under wet curing, with effective sealing observed for cracks ≤ 0.5 mm. Recovered compressive strength after healing reached 17.3 MPa, equivalent to 71% of the design strength. These findings demonstrate the potential of P. polymyxa as a viable non-ureolytic agent for self-healing concrete, offering a simple and scalable strategy to extend service life in resource-limited coastal regions while supporting Sustainable Development Goals 9 and 11. Full article

While self-healing concrete shows promise for infrastructure repair, its effectiveness is significantly compromised in low-temperature environments because of slowed reaction kinetics and the embrittlement of capsule shells. To address this limitation, novel composite microcapsules featuring an ethyl cellulose shell and a dual-core comprising expansive cement and epoxy resin were developed. These microcapsules were fabricated using a physical spheronization-coating method and subsequently incorporated into cement mortar. Response surface methodology was employed to identify the optimal system, which balances self-healing performance with the retention of mechanical properties: a microcapsule content of 3% (by mass of cement) and a particle size range of 1.4 to 1.7 mm. Under conditions of −20 °C, the optimal formulation achieved a crack surface healing ratio of up to 44.1% and a compressive strength recovery of up to 6.0%. Microstructural and spectroscopic analyses (SEM-EDS, XRD) revealed a synergistic healing mechanism. This mechanism involves the formation of calcium carbonate, C–S–H gel, and anorthite, all cohesively bonded within a polymerized epoxy network. This work establishes a functional material strategy for enabling autonomous crack repair in concrete structures subjected to cold climates. In such environments, even marginal strength recovery, when coupled with effective crack sealing, can significantly enhance structural durability. Full article

Concrete is the most widely used construction material worldwide, yet its production and disposal pose significant environmental challenges due to high carbon emissions and limited recyclability. While microbial colonization of concrete is often associated with structural deterioration, recent research has highlighted the potential of microorganisms to contribute positively to concrete recycling and self-healing. In this study, we investigated the bacterial and fungal communities inhabiting urban concrete samples using amplicon-based taxonomic profiling targeting the 16S rRNA gene and internal transcribed spacer (ITS) region. Our analyses revealed a diverse assemblage of microbial taxa capable of surviving the extreme physicochemical conditions of concrete. Several taxa were associated with known metabolic functions relevant to concrete degradation, such as acid and sulphate production, as well as biomineralization processes that may support crack repair and surface sealing. These findings suggest that concrete-associated microbiomes may serve as a reservoir of biological functions with potential applications in sustainable construction, including targeted biodegradation for recycling and biogenic mineral formation for structural healing. This work provides a foundation for developing microbial solutions to reduce the environmental footprint of concrete infrastructure. Full article

To address the issues of easy degradation, dehydration, and insufficient deep plugging strength of traditional pre-crosslinked gel particles (PPGs) in high-temperature and high-salinity reservoirs, this study innovatively introduced amphiphilic carbon dots (CDs) with both hydrophilic and hydrophobic structures as multifunctional modifiers. The carbon dot-reinforced PPGs (CD-PPGs) were successfully prepared through in situ polymerization. Through systematic characterization, microscopic visualization experiments, and macroscopic oil displacement evaluation, the performance enhancement mechanism and profile control behavior were deeply explored. The results show that the amphiphilic carbon dots significantly enhanced the material’s temperature resistance (up to 110 °C), salt resistance (up to 15 × 10⁴ mg/L salinity), and mechanical properties by constructing a “hydrogen bond-hydrophobic association” dual crosslinking system within the PPG network. More importantly, it was found that CD-PPGs exhibit a unique “self-aggregation” ability in deep reservoirs, which enables the in situ formation of high-strength plugging micelles at the target location while ensuring excellent injectability. At a permeability range of 539.0–2988.6 mD, the sealing rate of 0.5 PV CD-PPGs was greater than 95%. With permeabilities of 490.1 mD and 3020.5 mD under heterogeneous reservoir simulation conditions, the total recovery degree after the CD-PPGs was 52.6%, which was 20.5% higher than that of single water flooding. This study not only developed a high-performance profile control nanomaterial but also elucidated its strengthening mechanism, providing new insights and a theoretical basis for advancing deep profile control technology. Full article

Calcareous sandstones, acting as sealing layers, play a crucial role in hydrocarbon accumulation of formations with high sand content (sand content > 80%). However, the genetic mechanisms, sealing mechanisms, and effectiveness of calcareous sandstones remain unclear. This study takes the Zhuhai–Enping formations in the Panyu A Sag as an example. By comprehensively analyzing data from well logs, cores, cast thin sections, elemental geochemical analysis and carbon–oxygen isotopes, the genetic mechanisms, development patterns, and controlling effects on hydrocarbon accumulation of calcareous cement layers are investigated. The main findings are as follows: (1) The calcareous sandstone cements are mainly composed of dolomite, ankerite, and anhydrite. With increasing burial depth, dolomite transitions from micritic dolomite to silt-sized and fine-crystalline dolomite, and finally to coarse-crystalline dolomite. (2) The local transgression provided ions such as Ca²⁺ and Mg²⁺, forming the material basis for early dolomite formation. As burial depth increased, the diagenetic environment shifted from acidic to alkaline, leading to the dolomitization of early-formed calcite and the formation of ankerite. (3) The high source-reservoir displacement pressure difference effectively seals hydrocarbon accumulation. Vertically interbedded tight calcareous sandstones and thin marine transgressive mud-stones collectively control efficient hydrocarbon preservation and enrichment. This research addresses the current limits in the study of “self-sealing sandstone layers,” and provides new geological insights and predictive models for hydrocarbon exploration in sand-rich settings. Full article

Geothermal energy, recognized as a sustainable and clean resource, is playing an increasingly critical role in the global shift toward low-carbon energy systems. Nevertheless, the exploitation of fractured geothermal reservoirs is often impeded by severe lost circulation during drilling, where conventional plugging materials fail under high-temperature, high-salinity, and high-pressure conditions due to inadequate mechanical strength, poor thermal resistance, and lack of self-adaptive sealing behavior. In response, self-healing materials have emerged as an innovative strategy for developing intelligent lost circulation control technologies. Herein, we report a novel self-healing gel (XFFD) synthesized via inverse emulsion polymerization using acrylamide (AM), acrylic acid (AA), p-nitroblue tetrazolium (PNBT), and modified silica nanoparticles (PAS). The resulting material exhibits exceptional thermal stability, with decomposition onset above 356 °C, as determined by thermogravimetric analysis. Rheological and mechanical assessments reveal outstanding viscoelasticity, moderate swelling capacity (4.17-fold in deionized water), and a high self-recovery efficiency of 91.15%, accompanied by a bearing strength of 3.65 MPa. Mechanistic investigations indicate that the autonomous repair capability stems from dynamic non-covalent interactions—primarily hydrogen bonding and ionic associations—enabled by amide and carboxyl groups within the polymer network. Sand bed filtration tests under simulated geothermal conditions (150 °C, 8% salinity) demonstrate that XFFD forms a robust sealing barrier with significantly shallower invasion depth compared to conventional materials such as sulfonated asphalt and calcium carbonate. This work presents an effective self-healing gel system that ensures reliable wellbore strengthening and fluid loss control in challenging high-temperature, high-salinity geothermal drilling operations. Full article

Reinforced concrete durability depends on a passive oxide film protecting embedded steel, sustained by high-alkalinity pore solutions. Cracking fundamentally alters transport, allowing rapid chloride and carbon dioxide ingress, which undermines passivity and accelerates corrosion. Self-healing concrete technologies aim to autonomously restore transport barriers and reestablish electrochemical stability. This review critically synthesizes evidence on healing effectiveness for corrosion mitigation through a dual framework of barrier restoration and interface stabilization, integrating depth-resolved chloride profiles with electrochemical performance indices. Critically, visual crack closure proves an unreliable indicator of corrosion protection. Healing mechanisms exhibit characteristic spatial signatures: autogenous and microbial approaches preferentially seal surface zones with diminishing effectiveness at reinforcement depth, while encapsulated low-viscosity polymers achieve greater depth continuity. However, electrochemical recovery consistently lags transport recovery, with healed specimens achieving only partial restoration of intact corrosion resistance. Recovery effectiveness depends on crack geometry, moisture conditions, and healing mechanism characteristics, with systems performing effectively only within narrow, condition-specific windows. Effective corrosion protection requires coordinated barrier and interface strategies targeting both bulk transport and steel surface chemistry. The path forward demands rigorous field validation emphasizing electrochemical outcomes over appearance metrics, long-term durability assessment, and performance-based verification frameworks to enable predictable service life extension. Full article

Cracks in concrete are a persistent issue that compromises structural durability, increases maintenance costs, and poses environmental challenges. Self-healing concrete has emerged as a promising innovation to address these concerns by autonomously sealing cracks and restoring integrity. This review focuses on two primary healing mechanisms: autogenous healing and microbial-induced calcite precipitation (MICP), the latter involving the biomineralization activity of bacteria, such as Bacillus subtilis and Sporosarcina pasteurii (formerly known as B. pasteurii). This review explores the selection, survivability, and activity of these microbes within the alkaline concrete environment. Additionally, the review highlights the role of fiber-reinforced cementitious composites (FRCCs), including high-performance fiber-reinforced cement composites (HPFRCCs) and engineered cement composites (ECCs), in enhancing crack control and enabling more effective microbial healing. The hybridization of natural and synthetic fibers contributes to both improved mechanical properties and crack width regulation, key factors in facilitating bacterial calcite precipitation. This review synthesizes current findings on self-healing efficiency, fiber compatibility, and the scalability of bacterial healing in concrete. It also evaluates critical parameters, such as healing agent integration, long-term performance, and testing methodologies, including both destructive and non-destructive techniques. By identifying existing knowledge gaps and performance barriers, this review offers insights for advancing sustainable, fiber-assisted microbial self-healing concrete for resilient infrastructure applications. Full article

Reservoirs and caprocks overlap with each other in heterogeneous carbonate rocks. The sealing capacity of caprocks and their controlling factors are not clear, which restricts the prediction, exploration, and development of carbonate hydrocarbon reservoirs. We selected core samples from the Ordovician reservoirs and caprocks in the Tarim Basin, China, for scanning electron microscopy, thin section, breakthrough pressure (BP), high-pressure mercury intrusion porosimetry (HMIP), and nitrogen adsorption method (N₂GA). The experimental results show that the reservoir and caprock can be distinguished by BP. The BP of the reservoir is less than 3.0 MPa, and the BP of the caprock is less than 3.0 Mpa. We analyzed the heterogeneity characteristics and differences in reservoirs and caprocks with different lithologies from the perspectives of monofractal and multifractal. The results indicate that the differences in pore structure of grainstone, dolomite, and micrite/argillaceous limestone result in significant heterogeneity differences between samples. The correlation analysis between the fractal parameters and BP indicates that the characteristics of reservoir microporous structures have a decisive impact on BP (correlation coefficient > 0.7). The pore structure of the carbonate reservoir–caprock system exhibits self-similarity. The heterogeneity of the caprock has no significant control effect on BP (correlation coefficient < 0.3), while the higher the heterogeneity of the reservoir, the greater the BP. The sealing capacity of the caprock depends on the heterogeneity differences in pore types and pore structures between the reservoirs and caprocks. When both the reservoir and the caprock are grainstone, the micropores in the reservoirs and caprocks are dispersed but evenly distributed, and little heterogeneous differences can achieve sealing. When the lithology of reservoirs and caprocks is different, the enhancement of heterogeneity differences in micropores will improve the sealing capacity of the caprock. In summary, fractal dimension is an effective method for studying the heterogeneous structure and sealing capacity of pore–throat in carbonate caprocks. This study proposes a new perspective that the difference between the heterogeneity of micropore structures of reservoirs and caprocks affects the sealing capacity of carbonate rocks, and provides a new explanation and model for the sealing mode of carbonate rock caprocks. Full article

The integration of bacterial biotechnology into construction and geotechnical practices is redefining approaches to material sustainability, infrastructure longevity, and environmental resilience. Over the past two decades, research activity in construction biotechnology has expanded rapidly, with more than 350 publications between 2000 and 2024 and a five-fold increase in annual output since 2020. Beyond bibliometric growth, technical studies have demonstrated the remarkable performance of bacterial systems: for example, microbial-induced calcium carbonate precipitation (MICP) can increase the compressive strength of treated soils by 60–70% and reduce permeability by more than 90% in field-scale trials. In concrete applications, bacterial self-healing has been shown to seal cracks up to 0.8 mm wide and improve water tightness by 70–90%. Similarly, biofilm-mediated corrosion barriers can extend the durability of reinforced steel by significantly reducing chloride ingress, while bacterial biopolymers such as xanthan gum and curdlan enhance soil cohesion and water retention in eco-grouting and erosion control. The novelty of this review lies in its interdisciplinary scope, integrating microbiological mechanisms, materials science, and engineering practice to highlight how bacterial processes can transition from laboratory models to real-world applications. By combining quantitative evidence with critical assessment of scalability, biosafety, and regulatory challenges, this paper provides a comprehensive framework that positions construction biotechnology as a transformative pathway towards low-carbon, adaptive, and resilient infrastructure systems. Full article