Self-healing Agent Research Articles

Self-healing performance of silica nanoparticle-infused concrete based on microbial mineralization

This study investigates the effects of incorporating two substances–expanded perlite as a carrier for bacteria and nanosilica–into cement mortar. The objective of this study is to evaluate the effect of the dosage of these two substances on the strength and self-healing properties of mortars. The strengths of the specimens at different curing ages are tested using a pressure-testing machine and recorded. Additionally, precracks are introduced into the specimens. The cracks and their healing products are observed via electron microscopy, scanning electron microscopy, and X-ray diffraction to validate the experimental results. The results show that the self-healing agents agglomerate at the cracks and trigger a metabolic reaction, thus resulting in the formation of numerous calcium carbonate precipitates that sealed the cracks. Therefore, the addition of self-healing agents significantly improves the self-healing properties of the cement mortar. The nanosilica facilitates the hydration reaction of cement in mortar. Additionally, nanosilica undergoes a pozzolanic reaction with calcium hydroxide, which consumes calcium hydroxide and generates hydrated calcium silicate to fill the pores. Consequently, the incorporation of an appropriate amount of nanosilica effectively enhances the strength of the cement mortar. Therefore, simultaneously incorporating self-healing agents and nanosilica while controlling the dosage provides a new approach for optimizing both the mechanical properties and self-healing performance of concrete.

Research on the properties of crystalline admixtures: Self-healing healing materials for concrete from multiple perspectives

The research on the self-healing of concrete promoted by crystal admixtures provides a new direction for the green development of construction industry. In this study, three crystal admixtures, i.e., l-aspartic acid (LAA), Na2SiO3 and nano-silica (NS), were screened from the experimental results in terms of promotion of hydration, fast reaction, and effective filling. The three components were mixed as concrete self-healing agents, and the experimental ratio was designed by response surface method. Finally, the optimal ratio was selected according to the visual healing effect. The durability of mortar with the optimum ratio of self-healing agent was studied by the experiment of resistance to chloride ion and sulfate attack; its preliminary heat release was studied by hydration microcalorimeter. The microscopic analysis was carried out by X-ray powder diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) test and mercury injection method (MIP). The experimental results showed that the best healing effect was achieved when the dosage of LAA, Na2SiO3 and NS reached 0.5 %, 0.4 % and 0.15 % of the cement mass. In the process of healing, the early healing products are mainly calcium carbonate, and the late healing products are mainly ettringite and calcium silicate hydrate (CSH), and the healing agent effectively reduces the porosity and improves the pore structure, making the concrete matrix more dense.

Effect of super absorbent polymers on the self-healing capability of macrocracked ultra-high performance concrete under highly aggressive environments

In this study, the performance of superabsorbent polymers (SAPs) as self-healing agents in macrocracked ultra-high performance concrete (UHPC) was extensively evaluated, with a focus on compressive strength behavior in different aggressive environments. Three UHPC mixtures were designed: a control mixture, a UHPC with 0.3 % sodium polyacrylate (poly(AA)), and a UHPC with 0.3 % polyacrylate-co-acrylamide (poly(AA-co-AM)). Samples with macrocrack widths of 0.3 mm, 0.5 mm, and 1 mm, as well as uncracked samples, were prepared. The samples underwent immersion in deionized water, chloride saltwater, and compound saltwater. The performance of self-healing was evaluated by measuring crack closure rates, recovered compressive strength, and stereomicroscopic inspections. Further, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) was performed to monitor mineral formation and the healing process. The results indicate that both poly(AA) and poly(AA-co-AM) SAPs significantly enhanced the self-healing capabilities of UHPC, with poly(AA) demonstrating superior performance. Self-healing was more pronounced in samples with cracks width of 0.3 mm, whereas samples with cracks widths of 0.5 mm and 1.0 mm exhibited incomplete and negligible healing, respectively. The healed samples recovered a substantial portion of their compressive strength, regardless of the crack width. However, the presence of chloride and/or sulfate ions was found to impede the self-healing process. As observed from the SEM/EDX results, in addition to CaCO3 and C-S-H gel, undesirable healing products like Friedel’s salt and ettringite were also formed in chloride and compound saltwater environments which significantly affected self-healing durability.

Influence of Ti3AlC2 additions on CMAS corrosion resistance of porous LaMgAl11O19 abradables

The corrosion of calcium-magnesium-aluminosilicate (CMAS) is a critical degradation mechanism for the hot sections of aircraft engines, particularly affecting abradable components where inherent defects complicate the prevention of rapid CMAS melt penetration. To address this challenge, Ti3AlC2 was incorporated into the porous LaMgAl11O19 abradables at concentrations of 5–20 wt% as both a self-healing agent and sintering aid. Annealing at 1200 °C markedly improved crack closure and pore isolation within the coating, with these effects intensifying with higher Ti3AlC2 concentrations, and resulted in the retention of excess TiO2. CMAS interaction tests conducted at 1300 °C demonstrated that only the abradables with 20 wt% Ti3AlC2 addition significantly reduced the penetration of CMAS melt. This effect is attributed to the densification of the abradables caused by self-healing, which blocks the propagation of CMAS along defect channels, and the role of TiO2 as a nucleating agent that facilitates the crystallization of CMAS and the precipitation of CaAl2Si2O8. The La/Ca ratio in the solid solutions related to LaMgAl11O19 and LaTi2Al9O19 can be used to reflect the corrosion level of platelet-like grains, where a value below 1 is likely to trigger their dissolution.

Synergistic Effects of Ternary Microbial Self-Healing Agent Comprising Bacillus pasteurii, Saccharomyces cerevisiae, and Bacillus mucilaginosus on Self-Healing Performance in Mortar

In order to prevent structural damage or high repair costs caused by concrete crack propagation, the use of microbial-induced CaCO3 precipitation to repair concrete cracks has been a hot topic in recent years. However, due to environmental constraints such as oxygen concentration, the width and depth of repaired cracks are seriously insufficient, which affects the further development of microbial self-healing agents. In this paper, a ternary microbial self-healing agent composed of different proportions of Bacillus pasteurii, Saccharomyces cerevisiae, and Bacillus mucilaginosus was designed, and its crack repair ability was evaluated. When the mixing ratio was 7:1:2, the cell concentration was the highest, the precipitation amount of CaCO3 was the highest, and the crystallinity of calcite crystal was the highest. Compared to the single microorganism, the mortar specimens with ternary microorganisms had the largest repair area (up to 100%) and the deepest repair depth (CaCO3 presents at 9–12 mm from the crack surface). This is because when the concrete breaks, all three microorganisms are activated by water, O2, and CO2. Saccharomyces cerevisiae and Bacillus mucilaginosus accelerated the growth of Bacillus pasteurii and more mineralized products; CaCO3 was rapidly formed and quickly filled on the crack surface. When CaCO3 seals the surface of the crack, the internal Saccharomyces cerevisiae and Bacillus mucilaginosus continue to play a role. Bacillus mucilaginosus can accelerate the dissolution of CO2 produced by the anaerobic fermentation of Saccharomyces cerevisiae and the hydrolysis of CO32−, thereby improving the repair of the crack depth direction.

Advanced Micro/Nanocapsules for Self-Healing Coatings

The concept of intelligence has many applications, such as in coatings and cyber security. Smart coatings have the ability to sense and/or respond to external stimuli and generally interact with their environment. Self-healing coatings represent a significant advance in improving material durability and performance using microcapsules and nanocontainers loaded with self-healing agents, catalysts, corrosion inhibitors, and water-repellents. These smart coatings can repair damage on their own and restore mechanical properties without external intervention and are inspired by biological systems. Properties that are affected by either momentary or continuous external stimuli in smart coatings include corrosion, fouling, fungal, self-healing, piezoelectric, and microbiological properties. These coating properties can be obtained via combinations of either organic or inorganic polymer phases, additives, and pigments. In this article, a review of the advancements in micro/nanocapsules for self-healing coatings is reported from the aspect of extrinsic self-healing ability. The concept of extrinsic self-healing coatings is based on the use of capsules or multichannel vascular systems loaded with healing agents/inhibitors. The result is that self-healing coatings exhibit improved properties compared to traditional coatings. Self-healing anticorrosive coating not only enhances passive barrier function but also realizes active defense. As a result, there is a significant improvement in the service life and overall performance of the coating. Future research should be devoted to refining self-healing mechanisms and developing cost-effective solutions for a wide range of industrial applications.

Biomimetic anisotropic hydrogel as a smart self-healing agent of sustainable cement-based infrastructure

The durability improvement of cement-based infrastructure is an effective strategy to achieve sustainable development and reduce the carbon footprint. In this work, a biomimetic anisotropic hydrogel, alginate/polyacrylamide/halloysite nanotubes hybrid hydrogel (SA/AM/HNTs-RDC), was fabricated as a self-healing agent to enhance the self-healing ability and extend the service life of cement-based infrastructure. The effects of SA/AM/HNTs-RDC hydrogel on the formation and deposition of healing products and the self-healing behavior of cement in the different conditions (water condition and CO2-rich condition) were investigated. Compared with the matrix hydrogel (alginate/polyacrylamide, SA/AM), the crosslinking ions and anisotropic microstructure of SA/AM/HNTs-RDC hydrogel can stimulate the massive formation and dense deposition of healing products (ettringite (AFt) and monosulfo aluminate (AFm) in the simulated water condition, calcite and AFt in CO2-rich condition) to accelerate the performance recovery of the damaged construction. The self-healing measurements exhibited that the cracks around 200 μm in the cement paste with 1 % anisotropic hydrogel (RDC1) can be sealed completely after 14-day-curing in water, and its recovery ratio of the compressive strength increased by about 10 % compared with control samples. In CO2-rich condition, the closure rate of cracks was accelerated and the complete healing of cracks with similar width only needed 7 days. The compressive strength recovery increased by 13.7 % over control samples.

Method for evaluating healing state of self-healing ceramics using acoustic emission

Previous studies have evaluated the volume expansion rate of oxidation products and healing temperature and time. However, the bonding strength between the product and the matrix is yet to be appropriately evaluated. To develop a self-healing agent selection method for ceramics, this study proposed a method for examining the healing state and fracture behavior of self-healing ceramics through acoustic emissions (AE) generated during three-point bending tests. This study fabricated completely and incompletely healed SiC30 vol%/Al2O3 composite specimens by adjusting the healing time, and the crack length was assessed employing linear fracture mechanics, and effect of healing state on cumulative AE energy and AE frequency. The crack lengths were compared with those of the kinetic model of crack healing. The crack lengths of the 5-h healed specimens were estimated by linear fracture mechanics to be 12.5 μm for incomplete and 10.4 μm for complete healing, while that estimated by the kinetic model were 13.5 μm, indicating the usefulness of the kinetic model in the initial stages of crack healing. Furthermore, while the AE frequency at the initial stage of fracture was dominated by peaks below 100 kHz in damaged or incompletely healed specimen, there was a relatively high frequency peak of over 200 kHz in smooth and completely healed specimen, The average cumulative AE energies of smooth, damaged, 5 h-healed (incompletely), 5 h-healed (completely), and 24 h-healed specimens were 395, 0.89, 26.8, 189, and 318 V・μs, respectively. Thus, the AE energy that accumulated until rupture tended to increase as healing progressed, these findings suggest that the AE method can be used to determine healing conditions. These results will help establish a method for selecting self-healing agents according to the environment in which they are used.

Assessing self-healing in high-performance concrete with superabsorbent polymers by an innovative methodology

This study introduces a novel cracking methodology used in high-strength concrete (HSC) with superabsorbent polymers (SAP) to unveil its actual self-healing potential without fibre reinforcement. Although high-strength concrete allows for more creative structural designs and reduces the amount of building materials used, it often suffers from self-desiccation, which can cause cracking issues. SAP's inclusion in HSC not only addresses the autogenous shrinkage problem but also enhances concrete's self-healing capabilities. This research focuses on the dual role of SAP in mitigating autogenous shrinkage and promoting self-healing in high-strength concrete. An innovative technique was employed to induce uniform, controlled cracks under direct tension by isolating the self-healing agent's effect. The cracking process was developed using nonlinear finite element analysis. Two SAP concentrations (0.3 % and 0.6 %) were tested on specimens with a consistent crack width of 200 µm. These specimens underwent daily wetting-drying cycles over four months, with evaluations at 7 and 28 days post-cracking. Self-healing effectiveness was measured through mechanical recovery and microscopic examination of crack closure. Results, as expected, revealed a modest healing level but showed the actual potential of self-healing that this kind of concrete (HSC) can be counted on, offering crucial insights into self-healing concrete's practical applications and limitations. This study demonstrates SAP's versatility and highlights another advantage of SAP in high-strength concrete. This advantage, while slight, encourages the use of SAP in concrete and advances the creation of more durable construction materials.

Construction of Smart Coatings Containing Core-Shell Nanofibers with Self-Healing and Active Corrosion Protection.

With increasingly severe metal corrosion, coating preparation with high-performance corrosion protection has attracted more attention. Herein, the encapsulation of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) as well as the self-healing agent linseed oil (LO) in polyvinyl alcohol (PVA) and chitosan (CS) shells were realized by coaxial electrospinning, which was recorded as PVA/CS@LO/8-HQ core-shell nanofibers. PVA/CS@LO/8-HQ nanofibers were employed to promote the high-performance corrosion protection of the epoxy coating. The anticorrosion mechanism was that the change of the local pH on the metal surface stimulated the release of 8-HQ from the nanofibers, which were then chelated with iron ions to form a complex. When cracks occurred and caused rupture of the nanofibers, LO was released and reacted with oxygen to cure them so that the cracks could be healed autonomously. The dynamic potential polarization curves showed that the corrosion inhibition efficiency of the compound inhibitor LO + 8-HQ reached 87.54%, 90.31%, and 85.57% at pH = 3, 7, and 11, respectively, higher than that of the single corrosion inhibitor. Density functional theory calculations revealed that the LO and 8-HQ combination, forming a hydrogen bond interaction, promoted the adsorption of inhibitors on the steel surface. Scanning Kelvin probe and electrochemical impedance spectroscopy proved the self-healing corrosion protection properties of the epoxy coating. These results demonstrated that embedding PVA/CS@LO/8-HQ nanofibers in the coating could obtain self-healing properties, and promote the mechanical and corrosion protection of epoxy coating.

The effect of TiSi2 healing improver in self-healing ability of ceramics

A method to enhance the temperature range in which continuous self-healing fiber-reinforced ceramics (shFRCs) can self-heal is proposed to obtain a new high-temperature structural material. The effect of TiSi2 oxidation on self-healing was investigated using SiC, a typical self-healing agent, and TiSi2, which oxidizes at a lower temperature than SiC. Mixtures of SiC and TiSi2 powders were prepared by wet-mixing, and changes in their high-temperature oxidation behavior were investigated using thermogravimetry/differential thermal analysis. The oxidation of TiSi2 at 1000 °C enhanced the oxidation rate of SiC by 2–3 times. A shFRC consisting of an Al2O3 matrix, an interface layer of SiC and TiSi2, and Al2O3 fiber bundles was fabricated by slurrying and filament-winding. The strength recovery of the shFRC following three-point bending was investigated, and results indicated that the prepared material recovered 50 times faster than conventional shFRCs at 1000 °C. The self-healing improver described in this study can promote the oxidation of self-healing agents via its reaction heat. Thus, this improver may be applied as a practical component of self-healing materials.

Preparation of Graphene Oxide/Polymer Hybrid Microcapsules via Photopolymerization for Double Self-Healing Anticorrosion Coatings.

In this work, graphene oxide (GO)/polymer hybrid microcapsule-loaded self-healing agents were prepared via the combination of the emulsion template method and photopolymerization technology. The incorporation of GO in the microcapsule shell not only improved the impermeability, mechanical property, and solvent resistance property of the microcapsules significantly but also endowed the microcapsules with photothermal conversion property. By incorporating GO/polymer hybrid microcapsules in water-borne epoxy resin, a novel kind of anticorrosion coating with a double self-healing property was successfully fabricated. When the coating was scratched, the linseed oil (LO) encapsulated in the microcapsules could fill the crack, and the photothermal conversion property of GO could promote the molecular chain movement of the damaged area under near-infrared (NIR) irradiation to realize the close of the crack. Based on the filling of LO and photothermal conversion-induced scratch narrowing, the "filling" and "close" double self-healing effect can be realized under temporal NIR irradiation, which could lead to the complete recovery of the scratched coating. The |Z|f=0.1Hz value of the damaged coating with GO/polymer microcapsules after double healing was comparable to that of the intact coating, which was about 4 orders of magnitude higher than that of the scratched blank coating and single self-healing coating. As to the neutral salt spray test, the scratched blank coating failed in protection after 100 h, while the healed composite coating did not show any corrosion after 300 h.

Autonomous Self-Healing Agents in Cementitious Materials: Parameters and Impacts on Mortar Properties

The concept of self-healing materials and the development of encapsulated curing agents represent a cutting-edge approach to enhancing the longevity and reducing the maintenance costs of cementitious structures. This systematic literature review aims to shed light on the parameters involved in the autonomous self-healing of cementitious materials, utilizing various encapsulated healing agents such as pellets, granules, and capsules. This review also identifies and selects studies that offer additional insights into the efficacy of the self-healing process in cementitious materials and the influence of these specific encapsulated healing agents on the physical mechanical properties of mortars. This comprehensive approach provides a deep understanding of the interplay between self-healing and the physical–mechanical properties of mortars containing these encapsulated healing agents. The main findings indicate that the cement-to-sand ratio, characteristics of fine aggregates, and encapsulation methods significantly impact crack control, self-healing efficiency, and properties of mortar in both fresh and hardened states. The content of encapsulated healing agents within the cementitious matrix affects both the initial workability or flow and subsequent mechanical properties. While pellets coated with PVA film typically reduce workability in the fresh state and compressive strength, capsules coated with Portland cement and sodium silicate mitigate these effects and improve crack sealing in fresh and hardened states without compromising the self-healing capacity of cracks. The three-point flexural test has emerged as the preferred method for a pre-crack assessment over 28 days, with variations depending on the type of healing agent used. As noted in the literature, water has been identified as the optimal environment for autonomous healing. These findings underscore the potential of encapsulation techniques to enhance self-healing capabilities through the controlled release of agents within the cementitious matrix, thereby advancing the research on and development of intelligent construction materials and increasing the durability of cement-based structures.

MATERIALS FOR IMPREGNATION OF POROUS METALLIZATION THERMAL SPRAYED ANTICORROSIVE COATINGS OF SUBMERSIBLE OILFIELD EQUIPMENT. Part 2

The use of thermal sprayed coatings in aggressive petroleum fluid is limited due to the presence of porosity in it. When fluid gets into the pores, corrosion processes begin and thereby reduce the protective properties of thermal sprayed coating. The application of impregnating compounds makes it possible to seal open porosity and prevent the penetration of aggressive environments into the metal under the coating, thereby increasing the barrier properties of the coating. Epoxy polymer materials demonstrate high corrosion resistance and are widely used in the oil industry to protect pipeline elements and submersible oilfield equipment during operation. The second part of the article presents both traditional polymer impregnation materials and new compositions with magnetic nanoparticles and nanocarbon fillers (fullerenes, graphene and nanotubes) which, due to the created magnetic field, are evenly distributed throughout the polymer matrix and increase the crack resistance of the matrix. Polymer impregnating materials of both domestic and foreign production based on phenolic, epoxy, acrylic and urethane resins, modes of their application, conditions of their operation and temperature restrictions are considered. The possibility of using existing independent anti-corrosion polymer coatings as an impregnation of metallization thermal sprayed layers is discussed. Their advantages and disadvantages are highlighted. Examples of self-healing polymer matrices are given that are capable of recognizing the onset of corrosion processes and responding by releasing appropriate effective self-healing agents. The possibility of adding inhibitors to the polymer matrix is described, which helps to increase the anti-corrosion properties of the coating and thereby increase the time between failures of equipment. The issue of normative regulation of the use of impregnating compositions in various fields of industry is covered. The main directions of research that need to be carried out to solve the problem of using polymer materials as the most promising impregnating compositions for anti-corrosion thermal sprayed coatings of submersible oilfield equipment have been identified. First of all, it is necessary to reduce the viscosity of polymer resins to increase their penetration into open pores.

Enhancing the interfacial compatibility and self-healing performance of microbial mortars by nano-SiO2-modified basalt fibers

Fibers that enhance the self-healing ability of microbial mortar cracks have been widely studied. This study explored the impact of modified fibers on the self-healing performance and interfacial compatibility of microbial mortar by incorporating expanded perlite as a carrier of self-healing agents and basalt fibers modified with nano-SiO2. The effect of modified fibers on the mechanical properties of mortar was analyzed through compressive and flexural strength tests. The crack-healing effect of the specimens was evaluated using crack observation, UPV tests, and water absorption experiments, and the crack fillers were analyzed through SEM and XRD experiments to reveal the self-healing mechanism. The experimental results confirm that the nano-SiO2 loaded on the surface of the modified fibers exhibits Pozzolanic reactivity and can react with Ca2+ and OH− in the pore solution of the mortar to form secondary C-S-H on the fiber surface, which enhances the bonding ability between the fibers and the cement slurry, effectively improving the mechanical properties of the specimens. The rough surface of the modified fibers facilitates the deposition of calcite produced by microbes and hydration products, promoting the early-stage healing rate. Furthermore, due to the C-S-H shell on the surface of the modified fibers, the electronegativity of the fiber surface is improved, which is beneficial for bacterial adhesion and promotes the deposition of calcite, ultimately enhancing the self-healing capability.

Hybridized bio-based repair mortars: Effects on mechanical, self-healing, and cost performance via novel generalized indexing

This study delves into enhancing the mechanical properties and cost-effectiveness of self-healing cementitious materials through detailed investigation. It conducts a thorough characterization of different hybridized self-healing repair mortars, comprising a laboratory-prepared mortar and two commercial non-self-healing mortars, along with a commercial ready-mix self-healing repair mortar. By incorporating bacteria at varying levels of 1.5 % and 2.5 % as cement replacements, the study aims to reduce costs associated with the self-healing process. Additionally, a sustainability-focused hybridization is performed by combining the ready-mix self-healing repair mortar with the weakest of the three parent mixes. The research evaluates the impact of mortar composition on mechanical properties, particularly concerning the optimal proportion of self-healing agents to achieve maximum strength. Notably, the crack healing efficiency of bacterial-incorporated specimens exhibits significant effectiveness. The correlation between the mechanical properties of intact specimens and their crack healing efficacy is explored, uncovering the potential for creating an outstanding self-healing repair mortar with exceptional healing efficiency and robust mechanical performance. Furthermore, a comparative cost analysis and an overall performance evaluation using the Generalized Performance Index (GPI) demonstrate the feasibility of striking a balance between self-healing material costs and desired performance outcomes through the strategic approach of hybridization.

Enhancing self-healing performance of microbial mortar through carbon fiber reinforcement: An experimental analysis

The incorporation of fibers has been shown to be an effective means to enhance self-healing properties of biomass self-healers in cementitious materials. In this study, the mechanism of carbon fiber-enhanced self-healing ability for self-healing agent made by straw charcoal adsorbed bacteria in mortars was investigated. Mechanical properties, compressive strength restoration properties and permeability testing of microbial mortars were evaluated. Our findings reveal a synergistic effect between carbon fibers and the self-healing agent, notably in crack repair. Although fibers alone did not significantly increase compressive strength, can play a crucial role in promoting Ca2+ aggregation and facilitating the transformation of spores into bacteria, which resulted in the formation of structurally intact and layered calcium carbonate, result in significantly enhanced the self-healing efficacy of microbial mortars. The results of this study show for the first time that carbon fibers have a significant effect on the self-healing capacity of biomass mortar.

Self-healing coatings for large-scale damages via ultrahigh load capacity of healing agents in short kapok microtubules

Self-healing materials, due to their ability to autonomously repair damages, have been extensively applied in the field of metal corrosion protection. However, prior self-healing coatings are powerless against large-scale damages limited by their relatively low amounts of prestored self-healing agents in microcontainers, which severely restricts their long-term anticorrosion performance. Herein, to address this issue, we propose a simple strategy to prestore a water-soluble cerium-based corrosion inhibitor, cerium gluconate, into Kapok fibers through a cyclic process of vacuum drying after saturation with the inhibitor solution, and the load capacity of cerium gluconate in Kapok (CG@K) by this approach can reach up to 455 wt%. This new loading system is relatively easy to be carried out while give an ultrahigh load capacity, and applicable to encapsulate other healing agents theoretically. The Kapok fibers embedded uniformly in the self-healing coatings exhibit a dense three-dimensional network structure, which, along with the ultra-high loading content, renders the self-healing coatings distinguished corrosion resistance. It is worth noting that the self-healing coatings achieve a remarkable ability to autonomously repair large-scale cracks up to 400 μm. This work provides an option for fabricating high agent load capacity and shows tremendous potential for designing self-healing coatings for large-scale damages.

Experimental Study of a Superabsorbent Polymer Hydrogel in an Alkali Environment and Its Effects on the Mechanical and Shrinkage Properties of Cement Mortars.

As internal curing self-healing agents in concrete repair, the basic properties of superabsorbent polymers (SAPs), such as water absorption and release properties, are generally affected by several factors, including temperature and humidity solution properties and SAP particle size, which regulate the curing effect and the durability of cementitious composites. This study aimed to investigate the water retention capacities of SAPs in an alkaline environment over extended periods by incorporating liquid sodium silicate (SS) into SAP-water mixtures and examining the influence of temperature. The influence of SAP particle size on mortar's water absorption capacity and mechanical behavior was investigated. Two mixing techniques for SAPs (dry and pre-wetting) were employed to assess the influence of SAP on cement mortars' slump, mechanical properties, and cracking resistance. Four types of SAPs (SAP-a, SAP-b, SAP-c, and SAP-d), based on the molecular chains and particle size, were mixed with SS to study their water absorption over 30 days. The results showed that SAPs exhibit rapid water absorption within the first 30 min, exceeding 85% before reaching a saturation point, and the chemical and temperature variations in the water significantly affected water absorption and desorption. The filtration results revealed that SAP-d exhibited the slowest water release rate, retaining water for considerably longer than the other three types of SAPs. The mechanical properties of SAP mortar were reduced due to the addition of an SAP and the improved cracking resistance of the cement mortars.

Effect of acylhydrazone self-healing agents with different structures on the properties of SBS modified asphalt waterproofing membrane

To prepare SBS modified asphalt (SMA) waterproofing membrane with excellent self-healing performance, in this paper, four self-healing agents (ASHA-A, ASHA-B, ASHA-C, ASHA-D) with acylhydrazone bonds and carbon-carbon double bonds (CC) were synthesized, and were used to prepare self-healing SMA waterproofing membranes (SSMA-A, SSMA-B, SSMA-C, SSMA-D). The effects of ASHAs with different structures on the structure, high and low temperature properties, joint peel strength and self-healing performance of SSMAs were investigated. The Fourier transform infrared spectroscopy and fluorescence microscope results showed that acylhydrazone bonds of ASHAs were introduced into the chains of SBS molecules, and the SBS in SSMAs occurred crosslinking through the CC of ASHAs and SBS, the crosslinked network structures of SBS in SSMA-C and SSMA-D were denser and more complete because ASHA-C and ASHA-D contained more CC involved in the crosslinking reaction. The softening point and low temperature flexibility of SSMAs were enhanced by the formation of the SBS crosslinked network structure, and the optimum dosage of ASHAs was 0.6%. The joint peel strength of SSMA-A, SSMA-B, SSMA-C and SSMA-D increased by 26.68%, 31.25%, 49.52% and 56.97% compared to SMA. The introduction of acylhydrazone bonds with reversible fracture and rearrangement significantly improved the crack self-healing performance of SMA, the impermeability times of SMA, SSMA-A, SSMA-B, SSMA-C and SSMA-D were 13.28 min, 37.29 min, 42.53 min, 53.34 min and 59.67 min after self-healing at 40℃ for 8 h, which indicated that ASHA-D with benzene ring and multiple CC had the best improvement in self-healing performance of SMA.