Self-healing Agent Research Articles

Numerical Simulation of the Response of Concrete Structural Elements Containing a Self-Healing Agent

Self-healing of a crack is a relatively novel technique allowing for the partial recovery of the initial mechanical characteristics of a structural element after some period of exploitation. By a widely accepted convention, self-healing is either autogenous or autonomous. The former is a mechanism inherent for cementitious composites (in particular—concrete), while the latter is an engineered process. Both autogenous and engineered healing have recently been the object of numerous studies. Despite the large amount of research work being carried out, the potential of this technique has not yet been fully realized. The article focuses on the modeling and the finite element simulation of the recovery of the initial material properties resulting from the sealing of cracks. The employed numerical procedure uses a constitutive relation for concrete based on the continuum damage mechanics. It captures both the strain-softening and the inverse process—the crack healing. Finite element simulations of benchmark cases illustrate the effect of self-healing. The numerically obtained constitutive relations for specimens with and without a healing agent are compared.

Poly(dimethyl siloxane) anti-corrosion coating with wide pH-responsive and self-healing performance based on core−shell nanofiber containers

• Hydrophobic core-shell fibers were prepared and added them to the poly(dimethyl siloxane) (PDMS) coating. • The maximum self-healing efficiencies of the fiber-PDMS coating in alkaline and acidic solution are 95.96% and 97.04%, respectively. • The hydrophobic effect of fiber-PDMS coating remains above 88.2% before and after abrasion. • The nanofiber network structure ensures the effective release of the healing agent and repeats self-healing. • The C 17 H 33 COO − absorbed on the scratch and AVR cured film reach a double repair function. In this research, core−shell electrospun fibers loaded with the shell of cellulose acetate and the core of oleic acid and alkyd varnish resin were synthesized and used within poly(dimethyl siloxane) (PDMS) to prepare self-healing and pH-responsive coatings for a steel substrate. The morphology of the electrospun fibers was characterized by scanning electron microscopy, transmission electron microscopy and confocal fluorescence microscopy. Thermo gravimetric analysis and Fourier transform infrared spectroscopy revealed that the self-healing agents were loaded successfully with a loading rate of 2.9%. The properties of the fiber-PDMS composite coating were characterized by water contact angle measurements, mechanical tests, electrochemical impedance spectroscopy, and scanning Kelvin probe. Results show that the maximum self-healing efficiencies of the fiber-PDMS coating in alkaline and acidic solution are 95.96% and 97.04%, respectively. The composition of the self-healing agents at the damaged part of the coating was verified by an infrared mapping test and using an energy dispersive spectrometer. In addition, the sandpaper abrasion test shows the hydrophobic effect of fiber-PDMS coating remains above 88.2% and decreases slightly through the addition of abrasion cycles. This research can pave the way for the industrial applications of pH-responsive self-healing coatings.

A new application of fluid loss agent in enhancing autogenous healing ability and improving mechanical properties of oil well cement

Enhanced autogenous healing is a desirable solution to improve the long-time durability and sustainability of cementitious materials. Herein, a self-healing agent, also is called cement-polymer composite additive (CPCA), was prepared by pretreatment of cement grains with polymer to accelerate the autogenous self-healing process. The polymer used in CPCA is the siloxane (vinyltrimethoxysilane) modified fluid loss agent (FLA-V), which can greatly reduce the fluid loss from the cement slurry to formation. Water contact angle test showed that the hydrophobic group in the FLA-V endowed CPCAs with different degrees of hydrophobicity, and CPCA-4 had better hydrophobicity. Results of hydration kinetics showed that the addition of CPCA-4 formed the graded hydration system, which densified the micro-structure and further improved the compressive strength of hardened cement. The compressive strength at 7 days was approximately 32.71% higher than that of plain cement. Furthermore, the strength recovery and crack width visualization test indicated that the addition of CPCA-4 enhanced the autogenous healing effectivity of the matrix. The compressive strength of the specimens with 5% CPCA-4 recovered 101.26% of its initial compressive strength after curing for 21 days. The micro-cracks measuring approximately 150 μm were completely sealed after healing for 28 days. The comprehensive measurements of the healed area indicated that the self-healing products mainly consisted of CaCO3, CH, and C–S–H.

A critical analysis on role of nanoparticles in oil-well cementation

The main objectives of oil-well cementing are to restrict the movement of fluids from one zone to another and to provide a stable position for the casing string. Achieving greater compressive strength, tensile strength, and lower permeability are the main features for increasing the effectiveness of cement jobs. The conventional cementing job lacks the ability to attain these properties even with the usage of advanced materials like self-healing agents, fibers, and polymeric materials in cement slurry. However, a scope of improvement is required in providing better zonal isolation. According to studies, the inclusion of nanoparticles would improve cement efficiency by achieving sufficient compressive strength and durability, reducing potential maintenance costs and environmental effects. With the addition of nanoparticles to cement, slurry increases compressive strength, decreases settling time, and increases density by reducing the porosity and permeability of the cement sheath. This study provides an explanation of the alterations in oil-well cement properties with the addition of nanaparticles at different temperatures and incubation periods.

Direct writing of self-healing circuits on curvilinear surfaces

Directly written circuits on polymeric housings can reduce weight and enhance flexibility due to the wiring of electronic devices and systems in automotive and aerospace parts. These circuits must conform to a variety of geometries while maintaining electrical conductivity after deformations. To address these challenges, a hybrid copper-based ink has been developed capable of self-healing. Low melting temperature metals such as indium can work as a self-healing agent in response to deformational processes such as thermoforming. A new generation of devices is conceptualized utilizing printable hybrid copper-based ink, sintered and healed within a few milliseconds via intense pulsed light (IPL).

Effect of Microbially Induced Calcium Carbonate Precipitation (MICP) method on the Enhancement of Infrastructure Durability and Sustainability – A state of the art review

Cracks in concrete structures are common, allowing water and other hazardous chemicals to permeate the concrete through the cracks. Consequently, the durability and concrete strength has been reduced. Repairing concrete cracks and keeping it in good condition may be pricey. Due to the negative side effects of some chemical treatments, biological alternatives have been proposed as an ecologically friendly strategy for reducing concrete porosity and minimizing water absorption. Because of its potential to improve the quality of building materials, microorganism-induced calcium carbonate precipitation has found broad application in construction technology. To solve this challenge, the concrete has a unique self-healing mechanism that allows cracks to be healed by creating calcium carbonate crystals that which can have the ability to fill the micro cracks in the concrete. The combination of urease-producing bacteria and a calcium source causes calcite precipitation in concrete. This review research provides an overview of different types of bacteria, the possibilities of using bacterial cells in concrete, and how they might be employed as healing agents. Through microbiological experiments, the major focus was on choosing optimal bacteria for concrete fracture healing. In this study, Bacillus species bacteria such as Bacillus subtilis, Bacillus Pasteurii, Bacillus cereus, Bacillus licheniformis, and Bacillus halodurans were investigated as self-healing agents. The inclusion of the Bacterial substance in the concrete has led to reduction in the amount of water absorption, nature of porosity as well as permeability characteristics at all ages of concrete as a result of calcite precipitation, enhancing concrete properties. This review study’s conclusion quickly outlined the numerous qualities of concrete that change when bacteria are introduced, as well as how using bacteria enhances the mechanical and durability elements of concrete. The impact of microorganisms on various elements in concrete has also been proved to be beneficial to long-term development. According to the review research, the Microbially Induced Calcium Carbonate Precipitation (MICP) technique appears to be a suitable technology for sustainable infrastructure construction, based on features such as compressive strength of the concrete, permeability characteristics, rate of water absorption, and chloride ingression.

Gas chromatography to detect bacteria-based self-healing agents in concrete

In the concrete industry, legal disputes might occur when a built structure performs worse than it was supposed to during the design phase. When dealing with underperformance of self-healing concrete (e.g., no regain of water tightness after cracking), these disputes might likely be related to questioning if healing agents were actually included in the material or not. In this study, a methodology based on Gas chromatography is proposed to detect and quantify poly-lactic acid based-healing agents in cementitious materials. The applicability of this technique for this purpose has been demonstrated on mortar and concrete powders with and without healing agents. The amount of material needed to conduct the experiment is less than 200 mg, making the technique suitable for on-site application to limit any destructive action as much as possible. The application of gas chromatography to detect and quantify healing agent inclusions in concrete has the potential to be extended to other additives, depending on their composition.

In situ poly(melamine-formaldehyde) microencapsulation of diglycidyl ether of bisphenol-A epoxy and pentaerythritol tetrakis(3-mercaptopropionate) for self-healing applications

In this study, microcapsules as potential candidates for self-healing agents were prepared by in situ polymerisation, taking place in oil-in-water emulsion. Poly(melamine-formaldehyde) is employed as shell material and diglycidyl ether of bisphenol A as polymerisable core materials and Pentaerythritol Tetrakis(3-Mercaptopropionate) as its hardener. The geometry, shell features, size distributions, core content, and the reactivity of the microcapsules were studied by scanning electron microscopy (SEM), optical microscopy (OM), Soxhlet extraction method and differential scanning calorimetry (DSC). Microcapsules with different sizes and distributions were obtained by adjusting the stirring speeds during the preparation stage. From the results, it was established that the spherical microcapsules fabricated using this technique, resulted in satisfactory size and shell structure with shell thickness of less than 2 μm. The microcapsules possess high core content at about 90 wt.% for each size range of microcapsules and it was also observed that the viscosity of the core content decreased at an elevated temperature. The results obtained in this work indicate that these microcapsules possess the characteristics that can be potentially used for self-healing applications.

High Linoleic Waste Sunflower Oil: A Distinctive Recycled Source of Self-Healing Agent for Smart Metal Coatings

High Linoleic Waste Sunflower Oil: A Distinctive Recycled Source of Self-Healing Agent for Smart Metal Coatings

Self-healing concrete: application of monod’s approach for modeling Bacillus pseudofirmus growth curves

Despite limited knowledge on the proliferation of bacteria incorporated in concretes as a self-healing agent, there are efforts to standardize such a technology. Proper mathematical models could potentially assist the design of self-healing composites and enable to harness bacterially-induced calcite precipitation (BICP) more efficiently. Here, we employed Monod’s model to reproduce experimentally measured growth curves for Bacillus pseudofirmus, a strain resistant to the alkaline environment present in cementitious composites. The model correctly predicted the onset of individual growth phases, quantified the effects of temperature and concentration of nutrients on the concentration of bacteria, and revealed relationships between the concentration of nutrients and the maximum amount of bacteria. The study contributes to understanding the bacterial growth of Bacillus pseudofirmus and characterization of its proliferation.

Understanding the Impacts of Healing Agents on the Properties of Fresh and Hardened Self-Healing Concrete: A Review

Self-healing concrete has emerged as one of the prospective materials to be used in future constructions, substituting conventional concrete with the view of extending the service life of the structures. As a proof of concept, over the last several years, many studies have been executed on the effectiveness of the addition of self-healing agents on crack sealing and healing in mortar, while studies on the concrete level are still rather limited. In most cases, mix designs were not optimized regarding the properties of the fresh concrete mixture, properties of the hardened concrete and self-healing efficiency, meaning that the healing agent was just added on top of the normal mix (no adaptations of the concrete mix design for the introduction of healing agents). A comprehensive review has been conducted on the concrete mix design and the impact of healing agents (e.g., crystalline admixtures, bacteria, polymers and minerals, of which some are encapsulated in microcapsules or macrocapsules) on the properties of fresh and hardened concrete. Eventually, the remaining research gaps in knowledge are identified.

Self-healing Organic Coatings Based on Microcapsules – A Patent-based Review

: Self-healing coatings are intended to increase long-term durability and reliability and can be prepared by the use of microcapsules containing a self-healing agent capable of interacting with the matrix and regenerating the system. This review article provides an overview of the stateof- the-art patents published in the field of microcapsule-based self-healing organic coatings since the early 2000s. A discussion regarding coatings for corrosion protection is presented and the different self-healing approaches and mechanisms are also addressed, as well as future challenges and expectations for this kind of coatings.

Waterborne polyurethane coating based on tannic acid functionalized Ce-MMT nanocomposites for the corrosion protection of carbon steel

By encapsulating corrosion inhibitors in pH-responsive nanocontainers, the coating provides strong active protection against the aggressive environment, which is an effective way to develop highly efficient coatings. Here, tannic acid functionalized Ce-MMT nanocomposites were prepared and their effect on the anti-corrosion properties of waterborne polyurethane coating was investigated. Among them, the MMT plays the role of a physical barrier and a container; and Ce3+ as cathodic protectant. TA not only has the effect of anodic protection but also increases the dispersion of the nanocontainer. In a specific experiment, the anti-corrosion property of the composite coating was investigated by electrochemical. The results showed that WPU/TA@Ce-MMT coating had long-term anti-corrosion ability after soaking for 50 days, and the |Z|0.01Hz was two orders of magnitude higher than that of pure WPU. Also, the analysis of scratch coating demonstrated that Ce3+ and TA could serve as self-healing agents to block the corrosion process when the corrosive medium reaches the metal/coating interface through artificial scratches. This novel synergistic anticorrosion system opens a new possibility for manufacturing high-efficiency anticorrosion coatings.

Applying X-ray Microtomography to Study Microbial-Induced Self-Healing of Geopolymers

Geopolymers are one of the emerging sustainable materials for the building and construction industry. They are inorganic polymers produced from aluminosilicate waste materials such as coal fly ash and have been shown to have a lower carbon footprint as compared with Portland cement. However, geopolymers are a cementitious material like Portland cement-based concrete and are thus brittle and prone to develop cracks. The use of microorganisms has recently been considered as an approach to improve the self-healing capability of geopolymers through microbial-induced calcite precipitation. The application of X-ray microtomography to observe the potential of self-healing of bio-geopolymers is explored in this study. Bio-geopolymers were produced from the alkali activation of coal fly ash and mixed with self-healing agents using a form of biochar-immobilized spores of B. sphaericus and B. thuringiensis. These bio-geopolymers were then scanned using micro-focus XCT to obtain a visualization of the microstructure of the material via a non-destructive 3D imaging technique after self-healing. Coupled with image analysis, quantification of the segmented data allowed further investigation of self-healing through comparison with the other self-healing characterization method.

Environmental Life Cycle Assessment of Alkali-activated Material with Different Mix Designs and Self-healing Agents

Alternative low-carbon cementitious binders such as geopolymers are rapidly garnering scientific interest to replace Ordinary Portland Cement (OPC). Industrial waste by-products such as coal fly ash (CFA) and ground granulated blast furnace slag (GGBS) are usually utilized for this material. Microcapsules can also be added to geopolymers to enhance its self-healing capability as it has potential environmental benefits aside from cost savings. This study thus focuses on the cradle-to-gate LCA of geopolymer concrete containing microcapsules for self-healing. Two different microcapsules were considered: Urea-formaldehyde (UF)/Dicyclopentadiene (DCPD) and Poly(urea-urethane) (PUU)/Alkali-activator (AA). Three different geopolymer precursors were studied: CFA, GGBS and CFA/GGBS. OpenLCA software was used for the calculations and analysis, and the inventory data were obtained from Ecoinvent and OzLCI2019 supplemented by literature data. An impact assessment was carried out using CML 2001. Self-healing geopolymer concrete is better in terms of lower global warming potential but performs worse in other impact categories than conventional OPC concrete. Of the geopolymer concrete assessed, GGBS concrete has the lowest impacts. On the other hand, of the two self-healing microcapsules, UF/DCPD is better for the environment. The primary factor for this difference is the solvent used in microcapsule synthesis. From this result, it has been shown that self-healing GGBS concrete containing UF/DCPD microcapsules has the lowest impacts of the self-healing concrete assessed.

Encapsulation of Cerium Nitrate within Poly(urea-formaldehyde) Microcapsules for the Development of Self-Healing Epoxy-Based Coating

In order to study the release of cerium nitrate in a self-healing epoxy-based coating, poly (urea-formaldehyde) (PUF) microcapsules containing cerium nitrate were synthesized. The effects of healing agent concentration and weight percent of microcapsules in the epoxy resin were studied through the incorporation of microcapsules within an epoxy-based coating. The prepared microcapsules were characterized using thermogravimetric analysis and Fourier transform infrared spectroscopy and confirmed the successful encapsulation of cerium nitrate within PUF capsules. The self-healing performance of the prepared epoxy coating was investigated in 0.6 M NaCl solution using electrochemical impedance spectroscopy (EIS) tests. The EIS results indicated the successful release of encapsulated cerium nitrate from PUF microcapsules once the damage occurred in the epoxy coating, which led to effective self-healing of the epoxy-based coating. The presence of chlorine and cerium ions in the solution led to the precipitation of cerium hydroxides and oxides in the scratched area as a passive layer which hindered the corrosion in the damaged area. In addition, the EIS results showed that the healing performance of the coatings depends on the weight percent of microcapsules and the concentration of the self-healing agent. The highest self-healing performance was achieved for the maximum amount of microcapsule incorporation (10 wt %), while the increase in the microcapsule percent led to a decrease in the adhesion of the coating to the substrate.

Synthesis of robust polyaniline microcapsules via UV-initiated emulsion polymerization for self-healing and anti-corrosion coating

A novel kind of robust PANI microcapsules were prepared via a one-pot photopolymerization and interfacial aniline polymerization. In our strategy, lignosulfonate was employed as emulsifier to stabilize oil-in-water emulsion, in which the oil phase was composed of self-healing agent (tung oil), photo-crosslinkable acrylic monomer and crosslinker. Under UV light, the acrylic monomer and crosslinker were photo-polymerized and formed a cross-linked polyacrylic shell, endowing sufficient robustness to the microcapsules. Aniline was subsequently added to the water phase and polymerized at the oil-water interface, which converted to a second shell and endowed anticorrosion property. FTIR, TGA and SEM tests proved the successful preparation of PANI microcapsules, and the loading of tung oil in the microcapsules reached 55.1 wt%. These microcapsules could keep integrity and be uniformly dispersed in water-based epoxy coating. The incorporation of PANI microcapsules in the coating not only imparted self-healing properties to the coatings, but also greatly enhanced its anticorrosion performance. The scratch test indicated that the coatings containing only 5 wt% microcapsules could autonomously heal a scratch with 50 μm in width. In addition, the healed coatings with the microcapsules showed almost no corrosion products after 500 h salt spray test (SST), while for the scratched neat epoxy coating, a large area of coating peeled from the substrate after only 200 h SST. The remarkably enhanced corrosion protection capability was owing to the closure of the scratch by the self-healing effect and the inhibition efficiency of PANI.

Self-Healing Coatings for Corrosion Protection: The Importance of the Transport of Active Agents from the Coating Towards the Defect

In so called smart or intelligent self-healing coatings active agents that are safely stored inside the coating are released upon onset of corrosion. This release is triggered by a suitable trigger signal that should be a safe indicator for the onset of corrosion and its continuation. Different from the current standard where release from pigments occurs via leaching, the safe storage should ensure that there is no uncontrolled release of the active agents when they are not needed for inhibiting corrosion and restoring protection. While there are many studies on different concepts for storage and active release triggered by corrosion, achieving an efficient transport of the released agents to the defective site(s) is a likewise crucial but so far widely neglected issue. Recently it was proposed that the signal spreading from the defect into the coating can be significantly enhanced by the use of layers of conducting polymer, such as polypyrrole, applied as an intermediate layer between the metal substrate and the organic coating. In that case the decrease in potential is the signal that is spread. Here, we will show that by such polypyrrole layers also the transport of active agents can be significantly enhanced. To enable a fundamental in-depth study of the mobility of active agents from the coating towards the defective site, a dedicated experimental model set-up was designed especially for the study of ions transport. The main question to be addressed was whether the main transport will be along the metal│PPy interface or rather through the matrix of the reduced polypyrrole. Zinc was chosen as metallic substrate, owing to its importance in galvanized steel products. The corrosion potential at the defective site was used as a measure for the amount of corrosion inhibitor released into the defect and hence as a measure to reflect the ionic transport and self-healing efficiency of the coating by different corrosion inhibitors. The progress of polypyrrole reduction, in turn, was monitored by use of Scanning Kelvin Probe (SKP) for recording the change of potential as a function of distance from the defect and of time. The concentration of corrosion inhibitor at the defective site was also quantified using ICP-MS (OES) analysis of the solution in the defect at different times. In order to ensure for reliable quantification of the transport that released corrosion inhibitor moving towards the defect is not reacting with corroding metal at the interface special PVB│PPy│Au-Glass model samples were utilized. The results indicate that Ce4+ is more effective than Ce3+ for reaching and passivating the defect. In addition, organic corrosion inhibitors (8-HQ, β-CD and L-Car) were found to be highly efficient in inhibiting the defective site. This is proposed to be due through a synergistic mechanism, which is based on an interaction of the passivating effect of these corrosion inhibitors and the passivating effect of polypyrrole. The synergistic mechanism shows astonishing passivation effects, resulting in anodic potential shifts of the corrosion potential of more than 600 mV. Concerning the main path for ionic transport, it was found that this occurs mainly through the matrix of the (partially) reduced polypyrrole. Hence, the transport of positive ions should be favored compared to the one of negative ions.

Bacillus Subtilis as Self-Healing Agent in Cement Mortar: The Effect of Curing Time and Amount of Calcium Lactate on Strength

Crack growth is a major cause of failure in structures that are made using cement and concrete. Healing of these cracks can increase the life span of structures. In the present study micro-organism based self-healing of structures is studied. A commonly occurring micro-organism bacterium called Bacillus Subtilis, is used in the manufacturing of cement mortar blocks as a self-healing agent for cement mortar blocks, with the use of Calcium Lactate as feed for bacteria. In the first step, colonies of Bacillus Subtilis were grown and added with calcium lactate to produce a solution. The solution was then kept for one week to observe the metabolic product of Bacillus Subtilis. It was found that the bacterial product was composed of CaCO3 and thus the bacteria is suitable to be used as self-healing agent. Self-healing cement mortar blocks were made by adding Bacteria and Calcium Lactate with usual ingredients of cement mortar, i.e. cement, sand and water. It was found that the bacteria were also effective in converting Calcium Lactate to Calcium Carbonate, when mixed in cement mortar blocks. It was observed that the pores of cement mortar blocks were filled by Calcium Carbonate and that cracks get healed by the deposition of Calcium Carbonate in the cracks. Cement mortar blocks, with and without healing agent, were made to compare the effect of curing time. The samples were tested after seven, fourteen and twenty-eight days to compare the effect of healing agent. All the samples with the healing agent showed a higher compressive strength in comparison with the samples that were made without healing agent. Different percentages of Calcium Lactate, ranging from 1-7% were also used to find the best composition for future use. It was found that the compressive strength was increasing up to 5% while above 5% the increase was marginal thus it is proposed that Calcium Lactate should be used in between 5-7 % to reduce the cost of self-healing cement in construction industry.

Application of Superabsorbent Polymer as Self-Healing Agent in Self-Consolidating Concrete for Mitigating Precracking Phenomenon at the Rebar–Concrete Interface

Improved autogenous healing capacity of concrete using superabsorbent polymers (SAPs) was used as an efficient approach for mitigating damage between steel rebar and self-consolidating concrete (SCC). The results for normal concrete (NC) and those for SCC mixtures were compared. Two SAPs with different particle sizes and chemical compositions were used in the experimental program. Results showed that despite the greater reduction effect of SAP with a smaller particle size on compressive strength, SCC containing this type of SAP had the highest bond strength in uncracked specimens, compared with SAP with larger particle sizes, for SAP-modified NC and SCC mixtures. Moreover, results showed that SCC and NC containing SAP had considerably greater healing improvement factors for large crack widths (w≥0.30 mm) compared with mixtures without polymers; almost 46%, 30%, and 24% healing improvement factors were obtained for average bond stress, bond strength, and residual bond stress of SAP-containing concrete mixtures, respectively. Furthermore, complete strength recovery (100% healing improvement factor) was obtained for SCC mixture with w=0.10 mm after a 28-day healing period.