Compressive Strength Recovery Research Articles

Improving flexural response of rubberized RC beams with multi-dimensional sustainable approaches

This research presents a sustainable solution to waste tire disposal and raw material depletion by incorporating recycled rubber into concrete mixtures. To mitigate the reduction in mechanical properties, a novel slag pretreatment of rubber particles with controlled temperature is proposed. The study also investigates the effects of pouring concrete in layers with rubberized concrete (RuC) in tension side and normal concrete in compression side, as well as evaluating the use of GFRP compared to conventional steel, thereby introducing multiple innovative dimensions to enhance structural performance. The experimental study included a total of 27 specimens, consisting of normal concrete, untreated rubberized concrete, and treated rubberized concrete mixtures with 15 % rubber content. The study investigated both compression and tension mechanical properties of the concrete mixtures and assessed the flexural response of reinforced concrete (RC) beams. Parameters explored included rubber treatment, utilization of steel and GFRP as tensile reinforcement, and layered concrete pouring. Subsequently, a numerical study was conducted to address the impact of reinforcement ratio and layer depth on the behavior of slag-treated rubberized RC beams. The findings reveal a significant recovery of concrete compressive strength by 23 %, along with a 28 % enhancement in toughness and a 17 % increase in splitting tensile strength attributed to the application of slag treatment to rubberized concrete. The effect of rubber treatment was more pronounced in GFRP RC beams, as they showed similar load capacity as normal concrete. Furthermore, utilizing layered concrete beams with a 67 % depth of slag-treated RuC showed a comparable load capacity to normal RC beams, demonstrating only a 1 % reduction for steel-reinforced beams and a 2.4 % improvement for GFRP-reinforced beams. Notably, the numerical model emphasized this outcome and suggested that increasing the layer depth to 72 % of slag-treated depth displayed better performance.

Experimental evaluation of the synergistic effect of calcium precursor dosage and bacterial strain interactions on the biogenic healing potential of self-healing cement mortar

This study investigates the microbially induced calcium carbonate precipitation (MICP) in repair mortar, focusing on the impact of calcium precursor dosage and bacterial strain selection. C6H10CaO6·xH2O and (CH3COO)2Ca·xH2O were used as calcium precursors at dosages of 0.1, 0.25, and 0.4 M with Bacillus subtilis VEB4, Priestia megaterium TSB16, and Halobacillus halophilus MCC2188 microbes. Quantitative assessment of precipitate and optimization of precursor dosages were conducted before making mortar cube specimens of size 70.6 × 70.6 × 70.6 mm with bacterial spores and nutrients immobilized in Modified Expanded Perlite. Cracked cube specimens underwent automated wet-dry cycles of 12 h daily for 60 days to induce healing. Comparative analysis of biomortar specimens showed P. megaterium as the most effective in compressive strength recovery (up to 89.33%) and crack healing with a maximum healed crack width of 0.64 mm, followed by B. subtilis with significant CSR improvements. H. halophilus, less efficient in non-saline conditions, healed cracks up to 0.48 mm. Calcium lactate was considered the better calcium source choice for B. subtilis and P. megaterium strains, whereas calcium acetate improved MICP by H. halophilus. Microstructural analysis of healed precipitates collected from cracked cubes identified distinct morphology of MICP and the presence of polymorphs viz, calcite, aragonite, and vaterite. Tailored selection and dosage of calcium precursors for each strain significantly enhanced MICP and improved the quality of healing products in cracks, advancing the understanding of self-healing construction biomaterials.

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.

Damage and Recovery Behavior of Low-Replacement-Rate Fly Ash Concrete after Different High-Temperature Exposures.

This study focuses on investigating the strength recovery of fire-damaged fly ash concrete (FAC) with a low substitution rate of 10% through post-fire curing. The chemical and microstructural changes were analyzed using X-ray diffraction (XRD), derivative thermogravimetry (DTG), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and nitrogen adsorption. The findings indicate that the incorporation of fly ash slightly enhanced the strength after exposure to 400 °C; this was attributed to improved pozzolanic reactions, which were not observed at higher temperatures of 600 °C and 800 °C. Moreover, a positive effect on the recovery of compressive strength was observed due to the pozzolanic reaction. However, due to the relatively low fly ash content, depletion occurred at a later age, resulting in the inability to inhibit microstructural damage caused by the production of portlandite, thereby weakening the compressive strength. Interestingly, fly ash influenced the morphology of calcium carbonate and calcium silicate hydrate crystals, which is potentially ascribed to the role of high aluminum content acting as a crystallization-guiding agent.

Effect of nanocomposite cementitious capillary crystalline waterproofing material on self-healing properties of cementitious composites

There are limited studies about the effect of nanocomposite cementitious capillary crystalline waterproofing material (CCCW) on the self-healing properties of cementitious materials in different environments. Compressive strength recovery ratio(CSRR) test, electrochemical impedance spectroscopy (EIS) test, and macroscopic cracks healing observation test were adopted to study the self-healing properties of pure mortar specimens, mortar specimens mixed with CCCW, and nanocomposite CCCW respectively under three kinds of curing conditions. The self-healing mechanism of nanocomposite CCCW was analyzed using thermogravimetric analysis and differential scanning calorimetry (TG-DSC), mercury intrusion porosimetry (MIP), and scanning electronic microscope and energy dispersive spectroscopy (SEM-EDS) techniques. It was found that the curing condition significantly influenced self-healing performance, with touching water curing condition having the highest impact, followed by soaking water curing condition and natural curing condition. Nanocomposite CCCW promoted the healing performance of damaged specimens and significantly increased the CSRR. Under touching water curing condition, the CSRRs of the mortar groups with 3% nano-SiO2, 3% nano-CaCO3, and 2% nano-MgO were 26.1%, 11.5%, and 8.6%, respectively, higher than the CSRR of the single-doped CCCW group. After 28 days of touching water curing, change in charge transfer resistance before and after specimen healing (∆Rct) of the groups with 3% dosage of nano-SiO2, 3% dosage of nano-CaCO3, and 2% dosage of nano-MgO were 5.2, 1.8, and 2.7 times, respectively, higher than that of the single-doped CCCW mortar group. Throughout the healing process, the addition of the three nanocomposite CCCWs accelerated the hydration reaction to generate C-S-H gel, CaCO3, Aft, etc., improved the internal pore structure, reduced the size of the most probable pore diameter (MPPD) of the mortar specimens, and ultimately promoted the self-healing properties of the cementitious materials.

Study on Basic Pavement Performance of High-Elasticity Asphalt Concrete.

In order to improve the basic pavement performance of high-elastic asphalt concrete filled in the expansion longitudinal joints of seamless bridges, rubber particles and polyester fibers were added to optimize the mix proportion of elastic asphalt concrete, and the optimal asphalt-aggregate ratio was determined. The influence of rubber particles and polyester fibers on the basic pavement performance of high-elastic asphalt concrete was studied. The results show that when the dosage of polyester fiber is not more than 0.6%, the optimal asphalt-aggregate ratio is 1:5, and when it exceeds 0.6%, the optimal asphalt-aggregate ratio is 1:4. The incorporation of rubber particles reduces the compressive strength of high-elastic asphalt concrete but enhances its high-temperature stability, fracture performance, and deformation recovery ability. The incorporation of polyester fibers improves its compressive strength, high-temperature stability, fracture performance, and deformation recovery ability. In addition, the incorporation of rubber granules and polyester fibers promotes the use of green building materials and provides strong support for sustainable building practices.

High-Temperature Stirring Pretreatment of Waste Rubber Particles Enhances the Interfacial Bonding and Mechanical Properties of Rubberized Concrete

This paper innovatively proposes a method of 180 °C high-temperature stirring pretreatment for waste rubber particles and compares this method with untreated, NaOH-treated, and silane coupling agent KH570-treated waste rubber particles. Fourier-transform infrared spectroscopy, X-ray diffraction analysis, water contact angle measurement, scanning electron microscopy, and energy-dispersive X-ray study are used to investigate the effects and mechanisms of different pretreatment methods on waste rubber particles. The results indicate that compared to NaOH-treated and KH570-treated waste rubber particles, the 180 °C high-temperature-stirred pretreated waste rubber particles show significantly improved cleanliness and form a hard oxide film. The study also investigates the effects of different pretreatment methods on the mechanical properties and interface binding performance of rubber concrete made from pretreated waste rubber particles. The results demonstrate that rubber concrete prepared using 180 °C high-temperature-stirred pretreated waste rubber particles substituting 20% fine aggregate exhibits the best mechanical properties and interface bonding performance. The compressive strength recovery rates after 7 and 28 days are 41.6% and 37.3%, respectively; the split tensile strength recovery rates are 47.3% and 60.6%; the axial compressive strength recovery rates are 34.1% and 18.8%; and the static compression moduli of elasticity recovery rates are 46.8% and 26.3%. High-temperature stirring pretreatment of waste rubber particles is simple to operate and suitable for scaled production. Its pretreatment effect is superior to those of the KH570 and NaOH methods, providing a reference value for the scalable application of waste rubber particles as a substitute for fine aggregate in rubber concrete.

The study of double-network carboxymethyl chitosan/sodium alginate based cryogels for rapid hemostasis in noncompressible hemorrhage

Developing an injectable hemostatic dressing with shape recovery and high blood absorption ratio for rapid hemostasis in noncompressible hemorrhage maintains a critical clinical challenge. Here, double-network cryogels based on carboxymethyl chitosan, sodium alginate, and methacrylated sodium alginate were prepared by covalent crosslinking and physical crosslinking, and named carboxymethyl chitosan/methacrylated sodium alginate (CM) cryogels. Covalent crosslinking was achieved by methacrylated sodium alginate in the freeze casting process, while physical crosslinking was realized by electrostatic interaction between the amino group of carboxymethyl chitosan and the carboxyl group of sodium alginate. CM cryogels exhibited large water swelling ratios (8167 ± 1062 %), fast blood absorption speed (2974 ± 669 % in 15 s), excellent compressive strength (over 160 kPa for CM100) and shape recovery performance. Compared with gauze and commercial gelatin sponge, better hemostatic capacities were demonstrated for CM cryogel with the minimum blood loss of 40.0 ± 8.9 mg and the lowest hemostasis time of 5.0 ± 2.0 s at hemostasis of rat liver. Made of natural polysaccharides with biocompatibility, hemocompatibility, and cytocompatibility, the CM cryogels exhibit shape recovery and high blood absorption rate, making them promising to be used as an injectable hemostatic dressing for rapid hemostasis in noncompressible hemorrhage.

Autonomous self-healing behavior of geopolymer pastes under varied curing environments

This study examined the effectiveness of incorporating self-healing capsules based on sodium silicate in geopolymers containing fly ash and metakaolin. To evaluate the self-healing capabilities, geopolymer samples with the self-healing capsules were preloaded and subjected to different healing conditions: 100% relative humidity at room temperature, 100% relative humidity at 60°C, and water curing. The crack sealing capability, compressive strength recovery, and changes in the sorptivity coefficient of the geopolymer paste with varying amounts of self-healing capsules were investigated. The self-healing process performed under 100%RH-60°C resulted in the highest crack sealing efficiency (91.6±18.53%), mechanical recovery, and improved water tightness. XRD, FT-IR, and SEM-EDX techniques confirmed that primary self-healing products were amorphous aluminosilicates.

Effect of hemp fibers and crystalline admixtures on the properties and self-healing efficiency of lime and clay-based mortars

This study investigates the impact of hemp fibers on two fiber-reinforced compositions, clay-based and lime-pozzolan mortar. Three compositions were prepared for each mortar, reference samples without fiber incorporation, samples with untreated hemp fibers, and samples with hydrothermally treated hemp fibers with crystallines. Crystalline admixtures (CAs) were incorporated into the hydrothermal pretreatment of fibers to promote the self-healing properties of the mortar when needed. Physico-mechanical and thermal properties took place to address the overall effect of hemp on the mortars. Adding hemp fibers enhanced the mechanical strength and reduced the mortars' shrinkage. The hydrothermally treated fibers have better cohesion with mortars, preserving the best results. To evaluate self-healing efficiency, pre-damaged cubic samples from each composition were subjected to tap water immersion for lime-pozzolan mortars and a controlled humid chamber for clay mortars after a curing period. The healing rate was assessed by measuring crack closure, compressive strength recovery, and the dynamic modulus of elasticity recovery. The results indicated significant strength recovery in lime-pozzolan mortars with hemp fibers. Clay-based mortars showed moderate strength increases and limited self-healing.

Assessment of self-healing performance of cement-based materials incorporating ion chelator and industrial wastes

Ion chelator can enhance the self-healing of cracks and pores in concrete. To further improve the self-healing capability of cement-based materials, different industrial wastes (i.e. fly ash, limestone powder and blast furnace slag (BFS)) and ion chelator were mixed into mortar. The crack closure index, water permeability, water absorption, impermeability, compressive strength recovery and healing products of mortar were studied. The results showed that the mortar mixed with BFS and ion chelator possessed the best repair ability on cracks, the crack with a maximum width of 0.55 mm can be closed within 14 d. Meanwhile, the water permeability and water absorption of mortar incorporating ion chelator and BFS were obviously smaller than that of control mortar. After curing for 56 d, the chloride diffusion coefficient of mortar containing ion chelator and BFS was reduced by 73.7% compared with control mortar. The compressive strength recovery ratio of mortar containing ion chelator and BFS was 63.7% greater than that of control mortar after pre-loading 80% of the failure strength. In addition, scanning electron microscopy and energy dispersive spectroscopy displayed a large number of calcites at the edge of crack section in mortar containing ion chelator and BFS, the inside of crack was mainly repaired by the combined effect of calcium carbonate precipitation and hydration product.

A viscosity-soluble type biomimetic self-healing cement slurry system

With the development of cementing slurry technology, cementing self-healing has become one of the most effective technologies to prevent and treat oil and gas channeling and improve long-term sealing capacity of cement sheath. To solve the technical problem of annulus oil and gas channeling caused by the long-term sealing failure of cement sheath, this paper researches and develops a kind of viscosity-soluble type biomimetic self-healing cement slurry system from the perspective of chemical biomimetics, based on the technical idea of “prevention before blocking”. Then, the engineering performance of this biomimetic self-healing cement slurry system and the mechanical property of self-healing set cement are evaluated respectively. In addition, the mechanical recovery capacity and permeability reducing rate of the self-healing set cement conserved with methane are evaluated by creating fractures through splitting. Finally, the healing mechanisms of the self-healing cement are analyzed by means of SEM microscopic test and infrared spectrography. And the following research results are obtained. First, the set cement has excellent mechanical property. When the compressive strength decreases by 15 %, the elastic modulus of set cement decreases by 41 %, showing good toughness to play the role of “first prevention”. Second, when meeting hydrocarbon, the damaged set cement is excited to generate a kind of viscosity-soluble type gelatinous ester substance, which re-bonds the skeleton of the set cement. When the self-healing set cement is conserved with methane, its compressive strength recovery rate is up to 94.5 %, bending strength recovery rate is 58.6 %, gas log permeability drops by 99 %, and liquid log permeability drops by 100 %, so as to realize “blocking later”. In conclusion, the viscosity-soluble type biomimetic self-healing cement slurry system can effectively achieve cementing integrity and long-term sealing integrity through self-healing after the damage of cement sheath, which provides a strong technical support for preventing the production safety hazard of sustained casing pressure in oil and gas wells and is beneficial to solve the technical problem of annulus oil and gas channeling caused by long-term sealing failure of cement sheath.

PRODUCTION OF SELF-HEALING MORTAR USING BACTERIAL SPORES ENCAPSULATED WITH JUTE FIBRE

Cement-based composites have various advantages such as low cost, easy shaping, and high compressive strength. Therefore, they are widely used in the construction industry. However, their brittle structure makes them prone to cracking, which must be repaired promptly to avoid possible loss of strength and durability and ultimate structural failures. Microbially-induced calcite precipitation (MICP) offers an effective method for healing these cracks. Unlike other treatments, MICP method is a natural and environment-friendly option for self-healing of cracks. However, bacteria can be damaged by cement and mechanical impacts; therefore, encapsulation is necessary to protect them. Encapsulation in fibres is a simpler and more cost-effective method than the other techniques. This study tested the effectiveness of encapsulating Bacillus megaterium spores in jute fibres and added them to cement-based mortars. Different nutrient supplements were used, and physical analyses and compressive strength tests were conducted on 28-day cured cube specimens. Present findings revealed that Bacillus megaterium-type bacteria encapsulated in jute fibres improved the compressive strength recovery and healed the loading-induced cracks.

Strength recovery of thermally damaged high-performance concrete subjected to post-fire carbonation curing

This study investigates the efficacy of post-fire curing using carbonation with a 20% carbon dioxide concentration and a relative humidity cycle set between 40% and 90% for restoring the mechanical properties of thermally damaged high-performance concrete (HPC) specimens containing 0%–40% silica fume. The HPC specimens were exposed to temperatures of 600, 800, and 1000 °C for 1 h, and the compressive strength recovery was measured. The microstructure, porosity, pore size distribution, and chemical composition of the HPC specimens were analyzed to explore the strength recovery mechanism. After exposure to elevated temperatures, the average compressive strength of samples without silica fume decreased by 49.2 MPa. Subsequent carbonation recuring resulted in a significant recovery of 73.9 MPa in the average compressive strength. This recovery surpassed the original strength for the samples heated to 600 and 800 °C, attributable to the filling and coalescing effects of calcium carbonate polymorphs formed through the carbonation of residual cement particles and β-C2S. The samples containing 20% silica fume exhibited the second highest average strength recovery of 34.1 MPa. However, the strength recovery for the samples with 40% silica fume exposed to 800 and 1000 °C was negligible, as the microcracks exceeding 1 μm in width had barely been restored by the carbonation of the low-calcium calcium silicates with low reactivity. Overall, this study presents an exciting future prospect for the labor and cost-effective restoration of thermally damaged concrete structures through the use of carbonation curing.

Study on the properties of urea-formaldehyde resin in repairing microcracks of cement stone in oil well under CO2 acid environment

To solve the problem of microcracks caused by CO2 erosion in the cementing ring, an environmental responsive polymer (LJIY) was prepared to repair microcracks. LJIY was synthesized from formaldehyde and urea, and its structure and properties were analyzed by FTIR, SEM, laser particle size analyzer and environmental responsiveness test etc. The results showed that LJIY was microsphere with an average particle size of 5.33 μm. LJIY was responsive to environmental pH, structurally stable in alkaline environments, and crosslinkable in acidic environments. LJIY had obvious repair effect on the microcracks of cement stone. After 28 days of repair in CO2 solution, the compressive strength recovery rate of cement stone mixed with 5% LJIY was 87.2%, the permeability was reduced to 0.001 μm2, and the microcracks were basically healed. The healing mechanism of LJIY on cement microcracks was that when the microcracks in the cement stone were formed, CO2 penetrates into the cement stone, and the pH of the solution environment was reduced to acid. Under acidic conditions, LJIY crosslinked to form a polymer film that adhered or filled the microcracks, thereby healing the microcracks.

Preparation and application of Na2SiO3@EC microcapsules for self-healing alkali-activated slag

Alkali activated slag (AAS) is a promising green building material, but its application has been limited by the high risk of cracking. In this study, the self-healing technology was used in AAS system by introducing self-healing microcapsules. The Na2SiO3@EC microcapsules were designed with sodium silicate (Na2SiO3) as the core material and ethyl cellulose (EC) as the shell material, and the prepared microcapsules were characterized by leaching test and SEM-EDS. The effect of microcapsules on the self-healing of AAS mortars was verified by the post-repair compressive strength test, and the mechanism was discussed based on MIP and hydration heat. The results showed that the core–shell structured Na2SiO3@EC microcapsules were prepared with a core content of 69.42 wt%. The addition of microcapsules could improve workability and mechanical property of AAS mortars. The AAS mortars with Na2SiO3@EC microcapsules had a compressive strength recovery ratio of up to 26.82%. The Na2SiO3 released from microcapsules promoted the secondary hydration of the AAS mortars, and the hydration products refined the pore structure. Image processing methods were effective in visualizing and quantifying the changes in the cracks, and the image results further confirmed the long-term effectiveness of the microcapsules. This study provides guidance on the application of self-healing microcapsules in the AAS system and the visualization of self-healing behavior.

Enhancing self-healing efficiency of concrete using multifunctional granules and PVA fibers

Self-healing concrete can prolong the lifespan of structures by sealing cracks. This study assessed the self-healing efficiency of combined multifunctional self-healing granules (SHGs) and PVA fibers under different curing conditions in self-healing concrete. Microstructure analysis of self-healing specimens and products was conducted to reveal the self-healing mechanism. Compared to using SHGs or PVA fibers alone, the synergistic effect of SHGs and PVA fibers improved the compressive strength recovery rate, permeability coefficient recovery, and surface crack closure effect. PVA fiber inhibited crack propagation and provided attachment points for self-healing product deposition, while SHGs released self-healing agents and produced hydrated calcium silicate, calcium carbonate, and magnesium hydroxide to repair cracks. The addition of SHGs also increased the utilization of carbon dioxide and ions in seawater, thereby decarbonizing the environment and reducing the erosive effect of seawater ions.

Uncovering the Mechanism of the Role of Fly Ash in the Self-Healing Ability of Mortar with Different Curing Ages.

As an admixture of cement-based materials, the reaction of fly ash (FA) usually takes place in the late age of curing, so FA will affect the self-healing ability of long-age cement-based materials. The self-healing potential and the characteristics of self-healing products of cementitious materials before and after crack healing were analyzed by microscopic tests, and the mechanism of the effect of fly ash on the self-healing performance of cementitious materials was revealed. The results showed that the increase in fly ash content promoted the improvement of the self-repair performance of cracked specimens at 28 d, especially when the fly ash dosage was 40%, the crack opened after 30 d of healing in water was completely closed, the UPV value after recovery was close to 3000 m/s, the self-repair efficiency of maximum amplitude and main frequency amplitude was up to more than 60%, and the recovery rate of compressive strength was increased to more than 30%. However, the increase in fly ash content was not conducive to the self-repair of cracked samples at 210 d, and with the increase in fly ash content, the crack closure effect weakened, the UPV value after recovery decreased, the crack repair rate based on ultrasonic transmission decreased to about 20%, and the compressive strength recovery rate increased slightly. In addition, calcium carbonate precipitation was the main repair product of crack filling and healing, including calcite and spherulite. With the increase in fly ash content, the content of element C in the self-repair products of 28-day-old specimens gradually increased, and the size of calcium carbonate crystals gradually decreased, but the filling was denser, whereas the calcium carbonate crystals in the self-repair products of 210 d specimens gradually became fine and loose.

Synergistic effect of ion chelating agent and magnesium fluorosilicate on self-repairing ability and microstructure of mortar

Ion chelating agent (ICA) can stimulate the self-repairing of cracks and pores in concrete. In order to further improve the self-repairing capability of cement-based materials, the ICA and different dosage of permeable crystallization surface treatment agent (magnesium fluorosilicate) were mixed into the mortar. The compressive strength recovery, pore-size distribution, crack self-repairing and repair product of the mortar were studied. The results showed that after pre-loading 70% of the failure strength, the compressive strength recovery rate of mortar containing ICA and 0.50 wt% magnesium fluorosilicate was 24.4% higher than that of the control mortar. At 28 d, the ratio of harmful pores (pore diameter >0.1 µm) of mortar with ICA and 0.25 wt% magnesium fluorosilicate was decreased by 62.6% compared with the control mortar. The crack with a maximum width of 0.60 mm in mortar incorporating ICA and 0.5 wt% magnesium fluorosilicate could be completely repaired within 28 d. In addition, scanning electron microscope and energy dispersive spectrometer revealed that a lot of calcites in the crack of mortar mixed with ICA and magnesium fluorosilicate, which proved that the ICA and magnesium fluorosilicate had synergistic effect on the self-repairing properties of cement-based materials.

Interpretable Machine Learning for Prediction of Post-Fire Self-Healing of Concrete.

Developing accurate and interpretable models to forecast concrete's self-healing behavior is of interest to material engineers, scientists, and civil engineering contractors. Machine learning (ML) and artificial intelligence are powerful tools that allow constructing high-precision predictions, yet often considered "black box" methods due to their complexity. Those approaches are commonly used for the modeling of mechanical properties of concrete with exceptional accuracy; however, there are few studies dealing with the application of ML for the self-healing of cementitious materials. This paper proposes a pioneering study on the utilization of ML for predicting post-fire self-healing of concrete. A large database is constructed based on the literature studies. Twelve input variables are analyzed: w/c, age of concrete, amount of cement, fine aggregate, coarse aggregate, peak loading temperature, duration of peak loading temperature, cooling regime, duration of cooling, curing regime, duration of curing, and specimen volume. The output of the model is the compressive strength recovery, being one of the self-healing efficiency indicators. Four ML methods are optimized and compared based on their performance error: Support Vector Machines (SVM), Regression Trees (RT), Artificial Neural Networks (ANN), and Ensemble of Regression Trees (ET). Monte Carlo analysis is conducted to verify the stability of the selected model. All ML approaches demonstrate satisfying precision, twice as good as linear regression. The ET model is found to be the most optimal with the highest prediction accuracy and sufficient robustness. Model interpretation is performed using Partial Dependence Plots and Individual Conditional Expectation Plots. Temperature, curing regime, and amounts of aggregates are identified as the most significant predictors.