Superabsorbent Polymer Research Articles

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.

Phase change hydrogel formed by osmotic pressure for thermal energy storage

The present study investigates the potential of latent heat storage using phase change materials (PCMs) to reduce building energy consumption, addressing the common challenges of PCM leakage and compatibility with construction materials. We introduce a novel phase change hydrogel, created by encapsulating polyethylene glycol (PEG) within a superabsorbent polymer (SAP) network through osmotic pressure. The structural and thermal characteristics of the PEG/SAP composite were analyzed using differential scanning calorimetry (DSC), thermal gravimetric analysis (TG), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and polarizing optical microscopy (POM). Results demonstrated that PEG effectively filled the SAP network, forming a stable composite structure, with PEG as the core and SAP as the supporting matrix. The composite achieved a remarkable PEG mass fraction of 80 %, yielding a melting enthalpy of 129.7 J/g and a peak melting temperature of 51.89 °C. Additionally, PEG/SAP exhibited robust thermal stability up to 300 °C. Notably, when incorporated into cement, surface temperatures of phase change cement decreased by 12 °C compared to conventional Portland cement under constant heating. This approach highlights high latent heat capacity, low production costs, and straightforward fabrication, positioning PEG/SAP as a promising solution for large-scale applications in building energy conservation.

Formulation and characterization of super absorbent copolymer AA, ACN-grafted sodium acrylate for feminine napkin

Absorbency for feminine napkins is a research priority in the recent era, though commercial napkins are available with the same function properties achieved through finishing. One of those methods is coating SAPs, which act as hydrogels. Super absorbent polymers are generally coated in the second- or third-layer of the napkin. The present work deals with the coating of the SAP on the top layer by forming poly (acrylic acid)/sodium acrylate (ACN-g-PAA/SA) and demonstrating its absorption properties. Ultimately, we conducted a comparative analysis of all the SAPs prepared, and demonstrated an absorptive capacity of 104.35 g/g in tap water and 51.28 g/g in saline solution during free swelling. Additionally, under a specific load, it demonstrated 56.48 g/g in tap water and 27.42 g/g in saline solution. Based on the comparative results suggested by the TGA curve, water absorbency, and moisture content, the present work proposes a polymer suitable for coating the feminine napkin.

Prediction and investigation of water repeated absorption and release properties of superabsorbent polymers during the dry-wet cycles in different solutions

Superabsorbent polymers (SAP) with a three-dimensional cross-linked network structure are used in the concrete field due to their good water absorption and water retention properties. The changes of its repeated water absorption and release properties have an important impact on crack healing, but there is still a lack of relevant research. This study mainly uses the tea-bag method to explore the repeated water absorption and release behavior of sodium polyacrylate and polyacrylic acid-acrylamide copolymers in deionized water, cement filtrate, and saturated calcium hydroxide solution. The quantitative analysis of the change in the peak area of the water-absorbing functional group was performed by fourier transform infrared spectroscopy. The morphology and elements of SAP under different dry-wet cycles were analyzed by scanning electron microscope-energy spectrum analysis. The repeated swelling behavior of SAP was predicted using the classical models. The results showed that the repeated water absorption performance of SAP gradually decreased with the increase of the number of wet-dry cycles. The slope of the curve for the second-order equation gradually increases, and the peak area corresponding to the carboxyl functional group also gradually increases. And the rate and amount of water release gradually increase. For sodium polyacrylate, with the increase in the number of wet-dry- cycles, the increase in the content of calcium, magnesium, and aluminum elements is accompanied by a significant decrease in the content of sodium elements. In contrast, the calcium content on the surface of polyacrylic acid-acrylamide copolymer increased, but the sodium content only slightly decreased.

Exploring cement content's impact on self-healing in super absorbent polymer-modified concrete

This study shows the impact of varying cement content while maintaining a constant water-to-cement (w/c) ratio on the performance of self-healing concrete. It also explores the effect of F-type fly ash on the self-healing mechanism of concrete. Self-healing concrete, incorporating super absorbent polymers, offers a viable remedy to diminish the detrimental effects of cracks, enhancing the durability and lifespan of concrete structures. While the w/c ratio is a crucial factor influencing concrete properties, the impact of varying cement content under a constant w/c ratio in self-healing concrete remains understudied. Therefore, this experiment involved preparing 18 different concrete mixtures using three distinct cement contents under three specific w/c ratios. Fly ash was mixed in half of the specimens. Super absorbent polymers are incorporated into all mixtures to facilitate autonomous healing by absorbing and retaining water, which is released upon crack formation. Specimens were pre-cacked using a stress-controlled UTM machine. To evaluate the self-healing mechanism, low water pressure permeability test, water absorption test, and image analysis were conducted at 7, 14, 28, and 56 days. The findings of this study show that a w/c ratio of 0.35 yielded the best performance which indicates a lower w/c shows a higher self-healing performance. Additionally, the specimen containing a higher cement content exhibited enhanced healing capacity compared to other specimens. However, the specimens with fly ash failed to show a satisfactory result on self-healing capacity because the addition of silicon-based fly ash (F type) created an adverse effect on the self-healing mechanism.

Water retention and heat storage characteristics of phase change hydrogel in cooling pavement

Phase change hydrogel (PCH) combines the heat storage characteristics of phase change material with the water retention capacity of hydrogel, showing great potential in cooling pavement applications. This study aims to investigate the water retention and heat storage properties of PCH in cooling pavement, providing new insights for mitigating the urban heat island effect. Based on the principle of osmotic pressure, polyethylene glycol (PEG) solution was actively absorbed by superabsorbent polymers (SAP) to form stable PCH. By infusing the asphalt mixture skeleton with PCH-containing phase change grouting material (PCGM), a temperature-regulating phase change grouting pavement (PCGP) can be obtained. Morphological characterization showed that PCH was uniformly distributed in PCGM and effectively locked PEG during high temperature and water absorption/release processes without leakage. PCH imparted excellent water retention properties to PCGM, with a saturation water absorption rate of 44.1 %, which is 6.2 times higher than the control group, and a water retention rate of 34.31 % after heating at 60 °C for 12 hours. Furthermore, PCGM exhibited considerable heat storage performance, with a melting enthalpy of 15.74 J/g and a crystallization enthalpy of 12.07 J/g. Based on these, PCGP demonstrated outstanding temperature-regulating ability, reducing surface temperatures by 9.3 °C and 11.6 °C under dry and saturated conditions, respectively, compared to control pavement. In conclusion, this study provides a theoretical basis for the development of novel cooling pavement materials and shows great potential for its wide application in urban infrastructure construction.

Additive-assisted macroscopic self-assembly and control of the shape of assemblies based on host–guest interaction

In these decades, considerable attention has focused on supramolecular polymers due to their unique structures and properties. More recently, macroscopic supramolecular polymers have attracted increasing interest from not only biologists but also materials scientists inspired by the sophisticated structures and functions of living organisms. Since the functions of supramolecular polymers are strongly dependent on their shape, control of the shape is an important issue in controlling the functions of supramolecular polymers. However, the control of shape in macroscopic supramolecular assemblies has not yet been sufficiently investigated. Previously, we studied the macroscopic self-assembly behavior of super absorbent polymer (SAP) microparticles modified with β-cyclodextrin (βCD) and adamantane (Ad) residues (βCD(x)-SAP and Ad(y)-SAP microparticles, where x and y are the mol% contents of βCD and Ad residues, respectively). More elongated assemblies were formed at higher y, indicating that the shape of assemblies can be controlled by varying the interaction strength. The noteworthy is that 1-adamantanamine hydrochloride (AdNH3Cl) assisted the formation of assemblies from βCD(x)-SAP and Ad(y)-SAP microparticles, indicating that AdNH3Cl acts as a chemical stimulus for macroscopic assemblies of βCD(x)-SAP and Ad(y)-SAP microparticles. In this study, we have thus studied the assembling behavior of βCD(x)-SAP microparticles with Ad(y)-SAP microparticles and unmodified SAP microparticles assisted by AdNH3Cl, as well as the shape of the resulting macroscopic assemblies. AdNH3Cl assisted the formation of assemblies from βCD(16.2)-SAP and Ad(15.1)-SAP microparticles, in which AdNH3Cl crosslinked the SAP microparticles through the formation of inclusion complexes of βCD residues with the Ad residue and the electrostatic interaction of ammonium and carboxylate residues. Assemblies of βCD(26.7)-SAP and unmodified SAP microparticles were formed at the concentrations of AdNH3Cl ([AdNH3Cl]0) higher than a certain level (ca. 0.05 mM). The aspect ratio (a/b) of assemblies showed a maximum at [AdNH3Cl]0 ~ 0.10 mM, indicating that the chemical stimulus, i.e., addition of AdNH3Cl, controls the shape of assemblies formed from βCD(26.7)-SAP and unmodified SAP microparticles. This study suggests that other stimuli, e.g., heat, pH, light, redox, and force, can be utilized to control the shape of macroscopic assemblies based on supramolecular interactions.

Rapid hydrogen enclathration and unprecedented tuning phenomenon within superabsorbent polymers

Clathrate hydrate has emerged as a potentially viable storage medium for efficient hydrogen storage, owing to its eco-friendly characteristics and high hydrogen storage capacity. However, it is essential for its practical application to address the challenges posed by harsh thermodynamic formation conditions and slow formation kinetics for hydrogen hydrate. Here, we introduce the utilization of superabsorbent polymers (SAPs) as a dispersion matrix for tetrahydrofuran (THF) solutions to develop a method for rapid hydrogen enclathration. We investigated two distinct synthetic pathways, solution-borne and hydrate-borne routes. We also explored the relationship between hydrogen uptake/storage capacity, varying THF solution concentration within SAPs, and synthetic pathways for binary THF–hydrogen hydrates. The hydrogen storage capacity after 200 min enclathration reaction was relatively low for 1.0 mol% THF cases but significant for 5.56 mol% THF cases in hydrate-borne route (around 20 mmol H2/mol water), highlighting its potential for hydrogen storage material. The spectroscopic analysis revealed that the tuning phenomenon in THF 1.0 mol% hydrate was only observed in the solution-borne route, which facilitated hydrogen enclathration in partially vacant large cages of sII hydrates. It was striking that the tuning phenomenon was also observed in THF 5.56 mol% hydrate synthesized in both solution-borne and hydrate-borne pathways. Through phase equilibria measurements, we confirmed that less than 5.56 mol% of THF participated in forming binary hydrates. The different water and THF absorbability of SAPs resulted in a non-uniform distribution of THF solution within SAPs, causing the unprecedented tuning phenomenon. These findings provide valuable insights into the potential of SAPs for rapid hydrogen enclathration media, emphasizing the importance of understanding synthetic pathways and solution absorption properties for optimized hydrogen storage.

The research progress and Hotspot analysis of polymer cement mortar based on bibliometrics

Ordinary cement mortar is commonly used in building engineering due to its high strength, affordability, and easy access to raw materials. However, it suffers from high shrinkage and poor impermeability, which result in reduced building service life and significant carbon dioxide emissions during production. Polymer additives have been found to enhance the mechanical properties of cement mortar, leading to increased interest in polymer cement mortar by researchers. This study collected and analyzed 420 papers published between 1995 and 2023 in the field of polymer cement mortar. The analysis included publication trends, author cooperation networks, national cooperation networks, published journals, co-citation of references, and keywords. The findings reveal a rapid publication growth from 2018 to 2023, with China making the most significant contribution in this field. Among the scholars, Ru Wang has published the highest number of articles in the field of polymer cement mortar, while Ohama’s papers have been cited the most. The journal with the most articles is Construction and Building Materials. Research in polymer cement mortar focuses on mechanical properties, performance, hydration process, microstructure, and other related aspects. The reinforcement effect of polymer-modified cement mortar on reinforced concrete and applying superabsorbent polymer-modified cement mortar and polymer fiber in cement mortar have emerged as recent research frontiers. This study can help scholars quickly identify high-quality references and research frontiers in the field of polymer cement mortar while also providing research directions and ideas.

Target dispersion of pozzolanic materials nearby hydration-released calcium hydrates to improve the pozzolanic reaction degree

The random distribution of pozzolanic materials (PM) using direct mixing strategy reduces their contact possibility with hydration-released calcium hydroxide (CH), and limits the corresponding reinforcing efficiency to cement-based materials via pozzolanic reaction. In this study, a target dispersion strategy of PM nearby CH was proposed using super absorbent polymers (SAPs) as the carrier. On the one hand, nano silica (NS) and calcined clay (CC), two typical PM, can be encapsulated into SAPs through the hydrogen bonding interaction; on the other hand, the region around SAPs was enriched with more water and higher Ca2+ concentration, which triggered the in situ crystallization of CH. In this case, the contact possibility between the NS or CC (NS/CC) and hydration-released CH was improved by the target dispersion strategy, and resulted in a 60 %–253 % increase in pozzolanic reaction degree (PRD) of NS/CC. Furthermore, the reinforcing effect of NS/CC on compressive strength of cement paste was enhanced by 25 % through this strategy. Therefore, the current study introduces a novel method for increasing the pozzolanic reinforcing efficiency of cement-based materials by turning the random to target dispersion of PM nearby CH.

Cereal‐Based Intercropping Systems Improve Yield Advantage and Crop Yield Under Superabsorbent Application in Semiarid Conditions

ABSTRACTConsidering the yield advantage of cereal:legume intercropping in low nitrogen conditions, an experiment was laid out to examine the barley:chickpea intercropping treatments and their effects on biological yield and yield advantage of two plants under rain‐fed conditions as affected by a superabsorbent polymer (0, 50, 75, and 100 kg ha−1) in two cropping seasons. In both years, increasing the chickpea population increased the chickpea biological yield, total land equivalent ratio (TLER), competition index (CI), and barley and chickpea relative yields. Increasing the amount of the superabsorbent polymer to 100 kg ha−1 increased the chickpea competition ratio (0.86). The highest TLER (4.00) was related to 100:100 barley:chickpea intercropping without superabsorbent polymer application. In both years, the highest CI (0.21) was attained in the 100:100 barley:chickpea intercrop system in the first year. This was followed by the 100:100 barley:chickpea intercrop ratio (0.16) in the second year. The highest barley relative yields in the first year (3.91) and second year (3.57) were related to the 100:100 barley:chickpea plant ratio, which was higher than the yields for the 100:25 (38% and 35%), 100:50 (26% and 23%), and 100:75 (12% and 10%) ratios. Based on the results, the superiority of mixed cultivation, compared with pure cultivation, in the exploitation of production resources and integration of crop plants was observed.

Incorporation of polyzwitterions in superabsorbent network membranes for enhanced saltwater absorption and retention

BackgroundSuperabsorbent polymers (SAPs) have a remarkable ability to absorb significant quantities of water. However, their absorption capacity is significantly reduced when exposed to saline solutions, such as urine, due to the polyelectrolyte effect and charge screening. MethodsIn this study, we demonstrate a zwitterionic superabsorbent polymer (ZSAP) with excellent salt-water absorption and retention capacities. ZSAP was synthesized by grafting a copolymer of p(sulfobetaine methacrylate-co-2-hydroxyethyl methacrylate) (p(SBMA-co-HEMA)) onto an acrylic acid (AA)-based hydrogel via free-radical polymerization. The introduction of zwitterionic SBMA significantly enhances the hydrophilicity of the polymer, particularly in a saline solution due to the anti-polyelectrolyte effect, thereby accelerating the rate of salt absorption. Additionally, the hydroxyl groups from HEMA facilitate the formation of covalent bonds with the AA network membrane through esterification, effectively mitigating polymer leaching. The hydration/dehydration behaviors of linear polymers were measured using the dynamic vapor sorption (DVS) method. Moreover, the salt-water absorption capacity, centrifuge retention capacity (CRC), and absorbency under load (AUL) of ZSAP with various SBMA moieties and copolymer dosages were comprehensively evaluated in a 0.9 wt% sodium chloride solution. Additionally, the water retention under different temperatures and polymer leaching of ZSAP were investigated. Significant FindingsThe copolymer p(SBMA-co-HEMA) not only demonstrates a high salt-water absorption rate at 90% RH in a 0.9 wt% NaCl solution but also exhibits superior water retention at 0% RH compared to the AA polymer. Moreover, the ZSAP exhibits superior salt-water absorption capacity and AUL in a 0.9 wt% NaCl solution compared to conventional AA-based SAP. Additionally, the introduction of the hydroxyl moiety from the p(SBMA-co-HEMA) copolymer reduces free polymer leaching from ZSAP. This work presents an approach for the development of new SAP with high salt-water absorption and retention.

Shrinkage evolution and mechanism of self-curing concrete cooperatively cured with superabsorbent polymers and waterborne epoxy coatings

Shrinkage-induced cracking is a common phenomenon in concrete structures. To reduce concrete shrinkage, herein, a novel curing approach involving the concurrent application of internal superabsorbent polymers (SAPs) and external waterborne epoxy coatings (WECs) was adopted. Subsequently, the combined effects of the SAPs and WECs on the internal temperature, water retention behavior, relative humidity, and shrinkage performance of concrete were investigated. Furthermore, their underlying shrinkage-mitigation mechanisms were clarified and verified through mercury intrusion porosimetry tests. Results revealed that increasing the WEC application rates and number of spraying turns increased the relative humidities and reduced the shrinkage strains of the concrete specimens. The combined use of SAPs and WECs led to considerable reductions in the specimens’ humidity drop, water loss, and shrinkage values. The water losses of the concrete specimens exerted more considerable impacts on their relative humidity and shrinkage compared to their cumulative temperatures. Furthermore, the combination effects of the SAPs and WECs reduced the median pore diameters and increased the fractal dimensions of gel pores, thus triggered a reduce in capillary tension, and further mitigated the development of shrinkage strains. Overall, this study underscores the critical roles of evaporation, temperature, relative humidity, and pore-structure parameters on the shrinkage behavior of concrete. Additionally, it highlights the effectiveness of the combined application of SAP-based internal curing and WEC-based external curing, offering a feasible approach and technical support for reducing shrinkage in concrete structures.

Millimeter-scale soft capsules for sampling liquids in fluid-filled confined spaces.

Sampling liquids in small and confined spaces to retrieve chemicals and microbiomes could enable minimally invasive monitoring human physiological conditions for understanding disease development and allowing early screening. However, existing tools are either invasive or too large for sampling liquids in tortuous and narrow spaces. Here we report a fundamental liquid sampling mechanism that enables millimeter-scale soft capsules for sampling liquids in confined spaces. The miniature capsule is enabled by flexible magnetic valves and superabsorbent polymer, fully wirelessly controlled for on-demand fluid sampling. A group of miniature capsules could navigate in fluid-filled and confined spaces safely using a rolling locomotion. The integration of on-demand triggering, sampling, and sealing mechanism and the agile group locomotion allows us to demonstrate precise control of the soft capsules, navigating and sampling body fluids in a phantom and animal organ ex vivo, guided by ultrasound and x-ray medical imaging. The proposed mechanism and wirelessly controlled devices spur the next-generation technologies for minimally invasive disease diagnosis.

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.

Exploring the evolution of superabsorbent polymer in cementitious materials: insights into testing methods and their impact on properties

Exploring the evolution of superabsorbent polymer in cementitious materials: insights into testing methods and their impact on properties

Performance enhancement of cement mortar with superabsorbent polymer composite internally embedded with porous ceramsite sand

Superabsorbent polymer (SAP), which can act as water reservoir, was an internal curing (IC) agent with great potential to reduce the shrinkage and cracking of cement-based materials. However, the volume shrinkage of SAP after water release will lead to the formation of additional voids, which will lead to a clear reduction of mechanical properties. In present work, a novel SAP composite with a rigid skeleton (IP-PS) was synthesized by embedding in-situ polymerized SAP hydrogel into the pores of porous ceramic (PS). The results demonstrated that the compressive strength of IP-PS0.054 was above 10 % higher than that of SAP0.054 in the early and late stages, the compressive strength of IP-PS0.054 at 28 days reached 97.71 % of that of the control group, which was predominantly ascribed to the support provided by the embedded skeleton. The development of self-desiccation was also notably delayed by the incorporation of IP-PS, as evidenced by the approximately 12 % reduction compared to SAP0.054 and 47 % reduction compared to Control group in 7-day autogenous shrinkage, which was on account of the enhanced water storage and durable IC capacity of IP-PS. Furthermore, the impermeability of cement-based materials was also improved by the in-situ polymerized hydrogel modification.

Assessing the influence of superabsorbent polymers on corrosion resistance of reinforced ultra-high performance concrete exposed to chloride and compound saltwater via electrochemical impedance spectroscopy

The corrosion resistance of ultra-high performance concrete (UHPC) with superabsorbent polymers (SAPs) submerged in deionized water, chloride saltwater, and compound saltwater was studied. The investigated mixtures included a control UHPC mixture and UHPC mixtures with 0.3 % sodium polyacrylates and 0.3 % polyacrylate-co-acrylamide. The corrosion performance was evaluated using electrochemical impedance spectroscopy, while scanning electron microscopy-energy dispersive X-ray (SEM/EDX) analysis was used to analyze micro-morphology changes and chemical composition. Polarization analysis revealed that the control specimens exhibited the highest resistance to chloride and sulfate penetration, resulting in negligible corrosion rates after 240 days (icorr from 0.0013 to 0.0063 µA/cm2). The SAP-modified specimens also showed high resistance, with an initial low corrosion rate (icorr of 0.101 µA/cm2) that decreased to negligible levels after 28 days (icorr from 0.047 to 0.088 µA/cm2). SEM/EDX results revealed that SAPs facilitate the formation of Friedel’s salt and Ettringite crystals in chloride and compound saltwater, contributing to the reduction in corrosion resistance.

A synergetic self-sealing model for cement-based composite using granular expansive agent and crystalline admixture

The autogenous self-sealing model has been researched in previous work, which could help to characterize the self-sealing process with crystalline products. The model outcome was presented in the form of leakage water flow, which demonstrates the self-sealing capacity or the recovery of watertightness. While in the research area of cement-based material self-sealing, the expansive agent cannot be neglectable, for example the superabsorbent polymer (SAP). Especially for the building components exposed to free water, an efficient water flow blockage after cracking is crucial to ensure stable service. Hence in this study, the self-sealing process of a granular expansive agent inside the crack of cement-based material was simulated. The model outputs were compared with experimental results to verify the reliability. Additionally, the autogenous self-sealing model was incorporated into this model to simulate the “crystallization-expansion” synergetic self-sealing. The contribution of crystalline product and expanded EA to water flow blockage were compared during the crystallizing process. Overall, this model is of great use to evaluate the role of expansive agent on water flow blockage after the cement-based material cracking in hydraulic engineering or engineering components exposed to water.

Fracture properties and self-healing assessment of superabsorbent polymer modified hybrid fibre concrete

The aim of this study is to develop durable concrete with improved crack repair abilities by using a superabsorbent polymer (SAP). The experimental program investigates the effect of four different SAP concentrations, viz., 0.2 %, 0.4 %, 0.6 %, and 0.8 %, by weight of cement, on the properties of hybrid fibre concrete (HFC). The findings reveal that the mechanical properties, namely compressive strength, flexural strength, and tensile strength, are nearly equivalent to HFC up to 0.4 % SAP concentration. Specimens exhibit a decrease of 9.29 % and 17.3 % in compressive strength for SAP concentrations of 0.6 % and 0.8 %, respectively, in comparison to the HFC. Conversely, adding SAP to HFC specimens results in an increase in flexural toughness and fracture energy, with a maximum increase of 56.80 % and 55.13 % at a 0.4 % SAP concentration, respectively. Microstructural study reveals that SAP did not undergo any chemical reactions with the hydration products of concrete. However, because of SAP's internal curing effect, the hydration improved, especially in the vicinity of SAP particles. Thermogravimetric analysis (TGA) demonstrates that SAP concentration increases the degree of hydration proportionately. Crack healing efficiency was evaluated in terms of crack closure ratio and strength recovery ratio. The results indicate that cracks of up to 465 μm were completely sealed for all SAP concentrations studied. Furthermore, a 93 % and 90 % recovery in compressive strength was observed for 0.2 % and 0.4 % SAP-incorporated HFC specimens, respectively, after 28 days of healing. Conclusively, the addition of SAP at lower concentrations, in addition to crack-healing, enhances the fracture characteristics of concrete. It is reckoned that the current investigation will help in developing durable concrete with improved crack repairing abilities.