Superabsorbent Polymer Content Research Articles

Crack resistance, permeability, and microstructural analysis of recycled aggregate concrete with SAP

High shrinkage and cracking performance are among the main problems that hinder the wide application of recycled aggregate concrete (RAC). To analyze the influence trend and mechanism of superabsorbent polymers (SAP) on the crack resistance of RAC, the effects of the recycled coarse aggregate (RA) content and SAP content on the crack resistance of RAC were studied via a slab cracking test. Moreover, the compressive strength, chloride permeability, pore distribution, and microstructure of the concrete in each mixture were also tested. The results showed that the incorporation of RA will have a negative impact on the crack resistance of concrete. The greater the amount of RA, the shorter the initial cracking time of the concrete, and the larger the crack width and area of the concrete. The initial cracking time, maximum crack width, and cracking area of the RAC tended to decrease with increasing SAP content. However, the crack resistance of the RAC does not seem to change much when the SAP content exceeds 0.3%, and even the local cracks in the slab specimens of the RAC increase in size. NMR and SEM analyses revealed that the water absorption-release and microreservoir characteristics of SAP affect the degree of the hydration reaction in the early stage, alleviate the internal drying of concrete, reduce shrinkage and inhibit the development of inner cracks, and effectively reduce the cracking sensitivity of RAC. This process can continuously provide water for the hydration reaction of cement when the SAP releases water in the later stage of curing, optimize the pore structure of the recycled concrete system, enhance its compactness, and improve its compressive strength and impermeability.

Rheology of Superabsorbent Polymer-Modified and Basalt Fiber-Reinforced Cement Paste with Silica Fume: Response Surface Methodology

A composite's rheology can be changed by adding superabsorbent polymer (SAP) and basalt fibers and using silica fume. This study aimed to investigate the effects of these components on the viscosity and shear stress parameters of the paste. The proportions of the components were varied, with SAP content ranging from 0.01% to 0.03%, basalt fiber from 0% to 0.50%, silica fume (micro silica) at 15%, and water content from 0.40 to 0.50. Response surface methodology was used to optimize the mixture proportions, and the rheological properties of the resulting pastes were characterized using a rheometer. Results showed that the addition of SAP and basalt fiber had a significant impact on the rheological properties of the paste, with increasing amounts of both resulting in increased viscosity and shear stress. Overall, this study highlights the potential of SAP and basalt fiber in advances of the rheology of cement paste and provides insight into the optimal proportions of these components for achieving desired rheological properties. The findings of this study could be useful in developing high-performance concrete with enhanced rheological properties, which could have a wide range of applications in the construction industry. In addition, 0.50% BF, 0.01% SAP, and 0.445 water-to-cement were found as optimum proportions regarding the rheology of the cement paste.

Multi-scale characterization of SAP impact on self-healing behavior in UHPC under varied crack widths and environments

This paper studies the effects of the content and particle size of superabsorbent polymer (SAP) on the self-healing behavior of precracked Ultra-high-performance concrete (UHPC) under different crack widths. In this experiment, bending and compression-resistant internal damage to UHPC was first created with different amounts and particle sizes of SAP added, and then the damaged specimens were placed in a water environment, a dry environment, and a water-dry cycle environment for self-healing. Finally, the self-healing effect of pre-cracked UHPC was evaluated from the changes in crack width, recovery of mechanical properties, and changes in ultrasonic speed. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to conduct microscopic analysis of the products of the self-healing reaction. The experimental results show that SAP itself does not participate in self-healing chemical reactions. It mainly seals cracks by absorbing water and expands and promotes the continued hydration of the internal gelling materials of UHPC through water storage to improve the self-healing performance. Therefore, in a dry environment, SAP has almost no effect on the self-healing performance of UHPC. In moisture-rich environments, SAP can significantly improve the healing of macroscopic cracks with a width greater than 50 μm. In addition, the experimental results also show that under the same environment, changes in SAP content and particle size have a consistent effect on the recovery of UHPC's mechanical properties and the recovery of ultrasonic speed. The results of this study can promote the application of internal curing in the self-healing of UHPC cracks and further reduce the maintenance cost of UHPC throughout its life cycle.

A comprehensive evaluation of the most-sold baby diapers on the market

The performance of baby diapers is highly related to the occurrence of diaper rash. However, a comprehensive evaluation of baby diapers on the market is unavailable. Herein, we systematically investigated the performance of the six most-sold baby diapers on the market. We disassembled the selected diapers and investigated the structure and properties of the main components, including the top sheet, acquisition sheet, absorbent core, and back sheet. Then the urine absorption capability, excrement spreading capability, run-off, and wetback of the diapers were investigated using urine and loose stool to reflect the functions of diapers in practical usage. Our results indicated that the performance of baby diapers is highly dependent on the structure and properties of each diaper component. Specifically, excrement run-off and wetback were highly related to excrement absorption speed and excrement spreading properties, respectively, which depend on the complex interactions among the top sheet, acquisition sheet, and absorbent core. In particular, designing the top sheet with a three-dimensional convex–concave structure or large holes was beneficial to fast excrement penetration. Meanwhile, employing an acquisition sheet could improve the excrement spreading properties. In addition, an absorbent core with a high content of super absorbent polymer and an absorption channel also contributed to a better excrement absorption property. Notably, Pampers and Moony diapers exhibited relatively low urine wetback. Bobdog and Babycare diapers showed 0 g urine run-off. Besides, Huggies, and Moony diapers were relatively soft, which could provide a better contact feeling during usage. Furthermore, Beaba diapers exhibited the best air permeability of 42.511 mm s−1 due to the existence of more breathable holes. Our study may provide scientific inspiration for researchers and enterprises to develop next-generation high-performance baby diapers and serve as a guideline for consumers to choose the right baby diapers.

Synergistic effects of microencapsulated bacterial spores and superabsorbent polymer on self-healing performance in mortar

This study explores the feasibility of utilizing a superabsorbent polymer (SAP) to improve the self-healing performance of microbial-induced calcium carbonate precipitation (MICP) in cement-based materials. The amount of microencapsulated bacterial spores was varied from 0.25–1 % by cement weight. The SAP content was set to either 0 or 4 % by cement weight. As additives, the impact of SAP and MICP bacteria on mortar properties, including flowability and compressive strength, was assessed. The self-healing performance was evaluated based on crack-healing percentage and water permeability recovery. Microstructural analyses, including thermogravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), were performed to investigate the microstructural and chemical changes during the healing process. The findings revealed that specimens exclusively mixed with 4 % SAP exhibited a slightly lower crack-closure efficiency compared to those mixed exclusively with 1 % MICP bacteria. However, the SAP-containing specimens exhibited a higher degree of permeability recovery. Meanwhile, in the binary additive system with 0.5 % MICP bacteria and 4 % SAP, the specimens exhibited the highest crack-closure percentage of 91 % and a final water discharge rate of 15 mL/min after 45 days of healing. In contrast, specimens mixed exclusively with 1 % MICP bacteria showed a crack-closure percentage of 76 % and a final water discharge rate of 59 mL/min. These results suggest that incorporating SAP into the MICP system enables a reduction in MICP bacterial content without compromising self-healing performance.

Feasibility study on superabsorbent polymer (SAP) as internal curing agent for cement-based grouting material

The closed working condition of grouting materials leads to insufficient curing water supply during their strength development. In this work, the superabsorbent polymer (SAP) was used as the internal curing agent for grouting material. The effects of SAP content on the rheological and mechanical properties of grouting material were studied under various water-cement ratios (w/c) and curing environments. The time-dependent variation of fresh slurry's viscosity was measured by Brinell viscometer. The pore structure and micromorphology characteristics were analyzed by Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscope (SEM). The results indicate that the addition of SAP increases the viscosity of fresh slurry and decreases its fluidity, thereby improving the slurry's internal uniformity at a higher w/c. And in its actual working condition, grouting material's strength can be boosted with less than 0.3% SAP dosage. Although SAP will introduce some irregular mesoscopic pores (0.2 − 0.3 mm), the MIP data analysis proves SAP refines the microscopic pore structure of grouting materials. SEM data analysis proves SAP optimizes the microstructure of grouting material, which cured in dry environment. In general, SAP improves the internal uniformity of grouting material by absorbing excess mixing water and gradually releasing it to promote cement hydration, which improves the strength of grouting material. Hence, SAP is a practicable internal curing agent for grouting material and 0.2% is the recommended dosage.

Experimental Study On Acoustic Emission Characteristics of SAP Mortar Self-Healing Process

Self-healing properties of super absorbent polymer (SAP) concrete can reduce the harmful effects of concrete cracking in structures. This study examines the self-healing process of mortars with different SAP content under dry and wet conditions through acoustic emission testing (AE) and elastic wave velocity testing. Findings indicate that the SAP mortar healing process has three stages: rapid water absorption, smooth water absorption, and drying. In a dry environment, increasing SAP content enhances AE activity, indicating internal crack self-healing via further hydration of unhydrated cement particles. In a wet environment, AE activity increases with increasing SAP content during the second healing cycle, indicating self-healing of the mortar matrix. These results suggest the use of SAP concrete could potentially mitigate future structural damage.

Synergetic effect of superabsorbent polymer and shrinkage reducing admixture on the properties of alkali-activated slag binders

This research is to investigate the synergistic effects of superabsorbent polymer (SAP) and shrinkage-reducing admixture (SRA) on autogenous shrinkage, hydration and microstructure of alkali-activated slag system (AAS). Results revealed that the addition of SRA reduced the absorption capacity of SAP, resulting in a smaller size distribution of macrovoids throughout the AAS matrix. Nevertheless, the presence of SAP affected the ability of SRA to effectively reduce the surface tension of the pore solution of AAS. Instead, the addition of SAP resulted in an increase in surface tension by up to 14%. This phenomenon can be explained by the hydrophobic interactions between SAP networks and SRA molecules. The combination of SAP and SRA in AAS exhibited greater effectiveness in controlling autogenous shrinkage compared to using SRA alone, resulting in a reduction of around 53% compared to 46%. On the other hand, incorporating only SAP proved to be more effective, leading to a higher reduction of 90%. However, this combined effect is reported to be counteractive and dependent on the content of each component. Moreover, the hybrid system of SAP and SRA demonstrates a pronounced retardation effect on AAS hydration. The XRD patterns showed no new reaction products were formed. As revealed by SEM analysis, the microstructure of AAS containing SAP and SRA exhibited a distribution of microvoids ranging from 5 to 50 μm. This can explain the reduction of the compressive strength by incorporation a high content of SAP combined with SRA. However, incorporating a lower dosage of SAP is advantageous when combined with SRA in AAS systems. Finally, the integration of SAP and SRA had a positive influence on the properties of AAS mortars, thus compensating for the limitations of each constituent.

Effect of superabsorbent polymers and expansive agent on the properties and microstructures of self-stressing high performance concrete

In order to overcome the self-desiccation and high autogenous of high performance concrete (HPC), the superabsorbent polymers (SAP) and expansive agent (EA) are considered to be compositely incorporated, which has great significance to the HPC structures. This paper presents an experimental study on the compounded effect of SAP and EA on the properties of HPC. The workability, internal relative humidity (IRH), compressive strength and free expansive ratio as well as self-stress of HPC were examined. The influencing mechanism of SAP and EA on HPC was discussed. The results showed that the compressive strength of HPC generally decreases with the increases of EA and SAP contents and additional water ratio. The water release of SAP particles mainly occurs at 7–10 d to maintain a high IRH. The higher EA content induces the larger free expansive ratio and self-stress, caused by the increased hydration products of Aft and Ca(OH)2 bulks. For a low SAP content of 0.1%, the shrinkage is alleviated, but it becomes even worse for a higher SAP content. The total amount of pores increases with the inclusions of EA and SAP, except for the harm pores. The hydration products caused by EA could fill and compensate the pores left behind by the SAP particles, showing synergetic improvement effect. The self-stress values of HPC in this study are at the range of 2.73–3.44 MPa, From the present study, the SAP content of 0.1% is more recommended for the HPC in real engineering practices.

Experimental study on fracture and acoustic emission properties of internally cured concrete with super absorbent polymer subjected to high temperature

The three-point bending experiment was conducted on notched beams containing five different SAP contents to investigate the influence of high temperature on the fracture performance of Superabsorbent Polymer (SAP) concrete. Acoustic Emission (AE) technology was employed to monitor real-time crack propagation, and scanning electron microscopy (SEM) was utilized to analyze the micro-pore structure. The experimental results reveal the following findings. After exposure to high temperatures, the peak strength of SAP concrete continuously decreases. Compared to specimens at 20 °C, the strength loss after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 55%, and 87%, respectively. However, the introduction of SAP can reduce the proportion of strength loss in the concrete. Additionally, SAP improves the toughness of the concrete, with an increase in ductility coefficient ranging from 4.0 to 6.8 times as the loading temperature increases. Similar to the strength variation pattern, the initial fracture toughness of SAP concrete exhibits a significant decrease with increasing heating temperature. The loss in initiation toughness after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 42%, and 85%, respectively, while the loss in unstable fracture toughness is 11%, 46%, and 74%. Based on the experimental results, this study proposes two temperature-dependent fitting models for the peak strength and fracture toughness of SAP concrete, which are compared and validated with the experimental results. SEM analysis reveals a loose and porous internal structure in SAP concrete. Through the analysis of AE signals at different temperatures, the fracture process is elucidated based on the b-value method. Moreover, RA-AF analysis indicates that an increase in temperature reduces the proportion of tensile-type cracks in specimens with the same SAP content. From the temperature loaded results spanning 20 °C–600 °C, the proportion of tensile cracks decreases from 80% to 50%, indicating a transition in the failure mode from tension to shear. However, this trend is not significantly affected by the temperature increase, suggesting that the failure mode of the specimens is primarily determined by the internal pore structure of the concrete rather than the temperature load. The research findings provide experimental evidence for the application of SAP concrete in engineering projects.

Evaluation of crack self-sealing in flexural concrete members with SAPs by chloride ion penetration resistance

Self-sealing concrete is a technology to repair cracks using swelling properties of superabsorbent polymers (SAPs) without external work. Many studies have been conducted on SAPs as self-sealing materials that fill cracks in concrete. However, because each study evaluated self-sealing performance using different experimental methods, each study reported different results. Therefore, a standardized test method to evaluate the self-sealing performance of SAPs is needed. This study evaluated the self-sealing performance of cementitious materials with SAPs through water absorption, chloride ion penetration, and water flow tests and analyzed the correlations between the results. Two SAPs with different particle sizes were used, and their contents were set to 0.3%, 0.5%, and 0.7% depending on the binder weight. The experimental results revealed that the self-sealing performance improved with increasing particle size and SAP content. In the water absorption test, the amount of water absorbed by the surface of the original specimen and that absorbed through cracks were measured. However, the influence of the self-sealing ability of the SAPs on the total water absorption rate could not be clarified. A chloride ion penetration test was conducted to measure the chloride ion penetration depth directly, and the corresponding results indicated that the self-healing ability of the SAPs enhanced the resistance of the cementitious materials against the penetration of harmful ions. Finally, a water flow test was performed, and the results revealed that the short-term self-sealing performance of SAPs can be evaluated relatively independently.

The Effect of Superabsorbent Polymer on Fair-Faced Concrete Performance Based on White Cement

Introducing superabsorbent polymer (SAP) into white fair-faced concrete can achieve the purpose of internal curing, which is beneficial to the popularization and application of white fair-faced concrete. The effects of the SAP mixture and internal curing water content on the properties of white fair-faced concrete were investigated macroscopically through the indexes, including slump, electric flux, standard cube compressive strength, and tensile splitting strength. The mechanism of these influence laws was further analyzed by scanning electron microscope (SEM). The results show that the slump increases with the increase of SAP content and internal curing water; the incorporation of SAP can significantly reduce the electric flux of white fair-faced concrete and improve its durability; with the increase of SAP admixture and internal curing water content, the compressive strength of white fair-faced concrete decreases, which has a significant impact on the early compressive strength; the addition of SAP is beneficial to the improvement of the tensile properties and tensile-compression ratio of white fair-faced concrete. When the SAP content is 0.2%, and the internal curing water is ten times the mass of SAP, the optimal performance of white fair-faced concrete can be achieved; the water released by the SAP promotes the secondary hydration reaction, which can refine the internal structure of white fair-faced concrete.

Effect of Cement Type and Water-to-Cement Ratio on Fresh Properties of Superabsorbent Polymer-Modified Cement Paste

Superabsorbent polymer (SAP) is a material with the ability to absorb liquid and desorb liquid from and to the environment, and it can ensure the internal curing of cementitious composites. Although the fresh state properties of SAP-modified mixtures (SAPCP) are affected and have been investigated nowadays, the rheological properties of SAPCP are still a virgin field and they are worth studying. Hence, the current study was aimed and conducted to observe what occurred if cements with different chemical compositions, various ratios of water/cement (w/c) and SAP were used together. Accordingly, CEM I 42.5R, CEM II/A-LL 42.5R and CEM IV/B (P) 32.5R were selected as binders in the mixtures, and w/c ratios were 0.40 and 0.50 for SAPCPs. In total, 24 mixtures were designed, produced and tested in the laboratory and spreading table tests, Vicate tests, viscosity tests and shear tests were conducted on the fresh state of the mixtures to observe the fresh behavior of SAPCPs. As a result, it was determined that the SAP, cement and w/c combinations considered in the article were effective on SAPCP fresh properties and rheology. However, it was determined that the use of high amounts of SAP in the mixture, high cement fineness and high oxide ratios in the cement (ratios of silicon dioxide/calcium oxide and aluminum oxide/calcium oxide) negatively affected not only the fresh state properties, but also the rheology. Moreover, the coexistence of the aforementioned negative conditions was the most unfavorable situation: high SAP ratio + high cement fineness + high oxide ratio in SAPCP. For these reasons, it was concluded that cement fineness and chemical composition should be taken into account in the rheology/workability-based design of SAPCPs. Then, the SAP content can be regulated for design purposes.

Investigation on Performances and Functions of Asphalt Mixtures Modified with Super Absorbent Polymer (SAP).

The super absorbent polymer (SAP) has been attracting extensive concerns due to its strong capacity in water absorption and retention. The amorphous hydrogels formed by the post-absorbent SAP have the potential of clogging the micro-cracks in asphalt materials and refraining the rainwater from infiltrating. This provides the possibility of applying SAP in asphalt pavements to seal or fill the cracks and relieve the distresses caused by rainwater infiltration in the underlying layers. Before exploring the cracking sealing mechanism of SAPs in asphalt pavements, a series of experiments were performed to evaluate the feasibility and influences of SAPs in asphalt mastics and asphalt mixtures on their mechanical performances and functionalities. Firstly, the basic properties of SAPs were analyzed, and then the rheological properties of the asphalt mastics using SAP replacing mineral powder (10%, 20%, 30%, and 40% by volume) were explored. The water stability and infiltration reduction effect of the asphalt mixtures incorporated with SAP were evaluated by the Marshall stability test, immersion Marshall stability test, freeze-thaw splitting strength test, Cantabro test, and permeability test. The test results indicated that SAPs could be used in the asphalt mixtures to partially substitute mineral powder with desirable mechanical performances. When less than 10% of the mineral powder was replaced by the SAP, the high-temperature performance and fatigue life of the asphalt mastics could be improved to some extent, but both declined after the content of the SAP was larger than 10%. Due to the hydrogels formed by SAPs after water absorption, the water stability of the asphalt mixtures deteriorated with the increased content of SAPs. Moreover, the results from the permeability tests implied that the SAP hydrogels could fill the seepage channels in the material, thus improving the migration and infiltration resistances of the asphalt mixtures. With the increased contents of SAPs, the permeability coefficients of the asphalt mixtures could be reduced up to 55%. Based on the research findings in this study, when an appropriate amount of SAP was added in the asphalt materials, desirable temperature stability, water stability, and fatigue resistance could be achieved regarding actual requirements from applications. At the same time, the addition of SAPs could effectively refrain the infiltration and migration of rainwater in asphalt pavements, thus potentially mitigating the effect of water erosion on the underlying layers.

Effect of super-absorbent polymer on swelling pressure of compacted bentonite infiltrated by alkaline solutions

The application of bentonite in geological disposal of radioactive waste is still under evaluation, especially concerning the decreased swelling pressure of pure bentonite exposed to alkaline groundwater. In this paper, in order to improve the chemical resistance of bentonite to alkaline solutions, super-absorbent polymer (SAP), a hydrophilic polymer with much higher swelling ability than that of bentonite, was dry-blended with Gaomiaozi (GMZ) bentonite and compacted into blocks of different dry densities. Swelling pressure of the bentonite-SAP composites infiltrated with deionized water, NaOH and KOH alkaline solutions were tested, accompanied with scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X-ray diffractometer (XRD) tests conducted on the selected specimens. Results showed that, for the specimens hydrated by deionized water, the swelling pressure increased with increasing SAP content, dry density and concentration of NaOH solutions. With increasing concentration of KOH solutions, however, the swelling pressure decreased obviously and tended to undergo a slow long-term degradation. Results of SEM, MIP and XRD indicate that the SAP hydrogels swell extensively to clog the inter-aggregate pores and coat the aggregates (for high density specimens) or montmorillonite stacks (for low density specimens), while do not insert into the interlayer spaces. The swelling pressure was therefore mainly contributed by the crystalline swelling of montmorillonite and the osmotic swelling of SAP. The SAP chains could be associated with the montmorillonite crystallites, protecting them from chemical attack and thus improving the chemical resistance of bentonite to alkaline solutions.

Experimental and Theoretical Study on Carbonization Coefficient Model of NS/SAP Concrete

Carbonization coefficient research has great significance in concrete carbonization evaluation. Nano-silica (NS) can reduce the content of Ca(OH)2, which is generated during the hydration of concrete, resulting in improved carbonization resistance and compressive strength of concrete. This paper investigates the carbonization effects of concrete with internal curing, such as Super Absorbent Polymer (SAP). The research shows that SAP can promote hydration of the internal concrete but form tiny pores after releasing the water completely, which may cause a reduction of carbonation resistance of concrete. The concrete was modified by adding SAP, ranging from 0 to 0.24%, to ascertain the optimal content of SAP. The addition of NS changed the concrete from 0 to 1.5% to confirm the optimal range of NS. To establish a reasonable suitable theoretical model of NS/SAP concrete, the influence factors of the carbonization coefficient of concrete were analyzed first. Later, the accelerated carbonization test was carried out on 100 mm × 100 mm × 100 mm cube specimens with different carbonization time to obtain the compressive strength and carbonization depth to establish the carbonization coefficient model of NS/SAP concrete. Before analyzing experimental data, the specimens were randomly divided into fitting and validation groups. Based on the regression analysis of the fitting group, the carbonization coefficient model was established, which embodied the influence of various parameters on concrete carbonization, including SAP content, NS content, water–cement ratio, CO2 concentration, temperature, relative humidity, and compressive strength. According to the validation analysis of the verification group, the mean relative error of the model is 5.04%, and the residual mean square error is 0.1751. Compared with the literature models, this study’s carbonization model can accurately predict the carbonization depth of NS/SAP concrete.

Mechanical properties of loess subgrade treated by superabsorbent polymer

Moisture variation is one of the crucial factors affecting the strength and deformation of loess. In this study, superabsorbent polymer (SAP) was introduced as moisture regulator to enhance the ability of accommodating moisture variations of loess and then to improve the stability of loess subgrade. Water migration test was first performed to evaluate the variation law of the effect of SAP on the moisture content of loess in a closed system. Then mechanical tests were carried out to investigate the influence of SAP on the mechanical properties of loess. Besides, microscopic tests were conducted to find out chemical and physical behavior of SAP on the loess. Test results demonstrated that SAP can significantly reduce the water content of loess by 8.26–26.42 %. The unconfined compressive strength (UCS) of loess increased by 37 % after 14 days curing with an optimum SAP content of 1 %, reaching 100 kPa. The dynamic resilient modulus (MR) gradually decreased as a result of SAP addition. The dissipated energy and damping ratio of loess reached the maximum values (100 mJ and 5 %, respectively) at 1.0 % SAP content, which were 10 times and 5 times higher than that of pure loess, respectively. The treatment of loess by SAP was mainly caused by the coupling of physical and chemical water absorption of SAP in the water environment. The incorporation of SAP had no effect on chemical functional groups and mineral composition of loess, but caused water redistribution, thereby changing the mechanical properties.

Effect of Superabsorbent Polymers on the Self-Healing Properties of Pre-Damaged Concrete

Cracks in concrete structures reduce bearing capacity, durability, and safety. This paper reveals the effect of superabsorbent polymers (SAP) on the self-healing property of pre-damaged concrete based on mechanical properties tests, mercury intrusion porosimetry, scanning electron microscopy, and energy dispersive spectrometer. The experimental results show that SAP reduces the mechanical properties of the SAP-modified concrete under the same W/C ratio, but a small amount of SAP can improve the later strength under the 0.35 W/C ratio. The addition of SAP increased the volume of small capillary pores (<20 μm) and large capillary pores (>100 μm) and significantly reduced the former with an increase in age. The SEM-EDS analysis indicates that the water released by SAP promotes the formation of C-S-H gel. AFt in the cracks is the main reason for self-healing, and the addition of CO2 to produce calcium carbonate is another one. Furthermore, this study finds that SAP-modified concrete has the best self-healing effect and the densest structure when the W/C ratio is 0.35 and the SAP content is 0.25%. The self-healing performance makes the SAP-modified concrete have broad application prospects.

Effect of Super-Absorbent Polymer (SAP) Incorporation Method on Mechanical and Shrinkage Properties of Internally Cured Concrete.

To study the effect of SAP incorporation on the early shrinkage of SAP internally cured concrete with the aim to solve the problems of early shrinkage and cracking of bridge leveling-layer concrete, using the SAP incorporation method as a parameter, the mechanical properties test of internally cured concrete, the shrinkage performance test of ring restraint and the scanning electron microscope observation test were carried out. The effects of the SAP content and incorporation method on the flowability, mechanical properties, shrinkage performance and microstructure of internally cured concrete were analyzed. The experimental results show that when the content of the SAP in concrete is 0.2% of the mass of cementitious materials, it has the least influence on the compressive strength of concrete. The addition of preabsorbed water to the SAP can delay early cement hydration, increase the later cement hydration rate and final hydration degree, and improve the concrete strength. Preabsorbed water mixed with an SAP can effectively improve the shrinkage of concrete, and the shrinkage reduction effect is more obvious than that from the dry addition of the SAP; the early cracking risk of concrete without an SAP is high, and it will crack before day 28. The addition of an SAP can strengthen the microstructure of concrete and improve its density and crack resistance, effectively avoiding concrete cracking. It is recommended that the water-absorbent resin be incorporated in a preabsorbent manner, and the SAP preabsorbent ratio is equal to the maximum water storage rate of the SAP.

RETRACTED: Investigation of SAP content on the shrinkage and tensile properties of ultra-high performance concrete

• The effect of SAP content on the tensile properties of UHPC was investigated. • The pseudo-strain hardening response of UHPC was evaluated by using micromechanical principle. • The effect of SAP content on autogenous shrinkage and drying shrinkage of UHPC was study. • The change in strain field and the evolution of cracks on the surface of dog bone specimens were monitored using digital image correlation (DIC) technique. Extensive studies have focused on superabsorbent polymer (SAP) as an internal curing admixture to reduce the autogenous shrinkage of ultra-high performance concrete (UHPC). However, studies on the effect of SAP content on the tensile properties of UHPC are still limited. As we all know, tensile performance of UHPC is an aspect that cannot be ignored. Therefore, this paper investigates the effect of SAP content on the shrinkage and tensile properties of UHPC. First, according to mercury intrusion porosimetry (MIP) analyses, the moderate addition of SAP can refine the pore structure of matrix due to its internal curing effect. However, excess SAP brought more space filled with capillary water, thus increasing the porosity of matrix. The results of shrinkage test showed that the autogenous shrinkage of UHPC decreased first and then increased with the increase in SAP content. While the drying shrinkage of UHPC increased when SAP content increased. When 0.15% SAP was added, the 7 days autogenous shrinkage and 28 days total shrinkage of UHPC were the lowest, 51.3% and 30.1% lower respectively than those of UHPC without SAP. In addition, the moderate incorporation of SAP improved the tensile properties. Since the internal curing effect of SAP promoted the hydration of expand agents (EA) and cement, the microstructure of matrix became denser, enhancing the bond between fibers and matrix. Thus, the tensile strength of UHPC was improved. However, excess SAP have negative effect on the tensile strength due to the negative effect on pore structure. Furthermore, the tensile strain capacity of UHPC increased first and then decreased with the increase in SAP content. Finally, the micromechanical principle was proven to be a feasible method to evaluate tensile strain-hardening behaviors of UHPC. The trend of pseudo-strain-hardening ( PSH ) index and tensile strain capacity of specimen remained consistent. Additionally, when the ratio of maximum fiber bridging stress and matrix tensile cracking strength of UHPC was more than 1.1 rathan than 1.3, which was required in the filed of engineering cementitious composites (ECC), UHPCs exhibited obvious strain-hardening response. This indicated that the adjustment of the strength criterion in the micromechanical principle will be the key to its effective and reasonable evaluation of the tensile strain-hardening response of UHPC.