Absorption Of Superabsorbent Polymers Research Articles

Effect of absorption kinetics of superabsorbent polymers on printability and interlayer bond of 3D printing concrete

This study examines the effect of the material characteristics of superabsorbent polymers (SAPs) on the printability and interlayer bond strength of 3D printing concrete. Three types of SAP, including two acrylamide-co-acrylic polymers with coarse and fine particle sizes (S1 and S2) and an acrylic copolymer (S3), were employed. The investigated mortar mixtures had a fixed initial mini-slump flow of 195 ± 10 mm and yield stress of 290 ± 25 Pa. The fluidity of SAP-incorporated mortars was maintained by either adjusting the superplasticizer dosage or increasing the water content. Test results indicate that particle flocculation is dependent on SAP absorption kinetics shortly after the end of mixing. The use of S1 and S2 SAPs exhibiting high retention ability enhanced thixotropy, whereas the S3 SAP with rapid desorption reduced thixotropy. The S2 SAP improved the bridging effect of nucleation at early age due to its finer size, leading to a significant increase in the structuration rate at 30 min. Pull-out strength test and splitting tensile strength test were used to investigate the interlayer bond strength. The S1 SAP was the most significant in maintaining a higher internal relative humidity (IRH), thus resulting in higher 28-d interlayer bond strength, while the S2 SAP exhibited an intermediate ability to maintain elevated IRH, thus resulting in higher increase in 7-d interlayer bond strength.

Development of ultra-fine SAP powder for lower-shrinkage and higher-strength cement pastes made with ultra-low water-to-binder ratio

Superabsorbent polymer (SAP) as internal curing agent can effectively mitigate the autogenous shrinkage and promote cement hydration of ultra-high performance concrete (UHPC). However, it has a risk of impairing the mechanical performance of UHPC given the macro pores left. This study developed ultra-fine SAP powder aiming at securing the lower shrinkage and higher strength of UHPC. The influence of SAP powder on (average diameter (ds) of 5.78–60.85 μm) the water absorption/desorption characteristics, strength, shrinkage, and microstructure of cement paste with ultra-low water-to-binder ratio (w/b) was systematically studied. The results showed that the reduction of particle size of SAP can reduce the spacing distance of SAP in cement paste, which is beneficial for the internal curing, such as reducing the autogenous shrinkage, improving hydration of cement, and increasing the compressive strength. When the ds of SAP powder was 11.55 μm, it can reduce autogenous shrinkage by 72.4% without any reduction in the compressive strength compared to paste made without SAP powder. Such SAP powder led to about 5% higher hydration degree and 12.5% lower porosity compared to the conventional SAP. A quantitative approach considering the spatial distance and water absorption of SAP was proposed to describe their effect on internal curing.

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.

Evaluation of mechanical properties and microstructure of high-performance mortars with superabsorbent polymers and metakaolin by means of X-ray computed microtomography

Superabsorbent polymers (SAP) may provide internal curing in cementitious materials, consequently, they reduce autogenous shrinkage caused by low water/cement ratios and autodessecation of pores. This paper aimed to analyze the effect of Superabsorbent polymers in high-strength mortars, using metakaolin as supplementary cementitious material (SCM). A X-ray microtomography test was carried out on two mixtures of mortars, a reference mix (MKREF) and a mix containing 0.30% superabsorbent polymer (MKSAP30), and the acquired images enabled the evaluation of mortar phases, anhydrate cement and void content. Also, a compressive strength test was carried out at 3 ages for both mixtures. The superabsorbent polymer was added still dry in the mixture, and no extra water was used for SAP absorption, hence, all the mixtures had the same total water/cement ratios. The results point to an increase in mechanical properties on mortars modified with SAP of 51% at the age of 28 days. Also, a higher porosity was observed in MKSAP30 samples, however, the pores were of small diameters, showing that SAP may provide refinement in pores of the cement matrix. In addition, a higher pore connectivity was detected, and an increase in the number of pores accounted using microtomographic images and the software called Fiji/ImageJ software for MKSAP30. The SAP modified mortar also showed more pores tortuosity. Finally, a lower percentage of anhydrate cement remaining in the mixture with SAP was shown, pointing to an optimization of the hydration degree, corroborating to the improvement of mechanical properties.

Comparison of liquid absorption-release of superabsorbent polymers in alkali-activated slag and Portland cement systems: An NMR study combined with additional methods

In this study, 1H low-field NMR was used to compare the liquid absorption-release behaviour of superabsorbent polymers (SAPs) in Portland cement (PC) paste, NaOH-activated slag (SH-AAS) paste, and water glass-activated slag (WG-AAS) paste. The liquid absorption of SAPs in the PC paste was lower than that in the SH-AAS paste and the WG-AAS paste. The liquid release was also faster, which was mainly due to the higher Ca2+ concentration in the pore fluid of the PC system. In the AAS system, although the Ca2+ concentration in the pore fluid was low, the Na+ concentration was much higher than that in the PC system due to the activator. The Ca2+ in the PC system is an important factor affecting the swelling of SAPs, while in the AAS system, the swelling limitation of SAPs is the result of the combined effects of Ca2+ and Na+, with Na+ being dominant.

Early-age and long-term strength development of high-performance concrete with SAP

Internal curing of high-performance concrete (HPC) by the addition of Superabsorbent Polymers (SAP) has been proven to be effective in mitigating autogenous shrinkage. The issues of concern in research, however, is the extent to which strength development is impacted by the voids created by SAP as cement hydrates with age. In this study, the influence of SAP content, size, binder type, water/binder ratio (W/B) and curing age on the early-age and long–term strength development of a low W/B HPC was examined. HPC mixtures designed for a minimum 28-day target cube strength of 70 MPa (i.e. C55/67 – C100/115) were studied with 25 g/g extra water provided for SAP absorption. Mortar (50 mm) and concrete (100 mm) cubes were cast and cured in water for different hydration periods. The results reveal that the compressive strength of the HPC mixtures decreased slightly (both for the early-age and long-term) as SAP content increased. Statistical examination of the results further revealed that W/B and SAP contents significantly influenced the strength development while a simulation of the SAP’s water absorption into Powers’ Model show compatibility for prediction of strength development trends in HPC with SAP.

Rheological study of Portland cement pastes modified with superabsorbent polymer and nanosilica

This paper addresses the use of rotational rheometry in determining the rheological parameters (viscosity and yield stress) of cement pastes over time. This study employed Portland cement pastes modified with superabsorbent polymer (SAP) and nanosilica (NS). Nine pastes were tested: one reference paste, two pastes with different amounts of SAP, two pastes with different amounts of NS, and four hybrid mixtures. Flow tests were performed using a parallel plate geometry in a rotational rheometer to determine the viscosity by graphical results and yield stress via the Herschel–Bulkley model. The results show that the flow test is satisfactory for determining the rheological properties, primarily the viscosity. Statistical analysis was performed to quantify the effect of each random variable and their interactions on the rheological properties, providing graphical tools for analyzing the tendencies of the viscosity and yield stress for both additives (SAP and NS). SAP exerted a weak effect on the rheological properties; in contrast, NS caused large changes in both rheological parameters (viscosity and yield stress) in the tested pastes. For pastes containing 2% NS, the presence of SAP caused slight reductions (less than 10%) in the rheological parameters, casting doubt on the absorption of SAP when in contact with mineral additives.

Effect of superabsorbent polymers (SAP) and metal organic frameworks (MOF) wiping sandwich patch on human skin decontamination and detoxification in vitro

Most chemical warfare agents partition rapidly into stratum corneum (SC) and subsequently slowly diffuse through – or are retained in the membrane. Since chemicals can interact with SC components during the process, skin decontamination poses a challenging yet important problem. To address these issues, we have developed a new method in combination with wet and dry decon technologies with new materials for emergency or delayed contamination scenarios. An in vitro human skin diffusion system was employed to model various dermal exposures of radiolabeled chemical warfare simulants, followed by surface decontamination with metal organic frameworks (MOFs), super-absorbent polymers (SAP), and/or dermal decontamination gel (DDGel). All samples measured for radioactive recovery and acetylcholinesterase activity to ascertain relative decon efficacy. Results demonstrated powerful water absorption of SAP, strong catalysis of UiO-66 MOF, and decon enhancement of pre-wetting surface contaminants. SAP had no interfering interactions with MOF yet provided additional benefits as porosity and reactivity that allowed for fast liquidized chemical transportation, absorption, and degeneration. We then designed a cotton-based SAP/MOF patch that worked cooperatively in decontamination and detoxification. Together with pre-wet, SAP/MOF wipe, and DDGel applications, maximum effect was observed in early and/or extended dermal exposure, and no “wash-in” effect occurred.

The Behavior of Superabsorbent Polymers (SAPs) in Cement Mixtures with Glass Powders as Supplementary Cementitious Materials.

The absorption and desorption of superabsorbent polymers (SAPs) in cement mixtures containing two different glass powders as supplementary cementitious materials are examined in this paper. Two SAPs with different chemical compositions were synthesized in-house and used in the experiments. SAP absorption was investigated directly through the mass change of SAPs in cement slurries, as well as indirectly using the flow test. Scanning electron microscopy was used to monitor the desorption of SAPs using samples prepared with freeze-drying. Hydration and setting time were evaluated to explain the desorption behavior of SAPs. SAP absorption generally increased in pastes with glass powders. The desorption rate of SAPs in different pastes was shown to correlate with the onset of solid skeleton development in the pastes. The addition of SAPs reduced autogenous shrinkage in neat cement paste more than in pastes with glass powders.

Early-state water migration characteristics of superabsorbent polymers in cement pastes

Water exchange and migration of superabsorbent polymers (SAP) in cement paste is a very complicated process and governs the effectiveness of internal curing in concrete. The early state of SAP in real pore fluids was investigated under different water-cement ratios and hydration time. It is found out water absorption of SAP is not a constant value, but varies depending on these two factors. The absorption and desorption behavior of SAP is demonstrated in the shifted hydration peak location and the water-rich region around the SAP gels. The water exchange between SAP and cement pastes is quantified by the measured water content with time, from which a characteristic “two-stage desorption” driven by osmotic pressure and humidity gradient, respectively, is identified. The humidity-controlled desorption that is beneficial for internal curing is calculated. It is indicated the internal curing efficiency could be improved by shortening the osmotic stage and prolonging the humidity stage.

Effect of water absorption of SAP on the rheological properties of cement-based materials with ultra-low w/b ratio

Superabsorbent polymer (SAP) is an important internal curing agent for concrete with low or ultra-low water-to-binder ratio (w/b). When SAP is added, it will absorb water from fresh concrete fast. Thus, water absorption of SAP will affect the rheological properties of cement-based materials, especially at low w/b. Moreover, SAP with different particle size has a different absorption rate which will also affect the rheological properties. In this paper, two SAPs with different particle size are used to investigate its effects on the maximum shear stress, yield stress, plastic viscosity and thixotropy of cement-based materials within 80 min. Basic w/b of 0.18 was specified as reference values. Rheological results show that the absorption of SAP changed the evolution of yield stress, plastic viscosity and thixotropy of fresh mortar with time. Large SAP’s particles led to a high absorption rate and a long absorption time which increased the yield stress and plastic viscosity. The above effects of SAP are closely related to the availability of water near SAP in cement mortar which causes to be a nonlinear relationship between the amounts of SAP and extra water required. In addition, the amount of extra water should be adjusted according to particle size of SAP and the addition level of SAP.

Absorption and Desorption of Superabsorbent Polymers for Use in Internally Cured Concrete

Abstract Superabsorbent polymers (SAP) have been investigated as an additive for use in the manufacture of internally cured concrete. The ability of SAP to absorb and desorb fluid is important for the design of internally cured concrete mixtures. Internal curing research on lightweight aggregates (LWA) has typically focused on the absorption of water in the LWA internal curing agent. However, when SAP is used, the absorption test should be performed using a pore solution with a defined ionic concentration. To address the effect of the ionic composition of the pore solution on SAP absorption, pore solutions were extracted from fresh cementitious pastes, and their composition was evaluated using X-ray fluorescence. This study characterizes the absorption and desorption of a commercially available SAP, using both simulated and extracted pore solutions with a range of ionic concentrations. The teabag method was implemented to measure the absorption of the SAP. As expected, the absorption of the SAP decreased in solutions with higher ionic concentrations. In addition to studying solutions extracted from ordinary portland cement pastes, the effects of the inclusion of supplementary cementitious materials on the SAP absorption were studied. Results showed that the inclusion of supplementary cementitious materials had a relatively minor impact on the SAP absorption, primarily due to a dilution of the ionic concentration of the pore solution. This article examined the desorption of the SAP in two conditions: a reduction in the ambient relative humidity and after exposure of the SAP to solutions with a higher ionic concentration. It was observed that SAP-containing solutions with a higher ionic concentration had a reduced rate of desorption and a reduced overall desorption at a given relative humidity. In addition, moving the SAP from a solution with a lower ionic concentration to a more highly concentrated solution resulted in desorption. An equation was developed that expresses the SAP absorption as a function of the pH of the soaking solution. The expression was used to predict the desorption of SAP due to an increase in the ionic concentrations in a hydrating system. This equation was used to show that the desorption of SAP due to changes in the pore solution ionic concentration were significant during the first 72 hours. The findings and the techniques used in this study are meant to be used as an example for the characterization of SAP in concrete internal curing applications.

Importance of monovalent ions on water retention capacity of superabsorbent polymer in cement-based solutions

The effects of various ions in cement-based solutions on the water retention capacity and ion absorbency of superabsorbent polymers (SAPs) are studied herein. It is verified that the retention capacity of the SAP is reduced due to the absorbed Ca2+ from solution, and the SAP releases monovalent cations such as Na+ into the solution upon absorption of Ca2+. Importantly, it was determined that non-multivalent cations in solutions play a critical role in the retention capacity of SAPs. As the total ion concentration (TIC) of the solution increases, the retention capacity improves. Higher TIC yields a weaker osmotic pressure, which reduces the driving force for the initial absorption of SAP. Therefore, the amount of the Ca2+ absorbed in the SAP decreases and the retention capacity improves. Based on the accurately measured ionic characteristics during absorption and desorption, the complicated retention phenomenon and its ionic dependence in cement-based solutions are clearly understood.

Characterization of Polyacrylamide based Superabsorbent Polymers for potential use in PC Matrices with Supplementary Cementitious Materials

This paper compares three types of polyacrylamide based Superabsorbent Polymers (SAP) with different water absorption capacities for potential application in Portland cement composites. The analysed matrices contain Supplementary Cementitious Materials (SCM) such as ground granulated blast-furnace slag (GGBS), fly ash (FA type F), silica fume (SF) and lime (NHL 5). SAPs were characterized in terms of shape, size and molecular structure by the Laser Diffraction, SEM, and the Raman Spectroscopy techniques. Kinetics and capacity of SAPs absorption in different environments (deionised water, PC solution and various PC-SCMs solutions) were evaluated by the tea-bag method. pH of all solutions was determined after 24 hours. The effect of different SCMs on SAPs sorption behaviour has been presented. The experimental results show that SAPs do not affect pH of cementitious solutions. However, SCMs addition reduces SAPs' absorption capacity and increase their desorption features. This is related not only to the type of SCM, but also to the level of substitution.

An investigation into the influence of superabsorbent polymers on the properties of glass powder modified cement pastes

This study examines superabsorbent polymer (SAP) absorption, mechanical strength, hydration, and electrical resistivity of glass powder modified cement pastes. The absorption of SAP was monitored using optical microscopy and shown to be higher when glass powders were used. Addition of SAP was found to improve hydration due to internal curing. The cement pastes with SAP exhibited a decreased compressive strength due to macrovoid formation. The glass powder modified cement pastes experienced a large reduction in electrical resistivity as a result of SAP addition; increased pore connectivity in these cement pastes is suggested as a possible cause of the reduction in electrical resistivity.

Combined effect of shrinkage reducing admixtures (SRA) and superabsorbent polymers (SAP) on the autogenous shrinkage, hydration and properties of cementitious materials

This paper examines the combined effect of superabsorbent polymers (SAP) and shrinkage reducing admixtures (SRA) on the autogenous shrinkage, hydration, microstructure, and properties of cementitious materials. The addition of SRA was found to reduce the absorption of SAP in the extracted pore solution as well as in the cement pastes. It was shown that the cement pastes with both SAP and SRA exhibited a higher shrinkage than the cement paste with SAP, more notably at the early age. The hydration temperature peak of the cement paste with both SRA and SAP occurred sooner than that of the cement paste with SRA at early age. The non-evaporable water content measurement indicated a higher degree of hydration for the cement paste with both SRA and SAP than the cement paste with SRA due to the internal curing effect of SAP. The compressive strength and electrical resistivity of the cement paste with both SRA and SAP were shown to be lower than those of the cement paste with SAP and the cement paste with SRA. Addition of SAP appeared to promote increased Ca(OH)2 formation in the hydration product. SEM examination indicated a distribution of microvoids in the range of 10–20μm in the microstructure of the cement paste with SAP and SRA at 28days, which could be responsible for a lower compressive strength of the cement paste with SAP and SRA compared to the cement paste with SAP at this age.

Harvesting microalgae cultures with superabsorbent polymers: Desulfurization of Chlamydomonas reinhardtii for hydrogen production

It is presented in this work a new methodology to harvest fresh water microalgae cultures by extracting the culture medium with superabsorbent polymers (SAPs). The microalgae Chlamydomonas reinhardtii were grown in the Sueoka culture medium, harvested with polyacrylic SAPs and re-suspended in the culture medium tris-acetate-potassium without sulfur (TAP-S) to generate hydrogen (H2 ) under anoxic conditions. The H2 production as an alternative fuel is relevant since this gas has high-energy recovery without involving carbon. Before microalgae harvesting, a number of range diameters (1-7 mm) for SAPs spherical particles were tested, and the initial rate (V0 ) and the maximal capacity (Qmax ) were determined for the Sueoka medium absorption. The SAP particles with the diameter range 2.0-2.5 mm performed the best and these were employed for the rest of the experiments. The Sueoka medium has a high salt content and the effect of the ionic strength was also studied for different medium concentrations (0-400%). The SAPs were reused in consecutive absorption/desorption cycles, maintaining their absorption capacity. Although the Sueoka medium reduces the SAPs absorption capacity to 40% compared with deionized water, the use of SAPs was very significant for the desulfurization process of C. reihardtii. The presence of C. reinhardtii at different concentrations does not affect the absorption capacity of the Sueoka culture medium by the SAPs. In order to reduce the time of the process, an increase of the SAPs concentration was tested, being 20 g of SAP per liter of medium, a condition to harvest the microalgae culture in 4 h. There were no evident cell ruptures during the harvesting process and the cells remained alive. Finally, the harvested biomass was re-suspended in TAP-S medium and kept under anaerobic conditions and illumination to produce H2 that was monitored by a PEM fuel cell. The use of SAPs for microalgae harvesting is a feasible non-invasive procedure to obtain high concentrations of functional biomass at low cost; it offers an attractive alternative due to its versatility and simplicity.

Absorbency of Superabsorbent Polymers in Cementitious Environments

ABSTRACTOptimal use of superabsorbent polymers (SAP) in cement-based materials relies on knowledge on how SAP absorbency is influenced by different physical and chemical parameters. These parameters include salt concentration in the pore fluid, temperature of the system and SAP particle size. The present work shows experimental results on this and presents a new technique to measure the swelling of SAP particles. This new technique is compared with existing techniques that have been recently proposed for the measurement of pore fluid absorption by superabsorbent polymers. It is seen that the concentration of Na+, K+, Ca2+, OH-, and SO2-, in the exposure liquid influences the maximum absorption of SAP. Even very low concentrations of these may reduce the absorption to a third of the value measured in pure water at room temperature. Additionally, the influence of the SAP absorption on the ionic composition of the exposure liquid is investigated with atomic absorption spectroscopy. The paper provides the reader with knowledge about the absorption capacity of SAP in a cementitious environment, and how the absorption process may influence the cement pore fluid.