Presence Of Superabsorbent Polymer Research Articles

Study of synergistic effect of fly ash and superabsorbent polymers on properties of cement pastes

The main goal of this study is to observe changes in microstructural properties and the mutual interaction of cement pastes containing superabsorbent polymers (SAPs) and fly ash. SAP is a type of hydrogel additive, able to absorb large amounts of liquid in its structure. In cement-based materials, it is often used in the early stages of matrix hydration to absorb excess mixing water and to release it in the later stages, which is even more desirable when the material is exposed to higher temperatures. Another research goal is a partial substitution of binder (Portland cement) by the energy by-product of high-temperature ash, produced by the combustion of brown coal. A further goal is the observation of the interactions of these binders with the SAPs on the microstructural scale. For this purpose, computed tomography (CT), X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) were performed. Basic physical and mechanical properties such as compressive strength, flexural strength, and bulk density were also determined. In the early stages of hydration, viscosity and chemical shrinkage were determined. From the results obtained, it is obvious that the presence of SAPs has a significant impact on the properties of cement pastes. From the two tested SAPs, SAP HM has a positive effect on volume stability and the flexural strength of the composite. The results of the mineralogical composition showed that the effect of SAP incorporation influences the crystallization of portlandite, alite, belite, and calcite. SEM analysis confirmed the results of XRD analysis and proved that hydration products can grow into SAP cavities. It is clear from the evaluation of the pore structure that SAPs increase the porosity of cement composites. The admixture of high-temperature fly ash has a positive effect on reducing the volumetric changes of mixtures. The mechanical parameters of the composite with fly ash were similar to that of the reference test specimens.

Study on expansion effect and hydration characteristics of ultra-high strength cement-based grouting materials based on humidity compensation

The combination of superabsorbent polymer (SAP) and expansive agent can effectively reduce the shrinkage deformation of ultra-high strength cement-based grouting materials (UHS-CGM) in dry environment. However, there are differences in the compensation shrinkage mechanism of SAP and expansive agent, and the presence of SAP may have adverse effects on the working and mechanical properties of grouting materials. In order to evaluate the synergistic effect of SAP with different water adsorption and release characteristics and MgO expansion agent (MEA), the influence of different SAP size and dosage on the compressive strength, restrained expansion rate, internal relative humidity (IRH) and hydration characteristics of UHS-CGM containing MEA were investigated, and then the composition and content of hydration products were analyzed by TG and XRD, the microstructures were observed by SEM in this paper. The results show that SAP improved the hydration degree of UHS-CGM and the expansion efficiency of MEA, and significantly increased the restrained expansion rate of UHS-CGM under standard curing and sealed curing, while reduced the compressive strength of UHS-CGM, and the decreasing degree was aggravated with increasing size and dosage of SAP. Overall, small size SAP has better inner curing efficiency and compensates shrinkage effect.

The Structural Formation of Cement Stone Modified by a Solution of Superabsorbent Polymer

With the development of 3D technologies in construction, the development of formulations that are indifferent to the influence of the environment is in demand. Conditions of intense water loss from cement systems arise during the layer-by-layer printing process. This leads to a decrease in density, high shrinkage, and a decrease in the strength and durability of the composite. The use of superabsorbent polymer (SAP) solutions, in contrast to granules, will provide hardening Portland cement with a water supply for internal care of hydration processes. The aim of the work is to study the effect of SAP solution on the processes of structure formation of cement stone, hardening in unfavorable conditions. In this paper, the features of the structure formation of cement systems in the presence of SAP are established. It is shown that the use of polymer in an amount of no more than 1.5% by the weight of Portland cement provides the formation of a more perfect crystalline structure of the cement stone, which allows for an increase in the degree of cement hydration. When the amount of SAP is ≥ 1.5% by the weight of Portland cement, a decrease in the intensity of the maxima corresponding to hydration products is observed.

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.

Chasing the Bubble: Ultrasonic Dispersion and Attenuation from Cement with Superabsorbent Polymers to Shampoo.

This study aims to experimentally investigate the ultrasonic behavior of fresh cement focusing on the contribution of the entrapped air bubbles. Frequency dispersion and attenuation carry delicate information that is not possible to gather by traditional ultrasonic pulse velocity. This is measured by simple indicators that quantify the frequency dependence of propagation velocity of longitudinal waves through fresh cementitious media. It seems that dispersion shows much stronger sensitivity to the microstructural processes, since the presence of superabsorbent polymers in mortar induces a large difference in dispersion parameters when compared to reference cement mortar, while only marginal difference in threshold-based pulse velocity. To reach this aim, references are taken from, and comparisons are made to other liquids in order first in order to validate the reliability of the methodology and to better understand the contribution of the cavities in the obtained dispersion and attenuation curves. Ultrasonic dispersion assessment of cementitious media has the potential to bring a lot of information on the microstructure of materials, as well as the ongoing processes.

Improved flowability of iron ore using superabsorbent polymers

Numerous bulk solid processing plants have been experiencing flow problems during handling, storage and transportation. In the present work, the concept of using superabsorbent polymers (SAP) to improve the flow of bulk solids particularly iron ore was investigated. Physical properties, absorption properties and mechanical properties of different SAPs were determined. Flowability analysis was studied to understand the flow behaviours of iron ore at various moisture levels ranging from 4% to 12%. Flow function curves for 12% moisture iron ore showed the change of flow regime from cohesive to easy-flow in the presence of SAP. The dosage of 100 g/ton and retention time of 30 min were obtained and incorporated during plant trials. The iron ore processing plant has achieved an increase in production during trials and 24% increase for long run of SAP during monsoon.

Setting Characteristics, Mechanical Properties and Microstructure of Cement Pastes Containing Accelerators Mixed with Superabsorbent Polymers (SAPs): An NMR Study Combined with Additional Methods.

In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2) and 2D (T1-T2 maps) H1 nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators.

Association of carbon isotope discrimination with leaf gas exchange and water use efficiency in maize following soil amendment with superabsorbent hydrogel

The correlation of carbon isotope discrimination (△<sup>13</sup>C) with photosynthetic gas exchange and water use efficiency (WUE) in maize was investigated under low rainfall conditions with or without superabsorbent polymer (SAP). SAP (45 kg/ha) was mixed into the top 10 cm soil layer at sowing in lysimeters. Compared with the control plants not treated with SAP, the application of SAP increased net photosynthesis rate; stomatal conductance (g<sub>s</sub>); transpiration rate; chlorophyll content (Chl) and intrinsic water use efficiency at leaf level (WUE<sub>i</sub>), but decreased intercellular CO<sub>2</sub> concentration (C<sub>i</sub>) and leaf △<sup>13</sup>C. In plants supplied with SAP, leaf △<sup>13</sup>C was positively correlated with C<sub>i</sub> (r = 0.864, P < 0.01) and negatively correlated with g<sub>s</sub> and WUE<sub>i</sub> (r = –0.860 and –0.626, P < 0.01, respectively). Leaf △<sup>13</sup>C was not correlated with Chl with or without SAP. Grain △<sup>13</sup>C significantly decreased by 12.4% and showed a significant negative correlation with grain WUE under SAP treatments (r = –0.670, P < 0.05). These results suggest that in the presence of SAP, maize leaf and grain △<sup>13</sup>C could be good indicators for evaluating maize WUE during periods of low rainfall.

Liquid Lipase-Catalyzed Esterification of Oleic Acid with Methanol for Biodiesel Production in the Presence of Superabsorbent Polymer: Optimization by Using Response Surface Methodology

Liquid lipase-catalyzed esterification of fatty acids with methanol is a promising process for biodiesel production. However, water by-product from this process favors the reverse reaction, thus reducing the reaction yield. To address this, superabsorbent polymer (SAP) was used as a water-removal agent in the esterification in this study. SAP significantly enhanced the conversion yield compared with the reaction without SAP. The lipase-catalyzed esterification in the presence of SAP was then optimized by response surface methodology to maximize the reaction conversion. A maximum conversion of 96.73% was obtained at a temperature of 35.25 °C, methanol to oleic acid molar ratio of 3.44:1, SAP loading of 10.55%, and enzyme loading of 11.98%. Under these conditions, the Eversa Transform lipase could only be reused once. This study suggests that the liquid lipase-catalyzed esterification of fatty acids using SAP as a water-removal agent is an efficient process for producing biodiesel.

Influence of superabsorbent polymers on the surrounding cement paste

In the last decade, the influence of superabsorbent polymers (SAP) on the performance of cementitious materials has been studied extensively. However, the formation mechanism and properties of the affected zone around SAP are still not well understood. Spherical SAP particles of a large size (1.5–2mm) were used in this study to magnify the zone influenced by SAP. Hydration characteristics, capillary pore structure, microhardness and microstructure of the affected zone were investigated. The degree of hydration of the affected zone is higher than the unaffected zone by about 5%, an equivalent of an increase in w/c by 0.04. Capillary porosity is increased at early age, but reduced at later age, due to the desorption process of SAP. Results on the microhardness, the degree of hydration and the pore structure of the affected zone indicate a dense transition zone is produced in the presence of SAP.

Biopolymers as Novel Tool for Self-Sealing and Self-Healing of Mortar

ABSTRACTSynthetic superabsorbent polymers (SAPs) are used in concrete for various applications such as internal curing and frost resistance. However, the addition of these SAPs may lead to a significant decrease in mortar strength, especially when high amounts of SAP are necessary. This is the case for example when self-sealing and -healing of cracks is strived at. In order to overcome this bottleneck, the present work focuses on the application of biopolymers as SAPs. The work especially aims to evaluate the potential of both sodium alginate (NaAlg) as well as physically cross-linked calcium alginate (CaAlg) as SAPs to establish a sustainable approach towards self-sealing and -healing concrete without impairing mechanical strength. First, the swelling properties in both demineralized water and cement filtrate solution are tested. Subsequently, the mechanical properties of mortar mixtures in the absence and the presence of SAPs are compared by performing flexural and compressive tests. The alginates show a swelling capacity up to 72 times their own weight in aqueous solutions. Interestingly, they lead to a minor reduction in compression strength (up to 15% upon addition of 1m% SAP). These biopolymers show high potential for enabling concrete repair, more specifically, for the self-sealing and -healing of cracks without impairing the strength.