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The chemical and physical structure–property relationships of model superabsorbent polymer hydrogels were characterized with respect to swelling behavior and mechanical properties in different ionic solutions (Na + , Ca 2+ , and Al 3+ ). The model hydrogels were composed of poly(sodium acrylate-acrylamide) (PANa-PAM) copolymer with varying concentrations of PANa (0, 17, 33, 67, and 83 wt%) and covalent crosslinking densities of 1, 1.5, and 2 wt%. By synthesizing the hydrogels in-house, systems with independently tunable amounts of covalent crosslinking and anionic functional groups were created, allowing for the relative effects of covalent and ionic crosslinking on the properties of the hydrogels to be directly quantified. It was found that the presence of Ca 2+ and Al 3+ in the absorbed fluid significantly decreased the swelling capacity and altered the swelling kinetics of the PANa-PAM hydrogels. The presence of Al 3+ in solution resulted in the unexpected formation of a mechanically stiff barrier layer at the hydrogel’s surface, which hindered the release of fluid and caused the overall elastic modulus of the hydrogel to increase from O (10 kPa) for hydrogels immersed in Ca 2+ solutions to O (100 kPa) for hydrogels immersed in Al 3+ solutions. Tensile tests performed on isolated specimens of the stiff barrier layer yielded elastic moduli in the O (50–100 MPa) range.

This work investigated the rheological properties of pastes made from magnesia cement modified with superabsorbent polymers (SAPs), with the aim to uncover the mechanisms governing their interactions. The findings highlighted the significant improvement in static yield stress brought about by the addition of SAP, with minimal impact on dynamic flow properties. Furthermore, the incorporation of small quantities of methylcellulose was observed to amplify SAP's absorption capacity during the initial stages of hydration. This study also revealed that SAP's absorption behavior does not impede the rate at which hydration products form. In addition, the value of the critical strain can be used as a rheological indicator of SAP's degree of absorption. Overall, this investigation indicated that the incorporation of SAP was highly advantageous with respect to enhancing the rheological characteristics of magnesia cement, particularly with respect to facilitating its use in three-dimensional (3-D) printing applications. Keywords: magnesia cement; rheology; superabsorbent polymers (SAPs); three-dimensional (3-D) printing.

Internal curing of mortar through superabsorbent polymer hydrogels is explored as a solution to self-desiccation. Four different hydrogels of poly(sodium-acrylate acrylamide) are synthesized and the impact of chemical composition on mortar is assessed with relative humidity and autogenous shrinkage testing. The hydrogels are characterized with swelling tests in different salt solutions and compression tests. Chemical composition affected both swelling kinetics and gel network size. Mortar containing these hydrogels had increased relative humidity and markedly reduced autogenous shrinkage. Additionally, the chemical structure of the hydrogels was found to significantly impact the mortar’s shrinkage. Hydrogels that quickly released most of their absorbed fluid were able to better reduce autogenous shrinkage compared to hydrogels that retained fluid for longer periods (>4 h), although this performance was highly sensitive to total water content. The release of absorbed water in hydrogels is most likely a function of both Laplace pressure of emptying voids and chemically-linked osmotic pressure developing from an ion concentration gradient between the hydrogels and cement pore solution. If the osmotic pressure is strong enough, the hydrogels can disperse most of the absorbed water before the depercolation of capillary porosity occurs, allowing the water to permeate the bulk of the mortar microstructure and most effectively reduce self-desiccation and autogenous shrinkage.

The injection of polymer solutions into an oil basin can lead to enhanced oil recovery (EOR) by increasing the microscopic sweep of the reservoir, improving the water-oil motility ratio, and thus leading to greater yield from oil fields. In this contribution, we characterize both shear and extensional rheological response of aqueous solutions of partially hydrolyzed polyacrylamide (HPAM), the most commonly used polymer for EOR, for velocity gradients in both the flow direction (extensional) and perpendicular to flow (shear) arise in EOR applications. As HPAM is a charged polymer, to better emulate the environment in oil basins, the rheological response was investigated in presence of salt, sodium chloride, and calcium chloride, with concentrations 3.7 × 10 −4  − 1.5 M, as a function of polymer molecular weight (2–10 million g/mol) and concentration (0.005–0.3 wt%). The extensional relaxation times and extensional viscosity are measured using dripping-onto-substrate (DoS) rheometry protocols, and a commercial shear rheometer was utilized for characterizing the shear rheology response. The polyelectrolyte solutions formed by HPAM exhibit shear thinning in steady shear, but show strain hardening in response to extensional flow. Even though an increase in monovalent salt concentration leads to a decrease in both shear viscosity and extensional relaxation times, an increase in divalent salt concentration leads to an increase in extensional viscosity and relaxation time, implying that ion coordination can play a role in the presence of multivalent ions.

This research article will describe the design and use of polyelectrolyte hydrogel particles as internal curing agents in concrete and present new results on relevant hydrogel-ion interactions. When incorporated into concrete, hydrogel particles release their stored water to fuel the curing reaction, resulting in reduced volumetric shrinkage and cracking and thus increasing concrete service life. The hydrogel’s swelling performance and mechanical properties are strongly sensitive to multivalent cations that are naturally present in concrete mixtures, including calcium and aluminum. Model poly(acrylic acid(AA)-acrylamide(AM))-based hydrogel particles with different chemical compositions (AA:AM monomer ratio) were synthesized and immersed in sodium, calcium, and aluminum salt solutions. The presence of multivalent cations resulted in decreased swelling capacity and altered swelling kinetics to the point where some hydrogel compositions displayed rapid deswelling behavior and the formation of a mechanically stiff shell. Interestingly, when incorporated into mortar, hydrogel particles reduced mixture shrinkage while encouraging the formation of specific inorganic phases (calcium hydroxide and calcium silicate hydrate) within the void space previously occupied by the swollen particle.

This article presents the results of a round-robin test performed by 13 international research groups in the framework of the activities of the RILEM Technical Committee 260 RSC “Recommendations for use of superabsorbent polymers in concrete construction”. Two commercially available superabsorbent polymers (SAP) with different chemical compositions and gradings were tested in terms of their kinetics of absorption in different media; demineralized water, cement filtrate solution with a particular cement distributed to every participant and a local cement chosen by the participant. Two absorption test methods were considered; the tea-bag method and the filtration method. The absorption capacity was evaluated as a function of time. The results showed correspondence in behaviour of the SAPs among all participants, but also between the two test methods, even though high scatter was observed at early minutes of testing after immersion. The tea-bag method proved to be more practical in terms of time dependent study, whereby the filtration method showed less variation in the absorption capacity after 24 h. However, absorption followed by intrinsic, ion-mediated desorption of a specific SAP sample in the course of time was not detected by the filtration method. This SAP-specific characteristic was only displayed by the tea-bag method. This demonstrates the practical applicability of both test methods, each one having their own strengths and weaknesses at distinct testing times.

Processing-relevant relationships between the microstructure and flow behavior of concentrated surfactant solutions were determined by a combination of basic rheological experiments, rheo-flow velocimetry tests, and flow birefringence measurements. The most common surfactant microstructures found in liquid soaps and other consumer care products—spherical, worm-like, and hexagonally packed micelles and lamellar structures—were recreated by varying the concentration of sodium laureth sulfate in water from 20 to 70 wt% and adding salt in some cases. It was found that common features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of material responses including shear-induced wall slip in micellar samples and plug flow in lamellar samples. Knowledge of key processing-structure-property relationships for concentrated solutions will allow engineers to develop more efficient industrial workflows for the scalable manufacturing of materials and feedstocks with reduced economic and environmental costs. Graphical abstract

New methods are proposed for the verification of the presence of superabsorbent polymers (SAP) in freshly mixed concrete and estimation of SAP quantity. The methods are in general based on flushing concrete with excess water. They allow separating the light, water-sorbed hydrogel particles from the mineral components in the fresh concrete and making these particles available for further tests. Two types of tests are proposed: Test 1 serves for a visual verification of the presence of SAP (qualitative test), while Test 2 enables quantifying the mass of the collected SAP as a proxy of their concentration in concrete (quantitative test). Different procedures are proposed for these two test methods and their performance is evaluated. The testing procedures were scrutinized in an interlaboratory study carried out by 14 participants from 12 countries. All participating groups detected the presence of SAP in the mix using the qualitative procedures (Test 1). Based on this outcome, we suggest that this method should be applied in the field. In contrast, while most participants obtained reasonably reliable results with the quantification procedure of Test 2, some participants reported large errors. Therefore, the quantification method needs to be further refined, starting from the experience gained in this interlaboratory study.

This study aimed to characterize the effects of changes in binder characteristics on fresh and hardened properties of 0.42 w/b cement pastes and mortars internally cured with superabsorbent polymers (SAP) in the absence of additional “mixing water”. Industrially-sourced SAP was characterized in five binder systems: three different Type I portland cements (PCs) (each with different alkalinity and fineness), Type III PC, and a binary system (70% of Type I PC and 30% of slag cement). Characterization techniques included gravimetric absorption; mortar flow; isothermal calorimetry; thermogravimetric analysis; microstructural analysis of SAP voids; and determination of 3-, 7-, and 28-day compressive strength and 7- and 28-day flexural strength. SAP absorption capacity and mortar flow varied across binders. However, hardened properties of Type I PC pastes and mortars were similarly affected by the addition of SAP, regardless of cement source. Type III PC pastes and mortars containing SAP showed increased early-age compressive strength and rate of hydration. The 3- and 28-day compressive strength values for mortars prepared with binary cementitious system and SAP were higher than those of companion mortars without SAP. Across Type I cement sources, hardened properties of pastes and mortars were similarly affected by the addition of SAP, while changes in fresh properties due to the addition of SAP were influenced by changes in cement chemistry. Synergistic acceleration of strength and hydration was observed in Type III pastes and mortars with SAP and a mitigating effect of SAP was observed on the retardation of strength development in the binary cementitious system.

Recent science reform advocates for the inclusion of engineering design to teach science and represents a shift to so-called three-dimensional (3D) learning. This shift often requires science instructors to adapt their current curriculum to integrate 3D learning. To support this shift, the current study illustrates the collaborative development and use of a rubric for aligning existing curriculum with new reform. Collaborators include three undergraduate science content course (i.e., biology, chemistry, and physics) instructors who used the tool to adapt their current curriculum. In this article, we outline the phases of tool development and showcase its implementation by the chemistry content course instructor to integrate a rocket design task. Successes and considerations are discussed as they relate to science teacher education and professional learning.