Editorial

To study the permeability of superabsorbent polymer (SAP) modified concrete and the effect of internal pore characteristics on the permeability of concrete specimens, the results of the water penetration under pressure test, the mercury intrusion porosimetry (MIP) test, and scanning electron microscopy (SEM) of SAP concrete were obtained and analyzed. The research shows that the addition of an appropriate amount of SAP can effectively improve the anti-permeability performance of concrete. After adding 0.2~0.6% SAP of cement quality to concrete, the penetration height value was reduced by 35~45%, the porosity was increased by 21–95%, and the tortuosity is increased by 14–15%, and all indicators show regular changes with the increase in SAP usage. Adding SAP to concrete changes the internal connection state of concrete, thereby further improving its impermeability by reducing the capillary pressure and changing the shape of the pores. The liquid permeation resistance is increased by the “threshold effect” inside concrete; this “threshold effect” is caused by the addition of SAP.

Shrinkage reducing admixture (SRA), shrinkage compensating admixture (SCA), and superabsorbent polymer (SAP) have been commonly used to reduce shrinkage of high-performance concrete (HPC); however, their comparative effectiveness is still not clear. In this article, the effects of SRA, SCA, and SAP on strength, autogenous/drying shrinkage, restrained ring shrinkage, and pore structure of HPC were studied. The dosages of SRA, SCA, and SAP were varied within 2.5–7.5 L/m3, 2.5–7.5 %, 0.4–1.4 g/kg, respectively. The results indicated that SRA and SCA decreased the shrinkage with their dosages increasing. However, the presence of SAP in HPC mitigated the autogenous shrinkage weakly and raised the free drying shrinkage. SRA, SCA, and SAP all reduced restrained ring shrinkage. SCA was the best admixture to increase compressive strength and reduce shrinkage in HPC. Additionally, the micromechanisms of SRA, SCA, and SAP on shrinkage reduction were addressed based on pore structures. The reduction of mesopore percentage was a primary reason to restrain the shrinkage behavior with the addition of SRA, SCA, and SAP. Moreover, linear fitting models of shrinkages in function of mesopores percentage were proposed. The shrinkage property of HPC could be explained by the mesopores percentage.

Strain-hardening cement composites (SHCCs), characterised by strain-hardening and multiple cracking behaviours under direct tension, are generally recognised as ductile and durable construction materials. The effect of the addition of superabsorbent polymer (SAP) particles and curing condition on the mechanical performance and microstructure of binary cement-based SHCC material using ordinary cement and fly ash as the cementitious binder was investigated in this study. Three different SHCCs were designed and mixed; the SHCC mixtures were reinforced with 2% polyvinyl alcohol (PVA) fibres by volume and 1% SAP was added to one SHCC mixture. The mixtures were subjected to compressive, flexural and direct tensile tests. The sealing and healing of cracks after direct tensile tests were also monitored by a microscope. The experimental results showed that the use of fine SAP particles led to an improvement in the mechanical properties of the binary cement-based SHCC material even under air curing. The multiple cracking, ductility and crack sealing were also improved by introducing 1% SAP particles. It is thus concluded that the addition of SAP may be an effective method to improve the sustainability of binary cement-based SHCC materials.

Autogenous shrinkage and hydration property of alkali activated slag pastes containing superabsorbent polymer

Concrete of strengths classes ≥ C55/67 referred to as high strength or high-performance concrete (HSC/HPC) are noted to be generally of low water/binder (W/B), made from binary or ternary cements with silica fume (SF) being a necessary constituent, and often requiring internal curing. Non-availability and high cost of SF in most sub-Saharan Africa like Nigeria however makes HSC/HPC production in this region very difficult and hence the continued search for alternative supplementary cementitious materials (SCM) with good performance properties as constituents of ternary/binary cements in HPC. This study thereby examines the strength properties of metastable calcined clay (MCC) based HPC cured internally with superabsorbent polymer (SAP) 0.2–0.3% (by weight of binder (bwob)). HPC mixtures of varied MCC and Rice husk ash (RHA) contents containing two SAP grain sizes labelled (SP1 ˂ 300 µm and SP2 ˂ 600 µm) were cast in 100 mm cubes and cured for varying ages (7, 14, 28 and 56 days) before testing. The hardened specimens were subjected to compressive strength and water absorption tests at the varied curing ages for the performance assessment of the binder types and SAP grain sizes in HPC with age. This study revealed the possibility of achieving Class 1 HPC (50–75 N/mm2) utilizing industry manufactured calcined clay and locally produced RHA in Nigeria. The compressive strength of HPCs increased as the curing age increases for both SCM type, SAP contents and grain sizes. RHA based HPCs however showed better strength performance at the early ages than the MCC based. SAP addition in MCC based HPCs led to slight decrease in compressive strength as the SAP contents increased while the RHA based HPCs on the other hand, revealed slight increase in compressive strength with increase in SAP contents.

This study discusses the thermal behavior of the 6.5 Ah cylinder Ni/MH hydride battery with 0.5 wt% ytterbium oxide (Yb2O3) in nickel electrode and 1.0 wt% super absorbent polymer (SAP) in hydrogen-storage alloy (MH) electrode during charging to 150% of its rating capacity. Quantity of heat and heat generation rate of the battery during charging are studied by quartz frequency microcalorimeter. Heat generation curve is fitted into a function, and heat transport equation is solved. Using measured data, the internal temperature profiles at the terminal moment of charging at 1C, 3C, and 5C are simulated by FEM. Influence of Yb2O3 and SAP on the thermal behavior of Ni/MH battery is examined by the two-dimensional thermal model. Results show that addition of Yb2O3 and SAP can achieve substantial improvement for thermal behavior of Ni/MH battery at 1C,3C, and 5C charging.

Understanding the shrinkage behaviour of alkali-activated slag binders modified by the superabsorbent polymer

Effect of internal curing with super absorbent polymers on the relative humidity of early-age concrete

This paper presents the role of superabsorbent polymer (SAP) on strength and microstructure development in cemented clays with notably high water content. A series of unconfined compressive strength (UCS), scanning electron microscope (SEM) and X-ray diffraction (XRD) tests were performed to identify strength behavior and microstructure. Results showed that SAP significantly influenced the mechanical behavior of cemented clays with notably high water content, characterized by an increase in the unconfined compressive strength and a decrease in the after-curing water content with SAP content. This revealed that the strength increase due to SAP was directly related to the water absorption by SAP. Meanwhile, XRD results showed that the hydration products were controlled by cement and lime content, regardless of SAP content. That meant there was no chemical reaction between SAP particles used in this study and cement or lime. The microstructure analysis by SEM revealed that SAP played an important role in the microstructure of cemented clays. With an increase in SAP content, the water absorbed by SAP increased significantly, leading to a decrease in the pore volume and a denser soil fabric. This behavior indicated that the primary role of SAP on strength increase was to absorb and fix water in cemented clays. Consequently, the clay–cement cluster distance decreased with an increase in solid mass (soil particles and swollen SAP particles) and a decrease in pore water. The corresponding tighter flocculated fabric due to SAP eventually led to the strength increase.

The early-age shrinkage of concrete has a pronounced influence on the performance of the material during the whole service life. The casting of concrete in hot climatic conditions, which are harsh for early-age concrete, often lead to cracking which subsequently has an negative impact on various properties of the structural element, especially on its durability. The article at hand provides some additional insights on plastic and early-age shrinkage of two very different types of concrete: an ordinary concrete and a relatively new type of fiber-reinforced concrete — a strain-hardening cement-based composite (SHCC). These materials were produced and tested both without and with addition of a superabsorbent polymer (SAP), which was used as an internal curing agent for mitigating early-age shrinkage. Three climatic parameters were varied in a certain range: temperature of the surrounding air, its relative humidity and the wind velocity. The addition of SAP clearly reduces the capillary pressure within fresh concrete, which indicates the efficiency of its action as internal curing agent. The SHCC is able to successfully withstand the early-age shrinkage in the hot climatic conditions under investigation. In contrary, in the most cases a major crack developed in the ordinary through the entire height of the specimen and separated it in two parts.

In practical applications, Super absorbent polymers (SAP) can have certain adverse effects on concrete. Incorporation of SAP could lead to changes in the pore structure, thereby affecting strength. At the same time, SAP could also present cost challenges. To address these issues, a specific modifier can be incorporated into the SAP internally curing concrete. In this paper, the mechanical properties of nano-SiO2 and fly ash composite modified SAP internal curing concrete were investigated. The mechanical properties of the composite modified SAP were reflected through compressive strength and tensile strength tests as well as porosity mutual verification. The results indicate that nano-SiO2 and fly ash increase the strength of the modified SAP internal curing concrete and reduce the porosity. When the maximum content of nano-SiO2 reaches 3 %, the modification effect is more favourable. Under the combined effect of nano-SiO2 and fly ash, both the strength and porosity of SAP internal curing concrete are improved.

Background: Although Superabsorbent Polymer (SAP) microsphere has been useful in treatment of multiple and large hepatocellular carcinoma, efficient loading procedure of cisplatin onto SAP was not established. Loading efficiency of cisplatin was evaluated from the viewpoint of passive concentration gradient and ionic strength. Methods: To load cisplatin into SAP particle, 50mg of cisplatin powder was dissolved in three manners of aqueous solutions: (a) 50mg of cisplatin powder plus 35ml of warmed physiological saline solution (0.9%), (b) 5ml of physiological saline solution (0.9%) plus a half of solution (5ml) of the product made from 50mg of cisplatin powder in 10ml of iohexol 350mgI/ml, and (c) 10ml of iohexol 350mgI/ml plus 0.25ml of 10% NaCl solution Results: Cisplatin dissolved sufficiently in all the three methods. Average amounts of loaded cisplatin into SAP particles were 1.7mg in solution (a), 6.6mg in solution (b), and 11.8mg in solution (c). Since alteration of ionic strength in the method (c) significantly affect the extent of SAP swelling, addition of 0.25ml of 10% NaCl was unquestionably necessary. Release of cisplatin from SAP was evidently gradual, showing 83.1% after 6 hours in static elution experiment and 68.6% after 1 hour in dynamic elution experiment. Conclusions: Cisplatin-loaded SAP may act as a drug delivery system for treatment of liver cancer, and loading of cisplatin should be consciously performed considering cisplatin concentration and ionic strength. (225words)

Effect of air-entraining agents combined with superabsorbent polymers on pore structure and frost resistance of mortar prepared under low air pressure

Superabsorbent polymers (SAPs) are novel admixtures in cementitious materials in order to have internal curing. Neutron tomography is used to investigate and to visualize the water release by SAPs with different kinetics over time. This gives insight into the time window for effective internal curing as the results are linked to shrinkage and internal relative humidity measurements. One SAP showed complete mitigation of autogenous shrinkage and even a partial expansion effect (+121 µm·m−1 after two days), while another type of SAP proved to be less effective as the shrinkage (−189 µm·m−1) was more resembling a reference system with a higher effective water-to-cement ratio. The internal relative humidity after two days of hardening showed that the effective mixture still possessed a high relative humidity at 98% while the ineffective mixture had a lower internal relative humidity at 95% after 2 days. It was still unclear whether this ineffective SAP released its water too slow or too fast. The study with neutron tomography showed the necessary kinetics to mitigate autogenous shrinkage of one SAP between final setting and 30 h. However, the ineffective SAP released its water quickly after final setting and prior to 20 h, even though water is still necessary at later time intervals to mitigate further autogenous shrinkage and to maintain the internal relative humidity.

Utilizing superabsorbent polymers (SAP) in alkali activated slag (AAS) can promote internal curing and remarkably alleviate the shrinkage of AAS. This promising additive has attracted considerable attention for its potential to enhance the performance of AAS. In this research, rheological tests, Vicat tests, and isothermal calorimetry tests were conducted to investigate the effect of SAP particle size and content on the fresh performance of AAS. For AAS containing the theoretically required amount of SAP to compensate for self-desiccation, an insignificant effect is observed on the setting time, while the rheological characteristics vary substantially. With an increase of SAP from 0% to 0.6%, AAS exhibits higher yield stress and plastic viscosity, depending on their particle size. The addition of SAP generally reduces the initial structural build-up rate, while after resting for more than 30 min, the structural build-up rate of AAS with SAP is faster than that of the reference paste without SAP. At the same SAP concentrations, AAS pastes containing larger-sized SAP exhibit higher early viscous behavior compared to those with smaller-sized SAP, while after a longer resting period, they demonstrate a more rapid structural evolution. The second hydration peaks of AAS with SAP are delayed and reduced, despite achieving more thorough hydration at 7 days. Notably, the addition of more than 0.2% SAP results in a prolonged setting time, particularly with smaller particle size, due to the varying absorptions and release rates. This study provides a theoretical support for the practical applications of SAP in AAS, specifically in terms of rheological considerations.