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Incorporating superabsorbent polymer (SAP), which has the abilities of absorption and desorption in concrete can achieve the effect of internal curing. The influences of the volume, particle size and ways of entrained water of SAP on the workability, compressive strength, shrinkage, carbonation resistance and chloride penetration resistance of concrete were analyzed through the macroscopic and microscopic test. The results show that pre-absorbed SAP can increase the slump of the mixture, but SAP without water absorption and pre-absorbed SAP with the deduction of internal curing water from mixing water can reduce the slump. The improvement effects of SAP on compressive strength of concrete increase gradually with the increase of age. Especially from 28 days, the compressive strength of concrete increases obviously. At later age, the compressive strengths of SAP concrete under natural curing environment exceed the strength of reference concrete under natural curing environment and nearly reach the strengths of reference concrete under standard curing environment. SAP effectively reduces the shrinkage of concrete, improves the concrete’s abilities of carbonation resistance and chloride penetration resistance. The microscopic test results show that SAP can effectively improve the micro structure and make the pore structure refined. When SAP is added into concrete, the gel pores and small capillary pores are increased, the size of big capillary pores and air pores are reduced.

Superabsorbent polymers (SAPs) are three-dimensional crosslinked hydrophilic polymers, that can absorb and retain liquids up to hundreds of times their weight. These polymers have diverse applications across various fields, including agriculture, biomedicine, separation technologies, and wastewater treatment. Among these cellulose-based SAPs are prominent due to their biodegradable nature, sustainability, biocompatibility, cost-effectiveness, and natural abundance. The development of SAPs has evolved significantly since 1961, marked by advancements in polymerization techniques and their integration into numerous aspects of daily life. This review provides a comprehensive analysis of recent advancements in the field of cellulose-based superabsorbents, focusing on their polymerization methods, source of cellulose, and diverse applications. Furthermore, it highlights the mechanisms by which different forms of cellulose can enhance liquid absorption capacity and kinetics across various applications. The findings underscore the importance of cellulose-derived SAPs in promoting environmentally sustainable practices while addressing the growing demand for effective water retention solutions in agricultural and industrial contexts.

Agriculture is an important sector of the economy, but this industry consumes significant amounts of water, which is a precious and limited natural resource. Irrigation techniques and efforts to mitigate water usage influence the growth, survival, and yield of crops. However, superabsorbent polymers in combination with fertilizers can be employed to obtain sustained release of nutrients and improved water retention capacity of the soil. Despite significant recent progress in this area involving synthetic polyacrylate hydrogels, there are no industrially applicable solutions exhibiting similar performance using natural biopolymers or synthetic polymers enriched with natural components. This review focuses on biodegradable chitosan-based hydrogels (both natural and semi-synthetic), and discusses their potential agricultural and horticultural applications. The methods for synthesizing hydrogels via physical or chemical crosslinking, and the resulting functional properties of recently reported hydrogels, such as water retention and release of active ingredients, are presented herein.

Internal curing with superabsorbent polymers (SAP) is a method for promoting hydration of cement and limiting self-desiccation, shrinkage and cracking in high-performance, and ultra high-performance concrete with low water-to-binder ratio. SAP are introduced in the dry state during mixing and form water-filled inclusions by absorbing pore solution. The absorbed solution is later released to the cement paste during hydration of the cement. In this paper, cement pastes with low water-to-binder ratios incorporating superplasticizer and different dosages of SAP and corresponding additional water were prepared. Reference cement pastes without SAP but with the same amount of water and superplasticizer were also mixed. Isothermal calorimetry was used to measure hydration heat flow. Water entrainment by means of SAP increased the degree of hydration at later hydration times in a manner similar to increasing the water-to-binder ratio. Addition of SAP also delayed the main calorimetric hydration peak compared to the reference pastes, however, in a less prominent manner than the increase in water-to-cement ratio.

At present, the growing environmental concerns have strengthened the use of biodegradable and natural polymers in the synthesis of superabsorbent polymer (SAP) particularly in agriculture applications as natural polymers are much more efficient and environmentally friendly than synthetic ones. Starch is the most abundant carbohydrate polymer, biodegradable, and a renewable raw resource, with good chemical stability and high reactivity. Thus, starch-based SAP has gained huge interest in the agriculture field in the past few years. This review presents the significance of SAP in agriculture, starch-derived SAP, crosslinking and graft copolymerization techniques used in the synthesis of starch-based SAP as well as control release formulations and control release study of agrochemicals. The review significantly elaborates the synthesis techniques and various chemistries used for the preparation of SAP as well as the structure–property relationships like the effect of grafting or doping on the swelling kinetics and water absorbency. Furthermore, the various mainstream characterization techniques also reviewed which are generally used for the analysis of SAP.

The hybrid use of a superabsorbent polymer (SAP) and expansive agent (EA) is beneficial for mitigating the autogenous shrinkage of ultra-high-performance concrete (UHPC) without compromising strength. However, the unclear mechanisms behind the synergetic effect of the two materials may hinder the more effective applications of this method. This study clarifies the interactions between SAP and CaO-based EA (CEA) in a UHPC matrix by quantifying the content and distribution of water and hydration products, underlining their influence on the strength and autogenous shrinkage evolution. The high strength of 135 MPa can be achieved in systems with a reasonable combination (S1E1, 0.1 wt%SAP, and 1 wt%CEA), and after 7 days, a 24% reduction in shrinkage was found in the same system, which is more effective than the use SAP or CEA alone at the same dose. The mitigating effect on the autogenous shrinkage of a UHPC matrix with hybrid materials at different stages depends on the competition between the water retention for self-desiccation and portlandite formation. With the continuing formation of hydration products, the microporosity of UHPC matrix under internal curing conditions at 28 d is considerably reduced, resulting in a more compact microstructure. This study also finds a suppressed crystallization pressure of growing portlandite in the extra space provided by emptied SAP, which explains the lost expansion of CEA.

Most superabsorbent polymers (SAPs) are prepared based on synthetic polymers (from petroleum resources), making them costly, nondegradable, and not ecofriendly. To overcome these drawbacks, biodegradable and renewable natural materials are proposed as additions into SAPs. In this article, a new SAP composite was synthesized by using AA, AM, α-cellulose, and modified zeolite (MZE). The prepared SAP composites were analysed by FTIR spectroscopy, XRD, SEM and TGA. Then, their water absorbency and water retention capacity results were evaluated. AA and AM were successfully grafted to the α-cellulose chains, and MZE was uniformly dispersed in the SAP composite matrix as an inorganic filler, which endowed the SAP composites with a more undulant and coarser surface along with more abundant hydrophilic groups. In contrast with poly(AA-co-AM), the water absorbency of the prepared SAP composites increased by 93.88% in distilled water and 89.58% in 0.9 wt.% NaCl solution. Additionally, the water retention time of these SAP composites was 11.2 h when evaluated at 50 °C, which was a 71.79% increase. Moreover, both the T onset and T peak of the prepared SAP composites slightly increased compared with those of α-cellulose-poly(AA-co-AM), showing that the introduction of MZE could slightly improve the thermal stability of the SAP composites. These novel SAP composites with their excellent water absorbency and retention capacity could be applied to the agricultural and horticultural fields as water-keeping materials.

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.

Super absorbency is the extraordinary capacity of a substance to absorb and retain a large amount of liquid. Hydrophobic polymer chains are cross-linked to form superabsorbent polymer (SAP) hydrogels. Due to greater ability to absorb water, extended lifespans, and availability of a wide range of basic chemical resources, synthetic hydrogels gradually displaced natural hydrogels. These superabsorbent polymer hydrogels are in usage around the world in various applications for more than 50 years. Hydrogels are referred to as intelligent or smart materials since they respond to certain environmental stimuli and undergo a large volume phase shift in response to specific physical and chemical stimuli. The various forms of hydrogels and their wider applications are currently of research interests. The main goal of this review is to assess the literature on the various classification systems for hydrogels, their physical and chemical properties, and the technical viability of using them in civil engineering applications based on the newest publications in this field and the role of hydrogels as a new building material promoting environmental sustainability. A newly developed class of the most recent hydrogel material generations was also briefly discussed.Graphical abstract on superabsorbent polymers in cementitious materials

Superabsorbent polymers (SAPs) are hydrophilic, polymeric network materials renowned for their ability to enhance various properties of cementitious materials. This investigation examines the impact of SAP size on the hydration degree, porosity, and compressive strength of cement pastes and concrete under diverse curing conditions and ageing periods. The findings reveal that SAP addition stimulates the hydration of the C2S phase, particularly during the early curing stages, thereby favouring early strength development. However, the effect of SAPs on hydration promotion diminishes as their size increases. Conversely, the size of SAPs affects the hydration range of their action, and the 400 µm SAP demonstrates the most extensive range of hydration enhancement, reaching up to 105 µm. Additionally, SAPs effectively reduce porosity in small pores (4 nm–10 μm), with 200 μm and 400 μm SAPs exhibiting the highest efficacy. While analysing the effects of SAPs on larger pores (>10 μm), the results show that although larger SAPs result in larger average porosity, the total porosity is effectively reduced, particularly in samples incorporating 400 μm SAP. The compressive strength of cement paste, even after 28 days, is slightly reduced following the introduction of SAPs. However, the strength of concrete, due to the naturally occurring pores eliminating the negative effects of the pores produced by SAPs, is significantly increased following the introduction of SAPs, especially 400 µm SAP.