FULL PAPER www.ms-journal.de Effect of Hydrogel Nanocomposites on the Fresh and Hardened Properties of Cementitious Pastes Vitor A. S. Siqueri, Adhemar W. Filho,* Marcia R de Moura, and Fauze A. Aouada Cement is a material widely used in civil construction due to its physical and chemical properties, ensuring a good performance. Some polymeric materials, such as hydrogels, have been frequently added to improve these properties and mitigate autogenous retraction in cementitious matrices. This paper aimed to evaluate the influence of polymeric hydrogel on the fresh and hardened properties of cementitious pastes (water/binder ratio = 0.35). Fresh properties results showed that the consistency and exudation indexes of these matrices decreased with an increase in the amount of hydrogel. The values of the bulk density of all cementitious matrices are around 2.1–2.2 g cm -3 . Matrices containing up to 1.0% of hydrogel have satisfactory mechanical properties, reaching compressive strength of 60 MPa for 112 days of curing age. From these results, it is possible to conclude that hydrogels are promising materials for civil engineering applications, acting mainly as a filler and hydroretentor agent. 1. Introduction Concrete is one of the most widely used material in civil construction [1–5] due to their inherent characteristics such as facile production, workability, adaptability to different forms, and satisfactory mechanical behavior. This material, obtained from cement hydration reactions, must present satisfactory responses against the environmental factors that are exposed, either in its fresh or hardened state. To ensure that this matrix is dense and has good workability in the production phase, reaching adequate mechanical properties when hardened, it is necessary to develop new cement-products that attend these conditions. [4,6] In this context, advances in science and technology fields are increasingly contributing to improving construction techniques. [5,7] Recent research highlights that the development V. A. S. Siqueri, A. W. Filho, M. R de Moura, F. A. Aouada Grupo de Compósitos e Nanocompósitos Híbridos (GCNH) Department of Physics and Chemistry Programa de Pós-Graduação em Ciência dos Materiais São Paulo State University (Unesp) School of Engineering Ilha, SP 15385-000, Brazil E-mail: watanuki@ifsp.edu.br A. W. Filho Institute Federal of São Paulo (IFSP) Ilha Solteira SP 15385-000, Brazil DOI: 10.1002/masy.202000047 of new materials has allowed the inclu- sion of chemical concepts in civil con- struction, more specifically, in the pro- duction of special concretes, improving the setting time, reducing the porosity of the matrices, and other benefits. [8] Thus, for the production of cementi- tious matrix composites, a better control of mechanical (such as strength and mod- ulus of deformation), exudation, durabil- ity, and permeability properties is desired, what may contribute to increasing its life cycle. In the cementitious materials, the particles of the binder have a high ten- dency to agglomerate due to its elevate van der Waals and electrostatic forces. [8] Be- sides, the presence of this agglomerated im- plies in the retention of a certain amount of free water, forming open channels be- tween the particles, thus decreasing the hy- dration of surfaces of the cement particles. The addition of additives to concrete, mortar, or paste becomes an interesting alternative to improve the physicochemical prop- erties and workability of these matrices. Some additives added to the concrete are of polymeric origins, such as the hydrogels. These materials are known as high water-absorbing polymers, and as are formed by chains three-dimensionally cross-linked, they can retain the absorbed water and release over a longer period. [9–12] The compatibility between an inorganic matrix (such as Port- land cement) and an organic matrix (such as hydrogel) is still a topic of great discussion, interest, and innovation. [3] However, the application and investigation of these hybrid nanocomposite hydrogels in cementitious matrices is still little discussed and reported. Mostly, the published studies are focused on the use of commercial synthetic superabsorbent polymers (SAPs). Another important innovation is that the clay mineral–polymer nanocom- posites are of particular interest and can improve some physical properties and the biodegradability of polymers. [13–15] Moreover, they present advantages such as satisfactory mechanical behavior because the combination of nanoparticles and polysaccharide (forming a hybrid nanocomposite) is an emerging method for obtaining hydrogels with high strength, [16] excellent thermal, water, and solute sorption properties. [9] The presence of mineral clay, when associated with polysaccharide as carboxymethyl- cellulose (CMC) or others, [17] can also increase the hydrophilic properties of these nanocomposites. [18] Additionally, the nan- oclay can act as a reinforcing agent in the polymeric matrix, and their presence may extend the water release process inside the Macromol. Symp. 2020, 394, 2000047 © 2020 Wiley-VCH GmbH 2000047 (1 of 6)