ORIGINAL ARTICLE Desorption of superabsorbent hydrogels with varied chemical compositions in cementitious materials K. Farzanian . A. Ghahremaninezhad Received: 19 May 2017 / Accepted: 23 November 2017 Ó RILEM 2017 Abstract This paper examines the desorption of hydrogels synthesized with varied chemical composi- tions in cementitious materials. The absorption, chemical structure and mechanical response of hydro- gels swollen in a cement mixture were studied. The effect of the capillary forces on the desorption of hydrogels was investigated in relation to the chemical composition of the hydrogels. In the second set of experiments, the behavior of the hydrogels in a hydrating cement paste was monitored by tracking the size and morphology evolution of hydrogels interacting with the cement paste matrix. It was shown that the changes on the surface characteristics of hydrogels as a result of interactions with the pore solution and cement particles can affect the desorption rate of hydrogels in contact with porous cementitious materials. Scanning electron microscopic examination demonstrated two different desorption modes with distinct morphologies of hydrogels depending on the chemical composition of hydrogels. The effect of the interfacial bonding between the hydrogels and the cementitious matrix and its relation to the desorption is illustrated. Keywords Hydrogel Á Capillary forces Á Desorption Á Bonding Á Cementitious matrix 1 Introduction Internal curing has proven effective in alleviating autogenous shrinkage cracking in high performance concrete [1–8]. In internal curing, water is provided to a hydrating cementitious material from an internal reservoir of water in response to a reduction in moisture content in the surrounding cementitious material [3]. The use of superabsorbent polymers (SAP) in cementitious materials has seen an increased interest in the past decade due to its efficiency in mitigating autogenous shrinkage [3, 5–8]. It has been shown that the use of SAP can result in an improve- ment in the hydration of cementitious materials [6, 9]. Prior investigations [9–11] examined the influence of SAP on the transport properties of cementitious materials. SAP belongs to hydrogels, which are composed of hydrophilic polymeric networks with a relatively large water absorption capacity [7, 12–14]. The hydrogels used in cementitious materials are typically polyelec- trolytes, and as a result, are sensitive to the pH and ionic composition of the environment [1, 7, 12, 13, 15]. The SAP used in the cementitious materials are primarily composed of poly(acrylate-co-acrylamide) copoly- mers [3, 15, 16]. When exposed to distilled water, the K. Farzanian Á A. Ghahremaninezhad (&) Department of Civil, Architectural and Environmental Engineering, University of Miami, Coral Gables, FL 33146, USA e-mail: a.ghahremani@miami.edu Materials and Structures (2018) 51:3 https://doi.org/10.1617/s11527-017-1128-1