Sorption Kinetics of Superabsorbent Polymers in Cement Pastes Quantified by Neutron Radiography

摘要

Water desorption from superabsorbent polymers (SAP) into cement-based pastes was characterized by neutron radiography imaging to promote the understanding of the mechanisms behind internal curing of concrete. Two anionic SAP samples were used which differed in their inherent sorption kinetics in cement pore solution (SAP 1: self-releasing; SAP 2: retentive). Portland cement pastes with W/C of 0.25 and 0.50 and a paste additionally containing silica fume (W/C = 0.42, SF/C = 1/10) were investigated. Desorption from SAP 1 initiated immediately. SAP 2 released water into all the matrices as well, even in the cement paste with the high W/C of 0.50. In the other two pastes, which require internal curing by principle, SAP 2 retained its stored liquid for as long as the dormant period of cement hydration. Intense desorption then set in and continued throughout the acceleration period and even beyond. These findings explain the pronouncedly higher efficiency of SAP 2 as an internal curing admixture when compared to SAP 1.