title: Role of Adsorption Phenomena in Cubic Tricalcium Aluminate Dissolution.
abstract: The workability of fresh Portland cement (PC) concrete critically depends on the reaction of the cubic tricalcium aluminate (C3A) phase in Ca- and S-rich pH >12 aqueous solution, yet its rate-controlling mechanism is poorly understood. In this article, the role of adsorption phenomena in C3A dissolution in aqueous Ca-, S-, and polynaphthalene sulfonate (PNS)-containing solutions is analyzed. The zeta potential and pH results are consistent with the isoelectric point of C3A occurring at pH ∼12 and do not show an inversion of its electric double layer potential as a function of S or Ca concentration, and PNS adsorbs onto C3A, reducing its zeta potential to negative values at pH >12. The S and Ca K-edge X-ray absorption spectroscopy (XAS) data obtained do not indicate the structural incorporation or specific adsorption of SO42-on the partially dissolved C3A solids analyzed. Together with supporting X-ray ptychography and scanning electron microscopy results, a model for C3A dissolution inhibition in hydrated PC systems is proposed whereby the formation of an Al-rich leached layer and the complexation of Ca-S ion pairs onto this leached layer provide the key inhibiting effect(s). This model reconciles the results obtained here with the existing literature, including the inhibiting action of macromolecules such as PNS and polyphosphonic acids upon C3A dissolution. Therefore, this article advances the understanding of the rate-controlling mechanism in hydrated C3A and thus PC systems, which is important to better controlling the workability of fresh PC concrete.
authors.affiliation: Department of Civil and Environmental Engineering, University of California , Berkeley, California United States.|Yale School of Forestry & Environmental Studies, Yale University , 195 Prospect Street, New Haven, Connecticut 06511, United States.
authors.forename: Rupert J
authors.identifier: 0000-0001-6097-2088
authors.initials: RJ
authors.lastname: Myers
authors.affiliation: Department of Civil and Environmental Engineering, University of California , Berkeley, California United States.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Geng
authors.affiliation: Department of Civil and Environmental Engineering, University of California , Berkeley, California United States.
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Li
authors.affiliation: NORIE/UFRGS - Building Innovation Research Unit, Department of Civil Engineering, Federal University of Rio Grande do Sul , Porto Alegre, Brazil.|Polytechnic School of Civil Engineering, IMED , Passo Fundo, Brazil.
authors.forename: Erich D
authors.initials: ED
authors.lastname: Rodríguez
authors.affiliation: School of Environmental and Sustainability Sciences, Kean University , Union, New Jersey 07083, United States.
authors.forename: Juyoung
authors.initials: J
authors.lastname: Ha
authors.affiliation: Synchrotron Light Research Institute , 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand.
authors.forename: Pinit
authors.initials: P
authors.lastname: Kidkhunthod
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California , Berkeley, California 94720, United States.
authors.forename: Garrison
authors.initials: G
authors.lastname: Sposito
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California , Berkeley, California 94720, United States.
authors.forename: Laura N
authors.initials: LN
authors.lastname: Lammers
authors.affiliation: NORIE/UFRGS - Building Innovation Research Unit, Department of Civil Engineering, Federal University of Rio Grande do Sul , Porto Alegre, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Kirchheim
authors.affiliation: Department of Civil and Environmental Engineering, University of California , Berkeley, California United States.
authors.forename: Paulo J M
authors.initials: PJ
authors.lastname: Monteiro