Development of a clinker-free white binder of one-part CaO-activated GGBFS with TiO2 addition

Abstract

In this study, a new clinker-free white binder that exhibits whiteness comparable to that of white Portland cement was proposed by investigating the effects of an activator (i.e., CaO vs. NaOH) and added TiO2 (i.e., anatase vs. rutile, dosage) on the surface colors of activated ground granulated blast furnace slag (GGBFS). Overall, compared to the type or dosage of TiO2, the type of activator exhibited a more pronounced effect on the surface color although TiO2 was considerably beneficial for increasing whiteness. As determined by ASTM E313, the results revealed that all NaOH-activated samples are neither "white" nor "near white," even with the highest dosage of the added TiO2 , while all CaO-activated samples were nearly white even without the added TiO2. In addition, NaOH and CaO produced different tints (i.e., green by NaOH and red by CaO activation, respectively) regardless of the presence of TiO2. In CaO activation, rutile was more effective than anatase in improving all color indices and whiteness; however, in NaOH activation, the addition of anatase was better for reducing tints of yellowness and greenness. The whitest sample was obtained, which was whiter than white Portland cement on all days, by the addition of 16% rutile in CaO activation; however, if strength was considered in addition to whiteness, the same system with 4 wt% rutile would be the best candidate mixture. (C) 2020 Elsevier Ltd. All rights reserved.