Effect of relative humidity on the carbonation rate of portlandite, calcium silicate hydrates and ettringite. (September 2020)

• Record Type: Journal Article
• Authors: Steiner, Sarah; Lothenbach, Barbara; Proske, Tilo; Borgschulte, Andreas; Winnefeld, Frank
• Is Part Of: Cement and concrete research. Volume 135(2020)
• Publication Date: 2020-09
• Subjects: Carbonation -- Relative humidity -- C-S-H -- Ettringite -- Calcium hydroxide -- Calcium carbonate -- Thermodynamic modelling; Cement -- Periodicals; Cement -- Research -- Periodicals; Concrete -- Periodicals; Concrete -- Research -- Periodicals; Ciment -- Périodiques; Béton -- Périodiques; Cement; Concrete; Periodicals; 620.135
• DOI: 10.1016/j.cemconres.2020.106116
• Languages: English
• ISSNs: 0008-8846

Abstract

Abstract: The carbonation of portlandite, calcium silicate hydrate (C-S-H), and ettringite was investigated at 57% RH and 91% RH using X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and the phenolphthalein spray test. The experiments show that the carbonation of portlandite, ettringite, and C-S-H with Ca/Si = 0.7 is significantly faster at 91% RH than at 57% RH. Little effect of RH is observed for C-S-H with higher Ca/Si. Portlandite and C-S-H with Ca/Si = 0.7 carbonate only partially at 57% RH; complete carbonation is observed if the relative humidity is increased to 91% RH. In contrast, the carbonation of C-S-H with Ca/Si = 1.2 and 1.5 is complete at both relative humidities. The carbonation rate of C-S-H decreases with decreasing Ca/Si ratio, both at 57% and 91%RH. Carbonation at 57% RH promotes the formation of vaterite and aragonite over calcite; the precipitation of amorphous calcium carbonate is observed for C-S-H with Ca/Si = 0.7.