Changes of thermal events of macrodefect-free (MDF) cements due to the deterioration in the moist atmosphere

Abstract

Sulfoaluminate ferrite belite (SAFB) clinker premixed with Portland cement in mass ratio 85:15 was combined with hydroxypropylmethyl cellulose (HPMC) or sodium poly-phosphate (poly-P) for the macrodefect-free (MDF) process and subsequent moisture treatment. Mass changes as the measure of the moisture resistance and thermoanalytical traces of MDF cements gave useful information. The mass change depends more on the humidity than on the composition (polymer and inorganic constituents) of the MDF cement or duration of the original MDF cement synthesis. The values of mass changes at 100% relative humidity (RH) and at ambient conditions are affected by the nature of the polymer, poly-P being highly advantageous. Attack by environmental water and carbon dioxide increases the contents of C 4( A, F) S̄H 12( AFm) and CaCO 3, represented by thermogravimetry (TG) effects at 250°C and differential thermal analysis (DTA) peaks at 600–700°, respectively. In contrast, the quantity of cross-linking, where the decomposition of Al(Fe)–O–C(P) bonds typically produces TG–DTA effects at 250–550°C, remains intact during the moisture attack.