Abnormal setting of Portland cement

Abstract

It is proposed to distinguish the false setting from the abnormal one, considering the false as a variety of the latter. With false setting, the start of setting occurs in a short time, but then it spontaneously disappears, reappearing after a while. Such cements, in which the beginning of setting occurs faster than 50 minutes, and the end – after 5-12 hours, are proposed to be called abnormal cements. It is shown that when the start time of setting is more than 50 ∼ 60 minutes, the probability of abnormal setting decreases sharply. The kinetics of structure formation of cements with different setting patterns is considered. Methods for the identification of abnormal setting by the setting interval (τfinal – τstart)/τstart > 3, the kinetics of structure formation, heat release, and changes in the activity of calcium ions in the liquid phase of cement paste of normal density are proposed. It is shown that the measurement of the kinetics of heat release and the activity of Ca 2+ ions in the liquid phase of cement paste is of great interest for the development of automated and rapid control of the presence of anomalies during setting. It is established that the mixture of the inhibitor and the booster of the setting acts according to the rule of additivity, the use of mineral additives of acidic composition weakens the abnormal properties of cement systems. To combat the belated anomaly, it is necessary to monitor the properties of the cement 1-2 days before its application.

Study on the Properties of Belite Calcium Sulfoaluminate Cement–Ordinary Portland Cement Composite Cementitious System

“…In the Portland cement, the abnormal setting has close ties with the formation of large amounts of AFt at the initial hydration age [35]. In the BCSA-OPC composite cementitious system, the hydration of C 3 S leads to an increase in pH value, promoting the hydration of C 4 A 3 $, and the large amount of AFt generation leads to the abnormal setting of BCSA-OPC.…”

“…The initial needle penetration (I) changes are not obvious, while the final needle penetration (F) tends to decrease and then increase, reaching a minimum when the BCSA content is 70%. The flash set of B60, B70, and B80 is due to the mismatch between the amount and activities of gypsum and aluminate minerals in the cement [35,36]. When the C 3 A and C 4 A 3 $ are dissolved into the water and release the Ca 2+ rapidly into the liquid phase, the small number of negatively charged gypsum particles cannot provide sufficient inhibition, leading to the rapid setting of the cement.…”