6 Pages

A required condition of thaumasite formation in marine environments

ByT. Nozaki, S. Ogawa, H. Hirao, K. Kono & K. Yamada

ABSTRACT: In order to investigate the required conditions of thaumasite formation in marine environments, series of experiments were carried out. Following factors were considered: cement and sand types, water/cement ratio (W/C), temperature, solution composition such as water, seawater, sulfate solution, and exchanging interval of solution. In the case of sulfate solution with shorter exchange interval, typical external sulfate attack accompanying ettringite formation was observed at 5°C for higher W/C mortar. In the case of longer exchange interval at 5°C, some differences were observed in the deteriorated texture depending sand types for higher W/C mortar. Surface texture was pealed out when rectangular mortar specimens made of limestone sand were immersed in seawater and sulfate solution. In the deteriorated part, thaumasite was identified. The increase in pH by prolonging exchanging interval is estimated as a reason for thaumasite formation. In actual marine environments, seawater is continuously exchanged and this reduces the possibility of thaumasite formation even for concrete containing calcite. Stagnant condition is much more dangerous for thaumasite sulfate attack.