Delayed ettringite formation in heat-cured Portland cement mortars

A Portland cement mortar was subjected to elevated temperature curing at 10 0 degrees C for 12 h and then stored under water at room temperature. Expan sions, attributable to delayed ettringite formation, were found to develop over a period of 1 year. Sulfate ions released to the pore fluid at elevate d temperatures, and partly sorbed by C-S-H gel, evidently formed ettringite in the outer products and the paste-aggregate transition zones during subs equent water storage at room temperature. The results of X-ray microanalyse s implied that a potential for ettringite band formation had been establish ed in the mortar. Investigations of microstructural features by backscatter ed electron imaging indicated that the expansion was caused by generation a nd extension of these ettringite bands. No evidence in support of an altern ative mechanism based on a homogeneous expansion of the cement paste could be found. (C) 1999 Elsevier Science Ltd. All rights reserved.