|
Description: This research report describes the effect of moisture exposure on expansion in heat-cured mortars due to delayed ettringite formation (DEF). Mortar bar samples were cured at 90ºC, and then stored for more than 4 years under in moist air at 75%, 80%, 84%, 90%, 92%, 97%, and 100% relative humidity (RH). Periodic weight and length measurements were made along with chemical analyses. The results show that DEF-related expansion is influenced by the level of moisture exposure. The study suggests that a threshold level of moisture exposure for expansion to occur seems to be between 92% and 90% RH.
The research presented in this report studies the effect of moisture exposure on long term expansion in heat-cured mortars due to delayed ettringite formation (DEF). Mortar bar samples were prepared using standard Ottawa sand and cured at an elevated temperature of 90ºC, and subsequently stored for more than 4 years under several long-term storage conditions, including: immersed under pure water and above water in moist air at 75%, 80%, 84%, 90%, 92%, 97%, and 100% relative humidity (RH). Weight and length changes were recorded periodically, while relative humidity and temperature were constantly monitored. Mortar samples were also analyzed at different ages for chemical and mineralogical composition and microstructure characterization. Several techniques were used including X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and optical microscopy. Emphasis was placed on observing the different cracking patterns and expansion performance between samples stored under water and those stored above water. The study also looks at the effect of alkali leaching on occurrence and rate of expansion.
The results show that DEF-related expansion is influenced by the level of moisture exposure. Expansion occurs sooner for mortar bars stored under water. However, once expansion occurs for mortar bars stored in moist air, the observed maximum expansion exceeds that for samples stored under water. Expansion of samples stored in moist air occurs sooner for those stored at higher RH of 100%, 97%, and 92%, in that order. Samples stored at 90% RH and below did not show expansion, but did expand upon subsequent exposure to 92% RH. Alkali leaching seems to accelerate the occurrence of expansion for samples immersed under water. The study suggests that a threshold level of moisture exposure for expansion to occur seems to be between 92% and 90% RH.
|