Thaumasite in Orange County, Southern California: an inquiry into the effect of low temperature

Thaumasite has been found in similar to10 year old permeable concrete exposed to sulfate-bearing ground waters in Orange County, California, an area generally associated with a warm climate. The occurrences have usually been found in carbonated zones at or near the lower surface of concrete slabs in contact with the ground. Daily records of soil temperature over the 1990-2000 decade indicate that during the early part of this decade (1990-1993) daily minimum soil temperatures dipped below 15degreesC for appreciable portions of the winter months. Since 1993 a warming trend has been observed, and daily minimum soil temperatures fell below 15degreesC for only a very few days. It is not clear whether the thaumasite deposits observed in the subject concretes were formed entirely during the colder pre-1994 winters, or whether the thaumasite development continued even under the warmer temperatures experienced since then. (C) 2003 Elsevier Ltd. All rights reserved.