Portland-limestone cements (PLC) have been used in practice for a considerable period of time in several countries. In 2008, the CSA A3000 cements committee approved the addition of a new class of cement with up to 15% interground limestone. The CSA A23.1 concrete committee also approved the use of PLC in concrete in 2009. However, to date, due to uncertainty about the performance of Portland-limestone cements in sulfate environments, their use has not been allowed in sulfate exposures.
In this study, the sulfate resistance of five different Portland-limestone cements and their combinations with various amounts of supplementary cementitious materials (SCMs) were examined. Besides the standard tests performed at 23 °C, a modified version of the ASTM C1012 test was developed in this study (adopted in 2010 as CSA A3004-B) and used to investigate the possibility of thaumasite form of sulfate attack at 5 °C.
It was found for tests conducted at 23 °C that while 100% cement mixes deteriorated in sulfate exposure due to conventional sulfate attack, partially replacing the Portland cements and Portland-limestone cements with 30% or 50% slag was effective in making the mixes highly sulfate-resistant. In sulfate exposure at 5 °C, all of the 100% cement mortar bars failed the test and had completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30% slag was effective in controlling the deterioration at 5 °C only for Portland cements and not Portland-limestone cements. However, all the combinations of the cements with 50% slag were resistant to the thaumasite form of sulfate attack.
In a parallel study, the hydration of Portland-limestone cements and the relationship between strength and porosity of mortar samples were examined. The results of hydration studies revealed that the limestone portion of Portland-limestone cements reacts with the alumina phases and produces carboaluminates, which contributes to the strength. As the limestone content of the cement increased, the shift in the optimum level of SCM providing maximum strength and minimum porosity was attributed to the availability of more alumina, which allowed more limestone to participate in the hydration reactions, forming additional carboaluminate hydrates.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/32924 |
| Date | 04 September 2012 |
| Creators | Ramezanianpour, Amir Mohammad |
| Contributors | Hooton, Robert Douglas |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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