|Abstract or Summary
- There is renewed interest in North America for the use of calcium aluminate cement (CAC) in infrastructure repair. The interest is driven by the specialty properties that make CAC the ideal candidate for particular applications. These include rapid strength gain, even at temperatures approaching 0°C, the ability to customize fresh property characteristics, high abrasion resistance, and resistance to chemical corrosion. Despite the advantages that CAC can bring to infrastructure repair projects, it is still not well understood within the North American construction community. There are three main topics that are limiting the use of CAC in the construction industry today: (1) a general lack-of-understanding within the construction industry of the conversion process that occurs in CAC systems; (2) there is no standardized accelerated test method for determining the minimum converted strength of CAC concrete; and (3) there are insufficient data on the long-term performance of concrete made with CAC, particularly as a repair material in transportation infrastructure. The work presented in this dissertation addresses these topics in an effort to provide information for and tools for construction professionals interested in using CAC in infrastructure repair situations.
Conversion of the hydration products of concrete where CAC is the only binder is a well-known phenomenon which is accompanied by the formation of porosity and strength loss. Presented in this dissertation is an accelerated test method for determining the converted strength of CAC concrete that is convenient for use in the field. Robustness of this test method is examined. The effects of water to cement materials ratio (w/cm), curing temperature during initial 24 hours after casting, length of time prior to being placed in 50°C water bath, and aggregate source are examined. Results indicated that the test method is viable for use in the field, however writing of a standard based on this method will require careful consideration to take into account impact of temperature impact and aggregate source on time to conversion. Variability of the test method between four laboratories was also examined and showed that variability within CAC systems is higher when compared to ordinary portland cement (OPC) systems. Also presented is a study of the impact of replacing CAC with finely ground limestone (FGLS) at rates of 1%, 2%, 5%, and 10%. These results showed that replacement rates up to 5% can significantly improve the converted strength of CAC concrete without impacting rapid strength gain prior to conversion.
A further examination of the impact of aggregate type on hydration, conversion, and strength development in CAC systems is also presented. Concrete systems made with nine different coarse aggregate sources and six different fine aggregate sources were cast. Carbonate limestone aggregate systems experienced delayed times to conversion and experienced less strength reduction due to conversion compared to siliceous limestone and siliceous river gravel aggregates. Further examination was done to study the pore solution chemistry, porosity, and microstructure of one carbonate limestone and one siliceous river gravel system. These results indicated that the siliceous river gravel system had lower ionic activity within its pore solution at all ages, and had significantly lower pH compared to the carbonate limestone system. Additionally, the siliceous river gravel system formed poor interfacial transition zones and had higher overall porosity compared to the carbonate limestone system. Theories explaining the differences between these two systems are presented.
Finally, an examination of volume stability of CAC systems compared to calcium sulfoaluminate cement (CSA) and OPC systems is presented. Systems based on CAC experienced the highest levels of chemical, autogenous, and drying shrinkage. It was found that the rapid setting nature of CAC and CSA systems caused the pore structures to develop quickly resulting in an increase in the rate of early age shrinkage compared to the OPC system. Additionally, the impact of length of curing on drying shrinkage was examined for CSA and CAC systems. Results showed that length of curing did not impact overall drying shrinkage in either system.