Early-age behavior of calcium aluminate cement systems
Compared to the knowledge base for ordinary portland cement concrete (OPCC), relatively little information exists for calcium aluminate cement concrete (CACC), despite its existence for over 100 years. There is particularly a lack of knowledge related to early-age behavior of CACC, specifically volume change and cracking potential. To assess these early-age properties, two unique pieces of equipment were developed and employed: a rigid cracking frame and free deformation frame which enabled quantification of restrained stress generation and unrestrained autogenous deformation, respectively. These two pieces of equipment employed active temperature control and allowed a wide range of isothermal and realistic temperature conditions to be imposed upon hydrating cementitious samples. Match-cured samples (i.e. identical temperature curing to that in the frames) enabled the quantification of mechanical property development. Samples cured at discrete isothermal temperatures up to 30 °C developed tensile forces in the rigid cracking frame and exhibited shrinkage phenomena in the free deformation frame. At temperatures above 30 °C, the converse was true and significant compressive forces developed in restrained testing and expansion was observed in unrestrained testing. It was found that this was a direct result of microstructural development related to the formation of metastable phases (associated with shrinkage) and stable phases (expansion as a result of conversion from metastable to stable phases). Proper use of this material must take into account behavior associated with both types of hydrate assemblages, metastable and stable. Realistic time-temperature histories were also investigated based on field-scale concrete cast as part of this research project. It was found that volume change at earlyage was dominantly controlled by thermal history. Furthermore, it was not simply the maximum temperature reached, but the rate of temperature rise during hydration and the resulting duration of time spent at high temperature that profoundly influenced volume change and property development. The research described in this dissertation represents a significant advancement of the state-of-knowledge of this unique material and has further elucidated the role of temperature during hydration of CACC.