CONCRETE IS A UNIQUE MULTI-PHASE, RANDOM, complex, and composite material that provides both strength and impermeability to engineered structures. Unlike most construction materials, the properties of concrete continue to develop over time and in place—an aid in processing, but a complication in testing and quality assurance. This is clearly exemplified by the bread-and-butter test of concrete quality compliance, the 28 day compressive strength test. Having to wait 28 days to assure performance compliance is another unique feature of concrete, and not necessarily an attractive one. This holds true both for the field engineer, who would prefer to directly proceed with further aspects of the construction, and the industrial or academic researcher, who would prefer to avoid waiting 28 days (or more) before truly knowing the effects of a new chemical additive or an alternative processing methodology. Thus, many efforts have been made to predict (and ensure) concrete performance based on waiting periods of less than 28 days.