Abstract
Quality assurance of concrete consists of two kinds of quality control, production control through specified strength and structural strength control through sealed, saturated or cored specimen. This means three kinds of strength are applied to evaluate the concrete. They are equal to each other on average if certain required conditions are satisfied. But individually they will have some dispersion among them and their strength distributions are not exactly the same. This leads that percent defective expected at a concrete plant is not always maintained to structural strength. New method will be needed, just a check of specified strength is enough to assure the quality of high strength concrete in the structure.
