Abstract
In this study, the quality contral of high strength reacy-mixed concrete with design compressive strength of 420 kgf/$\textrm{cm}^2$ placed at a tail building for a long period is statistically investigated. The amount of cast-in-place high strength concrete is by about $15000\textrm{m}^3$. The required average compressive striength is 500 kgf/$\textrm{cm}^2$ according to KS F 4009 with assumed coefficient of variation of 11%. Since there are many concrete members in this construction, fly ash is used to reduce the heat of hydration of concrete. As the results of this study, the average actual 28-day compressive strength is 498 kgf/$\textrm{cm}^2$ and the coefficient of variation is 6.7%. The placing speed is comparable to normal strength concrete, however, the pump pressure is higher than that of normal strength concrete.