This paper is compiled into Divisions-I and II. In the former, a theoretical formula is derived for the relation between a mixing ratio of an ordinary solid mixture such as concrete and the breaking strength of it. Prom this derived in the latter is a practical approximate formula for an ordinary and light weight aggregate concrete. The values of breaking strength caluculated from these formulae have proved precisely well agreeable with the values found in tests on either ordinary or light weight aggregate concrete.

The water-cement ratio theory of the testing rule as to the breaking strength of concrete is proved fully explained by this theoretical formula.

* Manuscript received on February 9, 1966.
** Research Member of B.R.I , Ministry of Construction