,

.2)

1/ m

υ

where m – degree of homogeneity of material, taking into account the

character of defects distributing; A – constant value.

73

Development of structural theory of concrete strength began at the end of

the 19 century after establishment by Feret dependence between strength of

concrete and density of cement paste, modified late by Powers taking into

account the level of cement hydration. The Feret dependence became a

basis for development of Abram's law (rule of water-cement ratio) - the

fundamental dependence used at the calculation (proportioning) of concrete

mixtures.

In accordance with Powers compressive strength (R) of the specimens of a

different age and made at a different water-cement ratio can be calculated

from:

R АХn

=