,

(2.5

)

n c

.

m s

.

m st

.

pores

fm

where W – the water quantity which determined to the necessary workability of

mixture, kg/m3; C, S and St – accordingly quantities of cement, sand and

coarse aggregate, kg/m3; Kn.с, Km.s, Km.st – normal consistency of cement paste

and coefficients of moistening of fine and coarse aggregates; Х = (V/C)p/Kn.d –

relative index of moistening of cement paste in the concrete mixture ((V/C)p –

water-cement ratio of cement paste); Vpores – the water taken in by the pores of

aggregates, kg/m3; Vfm – water which physically and mechanically retained in

pores space between the particles of aggregates (free water), kg/m3.

Approximately simultaneously (at the beginning of 30th of 20

century) and independently from each other V.I. Soroker (Russia)

and F. McMillan (USA) had set the rule of constancy of water

quantity (RCW). It was found that at unchanging water quantity

the change of cement quantity within the limits of 200-400 kg/m3

does not influence substantially on workability of concrete

mixtures.

47

W, kg/m3

C/W

Fig. 2.7. Influence of cement-water ratio (C/W) on water

quantity

1.3 – slump of concrete mixtures: 10, 5, 2 sm.

4.6 –workability (Vebe): 30, 60, 100 sec

The top limit (W/C) of the rule of constancy of water

cr

quantity(RCW) can be calculated by formula:

where Km.s, Km.st –

coefficients of moistening of

+

fine and coarse aggregates;

(W / C) =

+

cr

( 35

,

1

... ,

1 65)

К S К

St

К

m s

.

m st

.

(2.6)