,

(4

.3)

where X-ratio between volume of cement hydrate gel and the sum of

volumes of cement gel and capillary space; A-coefficient characterizing

strength of cement gel; n-constant (from 2.6 to 3).

The parameter Х can be considered as a relative density of cement paste

(stone).

74

a P

, M

cmpR

Middle radius of pores (r⋅10-10 m)

Fig. 4.2. Relationship between compressive

strength (Rcmp) and middle size of pores of

cement paste (stone)

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The condition of development of crack in concrete can be determined from

Griffith and Orovan formula:

σ = Еν / d = kd 1

− / 2 , (4

.4)

ср

ср

where σ-tensile stress; E-modulus of elasticity; ν-effective energy of

destruction; d - average size of a crystal;

as

k = (Eν)−1/ 2 - coefficient of viscidity of destruction.

Strength of concrete depends on deformations arising up at loading.

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Rc.s, MPa

dср

as , 10-6m

Fig. 4.3. Relationship of strength of the cement

stone Rc.s and average size of crystals das

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4.2. Law (rule) of water-cement ratio

The fundamental works of Feret, Abrams, Bolomey and other researchers

determined wide application in practical technology of the water-cement

(W/C) law (rule) and based on it computation formulas.

After processing results more than 50 thousand tests, Abrams offered a

formula:

k

R =