),

(5.11)

m(τ)

m(max) а + τ

where а – age of loading; τ - age of concrete hardening;

C

– maximally possible creep.

m(max)

After rapid deformation at the beginning of load, deformation of creep

continues at a decreasing rate.

Amount of creep depends on the technological reasons and reasons

characterizing conditions of loading.

98

ep

cre

tivela

Re

days

month

MPa

Relative humidity

Age of the concrete when

Strength of the concrete

loading is applied

when loading is applied

Fig.5.7. Effect of conditions of loading on magnitude of creep

for typical normal-weight concrete

99

5.3. Own deformations. Concrete shrinkage

Own deformations of concrete are caused by moisture, temperature and

other influences on a concrete without applying of the external loading.

The change of concrete humidity can cause decrease or increase in

volume and accordingly deformations of shrinkage or expansion.

Deformations of expansion in cement stone and concrete at hardening

are results of formation of the crystallization stone structure.

The expanding (swelling) of concrete volume occurs during

continuous storage of the specimens in the water.

Deformation of contraction and drying shrinkage are developed due to

processes of concrete hardening.

100

Contraction is the result of reactions

of hydration of chemical cement

g n

compounds with water, therefore

absolute volumes of hydrates less

pandi

Time

than total volumes of initial waterless

Ex

compounds and water which

necessary for hydration.

Contraction shrinkage of concrete in

5...10 times less than drying

shrinkage.

age

Shrinkage of concrete at the

ink

change of humidity develops in two

Shr

stages:

1. when a fresh concrete mixture

has initial plastic consistency

(plastic shrinkage);

Fig. 5.8. Swelling and drying shrinkage of

cement specimens which hardened and

2. at the time of continuing

stored in water and in air with a different

hardening and drying of concrete.

relative humidity

101

Drying shrinkage has the most influence on quality and exploitation of

concrete constructions.

Internal tensions, stresses and cracks can occur due to the shrinkage

deformations. Shrinkage deformation has also a negative effect on frost

resistance and watertightness of concrete.

Amount of shrinkage of cement paste and concrete depends on age of

hardening, composition, specific surface and quantity of cement, quantity

of aggregates, water-cement ratio and other factors.

Some calculating formulas for determination of concrete shrinkage (ε )

shr

Formula

Author

ε

⋅106 0.125W W

,

(5

.12)

shr

=

E.Sherbakov

W-quantity of water, liters per cubic meter

5W / C

ε

⋅106 =

(667 C

(5.