3. Discussion of results of experiments
3. Discussion of results of experiments
Химические и минеральные добавки в цементы и бетоны - Синайко Н.П.
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Intensity of concreting was
estimated by a method of thermokinetic analysis on size of speed dQ/dr=-f (r) and
completeness Q=f (x) developments of heat /8/. Characteristics of strength were determined
by standard physical-mechanical methods.
3.
Discussion of results of experiments
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name=bookmark49>3.1. Crystallization temperature of a fluid phase
The temperature
of water crystallization and quantity of formed ice are determining parameters
of phase changes of water.
In cement stone of normal
concreting with the admixture decrease of T;ce of porous water
already in 1 day has made 12°C. This tendency is stored further. Gelation at
temperature -5°C proceeds more sluggishly. In 1 day of concreting
crystallization temperature of porous water made -9°C. But already to 3 days
due to formation of fine-crystalline structure of growths and reduction of pore
sizes Tice becomes lower, than at samples of normal concreting. To 8 days this
difference makes already 7°C.
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name=bookmark50>3.2. Character of an ice formation
The equilibrium state of
system “water-ice-admixture” depends according to the Raoult's law on
concentration. As shown on fig. 2, most essentially crystallization temperature
and quantity of ice drop with propagation of concentration up to 2 mass
percents. Its further increase results in minor alterations of crystallization
temperature and quantity of ice that is caused by braking of hydration
processes under influence of SAS.
As shown on
fig. 3, with propagation of concentration speed of an ice formation
monotonously decreases up to a minimum at 2 %. After that intensity again
begins to grow due to interaction of the accelerator with Ca(OH)2
with formation of low- and high basisity connections. Maximal speed of an ice
formation is observed with propagation of concentration from 2 up to 3 %. After
that process is retarded.
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name=bookmark51>3.3. Formation of porous structure
Influence of
the same concentration of the admixture on formation of porous structure of a
cement stone is reflected with the data of fig. 3.
At cement
concreting without admixture one area of distribution of pores on the sizes in
a range 7-120 nm with a maximum at 25 nm is formed. At introduction of the
admixture the fine-pored structure is formed. With propagation of concentration
from 1 up to 2 % the interval of distribution of pores is displaced according
from 7-21 nm to 5-12 nm. Change of pore formation character is caused by
increase of speed of hydration, condensation of structure, and also interaction
of components of the admixture with growths.
Integrated
porosity of a cement stone with propagation of concentration decreases (fig.
3,b). At 1 % the volume of pores drops from 0,245 sm3/g up to 0,239
sm3/g, at 2 % to 0,205 cm3/g. It is interesting, that
with increase of the contents of the admixture due to acceleration of gelation
on the distribution curve on the sizes an area of pores 5-7 nm appears. It is
caused by colmatation before formed pores by more shallow growths and,
accordingly, reduction of their sizes.