111.
111.
Химические и минеральные добавки в цементы и бетоны - Синайко Н.П.
153 
Antifreezing
admixture assists to the decrease of the total volume of pores from 0,12 cm3/g
to 0,03 cm3/g after hardening for 24 hours (Fig. 2,b). Its presence
stabilizes hexagonal hydroaluminate phases and retards the process of their
conversion. The influence of electrolytes upon silicate phases of cement and
calcium hydrosilicates is limited mainly by change of the solution ionic power
and of pH factor of the medium 111. As a result,
the hydration is accelerated on the account of increase of solubility of cement
silicate phases and increase of satiation of solutions.
This initiates
the evolution of constructive processes of formation of microporous structure
of cement stone, which is characterized by less volume of pores. As the
admixture is introduced, the pore volume decrease 4 times, and degree of cement
hydration for 24 hours increases from 47% to 71%.
The behavior of the changes
in the free water content (Fig.2,c) displays that the hydration is the most intensive
during the first 4 hours. After that the process gets stabilized. Under the
influence of the admixture this period is stretched to 6 hours, the rate of the
reaction increases. It is evidenced by the slope of the curvature. After 6
hours of hardening the rate remains stable. 1250 kg, sand - 560 kg, water - 195 1. The
concentration of the admixture made 2% from weight of cement. As the durability
of concrete with the admixture practically twice is visible from the given fig.
4 exceeds its meanings at a control sample in all terms of tests. At
introduction of the admixture the durability raises by three day with 2,7 up to
5 MPa, in 7 days this difference makes 5 MPa, in 14 - 8MPa.
The Table 1 displays that intensive formation of the gel porosity
begins after 6 hours of hydration, which corresponds to the moment of
initiations and development of the C-S-H phase (Fig.3).
It also can be found from the Table 1, that by the end of the 3-rd
day of hardening, the ratio of capillary and gel porosity of the cement stone
with the R2.3 admixture is 53 to 47%. The amount of the formed ice decreases as
well as do the volume of pores and tension of concrete.
The obtained results have been utilized for plotting
characteristic isometric surfaces, which reflect the changes in the amount of
ice during the freezing of the cement stone, enabling in this way the forecast
of the possibility of wintertime concreting.
Thus, the
studying of cement stone structure formation by means of differential scanning
calorimetry enables us to obtain various quantitative information on parameters
of porosity, ice formation and types of water bindings.
In result the
carried out(spent) work has allowed:
1.
To confirm efficiency of the admixture R2.3 as
antifreezing.
2.
To show high информативную ability of a method ДСК for study гидратации of cement and структурообразования цементного of a stone.