2. Materials and methods of research
2. Materials and methods of research
Химические и минеральные добавки в цементы и бетоны - Синайко Н.П.
155 
Let's consider
opportunities of decrease of frosty attack from positions of thermodynamics of
the superficial phenomena and theories of phase changes. The size of this
influence is determined by character of heat- mass-transfer from a surface of a
material to the centre and the mechanism of formation of crystals of ice in
pores. Thus the basic role is allocated to porous liquid. The opportunity of
hydration at temperatures lower than 0°C is caused by change of physical
properties of water at its interaction with a surface of particles of cement
and exothermic character. Within the framework of representations about
structure of a cement stone as result of interaction of solid, liquid and
gaseous phases /6/ it is possible to specify the purposes of concreting in this
plan. Anti-freeze admixtures should provide:
■
Decrease of
freezing temperature of mixing water;
■
Decrease of the
water-contents of a concrete mix;
■
Intensification
of concreting of cement and increase of strength of concrete.
Their action,
hence, should have complex character. To number of such
admixtures it is possible to relate the
Ukrainian multicomponent anti-freeze admixture “Relaxol - R-2.3” 111. In the given
work for an estimation of character of its action processes of hydration of
cements, gelations of a cement stone, ice formation at its freezing and
increase of concrete strength in conditions of temperatures lower than 0°C are
investigated.
2.
Materials and methods of research
<>
name=bookmark46>2.1. Admixtures and Cements
The admixture
“Relaxol - R-2.3” represents connection of accelerator + antifreeze (rhodanate
of sodium) and plastifier of lignin sulfonic type. Concentration of the
admixture varies in interval 0,5 - 4 % from weight of cement.
Cement
corresponds CEM 1 32.5R (C3S - 57 %; C2S - 23 %; C3A
- 8 %; C4AF -12 %).
<>
name=bookmark47>2.2. Methods of research
Thermoporometry is a method of an estimation
of the sizes, volume, distribution of pores on the sizes /8/. Dependence of
crystallization temperature of interstitial water on pore sizes is a basis of a
method. This dependence is positioned from a thermodynamic equilibrium of system
“solid matrix - water - ice” in view of a condition of boundary surface and
known equation by Laplas.
Distribution of
pores on the sizes is represented as dv/dR=Definition of
parameters of pores filled with water in a range 1,5... 100 nm is the feature of
thermoporometry that is caused by performance of Kelvin equation.
Gelation of a
cement stone was considered from positions of formation of microporosity.
Anti-freeze action of admixtures was characterized by temperature of an ice
formation Tlce and quantity of ice mice.