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Химические и минеральные добавки в цементы и бетоны - Синайко Н.П.
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moment x of its
development. These modifications are caused by adsorption of the admixture
mainly by hydrated new-formations.
Validity of reviewing of the concept about technological and
thermokinetic characteristics correlation confirms by results of investigation
of effectiveness of the individual and complex chemical admixtures of a system
“Relaxol” action. Its basis is made by the accelerator of concreting (a) -
yield of coke-chemical production, plastifier (p) - lignin sulfonic type and stabilizer (c)
- organic compounds modified by acids. “Relaxol” is be used in a concrete
technology for control of hardening rate and rheological behavior of concrete
mixtures, water- reducing, decrease of freezing temperature of a pore liquid in
winter conditions etc
Kinetics of
hydration of minerals C3A, C3S and portland
cement from Zdolbunov plant (C3S -57%, C2S- 23%, C3A -8%, C4AF- 12%) at the
presence of components of admixtures of a system “Relaxol” are an object of
thermokinetic analysis (TCA). The
concentrations of the admixtures in percentage of cement mass were selected
from the idea of reaching of maximal technological effect and its amplification
in composition of the complex admixtures. The experiments were carried out on a
differential microcalorimeter. Weight of a binders sample was 1 g. Water-solid
ratio for C3S and portland cement -0,5, for C3A - 1,0. Temperature - +30°C.
As follows from
the experimental data (fig. 2), the admixtures essentially do not influence on
character of dependencies dQ/dx=f(x) and Q=f(x), but change values of
thermokinetic indexes.
The hardening
accelerator (concentration 1 %) reduces only one characteristic
- an absolute value of basic exo-effect at hydration C3A - from
153 down to 140 cal/g. The values of completeness of heat evolution in case of
C3S and cement hardening during 24 h increase on 7 and 10%. This
effect is the testimony of reaction deepening by magnification of ionic
strengths because of presence of dissociated ions of electrolyte. The
intensification of hydration of C3S and cement at the presence of
accelerating component of a system confirms by higher values of a main effect,
which is reached in more short periods.
The plastifier
(concentration 0,2 %) for all investigated samples by braking and even
blockings of early stages of hydration is stipulated a significant decrease of
intensity and completeness of heat evolution. So, values of xind at C3S hydration
increase from 1.9 till 4.1 hours, and the hydration heat during 24 h reduces
almost in 4 times. At cement hardening the duration of an induction period
increases from
1.9
till 10.3 h,
and the completeness of heat evolution diminishes form 35.5 till
18.9 cal/g.
The stabilizer
(concentration 0.1 %) to a great extent compensates a decrease of intensity and
completeness of hydration under plastifier influence. On the thermokinetic
dependencies association of binders hydration in its presence come nearer to
control values.