Determining Activation Energy - I-Cal Ae - Calmetrix I-Cal 8000 User Manual

Calmetrix I-Cal 8000 User Manual © 2010 - 2012 Calmetrix Inc. – All rights reserved
H. DETERMINING ACTIVATION ENERGY – I-CAL AE (Optional Module)
What is Activation Energy?
The temperature dependency of the hydration rate of portland cement can be described by Arrhenius' law,
with faster hydration the warmer the concrete. See equation (1) where
(1)
k is the rate constant for the reaction, Z is a proportionality constant that varies from one reaction to another.
Ea is the activation energy for the reaction, which in case of most cementitious systems is the so-called
"apparent" activation energy, since several complex chemical reactions may take place during the hardening
process. R is the ideal gas constant in joules per mole Kelvin, and T is the temperature in Kelvin. According
to this equation, a plot of ln k versus 1/T should give a straight line with a slope of - Ea/R. The calculation of
the apparent activation energy is based on the assumption that the overall reaction proceeds along the
same path at different temperatures according to the Arrhenius law. It is assumed that the activation energy
is only dependent on the produced energy (the degree of hydration), and therefore the activation energy can
be evaluated at different degrees oh hydration from the slope of the logarithm of the thermal power vs. the
inverse of the absolute temperature.
How to use the I-Cal AE module.
To utilize the Activation Energy module, you will need to run tests at at least three different temperatures for
any given mix.
CalCommander uses two different methods to determine activation energy: the "S-shaped" method
developed by Anton Schindler and the "Generic" method developed by Lars Wadso. While there is no strict
guideline as to which method is best, in general terms, we recommend use of the "S-shaped" method for
mixes where Portland cement is the predominant cementitious material, and the "Generic" method for very
high substitution levels or geopolymer–type mixes.
23