T1-2: Rate and Degree of Hydration Flashcards
What is the procedure of measuring the heat of chemical reactions or physical changes (or for this case, the rate of hydration)
Calorimetry
Describe the rate of hydration graphs
Are hydration reactions exothermic or endothermic?
- There is a dormant period
- The second peak is when the Alite reaction occurs
- There is the formation of ‘secondary’ AFt, followed by the conversion of AFt to AFm
- They are exothermic reactions
What is the cumulative heat (from the hydration reaction) related to?
The amount of cement that is reacted
Describe the phase composition of the cumulation curve
[NAQ] example calculations for estimating the heat evolved at 100% reaction, from the phase composition
Using a heat evolution curve, how would you calculate the (very approximate) degree of hydration for the cement used?
Heat evolved after x hours (100% reaction) from graph / heat evolved (H_t) calculated from phase composition
x100 (%)
Name the five main factors that affect the degree of cement hydration/rate of reaction
- Cement composition
- Particle size distribution
- if bigger particle size, higher surface area, will react quicker - Water:Cement ratio
- Temperature
- higher temp = quicker reaction - Relative humidity of curing
What method can be used to measure directly the amount of unreacted clinker phases in near Portland cements?
Why can this method be used? When is it less useful?
Quantitative X-Ray Diffraction (QXRD)
They can do this as the unreacted clinker phases in near Portland cements are all crystalline
It is of less use when slag or pozzolanic materials are present, because they are largely X-ray amorphous
What method can be used to measure the degree of hydration for calcium hydroxide, and why?
Quantitative X-Ray Diffraction (QXRD)
Because it is crystalline
For calcium hydroxide, what can be used to give an indication of the degree of hydration?
Any property that at a given time is directly related to the amounts of the clinker phases that have reacted
How can the quantity of CH (carbon-hydrogen) in a hydrated cement paste be easily measured?
Thermal analysis
For thermal analysis, how can the amount of CH be calculated?
Ie. describe the three stages
[NAQ] see slides for process of calculating the quantity of calcium hydroxide in the paste from the TG curve
What is the reduction in volume (from the hydration reaction) called?
How can the amount and rate of this process be used?
Chemical shrinkage
The amount and rate of chemical shrinkage can be used to qualitatively determine the degree of hydration of the paste
What technique can be used to measure chemical shrinkage?
Dilatometry
During hydration, what can chemical shrinkage be directly related to, and why?
It can be directly related to the total heat evolved during hydration
The relationship between the cumulative heat liberated and the chemical shrinkage is essentially linear
