Identification and Quantification of
Components of Portland Cement
ICMA
Denver, CO
May 1, 2006
Charles E. Buchanan Jr
ROAN Industries Inc.
Bakersville, NC 28705
ROAN purchased a Perkin-Elmer, Model DSC 7 Differential Scanning Calorimeter
(DSC) several years ago with the idea in mind of determining the different forms of sulfate
present in Portland cement. Considerable work had been done on a leach test, (1) but that did not
provide information other than the relative proportions of gypsum and plaster of Paris.
DSC differs from Differential Thermal Analysis (DTA) in that differential power, rather
than temperature is measured. An ice bath is provided for cooling while electricity is used for
heat, the transfer of which is precisely measured, in order to maintain a constant temperature on
both the unknown sample as well as the reference. Heat is added or extracted depending on
whether the reaction is exothermic or endothermic.
1
A normal sample size is 10 milligrams (mg), but other sizes can be used. The sample is
placed in an aluminum pan, and that then placed in a platinum sample holder and covered with a
cap with two holes in it so that gases can escape.
Initially we used a sample in an aluminum pan and another aluminum pan with no sample
for balance. This gave us a curve, shown below, which was hard to interpret.
This sample was 0.56 mg of ettringite and you can note that there are three small bumps
at around 80 degrees, 130 degrees and 250 degrees.
In order to improve the curve, a sample of Ottawa sand was obtained, ground to
approximately cement fineness, and heated overnight to 1200 degrees C in order to eliminate any
volatile material. A 10 mg sample of Ottawa sand, is placed in the control pan, and if the sample
used in under ten milligrams, it is brought up to a weight of ten milligrams with the Ottawa sand.
In this manner we obtained nearly equivalent heat loads in the two sample holders. In addition,
we began using background correction and obtained the curve shown below on a similar sample
as above.
2
The y axis is in milliwatts (mW), and the area under the peaks is integrated in millijoules
(mJ). Also the delta H is calculated in Joules/gram (J/g), and the onset and peak in degrees C.
The instrument is calibrated at two points using indium and lead, both of which have very
precise melting points as well as heat transfer when melting.
Initially we attempted to assign a peak temperature to a particular component, but soon
realized that this was futile, as the peak changed with amount present, or the resultant mJ area
values. In order to overcome this, we then developed curves showing peak area versus
temperature. These curves are shown below for the following samples.








Ettringite-Supplied by CTL
Plaster of Paris-Reagent chemical
Gypsum-Reagent chemical
Mono-sulfate-Supplied by CTL
Syngenite-Supplied by CTL
Calcium sulfite-Reaction of calcium carbonate and sulfurous acid
Calcium hydroxide-Reagent chemical
3
Samples were then run at various mass levels using a balanced load of 10 mg in each
sample chamber. The results are shown below for qualitative identification by peak temperature.
Ettringite
225
200
Millijoules
175
150
125
100
75
50
25
0
68
70
72
74
76
78
80
82
84
86
Degrees C
Ettringite2
500
450
400
Millijoules
350
300
250
200
150
100
50
0
125
127
129
131
133
135
137
Degrees C
Ettringite3
250
Millijoules
200
150
100
50
0
254
256
258
260
Degrees C
4
262
264
Plaster of Paris
400
350
Millijoules
300
250
200
150
100
50
0
100
105
110
115
120
125
130
135
Degrees C
Gypsum
1200
milli Joules
1000
800
600
400
200
0
125
130
135
140
145
150
Degrees C
Mono-Sulfate
350
300
Millijoules
250
200
150
100
50
0
255
257
259
261
263
Degrees C
5
265
267
269
Syngenite
250
Millijoules
200
150
100
50
0
290
290.5
291
291.5
292
292.5
293
Degrees C
Calcium Sulfite
80
70
Millijoules
60
50
40
30
20
10
0
395
397
399
401
403
405
Degrees C
Calcium Hydroxide
2000
1800
1600
milli Joules
1400
1200
1000
800
600
400
200
0
420
425
430
435
440
Degrees C
You can note that the peak temperature is a function of area in mJ, or conversely for mg.
As the area goes up, the peak shifts to the right. An overlay of the output is shown in the
following for ettringite.
6
Ettringite-Various Weights
12
10
0.17
0.26
Milliwatts
8
0.55
6
0.98
1.21
4
1.51
2.1
2
0
50
100
150
200
250
300
Degrees C
The table below shows the approximate range of peak temperatures found for each
material.
Component
Ettringite
Ettringite-2
Ettringite-3
Plaster of Paris
Gypsum
Mono Sulfate
Syngenite
Calcium Sulfite
Calcium Hydroxide
Initial
Final
Deta H
Temperature Temperature Milli Joules/ gm
69
125
254
103
126
257
290
396
423
85
136
264
130
148
267
293
405
438
100
220
105
217
567
163
185
41
1264
Consequently, once an unknown is run, it is background corrected and then placed on the
appropriate curve to identify it.
A summary plot is shown below of mJ versus temperature.
7
Compound Identification
MilliJoules
2000
Ettringite
1800
Calcium Sulfite
1600
Gypsum
1400
Mono-Sulfate
1200
Plaster of Paris
Syngenite
1000
Ca(OH)2
800
Linear (Ettringite)
600
Linear (Gypsum)
400
Linear (Plaster of Paris)
200
Linear (Syngenite)
Linear (Mono-Sulfate)
0
0
100
200
300
400
500
Linear (Calcium Sulfite)
Linear (Ca(OH)2)
Degrees C
In the figure below, the mJ scale is reduced to show better precision.
Compound Identification
300
Ettringite
Calcium Sulfite
250
Gypsum
Mono-Sulfate
MilliJoules
200
Plaster of Paris
Syngenite
150
Ca(OH)2
Linear (Ettringite)
100
Linear (Gypsum)
Linear (Plaster of Paris)
50
Linear (Syngenite)
Linear (Mono-Sulfate)
0
0
100
200
300
400
500
Linear (Calcium Sulfite)
Linear (Ca(OH)2)
Degrees C
The next figures show the quantization of the materials tested.
8
Ettringite
2
Milligrams
1.75
1.5
1.25
1
0.75
0.5
0.25
0
0
25
50
75
100
125
150
175
200
225
Millijoules
Plaster of Paris
2
Milligrams
1.5
1
0.5
0
0
50
100
150
200
250
300
350
400
Millijoules
Plaster of Paris
Linear (Plaster of Paris)
Gypsum
2
Milligrams
1.5
1
0.5
0
0
200
400
600
Millijoules
9
800
1000
1200
Mono-Sulfate
1.8
1.6
1.4
Milligrams
1.2
1
0.8
0.6
0.4
0.2
0
0
50
100
150
200
250
300
350
Millijoules
Syngenite
1.8
1.6
1.4
Milligrams
1.2
1
0.8
0.6
0.4
0.2
0
0
50
100
150
200
250
Millijoules
Calcium Sulfite
2.5
Milligrams
2
1.5
1
0.5
0
0
10
20
30
40
Millijoiules
10
50
60
70
80
Calcium Hydroxide
1.8
1.6
1.4
Milligrams
1.2
1
0.8
0.6
0.4
0.2
0
0
500
1000
1500
2000
Millijoules
Based on these curves it is then a simple matter to run an unknown sample of
approximately 10 milligrams, identify the component from the temperature produced, calculate
the area of the peak in millijoules, calculate the milligrams of the component from the regression
line, and then determine the percentage of the component present.
We feel that improvements have been made in the identification and quantification of the
components making up Portland cement, and are comfortable with analyzing for these
substances. Some further areas of research are:


Evaluation of the degradation products of ettringite
Studies on hydration of cements to determine reaction products formed.
(1)
C. E. Buchanan Jr Cement Concrete and Aggregates CCAGDP Vol. 2 Winter 1980
pp84-88 Rapid Determination of the Predominant Form of Calcium Sulfate found in
Portland Cement and its effect on Premature Stiffening.
11