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Scientists who study Portland cement have developed their
own special nomenclature to describe the chemistry in their cement. There are probably some out there who think “I
took chemistry, I know chemistry’s symbols and what they mean.” Chemistry’s nomenclature is not always
applicable to Portland cement nomenclature.
First of all, cement refers to any glue. If you just say “cement” you could be
referring to Elmer’s glue, or rubber cement, or “Krazy glue” or any other type
of glue that cements things together.
One must specify Portland cement if one means to talk about Portland
cement. Portland cement refers to a very
specific composition, as I’ll describe and show presently.
The main ingredients that make up Portland cement are
Calcium Oxide, Silicon Oxide, Aluminum Oxide and Iron Oxide. More specifically, the oxidation states of
these metals are as follows: Calcium Oxide (CaO), Silicon Oxide (SiO2),
Aluminum Oxide (Al2O3), and Iron Oxide (Fe2O3).
What is “C” in Portland cement? Someone out there is thinking “Carbon! It’s Carbon!”
No, it is not. “C” represents CaO. What about “S”? Sulfur!
Somebody thinks… no, “S” is SiO2. “A” represents Al2O3,
and “F” represents Fe2O3.
Got that?
Taking this nomenclature one step further, we describe the
minerals as shown in the Table below. [taken from “Connexions; Chemical
Composition of Portland Cement” by Andrew R. Barron]
Mineral
|
Chemical formula
|
Oxide composition
|
Abbreviation
|
Tricalcium silicate (alite)
|
Ca3SiO5
|
3CaO.SiO2
|
C3S
|
Dicalcium silicate (belite)
|
Ca2SiO4
|
2CaO.SiO2
|
C2S
|
Tricalcium aluminate
|
Ca3Al2O4
|
3CaO.Al2O3
|
C3A
|
Tetracalcium aluminoferrite
|
Ca4AlnFe2-nO7
|
4CaO.AlnFe2-nO3
|
C4AF
|
In order to represent Portland cement’s composition, we look
at a phase diagram. In the phase diagram
below, the bottom left corner of the triangle is pure CaO, the bottom right
corner of the triangle is pure Al2O3, and the top corner
of the triangle (not shown) is pure SiO2.
The region of the diagram labeled “6” within this diagram is the composition
of Portland cement. Note that this is
not a specific point, but a region; meaning that the composition of Portland
cement can vary somewhat. [Phase diagram
taken from “Cement and Concrete Research” Volume 41, Issue 3, March 2011,pp.
324-329]
This concludes my brief discussion of Portland cement
nomenclature. My intention is simply to
make people aware that there is an entire field of science that concerns itself
specifically with Portland cement, entire careers have been spent studying
Portland cement, and there are still many unanswered mysteries in the realm of
Portland cement. I was fortunate to
study Cement Science under Dr. Vasantha Amarakoon, Director of the Center for
Advanced Ceramic Technology at Alfred University’s New York State College of
Ceramics. He opened my eyes.
