Sunday, February 24, 2013

Cement nomenclature: a short summary

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]
Chemical formula
Oxide composition
Tricalcium silicate (alite)
Dicalcium silicate (belite)
Tricalcium aluminate
Tetracalcium aluminoferrite

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.