Cement performance is governed by four key compounds — C3S, C2S, C3A, and C4AF — whose relative proportions determine strength development, setting time, and durability across every cement type
Understanding Cement Chemistry
Cement chemistry plays a crucial role in determining the properties of cement, with compounds such as C3S, C2S, C3A, and C4AF influencing its strength and durability
Cement is a hydraulic binder, i.e., an inorganic, non-metallic, finely ground substance which, after mixing with water, sets and hardens independently as a result of chemical reactions with the mixing water and, after hardening, it remains its strength and stability even under water. The most important area of application is therefore the production of mortar and concrete, i.e., the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects.
Portland cement is the name given to a cement obtained by intimately mixing together calcareous and argillaceous, or other silica, alumina, and iron oxide bearing materials, burning them at a clinkering temperature, and grinding the resulting clinker. Nevertheless, cement can be considered as being in frozen equilibrium, i.e., the cooled products are assumed to reproduce the equilibrium existing at the clinkering temperature.
Major Compounds in Cement: In all the Portland Cements, there are four major compounds. The variation in percentage composition of compounds influences the properties of cement. These compounds are given in table 1.1 below:
Table 1.1
Composition of cement
Frequently Asked Questions
What is Ordinary Portland Cement (OPC)?
OPC is the most common type of cement used in general concrete construction
What is Portland Pozzolana Cement (PPC)?
PPC contains up to 35% fly ash, allowing for lower concrete water content and maintained ultimate strength
What is Portland Slag Cement (PSC)?
PSC contains up to 70% ground granulated blast furnace slag, with improved durability and strength
Need deeper cement references?
The technical package combines used book copies, manuals, Excel tools, and practical notes into one concentrated reference base valued above $50,000 and offered for $249. Review the technical package here.
Related overview
For a broader introduction, see Types of Cement. For deeper reference material, review the technical package.
Cement Formula — the composition in summary
Cement formula is shorthand for the oxide composition of the Portland clinker. The cement chemical
formula most laboratories work with is expressed in oxide terms:
CaO ~60-67%, SiO2 ~17-25%, Al2O3 ~3-8%, Fe2O3 ~0.5-6%, SO3 ~2-3%, MgO ~1-3%, and the alkalis (Na2O, K2O) below 1%.
In a phrase, the formula of cement is CaO·SiO2·Al2O3·Fe2O3 — the four oxides that form the four
main phases below. The Bogue calculation then converts those oxides into the phase formula: C3S by 4.071 CaO – 7.600
SiO2 – 6.718 Al2O3 – 1.430 Fe2O3 – 2.852 SO3, with C2S, C3A and C4AF following the same family of simple arithmetic
(see the manufacturing formulas article for the full set).
Remember: the chemical formula of cement is not one molecule like H2O; it is an oxide recipe that
varies by brand and class. The table on this page, plus the LSF/SR/AR indexes, is how engineers compare whole plants.