The mill certificate that comes with your cement is a useful document that is often overlooked. Understanding mill certificate information just requires some basic knowledge of the composition of cement and the terms used to describe it. Among its complex chemistry, portland cement has four principal components, measured by a system developed by R. H. Bogue, and therefore known as the "Bogue Compounds."
Of the four Bogue compounds, tricalcium silicate is the most abundant. It hydrates and hardens quickly, and, consequentially, influences concrete's setting time and early age strength significantly. Dicalcium silicate, the second most abundant compound in portland cement, develops strength more slowly than tricalcium silicate. Most of its strength is contributed after four weeks. Tricalcium aluminate plays a major role in the characteristics of fresh concrete. It starts the hydration process quickly upon exposure to water, and contributes to the very early age strength.
The final Bogue compound, tetracalcium aluminoferrite is primarily a result of materials used in the cement manufacturing process to lower the temperatures required in the kilns. It hydrates rapidly, but contributes little actual strength. Its most significant effect on concrete is its influence on color.
In addition to Bogue compounds, two other values reported on a mill certificate are important to consider. The total alkalies will help determine if the cement may be used with reactive aggregates. Sulfate level can be important in controlling initial and final set time and performance with admixtures.