Ultimately, in detail, there are three fundamental stages in the production of Portland cement:

1. Preparation of the Raw Mixture
2. Production of the Clinker
3. Preparation of the Cement

Preparation of the Raw Mixture

The raw materials for Portland cement production are a mixture of minerals containing calcium oxide, silicon oxide, aluminum oxide, ferric oxide, and magnesium oxide. The individual raw materials are first crushed, typically to below 50 mm. Some or all of the raw materials are then roughly blended in a "prehomogenization pile". The raw materials are next ground together in a raw mill. Silos of individual raw materials are arranged over the feed conveyor belt. Accurately controlled proportions of each material are delivered onto the belt by weigh-feeders. Passing into the raw mill, the mixture is ground to raw mix. The fineness of raw mix is specified in terms of the size of the largest particles, and is usually controlled so that there is less than 5-15% by mass of particles exceeding 90 μm in diameter. It is important that the raw mix contains no large particles in order to complete the chemical reactions in the kiln, and to ensure the mix is chemically homogenous. In the case of a dry process, the raw mill also dries the raw materials, usually by passing hot exhaust gases from the kiln through the mill, so that the raw mix emerges as a fine powder. This is conveyed to the blending system by conveyor belt or by a powder pump.

The raw mix is formulated to a very tight chemical specification. Typically, the content of individual components in the raw mix must be controlled within 0.1% or better. Calcium and silicon are present in order to form the strength-producing calcium silicates. Aluminum and iron are used in order to produce liquid in the kiln burning zone. The liquid acts as a solvent for the silicate-forming reactions, and allows these to occur at an economically feasible temperature. Insufficient aluminum and iron lead to difficult burning of the clinker, while excessive amounts lead to low strength due to dilution of the silicates by aluminates and ferrites. In practice, the raw mix is controlled by frequent analysis. The analysis data is used to make automatic adjustments to raw material feed rates. Remaining chemical variation is minimized by passing the raw mix through a blending system that homogenizes up to a day's supply of raw mix.

Preparation of the Clinker

After its creation is completed, the raw mixture is heated in a cement kiln, which is a slowly rotating and sloped cylinder. Temperatures in the kiln increase over the length of the cylinder and reach a peak temperature of 1400-1450 °C. A complex succession of chemical reactions take place as the temperature rises. The peak temperature is regulated so that the final product contains sintered but not fused lumps. Sintering consists of the melting of 25-30% of the mass of the material. The resulting liquid draws the remaining solid particles together by surface tension, and acts as a solvent for the final chemical reaction in which alite is formed. The resulting material that emerges from the entire process is called clinker. On cooling, it is conveyed to storage, and will be a key raw material for the production of cement in the next stage of the process.

Preparation of the Cement

In the final stage of the cement production process, clinker is mixed with other materials, and ground and processed until it forms cement. In order to achieve the desired setting qualities in the finished cement product, a quantity of calcium sulfate, roughly reaching 5% of the total materials in the process, as well as gypsum or anhydrite are added to the clinker. The mixture is then finely ground to form the finished cement powder. This is achieved in a cement mill. The grinding process is controlled to obtain a powder with a broad particle size range, in which typically 15% by mass consists of particles below 5 μm diameter, and 5% of particles above 45 μm. The rate of initial reaction of the cement on addition of water is directly proportional to the specific surface. The cement is conveyed by belt to a silo for storage and can be delivered to end users in bags as well as by truck.