Science & Technology in Action

The most commonly used type of cement in Ireland is known as Portland cement; it is the principal ingredient of concrete and mortar. Concrete is made by mixing cement, sand and gravel and water and is the most important material used in the building industry. This versatile material can be preformed into blocks or beams for later use or poured on-site into moulds and allowed to set. 

Portland cement manufacture
Cement manufacture involves the following stages:

1. Crushing and grinding the raw materials: limestone andshale (a batch process).
2. Blending and milling these crushed materials in the correct proportions to produce a powdered material called raw meal (a continuous process).
3. Burning this raw meal in a kiln to produce a product called clinker (a continuous process).
4. Grinding the clinker along with 5% gypsum to produce the final cement.

The main raw materials used in cement manufacture arelimestone and shale. Limestone is a sedimentary rock consisting almost entirely of, CaCO₃, from the shells of molluscs and other invertebrate animals that lived hundreds of millions of years ago. 

Shale is also a sedimentary rock; it is more obviously layered than limestone and is generally easily broken into thin slices or flakes. Its composition is more variable than that of limestone but the following composition is fairly typical: 65% silica (SiO₂), 12%alumina (Al₂O₃), 5% iron III oxide (Fe₂O₃) and variable amounts of other minerals and organic matter. 

Shale forms by compaction of layers of clay or mud over long periods—millions of years. If subjected to high temperature and pressure it can change to slate silo. 

In the manufacture of cement the limestone and shale are extracted separately from local quarries and then crushed and stored.