Link to importance of concrete
Concrete has made building what it is today
Make sure you can partly improvise concrete it will help build fortifications and is paramount in the rebuilding of law and order.
Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It usually originates from limestone. It is a fine powder produced by grinding clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time).
Portland cement clinker is made by heating, in a kiln, a mixture of raw materials to a sintering temperature of about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate.
Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Second raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.