What is cement and how is it made?
Cement is comprised of carefully calculated amounts of calcium, silica, aluminium, and iron, which are mixed in controlled proportions and heated to extreme temperatures to create clinker. This material is ground into a fine powder to produce cement. The process gives it hydraulic properties, enabling it to bind sand and gravel together to form concrete.
Types of cement
There are various types of cement used in the construction industry. The material composition and properties vary between each type of cement depending on its intended use. During manufacture, additives are introduced to alter things like strength, curing time, colour, and chemical resistance.
The difference between cement and concrete
Cement is one of the ingredients used in the creation of concrete. Concrete is comprised of aggregates and cement paste. The paste is created by adding water to cement, and aggregates are made up of sand or crushed stone. Together, these materials harden to form the rock-like mass that we know as concrete.
Cement products are generally categorised by strength, ranging from 35.5, 42.5 and 52.5, with the higher number indicating a higher strength. The strength class is determined by standard tests conducted at either two or seven days, and again at 28 days. The strength class is usually followed by the letters ‘N’ or ‘R’, with the former indicating normal strength, and the latter indicating rapid strength gain.
How long does cement take to dry?
Most cement will set within 24 to 48 hours. At 7 days, the curing process will reach partial completion. During this phase, it is essential to keep the cement free from heavy loads. Construction can continue thereafter. Most cement mixes will be fully cured at 28 days, where maximum strength is reached.
Shelf life and storage
Cement has a shelf life of approximately 6 months inland, and 3 months on the coast. However, this can be affected by storage conditions. Cement should be stored in a dry and moisture-proof area. The bags should be stored about 20cm off the floor, on wooden pallets, in an area with as few windows as practically possible.
It is essential to exercise proper precautions when working with cement. Due to its alkaline nature, cement can cause irritation and burns when it comes into contact with skin. The fine powder of cement can also cause damage to eyes and lungs. Thus, the necessary protective equipment is required. This includes eye protection, gloves, safety footwear, and protective clothing.