Concrete and cement are very important materials used by the construction industry, and it is often mistakenly believed that the names for them are interchangeable. In fact they are entirely different substances.
Cement is comprised of limestone, calcium, silicon, aluminium, iron and a number of minerals. These materials are heated to a temperature of approximately 1,482°C, thereby creating ‘clinkers’, little spheroids somewhat resembling marbles. These are crushed and ground into a fine powder and gypsum is added, making a product that has the appearance and consistency of flour.
Concrete is comprised of 60-75% aggregate – crushed stones, sand or slag – water and cement. The cement, which is 10-15% of the mixture, glues the aggregate together as a mass which, when water is added, can be poured into moulds to create blocks or slabs.
The setting time is a function of the quantity of gypsum in the mixture, and this can be accelerated by adding calcium chloride or slowed by adding sugar. Other chemicals may be added to prevent splitting and cracking due to freezing and thawing. Concrete is the most ubiquitous man-made building material on earth, no doubt because of its durability.
Hydraulic and non-hydraulic are the basic types of modern cement. Hydraulic cement is by far the more commonly used owing to its quick drying time and versatility. Exposed to water, it hardens quickly in a hydrous chemical reaction independently of its water content. This makes it ideal for building in wet environments, even under water. Non-hydraulic cement is considerably cheaper, but because it is made from substances that do not harden when combined with water it takes a long time to dry and cannot be used in wet conditions.
Cement has been in use as a binding agent for construction materials for thousands of years. Its origins are unclear, but evidence of its use has been discovered in Macedonia long before King Phillip’s time.
It was developed by the Romans, who built roads, aqueducts, houses and such marvellous structures as The Circus Maximus with cement, popularising it throughout their empire. In those days, several kinds of cement were available, mostly made from lime or a volcanic ash known as pozzolana.
The most widely employed variety of cement is Portland cement, which itself has several varieties, the most popular of which is Ordinary Portland Cement (OPC).
As well as its use in concrete it is used to make stucco, mortar and grout. Mostly it is grey, but there is a white Portland cement, which is more expensive owing to the reduction of its iron content to below 0.5%.
Shades of white result from an iron content of around 0.9%, and other tints may be produced by the presence of trace elements. OPC was patented in 1824 by Joseph Aspdin, an English cement manufacturer, who created a process of superheating limestone and clay to create an artificial stone. He named it after the similar Portland stone, quarried on the island of that name which is part of the English county of Dorset. However, Aspdin had predecessors like John Smeaton, who was experimenting with forms of cement for constructing a lighthouse in the 1750s, James Parker, who patented his Roman Cement in 1796, and James Frost, who was making his own British Cement early in the 19th century.
All Mix Concrete are one of the leading suppliers of ready mix and on-site mixed concrete in Manchester, Warrington, Liverpool and the North West, providing competitively priced products and services for all domestic and commercial customers.