Readymix Concrete Generally Consists Of:
Portland cement is made from a mixture of finely ground limestone or chalk, clay and sand, which is heated almost to melting point (around 1,450oC) in a large rotating kiln. The cement clinker that emerges is then ground to a powder with a small quantity of gypsum, added to control the setting time of the end product.
Just as the Romans found the benefits of adding volcanic ash to their cement, so the properties of modern cement can be modified and enhanced by blending Portland cement with other cementitious materials. The most widely used of these are fly ash - one of the residues from burning coal - and slag, which is the waste from steelworks.
Blends incorporating fly ash are designated CEM II cements, while those using slag are known as CEM III. As slag and fly ash are by-products of other industries they are a recycled ingredient, which makes blended cement an environmentally friendly product reducing carbon footprint by up to a half.
Based on international research and agreed standards, Readymix uses the appropriate form of cement for each type of mix. This means that not only will you be supplied with the right concrete mix for each application, the concrete will also have good ‘workability’.
Aggregate and sand
The coarse aggregate used in concrete is of a prescribed size - typically 5-20 mm. It is extracted from quarries and from offshore reserves in a sustainable manner. Where practical, recycled concrete may be used as a replacement for primary, quarried aggregate.
A relatively coarse type of sand known as sharp sand is usually used to make concrete. Sharp sand typically has grains in the size 63 micron - 5 mm.
The dangers of adding too much water to concrete are well known. Excess water weakens the finished concrete and therefore the proportion of water to solids in Readymix concrete is always tightly controlled. It can be tempting to increase the amount of water to make the concrete ‘flow’ and find its own level but there are much better ways of achieving this, such as by using a free-flowing and self-levelling concrete designed specially for foundations.
A variety of admixtures are used in concrete to improve handling characteristics and the strength of the concrete when set. For example, a plasticiser may be added to improve workability, reduce water to improve strength and enhance durability.