Three Key Types of Concrete Additives
One of the key things about concrete is that not every type is the same. There are a number of chemical additives which can be used to create a specialist mix – known as admixtures. These normally come in the form of powders or fluids and mean that the concrete can be custom-made for a specific purpose.
Madmix are a leading concrete supplier in Cambridgeshire, with customers across the county and further afield. Here is our guide to the commonest types of chemical additives used in concrete today.
Many concrete buildings used a reinforced admixture, because the building or structure will be expected to cope with a lot of weight. It’s commonly used on farms, as tractors and combine harvesters are a lot heavier than the average vehicle, and in shops and offices where there is a lot of human traffic.
Often the extra strength needed is achieved by inserting steel rods or mesh into the concrete; however, steel can rust or corrode over time, weakening the structure. To avoid this problem, corrosion inhibitors such as sodium nitrite, calcium nitrite, sodium phosphate or sodium or potassium chromate are used. This can either be added as a solution during the concrete mixing process or applied to the surface of the finished structure.
At Madmix, we also offer fibre-reinforced concrete to customers in Ely, Royston and throughout Cambridgeshire and Hertfordshire. This admixture contains polypropylene fibres which are mixed directly with the concrete and add strength to the final product. The type of reinforced concrete will be decided by the project architect or engineer as part of their load-bearing calculations. We can provide either type to your exact specification as required.
The lower the water content of any concrete admixture (also known as the water-cement ratio), the stronger the finished product will be. However, this has the knock-on effect of making the concrete less ‘workable’ and more difficult to pour. These are particular issues when the project is a large one (and so you need the concrete to stay workable for longer) or if the concrete is being poured in bad weather and won’t stay in a workable condition for as long anyway.
One way of ensuring the concrete retains its strength and its workability is to add a plasticiser. In the concrete industry, the commonest type are lignosulfonates, a water-soluble polymer which is a by-product of the paper manufacturing process.
It is also possible to add a ‘superplasticiser’ to the mix; this will decrease the water content even more. However – as with plasticisers – if too much of these are added to the mixture, it can be much harder to achieve a consistent quality of concrete (the problem is known as ‘segregation’) and, over time, it will be more susceptible to shrinkage and cracking.
These also make the concrete more workable and easier to pour. This is particularly useful if the mixture needs to be pumped to its final destination – either because the site is large or inaccessible, or the concrete structure is a multi-storey building.
Air-entraining substances are often used to make concrete more pumpable; these contain small, stable bubbles which effectively act as ‘ball-bearings’ in the mixture, allowing the concrete’s sand particles in particular to circulate more freely, which improves its workability – and pumpability. Many of the pumping agents used in the concrete industry are resins which are by-products of the timber refining industry, although some are now manufactured artificially.
However pumping agents can also reduce the durability of the admixture over time, because they are effectively making the concrete less dense. This means the agents should only be used when absolutely essential.
Admixtures from Madmix, a Concrete Supplier from Cambridgeshire
Whatever type of concrete admixture you need, Madmix should be able to supply it. As well as steel and fibre-reinforced concrete, we also supply waterproof and pumpable concrete for building projects throughout Cambridgeshire and further afield.
We also offer admixtures for domestic customers as well, suitable for floor, paths, driveways and patios. If you are not sure what type you will need, call us on 01954 212212 and we will be happy discuss your requirements. You can also follow this link and fill in the online form.
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