Concrete consists of the following main components:
- Aggregate and sand
Ordinary Portland Cement (OPC) is made from a combination of chalk, clay and sand heated to 1450°C. The cement is then formed and blended into a powder mix with small quantities of gypsum added. Volcanic ash – generally fly ash, a by product from coal and slag, is also added to cement to increase its chemical resistance. Fly ash and slag ash contain large deposits of silicon dioxide and calcium oxide. Blends of fly ash are generally classified as CEM II cement and blends of slag ash classified as CEM III. Fly ash and slag are by products of other industries and blending these in cement adds to the environmental benefits of cement and concrete. Approximately 43% of the recycled fly ash is used in OPC production.
Generally, 5 – 20 mm quarry stone is used in concrete along with coarse sand which is typically up to a maximum of 5mm.
Water and admixtures are also added. It is vital that water is tightly controlled in order to achieve the correct mix and strength. Admixtures are used to improve strength, durability and workability of concrete depending on the application.
Fibers are often added to concrete to increase strength and structural integrity. Fibers are short and uniformly distributed in a random orientation.
Cold Weather Mixes
With regard to the extreme weather conditions we have encountered over the past few winters, we would remind our customers of the following British Standards (BS 8500) recommendations in respect of concrete mixes for paving of yards and lanes.
- PAV1 (C35N air-entrained concrete for yards and lanes)
- PAV2 (C40N air-entrained concrete for yards and lanes)
- Minimum 50N concrete
PAV1 and PAV2 air-entrained concrete mixes are recommended only where a tamped finish is used. They are not suitable for power-floated or brushed finishes. If a power-floated or brushed finish is to be adopted, then minimum 50N concrete is recommended.
Additional Protective Measures
There are additional protective measures which may be taken to help minimise the effect of frost on concrete. These include:
We recommend that during spells of cold weather de-icing salts are not used on concrete as this will cause damage to the concrete due to the freeze-thaw cycle.