Foundation (FND) Concrete Grade Guide

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Foundation (FND) Concrete Grade Guide

When it comes to constructing foundations for a property, it’s absolutely critical that soil and ground conditions are carefully considered.

In particular, if sulphates are present in the soil – but this risk isn’t correctly mitigated – this can lead to major disruption to the project. This is because sulphates can undergo a chemical attack against concrete which, over time, can lead to major foundation damage.

This is why, in the UK, construction projects depend on “Foundation” concrete. At iMix Concrete, we can mix concrete for any grade or strength and application.

In this article, we share a complete guide to foundation concrete. Keep reading to find out more about what foundation grade concrete is, what it’s used for, and the differences in foundation concrete grades.

What is foundation concrete?

Foundation concrete is a type of concrete that is specifically designed for use in constructing concrete foundations.

Foundation concrete (also commonly referred to as FND) is a designated concrete, which meets the British standard BS 8500.

This concrete type is invaluable in conditions where the soil has sulphates (or other chemicals that pose a risk to the structure’s stability).

This is because foundation concrete consists of a specific mix ratio. Not only is it extremely strong, but it also contains a minimum level of cementitious content, a unique water to cement ratio, and sulphate-resistant cement.

The result is concrete specially designed to cope with different levels of sulphate contents and soil aggressiveness, ensuring structural integrity and durability for the long term.

What are the grades of foundation concrete?

Foundation concrete is available in three main grades. These are FND2, FND3 and FND4.

Each grade denotes a different design chemical class of soil aggressiveness. The higher the design chemical class is, the higher the content of sulphates, or the greater the chemical attack risk that the soil poses.

So, by choosing the right FND grade for the soil conditions of your project, you will ensure that the concrete has the right level of resistance to the chemicals and sulphates present.

The primary properties of each FND grade are as follows:

FND2

• Suitable for DC-2 soils. These soils have a moderate sulphate risk, and are mildly aggressive.
• The concrete has a strength of ~30 N/mm² at 28 days.
• This type is a dependable “standard” foundation concrete, widely used in domestic and commercial construction projects, with moderately aggressive soil.

FND3

• Suitable for DC-3 soils. These soils have a higher sulphate risk, and present more aggressive environments (typically with a higher sulphate concentration, wetter soil or more reactive soil).
• The concrete has a strength of ~30 N/mm² at 28 days (the same as FND2 concrete).
• This type is ideal for use in conditions where an enhanced sulphate resistance is needed, or where clays or soils have moderate sulphate levels, or are generally more reactive.

FND4

• Suitable for DC-4 soils. These soils are aggressive, with a high sulphate concentration or a high chemical exposure.
• Typically, the concrete has a strength of ~40 N/mm² at 28 days.
• This concrete grade consists of specialist sulphate resistant cements, giving it a fantastic resistance to chemical attacks, and a long predicted lifespan even in harsh soil.
• FND4 is suitable for use in foundations where soils have high sulphate levels, or the sites are exposed to unusual conditions (e.g. industrial land, contaminated sites, or sites near the coast).

Choosing the Right Concrete Grade

When choosing the grade of foundational concrete for your project, ensure you first:

• Conduct a soil test, to gain a chemical analysis of the area. That way, you can ensure your concrete is compatible.
• Ensure that the concrete you choose is in-line with relevant standards and regulatory requirements (including BS 8500).
• Weigh up cost and risk. Higher grades of foundational concrete typically cost more, but give you protection against higher levels of risk. So, these factors need to be weighed up.
• Consider how easy it is to access the foundations or the site, once the project has been completed. If the foundations are buried or access would be very difficult, then it may be worth
• choosing a higher grade of concrete than the minimum that’s required, in order to safe-guard the construction for longer.

By working with a professional concrete supplier, you can ensure the best fit concrete grade is selected for your project.

At iMix Concrete, our expert team of ready mix concrete specialists will supply premium quality concrete, and offer dependable guidance for your specific project.

To order concrete for your project, don’t hesitate to get in touch.