Does a raft slab need a specific concrete strength grade?

Yes — your engineer specifies a particular concrete strength grade (measured in MPa) for your raft slab based on your building’s loads and your site’s soil conditions, not a generic figure applied regardless of project.

Higher strength grades are generally specified for more demanding conditions — heavier loads, more reactive soil requiring more robust performance — while more straightforward sites may need a comparatively standard grade.

This specification is a genuine, verifiable requirement in your engineering documentation, worth confirming your contractor is actually supplying and pouring the correct grade specified for your project.

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