Precast concrete garage Concrete grade C45/55 C35/45 C30/37

Currently, we are obtaining quotes for prefabricated garages and have come across different concrete grades, ranging from C30/37 to C35/45 to C45/55. With higher concrete grades, the garages naturally become more expensive at the same size, but unfortunately, we are not familiar with the material, so we currently have no idea how to assess the price-performance ratio.

How does the difference between C30/37 and C45/55 affect things in practice? Is the better concrete more durable so that the garage would last 20 years longer? Are there other aspects, e.g., sound insulation or similar? For wall thickness, companies mostly specify 8 cm or "at least 8 cm", while the model with C45/55 is specified with 10-12 cm.

Is the concrete grade a meaningful way to distinguish between providers, or does it ultimately not matter and other factors might be much more important? Many thanks!

PS: The maximum vehicle weight is usually specified as a permissible total weight of 2.5 tons, but our car has a permissible total weight of 3.1 tons. One provider stated "permissible total weight max. 2.5 tons, maximum axle load max. 1.6 tons." According to the axle load, it should be okay again, even if the permissible total weight is significantly exceeded. Is that still acceptable, or, for example, does the base plate then have to be made more stable? Has anyone had this before, can the price be roughly estimated?

Hi,

yes, the price differences between the classes are definitely noticeable. The difference in production between a C30/37 and a C45/55 is enormous.

Basically, higher-quality concretes have a denser structure (fewer pores). However, acoustically this has no significant impact. The dense structure positively affects the protection of the reinforcement, e.g., against CO2 (which is certainly a factor in garages). Nevertheless, the strength class alone is not a criterion; rather, the so-called exposure classes must be correct.

For understanding: a C30/37 is a very common concrete for watertight components in walls and ceilings of underground garages, a C35/45 is already in the premium category and is used in underground garage slabs where greater loads need to be carried, and a C45/55 is rather unusual. Above that there is only C50/60, and beyond that you’re out of the class of normal concretes.

Regarding the question of the floor slab and the load: The manufacturer will probably give you a guarantee for a certain service life. If you now have a car that deviates from the recommendations, there could be a warranty problem.

That already helps me a lot, thank you! The C35/45 garage builder said, when asked about the car, that a strip foundation would no longer be possible, but instead a continuous concrete slab would have to be poured. I am currently looking into the pricing, that will certainly be significantly more expensive than the approximately 4,800 euros offered for a 6x9 meter strip foundation. The interesting one is the C45/55 garage builder who (if I have not read wrongly) wrote that no concrete foundation is necessary at all, but compacted gravel or crushed stone is sufficient. I have to see whether that still applies to a car with a permissible total weight of 3.1 tons, then the additional costs of the garage would be quickly offset by the cheaper foundation.