uumm, yeah - I'm a concrete guy at the moment. PC = Portland Cement, 32.5 = MPa of force needed to overcome strength [1]. Normal concrete is in the 20 MPa to 50 MPa range and the strength needed is just a design parameter - it's not a quality issue. typically a slab for a house would be at the 20 MPa end and a massive industrial warehouse closer to 30 MPa (something to do with forklift wheels being small and hard), bridge spans etc ask a structural engineer. the fact that China is using a lot of grade 32.5 concrete is more likely due to the fact that they are building a lot of infrastructure that requires... 32.5 MPa strength. NB 'Grade' in the concrete industry refers to compression strength, not a quality statement. Every country has loads of standards about how cement is made, the constituents that can be added and how concrete is batched, delivered, structures designed etc. Cracks and crumbles are more likley due to inadequate design and placement of the fresh concrete. As others say, it's been around for literally 1000s of years but has infinite depth of complexity - i believe MIT found the actual formula for PC around 2010. amazing that we just used it for its bulk properties without knowing the actual chemical formula ;-)

[1] https://www.youtube.com/watch?v=_S-JnRMers8