Design Calculation and proportion for the grade above M25 is not available .
You have to design as per your site condition, material properties or different correction factor. You have to go for trial and error process.
Because it varies with material, climatic condition and temperature,etc.
Normally we have two types of mixes .nominal mix which is done by volume and design mix which is done by weight.These mixes have mix ratio till M25 only.Above of the M25 is depends on the type of structures,materials used,climatic condition etc..