What is the contractor's responsibility in specifying the strength of concrete? For example, would 2,500 PSI High Strength achieve the wind loads and 20ft wall heights? Or would 3,000 PSI CMU be needed for 20’ walls grouted 8” o.c.?
That is why you hire a structural engineer! It depends... on the location, height of the wall section, vertical load, fixity of end conditions, openings, lateral support, etc. You're not designing the wall section, simply offering advice on the availability and cost of materials along with potential problems with the use of various materials. Without designing the wall section myself - which would include understanding the entire structure that the wall is a part of - it isn't possible to challenge or advise him on the design.
Don Beers, PE, GC