We are bidding a job where the project engineer is requiring a 2500 psi block to meet an f'm of 1500 psi. We know that the new code allows a 2000 psi block to have an f'm of 2000 psi. What can we do?
Lets be clear, the project engineering can call for any strength block they desire - as long as it is called out in the project specs that are bid with the job. So if your project specs call for a 2500 psi individual block strength and an f'm of 1500 the 2500 wins and that is what you need to supply to the job.
On the other hand, if the specs ONLY call out for a masonry unit that meets 2000 psi f'm they MUST accept the current code and accept a 2000 psi individual unit strength. Requiring a higher strength unit than is required by the code, and not called out in the bid documents, would constitute a change to the project.
What strength do I need on my individual block to attain an f'm=2500 psi?
Under the FBC-Building 5th Edition you required an individual block strength of 3750psi to attain an f'm=2500. Under the new 6th Edition Florida Code you only need a strength of 3250 psi. The change is in Table 2 in TMS 602-16. The strength of masonry was increased by about 35% from the TMS 602-11 which was the Masonry Standard referenced in the 5th Ed FBC-Building.
Links to additional information:
Don Beers, PE, GC
Jerry Painter, FASTM