Lightweight CMU vs Medium weight CMU

[BAGW]

Hi,

I have a question regarding the lightweight vs medium weight CMU. I am looking at the TMS code and I don't see any parameters that differentiate the two types from structural capacities. The compressive strength and the shear strength seems to be the same whether its lightweight vs medium weight. Is this correct?

 

[masonrygeek]

The code is agnostic as to what type of block since it really just comes down to the strength of the unit. The type of aggregate used and its strength will dictate the unit compressive strength. Some lightweight aggregates are weaker and result in a weaker block. In many cases it may depend on how much cement is used in the mix. From a strength standpoint, it doesn't matter which type of block is used (MW, NW or LW), just its strength. Of course you may be choosing a LW unit for other reasons such as fire ratings or sound control. Those design parameters have to balanced with strength requirements.
And don't forget that the minimum f'm is now 2,000 psi and not the old value of 1500. Plus, many block manufacturers make stronger block so you might be able to use a higher f'm.