You helped me earlier with a spec sheet for our 8in block. It shows meeting the C90 spec, but do you have one showing the block meet the C129 spec also? This is for a project on a local military base. They are requesting the same specs for the following products, 8in part, 8in halves, lintels, bond beams, and jambs. They are also specifying a block strength of 2800 psi. Is this something you could help me with?
he C129 spec is a less restrictive version of the C90 spec. Any unit meeting the C90 spec will also meet the C129 spec. Additionally, the individual block strength of 2800psi is a pretty much meaningless number. In editions of the TMS 602 prior to the 2013 edition the 2800psi block strength gave you an f'm=2000psi. In editions of the TMS 602-13 the required strength of block to achieve f'm=2000 reduced to 2000psi (one to one). A block with a strength of 3250psi now yields an f'm=2500psi - which is now the new high strength block. A standard block (every C90 block) is now an f'm=2000psi. The required individual block strength for C90 has increased from 1900psi to 2000psi which, again, yields an f'm=2000psi. Specifying an individual block strength of 2800psi means that the specifier is looking at the OLD code. This is explained again in the blog below. Good luck with your project! Call if you have questions. The specifier is welcome to call me also.
Detailed Question: We have had several jobs recently specifying “high Strength Block”. Some has listed 2500 psi another I believe was 2800. Looking at C90 it seems to be open to interpretation and maybe job specific? We have a HS block but just trying to make sure we are fine. Is there a specified strength for this classification?
Detailed Answer: There are generally two block strengths that are readily available to the structural designer. For the sake of simplicity I will call them ""normal"" and ""high"" strength. The strengths have changed dramatically since January 1st, 2018. The new strength values for masonry come from either the 2013 or the 2016 edition of the TMS 602 specifications section 1.4B.2.b.Table 2. The Florida Building Code, 6th Edition, references the 2016 TMS 602 but the strength values are the same in both editions (and will be in future editions).
The compressive strength of an individual block of ""normal"" strength is 2000 psi which can be used to build a wall with an f'm=2000 psi.
An individual ""high"" strength block would have a compressive strength of 3,250 psi and would result in a wall with an f'm=2500 psi. This ""high"" strength block is stocked on some yards but is readily available on demand from most manufactures with minimal delay and only a slight increase in cost.
Walls designed with an f'm=2750 psi require that the individual block unit has a compressive strength of 3900 psi. These block are available from manufactures throughout Florida but are going to result in longer lead times (because they are almost never stocked). You can expect significant additional cost and longer holding times after manufacture to make sure they will achieve the required strength.
I would not recommend specifying masonry with a compressive strength f'm=3000psi. This strength requires an individual block with a strength of 4500 psi. This strength is closing on the natural limit of masonry produced with Florida aggregate. If you require a masonry unit of this strength consult with your block supplier on cost and availability. You will most like find that you are going to be better off specifying a "normal" strength 12" wide unit which is available off the shelf everywhere.
Jerry Painter, FASTM
Don Beers, PE, GC