Moderate Sulfate vs. CMU

[davab]

Hi guys,

The geotechnical report is asking to use 4000 psi concrete due to moderate sulfate exposure. I will specify 4000 psi for footings but what about the stem of the CMU retaining wall?

I want to use CMU retaining wall (fully grouted). If so, does CMU block need to be protected from sulfate?

Thank you all in advance. You guys are an amazing group of engineers!

 

[r13]

When it {sulfate] reacts with concrete, it causes the slab to expand, lifting, distorting and cracking as well as applying pressure to surrounding walls which can mean structural movement, significantly weakening the concrete.

As CMU block and mortar both are cementitious materials, what do you think?

 

[HouseBoy]

I'm wondering if this might have more to do with a concrete block product being dry cast vs wet cast.

I have heard recently that dry cast concrete products (like some modular retaining wall products) are susceptible to breakdown in sulfate exposed environments.

I could be way off base with this but.... maybe worth looking into that question for clarification.

 

[JLNJ]

If the sulfate attack is coming from the soil, then it might be worth thinking about if the block will be exposed to the same soil.

If all you want is meet the 4000 psi, then many, if not all, CMU manufacturers can produce this, even for "regular" 8" C90 block.