There were provisions to use a fill material for hollow units to increase the fire resistance rating. In past, materials like zonolite (vermiculite) were used and a 6\" filled hollow unit would provide over 4 hours of fire resistance. Due to asbestos issues, vermiculite is no longer used. Is there a similar product that can be used?
The fill material could be a variety of material, The key is what the CMU is manufactured with. If the 6" CMU is manufactured using sand and/or limestone aggregate you cannot reach a 4 hr equivalent rating. What you fill the cores with takes on the rating as the CMU. Full lightweight CMU with cores filled will meet a 4 hr requirement. A proper blend of sand and lightweight with filled cores may meet 4 hrs. The blend will have to be verified by an independent lab. Fill material can be practically anything that is fireproof itself. Perlite, sand, expanded clay aggregate and masonry cell fill (course or fine grout) are possibilities.
The Masonry Society has an excellent book on Fire Resistance of Masonry. Chapter 7 Section 722 covers calculated fire resistance in the IBC. I am attaching a link to the NCMA TEK that covers the same subject.
FIRE RESISTANCE RATINGS OF CONCRETE MASONRY ASSEMBLIES - NCMA
Thank you for contacting the MAF. Our goal is to make sure that when masonry is designed and installed correctly the public has the best wall system available.
Jerry M Painter, FASTM
Jerry Painter, FASTM
Don Beers, PE, GC
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