Aggregate Size
Aggregate Size
(OP)
We are designing Sequencing Batch Reactor tanks per ACI 350. The clear cover from the (#10@6") main reinforcing to the wall face is 2 inches. We have used aggregate grading #67 (3/4") from ASTM C 33 in the past. We're considering going to a larger size such as #57 (1") or 467 (1-1/2") to reduce shrinkage cracks in the 24 inch thick walls. Our field personnel have expressed concern over placement of a 1-1/2" maximum size aggregate with a 2 inch clear cover. Has anyone had any experience with this?





RE: Aggregate Size
RE: Aggregate Size
RE: Aggregate Size
The situation you describe satisfies the 3/4 cover rule.
There are many situations where the 3/4 cover rule does not apply...and your's is probably one. For instance, use of, #57 (1 inch MSA) for interior structural slabs with a cover of 3/4 inch does not create a problem. However, for thin vertical structural elements, not adhering to the 3/4 cover rule might lead to honeycombing.
LCruiser: The coarse aggregate size number designation comes from ASTM C 33 Table 2. It takes into account MSA and grading characteristics. No 1 is the coarsest with largest MSA and No. 8 is the finest and has the smallest MSA.
Other size designations are a result of combining aggregates with different size numbers. So No. 67 is a combination of No. 6 and the less coarse No. 7 aggregate. This means No. 67 falls in between No. 6 and No. 7 in terms of coarseness. No. 57, a blend of No. 5 and No. 7 and so on.
In Table 2 of ASTM C 33, No. 9 which is a fine aggregate, is included. This is because when it is combined with No. 8, it will produce No. 89 aggregate. See footnote A of the table.
I do not have a copy of ASTM C 125-Terminology Relating to Concrete and Concrete Aggregate...but I do believe it explains the rational behind coarse aggregate size numbers.
Tables 1 and 2 in the link provided below are based on ASTM C 33 Table 2. This should provide an idea of MSA as it relates to coarse aggregate size number.
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RE: Aggregate Size
Dik
RE: Aggregate Size
RE: Aggregate Size
Dik
RE: Aggregate Size
The ready mix suppliers around here prefer Granulated Blast Furnace Slag.
RE: Aggregate Size
Dik
RE: Aggregate Size
There is big difference between proportions containing a #67 and #57. Granted, the majority of all #57 will meet a #67 spec., but its surface area of the rock that matters in this case. Proportion with #67 rock will remain more stable and when using high slump or SCC, the stability factor plays a huge role. Even at lower slumps, say 4"-6", the 67 will consolidate much better, unless the rock is even graded. In that case, you will need to "gap grade" with a finer coarse aggregate material. My suggestion would be a 67, but if you have made your mind up, good luck with the 467. It should work ok, but I would suspect you may end up with a product that will need patching attention.