ACI 318-11 Chapter 5 "Class"

[MacGruber22]

What is the intention of the term "class" (of concrete) in chapter 5 (Quality assurance, control, etc.)? It doesn't seem to be properly defined. To me, it seems that it should mean something more than concrete class with respect to exposure in the durability chapter; rather a more general term to describe different groups of mixes with: different aggregate sizes, strength variations greater than 1000 psi, various durability requirements, etc. etc.

My project has a concrete supplier who is fighting submitting data to back up his mix designs and it is causing me a problem not understanding what "class" means in the context of submitting mix design data. We have a number of mixes, but it is tough nitpicking the submittal when I am not confident at this level of detail.



"It is imperative Cunth doesn't get his hands on those codes."

 

[dcarr82775]

My reading has always been a 'class' is a specific mix. Often drawings will call out different mixes for walls, columns, slabs on grade, suspended slabs, etc. Each of those is a class. I have always felt it is independent of 'class' per Chapter 4.

 

[MacGruber22]

Yeah, that was my take on it. Looks like the onerous is on us to define, Which means that our specs should use the term "class" so as to be clear to to the mix designer what he/she is required to submit different test data for.

Specifically, I am arguing that out of these mixes:
1. 4000 psi 1/2 gravel Hambro slab
2. 3000 psi 1/2 gravel stair pan conc.
3. 4000 psi interior slab with 3/4 gravel
4. 3000 psi footing conc with 3/4 gravel
5. 4500 psi exterior flatwork

...I need one set of tests for (1 & 2), (3 & 4), and 5 separately. To me, those are the classes of mixes. The supplier only wants to give data for numbers 3/4, because "he is just a small plant, never did this before, yada yada, yada".









"It is imperative Cunth doesn't get his hands on those codes."

 

[dcarr82775]

I see 5 classes of concrete. Just tell him size doesn't matter.

 

[MacGruber22]

dcarr,

How are you defining class? 5.3.1.1b allows records within 1000 psi

Concrete for background tests to determine sample standard deviation is considered to be "similar" to that required if made with the same general types of ingredients under no more restrictive conditions of control over material quality and production methods than on the proposed Work, and if its specified strength does not deviate more than 1000 psi from theJ~ required [see 5.3.I.I(b)]. A change in the type of concrete or a major increase in the strength level may increase the sample standard deviation. Such a situation might occur with a change in type of aggregate (i.e., from natural aggregate to lightweight aggregate or vice versa) or a change from non-air-entrained concrete to air-entrained concrete. Also, there may be an increase in sample standard deviation when the average strength level is raised by a significant amount, although the increment of increase in sample standard deviation should be somewhat less than directly proportional to the strength increase. When there is reasonable doubt. any estimated sample standard deviation used to calculate the required average strength should always be on the conservative (high) side.

That is how I justify combining the mixes into classes which require separate data. Still too much to them...

Just tell him size doesn't matter.

ha...

"It is imperative Cunth doesn't get his hands on those codes."