BS requirement for Gradation of Aggregates for concrete

Question

BS requirement for Gradation of Aggregates for concrete

dgsarath (Materials)

(OP)

22 Aug 13 07:02

As per the BS there are two types of coarse aggregates gradings specified. One is "single sized" and other is "graded"

For Concreting, is it acceptable If coarse aggregate comply only with single sized grading and falls within the "all-in aggregate" limits once it is mixed with sand.

Ron (Structural) · Answer 1 · 2013-08-22 17:43:19

Gap grading is generally not a good idea in concrete mixes.

dgsarath (Materials) · Answer 2 · 2014-02-06 03:41:27

Dear Ron

Thanks for your reply. May be, I have not forwarded my question clearly. If so, I questioned "what sort of action to be taken if the repeated slump is also a "sheared slump?". No action proposed by the BS.

I believe that the shear slump occurs due to less fines, poor grading of aggregates or poor cohesiveness.

Thanks

BigH (Geotechnical) · Answer 3 · 2014-02-06 05:42:41

Neville has a good section on "gap-graded aggregate" (Chapter 3 of his Properties of Concrete book, 4th Edition. He concluded that for pumping, gap grading is not ideal or desirable. Gap-grading can show a propensity for segregation so he would recommend only for mixes of low workability.

I think that the following quote taken from the Chapter is the clincher, though:

"Both gap-graded and continuously graded aggregate can be sued to make good concrete, but in each case the right percentage of fine aggregate has to be chosen. Thus, once again, it can be see that we should not aim at any ideal grading but find the best combination of the available aggregate."

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BS requirement for Gradation of Aggregates for concrete