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Lightweight concrete slump

Lightweight concrete slump

Lightweight concrete slump

(OP)
I am reviewing a mix design for lightweight concrete to be used over metal deck and also as a polished slab. We specified a 3000 psi mix with a max w/c = 0.45 and a slump of 4". The proposed mix design has a w/c = 0.42, but the slump is listed as 8" +/- 2". Is this slump common for lightweight concrete mixes? The 28-day concrete strength from the mix histories look good (5500 psi to 7000 psi).

Thanks!

RE: Lightweight concrete slump

Where I practice (Middle prairies of Canada) we have stopped specifying slump altogether and allow the contractor to specify the required slump for placement. This allows the mix designer to add water reducing admixtures to get where the contractor would like.

We will on some occasions specify slump, however it is rare. If you are specifying everything to do with the mix design, why bother even having a mix design submitted.

We specify required strength, required air, required concrete type (GU or HS etc), the exposure class and the curing type. The mix designer is required to submit a mix that meets the specifications outlined.

RE: Lightweight concrete slump

Your 4" slump is without an admixture I would assume. The only way to get 8" slump with a 0.42 w/c ratio is with an admixture.

8" sounds a little high but I had a 4000psi mix for a metal deck that had 6" slump.

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