No slump concrete
No slump concrete
(OP)
Hello all
I am working on a site where they are using a concrete mix of 1 cement 1.5 sand 3 aggregate and water:cement ratio of 0.4.
The mix is workable enough for columns, slabs etc when vibrated with a poker and the visible quality is good.
It is achieving 20N/mm2 and 24N/mm2 for 3- and 7-day stengths with a target strength of 35N/mm2.
However - when I carry out a slump test there is no slump (see attached photo - I didn't measure the slump as it didn't move at all).
Are the main issues (1) not being workable enough for a particular application, and (2) not having enough water to hydrate the cement.
If so is it acceptable?
Your advice would be greatly appreciated.
Kind regards
I am working on a site where they are using a concrete mix of 1 cement 1.5 sand 3 aggregate and water:cement ratio of 0.4.
The mix is workable enough for columns, slabs etc when vibrated with a poker and the visible quality is good.
It is achieving 20N/mm2 and 24N/mm2 for 3- and 7-day stengths with a target strength of 35N/mm2.
However - when I carry out a slump test there is no slump (see attached photo - I didn't measure the slump as it didn't move at all).
Are the main issues (1) not being workable enough for a particular application, and (2) not having enough water to hydrate the cement.
If so is it acceptable?
Your advice would be greatly appreciated.
Kind regards
RE: No slump concrete
RE: No slump concrete
RE: No slump concrete
RE: No slump concrete
It appears to be working fine for columns. When vibrated it's fluid enough. I've read that a w/c ratio of 0.35 is adeqate to hydrate the cement and I'm concerned that a higher ratio is more risky with regards to the strength. The surface is rough as the ACI note suggests but it is to be screeeded/rendered so it's not an issue.
RE: No slump concrete
RE: No slump concrete
RE: No slump concrete
With that being said, if your aggregates are not temperature/moisture controlled then they could be sucking up a lot of the free water causing your mix to be overly stiff. Are they shoveling the aggregate from large piles that are just sitting out baking in the sun? If your local aggregates are naturally porous, it will make matters worse.
Sounds like you are at about 740 lbs of cement per cubic yard and about 35 gallons of water. Normally, I like to be below 700 lbs of cement for most mixes, but allow some types of mixes to go over as extra paste is typically needed for things such as added fibers or pumping. Since it sounds like you are proportioning mixes by the old 1:1.5:3 methodology, I'm guessing you don't have access to plasticizers?