Water affecting concrete strength

[unbiased]

I have a project in which the concrete mix was done manually. The strength ahieved was 12N as opposed to 24N after 28days. Could the water used in the mix be the problem (Sulphur contamination)

 

[asixth]

water to cement ratio will have an affect on concrete strength. Was fly ash specified for the batch. Fly ash will delay strength gain of the concrete.

 

[unbiased]

There was no fly ash specified. Just the basic conrete mix. I am trying to trace the reason for the low strength of the cubes taken. The water seems to be the only logical culprit.

 

[Ron]

Please post your mix proportions. Sulfur in the water would not cause that. We make concrete in this area with "sulfur water" on a routine basis.

Also give the concentration of the sulfur, if you know it.

 

[unbiased]

The mix was 1:2:4 and it was used for a suspended floor slab and beam. It was tested using a schmidt hammer and the strength gotten was 12N as opposed to 25N expected.

 

[dik]

Can you take cores and test to determine f'c? As Ron suggested, can you post the actual mix design? including the moisture content of both the sand and aggregate.

Dik

 

[TXStructural]

The Schmidt Hammer is not accurate enough for this kind of test. You need to have cylinders or cores tested.

 

[unbiased]

Thanks everyone. I will get the cubes tested for a more accurate view of what is going on and get back to yourselves.

 

[JedClampett]

When we've had low strength results, it's almost always traceable to some obvious error, like out of date cement, reversing fly ash and cement proportions, etc. Just because a mistake was obvious doesn't mean it can't happen.
When you say the concrete was batched manually, did the workers understand the proportions and were they supervised?

 

[Ron]

Ditto on what TXStructural said....don't use a Schmidt hammer to determine compressive strength!!

Based on the proportions (assuming volumetric) you noted, that would be a difficult mix to work with, assuming reasonable specific gravities of the aggregate (say 2.55 to 2.65). Your water demand would be high and your workability would be compromised. Further, your unit weight would be quite high for a suspended floor slab application. Hope the dead weight is correct in the design!!

 

[JLNJ]

I have an old Hool and Whitney which gives the ultimate compressive strength of 1:2:4 as 2000 psi. Not much to brag about.