Beach Sand in Concrete

[tclat]

Hi,

I have a contractor who has used some sand for mixing concrete which may have questionable levels for chlorides (sodium chloride). I believe he may have mined some sand from a near by beach. I have taken a sample of sand for testing but would appreciate thoughts on the acceptable levels of chloride in concrete. We have since stopped the contractor but now need to establish the extent of demolition.

Thanks

 

[hokie66]

Any concrete made with beach sand should be rejected. The chloride content will not be consistent, but reinforced concrete made with beach sand is proven by time to be lacking in durability.

 

[Ron]

Site mixed concrete is usually not a good idea unless you have a large quantity, a well-controlled batch plant, qualified personnel and good procedures.

While there is historical evidence that mixing concrete with sea water has less detrimental effect than one would think, that is not particularly so with "beach sand". Chlorides tend to concentrate in the sand (from evaporation), thus increasing the chlorides in the concrete.

I would limit the amount of soluble chlorides to no more than 0.2% of the weight of cement or no more than 1 lb. of chloride per cubic yard of concrete.

 

[ACtrafficengr]

Also, beach sand granules are usually rounded and smooth. Wouldn't that affect bond strength?

 

[MiketheEngineer]

Agree w/ AC - even in Saudi Arabia where they have more sand than camels - they don't use desert sand. It is too rounded and does very poorly in concrete!!

 

[S275]

Did he perform the washing process for the sand before adding it to the mix?

 

[tclat]

The sand was not used for any major elements. The structure is only a single storey and we have established that it was used for filling masonry voids and casting a ring beam over the top of the blockwork.

I don't believe the sand was washed. I'm not overly conerned about bonding since the loads are tiny but I am more concerned about durability. We are several months behind schedule so if the chloride levels are very low say less than 0.1% we may be inclined to accept the concrete with a stern warning about future use of that type of sand. It perphas would get a bit more complicated if the the levels are on the border of what is considered acceptable by ACI.

Thanks for the responses.

 

[Lemony]

PCA Design and Control of Concrete Mixtures states that marine dredged aggregate may be used with caution. It goes on to state that marine aggregates containing large amounts of chloride should not be used in reinforced concrete.

If you are using plain concrete and the strength is okay, you are probably fine.