I was testing the normal consistency of a CPJ - CEM II/A (the addition used in cement manufacturing is natural pozolan).
The cement past gave a normal consistency for W/C = 0.277.
However, when I started the setting time test, the penetration of the needle made the test block bleeding; and the initial setting time was long.
My first hypothesis is that this bleeding could be due to the high SiO2 content in pozolan.
What do you think.?
Thank you Niloufar for your answer,
Well, I guess indeed I agree with you that the retarding effect should be due to the presence of natural pozzolan.
However, I didn't use any superplasticizer here it was only water.
Normal consistency occurs generally for W/C = 0.25, but it can normally range from 0.24 to 0.28.
So, as for here, personally I don't consider that a W/C = 0.277 as low.
Please indicate which kind of pozzolans you are using. Chemical composition?
May it be the organic content? Did you ascertain the loss on ignition?
The cement can loss its initial characteristics with time, and especially if it has not been well preserved (say in contact with humid environment). Some of the effects are strength losses and delaying in setting time.
I think that you would get more information regarding the cristallography of the pozzolana. XRD?
Well, the used cement here is not old, I bought it on the same day of it's production, and I conserved it in good conditions.
In fact, what I'm really wondering is the bleeding, while I only used water.
I think so too.
Because in the beginning the cement seems to absorbe water, then after a while the bleeding happens with the needle's penetration.
By adding an amount of lime powder, there was no more swelling.
So, indeed it was the natural Pozzolan which caused the swelling.
As mentioned in my previous published works, the binders water absorption is proportional to the C/S ratio.
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