Forum Message



Name:   
Heading: 1.1.1.1.1m100 grade concrete
Message:
mix is becoming very sticky , w/c ratio is 0.19 to 0.21,any solution to reduce the stickiness.




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gurdeep singh


Dear Gurdeep ,I can suggest 3 things.

1)Find the strongest superplastizer as possible (compatible to your materials),if it possible 40%water reducer.

2)Use silica fume >10%.The round spheres of silica fume will reduce the stickiness greatly.

3)Use HIGH energy mixer (which is very important).

by the way ,what is the maximum size of your aggregates?
Also pay attention to cap your cylinders with high strength molten sulfur mortar.

Best regards
Spiros

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spiros licoudis


thanks spiros

We are working as suggested ,

MSA is 20 mm,but we found that the aggregate got crushed at stress of 70 to 90 mpa .

we find difficult to reach the target of 120mpa .

We are using cubes instead of cylinders.
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gurdeep singh


Gurdeep,

Your mix is sticky because of all the fines. Adding superplasticizer or silica will only increase the stickiness. Same with the high energy mixer, which shears apart the cement particles.

You don't say what your other criteria are, but you say you are working on a 120 MPa design. Do you have air entrainment in the mix (which I doubt but I have to ask)?

At a 0.20 w/c you are probably not hydrating all the cement. What is your current cement efficiency (MPa/100kg of cementitious)?

Are you using a straight cement? If so, what type? If not, what mineral additives are you blending in?

You neglect to say where the concrete is being produced? Is this the Middle East? The use of dune sand can make the concrete sticky.

Basically, the ways to decrease stickiness are to:

1) Increase the space between the cement particles (i.e. add more water)

2) Use a workability enhancing admixture (like a water softener as opposed to a water reducer).

3) Decrease the amount of fines in the mix. Use less cementitious, use a coarser sand, use more or a larger coarse aggregate. Of course here you run into a problem of potentially not providing enough space for the paste to fill and get an over-pasted mix.

4) Use a ternery or quaternary blend of cementitious materials which can enhance the cementitious particle grading (i.e. it may be better to use a lower quantity of cement with 3% silica fume than to use straight cement with no silica fume).

The final question is, can you produce a non-sticky mix that will produce 120 MPa with the materials you have available. The answer may be "no".

Jay Shilstone
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Jay Shilstone


Gurdeep,

Unless special manufacturing processes are involved, the strength of your paste will occur at maximum paste density, which generally occurs at a w/cm of about 0.27 to 0.29. Trying to produce the concrete at a w/cm of 0.19 or 0.20 may be highly counter-productive. As Jay indicated, excessive fines can be a major cause of the stickiness you are experiencing. Increasing the sand coarseness, if possible, can be highly beneficial for workability. Many of these issues are addressed in my book "High-Strength Concrete; A Practical Guide" (Taylor & Francis pub).

Good luck!
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Michael Caldarone
 
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