ASTM and Fineness

Dear Experts!

- Please explain to me why ASTM standard is stipulate about air content in cement mortar and in concrete mortar.

- How to reduce the residue of cement on mesh size R045 from 14% to 5%. What is the factor has influence on the residue of cement on mesh size R045.

Thank inadvance,

HongMinh.

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Re: ASTM and Fineness

Hello HongMinh,

1. Air entrainment is necessary for concrete and mortar exposed to regular freezing and thawing environments. The more severe the freezing and thawing events, the higher the air content required to counteract early deterioration of the concrete.

2. There are several factors which influence the +45um residue of cement;-

• Material residence time in the mill
• Size-grading and loading quantity of ball charge
• Material hardness.
• Use of grinding aids.

    With respect to the material residence time in the mill, the main influencing factors are;-

• Feed rate
• Air flow
• Separator/Classifier efficiency (and in the case of a high efficiency separator mill, the speed of the separator)

The easiest waty to reduce the +45um residue in a high efficiency separator mill is to increase the speed of the separator.

Regards,

Ted.

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Re: ASTM and Fineness

Thanks Mr. Ted,

Please open clearly the thesis of "Air entrainment is necessary for concrete and mortar exposed to regular freezing and thawing environments. The more severe the freezing and thawing events, the higher the air content required to counteract early deterioration of the concrete".

In a few days, we have to try to reduce the fineness on R045 by follow your instruction by increase speed of the separator but we have received a little bit change on R045 from 14% to 11% and the Blaine increase from 3900 cm2/g to 4200 cm2/g. We afraid of influenced on the packing plant by higher Blaine.

Follow your opinion we should to increase or reduce the material residence time in the mill? and grit circulation to the mill increase of not?

 Thank inadvance,

HongMinh.

Reply

Re: ASTM and Fineness

Hello HongMinh,

Please see the following link for more information on air entrainment and resistance of concrete to freeze-thaw events;-

http://www.cement.org/tech/cct_dur_freeze-thaw.asp

In answer to your question about reducing +45um residue; it isn't really practical to reduce +45um residue and not increase the surface area of cement. Within a given milling system these two parameters are inversely related.

Reducing your +45um residue by so much (14% down to just 5%) is a big step and is almost certainly going to increase your Blaine significantly.

Regards,

Ted.

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