537 posts
Re: 28 days strength
Calahan/Lalbatros,
Liquid phase should theoretically have a negative correlation with 28d strength because of its indirect relationship to the total silicates (C3S + C2S).
ie The quantity of liquid phase is inversely proportional to the silica ratio which in turn determines the amount of total silicates (C3S + C2S) in the clinker. (Because of this relationship, some plants often increase their S.R. just to improve cement strengths.)
Although C3S hydrates faster, both C3S and C2S contribute to 28d strength, and I suspect to a lesser extent, so does C3A. Because at any point in time, the strength is the sum of the individual strength contributions of each clinker mineral.
In addition, cement strengths are not just dependent on the quantity of each different mineral present. The reactivity of those minerals plays an equal, or possibly even greater role. This reactivity is a function of how the clinker was burned and the concentrations of minor elements incorporated in the clinker minerals, not now much of each mineral is theoretically present according to Bogue.
Regards,
Ted.
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26 posts
re Re: 28 days strength
Actually the PSD also influence on cement strength, especially the 28days right? but how to define it?
537 posts
re Re: 28 days strength
Hello PhanMinh,
Yes, clinker mineralogy and reactivity are only part of the cement strength equation. As you rightly pointed out, the other important factor is cement particle size distribution. The PSD will affect the strength at all ages and therefore will influence both final strength and strength development.
The strength of a cement paste at any particular time after hydration has started is related to the speed at which the cement particles hydrate. Smaller particles hydrate faster and so contribute mostly to early strength. In fact, particles less than about 3 microns react so quickly that they contribute almost exclusively to 1d strength.
On the other end of the scale, particles larger than about 30 microns are too big to fully hydrate, even after 28days, and so do not contribute completely to cement strength. Therefore, the optimum particle size range for maximum 28d strength is 3-30microns. Maximising the proportion of particles in this size range will maximise your 28d strength (for a given clinker mineralogy)
Regards,
Ted.