huangyhg

fast setting concrete for elevated floor slabs
does anyone have any experience in the use of calcium aluminate cement or magnesium phosphate concrete for elevated floor slabs. are they appropriate for use in elevated floor slabs in lieu of standard concrete.
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high alumina cements will produce high early strengths. do you really need the strengths that quickly, though? be sure you actually need to strip forms or move quicker than standard concrete will gain its strength (about 70 percent f'c in 7 days). properties of high alumina and magnesium phosphate are not as predictable or as well known as standard type i portland cement. also, you will pay a significant premium for these cements, and availability might not always coincide with your schedule. ready mix suppliers don't usually have means of storage for high quantities of these materials. more often they are using admixtures to achieve similar results in "standard" pcc.
one of my engineers is proposing using this material due to a very tight construction schedule. my concern is using basically a patching material to construct an elevated slab. from what i know about them they have an extremely short placement time and workability is minimal. also, i would think that using that much material would generate large amounts of heat that may tend to crack the concrete. any other thoughts you may have would be appreciated.
i agree with your assessment. i think it would be much more practical to use conventional concrete and adjust to achieve strengths needed early on, even if all you do is go to a higher strength mix. greater workability and much better predictability.
thanks for the feedback.

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