Allowable amount of Unhydrated Cement Particles???
Allowable amount of Unhydrated Cement Particles???
(OP)
I am currently trying to find out what the allowable amount (percentage) of unhydrated cement particles is acceptable in a concrete mixture. If you can help by specifying what code or reference (any American Code/Reference) specifies this allowable percentage, it would be greatly appreciated.
Thanks,
Kwaz
Thanks,
Kwaz





RE: Allowable amount of Unhydrated Cement Particles???
As a practical matter, a water-cement ratio of about 0.25 to 0.30 is all that's required to hydrate common amounts of cement (in theory); however, many factors control the amount of cement that actually hydrates in a given time. Unhydrated particles can be found in concrete that is years old.
As an example, hydration of enough particles to provide cohesion and develop strength might occur in a few hours, leaving many particles yet to be hydrated. As strength increases (hydration occurs), porosity decreases as the calcium molecules particles bind with water molecules and increase in size. As this occurs, fewer and few particles get hydrated, some of which get isolated by the calcium compound formations (other compounds occur as well and contribute, I am just using calcium as an example because of its abundance in cement).
RE: Allowable amount of Unhydrated Cement Particles???
As the temperature increases the hydration of the cement increases and the HYDRATES (the result of the hydration of the cement) build up faster around the cement grain making it harder for the water to reach the cement or to be more exact harder for the ions to diffuse from the cement grain surface into the water.
Also when the hardened concrete isn't cured probably, much of the water will be lost, stopping the hydration of the cement.
when the fineness of the cement is increased, there is more surface for the hydrates to cumulate making it easier for more grains to achieve full hydration.
Because of the difficulty in measuring the percentage of the unhydrated cement particles, I doubt you will find a spec’s on that in any code.
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RE: Allowable amount of Unhydrated Cement Particles???
Curing moisture and temperature are the primary issues that affect the % of unhydrated cement.
RE: Allowable amount of Unhydrated Cement Particles???
- Chris
RE: Allowable amount of Unhydrated Cement Particles???