Max time for mix

[haojan]

Hi all,

Does anyone know what is the code maximum time between the introduction of mixing water to the cement and aggregate and completion of discharge is? Thank you in advance.


Jan

 

[Taro]

Unless specified otherwise by the purchaser, ASTM C94 requires the concrete to be discharged within 1-1/2 hours or 300 drum revolutions.

 

[Ron]

haojan...this parameter is not code mandated. Taro's comment is on target. Sometimes specifications are silent on this issue, so you are left to refer to "industry standards" as is Taro's reference.

Keep in mind the ambient conditions might well dictate a shorter time period, but longer than 90 minutes is certainly not recommended as you are flirting with the initial set time of the cement.

 

[Qshake]

Good points Taro and Ron. You can't factor out the temperature else you'll have "popcorn" inside the drum and the laborers will scream bloody murder which will cause the driver to want to add water by untold gallons!

Some state specifications for bridge decks allow only 60 minutes with a continuous discharge of 45 minutes.

 

[Abedkayrouz]

AS previously mentioned by all our friends about the maximum time for revolution referring to ASTM C94 is OK.
But you should specify more whether the concrete used contains additives such as retarder and/or superplasticizer reatrder. In this case you should test the compliance of admixture and permissible time for final and initial setting time of concrete with control mix. In addition you may perform trial mixes on site to check whether the addition of admixture affect or delay the setting time of concrete.