huangyhg

mass concrete in power plant applications
has anyone used temperature monitoring and cooling methods when pouring major equipment foundations at power plants? i am currently specifying that my 6 to 8 foot thick foundations and tabletops conform to the temperature control/monitoring requirements of aci 207. i have been told that this "is never done for power plants". since pca says >3' is mass concrete and aci 351 says to account for the requirements of aci 207 for major equipment foundations, i am confused as to how this has never been done. any help will be much appreciated.

i have been involved in the construction of several power plants with foundations 6' to 18' thick range. this is in south carolina, so there is plenty of hot weather. we did not need to use any special temperature monitoring or cooling methods.
what we did use in the summer was shaved ice (and lots of it) instead of mix water. on the hottest days there could be 100% ice. placements were scheduled to start in the very early morning hours. concrete temperature of each truck was checked, and accepted/rejected per aci requirements. wet curing was used.
one of these plants has now been operational for well over 20 years - no problems "have come back to haunt us".
working in the arizona desert, we do the same thing. summer high temperatures typically reach 110 degrees f and relative humidity is often 10% or less. concrete pours begin at 6 am and are finished by noon. adding flyash may retard your concrete set somewhat and give you a better product also
i'm also in arizona and worked on power plants (although the concrete was poured by the time i got there) and i've never heard of any cooling measures beyond ice.
i think the main place where cooling becomes critical is in concrete for dams (hoover dam comes to mind) and that volume of mass concrete. the interior poured concrete heat of hydration has no place to go and is further increased by the surrounding pours. but it takes many feet of concrete for this effect builds enough to become a problem.
years ago i cast some 3 meter thick x 5 meter wide compressor foundations in the middle east. we waited till winter to do this and actually shot ourseleves in the foot because the night time temperatures created a differential that cracked the foundations. i have since been informed that the main objective here is to keep the temperature differential between the internal concrete and the exterior surface below 20 degrees c. to accomplish that you can start with chilled water and crushed ice in the mix, but i would also advise using a mix with some fly ash or blast furnace slag (ggbs) to slow down the curing rate and reduce the heat of hydration. we tracked the internal temperatures with thermocouples which reached 60 or 65 degress c as i recall, so you might actually have to provide some insulation around the foundations if your night time temperatures are falling near the 20 degree differential. i am not familiar with aci 207 but companies that manufacture slag or fly ash should be able to provide helpful info on controlling the heat of hydration. if controlling the cracking is extremely critical (as it was with our compressor foundations) you might also consider casting a small mock-up and monitoring the interior and exterior tempratures.
hope this info was helpful
jedclampett - you are right about the dams. when they raised roosevelt dam, they used refrigeration to help keep it cool while it cured.

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