CONCRETE HARDENING/MIXING & LARGE INSTALLATIONS

by Bob
(Lansing, MI)

Q. I am watching a History Channel show entitled 'Jobsite: Concrete Countdown.' In this episode they tell the story of a concrete truck driver as he makes his way from one borough in New York City to Manhattan for a skyscraper that is being erected (episode was in 2009). The truck driver apparently has 90 minutes before the concrete hardens in his truck from the time the concrete and water are mixed together at the loading site to the off-load point in Manhattan. The drama is created by showing traffic jams which slow the driver and by revealing the driver has two late deliveries in a "three strikes and you’re out" rule. To make matters worse, the "slick line" on the off-loading pump has become plugged. My question is this: Why not add the water to the cement truck (and start the 90 minute time limit before concrete hardening) at the job site. It seems to me this could be incorporated into the operating procedures and the timing of truck deliveries pretty smoothly. I'm sure far more experienced and intelligent individuals have considered this option. Do you know why this is not done? Your consideration is greatly appreciated.

A. It takes about 300 to 350 gallons of water to properly mix a 10 yard load of concrete. (1 truck). That would be way too much water to store at most job sites.

Adding the mixing water at the jobsite would also increase the time the concrete truck is at the jobsite. Mixing 10 yards of dry concrete would take 2 to 3 times longer than if it was mixing while on the way to the site.