Conewago had a couple hundred cubic yards of concrete on order for gawd awful early in the morning. They asked for a close spacing to get it done quick. They were using 4500lb mix which sets up pretty quickly if your not careful. They neglected to communicate with dispatch to let them know to hold for a while. They had a couple silos that would take a lot longer to do. But instead the said nothing. We ended up with a bunch of trucks sitting on the job for much too long. When the crew poured the concrete out they quickly found themselves fighting to keep ahead of the quickly hardening mix.
Most people think of concrete as “mud”. Mix dirt and water and when it dries you get brick. If it gets too dry when working with it just add water to keep it where you want. This is NOT the case.
Concrete can actually set up under water assuming you keep the water from carrying it off. Basic concrete is a mix of aggregates (stone and sand mostly), water, and hydraulic cement. There are special recipes for more specialized concrete but that is for another story. Hydraulic cement is activated when mixed with water. The cement then begins “glueing” the stone and sand together to form a single solid mass. You can not unactivate the cement or undo the bonding (without ruining the concrete). You can add water to increase the slump or maintain the slump as the bonding process continues but this will permanently damage the cement’s ability to bond the particles together. It’s a case of use it or lose it. As time goes on the concrete will either get harder and stronger or if you add water it will delay getting harder but lose strength until there is nothing left after the process runs it’s course.