Q.: We would like to find a material that sets and hardens rapidly that we can use for repairing concrete in city streets and bridges without disrupting traffic any longer than absolutely necessary. We would prefer that this not be an epoxy or other organic material because we are concerned that differences in thermal expansion and contraction might eventually cause problems.

A.: You could consider a magnesium phosphate cement. Such a cement is used in the same manner as portland cement, though the concrete requires less mixing water, hardens rapidly, requires no moist curing and can be put in service within about an hour at ordinary temperatures. It can also be used for making patches at such temperatures as 10 degrees F when necessary. The cost is probably closer to that of epoxy concrete than that of portland cement concrete.