The truck mixer has moved into position on your jobsite and begins discharging concrete. With a quick field test, you determine that the concrete isn't suitable for the intended use. Fortunately, contractors may be able to fix some concrete mixes onsite by using water reducers and other admixtures available in preweighed portions. Packaged in bags, the admixtures can be conveniently tossed into the truck mixer, eliminating spillage and waste.

The manufacturer of these prepackaged products offers water reducers, superplasticizers, set retarders, and air-entraining admixtures that all conform to ASTM C 494, "Standard Specifications for Chemical Admixtures for Concrete." Some concrete producers and contractors keep a selection of these products on hand as a first-aid kit for many types of concrete emergencies.