A new system for recycling returned ready mixed concrete has been developed. The two-component chemical system controls cement hydration first with a stabilizer, then an activator. The stabilizer stops hydration by forming a protective barrier around cementitious particles. The barrier prevents portland cement, fly ash, and granulated slag from achieving initial set. When it's time to use the stabilized concrete, the driver remixes for a few minutes, sprays a measured amount of activator on the concrete surface, and mixes for several minutes more. Additional new concrete is then batched into the truck.
WASHOUT WATER TREATMENT
Using the stabilizer for washout water treatment saves up to 90% of the water normally used. To wash out an 8- or 10-yard truck, the driver adds 30 to 60 gallons of water and 32 to 64 ounces of stabilizer to the drum, mixing for several minutes.
STABILIZATION IMPROVES STRENGTH
Batches containing holdover concrete show a strength improvement over batches of normal concrete. The amount of stabilizer needed to hold concrete for later use depends on several factors: amount of concrete returned; amount of cementitious material; age of the concrete; air and concrete temperature; and duration of desired holding period.