In the Mojave Desert, Victorville, Calif.-based Service Rock Products delivers concrete as far away as 150 miles, or 3 hours, from its plant in Barstow, Calif. Out here the company faces extreme material and delivery conditions. Besides batching up to 20% of loads with stabilizing admixtures, Service Rock Products occasionally supplies helicopter pours in areas trucks can't reach. Moreover, Service Rock Products has created an operation and a united effort toward achieving quality control in extreme conditions.
In 1994, Fortin teamed with Bob Kelley and Marc Robert, who respectively oversee operations and quality control for three concrete plants, to summarize in a memo everything they had learned about hot-weather concrete production:
- Reducing coarse aggregate and sand temperature has the greatest impact on the temperature of most mixes.
- To reduce coarse-aggregate temperature to below that of the dry climate, sprinkling of the loadout face of a stockpile occurs at a rate slightly above the evaporation rate, and the maximum stockpile surface area is exposed to the air. The hot, dry, windy climate, while problematic for any finisher, actually aids evaporative cooling of coarse aggregate piles.
- Wheel-loader operators draw from rock piles and sand piles with different techniques. Surface rock has the best chance to cool via evaporation. Sand, in contrast, traps moisture, and moisture content impacts the temperature of below-surface sand to a much greater degree.
- The target loadout temperature for concrete is 10° F below that of the specified delivered temperature. A couple of variables that can reduce chilled water content are low slump and wet aggregate.
- Using ice and chilled water can reduce concrete temperature by as much as 12° to 14° F
The operation has an ice-processing system consisting of a refrigerated railcar, a chute, a conveyor, and a high-speed ice shaver. "A block goes from the chute to the shaver, which turns it into snow-cone material in about 3 seconds," says Vince Bommarito, Barstow area manager. "Then the shavings go to the conveyor for loading." The total cycle time for one block is about 30 seconds. Recently the company added a second silo to cool cement. The operation also uses first-in, first-out cement inventorying, drawing from the silo that has stored cement the longest, to maximize cooling time.