Concrete Products

JAN 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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62 • January 2019 www.concreteproducts.com COVER STORY BY DON MARSH ONE FOR THE AGES The National Ready Mix Mega Plant is built on an L-shaped parcel in an industrial zone along Interstate 10, separating downtown and south-central Los Angeles. It operates alongside truck terminals, dry goods ware- houses, wholesale food distribution facilities, and a metals service center. National Ready Mix and principal plant supplier, DHE Inc. of Tracy, Calif., mapped the Vernon material handling and storage scheme plus tanker, bottom dump and mixer truck routing on the elongated portion of the site, measuring about 200 x 500 ft. "After three or four months, we came up with the design and configuration to match mate- rial storage, variety and flexibility National Ready Mix would need to build and maintain market share," says DHE's Scott Humphrey. "In my experience, this is what we call a legacy batch plant; we see one delivered about every 40 to 50 years. This plant should run for generations." Binder versatility is the order of the day at Vernon. Twin, 545-ton silos for the dual alley plant have are divided into five dif- ferent compartments, three representing 25 percent each, the other two 12.5 per- cent. Shed plates in both silos ease cleaning during material change out. Tankers stage at one of two lanes serving each mixer truck alley, and transfer powder through 5-in. tubes at rates of 25-28 tons in 40-45 minutes. Silos gravity drop material direct- ly into weigh batchers. Vernon site conditions required capping of contaminated soils. That dovetailed crews' elevating much of the plot an average of 5 feet to create aggregate handling infrastruc- ture, mixer-charging alleys with 14 to 15 feet of clearance, and a massive stormwater stor- age vessel below a monolithic, 10-in. thick concrete pavement running to the property lines. Plant construction consumed nearly 10,000 yd. of concrete for pavements, foun- dations and above-ground structures. In contrast to many high volume urban ready mixed operations with central mixed only or dual wet-dry alleys, the Vernon plant is strictly transit mixed. The choice of dry versus wet reflects the type of orders National Ready Mix anticipates; quality control levels proved in sister transit mixed plants; pre- dictability of truck routing, typically 30 minutes, to downtown construction sites; and, the management team's concerns over maintenance, labor and energy costs incurred in central mixed plants. The Vernon site has access only along the 200-ft. front elevation, 26th Street, prompt- ing placement of 60-ft. and 40-ft. gates on the west and east sides of a new two-level office and driver break room building. Trucks enter the larger and exit the smaller gates. Dumps are routed to a three-lane ramp with grizzlies feeding three storage bun- kers. Cement tanker and mixer trucks traffic grade-level pavement paralleling the ramp. Tankers travel a perimeter route around the rear of the plant, and unload at one of four lanes (two east, two west) sandwiching the mixer charging alleys. Returning mixer trucks ribbon leftover concrete on a pad across from a four-section process water weir, with settled water piped to a larger open pit in front. All process water is recycled in plant and fleet operations, or in concrete orders—a widely adopted practice in southern Califor- nia public and private work. The plant equipment footprint above the pavement consumes less than a quarter of the site. Concrete Equipment Co., represented on the West Coast by DHE, had to assemble the structure in two phases due to the size lim- itations of its Blair, Neb., facility. Between Con-E-Co and the DHE shop, plant delivery entailed nearly 100 truckloads, as bins, silos, columns, conveyor supports and smaller com- ponents combined for 800-plus tons. Seismic design detailing and related building code requirements prompted specification of some of the largest steel beams available in the U.S.; most notably, 30-ft. members supporting the largest aggregate bins weigh 285 lbs./foot. Continued on page 64 STOCKPILE SUMMONS Jonel Engineering furnished National Ready Mix Vernon with two Archer Batch systems running the Con-E-Co equipment. Each operates an independent Archer Material Distribution System (MDS), which monitors up to 192 I/O points on a single screen. Material tracking starts with remote operator panels at each of three grizzlies; drivers need only press a start button before unloading sand & gravel. The Archer MDS determines which bunker or bin is empty, positions a shuttle or turnhead, and starts associated conveyors. High-level sensors in each vessel signal the Jonel system to halt material flow by stopping the grizzly conveyor and allowing bunker or bin convey- ors to clear. The shuttle or turnhead automatically positions to the next empty compartment and restarts the grizzly belt. The Archer MDS treats both batch plants' overhead bins as one large collection of storage compart- ments. A high-level sensor provides the MDS each bin's status; when a sand bin is empty, a diverter is automatically positioned and con- veyors are started. Depending on how the user has configured the mapping of ground storage, the appropriate bin gate will open and transfer material. Ground storage materials can be configured to dump from one or more bins simul- taneously; or where two or more bins can be drawn upon cyclically on successive requests from the overhead bins. When an overhead sand bin attains a high level, the ground storage gate will close and the conveyors will run until they clear. Overhead gravel bins operate in the same manner. Overhead specialty material bins utilize a turnhead instead of a diverter; it feeds one of eight compartments, and the Archer MDS is programmed to map a unique material to each one. The system is also able to manage mul- tiple materials on the conveyors by monitoring flow sensors in front of each ground storage gate and spaces materials on the belt based on user-configurable timers. PHOTO: Hugh Hunter for National Ready Mix

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