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Productive Measures

strescon mainStrescon overhauls flagship architectural line

By Don Marsh

Acquisitions and plant investment in the past decade have allowed OSCO Construction Group of Saint John, New Brunswick, to consolidate its role as a heavy civil contractor and leading ready mixed and manufactured-concrete producer in the Canadian Maritimes. Most recently, charter concrete business Strescon Limited has replaced a 40-year-old batch plant at its headquarters architectural precast/prestressed line, also in Saint John.

Even in the face of existing site and facility conditions limiting new equipment and technology options, the result has been a tripling of mix handling productivity, coupled with better cement utilization and much-improved weighing accuracies when measured against the predecessor plant scheme.

The Strescon architectural line rests within an enclosure that has grown to 70,000 sq. ft. since the operation’s 1963 opening. The building spans both architectural and structural product fabrication, with crews on each line placing mixes by crane and bucket or mixer trucks. Architectural crews were accustomed to using the old batch plant for colored mixes and a larger model—dedicated to the structural line and upgraded in 2003 with a twin shaft mixer—for higher-volume gray mix pours.

With two 0.7-yd. mixers, notes Strescon Capital Projects Manager George Lawson, “The old architectural plant had run its course. The equipment was so primitive, we had manual steps to load cement and aggregates. The bosses and I spent about six months looking at new batch plant options, trying to keep apples-to-apples comparisons on equipment and suppliers. I look at a batch plant as an enclosed machine. It makes sense to have a turnkey provider.”

Strescon awarded a single contract to Marcantonini S.R.L. of Italy and Buford, Ga.-based North American representative MCT Supply, Inc. It called for complete material storage, handling and transfer equipment; Sicoma MP-3750 (3.3-cu.yd. output) and MP1500 (1.3-yd.) planetary mixers; short-run, 5-yd. traveling mix bucket; Compumat Automation controls package; MCT reclaimer for aggregate and process water recycling; and, an insulated metal wall panel enclosure.

Most equipment and access structures are galvanized, excepting scales, which are painted. In addition to the insulated building, MCT supplied all lighting, receptacles, and motor controls, and incorporated ½-ton hoists on beams above stations where motors, pulleys, gear boxes and wear plates will need to be accessed for maintenance. As part of the Compumat system, MCT provided interface with Strescon’s Dynamic Color Solutions liquid color and JD Edwards EnterpriseOne accounting systems.

Strescon architectural crews had used a homemade cart to shuttle a mix bucket 20 ft. from undersized-mixers’ discharge gates to crane pick point. Succeeding it is a WiFi-controlled, rail-mounted traveling concrete bucket, shuttling between the mixers and eliminating the need for workers to hook, unhook and “touch down” heavy vessels. During a pouring schedule, the mixers and bucket are automatically washed, with process water dispensed to the reclaimer. It separates coarse and fine aggregates, which are recycled at the Saint John operation, or by sister OSCO concrete or construction businesses. The reclaimer also conveys slurry to a tank from which water is drawn for recycling back into concrete mixes.

The Strescon contract required MCT to negotiate a small exterior/interior footprint for aggregate delivery, storage and transfer. “We had to fit into a limited space because the site is along a river, and also needed to keep the old batch plant running throughout the new plant construction,” says MCT President Michael Jamieson. “Our approach to architectural products plants differs from other suppliers. We use a traveling aggregate weigh hopper instead of a weigh belt. The hopper is better designed to empty itself between loads, thus eliminating potential contamination. For moisture measurement, we have probes in coarse aggregate bins and at metering belts for sand.”

Strescon’s new architectural line batch plant has 375 tons of aggregate storage across 12 heated bins, enabling an array of different materials. Aggregates are weighed in the mobile hopper, controlled through the WiFi-enabled signal, and delivered to mixers by twin skip hoists. The Compumat-controlled scales and a feeder belt exhibit significantly improved weighing accuracy compared to the old equipment, which was prone to over-batching aggregate by 50 to 100 lbs.

Three 85-ton silos store fly ash, plus high early and white cement—the latter formerly dosed by the bag. Powders are screw-conveyed to each mixer’s twin scales, which afford redundancy for differing binders and minimize the amount of screw conveyor expanse in the tight enclosure space. The conveyors typically charge cement to within ½ percent of target. The two mixers allow Strescon to efficiently produce small to large concrete volumes, and limit the instances of using the structural product line’s batch plant for larger pours.

“The quality of mixes from old to the new system is night and day. We set the plasticity coefficient on the Compumat and it repeats batch after batch. Using the old equipment, operators checked consistency by opening mixer access doors,” says George Lawson. “We have cut by two-thirds the old 11- to 12-minute cycle of batching, transporting and pouring mixes and eliminated much worker exposure to mobile vessels that had presented some of our greatest safety challenges.”