Halifax quarry on the spot for Stevens
concrete business

By Andy Bateman, Engineering Editor

The operations new 37x49 Nordberg C125 primary jaw crusher has significantly reduced production delays caused by oversize feed rock.

Located 10 km NW of Halifax city centre, the main quarry operation of the Stevens Group is ideally placed to supply the company's area ready-mix concrete plants and construction projects as well as the local aggregate market.
     Gateway Materials Ltd. began production in the late 1960's and now extends over 200 acres. Two distinct types of rock, blue quartzite and granite, are quarried here, with current annual production of 500 000 tonnes split about 80 per cent quartzite and 20 per cent granite. The properties of the crushed granite make it an excellent source of concrete aggregate, as it has good particle shape, is nonÆreactive and has low absorption. Quartzite products include granular road base, together with material for residential and commercial applications.

The sandvik S4000 gyratory secondary crusher (left) and Sandvik H4000 Hydrocone tertiary crusher are mounted on the same plat platform and share a common product belt.

     Drilling and blasting practices at this operation reflect the proximity of neighbours, with a recent residential development close to the active quarry faces. The 15 m high seamy granite face is drilled in-house, utilising a Svedala Reedrill 402 hydraulic rig sinking 102 mm diameter blast holes on a 2.44 m by 2.44 m pattern. A typical shot contains 48 holes, in four rows of 12 holes each, for a yield of about 10 000 tonnes. After drilling, the holes are charged with a Dyno Nobel emulsion mixture, with blasts completed on a weekly basis except during the December to March winter shutdown.
     A Caterpillar 345 excavator completes primary loading duty, with two Caterpillar 769C haul trucks delivering shot rock to the quarry's production spread. This spread, new last year, has an unusually small footprint for one that incorporates three crushing stages and two full size screens. In a configuration not often seen, both secondary and tertiary crushers are mounted on the same platform and share a common product belt that conveys all crushed material to the spread's twin horizontal screen. A rinsing screen, intermediate surge/feed bin, control trailer and just six product stackers complete this tight setup.

An Eriez Magnetics magnet mounted over the reclaim tunnel conveyor belt recovers any tramp metal in the feed.    

    The new primary crusher is a 37x49 Nordberg C125 jaw that replaces a 32x42 unit. Stevens Group co-owner Scott Stevens notes that the increase in crusher size has significantly reduced delays caused by oversize, with any occasional oversize now dealt with by an excavator-mounted breaker. Product from the jaw is conveyed to a 400 tonne live capacity surge pile, where it is recovered by two 36x60 Jeffery HP 310 feeders in the surge pile's reclaim tunnel. From there, material is conveyed to the secondary system, with an Eriez Magnetics magnet mounted over the tunnel belt to recover any tramp metal. All the material then passes through a Sandvik S4000 gyratory secondary crusher before being conveyed to twin Simplicity 6x20 triple deck horizontal screens. Oversize from the screening operation is returned, via the intermediate surge/feed bin, to a Sandvik H4000 Hydrocone tertiary crusher mounted alongside the S4000.
     Stevens reports that the spread's production rate is up to 400 tonnes/h when set up for concrete aggregate production. Within this total, the yield of 20 mm x 5 mm concrete aggregate is about 120 tonnes, together with 25 tonnes of 25 mm clear size, 175 tonnes of 19 mm minus road base and 80 tonnes of 5 mm minus screenings.
     Another recent innovation at this operation is the electronic transfer of all sales information from the quarry scalehouse into the company's accounting systems. When loaded trucks pull onto one of the operation's two Weigh-tronix scales, all necessary customer and product information is recorded utilising Command Data's Command Aggregate Software. Once this information has been captured electronically, the data is fed through interfaces to the company's accounting software, enabling sales, invoicing and accounts receivable functions to be completed with a minimum of paper.

Corporate overview
    The Stevens Group is a vertically integrated construction materials and contracting business based in Dartmouth, Nova Scotia. The company's interests include two aggregate operations and the Quality Concrete division that operates 70 trucks from nine ready-mix concrete plants across Nova Scotia and New Brunswick.
     Activities of B.D. Stevens Ltd., the contracting side of the business, include general contracting, project management and design/build construction with a focus on Tilt-Up construction. Sister company Citadel Contractors Inc. is a Raleigh, North Carolina-based Tilt-Up contractor.
     Other group interests include a door and frame business, nursing home and several commercial and residential properties.

September/October 2002 issue

Aggregates and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca

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