The addition of a new secondary cone crusher to its portable aggregate plant is helping give the City of Calgary the increased flexibility it needs to produce a broad range of premium quality product including Superpave and Stone Mastic Asphalt (SMA) aggregates.

The City of Calgary has a long and proud history in the Canadian aggregates industry. The city has been crushing and screening gravel for its roads and streets since the turn of the last century. It has also been producing hot mix asphalt since the 1920s.

In spring 2001, a 60in Clemro XC1600 cone crusher with remote adjust capability and hydraulic tramp iron clearing, was installed in the cityowned and operated portable crushing and screening setup at the its Spy Hill pit, replacing a 30yearold, 66in cone. According to plant foreman, Dean Hedley, the existing cone was becoming increasingly costly to operate and maintain. Aggregate product quality and operating reliability were the key factors in purchasing the new cone. Hedley says the city developed design criteria for the secondary crusher and sent out bid packages based on these requirements.

This year the city will produce 490 000 tonnes of processed materials in 13 product gradations, ranging from pipe bedding  sand for its sewer and water projects to 32 mm drainage rock. Approximately 140 000 tonnes of this year’s total output will consist of 25 mm clear, 16 mm clear, 9.5 mm crushed and 4.75 mm manufactured sand for the asphalt operations. Other major quantities of spec products scheduled for this year include 60 000 tonnes of 20 mm road gravel, 50 000 tonnes of bedding sand, 45 000 tonnes of 2050 mm drainage rock, 40 000 tonnes of 9.5 to 19 mm pea gravel and 25 000 tonnes of 9.5 mm sanding chips for snow and ice controls on city roads, streets and sidewalks.

Spy Hill pit

For the past 10 years, the Spy Hill pit in northwest Calgary has been supplying the bulk of the city aggregate requirements. The 320acre, cityowned pit contains sufficient reserves for at least the next 40 years at current rates of extraction. The pit   shares the 640acre property with the city’s solid wastelandfill operation. Approximately 10 acres of the pit is actively mined each year to produce roughly 500 000 tonnes of finished products.

The deposit is covered with 6 m to 10 m of overburden, most of which is clay. The city contracts out the stripping operations on a yearly basis. Last year, Calgary based Top Notch Construction used a fleet of motor scrapers, excavators, dozers and off highway trucks to load and haul more than 100 000 m 3 of overburden. Most of the excavated clay is used to build containment cells for the solidwaste landfill site. The deposit, approximately 70 per cent gravel and 30 per cent sand, is extremely dense and abrasive. In addition to being abrasive, the deposit contains naturally cemented lenses with compressive strengths of up to 50,000 psi. These conditions make it impossible for a wheel loader to dig material out of the undisturbed bank. Kidco Construction of Calgary holds the contract to rip and doze the deposit in a production operation aimed at one hour of ripping/dozing for 1.5 hours or more of crushing. To carry out the work, Kidco employs a singleshank Caterpillar D10 dozer and a Caterpillar 245B excavator with a 2.3 m 3 front shovel attachment.

Hedley says some areas of the deposit can wear out a ripper tooth in four hours. The face is being worked to a maximum height of 30 m on a 3:1 slope using a 4.6 m 3 Cat 980G loader. At peak production, the loader averages 350 to 400 tonnes/h. In addition to the new cone crusher, the portable plant consists of a 1066 mm Clemro heavyduty, lowprofile belt feeder, a 7x20 Clemro doubledeck scalping screen, a Pioneer 2036 jaw crusher and a 7x20 Clemro tripledeck inclined screen which works in closedcircuit with the XC1600 cone. The cone is currently driven by twin 200 hp WEG electric motors and could also be driven by twin 250 hp motors if required.

A second portable setup comprises a 7x20 Clemro tripledeck inclined screen teamed with a Barmac Mark III impactor fitted with an 838 mm diameter rotor. This plant is used on an "as needed" basis to produce 9.5 mm crush or 9.5 mm sanding chips. If required, the screen can also used be used with the main setup to increase screening capacity.

The motor controls and switchgear for both portable plans are located in a 15 m long van with a hydraulically raised control tower. The plant is powered electrically from the city’s grid.

In operation, the belt feeder of the first spread discharges onto the 7x20 Clemro doubledeck scalping screen fitted with 100 mm opening punch plate on the top deck and 19 mm on the bottom. Approximately 30 per cent of the total feed is scalped off as pea gravel and bedding sand. Rock up to 300 mm is directed into the jaw where it is reduced to 75 mm minus. The jaw products are then conveyed to the 7x20 tripledeck screen. The 75 mm minus materials retained on the top two decks are directed into the new cone. The cone normally operates with a medium liner and a close side setting (CSS) of 16 mm. At this setting, the manufacturer’s specs give the cone a rated output of 332 to 415 tonnes/h.

The materials retained on the bottom deck along with the bottom deck throughs are either stockpiled as finished products or conveyed to the second 7x20 tripledeck finishing screen for splitting into additional products.

Maintenance

The crushing and screening operations run 10 hours a day, six days a week. The remaining two hours of each shift is devoted to maintenance. Dean Hedley and the pit crew take a great deal of pride in the condition and appearance of the aggregate machinery. The portable plants as well as the mobile equipment fleet are completely  overhauled each winter to make sure every component and part is in top shape for the upcoming season. The plant also receives a fresh coat of paint whenever required. A rigorous inspection and preventative maintenance program is in force throughout the construction season to keep unscheduled downtime to a minimum. Hedley says that since the comprehensive maintenance program was put into effect six years ago, availability has increased substantially. Another factor boosting availability was the parallel decision to standardize on the size of components used on each piece of processing and conveying equipment, where possible, to improve inventory control of spare parts. Hedley adds that the new cone is also contributing to increased uptime. The plant’s electrical power is frequently interrupted by bird strikes, causing the crushing circuit to shut down suddenly. With the previous cone, it could take the crew an hour or more to dig out the plugged cavity. With the XC1600’s hydraulic clearing system, the job is done in five minutes. The system also increases worker safety.

The 2002 season commenced on March 4 with the final day of production scheduled for November 8. From March until early April, the pit crew is running a screening operation to produce 80 000 tonnes of four products: bedding sand, pea gravel, 2050 mm drainage rock and ballast feed. This operation is using the 7x20 doubledeck scalping screen with 100 mm openings in the punch plate top deck and 19 mm openings on the bottom, the 2036 jaw to break rock greater than 152 mm, a 5x16 doubledeck screen and one of the two 7x20 tripledeck screens. The 19 mm minus material goes to the 5x16 screen for splitting into pea gravel and bedding sand while the 19 mm plus is belted to the 7x20 tripledeck to make ballast feed and 2050 mm drainage rock.

Production is averaging nine hours a day, six days a week. At the outset, a production target of 320 tonnes/h was established. However record cold temperatures and snow during the first week of operation have restricted plant output to about 250 tonnes/h. Hedley expects to bring production back on target as soon as the weather improves. Crushing is scheduled to commence in midApril.

The Spy Hill crushing and screening operations are administered by the Materials Plants Division of Calgary Roads with the daytoday management handled by Jay Henkel, plants and paving superintendent. Quality control and plant layout is the responsibility of Duane Sutherland, asphalt/crusher plant technologist. Each fourman pit crew is supervised by plant foremen, Dean Hedley and Joe Polski.

Aggregates and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 4879868 Fax: (514) 4879276
EMail: rocktoroad@sympatico.ca

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