Roads & Paving
Concrete investment pays off
With four high profile contracts among its credits, a roadbuilding contractor is firmly established
May 1, 2009 By Andy Bateman
For some time now, the proponents of rigid pavements have been
promoting concrete roads over flexible pavements built with hot mix
|Coco Paving (1990) Inc. has completed four high profile concrete paving contracts on Highway 401 utilising Gomaco GHP-2800 slipform pavers. |
For some time now, the proponents of rigid pavements have been promoting concrete roads over flexible pavements built with hot mix asphalt. Despite their best efforts, less than five percent of Canada’s roads are built with concrete and even fewer roadbuilders have successfully ventured into the concrete paving business in a big way. Coco Paving (1990) Inc. is one of those few, with a successful project list that now includes four concrete paving contracts on one of Canada’s busiest trading corridors to the U.S.
Aggregates & Roadbuilding saw Coco Paving’s concrete crew at work on a 6.1 km section of Highway 401 just east of Windsor Ont. where the company is prime contractor on MTO contract 2007-3043. This contract has an adjusted total tender value of $84.52 million, with Coco Paving’s scope of work including the placement of 300 mm of recycled Granular A base material, a 100 mm thick asphalt open graded drainage layer (OGDL) and a 260 mm thick unreinforced concrete slab. Facca Inc. is a principal subcontractor for the Walker and Dougall structure flyovers.
|This Erie Strayer portable plant maintained a continuous supply of concrete to the 24 hour paving job. |
|The red string line (foreground) was used to trim the granular base, control placement of the asphalt open graded drainage layer, provide grade and steering guide for the GHP-2800 slipform paver and accuracy in texturing and curing for the T/C-600 texture cure machine. |
|A Caterpillar 330 B excavator feeds recovered concrete and asphalt to Artscrushing and Recycling’s portable spread.|
ElRus triple deck 6×20 screen on the aggregate processing spread
separated oversize containing wood and other non-ferrous debris from
feed material larger than 19 mm.
|A Komatsu PC 600 LC excavator stockpiled finished product in the congested yard. |
product was stockpiled by a McCloskey 30.5m long stacker equipped with
an integral Caterpillar engine and anti-segregation paddle.
|Rom with a view – the trailer mounted elevating control room on Artscrushing and Recycling’s portable spread. |
After placing the Granular A base, the asphalt drainage layer was paved by Coco’s own asphalt paving crew and consists of a two per cent asphalt cement gap graded mixture designed to minimise potentially damaging water accumulation in the pavement structure. The drainage layer also provided a smooth and level surface for a Gomaco GHP-2800 slipform paver, one of two in Coco’s equipment fleet, as it placed a 7.50 m wide concrete slab for lanes one and two of the new pavement. The GHP-2800 is a multi-function unit that forms and consolidates the concrete, inserts bars for the pavement’s joints and provides initial surface finishing.
During concrete paving, the fleet of end dump trucks delivering concrete were controlled by a ground man in order to maintain the all-important steady feed of material to the paver. The advancing paver then moulded the concrete to the required width and depth, with vibration provided to the throat area of the mould to consolidate the concrete. At the rear of the paver, the float pan of the Gomaco auto-float unit oscillated longitudinally and sealed the surface as its scissor member traversed the width of the concrete slab. Working behind the paver, Coco’s crew hand finished both the surface and edges of the slab, using a traveling workbench when necessary to access the central area of the slab. A sheet of burlap dragged behind the workbench added longitudinal texture to the concrete surface ahead of a Gomaco TC/600 texture cure machine, the last major piece of equipment in the paving train. During its first pass over the concrete, the T/C-600’s tines cut fine transverse grooves in the fresh concrete surface to provide optimum skid resistance, with curing compound applied during the second pass.
For the adjacent paving run, a different pan would be utilised on the GHP 2800 to pave the narrower 4.25 m wide concrete slab for the 3.75 m wide driving lane of the new highway and a 0.5 m wide strip forming part of the paved shoulder.
This particular four track GHP-2800 slipform paver was equipped with front and side mounted bar inserter for longitudinal joints an In-the-Pan Dowel Bar Inserter (IDBI) for transverse joints and a rear sidebar inserter. At transverse joints, 32 mm diameter dowels bars were inserted at 300 mm centres, with twenty three bars inserted in the 7.5m wide, two lane paving configuration and twelve inserted in the 4.25 m wide configuration. The transverse joints were randomly spaced 3.7 m, 4.5 m, 4.0 m or 4.3 m with all programmed into and managed by the IDBI’s computer.
On this contract, grade and alignment control were provided by the same string line for several stages of the construction process. The string line was initially set out when the granular base had been placed and levelled close to its final grade and subsequently used to trim the base, control placement of the OGDL and provide grade and steering guide for the slipform paver. Even then the string line still had one more job to do, as the T/C-600 texture cure machine utilised the same line to provide accuracy in texturing and curing.
Manufacturer’s specifications indicate that the Gomaco GHP-2800 Slipform Paver is powered by a Tier II Caterpillar C9, 8.8 litre diesel engine delivering 335 hp (249.9 kW) and fuel economy of 51 l/h at 80 per cent of rated power. The GHP-2800 has an automated control system which features self-diagnostics for front and rear grade, cross slope, steering, reverse steering and selective steer controls for paving accuracy and ease of operation. The control system features dual grade controls for sensoring string line on both sides of machine simultaneously, while automatic on/off controls for vibrators and tamper bars are synchronized with machine movement. Gomaco’s G21/G22 operating system allows the GHP-2800 to be controlled by automated 3-D automated machine controls systems rather than string line. The GHP-2800 can pave at widths ranging from 3.66 m to 7.62 m without requiring frame inserts while optional paving widths up to 9.75 m are available with additional vibrators and frame inserts.
Concrete for the continuous paving job was supplied from a portable plant located on Highway 3, just west of the Town of Essex and about fifteen minutes by truck to the Highway 401 job site. To say the site was busy would be an understatement. A steady stream of trucks brought cement and aggregates to the concrete plant while some twenty tandem end dump trucks with payloads of 9m3 (20 tonnes) maintained a continuous supply to the concrete paver. The Erie Strayer plant produced up to 2000 m3 of 30 MPa road mix in a twelve hour shift, with the list of raw materials suppliers including St Mary’s Cement, Lafarge Canada’s Manitoulin quarry for 40 mm and 19 mm coarse aggregates as well as Smelter Bay Aggregates’ Thessalon quarry for fine aggregates.
Traffic volumes in the Highway 3 project yard were further increased by an aggregate recycling operation producing Granular A base material from recovered concrete and asphalt. Production output from the spread of crushing contractor Artscrushing and Recycling was a reported average of 400 tonnes per operating hour with peak rates of over 500 tonnes/h. In operation, a Caterpillar 988B loader carried a mixture of concrete and asphalt in a two to one ratio to a Caterpillar 330 B excavator feeding the plant. The feed was first reduced by a custom Hazemag horizontal shaft impact crusher with an integral grizzly bypass. After passing under a magnet to remove ferrous material, the material was conveyed to an ELRUS triple deck 6×20 screen. There, wood and other non-ferrous debris was separated and stockpiled while feed material larger than 19 mm passed under a Boxmag Rapid magnet before entering a custom built roll crusher in closed circuit with the screen. Finished product was stockpiled by a McCloskey 30.5m long stacker equipped with an integral Caterpillar engine and anti-segregation paddle at the discharge end. On the day of the visit, a Komatsu PC 600 LC excavator was stockpiling finished product to make the best use of limited space in a congested yard.
|Concrete roads deliver benefits says CAC|
According to the Cement Association of Canada (CAC), rigid concrete pavement outperforms flexible asphalt pavement by delivering economic, user and safety benefits as well as reduced environmental impacts. However, the association adds,governments in Canada typically award highway pavement construction contracts based only upon initial costs and asphalt pavements are often selected because they are perceived to be less expensive than concrete. Planners are now beginning to recognize that tenders for road infrastructure projects should include a life cycle cost analysis (LCCA) component, based on the estimated costs of a project over its entire service life. Life cycle costs include maintenance, rehabilitation, reconstruction and salvage value of pavements in addition to initial costs. When LCCA is applied, concrete pavement is, in many cases, said to be less expensive than an asphalt surface of equivalent design. Some Canadian provincial and municipal governments have already begun to choose rigid concrete pavements for selected projects and many cities are also using concrete pavements at high-traffic and high-wear intersections and bus stops. Concrete pavement reportedly lasts longer and requires less maintenance over its lifetime than asphalt, translating into safe highways that require less maintenance, with less disruption for road users. Concrete roads are said to perform well in cold climates and, due to the way concrete pavements distribute vehicle loads, are virtually unaffected by the seasonal weakening of the underlying granular bases and subgrade. Concrete pavement also reflects light in a diffuse manner compared to an asphalt pavement and so requires fewer lights per unit length of pavement to achieve the same level
When pavement repair becomes necessary, concrete pavement can be reused through restoration techniques that minimize the amount of new aggregate required to construct highways, and eliminate the need for disposal of the old material. Concrete pavement is 100 per cent recyclable and provides cost effective reconstruction options such as its use as a road base or aggregate for new concrete pavements. Compared to flexible asphalt pavement, rigid concrete pavement requires thinner granular bases because it distributes the weight of vehicles more evenly over a larger area. Typically, in most cases, up to 50 percent less granular material is required for a concrete highway road base, reducing both costs and the use of scarce resources. Additionally, less hauling of granular material results in significant fuel savings and associated emissions reductions.
Concrete often utilises fly ash, blast furnace slag and silica fume, industrial by-products that can improve concrete properties and would otherwise be landfilled. The relatively light colour and reflective properties of concrete also reduces the urban heat island effect where large cities can be several degrees warmer than outlying areas in the summer, due to the heat absorbed by dark surfaces.
At night, the light colour of concrete is again a benefit, resulting in better night-time visibility for motorists. Concrete also reflects light from vehicles and street lamps more effectively than asphalt pavement to illuminate potential hazards.
According to the U.S. Federal Highways Administration, nearly 30 per
Ironically perhaps, Canada is a net exporter of cement, at least
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