The Moose Creek project was commissioned by MTO and engineered by Stantec Consulting to try out several new precast construction concepts that could be used to speed up bridge construction in Ontario. This bridge has a single span of 22m, an overall width of 14.64m and a roadway of 13.5m. The bridge is supported on steel piles and has integral abutments.
The Faster the Better
The Moose Creek Bridge project is part of a
North American initiative - looking at ways to
speed up bridge construction to minimize
costs and inconvenience to the public.
This project used a total of 10 precast concrete substructure/abutment elements (3 stem units + 2 wingwall units per abutment). The precast concrete superstructure consisted of 6 girder/deck units consisting of CPCI 1200 girders precast with monolithic decks.
Project Specification Highlights
- Use of High Performance Concrete (HPC)
- Casting of Concrete Trial Batches
- Temperature Monitoring
- Temperature Restrictions
- Seven Day Wet Cure
Concrete Trial Batch
The final concrete mix developed for each precast unit was cast and tested prior to production of the units. Test results were submitted for 28 day strength, rapid chloride permeability and hardened air void tests. A comparably thick test unit was cast to monitor the core heat generated by the stem units during curing
Abutment and Wingwall Production
These units were cast at Pre-Con's Brampton precast plant. Units were cast with exposed face on down side of form. All units were cast with conventional reinforcing steel.
All units were cast with High Performance Concrete (HPC). Special curing requirements were carried out in conformance with the specifications.
The concrete temperature was monitored and controlled. Thermocouple wires were placed at the centre and the surface of the units. Wires were cast at 3 locations per unit to monitor the temperature. Thermocouple wires were connected to dataloggers for recording and downloaded daily. Temperatures were recorded every 30 minutes for 7 days. Manual temperature readings were taken at specified intervals during the 7 day curing period.
To prevent shrinkage and micro-cracking, the concrete temperature was maintained between 10 degrees celcius and 70 degrees celcius and the temperature difference between any one set of the centre and the surface thermocouples could not exceed 20 degrees celcius. If the limits were neared or exceeded, the surface temperature was raised or lowered through use of hot or cold water as necessary. The core temperature could not be influenced.
All units were wet cured with burlap or filter cloth for a 7 day period. Soaker hoses were used to keep units continuously wet during the 7 day curing period. Moisture vapour barrier was used to prevent air flow between layers during the curing period
One girder/deck unit cast per day was precast at Pre-Con's Woodstock precast plant using a reusable wood form. Units were prestressed and conventionally reinforced, similar to typical CPCI girder units - but with a monolithically cast deck slab above. The girder deck was formed with a parabolic shape in elevation and cross slope in section to account for girder camber and cross fall.
The side of deck form was notched for projecting reinforcing steel - to ensure proper alignment with steel in adjacent units. The focus was placed on the edge detail, girder-to-girder.
High Performance Concrete was required for production of these units, together with similar curing and temperature restrictions/monitoring procedures used for the abutment and wingwall units. Centre and surface thermocouples were cast into unit: 3 wires/deck, 2 wires/girder and 3 locations per deck and girder (15 thermocouples/unit total).
A 7 day wet cure with burlap was maintained, including a layer of plastic vapour barrier. Temporary steel stands were required for stability after the girder/deck units were removed from the wood form.
Temporary steel strands were also needed for stability during shipping.
The precast units were erected in two mobilizations. First the stems and wingwalls were installed beginning July 28, 2004. Units were shipped flat. The steel pile and HSS knee bracing system was installed by General Contractor. This system also acted as a temporary lateral support for abutment stem units.
For stability, the outer abutment stem units were erected first. Wingwall end reinforcing was threaded through the reinforcing of the stem units. Wingwall units were set on steel piles and connections were made between stem and wingwall units. Installation of the stem and wingwall units took place over two days
Post-Abutment Installation Site Work
Cast-in-place bearing seats and closure strips between stem units were poured by the General Contractor after installation was completed. Lateral bracing was removed when the concrete reached minimum strength.
Minimum design strength of the cast-in-place substructure portions was required prior to girder/deck erection. Units were erected on August 19, 2004 - 3 weeks after the stems and wingwalls. Units were shipped over a two day period to reach site at the required time. Units were erected from a temporary bridge adjacent to the site. The middle units were placed first and braced temporarily to the stem units for stability before adding the permanent steel diaphragms. Adjacent units were then installed and connected to the diaphragm steel before releasing the crane.
Differential camber was monitored in the plant and checked at erection to ensure allowable tolerances were not exceeded. The deck cross slope checked after each girder was installed to maintain a constant cross fall. Installation continued outwards until the entire deck was complete. Bracing from the middle unit to stem could then be removed. Installation progressed quickly and was completed within one day.
Post-Girder/Deck Installation Site Work
Cast-in-place was installed in the pour strips between adjacent girder units. The end diaphragms were poured by the General Contractor after the precast units were erected - along with the other work performed on a typical bridge structures (approach slabs, barrier walls, etc.).
Moose Creek Bridge Opening
The bridge was opened to traffic on the evening of October 27, 2004.
Owner: Ministry of Transportation of Ontario (MTO)
Precaster: Pre-Con Inc.
Engineer: Stantec Consulting
General Contractor: Miller Paving