Whitemans Creek Bridge: Accelerating construction with UHPC and FRP

by Elaina Adams | July 1, 2012 3:04 pm

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By Vic H. Perry, MASc., P.Eng., Wade F. Young, M.Eng., and Brent I. Archibald, P.Eng.
On bridge projects around the world, delays caused by traffic congestion and detours at infrastructure construction sites have significant impacts on indirect costs. Consequently, there is a need for speed—and a construction method called accelerated bridge construction (ABC). {This article was based on a paper by W.F. Young, J. Boparai, V. Perry, B. Archibald, and S. Salib, entitled “Whitemans Creek Bridge: A Synthesis of Ultra-high-performance Concrete and Fibre-reinforced Polymers for Accelerated Bridge Construction.”)

According to the U.S. Federal Highways Administration (FHWA), ABC is defined as “a paradigm shift in the project planning and procurement approach where the need to minimize mobility impacts, which occur due to onsite construction activities, are elevated to a higher priority.”

Benefits of ABC include improvements in:

• safety;
• quality;
• durability;
• social costs; and
• environmental impacts.

This approach uses safe and cost-effective planning, design, materials, and construction methods to lower the onsite construction time occurring when building new bridges or replacing and rehabilitating existing ones. (For more,, see the Federal Highways Administration’s, “What is ABC?” at www.fhwa.dot.gov/Bridge/ABC[2]).

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In 2011, the Ministry of Transportation of Ontario (MTO)–West Region completed its first ABC project: Whitemans Creek Bridge, located on a rural, two-lane highway (#24) near Brantford, at the bottom of a curve, within a natural valley with residential property and environmental constraints. By using factory precast concrete elements on the bridge superstructure and substructure, MTO was able to replace the entire bridge within seven weeks instead of several months associated with conventional construction. In conjunction with the precast concrete elements, the use of fibre-reinforced polymer (FRP) reinforcing, along with ultra-high-performance concrete (UHPC) (For past articles on ultra-high-performance concrete (UHPC), see “An Ultra-high-performance Upgrade” by Gaston Doiron, M.Eng., P.Eng., and Kelly A. Henry, M.Arch., MBA, LEED AP, in the December 2011 issue of Construction Canada. Also see “Precast Solution for Performance Cladding: Ultra-high-performance Concrete for B.C. Building” by Don Zakariasen and Peter Seibert, M.Sc., MBA, P.Eng., in the September 2010 issue of Construction Canada. To see the article, visit www.constructioncanada.net[4] and select “Archives.”) for the joints, shear pockets, and haunches, has significantly increased the structure’s performance and durability levels.

The existing bridge—a three-span concrete T-beam structure and a length of 33.5 m (110 ft)—was slated for replacement due to its age, condition, and structural deficiencies. As a result of the site conditions and constraints of the surrounding terrain and residential properties, it was decided to replace the structure using rapid construction techniques.

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The MTO Northwest Region Office in Thunder Bay pioneered the use of UHPC in Ontario. By the end of 2010, they had constructed nine UHPC bridge projects. The first, in 2006, was the CN Overhead Bridge at Rainy Lake, which incorporated precast deck panels with UHPC joint fill (i.e. the UHPC material cast in the field to integrally connect the precast components into a structurally monolithic unit). (For more on the Rainy Lake Bridge, see “Innovative Bridge Decks Field-cast UHPC Joints for Precast Bridges” by V.H. Vic Perry, FCSCE, M.A.Sc., P.Eng., Primo A. Scalzo, M.Sc., P.Eng., PE, and Gary Weiss, P.Eng., MBA, in the September 2007 issue of Construction Canada). Observations made to date indicate outstanding performance. After five years of service in a northern climate, there is neither material deterioration nor any joint opening. (For more, see J. Lee, B. Craig, P. Loh, and V. Dimitrovski’s “Working Toward Maintenance-free Bridge Decks Using Glass Fibre-reinforced Polymer Reinforcing Bars,” from the 8^th International Conference on Short and Medium Span Bridges in Niagara Falls, Ont. [2010]).

Since then, MTO Northwest Region has used UHPC joint fill for the interconnection of precast bridge elements, including:

• full-depth precast deck panels;
• side-by-side precast girders;
• full-depth precast approach slabs; and
• precast concrete deck curbs (Figure 1).

During 2010, two Ontario bridges (Eagle River and Wabigoon) used UHPC field-cast joints for live-load continuity over internal piers in precast girder bridges. This joint design (Figure 2) completely eliminated the need for post-tensioning and provided for fast, simple field connections of precast bridge elements.

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MTO has also used UHPC field-cast expansion joints as a means to provide strong and durable solutions to solve damage with freeze–thaw degradation, de-icing material, and the constant impact and abuse from trucks and snow ploughs crossing the expansion joints. The use of UHPC for expansion joints eliminates the need for embedded steel edges or cast-in-place concrete between the precast deck and steel embed.

MTO has also built numerous trial projects with glass-fibre-reinforced polymer (GFRP) reinforcement bars, using its non-corrosive properties with the intent of building more durable structures. (See Canadian Standards Association (CSA) S807-10, Specifications for Fibre-reinforced Polymers). The bridge performances are currently being monitored, and testing to date has been very encouraging. Currently, in Ontario, the material cost of GFRP reinforcement bars is about the same as epoxy-coated steel, and about double that of conventional steel when calculated by length.

Due to the low modulus of elasticity of GFRP reinforcing (E ≈ 40–60 GPa [5800 to 8700 psi] versus 200 GPa [29,000 psi] for steel), (For more, see S. Salib’s “Strength of Concrete Beams Reinforced and/or Prestressed with FRP Bars,” a PhD thesis submitted to the Civil and Environmental Engineering Department at the University of Windsor in 2001). crack control in concrete becomes the governing criteria for design. The difference in material properties requires reduced bar spacing as well as increased bar size when GFRP reinforcing is used as the primary tension reinforcing. A bridge deck using only GFRP reinforcing requires an average of 60 to 70 per cent additional reinforcing by length when compared to a similar bridge with steel reinforcing.

The project
The new bridge structure consists of a 40-m (131-ft) single-span steel plate girder structure with a 225-mm (9-in.) thick concrete deck. It measures 14.5 m (48 ft) in overall width and is supported on a single row of steel H-piles made integral with the abutments. To reduce construction time, precast concrete was used for all the reinforced concrete elements, including the integral abutments, with the exception of the barrier wall, which was cast-in-place after the structure was opened to traffic. Durability was enhanced by incorporating two emerging materials into the project—UHPC and GFRP reinforcing.

UHPC has been proven on several projects and is considered by FHWA to be a superior material when used as a joint fill between prefabricated components in bridge decks. (See B. Graybeal’s “Behaviour of Field-cast Ultra-high-performance Concrete Bridge Deck Connections Under Cyclic and Static Structural Loading,” in FHWA’s November 2010 report FHWA–HRT-11-023. Also see V. Perry, P. Scalzo, and G. Weiss’s “Innovative Field-cast UHPC Joints for Precast Deck Panel Bridge Superstructures: In Overhead Bridge at Rainy Lake, Ontario,” from the Precast/Prestressed Concrete Institute (PCI)–FHWA National Bridge Conference from 2007).

The non-corroding property of GFRP reinforcing is being increasingly used by MTO as a measure to build maintenance-free bridge decks.⁹ In addition to its non-corroding properties, the GFRP reinforcing weight is only about 30 per cent less than steel; this facilitates reduced labour expenses. Also, to achieve an optimal bridge design, GFRP reinforcing was used for the top mat and steel for the bottom, balancing durability and cost.

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UHPC joint fill for precast concrete
In terms of durability, construction joints between precast elements have traditionally been the weak link in the system, thus reducing the overall benefits of precast. However, using UHPC to connect precast elements promises to eliminate this issue and, in fact, make the joints the strongest link. For the Whitemans Creek Bridge, UHPC was used to fill the voids between the precast abutments and the H-pile foundations, and in the joints between the precast panels for both decks and approach slabs. All precast elements were constructed using 35-MPa (5075-psi) concrete.

The UHPC technology used for the joint infill is an ultra-high-strength, ductile material (Figure 3) made with:

• portland cement;
• silica fume;
• quartz flour;
• fine silica sand;
• superplasticizer;
• water; and
• steel fibres.

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The concrete’s ultra-high-strength properties and low permeability provide for excellent reinforcement protection against corrosion and improved bond with the rebar, thereby providing short bond development lengths. The use of fibres in UHPC provides superior durability and crack control by dispersing any strains into well-spaced, tightly closed micro-cracks. For field-cast UHPC, compressive strength specimens for quality control are typically 75 x 150-mm (3 x 6-in.) cylinders tested at 28 days. Field-cast results are typically lower in compressive strengths compared to lab or precast due to mix adjustments for field-batching, hot-weather-batching, and field-curing (as opposed to thermally treated).

While compressive strength tests are used to validate field quality assurance/quality control (QA/QC) during casting operations, it is the short bond development length that governs the design. All UHPC testing for joint fill has been done on specimens with a 100-MPa (14,500-psi) compressive strength to validate minimum strengths for opening to traffic.

The UHPC was batched with a mini-slump flow of 200 to 250 mm (8 to 10 in.) and will slowly self-level and fill voids without using any vibration. To ensure complete joint filling and accommodate the release of any trapped air, a small hydrostatic head of up to 200 mm is maintained. The concrete used is self-consolidating during the material’s initial setting and also exhibits superior durability with the chloride ion permeability (i.e. < 100 coulombs); this is very low compared to the 1000-coulomb permeability specified for high-performance concrete (HPC) in Ontario.

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Integral abutment connection
The abutment stem was precast in four sections; the two central and the two outer sections being 3.8 and 2.6 m (12.4 and 8.4 ft) wide, respectively. Since the abutments were precast, and the integral connection required the ability for the abutment to transfer both axial and flexural loads directly into the piled foundation, a suitable connection between the abutment and steel pile foundations needed to be developed. Pockets that were 600 x 600 mm (24 x 24 in.) were formed into the underside of the precast abutments to accommodate the piles and allow for acceptable tolerances on the pile-driving operation (Figures 4 and 5). UHPC was selected as the material to fill the void around the piles due to its self-consolidating, permeability, and shrinkage-compensating properties to ensure full contact between the precast abutment and the steel piles.

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Deck slab connections
UHPC’s outstanding strength allows the width of joints between precast elements to be minimized due to the material’s ability to allow for reduced lap splices in the deck reinforcing. For the transverse joint, the specified 160-mm (6.2-in.) wide opening could have been further reduced; however, from a practical necessity to quickly place the UHPC, a narrower opening would slow the material’s placement. Similarly, the 350-mm (14-in.) wide longitudinal joint specified has enough width to allow for shear stud placement on the girders.

The deck slab consists of 16 pairs (32 total) of precast panels, each 225 mm (9 in.) thick x 2240 mm (88 in.) wide x 7075 mm (279 in.) long. Pockets in the panels were required over the girders for the shear stud connection to them. At the centre girder, there was a continuous longitudinal gap of 350 mm. The slabs were not post-tensioned as the UHPC joint fill provides sufficient durability when combined with asphalt and waterproofing. Additionally, the precast panels were detailed so the need for formwork was eliminated, which greatly contributed to the construction speed.

Before slab erection, 50-mm (2-in.) wide strips of ethylene vinyl acetate (EVA) foam were glued to the top flange’s outside edges to contain the UHPC. The first slab was placed and adjusted to grade via six levelling devices (two at each girder), ensuring proper load distribution of the precast panel to the supporting steel girders. The panel’s weight was used to compress the EVA foam strips, resulting in a leak-proof system.

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The shear pockets and haunches over the girder flanges were grouted starting at the low end, followed by the longitudinal joint along the bridge’s centreline (Figures 6 and 7). As grouting progressed, plywood forms were placed over the pockets and fastened down to prevent the UHPC from overflowing due to the inherent grade of the bridge, since UHPC is self-levelling. The transverse joints between the precast panels were subsequently placed (Figure 8).

Normal daily productivity for this operation was approximately 12 to 16 m³ (424 to 565 cf), based on a crew of five people and two high-capacity mixers. The 21 m³ (742 cf) of UHPC needed for the bridge deck thus required two days for placement and an additional four days for normal curing (with accelerated curing, this can be reduced to 12 hours).

The approach slabs consist of six precast panels each 250 mm thick x 2079 mm (82 in.) wide x 6000 mm (236 in.) long with 200-mm (7.8-in.) wide joints between the segments. After the abutments reached 20 MPa (2900 psi), the precast approach slab panels were installed on the finely graded subgrade and the joints filled with UHPC (Figure 9). The ends of the approach slabs were detailed with preformed holes to allow the slabs to be connected to the abutments using straight vertical dowels with the annular space also filled with UHPC.

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Testing and development of UHPC for joint fill
As with any new technology, it is necessary to prototype solutions and conduct full-scale testing before deployment. While UHPC has been around for more than 20 years, its use as a joint fill material in bridge decks is relatively new.

Full-scale cyclic and static loading
FHWA has been actively studying UHPC application in bridge decks for about 12 years. Slab specimens were cast in two pieces and joined together at mid-span by a 150-mm (6-in.) UHPC joint. Various arrangements of 15M bars—some straight, some headed, and some bent—were used to connect the two pieces together. Loads were immediately applied adjacent to the joint, via a 254 x 508-mm (10 x 20-in.) load patch, and tested at three levels (Figure 10).

Under cyclic loading (Levels A and B), there was no interface de-bonding and no leakage through the joint. Under cyclic loading (Level B), a single flexural crack in the concrete became tightly spaced micro cracks through the UHPC joint. Under ultimate loading (Level C), the panel behaved as would be expected of a monolithic concrete slab without any joint or dissimilar materials.

Pullout tests on GFRP reinforcement bars
Testing of UHPC reinforcing’s pullout resistance has been conducted over the last several years to demonstrate the bond characteristics and determine suitable development and lap lengths.

With the introduction of GFRP reinforcement bars, pullout tests in accordance with Canadian Standards Association (CAN/CSA) S6-06, Canadian Highway Bridge Design Code (CHBDC), were performed to obtain approval for using GFRP in the UHPC deck joint fill for specific MTO projects. Pullout test specimens were manufactured with 15-mm (0.6-in.) bar sizes with embedment depths of 100 and 150 mm (4 and 6 in.). Failure behaviour of the pullout test conducted on all samples was delamination between the GFRP’s core and skin (an epoxy sand layer).

Future UHPC applications for bridges
The use of UHPC field-cast connections is a relatively new solution. However, this early adoption has provided excellent field experience and validation of the methodology. It has also meant exposure and confidence in the technology, which has led to innovations for UHPC use for other types of field connections for precast bridge systems, which MTO will consider for future projects.

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Field-cast connections for precast waffle deck panels and hidden shear pockets
UHPC use for precast waffle deck panels (Figure 11) provides a lightweight, durable bridge deck system suitable for new or rehabilitated bridges. Installing UHPC joint fill between the UHPC waffle deck panels provides an entire bridge deck that is made from UHPC. To further reduce dead load and improve the deck durability, the waterproofing and wearing surfaces are removed, thereby leaving the entire UHPC deck exposed to provide the highest durability where it is most needed—at the riding surface.

As an alternative to cast-in-place components, precast parapets or barrier walls may be supplied to the bridge already integral with the deck or as separate units (Figure 12) to be field-attached. In both cases, the precast parapet units need to become fully composite with the bridge deck system to carry the traffic barrier loadings. Field-cast UHPC connections for precast parapets and barriers provide integral continuity and further help speed up bridge construction.

Field-cast UHPC for thin-bonded overlays
Another promising use for UHPC field-cast rehabilitation is thin-bonded overlays (or ‘hybrids’) to re-strengthen deteriorating bridge decks. Several state DOTs, co-operatively with universities, are investigating UHPC use as a cost-effective method to significantly extend the life of bridge decks that are approaching their service life.

The use of this system is being investigated as both a field-cast topping for in-situ deck repairs and as a precast system. The precast ‘hybrid’ would be cast top-surface-down where the UHPC is first cast in a textured form liner and then the HPC as a structural backup. Then panels would be cured, flipped, and ready for delivery to the site. The precast hybrid panels would be connected with field-cast UHPC. Hidden shear pockets may also be used with this system.

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Field-cast UHPC for accelerated bridge construction
UHPC is a family of products where the mix designs can be formulated to provide a wide range of slump flows, hardened mechanical properties, and rate of strength gain. One UHPC product formulated specifically for accelerated bridge construction provides a high early strength of 55 MPa (7980 psi) in 12 hours at normal ambient temperatures. The product has similar fluid workability to other UHPCs and a rapid strength designed for ABC projects that may be executed during weekend closures or other time-limited repairs.

Conclusion
Traditional reconstruction of non-complex bridges typically requires a minimum of four to six months to build, or longer if the bridge work is staged to maintain traffic during construction. Alternately, using accelerated bridge construction techniques or rapid bridge replacement (RBR)—using heavy lift equipment or overnight/weekend construction—reconstruction of a bridge superstructure can be reduced to as little as 48 hours or one weekend. This is typically done in urban areas or on freeways, where the extra cost of using ABC can be easily justified when user expenses—prices associated with public traffic inconveniences (or perhaps even lost job force productivity) combined pointed to the solutions used—are taken into account.

Between these two extremes are options to employ more traditional equipment and maximize prefabrication with the use of UHPC. With a small premium, significant savings in construction duration can be realized. By using ABC techniques, the Whitemans Creek project construction duration was effectively reduced to just seven weeks, with only a 15 per cent premium over traditional methods.

This project also created a unique opportunity for a synthesis of ABC, UHPC, and GFRP. The road closure necessary for the highway reconstruction demanded use of accelerated bridge construction.  Incorporating UHPC ensures the joints between precast elements will be durable and can be constructed quickly (i.e. no formwork). Finally, the glass-fibre-reinforced polymer that was used for the top mat deck eliminates corrosion of the top mat reinforcing. By synthesizing all three elements, this project is yet another step toward building more durable structures, rapidly. (The authors would like to thank the Whitemans Creek Bridge project team, which included Ministry of Transportation Ontario (MTO) staff, Delcan Corp., Lafarge Canada, and Dufferin Construction Ltd., for the collaborative partnership throughout the design and construction of this project).

Vic H. Perry, MASc., P.Eng., is the vice-president and general manager for Ductal, Lafarge’s ultra-high-performance concrete. Based in Calgary, he holds a bachelor’s degree in civil engineering and a master of applied science in structural engineering from Dalhousie University (Halifax, N.S.). With 30 years of industry experience, Perry is also a fellow and past-president of the Canadian Society of Civil Engineers (CSCE). He can be contacted via e-mail at vic.perry@larfarge-na.com.

Wade F. Young, M.Eng., is head of the structural section, West Region, for the Ministry of Transportation Ontario (MTO). Based in London, Ont., he has 35 years of industry experience and is a member of the Precast/Prestressed Concrete Institute (PCI). Young can be reached at wade.young@ontario.ca.

Brent I. Archibald, P.Eng., is a senior principal and technical director for Delcan Structures, based in Markham, Ont. Responsible for the technical excellence, quality assurance (QA), and quality control of structure projects in Eastern Canada, he is an alumnus of the University of Toronto (UofT). Archibald is a member of Professional Engineers Ontario (PEO) and the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC). He has 15 years of experience in the engineering, design, and construction of roadway and railway bridges. Archibald can be contacted at b.archibald@delcan.com.

Source URL: https://www.constructioncanada.net/whitemans-creek-bridge-accelerating-construction-with-uhpc-and-frp/

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