Harold Hamada, KSF, Inc.
The North-South Road Project, in the District of Ewa on the Island of Oahu, HI, involves the construction of a limited access, 2.2-mile (3.5-km) long principal arterial highway that connects Interstate Route H-1 to the proposed Kapolei Parkway. A grade separation structure was required to connect the North-South Road to the H-1 Freeway. The H-1 Freeway is the principal arterial highway connecting West Oahu to Honolulu.
The grade separation structure consists of two separate parallel bridges that span 165 ft (50.3 m). Each bridge is 56 ft (17.1 m) wide, with three 12-ft (3.7-m) wide traffic lanes and two 10-ft (3.1-m) wide shoulders. Eight precast, spliced girders are used in the 56 ft (17.1 m) width. The bridge deck consists of precast reinforced concrete planks and a cast-in-place (CIP) topping. Four, 5-ft (1.5-m) diameter drilled shafts support each abutment. The grade separation structure is an integral abutment bridge with no joints.
Spliced Girders
The girder cross section is a 66-in. (1.68-m) deep modified Washington WF74PTG girder. The precaster fabricated 80- and 40-ft (24- and 12-m) long girder segments in Tacoma, WA, loaded the segments on barges, and shipped them to Hawaii. The specifications required a compressive strength of 10,000 psi (69 MPa) at 28 days. The average compressive strength was 12,120 psi (83.5 MPa) with a standard deviation of 1286 psi (8.37 MPa). The concrete was steam cured at a temperature of 140 to 160°F (60 to 70°C) until the concrete achieved a compressive strength of 5000 psi (34 MPa) before release of the prestressing strands. During the steam curing operation, a maturity meter was used to estimate the concrete compressive strength.
The contractor spliced the 40-, 80-, and 40-ft (12-, 24-, and 12-m) long segments in the field to achieve the desired 165 ft (50.3 m) span. Concrete for the splice had a specified compressive strength of 9000 psi (62 MPa) at 28 days and a specified slump of 7 ± 2 in. (178 ± 50 mm). The concrete contained a water reducer, high-range water-reducer, viscosity modifying admixture, and a corrosion inhibitor. The post-tensioning operation commenced after the splice concrete reached a compressive strength of 8000 psi (55 MPa).
Bridge Deck
The bridge deck comprised 3-1/2-in. (90-mm) thick precast reinforced concrete planks spanning 7 ft 6 in. (2.3 m) with a 5-in. (125-mm) thick CIP composite topping. The topping concrete materials and proportions were selected to minimize drying shrinkage, enhance fatigue endurance, minimize bleeding, and reduce plastic shrinkage compared to previous deck mixes. A shrinkage-reducing admixture (SRA) was used to reduce drying shrinkage. Polypropylene macro-fibers were used to increase the fatigue endurance limit and toughness. Polypropylene micro-fibers were used to limit plastic shrinkage cracking. A synthetic air-entraining admixture (AEA) was used to improve the workability of the concrete. A synthetic admixture is more stable than typical surfactant AEAs because of the chemically inert polymers. In addition to the SRA and AEA, a water reducer, high-range water reducer, hydration stabilizer, and a viscosity modifying admixture were included in the concrete mix. No supplemental cementitious materials were used. During the deck casting operation, balling or clumping of the fibers, bleeding, and plastic shrinkage cracks were not observed. The deck received a 7-day continuous wet cure. The 3-1/2-in. (90-mm) thick precast reinforced concrete planks were 3 ft 11 in. (1.19 m) wide by 7 ft 11 in. (2.41 m) long and made with 6000 psi (41 MPa) compressive strength concrete. The concrete mix for the planks was similar to the mix for the CIP topping, but without the SRA and fibers. The contractor removed the precast planks from the forms 24 hours after casting when the concrete compressive strength ranged from 2500 to 3200 psi (14 to 22 MPa).
The grade separation structure was opened to traffic in January 2009 and to date no drying shrinkage cracks have been observed. The grade separation structure is functioning as designed.
Concrete Materials
| Property | Precast Segments | CIP Splice | Precast Planks | CIP Deck |
| Specified Compressive Strength at 28 days, psi | 10,000 | 9000 | 6000 | 6000 |
| Water-Cementitious Materials Ratio | 0.27 | 0.33 | 0.33 | 0.33 |
| Cement Type | III | I/II | I/II | I/II |
| Fine Aggregate Source | Tacoma Quarry | British Columbia | British Columbia | British Columbia |
| Coarse Aggregate Source | Tacoma Quarry | Kapaa Quarry 3 F Basalt(1) | Kapaa Quarry 3 F Basalt(1) | Kapaa Quarry 3 F Basalt(1) |
Further Information
For further information about this project, please contact the author at [email protected].