Kojima-Sakaide Route

This is a highway-railway combined route which starts from near Okayama City in Honshu and terminates at Sakaide City in Shikoku, crossing the narrowest straits (approx. 10 km. in width) in the Seto Inland Sea. The total length of the highway is 37.3 km. and that of the railway is 32.4 km. Over the Straits, the route passes on highway-railway combined bridges which are total approx. 13 km. long, but the highway and the railway separate when reaching Honshu/Shikoku. For the construction of this route, over 700,000 tons of steel and 3,640,000 cu.m. of concrete have been used. The Straits section consists of various long span bridges, and the total area of steel bridge decks exceed 140,000 sq.m., which have received Trinidad based Gussasphalt lower layer (base course) This is almost equivalent to all the surface area of Gussasphalt laid a year in this country. Paving Over 140,000 sq,. of Steel Bridge Decks for the paving contract, the Route over the stratis is divided into 2 sections, i.e. north and south. The north section was awarded to the joint venture of Taisei Road Construction, Seiki-Touku Construction and Nisiki Construction, and the south section to the joint venture of Nippon Hodo and Nippon Road companies. The paving work on steel bridge decks carried out in accordance with "Honshu - Shikoku Bridge Authority Deck Pavement Standards (Tentative), 1983" which may be summarised as follows:-

1. Clean the steel deck surface previously coated with an inorganic zinc rich paint. Where rust is shown on the paint, grit - blast to remove it
2. Apply 2 coats "CATICOAT" rubberised bitument solution at the rate of 0.2 1/m2/coat as bonding coat.
3. Lay 40 mm thick Gussasphalt lower layer (base course)
4. Apply a rubberised bitumen emulsion at the rate of 0.3 1/m2 as tack coat
5. Lay 35mm thick Modified Asphalt Concrete upper layer (wearingcourse)

The Gussasphalt mix is a stable type which has proved durable under the particular conditions of Japan. For example, road surface temperatures exceed 60°C in summer and the traffic volume on this route is expected to be around 48,000 vehicles/day. "Honshu - Shikoku Bridge Authority Deck Pavement Standards (Tentative) 1983" specifies the requirements for Gussasphalt. The hard binder consists of 25% Trinidad Lake Asphalt and 75% straight-run bitumen 20-40. Wheel Tracking Test at 60°C is often used to access stability of Gussasphalt in this country. Minimum 300 passes/mm is equivalent to maximum 8.4 mm/hr. Gussasphalt was laid from July to November 1987 by three paving teams. Each team laid about 120 tons of the mix a day on average, using 6 or 7 lorry mounted stirred cookers. About 20 cookers in total were used on this route alone (total number of cookers used in Japan would be around 35) and all of them are made in West Germany such as BENNINGHOVEN GT11 and ABG GT9. Two of the three Gussasphalt finishers are made in West Germany too and one is VOGELE GAF82. Actual procedure at the Yoshima plant and the paving job on Kita Bisan-seto Bridge was like this. Trinidad Lake Asphalt was crushed in a roll crusher to 50 mm down and then fed into 6 ton blending tanks for mixing with straight-run bitumen heated to 200°C. 2 blending tanks were able to produce up to 16 tons/day of the blended binder. The plant could produce up to 200 tons of Gussasphalt mix a day, but usually about 120 tons/day on average. A typical mix proportion was:-

Mix temperature was 220°C when discharged from the batch mixer and was increased to 240°C during at least 1 hour cooking in the cooker. On the steel bridge deck, a new Gussapshalt finisher developed by Nippon Hodo laid the mix smoothly at a speed of about 2 m./min. This is a simple but effective finisher. The mix discharged from the cooker was placed direct on the steel bridge deck just under the finisher and then leveled with a non-vibrating screed plate. The working width was fixed to 3.5 m., i.e. one lane. Over 140,000 sq.m. of steel bridge decks on the Kojima-Sakaide Route were laid with Gussasphalt lower layer (base course) by the end of November and now ready for Modified Asphalt Concrete upper layer (wearing course) to be laid in January and February, 1988. It is interesting to note that Trinidad Lake Asphalt will also be used for a Rolled Asphalt wearing course of the helix ramp leading from Yoshima Elevated Bridge to a resort area in Yoshima Island. The binder will be a blend of 30% Trinidad and 70 % straight - run bitumen.

Extracted from: "Trinidad based Gussaphalt laid on various bridges of Kojima - Skaide Route, the first highway/railway to link Shikoku with Honshu - by J. Nozaki, Toa Boeki Kabushiki Kaisha, Osaka, Japan

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