Earthquake Memorial Park draws 300,000 visitors, exemplifies impact of bridge's construction The foundation—the soul of the suspension bridge: 15,000-ton steel caissons Bridge firmly supported by century's largest bottom-fixed offshore concrete structures Wind-speed resistance of 78 m/sec. in wind tunnel testing using a 1/100-scale model The longest suspension bridge to survive a magnitude 7.2 quake during construction—technology to share with the world *** Realization of "Dream Suspension Bridge" Key to Future Prosperity in the Kansai Economic Zone ***

Bridge firmly supported by century's largest bottom-fixed offshore concrete structures

After the caissons were placed, they were plugged with a new type of marine concrete, called "anti washout underwater concrete," specially developed to resist dissolution in seawater. The placing work involved displacing seawater from inside the caisson with concrete to build up a thick pillar. A conventional concrete is made by mixing water, cement, aggregates, and admixtures; but since these constituents easily separate in water, it is difficult to keep them uniformly distributed in the flesh concrete. In view of the quality of concrete necessary to support such a massive bridge, it would have been too difficult to place such a large concrete structure under seawater with conventional method. This necessitated development of a new concrete that could be placed under water-without its constituents separating. Shuusuke Harada, who participated in the concrete development as the senior researcher of the Cement & Concrete Research Laboratory at Sumitomo Osaka Cement Co., Ltd., explains how the problem was dealt with. "In short," Harada says, "the aggregates and cement are bound together to prevent their separation in water, yet the fresh concrete must be sufficiently fluid to spread uniformly at the placement site; but achieving this fluidity made it difficult to get the concrete to set quickly enough." Another problem during hardening was the generated heat with the hydration of cement and consequent changes in volume, characteristics that would threaten the durability of such a massive concrete foundation. The development of a cement with highly suppressed exothermic properties was needed; but this low heat requirement further complicated the control of setting. To the engineers, the challenge of finding an antinomic balance between fluidity and setting characteristics seemed almost insurmountable, according to Harada. The engineers, who were also involved with aspects of the project such as R&D, sales, production, dedicated themselves to a round-the-clock shift rotation and summoned the latest in technology to unveil a new type of concrete using "super low heat cement".

This concrete was produced aboard a 24,000-ton concrete factory ship berthed alongside the caissons, and it was placed with special care for protecting the environment.