Numerical Simulation for Early-age Cracking Mitigation in Durable RC Deck Slab on Multiple Span Steel Box Girder Bridges Considering Thermal and Stepwise Construction Stresses

Since 2015, a new durable concrete design in a concept of multiple protection countermeasures has been applied to many bridges in Tohoku region of Japan to enhance the durability of RC deck slabs. Various studies pointed out that the utilization of expansive additive (EA) (dosage of 20 kg/m³) for ground granulated blast furnace slag concrete has been confirmed to be indispensable for reducing the early-age thermal tensile stress, which resulted in successful crack mitigation in highly durable RC slab of several steel girder bridges with one or two-span until the completion inspection. Nevertheless, in the newly constructed RC slab of bridges with three or more spans where stepwise construction stresses were added, noticeable transverse cracks were reported. In this study, tensile stresses produced by the stepwise construction of a four-pan steel box girder bridge were numerically investigated using a numerical simulation following layered model. Furthermore, the three leveled systematic thermal stress analysis for the durable RC deck slab of the bridge was also performed using FEM. According to the stepwise construction stress analysis, the authors proposed to increase the amount of EA from the standard dosage of 20 kg/m³ to 25 kg/m³ to further reduce thermal tensile stress in risky locations. Additionally, influential factors affecting the early-age thermal stress of the durable RC slab were numerically presented considering the application of the increased 25 kg/m³ EA. Finally, the cracking risk of the durable RC slab during 28 days of curing was discussed based on combined thermal and stepwise construction stresses.