ABSTRACT
RC slabs on girder bridges are highly susceptible to deterioration under severe cold and aggressive environment. The occurrence of thermal and shrinkage cracks in RC slabs restrained by girders provide rapid routes for harmful agents aggravating deterioration. A highly durable concrete was formulated incorporating blast furnace slag cement with low water-binder ratio and expansive additive and applied in RC slab constructions in Tohoku region in Japan to prevent such deterioration. However, the occurrences of early age transverse cracks in RC slabs of durable concrete were reported in case of multiple span continuous girder bridges. In this context, the present research aimed to determine the early age cracking risk in RC slabs by establishing a systematic analytical scheme for FEM full scale real structural simulation based on thermal stress analysis. First, laboratory investigations were conducted to measure the material properties of corresponding slab concretes. Second, these material properties were calibrated and utilized in member level numerical models to simulate volume changes which were successfully verified by experimental results. Third, full scale 3D structural models were established for multiple span continuous steel box girder as well as single span I-section steel and PC composite girder bridges confirming rational thermal and structural boundary conditions. The simulated thermal and volumetric changes in RC slabs were successfully verified with the monitored data in corresponding real structures. Thermal stress simulations confirmed the potential risk of early age cracking in RC slabs on multiple span continuous girder bridges where the accumulated tensile stress due to the stepping construction was comparatively high. Moreover, validated bridge models were successfully utilized in parametric studies to determine the factors influencing thermal cracking such as coefficient of thermal expansion, concrete placing temperature, ambient temperature etc. and revealed that thermal cracking risk of RC slabs incorporating expansive additive is insignificant in case of single span I-section steel girder and PC composite girder bridges when appropriate construction procedures are ensured.
