Shrinkage and cracking sensibility of steel-alkali activated UHPC composite bridge decks

Alkali-activated ultra-high performance concrete (AAUHPC) is a concrete containing excellent properties such as high strength, high durability and low carbon emission. In this study, tests were carried out to investigate the basic mechanical properties of AAUHPC and restrained shrinkage behavior of steel-AAUHPC composite bridge decks. The effects of different parameters (e.g. the stiffness of steel deck, the thickness of AAUHPC layer, arrangement of studs and the temperature and humidity) on the early age contraction and cracking sensitivity of steel-AAUHPC composite bridge decks were investigated. The results showed that the AAUHPC deck without any internal or external restraint showed a higher shrinkage at a faster rate in the early stage. The rate of shrinkage in the later stage declined gradually with age, and the overall shrinkage deformation was found to be stable at the age of 28 days. For the reinforced AAUHPC composite decks subjected to internal and external constraints, the restrained effect of steel deck, studs and steel reinforcement on the shrinkage of AAUHPC was quite prominent which increased with the increase of steel deck stiffness and the thickness of AAUHPC, where as the temperature and humidity of environment showed a minor effect on the restrained shrinkage deformation at 28 days. The tensile properties and toughness of AAUHPC with steel fibers were found to be high. During the entire test, no cracks were observed on the surface of the reinforced AAUHPC composite bridge decks. However, the cracking risk of AAUHPC was high in the first 2 days, and the cracking risk coefficient in the later stage was about 0.2. In addition, the accuracy of the experimental results was verified by finite element analysis.