This paper investigates the causes of excessive long-term deflection of PC bridge viaducts by using 3D integrated material- structural analyses to take into account the coupled chemo-physics at various scales from the molecular size of water to the structural members. The excessive deflection observed at site is found to be rooted in the deformation of cement paste stemming from both externally applied loads and internal stresses driven by capillary surface tension and disjoining pressures in micro-pores. Not only the former but also the later effect is focused in the serviceability control of PC viaducts. It is found that the nonlinear, long-term deflection of the bridge viaduct can be approximately separated into the components of deflections provoked by external mechanistic and internal thermodynamic actions, even though each component is nonlinearly associated with the thermodynamic states of moisture in micro-pores of cement hydrates. Copyright © 2012 Japan Concrete Institute.