## 1 Introduction  
Hydration occurs as soon as cement comes into contact with water to form micro-pore structures while precipitating hydration products. Moisture contained in multiscale pores is transported in both liquid and gas phases according to thermodynamic equilibrium, inducing internal stress and volumetric changes, which are closely related to the occurrence of fractures. The internal states of concrete including re-bars continuously change due to external forces and environmental actions, influencing the long-term durability and time-dependent behavior as a reinforced concrete (RC) structure. The Concrete Laboratory of the University of Tokyo has been developing an integrated microphysics and macro-structural analysis system to predict the overall behavior of a RC structure in various conditions in a unified approach for its entire service life [1]. This integrated system synthesizes the following two systems: one simulating micro-pore structures and thermodynamic states in multiscale pores based on physical chemistry, considering hydration and environmental actions [2], and the other relating to structural mechanics modeling to estimate non-linear dynamic macroscopic behavior of a RC structure, even if including damage, under mechanical actions [3]. They are generally referred to as DuCOM (Durability of COncrete Model) and COM3, respectively [1; 4]. Figure 1 illustrates the scheme of the integrated multiscale analysis system in which (A) DuCOM and (B) COM3 are linked with (C) the multiscale constitutive model. The driving force behind volumetric changes is assumed to be related to either capillary pressure or disjoining pressure according to the calculated thermodynamic moisture state in micro-pores in DuCOM. As shown in (C), concrete is idealized as a two-phase composite of elastic aggregate and hardening cement paste and its hardening is expressed by the progressive formation of finite fictitious clusters as the hydration proceeds based on the solidification theory [5]. Each component is composed of an elastic spring, a dashpot and a slider whose parameters are associated with thermo-hydro states. Given input data such as mix proportions, material properties, the geometry of a structure and boundary conditions, the time-dependent deformation can be computed without conventional classification such as autogenous/drying shrinkage and basic/drying creep, dealing with macroscopic structural responses based on the smeared crack model in COM3. In addition, microcracks caused by drying are taken into account in the micro-fracture model [6]. It has been reported that the integrated system could simulate large-scale structural behavior such as long-term deflection of prestressed concrete viaducts with good consistency [7; 8] and contributed to early cracking assessment of actual RC bridge decks [6]. In this way, each constitutional model in DuCOM-COM3 and the integrated system have been well verified by efforts of so far engaged researchers over decades for general conditions as input data [1; 2; 3; 4; 5; 6; 7; 8]. On the other hand, applications of low water-to-cement ratio (W/C) mixtures to practical structures have been increasing to enhance seismic resistance and long-term durability to meet modern severe requirements [9]. In the case of a large structure with a low W/C mixture, it takes a very long time for the internal moisture state to reach equilibrium with the external environment. Additionally, hydration continuously proceeds for a long time because of the existing inner unreacted particles and most of the formed micro-pores falling into an unsaturated state due to self-desiccation. Thus, numerical prediction of time-dependent deformation on a large scale becomes increasingly difficult especially with a low W/C. Moreover, thermal loading on such a structure can cause even more complex and sensitive phenomena.