Associate Professor in Civil Engineering, Honorary Scientist of Shanghai Pujiang Scholars, School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University, China

Biography: Dr Liu’s research activities mainly focus on concrete durability particularly in the fields of multi-component transport in porous medium, electrochemical rehabilitation, service life prediction as well as chloride-/carbonation-/ASR-/freeze&thaw-/sulphate-/leaching-induced problems, aiming at better understanding deterioration mechanisms of concrete. So far, Dr Liu has published more than 70 peer reviewed papers, and acts as PI for 11 government supported research programs including 3 national projects and 4 talent program. He also serves as editorial board members for the Journal - “Materials” as well as committee members of 13 international academic associations.

Speech Title: Multi-Phase Modelling of Multi-Component Ionic Transport in Unsaturated Concrete under Drying-wetting Cycles

Abstract: Concrete is always treated as an inhomogeneous composite material, whose response of inclusion structures and ionic transport mechanisms are crucial to the service life of concrete-based infrastructure and buildings. The situation becomes more serious when concrete structures are subjected to drying-wetting cycles (DWCs) in tidal and splash zones, which leads to serious chloride-induced corrosion of reinforcement. To facilitate understanding on mechanism of chloride-induced durability problems in concrete structure under DWCs, a prediction “double-multi” model was developed, which considered not only the multiple meso/micro phases (i.e., aggregates, cementitious materials, interfacial transition zone (ITZ), cracks, etc.), but also the multiple ionic species (K+, Na+, Ca+, Cl-, OH-, SO42-, etc.). The proposed “double-multi” model is very suitable for further investigating a set of research areas, e.g., diffusivity prediction, binding effect, EDL effect, cracking effect, ITZs, aggregate morphology, etc. By introducing the Poisson Equation, this paper investigated the ionic interaction of multi-species under both diffusion and convection in a multi-phase unsaturated concrete. By solving the modified Fick’s second law, the spatial-temporal concentration distributions of chloride and other ionic species were obtained by using the present model. Further, the parametric sensitivity analysis was performed on a series of significant influencing factors (i.e., time ratio of wetting and drying process, initial saturation of concrete pores, temperature and humidity of the external environment), which significantly affect the maximum value of the chloride concentration and the depth of the convection zone.

Keywords: Composite material; Cementitious material; Unsaturated concrete; Multi-phase; Multi-species; Diffusion; Convection; Drying-wetting cycles