Chikako Fujiyama

Rate‐dependent model of structural concrete incorporating kinematics of ambient water subjected to high‐cycle loads

Purpose – The paper aims to propose a rate‐dependent model of structural concrete in combination with the kinematics of condensed water.Design/methodology/approach – First, the paper proposes the coupling model of water versus cracked concrete with a mathematical completeness of equilibrium and deformational compatibility. The proposed model deals with anisotropy of structural performance and of permeability, which is a particular issue of concrete caused by cracks. The governing equation for saturated concrete in this study is based on Biots theory that deals with particle assembly as a two‐phase composite. Second, the paper shows the possible reduction of the fatigue life of real‐scale bridge RC decks owing to the water residing in structural cracks under moving wheel‐type loading.Findings – The paper shows that the existence of water possibly has an influence on the rate‐dependency of structural performance. The comparison of transition of pore pressure and principal strain indicates that damage to th...

Crack Water Interaction and Fatigue Life Assessment of RC Bridge Decks

A rate-dependent model of structural concrete incorporating kinematics of ambient condensed water is presented. The constitutive laws of solid concrete skeletons and the pore water inside cracks are consistently coupled, and the anisotropy of both solid stiffness of cracked solid and crack-orientation dependent permeability of water are taken into account with full compatibility. The nonlinear finite element analysis of RC slabs is conducted under various ambient moisture states and high-cycle fatigue loads of different rates. The analytical results indicate that a high loading rate shortens the fatigue life of saturated concrete bridge slabs.

Strain Rate Effect of Cementitious Materials Influenced by Existence of Water and ITZ Around Aggregates

The strain rate dependent responses of concrete mortar and cement paste cylinders were investigated using uniaxial compression tests with high and low loading rates. The influence of the cracking process was focused on first. Pre-cracked specimens of concrete and mortar were examined. The results suggested that the influence of the cracking process is possibly more dominant than the influence of the water content. The movement of water through micro-pores of a matrix was focused on next. The water inside the mortar specimens was controlled by temperature. The specimens were frozen to temperatures between approximately −20 to −197 °C by using ice, dry ice, and liquid nitrogen. A special device for thermal insulation during loading was developed for this study. The strengths of the most specimens were magnified at high strain rates, although the movement of water through micro-pores was partially prevented by the freezing of pore water. The results indicated that the movement of free water in the micro-pores of the matrix did not always dominate the strain rate effect of the mortar. Lastly, the specimens made of cement paste were examined in order to examine the influence of interfacial transition zones (ITZ) around the aggregates. The results suggested that the existence of the ITZs discouraged strain rate effects because ITZs dispersed the initiation of micro cracks.