Nobuhiro Chijiwa

Delayed Shear Crack Formation of Shallow RC Box Culverts in Service

Long-term excessive deformation of underground reinforced concrete (RC) box culverts in service was monitored over 20 years and its mechanism is analytically discussed in this study. The long-term excessive deformation possibly attributes to synergy effects accompanying delayed shear failure of RC slabs subjected to vertical soil pressures and the time-dependent creep-shrinkage of structural concrete. Special attention is directed to the delayed shear cracking which was actually found in real underground box culverts over the service life. The delayed shear crack is experimentally reproduced in the laboratory as well as the multi-scale computational simulation.

Chloride Binding Ability and Anti-corrosion Properties of Supersulfated Cement in Seawater/Sand Mixing Concrete

In this study, we aim to shift attention to ability of chloride binding of supersulfated cement and its use for formulating sea water/sand mixing concrete. To formulate SSC cement, slag as main component is activated by high alkaline of C-H and the following reaction with SO4 2−. Material analysis (XRD, SEM/EDX) showed that effectively low-Ca-ettringite products were formed abundantly at early age and others chloride binding products such as Friedel’s salt, hydrotalcite in their turn were resulted at later age in high Cl− solution. Notable high ratios of bound Cl− on total Cl− indicate eventually capacity of hydrated cement matrix in neutralizing chloride content in seawater. As an addition, very low Cl− permeability of mortar specimen could be taken into account. By monitoring the corrosive state of embedded steel bar ϕ8 mm (inside mortar prism 40 × 40 × 160 mm, with seawater exposure condition), we observe no major deterioration due to such natural anti-corrosion phenomenon.

Multi-Scale Seismic Simulation of RC Building Coupled With Drying Shrinkage and Steel Corrosion

The multi-scale thermo-hygral modeling is applied to full-scale RC structural systems under combined long-term ambient and short seismic actions, and experimentally verified in reference to a shaking table test of the real scale RC building. Here, the effect of drying shrinkage on seismic responses of framed buildings is numerically investigated and the coupling with steel bar corrosion is discussed as a complex durability problem. It is concluded that the drying effect of structural concrete has the substantial impact on shear capacity of RC members and the story drift of buildings when thin shear walls play a major role of the seismic resistance, and that the deformational mode may vary according to the corrosion of reinforcement as well.