高温暴露後のモルタル，コンクリート中の水分挙動

広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora

Evaluating Damaged Concrete Depth in Reinforced Concrete Structures under Different Fire Exposure Times by Means of NDT and DT Techniques

After a severe fire, concrete structures are generally capable of being repaired rather than demolished. To determine whether the fire-damaged structure can be repaired, an assessment of structural integrity must be conducted. In this research, a laboratory assessment of fire-damaged reinforced concrete (RC) slabs was carried out by using Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The study aimed to evaluate the depth of damaged concrete in RC slabs exposed to fire for different periods of time (30, 60, 90 and 120 minutes) based on the correlation between the experimental results of DT and NDT methods. The experiment was conducted with two concrete grades of 24 and 35 MPa. Limestone aggregates were used in this study.After a severe fire, concrete structures are generally capable of being repaired rather than demolished. To determine whether the fire-damaged structure can be repaired, an assessment of structural integrity must be conducted. In this research, a laboratory assessment of fire-damaged reinforced concrete (RC) slabs was carried out by using Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The study aimed to evaluate the depth of damaged concrete in RC slabs exposed to fire for different periods of time (30, 60, 90 and 120 minutes) based on the correlation between the experimental results of DT and NDT methods. The experiment was conducted with two concrete grades of 24 and 35 MPa. Limestone aggregates were used in this study. The experimental results indicated that 30 minutes of heating time did not show severe effects on reinforced concrete slabs in comparison with the other cases. A damaged concrete layer of 30 – 45 mm was observed for slabs exposed to fire in 60 and 90 minutes. Besides, 24 MPa slabs also showed a lower damage level compared with 35 MPa slabs

An investigation on moisture and water absorption in cement paste with electrical resistance method

Moisture in concrete is one of main factors related to degradation and deterioration of concrete structure, and there are various moisture transport phenomena in concrete such as drying and absorbing. There are a lot of previous studies on the drying process of concrete to clarify the mechanisms of creep as well as shrinkage. However, few studies have been reported on the process of water absorption and moisture absorption although carbonation and chloride attack are strongly related to moisture and water absorbing. It is necessary to investigate moisture transfer in concrete in detail. This study investigated the moisture transfer in moisture and water absorbing processes in cement paste by using electrical resistance method to understand how moisture and water transfer into concrete. Cement paste specimens with water-to-cement ratios (W/Cs) of 0.35 and 0.55 were prepared in this study. Stainless steel rods of 0.9 mm in diameter were arranged at an interval of 4 mm in the specimen for measuring the electrical resistance. The specimens for moisture and water absorbing test were cured in water at 20 ºC for 28 days and stored at 20 ºC and a relative humidity of 0% and 70% as reference and the national average of the annual average relative humidity in Japan, respectively. The electrical resistances were measured through the stainless-steel rods and converted to electrical resistivity. The calibration test was also conducted to obtain the relationship between the electrical resistivity and the internal relative humidity (IRH), which was used to know IRH in cement paste specimen. As a result, the rate of moisture transfer in the specimen at initial internal relative humidity (IIRH) of 0% was higher than that at IIRH of 70%. Additionally, the rate of moisture transfer in the specimen at any IIRH depends on the total pore volume in the specimen