Hidehiko Ogata

EFFECT ON OXIDATION-REDUCTION POTENTIAL OF MIXING WATER TO HEXAVALENT CHROMIUM LEACHED FROM CEMENT

There is a possibility that the amount of dissolved hexavalent chromium in the cement exceeds the environmental standards. However, there are few cases and drastic countermeasures have not been taken yet. This study examined the possibility on reduction of dissolved hexavalent chromium, reduced into trivalent chromium, using adjusted oxidation reduction potential (ORP) of water for mixing, as a simple preventive countermeasure. As a result, it was confirmed that hexavalent chromium contained in ordinary portland cement and blast furnace slag cement were deoxidized to trivalent chromium. Amount of dissolved hexavalent chromium decreased with reduction of ORP. Meanwhile, mixing water that adjusted ORP didn’t affect the stability and strength characteristic of cement.セメントに含まれる六価クロムの溶出量が環境基準値を超える可能性があるが、現状ではこのような事例は少ないことから抜本的な対策は講じられていない。そこで本研究では、簡易な予防保全的対策として酸化還元電位を調整した水を練混ぜ水として用いることにより、六価クロムを三価クロムへ還元することが可能か検討した。その結果、普通ポルトランドセメントおよび高炉セメントに含まれていた六価クロムは三価クロムに還元され、練混ぜ水の酸化還元電位低下に伴い六価クロムの溶出量が減少することを確認した。また、酸化還元電位を調整した練混ぜ水を使用してもセメントの安定性、強度特性に影響を及ぼすことは確認されなかった。

Interaction between Engineered Cementitious Composites Lining and Foundation Subsurface Drain

The effect of cyclic loads on the surface profiles of ECC linings cast on foundations comprising crushed stone and compacted soil was investigated. A geotextile was embedded between the crushed stone and ECC lining for some of the samples. After 28 days of water curing, the hardened surfaces were loaded and monitored for roughness and crack development by measuring surface levels and crack widths, respectively. Neither cracking nor significant variations in the lateral profiles were observed on all the samples for all the loads applied. However, significant variations which depended on the foundation types were observed in the vertical profiles. It was concluded that while ECC can resist cracking due to its high strain capacity, its flexibility causes ECC linings to assume the shape of the foundation material, which can increase the surface roughness at certain loading configurations.