Concrete with high‑purity volcanic glass fine powder manufactured from pyroclastic deposit

摘要

Volcanic deposits, which are pozzolanically reactive, have long been known to improve the durability of concrete. Nevertheless,it has also been pointed out that the use of a natural pozzolan as a supplementary cementitious material (SCM)can pose problems of low workability and slow strength development. Also, in addition, its composition and physicalproperties have large variety and variability. We have been conducting studies on the total utilization of volcanic depositsfor applications suitable for respective properties by classifying them by floating speed difference and particle diameter.It is reported that sorting out particles less than 2.4 g/cm~3 by dry gravity classification and removal of smaller clay fractionby dust collector is technically effective to recover high purity volcanic glass from pyroclastic flow deposits called“Ito-Shirasu”, which is a local name for pyroclastic flow deposits in Japan. In this study, concrete containing high-purityvolcanic glass powders with different finenesses are investigated regarding fresh properties, strength development,chloride ion penetration and CO_2reduction. As a result, it was found that volcanic glass powders made an excellentcontribution to the improvement of flowability comparable to fly ash, the enhancement of strength comparable to silicafume, and the restraint of chloride ion penetration. Volcanic glass powders can also contrbute to the reduction of CO_2emission because the content of Portland cement can be significantly reduced to obtain the same strength comparedto concrete with 100% Portland cement. This study provides a possibility to produce high performance SCMs in volcanicregions worldwide from volcanic ejecta by sorting out a high purity volcanic glass by the same method.