Utilization of volcanic ejecta as a high-performance supplementary cementitious material by gravity classification and pulverization

The reaction of natural pozzolans is caused by volcanic glass composed of amorphous silicate; however, volcanic ejecta also contains crystal mineral, pumice, and sometimes weathered clay fraction in their natural conditions. By focusing on the differences of physical properties between these components, high-purity volcanic glass powder (VGP) was manufactured by dry gravity classification and pulverization. This paper reports the results of investigations to utilize pyroclastic flow deposits as a supplementary cementitious material (SCM). Through this method, the glass content of VGP increased to 88% with a mean particle size of 1 μm, when that of the raw material is about 60%. Chemical analysis indicated that VGP is principally composed of silica (about 72%) and alumina (about 13%). The performance of VGP as a SCM was evaluated by conducting tests on concrete mixtures, replacing 0% to 30% by weight of portland cement by VGP with a 20% to 60% water to cement ratio. VGP concrete showed better results of 7-and 28-day compressive strength compared to control concrete in all experiments. In particular, VGP demonstrated better flowability and strength development in concrete with a low water-binder ratio in comparison to silica fume.