Abstract
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.
Highlights
Ancient concrete used in the Pantheon in Rome contains volcanic ejecta, which is known as pozzolana
On the other hand, when crushed to a mean diameter of 1 μm and BET of 15 m2/g, it turns into a supplementary cementitious material that contributes to strength beginning from 1 week
The following were found in this study: (1) When utilizing volcanic ejecta for engineering purposes in the concrete field, the fraction with a density 2.4 g/m3 or less is found effective from the aspect of the inclusion of clay minerals
Summary
Ancient concrete used in the Pantheon in Rome contains volcanic ejecta, which is known as pozzolana. Fine powder with a mean particle size of 1 μm (VGP 1) and coarse powder, 3 μm (VGP 3), are recovered from the bag filter and cyclone separator, respectively In their previous research [10,11,12,13] on the total utilization of pyroclastic flow deposits as construction materials, the authors clarified that dry gravity classification is effective in dividing Ito‐shirasu into crystalline mineral, pumice, high‐ purity volcanic glass, and clay fraction. The density of individual volcanic particles may vary; but it was reported that the ones of pumices are generally between about 0.7 and 1.2 g/m3, glass shards commonly have densities of 2.35 to 2.45 g/m3, lithic fragments range from 2.7 to 3.2 g/m3, and crystals vary from about 2.6 to 5.2 g/m3 [6] These results demonstrate that sorting out particles less than 2.4 g/cm by dry gravity concentration and removal of smaller clay fraction by bag filter is technically effective. These were crushed to less than 150 m and subjected to ion chromatography to quantify chloride ions in accordance with JIS A 1154 (Method of test for chloride ion content in hardened concrete)
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