Abstract

When obtaining rocks as concrete aggregates at dam construction sites, rocks are used after separating good materials from wastes followed by drilling and blasting in quarry sites. Although on-site evaluation methods for classification are visual observation and hammer sounding, it is important to establish an evaluation method based on quantitative indices to secure the amount of good materials. On the other hand, in the laboratory outside the construction site, density and absorption are examined. It usually takes two to seven days to obtain the test results. Testing time should also be reduced.

The authors examined an on-site simple and quick classification method of concrete aggregates, using portable and quantitative analyzers. Since the main reasons for reducing the rock quality when used as aggregates are deterioration induced by weathering and alteration, capturing the physical and chemical characteristics would enable to classify the good materials from wastes. Based on these concepts we chose three different analyzers: colorimeter, magnetic susceptibility meter and X-ray fluorescence (XRF) analyzer. We then examined the applicability of these analyzers to andesitic and granitic rocks, which are representative rock types for concrete aggregates. We also compared the correlations of the analyzed data such as color value, magnetic susceptibility and weight percent of the constituents with density and absorption used mainly as quality control indices. As a result, it was found that the magnetic susceptibility and calcium composition are effective for andesitic rocks, while color values and calcium composition are effective for granitic rocks to classify good materials from wastes.

1. Introduction

Using color values is one of the on-site simple, quick and quantitative classification methods of rocks (Nishiyama et al., 2011). In addition to the color values, the authors examined rock quality, in terms of magnetic susceptibility. However, it was found not useful for granites since the magnetic susceptibility was low (Ichiki et al., 2015; Yamagami et al., 2014). The authors then focused on the portable X-ray fluorescence (XRF) analyzer used for the soil contamination surveys (Marumo et al., 2007), to evaluate the degree of weathering and alteration for andesitic and granitic rocks. As a result, it was found that the magnetic susceptibility and calcium composition are effective for andesitic rocks, while color values and calcium composition are effective for granitic rocks, to classify good and waste materials.

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