Fundamental Study on Leaching of Coarse Aggregate Using Limestone from Concrete Irrigation Facilities in Tohoku Region

Abstract

In irrigation facilities in the Tohoku region where concrete made with limestone (hereinafter referred to as LS) coarse aggregate is used, crater-like depressions have formed as a result of selective leaching of the coarse aggregate underwater. This study sought to clarify the mechanism of this phenomenon through field surveys, aggregate tests, and replication tests of coarse aggregate leaching using concrete specimen under various flow velocity conditions. In field surveys, leaching was confirmed in a precast concrete water channel made with coarse LS aggregate, a cast-in-place concrete water channel, and the spillway of a concrete dam. Abrasion test showed that coarse LS aggregate meets the JIS standard but is inferior to andesite coarse aggregate. Leaching replication test using coarse LS aggregate showed that the leaching depth of coarse aggregate is directly proportional to the number of days elapsed and more evident in areas with greater flow velocity; in addition, leaching depth of LS coarse aggregate was predicted as 0.5 mm/year at a flow velocity of 0.5 m/s.