2022 Volume 78 Issue 4 Pages 321-340
Slope protection frames are indispensable to prevent local disasters in Japan where torrential rains and earthquakes occur frequently. Conventional slope protection frames, which are typically constructed by shotcreting using low-slump mortar delivered by air, often face a problem of inadequate strength due to separation of aggregates. We developed a material delivery system in which a typical concrete pump for civil works is used to deliver the material and air is injected at the end of the delivery pipe. With this system, a high-slump material can be delivered over a long distance to a high-altitude site without causing material separation and can be placed in formwork at a steep slope using compressed air. Blowing air into the material reduces the slump and enables the material to be placed without causing separation or flow-out. When air is added to the material, water droplets are scattered at the nozzle. We focused on this phenomenon and developed measures to control the slump after placement. Moreover, addition of sepiolite improved separation resistance and flow-out resistance of the mortar after placement, which led to an improvement in the product quality of the slope protection frames.
