Development of a New Recycling Process for Concrete Sludge Generated From Concrete Pole Plant

A new recycling process for concrete sludge using carbon dioxide (CO2) was investigated. Concrete sludge is a slurry waste mainly consists of water and cement particles. An actual concrete sludge sample generated from a centrifugal-reinforced concrete pole plant in Japan was collected and used in this study. An alkali component, mainly calcium hydroxide (Ca(OH)2), is repeatedly extracted from cement particles by repeating water addition and subsequent solid-water separation. Calcium carbonate (CaCO3) is precipitated by introducing gaseous CO2 into the obtained Ca(OH)2 solution. In this process, concrete sludge is neutralized by gaseous CO2, and CaCO3 particles can be obtained. The calcium extraction and CaCO3 precipitation reaction rates were measured, and feasibility of the recycling process was discussed.