Improvement mechanism of recycled concrete using C-S-H type accelerator and modifying recycled aggregate by carbonation technology

In Japan, there is concern that concrete blocks due to demolition will increase with the renewal of concrete structures. Although it has been used for roadbed materials as recycling, in recent years, aggregates are removed from the concrete mass by crushing and grinding and used again as concrete aggregates. In concrete using recycled aggregates, it is necessary to take account of insufficient strength, drying shrinkage, freeze-thaw resistance. In previous study, the quality of recycled aggregates was improved by adsorbing carbon dioxide to recycled aggregates, and recycled concrete used the modified aggregates has been confirmed to increase strength and reduce drying shrinkage. In this study, we focused on the aggregate interface of concrete such as the interfacial transition zone for the purpose of clearing the quality improvement method of recycled concrete. We attempted to modify the aggregate interface using a C-S-H hardening accelerator using two recycled aggregates of different quality and concrete using ordinary aggregates. We will also compare which is more effective, concrete that tried to modify the aggregate interface and recycled concrete that uses carbonated modified recycled aggregate. We try include strength test, drying shrinkage test, and freeze-thaw test. We clarify the matters concerned about recycled concrete.