Study of Environmentally Friendly Concrete Combining Recycled Aggregate with Blast Furnace Slag Cement

The environmental issues need transition to promoting the formation of recycling-based Society as well as realization of carbon neutrality. In the concrete field, there is an attempt to use demolished concrete structures as recycled aggregate. It has not been widely used because of it is low quality compared to natural aggregate. However, since the water absorption and porosity can be modified by carbonation technology, it has recently been focus as a CCU material. In this study, we aimed to achieve carbon neutrality by using a combination of carbonated recycled aggregate with blast furnace slag cement, which emits less CO2 emissions than ordinary Portland cement. As a result, the CO2 balance approached zero when ground granulated blast furnace slag replacement ratio was high and carbonated recycled aggregate was used. However, strength of these concrete was lower than that using recycled aggregate. It could be attributed to the increased porosity of the new mortar section. As a solution to this problem, the addition of a C-S-H type accelerator which promotes hydration resulted in improved strength.