Carbonated rankinite binder: effect of curing parameters on microstructure, strength development and durability performance

Due to the high CO2-footprint of ordinary Portland cement (OPC), the search for alternative binders is now in a full swing. Rankinite-which is a hydraulically inactive material and low in calcium, is a real alternative to OPC, as it absorbs the harmful greenhouse gas from the air through carbonation hardening. Nevertheless, the carbonation hardening has not yet been fully clarified and sufficiently investigated. In this study we show that rankinite achieves a final strength exceeding 100 MPa at 45 degrees C and 24 h, whereby the binder is only similar to 50% carbonated. The reaction is diffusion limited while a dense layer of carbonation products around the rankinite grains hinders a higher degree of carbonation. The carbonation reaction could be fully characterized by spatially resolved microanalysis such as LA-ICP-MS, NMR and XRD. Finally, durability tests show the excellent suitability of the rankinite binder for a wide range of applications, making it an attractive material not only from an environmental point of view.