Drying-Participating Water and Drying-Induced Air Voids in the Post-curing Drying of Cement-Based Material

Cement-based material fabrication typically involved cement-mix curing, followed by drying, which partially removed the evaporable water. The post-curing drying of cement-based materials is addressed with unprecedented determination of the drying-participating water (DPW) and drying-induced air voids (DIAV), which in this work involve drying at 23 °C and 40% relative humidity, and differ from the widely reported greater quantities for elevated-temperature drying. This work also provides a simple method for the determination in real time during drying. Prior methods, such as porosimetry and density measurement, are inadequate. Of significance is the finding that increasing the water/cement ratio caused the DPW and DIAV contents to grow, but the fraction of the drying-induced pore volume occupied by air remained unaffected. Here, “complete drying” means complete removal of the part of the evaporable water that can be removed under the drying conditions used (23 °C, 40% relative humidity, 30 days), i.e., DPW during post-curing drying. The cured material was saturated with water before drying started. During drying, the DPW content diminished while the drying-induced air voids (DIAV, the part of the total air voids resulting from drying under the drying conditions used) content grew, with air (rather than water) increasingly occupying the drying-induced pores. The density and DPW + DIAV (drying-induced porosity) decreased slightly during drying. Increasing the water/cement ratio caused the DPW and DIAV contents to grow, but the fraction of the drying-induced pore volume occupied by air remained unaffected. This work provides a new method of real-time determination of DPW and DIAV during drying.