Ice content is an essential factor that affects the internal pressure of cement-based materials during freeze-thaw cycles (FTCs). Since the electrical conductivity of mortar is closely related to its moisture content, it is possible to estimate the ice content based on electrical conductivity variation of mortar. As a result, the ice formation process during FTCs can be monitored. This paper proposed a model to estimate the ice content by applying electrical measurements and clarified the combined effects of temperature and moisture content for electrical conductivity of mortar. The ice content of mortar was estimated with the model by conducting the electrical test. The results are found in acceptable agreement with theoretical results from thermodynamic analysis, and the relationship between ice content and temperature is similar to existing calorimetric test results, which confirm the reliability of the model and the proposed test method.
This study proposes a novel method for recycling concrete waste by compaction. The advantages of the proposed method include its high production speed and complete recycling; all of the concrete waste was used without segregation of gravel or other components. First, hardened cement paste (HCP) was examined, crushed, milled, and compacted. These formed compacts showed high strength. Compacts of hardened concrete (HC) were prepared after crushing and milling; however, their strength was low. The processes of adding HCP or sludge cakes and performing carbonation treatment were investigated to increase the HC compact strength, and all treatments were found to be effective. Another advantage of this compaction method is that the control of volumetric changes due to moisture loss or absorption can be achieved by adequately drying the powder before compaction.