Xiang Xi

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.

Pyropermittivity, pyroresistivity, and pyroelectret refer to the effect of temperature on permittivity, resistivity, and inherent electric field. They are emerging thermoanalytical methods that are relevant to capacitance-based, resistance-based, voltage-based temperature self-sensing, and thermal energy harvesting. This work provides the first determination of temperature coefficients of permittivity (associated with AC polarization), resistivity (associated with DC conduction), and inherent electric field (associated with DC polarization) for carbon-carbon composites (C/C). The coefficients are -(5.1±0.2)×10 ^-3 K ^-1 , (2.0±0.1)×10 ^-3 K ^-1 , and (0.43±0.02) K ^-1 in terms of resistivity, permittivity, and inherent electric field, respectively. The highest coefficient for the inherent electric field means DC polarization is more sensitive to temperature. The activation energy required for the inherent electric field ((0.25±0.01) eV) is significantly higher than for resistivity ((56.6±1.6) meV) and permittivity ((21.4±0.6) meV), suggesting that the formation of electrets through carrier-atom interaction is more challenging during heating than the interaction under AC conditions and carrier drift under DC conditions. Mild heating increases the volumetric power density (by 600 times), gravimetric power density (by 600 times), and current density (by 28 times) significantly. The pyropermittivity-based energy density is (4.96±0.15) × 10 ^-6 J/m ³ when the temperature increases from 20 °C to 70 °C. The temperature self-sensing and self-powering behavior make C/C a highly promising smart material.

To address the issues of low strength, poor water stability, and hazardous substance leaching associated with using phosphogypsum (PG) as a direct road-based material, the traditional approach involves employing inorganic cementing materials to stabilize PG, effectively addressing the problems. This study innovatively utilizes the xanthan gum (XG) and sodium methylsiliconate (SM) as curing agents for PG to solve the above problems. An organic curing agent stabilized PG was prepared by dry mixing XG and PG. The unconfined compressive strength, water stability, and leaching behavior of stabilized PG were investigated, the leaching behavior was characterized by ion leaching concentration, and the mechanisms behind the strength development of stabilized PG were explored by SEM and FTIR. The experimental results indicate that the single incorporation of XG reduced the strength and water stability of stabilized PG, while the single incorporation of SM had a limited effect on strength and water stability. In addition, the dual incorporation of XG and SM significantly improved the strength and water stability of stabilized PG. At the same time, the dual incorporation of XG and SM greatly reduced the leaching of hazardous substances from stabilized PG. These results demonstrate the feasibility of using stabilized PG for road base materials.