PDMS/CNB-impregnation treatment for improving the electrical and piezoresistive properties of recycled fine aggregate mortar

Abstract

Self-sensing mortar prepared by recycled fine aggregate (RFA) has great significance for recycling of waste concrete. However, recycled fine aggregates have not been widely used in self-sensing mortar due to their inferior properties to natural fine aggregates. Therefore, the purpose of this study is to improve the properties and conductivity of RFA by the impregnation pretreatment in polydimethylsiloxane emulsion (PDMS) solution containing nano carbon black (NCB), and use modified RFA to prepare self-sensing RFA mortar. The effects of several factors, including modified RFA replacement ratio, temperature and humidity on the resistivity of as-prepared RFA mortar were studied by four-electrode method. The results show the micro-pores of RFA have been filled by PDMS, reducing the water absorption by 1.64%. At the same time, the NCB particles in PDMS have successfully been coated on the surface of RFA by this impregnation pretreatment. The resistivity of mortar decreases with the increases of modified RFA replacement ratio. When the replacement ratio of modified RFA is between 50% and 60%, the threshold percolation concluded by the sharp decline of mortar resistivity begins to appear. Besides, the conductivity of modified RFA mortar has good temperature sensibility and humidity adaptability. Under cyclic loading of stress, the modified RFA mortar has 1.82%/MPa stress sensitivity, 9.47% linearity, 176.1 sensitivity, 10.95% repeatability and 6.39% hysteresis in percolation zone, which of the piezoresistive properties are better than those in insulation and conductive zones. In addition, the stress sensitivity of modified RFA mortar in different zones decreases with the increase of loading rate.