Improvement of stability and mechanical properties of cement asphalt emulsion composites using nano fibrillated celluloses

Abstract

Cement asphalt emulsion composites (CAEC) are a promising environmentally friendly construction material containing two binders, cement and asphalt emulsion (AE). However, researchers have confirmed the instability of fresh CAEC and its resulting adverse effects on macroscopic performance. In this work, the stabilizing effect and mechanism of nano fibrillated celluloses (NFCs) on the fresh CAEC and its positive effect on the mechanical properties of hardened CAEC are thoroughly studied and discussed. Results show that the stability of fresh CAEC paste is positively correlated with AE/cement (A/C) and the content of NFCs, which can be attributed to the retardation caused by the unbroken asphalt particles and the steric hindrance provided by the NFCs adhering to the surface of cement and AE particles. Besides, the stability of fresh CAEC paste is negatively correlated with water bath temperature. The absolute value of zeta potential of cement and CAEC decreases with the increase of NFCs’ content, which is contrary to the other more convincing experimental results, indicating the inability of the charge theory and thus advancing the steric hindrance theory. NFCs can greatly improve the early mechanical properties of CAEC by improving the dispersion between cement and AE particles during early contact. However, the mid-term (28 d) mechanical properties of the mortar with NFCs was slightly weakened due to the strong water absorption of NFCs that can affect the hydration of cement. It is an effective way to utilize NFCs in enhancing the stability of fresh CAEC and improving the mechanical properties of hardened CAEC.