Effect and mechanisms of nanomaterials on interface between aggregates and cement mortars

As the weakest zone in concrete, the interfacial transition zone (ITZ) between aggregates and cement mortars has important effects on the properties of concrete. This paper aims to investigate the effects and mechanisms of nanofillers on the bond strength and interfacial microstructures between aggregates and cement mortars. A total of 8 representative types of nanofillers (namely nano-SiO2, nano-TiO2, nano-ZrO2, untreated multi-walled carbon nanotubes (MWCNTs), hydroxyl-functionalized MWCNTs, nickel-coated MWCNTs, multi-layer graphenes (MLGs), and nano boron nitride (nano-BN)) were selected to fabricate specimens with scale-up aggregate-cement mortar interface that can be characterized by the three-point bend test. The experimental results indicate that all types of nanofillers can enhance the bond strength between aggregates and cement mortars. The highest relative/absolute increases of 2.1 MPa/35.1%, 2.32 MPa/38.8% and 2.56 MPa/42.8% in interfacial bond strength are achieved by incorporating 2 wt% of nano-ZrO2, 0.3 wt% of nickel-coated MWCNTs, and 0.3 wt% of nano-BN, respectively. Scanning electron microscope observations show the presence of nanofillers can improve hydration products and increase interfacial compactness. Energy dispersive spectrometer results suggest that local content of nanofillers in the ITZ is higher than that in the bulk cement mortars. These findings indicate the nanofillers can transfer with water migration toward aggregates and enrich in ITZ, thus improving the bond strength and interfacial microstructures between aggregates and cement mortars through the nano-core effect. (C) 2019 Elsevier Ltd. All rights reserved.