Microstructural characteristics of bonding interfacial transition zone of concrete and magnesium ammonium phosphate cement

Abstract

Microstructural characteristics of bonding interfacial transition zone (ITZ) are vital to the bonding performance of new-old concrete, which remains difficult to characterize accurately. In this paper, the microstructural characteristics of ITZ based on magnesium ammonium phosphate cement (MPC) bonding to ordinary Portland concrete (OPC) were investigated by the combination of BSE-EDS and microhardness. It was found that ITZs were distinguished into MPC bonding to OPC paste (ITZ-P) and aggregate (ITZ-A). Meanwhile, Gaussian Kernel Smoothing was suitable to the statistical analysis of microhardness. The peak interval of microhardness in ITZ-P for 113.1 MPa was higher than that in ITZ-A for 87 MPa. It was reflected by the observation of denser hydration products and calculation of lower porosity in ITZ-P, especially the observation of enriched pore area in ITZ-A. Moreover, based on the interrelation of indentation lattice and corresponding distribution of element, the hydration products was quantitatively analyzed. The denser hydration products and lower porosity in ITZ-P are 41.4% and 4.3%, respectively, compared with the 29.3% and 12.5% in ITZ-A. The exposure of more aggregate is not conducive to the attachment of the hydration products of MPC.