Quantitative analysis of microstructure of ITZ in UHPC

Abstract The fiber-matrix interfacial transition zone (ITZ) governs the mechanical performance and durability of Ultra high performance concrete (UHPC). UHPC has dense microstructure and low porosity, and the thickness of ITZ in UHPC is extremely small. The analysis of microstructure of ITZ in UHPC is very limited. Backscatter electron image (BSE) in combination with traditional methods are applied to the precise quantitative analysis of ITZ in this paper. The results indicated that the porosity decreased rapidly with the increase of the distance from fiber surface. The thickness and porosity of ITZ in SF1-UHPC1, SF2-UHPC2, SF2-UHPC3 were about 38 μm and 12.7%, 18 μm and 12.5%, 12 μm and 9.9%, respectively. With the increase of UHPC strength, the porosity of matrix and ITZ decreased rapidly, and the thickness of ITZ also decreased rapidly.