Interfacial Transition Zone in Mature Fiber-Reinforced Concretes

[EN] The interfacial transition zone (ITZ) in concrete is the region of the cement paste that is disturbed by the presence of an aggregate or fiber. This work focuses on the ITZ around silica and dolomite grains and steel fibers. The analysis performed is based on: the macroscale properties of the specimens; petrographic analyses with polarized microscopy; and qualitative and quantitative SEM analyses. The following types of concrete were tested: standard quality (SQ); high-quality with steel fibers (PFRC); and ultra-high-performance fiber-reinforced concrete (UHPFRC). The most important parameters affecting ITZ are the properties of the disturbing elements and the mixture composition of the concrete. In PFRC, a differentiated zone of thickness 20 ¿m (787.40 ¿in.) was observed around a dolomite grain, showing a preferential growth of Ca-based compounds. In UHPFRC, SEM-EDS analysis revealed C-S-H of lower Ca/Si ratios in the proximity of fibers and aggregates.