Petrography evidence of the interfacial transition zone (ITZ) in the normal strength concrete containing granitic and limestone aggregates

Interfacial transition zone (ITZ) is one of the key factors that associated with concrete strength and durability and its characterization has been a crucial parameter in concrete technology. Many previous researchers have conducted various microstructure assessments to evaluate variations in the ITZ and consensually accept that this zone exhibits specific changes in mineralogy and microstructure. Although the previous studies had elaborated the nature of ITZ, but the role of aggregate variation in the development ITZ microstructure in normal strength concrete is still in conclusive. Consequently, in this paper, the ITZ in normal strength concrete has been examined more closely by using three different granitic aggregates and one limestone source. Collectively, this research provide some petrography evidence that in normal strength concrete with a water/cement (w/c) ratio of 0.5, the inclusion of different types of aggregate significantly affected the heterogeneity of the ITZ microstructure. Thus heterogeneity consequences are also verified by the semi-quantitative estimation such as the percentage fraction of porosity, hydrated/unhydrated cement grains, microhardness, orientation index of calcium hydroxide (CH) and thickness.