Structural lightweight concrete: influence of expanded clay on the microstructure of the interfacial transition zone

Abstract This paper presents the results of a study on the effect of expanded clay on the microstructure of the interfacial transition zone (ITZ) between Portland cement paste and aggregates. A scanning electron microscope (SEM) equipped with an energy dispersive X-ray analysis system (EDX) was used to determine the ITZ thickness. In plain concrete a marked ITZ around the aggregate particles (55 (m) was observed, while in concretes with expanded clay, the ITZ was less pronounced (30 (m). It was also verified that the ITZ of concrete with expanded clay had lower levels of porosity and calcium hydroxide than that observed in plain concrete.