The Interfacial Transition Zone: ‘Direct’ Evidence on Compressive Strength

There is little question that the strength of the interfacial transition zone (ITZ) between cement paste and aggregate affects the compressive strength of concrete. The key question, rather, is to what degree? It is difficult to directly measure the response of the overall composite to changes in interfacial properties, since it is difficult to isolate interfacial strength as the only variable. Research on the effects of interfacial strength on the compressive response of concrete that comes the closest to providing direct evidence is summari7.Cd. The studies, dating to the 1950's, include both experimental and analytical efforts aimed at isolating the effects of the ITZ, as well as experimental efforts that are considered to provide strong indirect evidence. The research shows that the ITZ plays a measurable role in the response of concrete to compressive stress, but that its role is overshadowed by the properties of the cement paste and aggregate constituents of concrete and the heterogeneous nature of the composite