Pop-outs found in a hematite colored basement floor subjected to wetting and drying action were attributed to shale introduced into the concrete as fine aggregate. The shale particles in pop-outs were characterized by clear gel rims associated with the alkali-silica reaction as well as red-brown hydrated iron oxide gel caused by oxidation of indigenous iron. Fresh shale particles from the same fine aggregate source used in the concrete under investigation were placed in sodium hydroxide which developed reaction zones characteristic of the concrete reaction and were interpreted as evidence supporting the instability of this material in alkaline environment. The hematite color which marked the original particle surfaces, indicated that reaction rims were developed entirely within the shale particle. Further study of the rim gel is needed to explain the pathway and interactions between the iron oxidation reactions and the alkali-silica reactions.
Proceedings of the Iowa Academy of Science
©1967 Iowa Academy of Science, Inc.
Elwell, James H. and Lemish, John
"Pop-outs in Hematite Colored Concrete Floor,"
Proceedings of the Iowa Academy of Science, 74(1), 117-121.
Available at: https://scholarworks.uni.edu/pias/vol74/iss1/21