Expansive mechanisms in concrete

The purpose of this paper is to remind readers that past experience with cement and concrete has useful information to offer for clarification of current problems in technology and research. Early experience with expansive reactions of free lime, CaO, and magnesia, MgO, in cement and concrete are referred to and compared with later observations of non-expansive recrystallisation of secondary calcium hydroxide, Ca(OH) 2, and magnesium hydroxide, Mg(OH) 2, in field concrete. Mechanisms of expansive vis a vis non-expansive reactions in cement paste, mortars, and concrete in field concrete and laboratory test specimens are explained with reference to the described observations.