Volume 40, Issue 3 (May 2012)
Time Zero Value Based on S-Wave Reflection Loss Measurement for Early Age Shrinkage Monitoring of Cementitious Specimens Subjected to Sealed and Unsealed Curing Conditions
Estimating the time at which to start monitoring early age shrinkage, especially of high performance cementitious materials, can be crucial. Despite numerous studies on early age shrinkage monitoring, there is no general agreement on the time at which early age shrinkage measurements should start (i.e., the “time zero” value [TZV]). The present paper proposes the use of the stiffening time measured via S-wave reflection loss as the TZV for early age shrinkage monitoring of high performance cementitious materials subjected to both sealed and unsealed curing conditions. The results imply that in the case of autogenous or sealed specimens, similar stiffening times occur throughout the specimen depths. In the case of unsealed specimens, however, the results show that the stiffening time might vary with depth depending on the water-to-cementitious ratio used. It is postulated that water redistribution within the specimen, as well as the formation of a “skin layer,” might significantly affect the stiffening time measured in the case of unsealed specimens used for early age drying shrinkage monitoring.