Continuous monitoring of sand–cement stiffness starting from layer compaction with a resonant frequency-based method: Issues on mould geometry and sampling

The application of a vibration-based methodology for the continuous measurement of the stiffness of sand–cement has recently been proposed by the authors of this work. Such methodology consists of placing the sand–cement sample into a mould, then placing the mould in simply supported conditions, and finally monitoring it over time to assess the evolution of its resonant frequency. This evolving resonant frequency of the system can be analytically correlated to the stiffness of the tested material. Based on the success of the pilot application, this work has been extended to the methodology of in situ sampling. Such an extension involves the use of new geometries and materials for the moulds. The performance of the adapted technique is verified by comparing its results to those obtained through uniaxial compression cyclic tests up to the age of 28 days. This work also encompasses the characterisation of the hydration kinetics of a cement paste, made with the same cement as that used for cementing sand, and draws conclusions about the relationship of stiffness evolution in both materials.