Measurement of the E-modulus of cement pastes and mortars since casting, using a vibration based technique

The use of ambient vibration tests to characterize the evolution of the E-modulus of cement pastes and mortars during hydration, and immediately after casting, is addressed in this article. The methodology consists of using 550 mm long hollow acrylic tubes, with an internal diameter of 16 mm, as a formwork for the cementitious material under study (cement paste or mortar). Along hydration the hardening material together with the external tube will endure a composite behaviour; through clamping of one extremity of the resulting composite element and leaving the other extremity free, a 450 mm long cantilever is then obtained. By continuously monitoring the accelerations at the free end of this cantilever, and using an ambient vibration technique, the first resonant frequency of vibration can be identified, which allows to determine the growth of the instantaneous E-modulus of the cementitious material, and therefore to trace its evolution during hydration. A detailed description of the experimental setup and test procedures is presented first, and afterwards some exploratory experiments performed with cement pastes are commented, illustrating the capabilities of this novel method, as well as its robustness.