Atomic Force Acoustic Microscopy to Measure Nanoscale Mechanical Properties of Cement Pastes

The measurement of elastic properties at the nanoscale is a prerequisite to building a foundation for nanomechanics applications. At present, nanoindentation is widely used to measure the properties of elasticity. Under this method, a sample is indented with a rigid probe and the resistant force of the indentation is measured. The reduced modulus measured on the basis of the resistant force and the indentation depth is then converted to the elastic modulus of the sample. However, its spatial resolution, the distance between two consecutive locations of measurement, is limited to about 5 μm because of the area of the indented tip. Ultrasonic atomic force microscopy is an alternative method of attaining spatial resolution at the nanometer level. It uses information based on the vibrations transferred from the piezoelectric actuator at the bottom of a sample to the cantilever contacting the top surface of the sample. The cantilever makes contact with a relatively small force; as a consequence, it decreases the contact area and improves the spatial resolution. The application of atomic force acoustic microscopy to a cementitious material is described, and the results of the measurement of the elastic modulus of a cement paste are presented.