Tensile strength of hydrated cement paste phases assessed by micro-bending tests and nanoindentation

Abstract

The paper is focused on the experimental investigation of cement paste's tensile strength and related mechanical properties at the micrometer level. Small scale specimens with micrometer dimensions in the form of cantilever beams having a triangular cross section and ≈20 μm in length are fabricated by means of a focused ion beam and tested in bending with the aid of a nanoindenter. Elastic properties are evaluated from both bending and nanoindentation tests for all the phases with very close agreement. The phase separation is performed with SEM-based image analysis and the deconvolution of grid nanoindentation results. The load-deflection curves of bent beams are monitored up to the failure for distinct microlevel phases, namely for inner and outer products and Portlandite. The tensile strength of the phases is directly derived from the load-deflection curves in the range of 264 MPa (for the outer product) to 700 MPa (for the inner product and Portlandite). Moreover, the load-deflection curves are used for the supremum estimates of fracture energies for individual hydrated cement phases. Low values of the energies in the range of 4.4 − 20 J/m2 were found. The values obtained experimentally in this paper correspond well with those published in recent multiscale or molecular dynamics models.