Influence of stress and specimen geometry on three-point bending DMA in hardened cement pastes

Dynamic Mechanical Analysis (DMA) is a valuable tool for studying short-term viscoelastic behaviour in millimetric cementitious specimens. Among available configurations, three-point bending is particularly suited for stiff materials like hardened cement paste. However, unlike in other material classes, the influence of experimental variables such as stress levels and specimen geometry has not been quantitatively assessed in this context, limiting the reliability and usefulness of DMA data. This study addresses this gap by evaluating how static and dynamic stresses, as well as specimen geometry, affect storage modulus and loss tangent in three-point bending DMA tests. The DMA operational range was first established to ensure measurement validity. Tests at 1 Hz and 25°C were conducted on three groups of rectangular specimens with distinct geometries, varying static and dynamic stresses independently and jointly. The effects of static and dynamic stress were found to be opposite and followed a logarithmic trend. A unified logarithmic model was successfully applied to capture these effects using a simple analytical form, dependent on maximum stress and stress ratio, an approach not previously reported for DMA in cementitious materials. Geometry effects were linked to drying and carbonation, highlighting the technique’s sensitivity to environmental interactions. Microstructural mechanisms consistent with reversible, short-term creep were discussed. Finally, practical recommendations were proposed to guide future DMA testing protocols.