Micro-scale testing methods and comparative analysis of mechanical and creep properties in cement-based materials

The accurate characterization of the micro-scale creep behavior of cement-based materials is key to developing multi-scale predictive models. To address the limitations of the current mainstream nanoindentation method, such as stress concentration and the inability to directly measure strength, this study introduces a complementary method based on micropillar compression, enabling measurement of elastic modulus, creep behavior, and compressive strength under (quasi-)uniform compressive stress. We detail the testing principles, loading protocols, and analysis procedures for both nanoindentation and micropillar tests, and compare the resulting material parameters. Results show that measured microscale creep is strongly method-dependent: the creep compliance obtained from micropillar tests exhibits linear creep characteristics and a power-law evolution within a stress-to-strength ratio of 0.15–0.70, making it suitable for short-term creep characterization and parameter identification; by contrast, the contact-scale creep function derived from nanoindentation follows a logarithmic law, which is advantageous for characterizing long-term creep response and modulus. Additionally, the size effect of C-S-H micropillar samples was analyzed: compressive strength increases significantly as the micropillar size decreases, while the size effect on elastic modulus is relatively weak. The micropillar compression method provides a new approach for testing the micro-mechanical properties of cement-based materials and complements the nanoindentation method.