The micromechanical signature of high-volume natural pozzolan concrete by combined statistical nanoindentation and SEM-EDS analyses

Although concrete sustainability can be remarkably improved by replacing high amounts of Portland cement clinker with supplementary cementitious materials (SCMs), this approach is far from being fully exploited. To compete with conventional concrete, a better understanding of low-cement concrete is needed regarding both microstructural features responsible for mechanical performance and key parameters for robust mix design. In particular, this paper aims at disclosing the microstructure of cementitious systems in which up to 60% of Portland cement has been replaced with natural pozzolan (NP), without significantly affecting the 90-day mechanical strength and stiffness (using a fixed water-to-binder ratio of 0.35). The study carries out coupled nanoindentation/energy-dispersive X-ray spectroscopy analyses, micromechanics modelling and image analysis to disclose the mechanical effects of NP on the overall stiffness and strength (i.e., the formation of a micro-granular skeleton of hard anhydrous inclusions and the transformation of Portlandite into calcium-aluminum-silicate-hydrate [C-A-S-H]).