Effect of fly ash on the atomic scale structure of C–S–H during Portland Cement hydration

Cement hydration has a direct influence on the mechanical and durability properties of concrete. Understanding the formation and evolution of hydration products at atomic scale during different stages of hydration is important in order to engineer the material for specific performance. However, research investigations on effects of addition of supplementary materials like fly ash (FA) on the development of atomic scale structure of the major hydration product (namely, Calcium-Silicate-Hydrate C-S-H) and its correlations with nano-mechanical properties (through complementary physico-chemical and nano-mechanical techniques) are scanty. In this work, fly ash was added to Portland Cement (PC) in different percentages (20% and 40%) to study its effect on the structural and mechanical properties at different phases of hydration (3 to 90 days). The evolution of C-S-H at atomic scale in cement-FA systems has been studied using XRD, APDF, HRTEM, FESEM and FTIR, and mechanical properties at different ages have been evaluated using nanoindentation technique. The information and critical observations from the present study provide significant information on intrinsic properties of hydrating cement composites which will help in developing low-energy cement composites for sustainable structures.