Long-Term Influence of Nanosilica on the Microstructures, Strength, and Durability of High-Volume Fly Ash Mortar

Abstract

Nanosilica has been proven able to strengthen the early-age performance of high-volume fly ash (HVFA) cementitious composites. However, the long-term influence of nanosilica on HVFA composites is yet unclear. This research aimed to investigate the long-term microstructures, strength, durability and volume stability of HVFA mortars incorporating nanosilica. In this study, nanosilica was added to cement mortar where 50% of the binder was fly ash. At the age of 2 years, despite some fly ash particles remaining incompletely hydrated, the benefits of nanosilica could still be retained in HVFA mixtures. The experiments revealed that a 2% nanosilica addition could increase the compressive strength of HVFA mortar by 50% and reduce the water sorptivity, chloride-ion penetration, and drying shrinkage by 80%, 90%, and 13%, respectively. The improvements on the various measurements are attributed to the reduced porosity and refined pore size by nanosilica.