Strengthening mechanism of fracture properties by nano materials for cementitious materials subject to early-age frost attack

Abstract With the increasing interest and utilization of nano materials to cementitious materials, the mechanical properties of the nano materials-modified cementitious materials under the severe environmental conditions is critical for their successful application. This study investigates the fracture toughness of nano materials-strengthened cement paste by nano silica particles and carbon nanotubes at the micro and macro scales by using nano-scratch technique and the conventional three-point bending test, respectively. The aim is to better understand the strengthening mechanism of these two nano materials on the fracture properties of cementitious materials subject to early-age frost attack. The paste sample is designed subject to freeze-thaw cycles at the age of 1, 3, and 7 days, and then sealed cured after the 7 days’ freeze-thaw period until the age of 28 days. The micro fracture toughness of the unreacted clinker, the hydrates, and the interfacial transition zone (ITZ) between the unreacted clinker and the surrounding hydrates is measured as well as the thickness of ITZ. The effect of nano silica and carbon nanotubes on the fracture properties are discussed and compared, and the different strengthening mechanism of these two nano materials are recognized. The results of this study are beneficial for designing mixtures to achieve better early age frost resistance that satisfies the engineering applications.