Cement pastes modified by cellulose nanocrystals: A dynamic moduli evolution assessment by the Impulse Excitation Technique

Abstract

Annual cement production has surpassed 4 billion tonnes worldwide, strongly contributing to carbon footprint. However, more sustainable and efficient cement based materials have been achieved by incorporating cellulose into the mixture. More specifically, cellulose nanocrystals (CNC), nanorods of pure crystalline cellulose, not only present excellent mechanical properties, but also, influence cement hydration by a process termed short circuit diffusion, due to great interaction with water. Therefore, cement pastes prepared with varying contents of CNC, along with a polycarboxilate superplasticizer (SP) were tested with the Impulse Excitation Technique, a nondestructive testing, which allows replicability over time. Hence, to explore the effects of both CNC and SP on the early hydration, tests were conducted on 3, 5, 7, 14 and 28 hydration days for a complete scenario. For a complementary analysis, the degree of hydration, dry and bulk densities and the volume of permeable pores were determined at 7 hydration days. It was found that lower contents of CNC positively affect cement hydration at early ages, resulting in higher dynamic modulus of elasticity (Ed) and lower porosity. Nevertheless, at 28 hydration days, CNC seems to have no greater influence over the SP effect, and all mixtures presented similar Ed.