ABSTRACT
The incorporation of renewable materials such as mineral additions and recycled aggregates in mortars and concretes formulations reduces greenhouse gas emissions and promotes low-carbon construction. These substitutions significantly affect the hydration mechanism and modify the physical, mechanical and durability properties of mortars and concretes. In the present work, experimental and micromechanical investigations are conducted on recycled mortars incorporating ground granulated furnace slag (GGBFS) and recycled sand. Various mortar mixtures are designed involving different replacement ratios of Portland cement and natural sand by GGBFS and recycled sand . Microstructural and macroscopic properties are therefore investigated thanks to experimental setups such as nano and micro indentation, thermogravimetric test analysis and mechanical testing (compressive strength and elastic modulus). On the other hand, a modeling approach is proposed based on a simplified representation of the representative volume element (REV) of low carbon mortars and fed with data collected on the microstructure. Slag blended cement hydration model including kinetic aspects is therefore developed using Avrami and Knudsen kinetic laws [1] for respectively clinker and slag hydration mechanisms. The influence of parameters such as the replacement ratio of Portland cement by slag, the water-to-binder ratio, the portlandite consumption is captured using stoichiometric relationships between the reactants and the products. Volume fractions of hydration products in slag blended cement pastes at different curing ages are also estimated and discussed in this work. Finally, the overall elastic properties of REVs of recycled mortars are computed so as the compressive strengths at different curing ages using the downscaling principle and the well-known Drucker-Prager failure criterion [2]. Compared to the experimental results, the established model is found to predict accurately the macroscopic elastic modulus and the compressive strengths of mortars containing slag and recycled sand at different curing ages.
