A renewable admixture to enhance the performance of cement mortars through a pre-hydration method

Aiming to reduce the carbon emission associated with ordinary Portland cement (OPC) based cementitious materials, this study explores a ubiquitous biomolecule, Tannic Acid (TA) to enhance the eco-efficiency of cement mortars through a pre-hydration process. To this end, a small amount of cement is first hydrated in the presence of TA. Due to multiple interactions between the TA and the hydration products of cement, nanoparticles are in situ produced and well-dispersed in the produced cement slurry, which is then used to mix cement mortar. The filler effect of these nanoparticles, together with the dispersing effect of the residual TA in the slurry, can improve the particle packing of the mortar, leading to significant enhancement on the mechanical properties of the produced mortars. Aiming to understand the underlying working mechanisms of the proposed method, a comprehensive experimental program was carried out to characterize the produced nanoparticles and evaluate the effects of the proposed method on the hydration kinetics, workability, setting time, compressive strength, pore structure, and nanomechanical properties of the cement mortar. Testing results show that the proposed method alters the hydration kinetic, increases in the workability of the mortar by up to 7.58%, and reduces the porosity of the cement pastes by more than 17.50%. As a result, the proposed method improves the compressive strengths of the mortars at 180d by up to 45%, significantly enhancing the eco-efficiency of the produced mortars. This study opens news routs and creates new opportunities to identify and design a new generation of chemical admixtures. Unlike traditional, nonrenewable fossil carbon-based admixtures, the new admixtures are renewable, low-cost, and nontoxic.