Low-cost, ubiquitous biomolecule as a strength enhancer for cement mortars

Abstract

This study explores a bioinspired, low-cost, and ubiquitous biomolecule – tannic acid (TA) – as a small-dose molecular-scale admixture to modify the nano- and micro-structures of the major hydration product of ordinary Portland cement (OPC) (e.g., calcium silicate hydrate (C-S-H)) so that the performance and eco-efficiency of the concrete can be significantly enhanced. With abundant reactive terminal phenolic hydroxyl groups, TA can cross-link macromolecular sites through multiple interactions, including hydrogen and ionic bonds and hydrophobic interactions. Therefore, TA can be used to manipulate the structure of C-S-H gel, and to fundamentally modify the properties of concrete. Testing results show that adding TA could reduce the total porosity of the mortar by up to 31%. Particularly, the capillary pores with size within 10 nm – 50 nm were significantly reduced. Both the packing densities and elastic modulus of the hydration products were also increased by adding TA, as indicated by nanoindentation testing. As a result, much better mechanical performance is achieved. Furthermore, finite element simulation revealed that more uniform distribution of stress is achieved by the presence of TA. This study broadens the application of bio-based molecules in concrete, bringing new possibilities of reactivity and offering higher specificity for interaction with targeted phases. Compared with existing petroleum-based admixtures, bio-based molecules enjoy many advantages, such as abundant, renewable, safe, yet low-cost.