Bioinspired brick-and-mortar geopolymer composites with ultra-high toughness

Geopolymer cement is a promising alternative to ordinary Portland cement as it offers comparable mechanical properties and greater durability with lower carbon emissions. Despite its advantages, the brittleness of geopolymer hinders its application as a structural material. In this work, a bioinspired brick-and-mortar structure is explored as a design paradigm to overcome this brittleness and to further augment geopolymer mechanical performance. To this end, composites were prepared with geopolymer as the brick phase and 3D-printed polymers as the mortar phase, with focus on the influence of the mortar phase stiffness. Bending and fracture results reveal strong and tough geopolymer composites can be achieved through a bioinspired brick-and-mortar structure. The geopolymer based composites showed up to 830 times greater toughness with simultaneous gains of 48% in strength compared to the bulk geopolymer. This composite exceeds bending strength and toughness of both its constituents. Stiffer soft phases generate tougher composites compared to more compliant soft phases. Various toughening mechanisms, including brick interlocking, crack bridging and crack deflection, triggered by the bioinspired design, were revealed through Digital Image Correlation, indentation, and microscopy.