Crack Binding and Filling Properties of Modified Proteins in Sustainable Cementitious Materials

This study aims to investigate the effect of two modifying agents, sodium dodecyl sulfate (SDS) and lignin, on the properties of five different proteins and their crack binding and filling in the cementitious surface. The molecular structure and physicochemical properties of the modified proteins were examined using Fourier transform infrared (FTIR), differential scanning calorimetry, ζ-potential, and surface tension measurements. The binding between the modified proteins and the cementitious surface was evaluated using the interfacial shear lap test. The effect of the modified proteins on crack filling and healing of cementitious materials was studied by using flexural testing, optical microscopy, and X-ray microcomputed tomography. FTIR showed reduced intensities of the amide groups in the molecular structure of the modified proteins compared with the unmodified proteins. Proteins showed an increased viscosity in the synthetic pore solution (SPS) compared to that in deionized water, due to protein unfolding at a high pH of the SPS and subsequently cross-linking via Ca2+ bridging. Modifying with SDS generally increased the viscosity of the proteins due to increased cross-linking, while lignin did not seem to change viscosity. The proteins modified with SDS and lignin exhibited a general increase in interfacial shear strength between the modified proteins and the cementitious surface. It was found that modifying the protein sodium bovine immunoglobulin with SDS enhanced the crack healing and filling in cementitious materials, while modifying with lignin was not effective.