Study of the strength regulation factors for the adhesive bonding "cement matrix - reinforcing fiber" in composites for 3D-build printing

Introduction. As part of the solution for the problem of creating a new class of materials for building additive technologies, cement composites reinforced with high-strength fiber, this work presents the results of experimental studies of the strength of the adhesive bonding between cement matrices and reinforcing fibers with different chemical compositions, diameters, and tensile strength. Materials and methods. Rheological properties of cement systems were studied using shear and squeeze rheometry, the method of micromechanical testing for determining the strength of the adhesive bonding "cement matrix - reinforcing fiber" based on the pull-out test, which involves pulling out the fiber from the cement matrix layer; after the pull-out test for all the studied systems, the microstructure of the contact surface "cement matrix - reinforcing fiber" was assessed using a Thermo Scientific™ Phe-nom™ Desktop SEM scanning electron microscope; the compressive strength of hardened cement paste-samples was determined using an INSTRON Sates 1500HDS testing machine. Results and discussions. It was established that the combination of strength characteristics of matrices, fibers, and adhesive strength at their interface allowed securing the required strength characteristics of reinforced construction composites. In the "cement matrix - carbon fiber" systems, the value of adhesive strength was 9 - 11 MPa; in the "cement matrix - steel wire" systems, the value of adhesive strength was 3 - 4 MPa. Conclusions. Matrices with viscosity modifiers containing nano- and micro-sized particles of SiO2 (complex nano-sized additive and metakaolin) are reasonable options for combinations of the "cement matrix - reinforcing fiber" components. Carbon fiber and steel wire are recommended to be used as reinforcing fibers.