Waste polymer addition for 3D cementitious printing materials

Background/ Objectives and Goals During the last 30 years, extensive researches were performed an attempt to reuse the waste tires by grinding them into granulated samples and use as aggregates in cementitious materials. The innovative purpose of this work is to investigate the feasibility of applying tire rubber-modified cement compounds to 3D additive construction technologies. The influence of crumb rubber on the rheological, durability and structural performance of these mixtures was evaluated in terms of printability properties, water repellency, mechanical strength, and thermo-acoustic insulation. Methods Four mix designs involving different volume content of 0-1 mm rubber powder and 2-3 mm rubber granules were developed. A robotic arm-based printing machine was used to evaluate the print quality of the compounds. For each formulation, prismatic, beams, and cubic specimens were collected from 3D printed slabs of 230 x 160 x 55 mm. Water sorptivity (Sw) test and water contact angle (WCA) analysis were performed to evaluate the influence of rubber aggregates on the fluid permeation inertia of the cementitious materials. Mechanical performances were tested by bending and compressive tests, determining the strength isotropy of the printed samples by testing in two loading directions. Thermal and acoustic properties were analyzed by heat conductivity (k) and sound insertion loss (SIL) measurements, to evaluate how the rubber functionalization affects the insulation properties of the material. Microstructural characterization of the samples was inspected by optical (OM) and scanning electron microscopy (SEM). Expected Results/ Conclusion/ Contribution The non-polar nature of rubber modifies the rheology of the cement mixture, promoting greater inter-layer adhesion than the reference formulation. The modification with polymer fillers retains good water absorption properties. WCA analysis reveals a local hydrophobic behavior of rubberized compounds. The polymer particles represent sites that hinder the permeation of water or corrosive fluids into the material. Lower mechanical strength of the rubber-cement compounds than neat ones, due to the low density and the weak rubber-cement interface, is compensated by the higher toughness, pre-failure deformability, and mechanical isotropy. The addition of lightweight and elastomeric rubber aggregates improves the thermal insulation properties of the material and enhances its vibro-acoustic damping