Effect of different surface modification methods of small particle size recycled rubber powder on mechanical properties of 3D printed concrete

Abstract

Due to the relatively weak adhesion between rubber and the concrete matrix in 3D printed rubber concrete, the mechanical properties of the concrete undergo considerable losses. This study employs solutions of varying concentrations to treat the surface of small particle size rubber (SPSR) through an immersion method, aiming to reduce its hydrophobicity and enhance the strength of 3D printed small particle size rubber concrete (3DP-SPSRC). The mechanical properties of 3DP-SPSRC modified with three types of solutions are tested and verified that all three solutions can improve the mechanical properties of the concrete to varying degrees. Among them, the concentrations of the three solutions that yield the best modification effects are as follows: 15 % sodium hydroxide solution (NaOH) for modification, 10 % sulfuric acid solution (H₂SO₄) for modification, and 5 % potassium permanganate solution (KMnO₄) for modification. The improvement range of compressive and flexural strength of 3DP-SPSRC by them is between 4.3 % and 35.93 %. Among the three solutions evaluated, 5 % KMnO₄ treatment demonstrates the most significant improvement in mechanical strength. Through comparative analysis of the activation index and contact angle measurements of SPSR before and after modification, it is evident that both parameters exhibit a marked reduction post-treatment, which indicates that the modification processes employed effectively enhance the hydrophilic properties of the rubber. Notably, 5 % KMnO₄ modified rubber displays superior hydrophilicity compared to the other treatment conditions. Based on SEM, the micro - morphology of the modified rubber is observed and analyzed. The workability and extrudability tests demonstrate that the modified 3DP-SPSRC could be well-suited for the self-developed 3D concrete printer, and the interlayer bond strength is significantly increased by 46.63 %. In this study, recycled rubber powder made from waste tires is added to concrete and applied in 3D printing technology, which alleviates the environmental pressure caused by waste tires. The methods of surface modification of SPSR are explored and verified the feasibility of surface - modifying SPSR to improve the mechanical properties of 3D - printed rubber concrete