Reinforcement and modular system for 3DCP geopolymer structures using construction and demolition waste

The increasing demand for virgin raw materials, the unresolved accumulation of high volumes of waste materials resulting from construction activities, and the construction sector's lag in adapting to advancing industrial developments highlight an urgent need for sustainable solutions. Addressing these pressing issues, this paper investigates reinforcing strategies for 3D-printed geopolymer structures using construction and demolition waste (CDW) and explores the feasibility of modular systems in 3D-printing construction. The geopolymer synthesis involves CDW-based brick waste, concrete waste, industrial waste-based slag, and silica fume, combined with a 5 M NaOH activator. Reinforcing methods are employed to enhance bending strength, out-of-plane strength, and interlayer bond strength. Diverse reinforcement methods, such as fiber and steel in printed structures, varied wall designs including simple box, zigzag, crosstie reinforced wall, and specific interlayer bond strength enhancement applications like wetting, chipping, and shear stud were investigated by conducting three-point bending and compressive strength tests. Furthermore, modular 3D-printing wall performance was compared with the monolithic printed wall by performing direct tensile test. The results indicate that the inclusion of steel reinforcement led to notable improvement in bending capacity, with an enhancement of approximately 26 % for single steel reinforcement and 163 % for structures employing multiple steel reinforcements, compared to the plain structure. Besides, results showed that out-of-plane capacity of 3D-printing walls could be modified significantly by altering the cross-sectional geometry. The implemented reinforcing strategies including wetting, chipping and shear stud significantly improved the interface bond strength capacity by 80 % compared to scenarios with no interface treatment. Also, it was observed that printing time interval had notable influence of interlayer mechanical performance of 3D-printing structure. The tests conducted on modular system showed that tested modular connection effectively transmits an equivalent tensile load as its non-modular counterpart and exhibits similar failure behavior. The findings advance the understanding of reinforcement strategies for 3D-printed structures and offer practical insights for improving their structural integrity and sustainability.