Application of recycled tile as internal curing material in 3D-printed engineered cementitious composites

3D concrete printing (3DCP) offers design flexibility and construction efficiency but faces challenges like weak interlayer bond strength and shrinkage. This study uses recycled tile fine aggregate (RTFA) as an internal curing material in 3D-printed engineered cementitious composites (ECC) to improve interlayer bond strength and reduce shrinkage. The effects of different RTFA replacement ratios (20 %, 40 % and 60 %) on hydration products, pore structure, interlayer bond strength and shrinkage of 3D-printed ECC are investigated. The results show that RTFA increases the degree of hydration of 3D-printed ECC and reduces interlayer porosity, thereby improving interlayer bond strength and reducing shrinkage. A 20 % RTFA replacement shows the best mechanical performance. Compared with the control group without RTFA, the compressive strength, tensile strength and interlayer bond strength increase by 15.1 %, 11.1 % and 13.2 %, respectively. Shrinkage results show that RTFA60 reduces autogenous shrinkage by 35.6 % and free shrinkage by 22.7 %. These findings demonstrate that RTFA is a viable internal curing material for 3D-printed ECC and support the development of more sustainable construction 3D printing with recycled ceramic waste.