Sustainable 3D printed mortar with CO2 pretreated recycled fine aggregates

Abstract

Recycling of construction and demolition wastes (CDW) for the development of intelligent construction materials has the potential to lower the environmental burden and promote the development of intelligent construction. Herein, CO2 pretreatment to a type of recycled fine aggregate (RFA) was employed to upcycle the waste for developing 3D printable mortar (3DPM). The replacement ratios of natural fine aggregates (NFA) by recycled fine aggregates (RFA) and carbonated recycled fine aggregates (CRFA) up to 100% were designed, and the engineering properties, including compressive strength, flexural strength and interlayer bonding strength, of 3DPM were investigated. Comprehensive microscopic tests with X-ray diffraction (XRD), scanning electron microscopy-backscattered electrons (SEM-BSE), and X-ray computed tomography (X-CT), were used to demonstrate the microstructure mechanism of the 3DPM specimens with upcycled fine aggregates at the microscopic level. Systematical enhancements in engineering properties of 3DPM with CRFA were reported when compared with those of 3DPM with RFA. The compressive strength at 28 days was noticeably enhanced by 68.5% for the 3DPM with 100% upcycled fine aggregates. Carbonation enables significant calcite precipitates in the adhered cement paste area and formation of cement hydrates in the new cement paste area. The findings of the present work not only deepen the understandings in the microstructure alterations of RFA by CO2 pretreatments, but also pave a path towards the upcycling of CDW towards sustainable intelligent constructions.