Effect of drying environment on mechanical properties, internal RH and pore structure of 3D printed concrete

Abstract 3D printed concrete (3DPC) is fabricated by depositing printable materials without formwork which increases the surface exposed to environmental condition, and by default, eliminates the curing procedure. As a result, moisture evaporation from printed concrete mitigates the hydration of cement and impacts the development of the mechanical properties. In this study, the effects of drying (RH = 60%±5%), wind (3 m/s) and exposed area on the mechanical properties of 3DPC at 20℃±5℃ were investigated. Furtherly, the internal relative humidity evolvement was measured by humidity sensor and the pore distribution was evaluated by X-ray computed tomography. Curing condition were found to have a significant influence on compressive and flexural strength development for samples cut from printed elements and cast samples, but had less significant effect on splitting tensile strength. Furthermore, compared with cast specimens, samples cut from printed elements were more sensitive to curing condition. Evidence on the pore structure seemed to explain the difference: the pore connectivity increased and the pore distribution varied for samples cut from printed elements. We also confirmed the existence of anisotropy for samples cut from printed elements and found that it did not aggravate in drying and wind conditions.