Effects of printing paths and recycled fines on drying shrinkage of 3D printed mortar

Abstract

3D printing process poses great impacts on the properties of mortar, especially on the shrinkage behavior of 3D printed mortar (3DPM) prepared with recycled fine aggregate (RFA) and recycled powder (RP). This study focuses on the effects of printing paths on the flowability and the drying shrinkage of 3DPM. RFA and RP, together with their contents, are used as variables in 3DPM. The results show that the flow loss of mortar during the first 30 mins increased with the incorporation of recycled fines due to the high water-absorption of RFA and the low hydration reactivity of RP. The drying shrinkage development of 3DPM was higher than that of cast mortar during the first 28 days, but exhibited a deceleration in shrinkage increasing rate after 28 days. Printing path showed a limited effect on the mass loss of 3DPM during the test period, but had significant impacts on the drying shrinkage and the shrinkage development trend. An increase in drying shrinkage of 3DPM was caused by 50 ∼ 100% RFA replacement (29.1 ∼ 57.9% in 60 days), while 10 ∼ 20% RP content decreased the drying shrinkage of 3DPM (3.3 ∼ 12.4% in 60 days). Additionally, the incorporation of recycled fines delayed the development of 3DPM drying shrinkage.