Extrusion-based concrete 3D printing is at its infancy and many aspects of this new technology need to be thoroughly investigated to pave the way for its widespread use in construction. Since the inherent drying shrinkage of the hardened cement paste is the source of the drying shrinkage of 3D printed concrete, the shrinkage behavior of cementitious 3D printing materials with very high cement to fine aggregate ratios is one of the major challenges for researchers working on this innovative technology. Besides, due to the absence of formwork in this technique, an outdoor 3D printing environment causes excessive moisture loss and drying shrinkage cracking. This paper presents the first comprehensive investigation on the effects of different outdoor environmental conditions i.e. relative humidity (RH) and temperature on the moisture loss, drying and autogenous shrinkage of cementitious 3D printing materials, considering different sand to cement (S/C), and surface to volume (S/V) ratios of free-formed specimens. Mass loss and length change of mortars which were cured for up to 168 days under standard condition (24 ̊C-50%RH with 24 h of sealed initial curing) were compared with those at 24 ̊C-50%RH, 35 ̊C-85%RH and 35 ̊C-45%RH (free-formed specimens without initial curing) to investigate the effect of outdoor printing environment and the absence of formworks on the deformations caused by shrinkage. The drying shrinkage results indicate that 28 days free-formed specimens under different non-standard curing conditions show a length change up to 30% lower than specimens in the standard environment. Moreover, increasing the sand to cement ratio from 0.8 to 1.0 results in a 10% decrease in the drying shrinkage strain. This study also discusses the higher susceptibility of free-formed specimens to carbonation shrinkage and demonstrates that printed specimens have higher shrinkage deformation in the longer term compared to conventional casting specimens. The results of nitrogen adsorption-desorption analysis also prove that the total porosity in free-formed specimens in all environmental conditions reduces and reaches a finer pore structure after 112 days compared to conventional casting specimens. These results point to the importance of internal or external curing for reducing shrinkage in concrete 3D printing.

基于挤压的混凝土 3D 打印还处于起步阶段，需要彻底研究这项新技术的许多方面，为其在建筑中的广泛应用铺平道路。由于硬化水泥浆的固有干缩是 3D 打印混凝土干缩的来源，因此水泥与细骨料比率非常高的胶结 3D 打印材料的收缩行为是研究人员面临的主要挑战之一。技术。此外，由于该技术没有模板，室外3D打印环境会导致水分流失过多和干燥收缩开裂。本文首次全面研究了不同室外环境条件，即相对湿度 (RH) 和温度对水分流失的影响，水泥 3D 打印材料的干燥和自收缩，考虑到不同的砂与水泥 (S/C) 以及自由成型试样的表面与体积 (S/V) 比。将在标准条件（24 ̊C-50%RH，密封初始固化 24 小时）下固化长达 168 天的砂浆的质量损失和长度变化与 24 ̊C-50%RH、35 ̊C-85% 的情况进行比较RH 和 35 ̊C-45%RH（未初始固化的自由成型试样）研究室外印刷环境和没有模板对收缩引起的变形的影响。干燥收缩结果表明，在不同非标准固化条件下28天自由成型试样的长度变化比标准环境下的试样低30%。此外，将砂与水泥的比例从 0.8 增加到 1。0 导致干燥收缩应变降低 10%。本研究还讨论了自由成型试样对碳化收缩的更高敏感性，并证明与传统铸造试样相比，打印试样在长期内具有更高的收缩变形。氮吸附-解吸分析的结果还证明，与常规铸造试样相比，在所有环境条件下，自由成型试样的总孔隙率在 112 天后降低并达到更细的孔隙结构。这些结果表明内部或外部固化对于减少混凝土 3D 打印收缩的重要性。本研究还讨论了自由成型试样对碳化收缩的更高敏感性，并证明与传统铸造试样相比，打印试样在长期内具有更高的收缩变形。氮吸附-解吸分析的结果还证明，与常规铸造试样相比，在所有环境条件下，自由成型试样的总孔隙率在 112 天后降低并达到更细的孔隙结构。这些结果表明内部或外部固化对于减少混凝土 3D 打印收缩的重要性。本研究还讨论了自由成型试样对碳化收缩的更高敏感性，并证明与传统铸造试样相比，打印试样在长期内具有更高的收缩变形。氮吸附-解吸分析的结果还证明，与常规铸造试样相比，在所有环境条件下，自由成型试样的总孔隙率在 112 天后降低并达到更细的孔隙结构。这些结果表明内部或外部固化对于减少混凝土 3D 打印收缩的重要性。氮吸附-解吸分析的结果还证明，与常规铸造试样相比，在所有环境条件下，自由成型试样的总孔隙率在 112 天后降低并达到更细的孔隙结构。这些结果表明内部或外部固化对于减少混凝土 3D 打印收缩的重要性。氮吸附-解吸分析的结果还证明，与常规铸造试样相比，在所有环境条件下，自由成型试样的总孔隙率在 112 天后降低并达到更细的孔隙结构。这些结果表明内部或外部固化对于减少混凝土 3D 打印收缩的重要性。