This paper examines the printability of concrete formulations made using lightweight expanded clay aggregates (LECA) of maximum size 10 mm. The effect of coarse aggregate addition on the two essential aspects of printing, i.e., extrudability and buildability are examined using a piston-pump-based 3D printer system. The extrudability is assessed by measuring the desorptivity, a fundamental material parameter for assessing the phase separation tendency during the extrusion process. It is found that increasing the coarse aggregate content increases the desorptivity, thereby decreasing the water retention capacity. Mixes with up to 30 % volume substitution with coarse aggregate were extruded successfully. However, for mixes with volume substitution higher than 30 %, a significant amount of phase separation is found to occur during the extrusion process, resulting in blockages. To assess the effect of coarse aggregate on buildability, uniaxial compression tests were carried out on concretes after different ages of casting. For both the mixes with and without coarse aggregates, the material behaviour changes from an elasto-plastic type response at early ages to a straining softening type response (typical of hardened concrete) at later ages. At any given age, it is found that the addition of LECA, increases both the strength and elastic modulus of the concrete. This may be attributed to the increase in the internal friction angle as the size of the aggregate increases, as well to the higher amount of dewatering that occurs during the extrusion of mixes containing coarse aggregates resulting in a relatively stiffer mix after extrusion. Finally, discussions are provided on the effect of using low-density aggregates like LECA on improving the resistance to both plastic and buckling type collapse that may occur during printing.

本文研究了使用最大尺寸为10 mm的轻质膨胀粘土集料（LECA）制成的混凝土配方的可印刷性。使用基于活塞泵的3D打印机系统检查了粗骨料添加对打印的两个基本方面的影响，即可挤出性和可建性。可挤出性通过测量解吸率来评估，解吸率是评估挤出过程中相分离趋势的基本材料参数。发现增加粗骨料含量会增加解吸能力，从而降低保水能力。成功挤出了体积高达30％的被粗骨料替代的混合物。但是，对于体积替代高于30％的混合物，发现在挤出过程中发生大量的相分离，从而导致堵塞。为了评估粗骨料对可建造性的影响，在不同龄期的铸造后对混凝土进行了单轴压缩试验。对于具有和不具有粗骨料的混合料，材料性能都从早期的弹塑性类型响应变为后期的应变软化类型响应（通常为硬化混凝土）。发现在任何给定的年龄下，添加LECA都会增加混凝土的强度和弹性模量。这可能归因于随着集料尺寸的增加，内摩擦角的增加，以及在含有粗骨料的混合物挤出过程中发生的脱水量更高，导致挤出后的混合物相对较硬。最后，提供了有关使用低密度聚集体（如LECA）对提高在印刷过程中可能发生的对塑料和屈曲型塌陷的抵抗力的影响的讨论。