关键词: 3D打印, 黄河砂, ECC, 可打印性能, 取代率, 流变性能

Abstract: Engineered cementitious composites (ECC) were prepared using Yellow River sand, and their printability was systematically investigated based on a printability evaluation system, including extrudability, buildability, flowability, rheological properties, setting time, and heat of hydration. The results show that both the extrusion width and the total vertical height increase with the increase replacement ratio of Yellow River sand. In contrast, the change rates of total vertical height, the change rate of the bottom layer strip thickness, and the ratio of the difference between half of the top width and half of the bottom width to the actual total vertical height (tan θ) decrease continuously with the increase replacement ratio of Yellow River sand. The flowability decreases first and then increases with the rise in the replacement ratio of Yellow River sand, reaching a peak at a 100%(mass fraction) replacement ratio. As the Yellow River sand replacement ratio increases, both the thixotropic loop area and the static yield stress increase continuously, while the dynamic yield stress and consistency coefficient decrease. This indicates that the Yellow River sand ECC exhibit shear-thinning pseudoplastic fluid characteristics. The initial setting time gradually decreases with the increase of Yellow River sand replacement ratio. In the heat of hydration test, 90% of the total heat of hydration release occurrs within the first 50 h, and the heat evolution curve exhibits a bimodal pattern, indicating that the early hydration reaction of Yellow River sand ECC is rapid, follow by a stable mid-term hydration process, which is beneficial to the early strength development of printed component.

Key words: 3D printing, Yellow River sand, engineered cementitious composite, printability, replacement ratio, rheological property