To reduce the extremely high autogenous shrinkage deformation of ultra-high performance concrete (UHPC) caused by low water-to-binder ratio and high binder materials content, this work aimed to designed and prepared low shrinkage UHPC containing MgO-based expansive agents (MEA). The effects of UHPC with different reactivity of MEA (R-MEA and S-MEA) were compared in terms of fluidity, mechanical properties, hydration characteristics, shrinkage deformation, pore structure and microstructure. The results indicated that the incorporated of MEA decreased the fluidity and mechanical properties of UHPC, while the autogenous shrinkage deformation was compensated significantly. When 6 % R-MEA was incorporated, the flow and compressive strength decreased by 16 % and 7.9 %, respectively, but the autogenous shrinkage at 7 days also decreased by 70.1 % at the same time. The same amount of S-MEA showed lower compensation for the autogenous shrinkage of UHPC than R-MEA, but with the same reduction in compressive strength loss. This was due to the highly reactive R-MEA showed higher hydration degree and larger swell increment, which caused more compensation for shrinkage in UHPC, while it had slight adverse effect on the strength development. It is worth noting that the compensation effect of autogenous shrinkage is very limited when the doping is higher than 6 % for either MEA, but the loss of mechanical properties is serious. In addition, the microstructure showed that the crystal growth pressure of brucite forced the pastes to expand and thus resulted in increase on the porosity for UHPC. This study provides a feasible and effective way for mitigating the autogenous shrinkage of UHPC.

中文翻译：

---

掺MgO膨胀剂的超高性能混凝土（UHPC）的力学性能、水化行为和收缩变形


【摘要】：为了减少超高性能混凝土(UHPC)因低水胶比和高粘结材料含量而引起的极高的自收缩变形,本工作旨在设计和制备含MgO基膨胀剂的低收缩UHPC(MEA) ）。比较了不同反应性MEA（R-MEA和S-MEA）的UHPC在流动性、力学性能、水化特性、收缩变形、孔隙结构和微观结构方面的影响。结果表明，MEA的加入降低了UHPC的流动性和力学性能，同时自收缩变形得到了显着补偿。当掺入6%的R-MEA时，流动强度和抗压强度分别下降了16%和7.9%，但7天的自收缩率也同时下降了70.1%。相同量的 S-MEA 对 UHPC 自收缩的补偿比 R-MEA 低，但抗压强度损失的降低程度相同。这是由于高反应性的R-MEA表现出较高的水合度和较大的溶胀增量，这对UHPC的收缩产生了更多的补偿，但对强度发展产生了轻微的不利影响。值得注意的是，当两种MEA的掺杂量高于6%时，自收缩的补偿效果非常有限，但机械性能损失严重。此外，微观结构表明水镁石的晶体生长压力迫使浆料膨胀，从而导致UHPC的孔隙率增加。该研究为减轻UHPC的自收缩提供了一种可行有效的方法。