Despite the wide application of shotcrete in underground constructions, its long-term performance is greatly affected by the challenging service conditions. Thus, improving the performance of this material is critical for the safety and stability of underground shotcrete structures. This paper reviews the long-term performance of shotcrete in varying service conditions. First, the microstructural characteristics of shotcrete were presented and analyzed. Then, the relevant long-term mechanical strengths, shrinkage, and durability were summarized and discussed. Results showed that shotcrete exhibited superior initial mechanical strengths, but gradually decreased over time. In terms of shrinkage performance, shotcrete had high shrinkage strain values resulting from high cement content and effect of accelerators. The durability of shotcrete deteriorates over time owing to increased porosity of the matrix caused by the effect of accelerating agents. Potential improvements in some of these properties can be achieved with the inclusion of supplementary cementitious materials (SCMs), fibrous reinforcements (FRs), chemical admixtures (CAs), and other additives (OAs). The review finally provides new research directions for further studies and development of innovative shotcrete mixes with improved long-term mechanical and durability characteristics.

中文翻译：

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促进剂对喷射混凝土长期性能的影响及其改进策略：综述

尽管喷射混凝土在地下建筑中得到了广泛的应用，但其长期性能受到具有挑战性的使用条件的极大影响。因此，提高这种材料的性能对于地下喷射混凝土结构的安全性和稳定性至关重要。本文回顾了喷射混凝土在不同使用条件下的长期性能。首先，对喷射混凝土的微观结构特征进行了介绍和分析。然后，对相关的长期机械强度、收缩率和耐久性进行了总结和讨论。结果表明，喷射混凝土表现出优异的初始机械强度，但随着时间的推移逐渐下降。在收缩性能方面，由于水泥含量高和速凝剂的作用，喷射混凝土具有较高的收缩应变值。由于促进剂的作用导致基质孔隙率增加，喷射混凝土的耐久性随着时间的推移而恶化。通过添加辅助胶凝材料 (SCM)、纤维增强材料 (FR)、化学外加剂 (CA) 和其他添加剂 (OA)，可以实现其中一些性能的潜在改进。该综述最终为进一步研究和开发具有改进的长期机械和耐久性特性的创新喷射混凝土混合物提供了新的研究方向。