超高性能混凝土收缩综述

分析了超高性能混凝土(UHPC)的收缩特性及其随时间发展的一般规律, 总结了材料组成、养护制度与内部温湿度场对UHPC收缩的影响。研究结果表明: UHPC收缩早期(0~7 d)发展快, 占总收缩的61.3%~86.5%, 中期(7~28 d)发展缓慢, 占总收缩的13.5%~27.9%, 后期(28 d后)趋于稳定; UHPC以自收缩为主, 占总收缩的78.6%~90.0%, 是早期开裂的主要诱因; 收缩测试起始时间可取试件成型后1 d(24 h), 终止时间可取90 d或120 d; 在结构设计时, 可参考各国规范取收缩为500~800 με, 热养护后可不考虑残余收缩; 对于收缩预测模型, 各国规范尚未统一, 多借鉴现有的收缩模型, 应完善与修正收缩预测模型; 对于材料组成, 目前集中于纤维、矿物掺合料的种类和掺量对收缩的定量影响, 且各组分对收缩的影响不同, 评价指标较为单一, 应结合结构用途、制备工艺与施工过程等进行综合评价; 对于内部温度与湿度场, 研究对象主要集中于28 d后的普通混凝土与高强高性能混凝土, 应深入研究胶凝材料含量大、组分差异性明显、活性矿物掺合料掺量高的UHPC早期内部温度与湿度场; 为了降低收缩, 基本采用内养护, 添加膨胀剂、减缩剂与粗骨料等措施。可见: 为了减小UHPC收缩的同时又不降低其力学性能, 应该优化UHPC配比, 合理使用外加剂, 采取适当养护制度等措施。 

Review of ultra-high performance concrete shrinkage

The shrinkage characteristics of ultra-high performance concrete (UHPC) were analyzed.The general rules of UHPC contraction with time were introduced.The influences of material composition, curing regime, internal temperature and internal humidity on UHPC shrinkage were summarized.Research result indicates that the shrinkage of UHPC develops rapidly at 0-7 d, accounting for 61.3%-86.5% of total shrinkage, develops slowly from 7 dto28 d, accounting for 13.5%-27.9%, and becomes steady after 28 d.Autogenic shrinkage is the main cause of early cracking of UHPC, and accounts for 78.6%-90.0% of total shrinkage.In term of the start point about shrinkage test, the initial time of test is 1 d (24 h) after specimen forming, and the termination time is 90 dor 120 d.In term of structural design, it may refer to the values (500-800με) in various countries' standards, and not to consider the residualshrinkage after heat curing.In term of shrinkage prediction models, the norms of all countries have not been uniformed yet, it can only refer to the existing models, and the shrinkage prediction models should be improved and revised.In term of component research, the quantitative impacts of types and contents of fibers and mineral admixtures on the shrinkage are research emphasis, the effect of each component on the shrinkage is different, and the evaluation indexes are relatively simple and should be combined with structural applications, preparation techniques and construction process to comprehensively evaluate the shrinkage.In term of the internal temperature and humidity fields, the research mainly concentrates on normal concretes, high-strength and high-performance concretes after 28 d, and it should be more in-depth study on the early internal temperature and humidity fields of UHPC with the large content of cementitious material, obvious difference of components, and high content of active mineral admixture.In term of reducing shrinkage, internal curing, expansive agent, shrinkage-reducing agent, coarse aggregate, and other measures are applied.Therefore, it should optimize the ratio of UHPC, rationalize the use of admixture, and adopt proper curing system and other measures to reduce the shrinkage of UHPC, but not to reduce its mechanical properties.