材料组成与养护方式对UHPC变形历程的影响

论文总字数：43388字

摘 要

超高性能混凝土（UHPC）是一种比强度高、韧性好且耐久性优异的新型建筑材料，在桥梁、建筑和修复工程中均有应用。然而UHPC的收缩变形很大，且在早期发展迅速，严重限制了UHPC的应用范围并降低结构的安全性。因此，本文旨在探索UHPC的减缩方案，重点分析了UHPC早期收缩性能。

本文首先研究UHPC凝结时间测试方法，确定自收缩零点；其次，采用波纹管、激光以及千分表测试自收缩等多种方式相结合的方法，系统研究了水胶比、纤维、膨胀剂、减缩剂（SRA）、水化温升抑制剂（HHRM）和塑性膨胀剂（PEA）对UHPC收缩性能的影响，同时研究了各因素对UHPC力学性能以及水化特性的影响；最后，结合UHPC实际应用情况，探讨了试件尺寸和养护方式对UHPC收缩变形历程的影响。通过研究得到以下结论：

（1）基于密封条件下混凝土内部早期毛细管负压的增长规律与贯入阻力增长的规律完全一致的原理，确定了UHPC初凝和终凝时的毛细孔负压值，将毛细孔负压40kPa作为自收缩零点，为UHPC收缩性能的准确测试奠定基础。

（2）UHPC早期收缩变形随水胶比的上升而下降。钢纤维对于UHPC收缩变形影响很小。在外加剂中，UHPC收缩变形随膨胀剂掺量增加而减小。减缩剂的掺量对收缩变形影响不大。HHRM可延缓水化过程，与膨胀剂复合使用时可以更好地发挥膨胀剂的补偿收缩效果。塑性膨胀剂可降低收缩变形，但与膨胀剂复掺时会损害膨胀剂的补偿收缩效果。

（3）外加剂均一定程度上降低了UHPC的抗折和抗拉强度。综合各类外加剂对UHPC收缩性能和力学性能的影响，认为3%膨胀剂与0.3%水化温升抑制剂复掺可实现补偿收缩历程与UHPC变形历程相匹配，可有效控制UHPC的收缩变形，且对力学性能负面影响较小。

（4）试件尺寸越大，早期内部温升越高，UHPC自收缩越大；热养护UHPC的整体收缩大于常温养护试件。

关键词：超高性能混凝土，自收缩，膨胀剂，减缩剂

Abstract

Ultra-high performance concrete (UHPC) is a new type of building material with high strength, good toughness and excellent durability. It is applied in bridge, civil engineering and repair engineering. However, the shrinkage of UHPC is very large, and it develops rapidly in the early-age. This severely limits the scope of application of UHPC and reduces the safety of the structure. Therefore, this paper aims to explore for the shrinkage-reducing program of UHPC, focusing on the early-age shrinkage behavior of UHPC.

In this paper, firstly the setting time of UHPC was tested to acquire the time-zero of autogenous shrinkage. Then, the effects of water-binder ratio, fiber, expanding agent (EA), shrinkage-reducing agent (SRA), hydration heat reducing material (HHRM) and plastic expanding agent (PEA) on the shrinkage performance of UHPC were studied by a set of shrinkage testing methods. The effects those factors on mechanical properties and hydration characteristics were studied, either. Finally, considering the application of UHPC, effects of specimen size and curing regime on the shrinkage of UHPC were discussed. Through the research, we could draw the following conclusions.

(1) Based on the principle that the capillary pressure and the penetration resistance of UHPC develops in almost the same pattern, the capillary pressure at the initial and final setting of UHPC was determined. The time-zero was considered as the time when the capillary pressure reaches 40kPa, laying the foundation for accurate testing for UHPC shrinkage.

(2) The early-age shrinkage of UHPC decreases with the increase of water-binder ratio. The addition of steel fiber has little effect on shrinkage deformation of UHPC. For the admixtures, shrinkage deformation of UHPC decreases with the increase of EA content. The change in the amount of SRA has little effect on shrinkage deformation. HHRM can delay the hydration process. When it’s used with EA together, it can promote the expanding properties of EA. PEA can reduce shrinkage deformation. However, when it’s used with EA, it can do harm to the expanding properties of EA.

(3) The admixture reduces the flexural and tensile strength of UHPC to a certain extent. Considering the effect of admixtures on both shrinkage and mechanical properties of UHPC, the addition of EA at 3% and HHRM at 0.3% by cementitious material weight is the proper shrinkage reducing program for UHPC, which can effectively control shrinkage. Its negative impact on mechanical properties is small.

(4) With the increase of specimen size, the internal temperature rise in the early-age increased, and the autogenous shrinkage of UHPC increases, either. The total shrinkage of the heat cured UHPC specimen is greater than the specimen cured at room temperature.

KEY WORDS: ultra-high-performance concrete, autogenous shrinkage, expanding agent, shrinkage-reducing agent

目 录

摘 要 I

Abstract II

第一章 绪论 1

1.1研究背景及意义 1

1.2国内外研究现状 1

1.2.1超高性能混凝土概述 1

1.2.2UHPC变形特性与机理 3

1.2.3收缩变形的影响因素 5

1.2.4收缩变形测试方法 7

1.2.5存在的问题 9

1.3研究目标及研究内容 9

1.3.1研究目标 9

1.3.2研究内容 9

第二章 原材料、配合比与试验方法 10

2.1试验原材料 10

2.1.1水泥 10

2.1.2矿物掺合料 10

2.1.3细集料 10

2.1.4外加剂 10

2.1.5纤维 10

2.2制备养护方法 11

2.2.1制备方法 11

2.2.2养护制度 11

2.3试验方法 11

2.3.1自收缩零点的确定 11

2.3.2早期自收缩测试 12

2.3.3较长龄期的自收缩测试 12

2.3.4力学性能测试 13

2.3.5水化速率与水化程度测试 14

第三章 UHPC收缩性能研究 15

3.1试验配合比 15

3.2凝结时间的确定 15

3.3 原材料组成对UHPC收缩性能的影响 16

3.3.1 水胶比 16

3.3.2 纤维 16

3.3.3 外加剂 17

3.4 养护方式对UHPC收缩性能的影响 21

3.5 本章小结 21

第四章 UHPC力学性能及水化特性研究 23

4.1原材料组成及养护方式对UHPC力学性能的影响 23

4.1.1原材料组成 23

4.1.2养护方式 27

4.2原材料组成及养护方式对UHPC水化特性的影响 27

4.2.1原材料组成 27

4.2.2养护方式 30

4.3减缩措施优选 30

4.4本章小结 31

第五章 结论与展望 32

5.1结论 32

5.2创新点 32

5.3展望 33

参考文献 34

致 谢 38

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