论文总字数：36580字

摘 要

随着现代混凝土技术的发展，各种超高、超长、超深结构不断涌现，对高性能混凝土施工性能提出了更高的要求。聚羧酸减水剂具有高减水、高保坍等显著优势，已成为制备具有低水胶比、复杂组分等特征的高性能混凝土重要组分。然而，目前聚羧酸减水剂性能主要通过简单的流动度评价，且水灰比较高，无法从本质上建立其与高性能混凝土施工性能的关系，基于混凝土性能需求的羧酸减水剂开发或应用尚不成熟。

基于此，本文以影响聚羧酸减水剂性能关键因素之一的分子量作为考察对象，基于流变学原理，系统研究了4个水灰比下（0.40、0.30、0.25、0.20），分子量在20000 g/mol~ 64000 g/mol之间的5种分子量聚羧酸减水剂对水泥浆体流变性能的影响规律，并结合聚羧酸减水剂在水泥颗粒表面吸附行为和浆体中颗粒堆积密实度，探讨其对浆体流变性能的影响机制。该研究对于提升高性能混凝土的性能与发展聚羧酸减水剂均具有重要的意义。通过研究得到以下结论：

（1）随分子量的增大聚羧酸减水剂减水率先增大后减小，在分子量M_w 29600 g/mol时达到最大；相同减水剂掺量时，水泥浆体屈服应力和表观粘度均随着聚羧酸减水剂分子量增加先减小后增大，在减水剂分子量29600 g/mol时达到最小值，该变化规律与水泥浆体流动度的变化规律相反；相同流动度时，水泥浆体屈服应力不随聚羧酸减水剂分子量变化而变化，但随着水灰比的降低逐渐增大，水泥浆体表观粘度随着聚羧酸减水剂分子量的增加而逐渐降低。

（2）聚羧酸减水剂在水泥颗粒表面的吸附量与吸附率均随着减水剂分子量的增加而逐渐增大；颗粒堆积随着减水剂掺量的增加逐渐增大，相同流动度时掺入较大分子量（63600 g/mol）减水剂的颗粒堆积最为密实；浆体的流变性能与聚羧酸减水剂在水泥颗粒表面的吸附行为以及颗粒堆积密实度密切相关，相同流动度时，颗粒堆积密实度越高、减水剂吸附量越高，则间隙液粘度越低、颗粒间作用力越小，进而浆体表观粘度越低。

关键词：水泥浆体，聚羧酸减水剂分子量，流变性能，吸附性能，堆积密实度

Abstract

With the development of modern concrete technology, the mumber of ultra-high, ultra-long, and ultra-deep structures is gradually increasing, which leads to higher demands on the performance of high-performance concrete. Polycarboxylate superplasticizer (PC) has significant advantages such as high water reduction and high slump retention ability, and has become an important component of high-performance concrete with features such as low water-binder ratio and complex components. However, at present, the performance of PC is mainly evaluated by flow spread of paste with high water-cement ratio, so it cannot establish the relationship between the flow spread and the high performance concrete workability. Moreover, the development and appliction of PC based on the performance requirements of concrete is not yet mature.

Based on this, the molecular weight of, which is one of the key factors influencing the performance of PC was investigated. Based on the principle of rheology, four water-cement ratios (0.40, 0.30, 0.25, and 0.20) were systematically studied. The effect of five kinds of molecular weight of PCs, which ranging from 20000 g/mol to 64000 g/mol, on the rheological properties of cement paste was investigated. Moreover, its influence mechanism on the rheological properties was also discussed by considering the combined effect of adsorption behavior of PC on the surface of cement particles and the packing density of particles in the cement pastes. This study is of great significance for improving the performance of high performance concrete and developing PCs. The following conclusions were obtained:

(1) With the increase of the molecular weight, water-reducing rate of the PCs first increases and then decreases, and water-reducing rate is highest for PC with molecular weight Mw of 29600 g/mol. For cement paste with the same dosage of PCs, yield stress and apparent viscosity decreases firstly and then increases with the increase of the molecular weight of PCs. This change rule is contrary to flow spread of the cement paste. For cement paste with same flow spread, yield stress does not change with the change of PCs’ molecular weight, but gradually increases with the decrease of water-cement ratio. However, the apparent viscosity of cement paste gradually increases with the increase of the PCs’ molecular weight.

(2) The adsorption amount and adsorption rate of PCs on the surface of cement particles increase with the increasing of the M_w, and the packing density gradually increases with the increase of the dosage of PCs. For cement paste with flow spread, particles in paste with PC which has the largest molecular weight (63600 g/mol) were densely packed. The rheological properties of cement paste were closely related to the adsorption behavior of the PCs on the surface of cement particles and packing density. For cement paste with the same flow spread, the higher the packing density and the higher the adsorption capacity of the PCs will result in lower the viscosity of interstitial fluid, the smaller the intergranular forces, and then the lower apparent viscosity of cement paste.

KEY WORDS: cement pastes, molecular weight of superplasticizers, rheological properties, adsorption behavior, packing density

目录

摘要 I

Abstract II

第一章 绪论 1

1.1 研究背景 1

1.2 国内外研究现状 2

1.2.1 聚羧酸减水剂 2

1.2.2 水泥浆体流变性能 6

1.3 本文研究内容及意义 8

第二章 原材料性能与试验方法 9

2.1 原材料性能 9

2.1.1 水泥 9

2.1.2 聚羧酸高性能减水剂 9

2.2 试验方法 9

2.2.1 水泥浆体制备方法 10

2.2.2 水泥浆体流动度测试方法 10

2.2.3 水泥浆体流变性能测试方法 10

2.2.4 减水剂在水泥颗粒表面吸附量测试方法 11

2.2.5 水泥颗粒堆积密实度测试方法 12

第三章 聚羧酸减水剂分子量对水泥浆体流变性能的影响 14

3.1 水泥浆体流动度 14

3.2 水泥浆体流变特性 15

3.2.1 流变模型选择 15

3.2.2 相同掺量下减水剂分子量对水泥浆体流变性能的影响 17

3.2.3 相同流动度下减水剂分子量对水泥浆体流变性能的影响 20

3.3 本章小结 24

第四章 聚羧酸减水剂分子量对吸附行为的影响及作用机制 25

4.1 聚羧酸减水剂在水泥颗粒表面的吸附行为 25

4.1.1 相同掺量下减水剂分子量对其吸附性能的影响 25

4.1.2 相同流动度下减水剂分子量对其吸附性能的影响 27

4.2 水泥颗粒堆积密实度 30

4.3 聚羧酸减水剂分子量对水泥浆体流变性能的影响机制 31

4.4 本章小结 33

第五章 结论与展望 34

5.1 结论 34

5.2展望 34

致谢 36

参考文献 37

第一章 绪论

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