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This thesis studies the effects of superplasticizers, polyacrylate latexes and asphalt emulsions, which differ in molecular/particle size from nanometers to microns, on the rheological properties of fresh cement pastes (FCPs), as well as the action mechanisms involved. It systematically investigates the rheological properties and microstructure of cement-based materials, and elucidates the adsorption behaviors of polycarboxylate polymers with different functional groups and their effects on cement hydration. Moreover, it reveals how the working mechanism of naphthalene sulfonate formaldehyde (NSF) differs from that of polycarboxylate ether-based (PCE) superplasticizers. Lastly, it develops a conceptual microstructure model and two rheological equations. These findings lend theoretical support to the development of new chemical admixtures and new, higher-performance, cement-based composites.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Concrete is regarded as a key material to satisfy the requirements in the global housing and modern infrastructure. Currently, the annual global cement production has reached 4.0 billion tons and the corresponding concrete production is more than 10 billion cubic meters.
Yanrong Zhang

Chapter 2. Methodology

Abstract
In this chapter, the raw materials, the preparation of specimens, the testing methods and the equipments used in this research are introduced in detail. On the basis of the following measurements, the obtained experimental data are discussed in the following chapters.
Yanrong Zhang

Chapter 3. Rheological Properties of Fresh Cement Pastes

Abstract
Rheological properties of fresh cement pastes (FCPs) play essential roles in determining the workability of fresh mortars or concrete during the construction process and even affecting the mechanical properties and durability of hardened concrete to some extents (Huang in China Concr Cem Prod (4):3–4, 2000; Pu in Super high strength high performance concrete. Chongqing University Press, Chongqing, 2004). In modern mortars and concrete, various chemical admixtures are incorporated to improve the rheological properties of FCPs. Much research has been dedicated to correlating the rheological properties of cementitious systems with their mixture compositions and the environmental factors like temperature. However, there is little research regarding the combined effects of various influencing factors from the microstructure point of view and as a result, some controversial phenomena have not been well explained so far.
Yanrong Zhang

Chapter 4. Mesostructure of Fresh Cement Pastes

Abstract
From the microscopic point of view, the macroscopic properties of fresh cement pastes (FCPs), especially the rheological properties are primarily determined by their microscopic structure (Barnes and Hutton in An introduction to rheology. Elsevier, Amsterdam, 1989; Xu in J Wuhan Univ Technol 11(4):431–436, 1989). In order to elucidate the working mechanisms of various chemical admixtures on the rheological properties of FCPs, special attention should be paid to the changes on the microstructure of pastes caused by the chemical admixtures. The observation of FCPs by microscopes is a direct way to analyze the microstructure of the FCPs. However, few literature concerning the microstructure of FCPs is found due to the lack of effective measuring and analytical methods. For example, the obtained images from a regular optical microscope are far from being satisfied due to its low resolution and the limited measuring area. SEM and TEM with high resolution are usually used to observe the local morphology of hydrates rather than the global microstructure of pastes.
Yanrong Zhang

Chapter 5. Mechanism of Chemical Admixtures: Adsorption, Hydration and Rheology

Abstract
The understanding of the working mechanisms of chemical admixtures is essential for developing new types of admixtures with more efficient and robust performance and eventually adjusting the rheological properties of FCPs. Although much research has been dedicated to exploring the structure-property relationship of superplasticizers, there are still unsolved questions with regard to the specific mechanism through which various chemical admixtures affect the rheological properties of FCPs. Therefore, it is necessary, both practically and scientifically, to conduct in-depth investigation to elucidate the working mechanisms of different chemical admixtures in fresh cement pastes.
Yanrong Zhang

Chapter 6. Microstructure Model and Rheological Model of Fresh Cement Pastes

Abstract
Various chemical admixtures are practically used to modify the rheological properties of FCPs through changing the microstructure of FCPs and impacting the interactions of cement grains (Banfill et al. 2007; Ferrari et al. 2010; Kauppi et al. 2003; Roncero et al. 2002).
Yanrong Zhang

Chapter 7. Pore Structure and Impermeability of Hardened Cement Pastes

Abstract
With the development of cement hydration, the modification in the microstructure of FCPs by the addition of chemical admixtures will be persistently extended to the formation of the microstructure during the hardening period of cement pastes, thereby influencing the final properties of hardened cement pastes (HCPs).
Yanrong Zhang

Chapter 8. Conclusions of the Research

Abstract
This chapter presents the conclusions of the research based on the main findings stated in the previous chapters. The original contributions to the knowledge and the practical applications in real cases are also discussed. Future work arising from the research with regards to the impacts of chemical admixtures on cement mortars and concrete as well as a more general outlook are proposed.
Yanrong Zhang

Backmatter

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