新拌混凝土工作性的好坏不仅决定了混凝土能否顺利施工，对混凝土的后期性能也至关重要。目前混凝土的施工方法有泵送、现浇、自密实、水下、喷射以及碾压混凝土等，其对流变要求各不相同。新拌混凝土被认为是宾汉姆流体，其流变特性中最重要的两个参数是屈服应力和粘度。通过水灰比来调整混凝土的流变性，但受制于强度以及成本的要求，范围有限。随着外加剂技术的发展，减水剂和粘度调节剂（VMA）的组合，在理论上可以设计满足各种流变要求的混凝土。但前提是对减水剂特别是聚羧酸减水剂（PCE）（其为目前工程中最常用的类型）以及VMA的结构与性能已经明晰。从已有文献来看，PCE、VMA等结构性能关系的结论仍未明确。另外关于高温下使用（如固井工程）的PCE的研究也非常缺乏。在混凝土中引入PCE或VMA后，二者均会明显抑制水泥水化产物的成核过程因而有缓凝作用。因此，在解决工作性的前提下，能够促进水泥早期水化以快速提升早期强度的外加剂，成为许多工程迫切需要解决的问题（如预制混凝土构件）。最近出现了把C-S-H成核剂外加到水泥浆里来促进水泥水化的方法，其早强效果显著且对后期强度无不利影响，从机理上适合于用来解决PCE和VMA带来的缓凝作用。但从已有文献来看，成核剂的制备方法及其作用机制还不是很清楚。 合成了一系列结构不同的PCE，通过显微镜观察高水灰比的水泥浆体中颗粒的分散形态来揭示PCE结构与性能的关系。用动态激光散射（DLS）测试溶液中Ca2+对PCE流体力学半径的影响。二价阳离子和非吸附聚合物（NAP）对PCE减水性能的影响。结果表明PCE结构中的侧链不仅是为了增加空间位阻，更是有效地抑制Ca2+桥接用而导致的水泥颗粒团聚絮凝，且侧链越长、侧链密度越大，效果越强。二价阳离子会影响PCE的分散性能，而NAP则能增强PCE的减水性能。 合成了一系列结构的VMA（降失水剂，FLA，用于降低水泥浆失水）。测试了其抗水泥浆泌水和降失水性能，对浆体屈服应力和粘度的影响以及在水泥表面的吸附以及在溶液中的流体力学体积。结果表明，VMA（FLA）对水泥的吸附及VMA（FLA）分子的流体力学体积是其调粘和降失水的两个关键参数。VMA（FLA）分子中应具有强吸附锚固基团及较大流体力学体积的水化链段两个重要部分。 采用溶胶-凝胶法合成了纳米的C-S-H粒子并进行了表征，用等温量热法，XRD，FTIR，TGA，ICP-OES以及SEM来研究纳米C-S-H对水泥水化的影响，并测试了其对砂浆早期以及28天强度的影响。

In the concrete industry, the workability of fresh concrete, which is the characteristics describing the ability of fresh concrete to move and to be compacted, is one of the essential properties among all properties of concrete such as mechanical properties, durability etc. The appropriate workability of fresh concrete is the key for successful construction of concrete structures, which ensures the transportation and casting of fresh concrete mixture, and is also benefical to the long-term performances of concrete during service. The required workability for casting concrete depends on the type of construction technique, e.g.placement and consolidation methods, such as pumping, self-compacting concrete (SCC), underwater concrete, shotcrete or roller compacted concrete. Theoretically, concrete workability is characterized by its rheological properties. The rheology behavior of fresh concrete is usually defined as a Bingham fluid, characterized by parameters of yield stress and plastic viscosity. Water to cement ratio, optimization of binder system and concrete formuation are the traditional tools to adjust the workability of fresh concrete, which which however is limited by the strength requirement of the final concrete. The considerabe progress of the chemical admixtures technology in the last decades, such as the polycarboxylate superplasticizers (PCEs) and viscosity modifying admixtures (VMAs), provides a more powerful tool allowing us to adjust the workability of fresh concrete in a much wider range without negatively affecting the long-term performances of final concrete. Despite the vast practical application of the various chemical admixtures, the fundamental understanding of the structure-performance relationship of those chemical admixtures is still unsatisfactory. In addition, more application of PCE such as in oil well cementing project requires more fundamental investigation due to the extremely severe condition such as the high environmental temperature. Therefore, one of the main tasks of this thesis is to provide more fundamental insights into the structure-performance relationship of the two types of typical chemical admixtures, PCEs and VMAs.On the other hand, the incorporation of the PCEs or VMAs brings great influences on the cement hydration process, usually retardation effect, which in ture delay the setting and strength growth of concrete. The updated understanding of the retardation mechanisms of those chemical admixures is the so-called nucleation poisoning effect. That is to say, the nucleation process of hydration products, C-S-H is significantly inhibited by the addition of the PCEs and VMAs. In recent years, a novel approach to accelerate cement hydration has been proposed by adding external C-S-H nuclei into a hydrating cementitious system, which is called seeding technology. It is believed that such seeding technology is a promising technique to compensate the retardation effects of the PCEs or VMAs. The preparation method and specific working mechanism of C-S-H seeds are unfortunately still not very much documented. Therefore, another task of this thesis is to prepare the C-S-H seed and to explor the working mechanism of C-S-H seed. In this thesis, a series of PCEs with varied molecular structure are prepared by radical polymerization and fully characterized. The dispersion morphology of cement grains in fresh cement pastes containing PCEs was observed by Morphologi G3 microscope. Particular attention was paid to the interaction between the PCEs and of the ions, especially Ca2+ ion in the interstitial solution of fresh cement paste by measurement of the average hydrodynamic radius (Rh) of PCEs using laser scattering technique. In the cement pastes, the effect of bivalent cation and non-absorbed polymer on the dispersion of PCEs was investigated. Results showed that the functions of side chain in the comb-like PCE not only generate steric hindrance effect but also hinder the bridging effect of ion once they are adsorbed on surface of cement grains. In fresh cement pastes, the bivalent cations would reduce the PCE’s dispersion effect.Longer side chain and higher side chain density is beneficial to the hindrance of the Ca2+ bridging effect. A series of VMAs (or Fluid loss additives, used to reduce water loss from the cement slurry in oil well cementing) with varied structures are prepared. The bleeding (or water loss) were tested to compare the performance of the obtained polymers as VMAs or FLAs in cement pastes. The rheology of fresh cement pastes containing the polymers is also investigated by Brookfield rheolometer. The adsorption of polymers on cement was measured by TOC. The hydrodynamic radius of the polymers was calculated with Einstein viscosity equation. Results showed that the VMA polymers could significantly decrease the bleeding tendency or water loss of the cement pastes. On the other hand, the VMA polymers also increased the plastic viscosity and the yield stress of fresh cement pastes. Further experiments showed that their performances were related with their adsorption capacity on surface of cement grains and their hydrodynamic radius in pore solution. Therefore, it is concluded that the anchoring groups and the long hydrated polymer backbone are the two necessary components of VAM polymers. By sol-gel method nano-sized C-S-H particles (Nano-C-S-H) were prepared and fully characterized using techniques of FTIR, XRD, TEM, DLS etc. The Nano-C-S-H particles were added as admixture into Portland cement (OPC) systems. The working mechanism of the C-S-H particles in accelerating cement hydration was systematically investigated by using techniques of isothermal calorimetry, XRD, SEM and ICP-OES. Strength development of the mortar with inclusion of Nano-C-S-H was followed in the age of 28d.