不同尺度纤维素纤维对水泥胶凝浆体微观结构及水化特性的影响

发布时间：2018-03-22 02:02

本文选题：酸解法　切入点：微纳米级　出处：《武汉纺织大学》2017年硕士论文　论文类型：学位论文

【摘要】：水泥胶凝浆体在微结构形成过程中由于各组分水化性能差异而引起内力不均,进而产生原生缺陷是引起其损伤劣化及耐久性问题的根源。利用纤维改性水泥基复合材料成为一种有效提高其综合性能的手段,其中纤维素纤维具有长径比大、比强度高、比表面积大、抗拉拔韧性高、粘着吸附能力强、价格低廉等优点,使其在胶凝浆体微结构诱导、强韧化改性方面具有突出优势。本文采用H_2SO_4酸解法处理脱脂棉纤维,制备得到亚微级和纳米级尺度的纤维素纤维,采用红外光谱、SEM、粒径分析等测试手段对样品进行表征。结果证明:纤维素纤维经酸解作用后,其特征基团、分子结构并不发生改变,而只是在尺度上逐渐减小,即天然纤维素纤维在酸解作用下逐步剥离成为直径从十几微米到几百纳米的纤维,其直径随着H_2SO_4溶液浓度的增大、反应时间的延长而逐渐减小。将不同尺度的纤维素纤维引入水泥浆体,运用SEM研究纤维素纤维尺度对胶凝浆体微结构的影响。结果表明:纤维素纤维的亲水性和超强吸附性使水泥水化产物C-S-H凝胶依附在其表面生长;宏观尺度纤维素纤维在水化早期吸水溶胀,后期释水后发生干缩、脱空现象,降低水了泥浆体的密实度,从而影响水泥基复合材料的体积稳定性;微纳级纤维素纤维在尺度上与水泥水化产物C-S-H凝胶尺度匹配,其晶核作用在早期诱导水化产物沿纤维方向蔓延生长,在一定程度上促进水泥的水化,随着纤维表面水化产物的不断生长,纤维逐渐被包埋其中。采用IR、TG-DSC、水化热、NMR、XRD等测试技术研究纤维素纤维对水泥水化特性的影响。结果表明:纤维素纤维初期会吸收水分降低浆体的实际水灰比,水化放热速率低,早期放热量低;后期水泥浆体内部水分逐步消耗,纤维素纤维所吸的水分在湿度梯度和毛细压的作用下向外释放,保证水泥颗粒的持续水化,故总放热量与纯水泥相当;纤维素纤维本身不参与水泥的水化反应,但微观尺度纤维的诱导调控作用有助于提高C-S-H凝胶聚合度。本文还对纤维素纤维水泥基复合材料的宏观力学性能进行了研究。结果表明:小尺寸纤维素纤维能够明显提高水泥基复合材料的抗折强度,抑制水泥浆体的收缩度,且纤维尺寸越小,效果越明显。
[Abstract]:During the formation of the microstructure of the cement paste, the internal force is uneven due to the difference of the hydration performance of each group. Then the original defects are the root of the damage deterioration and durability problems. The use of fiber modified cement matrix composites has become an effective means to improve its comprehensive properties, among which cellulose fiber has a large aspect ratio and high specific strength. The advantages of large specific surface area, high tensile toughness, strong adhesion and low price have made it have outstanding advantages in the modification of cemented pulp microstructure and toughening. In this paper, H_2SO_4 acid hydrolysis was used to treat the degreased cotton fiber. The submicro and nanometer scale cellulose fibers were prepared and characterized by infrared spectroscopy and particle size analysis. The results showed that the cellulose fibers were characterized by acidolysis. The molecular structure did not change, but only gradually decreased on a scale, that is, natural cellulose fibers were gradually stripped off into fibers ranging from 10 microns to hundreds of nanometers in diameter under acidolysis, and their diameters increased with the concentration of H_2SO_4 solution. When the reaction time was prolonged, the cellulose fibers of different sizes were introduced into the cement paste. The effect of cellulose fiber size on the microstructure of cement paste was studied by SEM. The results showed that the hydrophilicity and super adsorption of cellulose fiber made the cement hydration product C-S-H gel grow on its surface. The macroscopical cellulose fiber absorbs water at the early stage of hydration and expands in water at the later stage of water release. The phenomenon of dry shrinkage and emptying occurs, which reduces the density of the water slurry and thus affects the volume stability of the cement matrix composite. The micro- and nanoscale cellulose fiber matches the C-S-H gel scale of cement hydration product on the scale, its crystal nucleus action induces the hydration product to propagate along the fiber direction in the early stage, and to some extent promote the hydration of cement. As the hydration products on the surface of the fibers continue to grow, The effects of cellulose fibers on the hydration properties of cement were studied by means of IR TG-DSCand NMR-XRD. The results showed that the moisture absorption of the cellulose fibers at the initial stage decreased the actual water-cement ratio of the slurry, and the hydration heat release rate was low. In the later stage of cement slurry, the moisture absorbed by cellulose fiber was released outward under the action of humidity gradient and capillary pressure to ensure the continuous hydration of cement particles, so the total heat release was equivalent to that of pure cement. Cellulose fiber itself does not participate in the hydration of cement, However, the induction and regulation of microfiber can improve the degree of C-S-H gel polymerization. The macroscopic mechanical properties of cellulose fiber cement matrix composites are also studied. The results show that the small size cellulose fiber can improve the polymerization degree of C-S-H gel. Obviously improve the flexural strength of cement matrix composites, The shrinkage of cement paste is inhibited, and the smaller the fiber size, the more obvious the effect is.
【学位授予单位】：武汉纺织大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ172.1;TB332

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