【作者】 孙海燕；

【导师】 何真；

【作者基本信息】 武汉大学 ， 水工结构工程， 2010， 博士

【摘要】 粉煤灰替代水泥掺入到混凝土中,不仅可以提高固体废弃物的资源化利用率,还可以减少水泥水化放热量,改善混凝土力学及耐久性能,具有技术、经济双重效益。然而,限于过去测试手段和传统观念的局限性,对水泥基材料低尺度下,水化浆体主要产物C-S-H的组成、结构、表面形貌及微观力学特性、水泥-粉煤灰材料体系中微结构形成和劣化过程中粉煤灰临界掺量以及水泥基材料宏观性能与微结构结构间的内在联系上还没有系统的研究,对这些问题的深入解析,对水泥基材料的研究、工程应用以及高值化利用粉煤灰均具有重要的现实意义。本文针对上述问题,在国家重点基础研究发展计划项目(973)、国家自然科学基金项目(50972109)和中国水电工程顾问集团公司科技项目的资助下,对不同掺量粉煤灰水泥基材料微结构形成和劣化过程中的宏观及低尺度下微观性能进行了系统深入的研究,并最终确定粉煤灰-水泥体系中粉煤灰的临界掺量。主要研究成果如下：1、系统研究了不同粉煤灰掺量水泥石在微结构形成过程中,粉煤灰的作用机理,得出了水泥石微结构形成过程中粉煤灰的临界掺量。(1)在水化早期,粉煤灰的最佳活性效应位置点和孔结构出现在粉煤灰40%掺量时,而随水化龄期的延长,粉煤灰的最佳活性效应位置点和孔结构向后推移至粉煤灰掺量为50%时。不同水化龄期时各掺量粉煤灰砂浆孔结构参数(α和λ)与其强度试验结果间相关性较好。(2)当粉煤灰掺量不超过50%时,粉煤灰对水泥石的强度影响不大,对其孔结构改善效果较好,水化浆体增加的孔容主要是源于无害孔和少害孔孔数量的增加,当掺量超过50%后,水泥石的强度和孔结构开始出现劣化趋势,粉煤灰掺量增加到70%时,水化浆体增加的孔容主要是源于有害孔和多害孔孔数量的增加。(3)粉煤灰掺量为50%是C-S-H结构与组成发生明显改变的一个临界点,水化浆体结晶度在降低幅度较大。在粉煤灰掺量不超过50%时,水化浆体内链状C-S-H和铝代C-S-H的生成量是在增加的,Si-O伸缩振动叠加峰中心均向高波数迁移；而粉煤灰掺量增加到70%时,链状C-S-H的生成量又开始减少,Si-O伸缩振动中心附近,开始出现很宽、底部有两个中心的吸收带。(4)浆体内组群状C-S-H的生成量随粉煤灰掺量的增加而减少,研究发现,虽然链状C-S-H生成量的增加在一定程度上也可以提高水泥石的强度,但相比较而言,组群状C-S-H对水泥石强度提高更有利。2、给出一种适合水泥水化浆体C-S-H簇表面形貌测试的制样方法和C-S-H簇粘聚力定量化的测试手段。(1)对自然断面法、磨抛处理法、复型法以及旋涂法4种制样方式比较分析,最终确定在控制观察面不被破坏的前提下,磨抛处理法是一种适合硬化水泥基材料C-S-H表面形貌和微观力学特性研究的制样方法。(2)以溶胶-凝胶法合成的C3S水化浆体为研究对象,在组分相对单一的情况下,研究水化C3S浆体中C-S-H的表面形貌及颗粒堆聚结构特征,结果表明,C-S-H簇在纳米尺度下,是由一团团无定形球形纳米颗粒堆聚而成。(3)水化90d时,基准和掺有30%粉煤灰的水泥水化浆体中C-S-H颗粒堆聚密度有增加的趋势,且掺有粉煤灰一组更为显著；掺有粉煤灰水化浆体中C-S-H颗粒形状对比基准水泥样不规则化程度加剧,球形颗粒明显减少,以扁平状颗粒居多。(4)水化3d时,掺有30%粉煤灰水化浆体C-S-H簇与针尖间作用力对比基准水泥水化样明显降低；水化90d时,两种材料体系下C-S-H簇与针尖间作用力均得到明显提高,且掺有30%粉煤灰水化浆体提高更为显著,水化浆体C-S-H簇低尺度下微观力学表现与水泥石的宏观强度试验结果基本是一致的。3、系统研究了不同掺量粉煤灰水泥石在溶蚀破坏后的宏观及微观性能,给出水泥石的劣化过程中粉煤灰的最佳掺量。(1)水化浆体累积CaO溶蚀量、强度下降率和孔结构劣化等角度分析认为,水泥中掺入一定量粉煤灰提高水泥石的抗溶蚀破坏能力；粉煤灰掺量为50%时,溶蚀后强度下降率最小、孔容和比表面积最小,水泥基材料的抗溶蚀效果达到最佳值。(2)溶蚀后各水化浆体组群状C-S-H被不同程度地缩聚为链状C-S-H,对应于试样宏观强度有不同程度的降低。对比3组掺有粉煤灰水泥样,基准水泥样溶蚀后水化浆体中Q1／Q2降低幅度最大,对应其宏观力学性能,发现溶蚀后强度下降幅度最大；而当粉煤灰掺量为50%时,Q1／Q2对比其它3组试样略有提高,对应溶蚀后强度下降幅度最小,从而有利于其抗溶蚀性能提高。溶蚀后各组试样中Si-O伸缩振动均向高波数迁移且相对强度降低,表明C-S-H聚合度提高和平均链长增长。(3)不同掺量粉煤灰水泥浆体溶蚀后Ca-OH伸缩振动的相对强度,均较其对比样明显降低,表明在溶蚀过程中,各水化浆体中Ca(OH)2含量均有不同程度的减少。同时发现各水化浆体中C-S-H的聚合度和平均链长也发生了明显的改变,说明在溶蚀破坏过程中,浆体内Ca(OH)2和C-S-H中钙的溶出彼此交织进行的,在NMR和FTIR试验结果均发现,在溶蚀期间,水泥石且未水化水泥熟料中钙也会被一并溶出。(4)对比掺有50%粉煤灰的水泥砂浆,基准水泥砂浆溶蚀后纤维状C-S-H水化产物量显著增加,试样的表面形貌变得更为疏松,水化产物相之间孔隙增多,再次说明水化浆体中组群状C-S-H被大量转变为链状C-S-H,水化浆体的比表面积增大；而掺有粉煤灰砂浆溶蚀后试样,C-S-H表面形貌由纤维状变为薄片状,说明粉煤灰二次水化反应生成的低钙硅比C-S-H稳定性较好,受溶蚀破坏影响较小。更多还原

【Abstract】 Fly ash (FA) has become one of important components in the hydraulic concrete. While improving resource utilization of solid waste, due to replacing cement by FA, hydration heat of cement is reduced, mechanical properties and durability of concrete is improved, which take on the technical and economic double benefits. However, due to the limited measuring methods previously, it is devoid of the systematic study about C-S-H structure, composition, surface morphology and micro-mechanics properties due to the mixing fly ash, FA critical dosage during the microstructure formation and degradation process microstructure in the cement-fly-ash materials system and the relationship between macro-properties and microstructure. Through the thorough analysis of these problems, there is the important practical significance on materials research and engineering application and using fly ash with high efficient.Financial supported by National Basic Research Program of China (973) (No. 2009CB623200), National Natural Science Foundation Project (No.50972109) and Science and Technology Project of China Hydropower Engineering Consulting Group Company (CHECC). Aiming at the above-mentioned problems, the systematic study in this thesis focus on the correlation between microstructure and macroscopic mechanical properties, including microstructure formation and deterioration process of the cement-based materials, which is the low water to binder ratio and the different dosages fly ash. The main research results are listed as follows.1. The limit dosage of fly ash in the process microstructure formation is put forward based on the correlation between microstructure and macroscopic mechanical properties in the cement pastes incorporating with the different dosages fly ash.(1) When FA dosage is 40%, there is the best activity effect and pore structure at the early age. However, with increase of curing age, the lapse of FA dosage is 50%. There is the better relationship between the parameters of pore structure(α和λ) and strength of the cement pastes with the different FA dosages at the different curing ages.(2) Decrease of strength in the cement pastes is not obvious with increasing FA dosages compared to reference before FA dosages less than 50%. Pore structure is also improved with increasing FA dosages until more than 50% dosages, that is, the optimum parameters value of pore structure could achieve when FA dosage increasing to 50%, but after increased continuously to exceed 50%, strength and pore structure of cement pasts begin to be deteriorated.(3) FA dosage 50% is critical in that crystallinity is declined with the highest extent and structure and composition of C-S-H are varied significantly. When FA dosages less than 50%, the silicate polymerization and mean silicate chain length and aluminous of C-S-H are increased. The center of overlaping peak of Si-O stretching vibration is migrated to the high wave number. But after FA dosages more than 50%, chains begin to reduce. There are two center of absorption band of Si-O stretching vibration.(4) With the increase of fly ash dosages, silicon-oxide bodies with end groups are reduced in the cement pastes. An important observation in this thesis is that silicon-oxide bodies with end groups C-S-H in the cement pastes was more advantaged to the development of strength when comparing to mean silicate chain length C-S-H by XRD/NMR/FTIR testing.2. A kind of method is put forward for measuring the surface morphology and C-S-H cluster quantitative cohesion in the cementitious pastes.(1) Through the analyses and comparison of the advantages and disadvantages of four kinds sample preparation methods(natural section, polishing, replica and spinning) respectively, it is provided that the polishing method is the most suitable method for measuring the nano-scale surface morphology of C-S-H clusters in the cementitious pastes by AFM.(2) Characteristics of surface morphology and particle packing structures of C-S-H clusters by AFM are studied by adopting the single relatively component of the C3S pastes, which is synthesized by sol-gel method. C-S-H clusters are packed with the round and round amorphous nano-scale particles, whose size ranges are from twenty to thirty nanometers.(3) Comparison with the curing 3d, the packing density of C-S-H clusters is increased by the surface morphology research after 90d. Moreover, packing density of the cement pastes improved obviously than reference cement. In addition, C-S-H clusters in the pastes with incorporated 30% FA become more irregular and flat when contrasting with reference sample.(4) Interactions between the nanoscale C-S-H clusters in the cementitious pastes and the AFM Si3N4 tip are described by measuring force-distance curve in the real atmospheric conditions. Comparison with reference sample, force values of interactions in the cement pastes incorporated 30% FA are decreased significantly at the early age. But just the opposite at the later age, force values of interactions in the cement pastes incorporated 30% FA are almost equal with ones of the reference sample, which is coincident with their test results of the macroscopic mechanical properties.3. The optimal dosage of fly ash in the degradation process is put forward based on the correlation between microstructure and macroscopic mechanical properties in the cement pastes incorporating with the different dosages fly ash.(1) According to cumulative CaO dissolution, decreasing rate of compressive strength and pore structure in the cementitious pastes, mixing FA is advantage to dissolution resistance of the cement pastes. With increasing FA dosages, cumulative CaO dissolution was declined, but decreasing rate of compressive strength and specific surface area and porosity took on the first reduce after increased, the highest dissolution resistance is achieved at the 50% FA. (2) Due to condensation polymerization of dissolution, silicon-oxide bodies with end groups are inverted into mean silicate chain length C-S-H. Q’/Q2 of C-S-H after dissolution of the reference sample is declined more obviously than others, which is responding exactly to its macroscopic mechanical properties after dissolution decreased maximum. However, Q1/Q2 of C-S-H after dissolution of the sample with 50% FA dosages is increased slightly, which is responding exactly to its macroscopic mechanical properties after dissolution decreased minimum, that is, the highest dissolution resistance is achieved when FA dosage is 50%.(3) Due to the dissolution, the relative intensity of Ca-OH stretching vibration in the cement pastes is declined remarkable when comparing to their control sample, which indicate that Ca(OH)2 is also declined with the different range. An important observation in this thesis is that silicate polymerization and mean silicate chain length of C-S-H are increased in all cementitious pastes, which means that the dissolution of Ca(OH)2 as well as decalcification of C-S-H gel is happened in all cementitious pastes meanwhile the dissolution of unhydrated cement clinker.(4) Compared with mortar with 50% FA, after dissolution, fibrous C-S-H is significantly increased in the reference sample, its surface morphology becomes more loose and porous, which indicates also that silicon-oxide bodies with end groups are inverted into mean silicate chain length C-S-H with the high specific surface area. Mortar mixing 50% FA after dissolution, C-S-H is inverted from fibrous into thin sheets, which shows that the low ratio of calcium and silicon C-S-H produced by the pozzolanic reaction of FA has the better stability for dissolution resistance.更多还原