【作者】 王稷良；

【导师】 周明凯； 李北星；

【作者基本信息】 武汉理工大学 ， 材料学， 2008， 博士

【摘要】 随着基础设施建设的快速发展和环境保护的加强,天然砂资源越来越匮乏,使用机制砂已成为必然趋势。但机制砂在粒形、级配、表面质构以及0.075mm以下颗粒含量等方面与天然砂存在显著差异。因此,开展机制砂的上述特性对混凝土性能的影响及作用机理研究具有重要的实用价值和理论意义。首先研究了石英岩、片麻岩、花岗岩、玄武岩、石灰岩、大理岩等六种具有代表性岩性的石粉对化学外加剂作用效果的影响及对混凝土性能的影响。结果显示,石粉岩性的变化对化学外加剂特别是聚羧酸系减水剂的选择适应性表现显著,而石粉岩性对矿物掺和料的作用效果没有显著影响;石粉岩性变化对混凝土工作性、强度与体积稳定性略有影响,但影响差异并不显著,而石粉岩性变化对混凝土耐久性基本没有影响。其后,以石灰岩石粉为研究对象,研究了机制砂中石粉含量对混凝土性能的影响。结果显示,适量的石粉可以起到完善机制砂的级配、增加浆体数量和填充颗粒空隙的作用,改善机制砂混凝土的工作性,提高机制砂混凝土的强度,但对于不同强度等级混凝土而言,机制砂中石粉的最佳含量不同。同时,适量的石粉有利于机制砂混凝土抗氯离子渗透、抗冻融、抗硫酸盐侵蚀和抗磨等耐久性能的提高,但机制砂中石粉含量超过7%～10%不利于混凝土塑性收缩与干燥收缩的控制。综合研究成果提出,可将国标《建筑用砂》中机制砂中石粉含量限值适当放宽到5%,7%,10%,甚至更高。接着,研究了机制砂的粒形、级配、压碎值等机制砂特性指数对混凝土性能的影响。研究发现,受机制砂级配与石粉含量的影响,常规测试机制砂粗糙度的试验方法不能准确反映出机制砂的颗粒形貌特征。研究还发现,机制砂的多棱角的特性,一方面增加了混凝土的屈服应力而降低了混凝土的工作性,另一方面则有利于提高混凝土的强度与体积稳定性,但机制砂的压碎值与混凝土强度之间没有明显的相关性。通过砂浆流变性试验发现,适当提高机制砂中0.15～0.3mm与0.3～0.6mm的颗粒更有利于提高机制砂混凝土的工作性。还采用外加泥粉的方式研究了机制砂MB值变化对混凝土性能的影响。研究结果证实了机制砂MB值与机制砂岩性和石粉含量无关,而与泥粉含量成正比,同时还发现机制砂MB值也受泥粉液限指数的影响。机制砂MB值的提高,增加了混凝土的塑性粘度,增大了对化学外加剂特别是对聚羧酸系减水剂的吸附,对混凝土的工作性与体积稳定性劣化最为显著,但对于机制砂混凝土力学性能与耐久性的影响规律则与混凝土的强度等级有关,对于低强度等级混凝土而言,适当的MB值有利于机制砂混凝土强度与耐久性的提高,但对于高强度等级混凝土而言,MB值的提高则会导致机制砂混凝土强度与耐久性的劣化。最后,论文还采用XRD、SEM、MIP以及微区硬度、水化微量热等微观测试方法,研究了石粉对水泥水化的促进作用以及对混凝土孔隙填充作用的机制。研究发现,石粉具有晶核效应,且石粉中的CaCO₃微粒参与了C₃A的水化反应,从而促进了水泥初期水化放热,石粉中碳酸盐矿物颗粒含量越高,对水化促进越显著。机制砂中适量的石粉使混凝土过渡区密实化,改善硬化混凝土的孔结构,从而增强混凝土的性能,但当石粉含量过高时,水泥石中或界面过渡区出现游离态的石粉,则将不利于集料与水泥石的粘结,降低混凝土性能。更多还原

【Abstract】 With the rapid development of infrastructure construction and increasing attention being paid to environmental protection, there is a lack of the natural sand used to meet the requirements for engineering construction, so the use of manufactured sand （MS） to prepare concrete has become a trend. However, compared with natural sand, manufactured sand has remarkable differences on its shape, gradation, surface texture and the content of particles whose size is less than 0.075mm. Therefore, it has a practical and theoretical significance to research the influence of these characteristics of manufactured sand on performances of Portland cement concrete and its mechanism.Firstly, the influence of six stone dusts with representative lithologic characters on the action effect of chemical admixtures and the concrete performances were researched, which include quartzite, gneiss, granite, basalt, limestone and marble. The results showed that the change of lithologic characters of stone dust had an obvious effect on the adaptation of chemical admixtures, especially the polycarboxylate superplasticizer, while had no significant effect on the action of mineral admixtures. The change of lithologic characters of stone dust had a slight influence on concrete workability, strength and volume stability, and had little effect on the durability of MS concrete.Secondly, the effect of limestone dust content in the manufactured sand on concrete properties was studied. The results showed that the proper amount of stone dust could improve the gradation of MS, increase the paste volume and fill the void among particles, which could improve the workability and strength of MS concrete. However, the optimum content of stone dust in MS was different for MS concretes of different strength grade. The proper amount of stone dust could improve the durability of concrete, including the resistance to chloride ion permeation, the frost resistance, the sulfate resistance and abrasion resistance. But it was harmful to control the drying and plastic shrinkage that the stone dust content was more than 7%～10%. So, it is provided that the limited value of stone dust in MS in the national standard "Sand for Building" can be raised to 5 %, 7 %, and 10% or even higher.Thirdly, the effect of characteristic indexs of MS on the concrete performance was studied, such as particle shape, graduation, crushing value, et al. It was found that the routine test method of the sand roughness could not reflect the particle shape of MS accurately influenced by its graduation and stone dust content. It was also found that the angular MS could reduce the workability of MS concrete due to the increase of yield stress, and improve its strength and volumetric stability. However, there is no obvious correlation between the strength of MS concrete and its crushing value. The mortar rheological test results showed that the proper increase of particle content of 0.15～0.3mm and 0.3～0.6mm was helpful to improve the workability of MS concrete.Fourthly, influence of the change of MS MB value on the concrete properties was studied by adding clay powder into MS. The results showed that MB value had no correlation with the lithologic character and stone dust content of MS, while was in direct proportion to clay powder content. It was also found that MB value was influenced by liquid limit index of clay powder. With the increase of MS MB value, the plastic viscosity of concrete and its adsorption of the chemical admixtures, especially polycarboxylate superplasticizer, were increased. Due to the increase of MS MB value, the workability and volumetric stability of MS concrete was deteriorated significantly. But the mechanical properties and durability of MS concrete were also influenced by its strength grade. The proper MB value could improve the strength and durability of MS concrete for low-strength concrete, while for high-strength concrete, the increase of MB value could lead to the deterioration of strength and durability of MS concrete.Finally, the promotion of stone rust on cement hydration and its filling effect on concrete void were studied by using XRD, SEM, MIP, micro-hardness, micro-calorimeter, et al. The results showed that stone dust had crystal effect, and its CaCO₃ particulate participates the hydration of C₃A, promoting the early hydration of cement. With the higher CaCO₃ content in stone dust, the hydration promotion could be more notable. Proper amount of stone dust in MS densified the interfacial transition zone （ITZ） and improved pore structure of MS concrete, which enhanced the properties of MS concrete. However, if the quantity of stone dust was too high, the free stone dust could exist in ITZ, which was harmful to the bond between aggregate and hardened cement paste, and decreased the performance of MS concrete.更多还原