【作者】 张征；

【导师】 郭进军；

【作者基本信息】 郑州大学 ， 水利工程， 2021， 硕士

【摘要】 我国西部地区干燥少雨,昼夜温差大,盐渍土分布广泛。在这种环境下,施工期混凝土在大温差和盐类侵蚀的影响下更易开裂。向混凝土中掺入矿物掺合料能够有效减小混凝土的早期收缩,减少施工期裂缝的出现。但目前关于大温差和盐类共同作用下矿物掺合料改性混凝土早期抗裂性能的研究还较少,无法明确恶劣环境下混凝土中矿物掺合料的最优复掺方式。所以,本文以西部新疆地区环境为参照,将粉煤灰和矿粉按照不同比例掺入混凝土中,研究施工期混凝土的抗裂性能,并通过对混凝土微观结构的观测,阐释混凝土抗裂性能的变化机理。主要研究内容和结论如下:（1）研究了大温差环境下矿物掺合料改性混凝土的抗压强度、抗折强度和断裂特性随龄期的变化规律,结果表明:不同组混凝土的抗压强度随龄期增加而增长,抗折强度随龄期增加先增长后降低,14d达到最大值。混凝土断裂韧度和断裂能随龄期的变化情况和抗折强度相同,矿物掺合料混凝土断裂韧度高于基准混凝土。大温差环境下,掺入10%粉煤灰和20%矿粉对混凝土宏观力学性能的提升效果最好。（2）研究了大温差环境下矿物掺合料改性混凝土的微观结构。对比分析了不同组混凝土的微观界面、物相组成和孔结构参数,结果表明:掺入10%粉煤灰和20%矿粉的混凝土的微裂纹宽度更小,硅酸钙（C₂S/C₃S）衍射峰最低,混凝土平均孔径更小,1-30μm小孔数量明显多于基准组,孔隙率低。（3）研究了大温差侵蚀环境下矿物掺合料改性混凝土的抗压强度、抗折强度和断裂特性随龄期的变化规律,结果表明:不同组混凝土的抗压强度和抗折强度随龄期的增加而增长,矿物掺合料混凝土28d的抗压强度略低于基准混凝土。矿物掺合料混凝土14d前抗折强度低于基准混凝土,但其后期强度增长速率大。分析不同组混凝土断裂韧度和断裂能发现,矿物掺合料的掺入降低了混凝土早期断裂性能,但对混凝土后期断裂性能的提升更明显。综合比较,掺入15%粉煤灰和20%矿粉对大温差侵蚀环境下混凝土宏观力学性能的提升效果最好。（4）研究了大温差侵蚀环境下矿物掺合料改性混凝土的微观结构。对比分析了混凝土的微观界面、物相组成和孔结构参数,结果表明:随着龄期的增加,混凝土中水化硅酸钙凝胶由各自成簇的状态逐渐向稳定的层片状转变,大温差侵蚀环境下混凝土中氢氧化钙的含量更低,粉煤灰和矿粉发挥火山灰效应生成更多的水化产物。掺入15%粉煤灰和20%矿粉的混凝土的孔隙率略高于基准混凝土,但平均孔径更低,气孔间距系数更大。（5）研究了大温差侵蚀环境下混凝土表层氯离子含量,结果表明:混凝土内部氯离子含量随深度的增加而降低,矿物掺和料的掺入有效降低了混凝土内部氯离子含量,粉煤灰对氯离子渗透的抑制效果优于矿粉。参考相关规范对混凝土构件最大氯离子含量的要求,认为大温差侵蚀环境下28d混凝土中的游离氯离子还不足以引起钢筋锈蚀开裂。更多还原

【Abstract】 The western region of my country is dry and less rainy,the temperature change between day and night is large,and saline soil is widely distributed.In this environment,concrete is more prone to cracking under the influence of large temperature change and salt erosion during construction.Incorporating mineral admixtures into concrete can effectively reduce the early shrinkage of concrete and reduce the appearance of cracks during construction.However,there are few researches on the early anti-cracking performance of concrete modified by mineral admixtures under the combined action of large temperature change and salt erosion,and it is impossible to clarify the optimal compounding method of mineral admixtures in concrete under harsh environment.Therefore,this article takes the environment of the western Xinjiang region as a reference,mixes fly ash and slag into concrete in different proportions,studies the crack resistance of concrete during construction,and explains the crack resistance of concrete through observation of the microstructure of concrete.The main research contents and conclusions are as follows:（1）The compressive strength,flexural strength and fracture characteristics of mineral admixture concrete change with age under a large temperature change environment.The results showed that the compressive strength of different groups of concrete increased with age.The flexural strength increased first and then decreased with the increase of age,reaching the maximum at 14 days.The changes in fracture toughness and fracture energy of concrete with age were the same as the flexural strength,and the fracture toughness of concrete with mineral admixtures was higher than that of reference concrete.In the large temperature change environment,adding10%fly ash and 20%slag had the best effect on improving the macro-mechanical properties of concrete.（2）The microstructure of mineral admixture concrete under a large temperature change environment is studied.The micro-interface,phase composition and pore structure parameters of different groups of concrete were compared and analyzed.The results showed that the micro-crack width of concrete mixed with 10%fly ash and 20%slag was smaller,and the diffraction peak of calcium silicate（C₂S/C₃S）was the lowest,the average pore diameter of the concrete was smaller,the number of small pores of 1-30μm was obviously more than that of the benchmark group,so the porosity was low.（3）The compressive strength,flexural strength and fracture characteristics of the concrete with mineral admixtures under the environment of large temperature change and salt erosion were studied.The results showed that the compressive strength and flexural strength of different groups of concrete varied with age.As the age increased,the 28d compressive strength of the mineral admixture concrete was slightly lower than that of the benchmark concrete.The flexural strength of the mineral admixture concrete before 14d was lower than that of the benchmark concrete,but its strength growth rate in the later period was large.Analyzing the fracture toughness and fracture energy of different groups of concretes,it was found that the incorporation of mineral admixtures reduced the early fracture performance of concrete,but it improved the later fracture performance of concrete more significantly.In a comprehensive comparison,adding15%fly ash and 20%slag had the best effect on improving the macro-mechanical properties of concrete under a large temperature change and salt erosion environment.（4）The microstructure of mineral admixture concrete under the environment of large temperature change and salt erosion was studied.A comparative analysis of the microscopic interface,phase composition and pore structure parameters of the concrete showed that with the increase of age,the hydrated calcium silicate gel in the concrete gradually transformed from its clustered state to a stable lamellar shape.The content of calcium hydroxide in concrete was lower in the environment of large temperature change and salt erosion,and fly ash and slag exerted the pozzolanic effect to generate more hydration products.The porosity of the concrete mixed with 15%fly ash and 20%slag was slightly higher than that of the benchmark concrete,but the average pore diameter was lower and the pore spacing coefficient was larger.（5）The chloride ion content of the concrete surface under the environment of large temperature change and salt erosion was studied.The results showed that the chloride ion content in the concrete decreased with the increase of depth.The incorporation of mineral admixtures effectively reduced the chloride ion content in the concrete.The inhibitory effect on the penetration of chloride ions was better than that of slag.With reference to the requirements of the relevant specifications for the maximum chloride ion content in concrete,it was believed that the free chloride ion of concrete at 28d under the salt erosion environment was not enough to cause corrosion and cracking of steel bars.更多还原