冻融循环作用下纳米掺合料对大坝混凝土性能影响试验研究

Experimental study on the effect of nano admixture on the performance of dam concrete under freeze-thaw cycles

为改善高寒地区大坝混凝土长期遭受冻融循环作用导致的性能衰减问题,基于对抗冻机理的认知进行混凝土配合比定量设计,在低热水泥、粉煤灰胶凝材料体系中掺加了高活性纳米掺合料对混凝土微结构进行协调优化,配制了高抗冻混凝土。研究了冻融循环作用下纳米掺合料混凝土的抗压强度、劈拉强度、氯离子扩散系数、相对动弹性模量和质量损失率,分析了气泡参数对混凝土抗冻性的影响,并与水利工程中普遍采用的大坝混凝土进行性能对比。结果表明,掺入纳米掺合料可使大坝混凝土的用水量降低6 kg/m^(3),混凝土和易性得到改善;在长期冻融循环作用下,纳米掺合料混凝土的抗压强度提高了3.1%~8.0%,劈拉强度提高了7.6%~19.3%,抗氯离子渗透性提高了27%~59%;纳米掺合料的掺入使混凝土内部气泡孔径细化,微结构得到优化;混凝土抗冻等级大于F800,气泡间距系数小于0.25 mm,具有优良的抗冻性能。该研究成果为纳米掺合料在高寒地区大坝混凝土的应用提供了参考和依据。

In order to improve the long-term performance of dam concrete in the alpine region,mix proportion of concrete is quantitatively designed based on the mechanism of frost resistance,high-activity nano admixture is added into the cementitious material system of low heat cement and fly ash to coordinate and optimize the microstructure of concrete,and high frost concrete is prepared.The change rules of the compressive strength,splitting-tensile strength,chloride ion diffusion coefficient,relative dynamic elastic modulus and mass loss rate of nano-concrete(concrete with nano admixture)under freeze-thaw conditions are studied and compared with dam concrete commonly used in hydropower projects.The influences of air bubble parameters on frost resistance of concrete are also analyzed.The results show that the workability of nano-concrete is improved and the water consumption is reduced by 6 kg/m^(3).The compressive strength,splitting-tensile strength and chloride ion permeability of nano-concrete increase by 3.1%~8.0%,7.6%~19.3%and 27%~59%,respectively under long-term freeze-thaw cycles compared with ordinary concrete.Microstructural analysis show that the pore size is refined indicating that the microstructure of nano-concrete is optimized.In addition,the bubble spacing coefficient of nano-concrete is less than 0.25 mm.The experimental results show that the frost resistance of nano-concrete is excellent with the grade greater than F800.Nano admixture has a great application potential in dam concrete in alpine region.