Experimental Study On Mechanical And Frost Resistance Properties Of γ-phase Nano-alumina Modified Concret

In the field of architecture,in order to make the performance of concrete meet the development needs of building structures,many domestic and foreign scholars have carried out a lot of exploration,and put forward the method of using nanomaterials to modify concrete to improve its performance.After research,γphase nano-Al₂O₃ has a large specific surface area and high catalytic activity.Applying it to concrete materials for modification will bring unique performance improvement.In this paper,γphase nano-Al₂O₃ was selected as the modified material of concrete,and the dosage was 1.5%,3.0%and 4.5%of the cement mass.Theγphase nano-Al₂O₃modified concrete in the experimental group and the ordinary concrete in the control group were made.The slump test,cube compressive strength test,splitting tensile strength test and rapid freeze-thaw test were carried out to analyze the effects of different dosages ofγphase nano-Al₂O₃ on the working performance,mechanics and frost resistance of concrete from a macro perspective.The modification mechanism was analyzed by XRD（X-ray diffraction phase）and SEM（scanning electron microscope）.In this paper,the modification effect ofγphase nano-Al₂O₃ on concrete was studied from macroscopic and microscopic perspectives,and the performance ofγphase nano-Al₂O₃ in improving the mechanical and freezing resistance of concrete was discussed,so as to meet the new requirements of concrete material properties proposed by the development of the industry and improve the ability of concrete to be damaged by freezing and thawing in cold climate.It provided a new idea of how to improve concrete performance under the new development requirements.The results of this study are as follows:（1）Through the slump test,it is found that the incorporation ofγphase nano-Al₂O₃will reduce the slump of concrete mixture and affect its fluidity.The slumps of ordinary concrete and modified concrete with 1.5%,3.0%and 4.5%content in the control group are 62mm,51mm,34mm and 10mm respectively,but it has little effect on the cohesion and water retention of concrete mixture.（2）Through compressive strength test and splitting tensile strength test,it is found thatγphase nano-Al₂O₃ can improve the compressive strength,splitting tensile strength and toughness of concrete,and is beneficial to the development of early strength.When the content is 3.0%,the mechanical properties ofγphase nano-Al₂O₃ modified concrete are the best.The compressive strength and splitting tensile strength of 3d and 7d can be increased by more than 30%compared with the control group,and the 28d and 60d ages can also be increased by more than 15%.（3）Through XRD and SEM tests,it is found that an appropriate amount ofγphase nano-Al₂O₃ can promote the hydration balance of cement to move to the right,increase the content of hydration products,and increase the compactness of concrete.Excessive amount will lead to agglomeration and accumulation of nanoparticles in concrete,resulting in defects and reducing concrete strength.（4）Through the rapid freeze-thaw test,it is found thatγphase nano-Al₂O₃ can reduce the mass loss and relative dynamic elastic modulus loss of concrete caused by freeze-thaw damage,and effectively improve the frost resistance of concrete.In this study,the optimal content ofγphase nano-Al₂O₃ to enhance the frost resistance of concrete is 3.0%.At 100 freeze-thaw cycles,the mass loss rate of the 3.0%group is 0.82%lower than that of the control group,and the relative dynamic elastic modulus is 9.40%higher than that of the control group.