氧化石墨烯对再生混凝土界面过渡区的影响

利用纳米压痕仪和扫描电镜等设备研究了氧化石墨烯再生混凝土界面过渡区的微观力学性能和微观结构特征。结果表明:加入氧化石墨烯再生混凝土新砂浆和骨料（XJ-G）界面过渡区弹性模量平均增加18.54％，通过纳米压痕理论计算的高密度水化硅酸钙（HD C-S-H）相体积平均增加17.8％，孔隙体积平均降低9.1％；加入氧化石墨烯再生混凝土新旧砂浆 （XJ-JJ）界面过渡区弹性模量平均增加16.25％，HD C-S-H相体积平均增加16.25％，孔隙体积平均降低6.4％；利用扫描电镜观测了加入氧化石墨烯再生混凝土微观结构，其晶体呈片状，晶体排布更趋于无序化，削弱了氢氧化钙（CH）晶体的取向性，微观结构更加密实；根据弹性模量变化定义了界面过渡区的宽度，氧化石墨烯能使XJ-G界面过渡区宽度减少25％，XJ-JJ界面过渡区宽度减少37.5％；氧化石墨烯使界面过渡区弹性模量分布更加稳定，其弹性模量均值基本趋于一致；由再生混凝土微观力学性能与宏观力学性能的联系，得到氧化石墨烯可以增强和改善再生混凝土新旧界面过渡区的力学性能和微观结构，进而提高和改善再生混凝土的宏观力学性能。

Effect of Graphene Oxide on Interfacial Transition Zone of Recycled Concrete

The micro-mechanical properties and microstructure characteristics of the interfacial transition zone of graphene oxide recycled concrete were studied by means of nanoindenter and scanning electron microscope. The results show that the elastic modulus of new motar and aggregate （XJ-G） interfacial transition zone increases by 18.54%, and the average volume of high density calcium silicate hydrate (HD C-S-H) phase increases by 17.8%, and the pore volume decreases by 9.1% using nanoindentation theory. The addition of graphene oxide makes the elastic modulus of the transition zone of recycled concrete new and old mortar (XJ-JJ) increases by 16.25% on average, the volume of HD C-S-H phase increases by 16.25% on average, and the pore volume decreases by 6.4% on average. The microstructure of the graphene recycled concrete is observed by scanning electron microscopy. The crystals are in the form of flakes, and the crystal arrangement becomes more disordered. The orientation of calcium hydroxide (CH) crystal is weakened and the microstructure is more compact. The interface is defined according to the change of elastic modulus. The width of the transition zone is found to reduce the width of the transition zone of XJ-G interface by 25% and the width of the transition zone of XJ-JJ interface by 37.5%. Graphene oxide makes the elastic modulus distribution in the interfacial transition zone more stable, and the mean value of the elastic modulus tends to be uniform. From the relationship between the micromechanical properties and macroscopic mechanical properties of recycled concrete, it can be obtained that graphene oxide can enhance and improve the mechanical properties and microstructure of the transition zone between new and old interfaces of recycled concrete, and can improve the macroscopic mechanical properties of recycled concrete.