Experimental Study On Leaching-abrasion Behavior Of Cement-based Materials Mixed With Nano Minerals

Long-termly served in flowing water environments,such as oceans and rivers,concrete structures are easily subjected to the action of leaching and abrasion of flowing water,resulting in their durability deterioration and service life reduction.The water-induced leaching can lead to the dissolution of solid calcium phase in concrete,causing the microstructure deterioration and strength reduction of concrete,while the abrasion of flowing water can result in the layer-by-layer failure of concrete surface.The optimization of concrete microstructure can improve the leaching resistance and abrasion resistance of concrete,which is important for extending the service life of concrete structures in various water environments.For improving the leaching resistance of concrete,this paper carried out an accelerated leaching experiment by using the specimens of composite nano-mineral concrete,and the improvement mechanism of nano-TiO₂and nano-SiO₂ on the leaching resistance of cement-based materials was investigated.Then,by applying the experimental setup,the abrasion experiments were performed on the specimens of cement mortar with different surface leaching degree,and the influence of the nano-minerals content and leaching degree of specimens on their abrasion resistance was revealed.The main research contents and conclusions are as follows:（1）The specimens of composite nano-mineral cement mortar were prepared by replacing concrete with cement mortar,and their flexural strength and compressive strength were tested at different curing time（3d,7d and 28d）.The influence of nano-mineral on the macroscopic properties of cement-based materials were analyzed.（2）The cement mortar specimens with different nano-TiO₂ content were prepared,and the accelerated leaching experiments were performed.By using some microscopic test method,the changes of specimen porosity,solid calcium content,calcium-silicon ratio,phase composition and microstructure morphology were analyzed,and the improvement mechanism of nano-TiO₂on the leaching resistance performance of cement mortar specimens was revealed.According to the experimental results,it can be known that the incorporation of nano-TiO₂ into cement-based materials can effectively improve their microstructure,further reducing their leaching rate in corrosive solutions and extending the service life of cement-based materials.（3）The cement mortar specimens with different nano-SiO₂ content were prepared,and the accelerated leaching experiments were performed by using ammonium chloride solution.At different leacing time（30d,60d and 90d）,the changes of calcium content,specimen porosity,phase composition and microstructure morphology were analyzed by using the saturation-drying weighing method,X-ray diffraction method,scanning electron microscope,respectively,and the relationship between the microstructure of specimens and their leaching resistance was obtained.The above results show that nano-SiO₂ can effectively improve the microstructure of cement mortar specimens and slow down their leaching process,further improving the leaching performance of specimens.（4）The abrasion experiments of cement mortar specimens with different leaching degree were performed.By characterizing the abrasion strength with the mass loss of specimens,the influence of nano mineral and leaching degree of specimen surface on the leaching resistance of cement-based materials was invesigated.The parameters like surface porosity and calcium concentration are regarded as the failure criteria,and the functional relationship between the above parameters and leaching resistance of specimens was established by the data fitting.