Effect And Mechanism On The Hydration And Chloride Erosion Of Cement-based Materials By CNTs

As the one of the most hopeful nanoscale materials in the 21st century,Carbon Nanotubes?CNTs?are universally noticed by various researchers because of its excellent mechanical properties,electrical properties and durability performances.The research of CNTs on the properties of cement-based materials had become one of the hot topics in Civil Engineering academic community over the world.In this paper,the hydration process of cement-based materials and the mechanism of chloride erosion have been investigated.The experimental results are summarized as the following:The mechanical properties,setting time?including initial setting time and final setting time?,electrical resistivity and releasing heat of hydration process experimental result by comparing the cement paste with different dosages of CNTs to determine the effect of CNTs in the hydration process of cement-based materials and analyze the hydration products combined with thermal analysis.The results showed that CNTs can inhibit the generation of hydration products of C₃A and the formation scale and maturity of C-S-H in the early stage of cement hydration;CNTs greatly promote the hydration reaction of C₃S to increase the amount of calcium hydroxide in the middle stage of cement hydration;The hydration process has been carried out quite thoroughly in the middle stage,so the rate has decreased in the later,and it has been found that the CNTs have no significant influence in the total CH content formed in the whole hydration process.By using scanning electron microscopy?SEM?,EDS and X-ray phase analysis?XRD?on CNTs cement-based materials under different hydration time of microscopic test,it provides further explanation on the microscopic mechanism and theoretical basis for CNTs on the hydration process of cement paste.The results show that CNTs inhibit the hydration of cement by observing the change trend of calcium in hydration products and coating layer effect in the early stage of cement hydration;CNTs promotes the hydration of C₂S and C₃S by observing the extent of C₂S and C₃S to CH.Combining with the thermal experimental analysis results,the addtion of CNTs did not significantly change total CH amount during the hydration phase but affect the crystal form of CH hydration products.Through the hydration process of CNTs cement-based materials,it exists good linear relationship among the dosage of CNTs,initial setting time and the lowest resistivity point?R point?in curve,corresponding mathematical formulas were established to lay solid technical foundation to predict the setting time and electrical resistivity for CNTs cement-based materials.This paper proceed two types of chloride ion erosion environment?accelerated chloride ion electric erosion,the natural state of chloride ion erosion?for different dosages of CNTs cement mortar to compare the differences and research the chloride erosion depth.Chloride ion erosion experiments in the natural state were titrated to observe the change of free chloride ions.The results showed that CNTs can make chloride ion migration coefficient rise by 3.35⁴.2 times,trends of chloride erosion accelerates with the increase of CNTs content.It exist a good linear relationship between the dosage of CNTs and chlorine ion migration coefficient,which can determine the chlorine ion migration coefficient rapidly under the accelerated chloride ion electric erosion.The erosion depth and free chloride ion content increased with the addition of CNTs at the same erosion time,which indicated that the erosion of chloride ion in cement matrix could be accelerated by CNTs in natural state.