| With the vigorous development and utilization of hydraulic resources,my country has planned and built many large-scale water conservancy and hydropower projects in the middle and upper reaches of the Changjiang River,the southwestern rivers,and the Yajiang River in Tibet.Among them,the climate environment in the western region has the characteristics of high radiation intensity and large temperature difference,which puts forward higher requirements for the durability of the protective materials on the concrete surface.Polyurea coating materials as hydraulic concrete surface protection material with excellent mechanical properties,strong corrosion resistance and good high temperature resistance,are widely used in various water conservancy and hydropower projects.Polyurea coating materials can be divided into two-component polyurea and single-component polyurea according to the composition.At present,many scholars have studied the aging mechanism of two-component polyurea.But for single-component polyurea coating materials,there are few studies on aging laws and aging mechanisms.Therefore,studying the aging rules and aging mechanism of single-component polyurea is of great significance for the use of single-component polyurea in hydraulic protection projects.In this paper,a single-component polyurea coating material was tested in indoor accelerated ultraviolet aging,indoor accelerated thermal aging and indoor accelerated humid heat aging.The tests found that the bonding strength,tensile strength and elongation at break of the single-component polyurea coating material all showed a downward trend under the three aging conditions.Among them,in the ultraviolet aging time of 42 d,the bonding strength of the single-component polyurea coating material is linearly related to the aging time,and the tensile strength and elongation at break are logarithmically related to the aging time.In the heat aging time of 90 d,the bonding strength,tensile strength and elongation at break of the one-component polyurea coating material are linearly related to the aging time(after 15d);during the 90-day humid heat aging time,the one-component polyurea coating.The bonding strength and elongation at break of the material are linearly related to the aging time(after 15d),and the tensile strength is logarithmically related to the aging time(after 15d).The effects of three aging methods on the mechanical properties of single-component polyurea coating materials were studied.The color changes and scanning electron micrographs of the single-component polyurea coating materials during each period under the three aging methods were observed.It was found that during the UV aging,the surface of the one-component polyurea coating material changed from bright gray to yellow-gray,and the color became dark.After 35 days of ultraviolet aging,holes appeared on the surface;during heat aging,the surface of the one-component polyurea coating material The color changes from bright gray to earthy yellow,and holes appear after 90 days of heat aging;during wet and hot aging,the surface color of the single-component polyurea coating material changes from bright gray to yellowish gray,and the color becomes dark,and the surface appears after 45 days of wet and heat aging Holes.This test found that,during UV aging,the single-component polyurea coating material breaks due to the N-H bond and C-H bond,and the mechanical properties of the hydroxyl and urea bonds decrease.During thermal aging,the C-H bond breaks,When the urea bond decreases,its mechanical properties decrease;during wet-heat aging,the mechanical properties decrease due to the decrease of urea bonds.During the aging process,the content of urea bonds in the one-component polyurea coating material mainly affects the tensile properties of the coating material,and the hydrogen bonding and hydroxyl content in the one-component polyurea coating material mainly affects the adhesion of the coating material.This experiment only studied the aging rule of single-component polyurea coating materials under one ultraviolet intensity,one high temperature environment,and one hot and humid environment.In the later experiments,different ultraviolet intensity,different temperature,and different humidity The component polyurea coating materials were studied for aging properties and aging rules. |
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