Papers by Keyword: Dry-Wet Circulation

Abstract: Researches of spray pure polyurea technology for hydraulic concrete protection in water conservancy facilities to ensure long term security operation has a great significance. With an emphasis upon mechanical properties and surface morphology of spray pure polyurea coatings comparing before and after aging by means of the artificial accelerated xenon arc lamp(AAXAL) and scanning electron microscope(SEM) in this paper. Besides, the dry-wet circulation resistance performance of coatings wre analyzed through experiment. It is shown that tensile strength, elongation at break and tear strength of coatings increased by 0.2%, 0.5% and 1.7% respectively after AAXAL aging 720h. By contrast, after aging 3000h the results were 22.6%, 3.8% and 17.4% respectively, the tendency of increasing at first and then reducing can be obtained. The mechanical properties reduced slightly for adding defects of coating surface after aging, however, the resistance performance of ultraviolet ray was excellent. The similar development trend of mechanical properties were gained from dry-wet circulation experiment. After aging 200 cycles, the tensile strength and tear strength descended by 4.1% and 1.7% severally but the elongation at break ascended by 5.0%. In a word, it is suggested that the aging of coatings were negligible in dry-wet circulation in short term.

Abstract: Abstract. Silt in some areas of our country is very extensive, its distribution is different from the cohesive soil, or sand soil, has unique engineering characteristic. Silt regional characteristics make it has many unique physic-mechanical performance. This article take the G209 (Inner Mongolia Helin to Qingshuihe section) the roadbed silty soil as the study object, study its basic physics, the mechanical properties as well as the distortion and the intensity change rule under the dry-wet circulation, do a comprehensive and systematic analysis about varieties of basic engineering characteristic of the silt in the region Through the condition of dry-wet circulation of unconsolidated tri-axial tests, this article study the silt sample failure pattern under different degree of compaction, stress-strain relations and the change rule of strength. The test results show that: as cycle index less and confining pressure down, test sample is basically brittle failure, on the contrary case, it is behaved for plastic failure and stress-strain curve is close to sclerosis type; When cycle index increase gradually, the cohesion of silt reduced significantly ,with the increase of dry-wet circulation times internal friction angle is on the trend of the attenuation oscillation ; On this basis, we build the relationship expression of shear strength parameters cohesion internal friction angle and dry-wet circulation times.

Abstract: Acceleration penetration tests of chloride ion were conducted for typical diurnal and semidiurnal tidal types in China with consideration of various values of soaking time. It was found that the content of chloride ion from shallow area near the surface of concrete to the pure diffusion area of concrete reduced more significantly with the depth than that in the pure diffusion area of concrete. Based on Fick’s second law, the variation laws of chloride ion content at the edge of the pure diffusion area and chloride ion diffusion coefficient in the pure diffusion area under different soaking time ratios were identified by using the chloride ion content distributions that were established based on the test results of concrete in the pure diffusion area. It was found that the chloride ion content and the apparent chloride ion diffusion coefficient in pure diffusion area may be very high when the ratio of soaking time ratio is between 0.3 and 0.42 or 0.6 and 0.7 for diurnal tidal type and 0.83 for semidiurnal tidal type, which will cause severe erosion in concrete structures in tidal zone.

Abstract: This paper mainly studies the mechanical properties and microstructure of polyurea coatings (SPUA) through the experiment of dry-wet circulation. The influence of different curing time of SPUA coating before and after the dry cycle of the mechanical properties and surface morphology changes were researched. Use the alternating temperature and low bending tests to research,the variation of temperature changes to the SPUA of different curing time. The result of the dry-wet circulation experiment shows that the tensile strength of cured 1d, 3d and 7d SPUA coating after 30d dry-wet circulation increased 9.6%、19.2% and 44.7% respectively, the tear strength increased 3.2%、5.6% and 47.3% respectively. The microstructure research shows the 7d cured SPUA coating after 30 times dry-wet circulation will reduce the holes and narrow the hole diameter in a certain degree. The temperature change experimental results show that during -20 ～50 alternating temperature process, the tensile strength of the coating appears to increase, 3d and 7d cured SPUA coating after 40d temperature alternating tensile strength changing rate is -14.2% and 9.8% respectively. Low-temperature bending test shows that the SPUA coating will not appear any cracks cracking phenomena after placed the coating in （-20+2 ）for 168h.