• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Abrasion test of flexible protective materials on hydraulic structures

    2014-03-06 06:21:59XinWANGShaozeLUOGuangshengLIULuchenZHANGYongWANG
    Water Science and Engineering 2014年1期

    Xin WANG*, Shao-ze LUO, Guang-sheng LIU, Lu-chen ZHANG, Yong WANG

    1. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, P. R. China

    2. Beijing Oriental Yuhong Waterproof Technology Co., Ltd., Beijing 100123, P. R. China

    Abrasion test of flexible protective materials on hydraulic structures

    Xin WANG*1, Shao-ze LUO1, Guang-sheng LIU2, Lu-chen ZHANG1, Yong WANG1

    1. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, P. R. China

    2. Beijing Oriental Yuhong Waterproof Technology Co., Ltd., Beijing 100123, P. R. China

    In this study, several kinds of flexible protective materials sprayed with polyurea elastomers (hereinafter referred to as polyurea elastomer protective material) were adopted to meet the abrasion resistance requirement of hydraulic structures, and their abrasion resistances against the water flow with suspended load or bed load were studied systematically through tests. Natural basalt stones were adopted as the abrasive for simulation of the abrasion effect of the water flow with bed load, and test results indicate that the basalt stone is suitable for use in the abrasion resistance test of the flexible protective material. The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the time of abrasion. If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea, and over five times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with suspended load. It is also about 50 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load. Overall, the abrasion resistance of pure polyurea presented a decreasing trend with increasing hardness. Pure polyurea with a Shore hardness of D30 has the best abrasion resistance, which is 60 to 70 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load, and has been recommended, among the five kinds of pure polyurea materials with different hardness, in anti-abrasion protection of hydraulic structures.

    flexible protective material; polyurea elastomer material; abrasion resistance; hardness influence; hydraulic structure

    1 Introduction

    Erosion and abrasion have been the most common problems in hydraulic structures. Overflow surfaces, flip buckets, spillway tunnels, flushing sluices, and stilling pool base slabs are all easily damaged by abrasion. The Fengman Hydropower Station overflow dam’s ogee section was damaged to a depth of 3 to 4 m because of flow erosion, and the maximum abrasion depth of the apron reached 4.5 m (Dai and Xu 2009). Behind the work gate of theSanmenxia No. 2 bottom hole, a large area of abrasion-induced damage occurred, and the average abrasion depth was 14 cm. In the Yantan Hydropower Station, the bucket concrete surface was widely eroded, and the average thickness of exposed aggregate was 2 to 5 cm (Xia 1988). The stilling basin of the Indian Barkla Dam also had severe sediment erosion records (Vegas Merino et al. 2005). With increasing water conservancy project scale, the flow rate over discharge structures generally exceeds 35 m/s, and in some cases reaches 50 m/s, leading to more serious abrasion.

    At present, in order to resist abrasion, high-performance concrete is mainly used. Lots of related research has been conducted, and some new kinds of abrasion-resistant concrete have been produced, with the abrasion resistance improved to some extent. With the progression of the research, polyurea, a new organic polymer abrasion-resistant material, has gradually drawn people’s attention (Henningsen 2002; Chen 2006). As an effective and environmentally friendly material, polyurea was used in construction of spillways and flip buckets at the Xin’anjiang and Fengman hydropower stations (Sun et al. 2006), the concrete volute at the Nierji Hydropower Station (Sun et al. 2009), the de-silting tunnel at the Xiaolangdi Hydropower Station, the plunge pool at the Xiaowan Hydropower Station, the stilling basin at the Guandi Hydropower Station, and the middle hole of the Three Gorges Dam in China. Outside of China, the discharge hole of the Tehri Dam in India is the most typical example of polyurea application in hydropower projects.

    Spraying polyurea has been presented in the field of water resources and hydropower engineering for a few years. So far, though, the abrasion resistance of the polyurea material has not been studied systematically. Few indicators related to abrasion resistance can be referenced, and optimization of components of polyurea protective materials has never been conducted to meet the requirement of the abrasion resistance of hydraulic structures. Existing research on abrasion resistance is only based on a few simple tests and roughly qualitative evaluations. Through the high-speed erosion test, Wu (2005) showed that the abrasion resistance of polyurea materials was much higher than that of the C60 silica fume concrete. Zhong et al. (2007) evaluated the abrasion resistance of the polyurethane- or polyurea-coated layer in high-speed sediment jets using the wear-and-tear experimental machine and high-pressure water jet erosion tester. Guo et al. (2011) analyzed the main factors leading to the surface abrasion of the elastomeric coating. It was shown that the impingement of high-speed particles could lead to untimely dissemination of the stress wave in elastic bodies, which caused surface debacle. Chen et al. (2011) found that two-component polyurea material has a high ability to resist water erosion and abrasion. Some foreign research has focused on the mechanical properties of polyurea (Grujicica et al. 2010; Roland and Casalinj 2007; Sarva et al. 2007; Aly and Hussein 2010). However, study of the abrasion resistance has not been found reported aboard. This study aimed to determine the law of abrasion-induced damage and indicators related to the abrasion resistance of polyurea materials based on a series of tests.

    2 Materials and samples

    Polyurea elastomer protective material has the properties of fast curing, high impermeability, a high degree of toughness, high tensile strength, elongation, chemical resistance, abrasion resistance, impact resistance, and aging resistance, as well as strong bonding with a variety of substrates, and the proportion of its components is arbitrarily adjustable. It has been used in many tasks, especially in waterproofing, wearing resistance, anticorrosion, and decoration.

    Beijing Oriental Yuhong Waterproof Technology Co., Ltd. has been committed to development of abrasion-resistant polyurea material for anti-abrasion protection of hydraulic structures, and has produced three formulas for abrasion-resistant polyurea material. The main performance parameters of three kinds of abrasion-resistant polyurea materials used as the surface protective materials in this study are listed in Table 1, and are abbreviated as follows: S for the 351 pure polyurea, G for the pure polyurea with a high degree of hardness, and Z for the aliphatic polyurea.

    Table 1 Performance parameters of polyurea protective material

    The concrete specimens were made according to the test content and equipment requirements in this study. Abrasion-resistant concrete, CM for short, used in the Longtan Hydropower Station, was used as the concrete substrate of specimens, and the contents of water, cement, fly ash, sand, and stone of the concrete substrate were 146, 414, 73, 584, and 1 134 kg/m3, respectively, with a reducer ratio of 1%. The compressive strength of the concrete substrate at an age of 60 days could reach 64 MPa. The spraying of surface protective materials began when the concrete substrate had been cured for 28 days. The curing process of concrete specimens was the same as that of on-site construction. The spraying thickness of polyurea protective materials was 4 mm, and the test was conducted after the specimens sprayed with protective materials had been cured for seven days.

    3 Test methods

    Abrasion tests of concrete samples with and without spraying surface protective materials were conducted under the abrasion conditions of the water flow with suspended load and bed load, respectively. Silicon carbide was used as sand in high-speed flow to simulate the abrasion conditions of the water flow with suspended load, and underwater balls and basalt stones were employed to simulate the abrasion conditions of the water flow with bed load. The relative resistance of the surface material corroded by underwater high-speed moving mediawas determined, and the surface abrasion resistance was evaluated. Improved wear testing equipment was used in the abrasion test of the suspended load flow, and the maximum test flow speed reached 60 m/s. Compared with traditional equipment, the new equipment had stronger destructive effects, and the test time was shortened (Gao et al. 2011; Wang et al. 2012). In this test, the sand rate was 7%, the flow speed was 40 m/s, and the test time was determined by the effects of abrasion. The HKS-II anti-abrasion testing machine was used in the abrasion test of the bed load flow. The test was carried out according to the Test Code for Hydro-concrete (SL352-2006), and the specimens were abraded for a period of 72 hours.

    The test process was as follows: At first, the specimens were soaked in water for 48 hours to reach full saturation before the test. Then, we took the specimens out of water and wiped off the surface water. After that we weighed the specimens and put them into the test apparatus. After testing, the specimens were removed from the test apparatus, with the surface water wiped off. We weighed the specimens again and calculated the weight loss, wear rate, and abrasion resistance strength. In addition, the morphological changes and damage characteristics of the specimens were observed.

    4 Test results and discussions

    4.1 Abrasion by suspended load flow

    The surface morphology contrast of the specimens with or without a protective coating before and after two hours of abrasion by the suspended load flow is shown in Fig. 1. For the specimen with a protective coating G, the protective coating and concrete substrate remained firmly bonded without bubbling or peeling after two hours of abrasion. Although the original smooth coating surface became corrugated, and rippled abrasion marks appeared, the destruction was slight, and there was little variation of the coating thickness. However, the concrete surface without a protective coating flaked with exposed aggregates, and was more seriously damaged than the protective coating.

    Fig. 1 Surface morphology comparison after two hours of abrasion by suspended load flow

    The average wear rate and abrasion resistance strength of specimens after two hours of abrasion in water flow with suspended bed are shown in Table 2. The abrasion resistance of the protective coating is more than 10 times higher than that of the concrete surface according to the measured data of mass loss, and the wear thickness of the concrete specimen without the protectivecoating is about five times those of the specimens with the protective coating. The 351 spraying pure polyurea has the best abrasion resistance of the three kinds of protective coatings.

    Table 2 Abrasion resistance parameters after two hours of abrasion by suspended load flow

    4.2 Abrasion by bed load flow

    4.2.1 Abrasion by underwater steel balls

    The surface morphology contrast of the specimens before and after 72 hours of abrasion by underwater steel balls is shown in Fig. 2. The diameter of all the circular specimens is 29.5 cm. As shown in Fig. 2, the protective coating was basically intact, in addition to the fact that the surface gloss receded slightly. However, the concrete surface was seriously damaged with exposed coarse aggregates. Table 3 shows large differences between damage of the protective materials and the concrete specimen without a protective coating after the abrasion test by underwater steel balls, but the abrasion resistances of the three kinds of protective materials are almost the same.

    Fig. 2 Surface morphology comparison after 72 hours of abrasion by underwater steel balls

    Table 3 Abrasion resistance parameters after 72 hours of abrasion by underwater steel balls

    The abrasion tests showed that the polyurea elastomer protective coatings were basically intact under the abrasion by underwater steel balls but were slighted damaged under the high-speed suspended load flow. This is mainly due to different wear mechanisms of the two abrasion conditions. The wear mechanism of the high-speed suspended load flow is mainly the impacting and cutting actions of silicon carbide on the specimen surface, while the wearmechanism of underwater steel balls is mainly the rolling, jumping, and friction actions of underwater steel balls (bed load). For the polyurea elastomer coating, the cutting action of the suspended load flow will cause a certain degree of abrasion, but with elastic deformation, it is difficult for the smooth ball to cause the damage by abrasion. Therefore, underwater steel balls are not suitable for use in the abrasion test of polyurea elastomer protective materials, and other appropriate methods should be proposed for reasonable simulation of the abrasion action of the bed load flow.

    4.2.2 Abrasion by basalt stones

    To compensate for the deficiency of underwater steel balls in the abrasion resistance evaluation of polyurea elastomer protective materials, hard natural basalt stones with different shapes and sharp corners were proposed to replace steel balls as the abrasive. In this study, natural basalt stones of 1 to 2 cm in diameter and 1 kg in weight were chosen at random, as shown in Fig. 3(a), and added into each test apparatus. After a continuous 24 hours of abrasion, the edge of basalt stones became rounded and smooth as pebbles, and the abrasion effect became relatively weak, as shown in Fig. 3(b). Thus, basalt stones should be replaced every 24 hours in the test process.

    Fig. 3 Variation of basalt stones before and after 24 hours of abrasion

    The abrasion process of the high-level hardness pure polyurea is shown in Fig. 4. Except for the small central region, most of the area of the sample surface was significantly worn. With the abrasion going on, the protective layer gradually became thin. The test indicates that basalt stones are more suitable for simulation of the abrasion effect of the bed load flow than steel balls. The surface morphology contrast of abrasion-resistant concrete and three protective materials after 96 hours of testing is shown in Fig. 5. The concrete surface without a protective coating was seriously damaged, while the three kinds of protective materials were slightly worn.

    Fig. 4 Surface morphology variation of concrete specimen with coating G during testing process

    Fig. 5 Surface morphology comparison of different materials after 96 hours of abrasion

    The mass loss during the abrasion process and the abrasion resistance parameters are listed in Table 4. The mass loss of each material was relatively uniform for every 24 hours, and the non-protective concrete surface was severely damaged. The three kinds of protective coatings have far superior abrasion resistance to concrete, about 40 to 100 times according to the mass loss and about 20 to 50 times according to the wear thickness. The abrasion resistances of the high-level hardness pure polyurea and aliphatic polyurea are almost the same, while that of the 351 pure polyurea is about twice the amount. Therefore, the 351 pure polyurea has superior abrasion resistance.

    Table 4 Abrasion resistance parameters during abrasion test with basalt stones

    The average wear thickness was calculated according to the mass loss, and the relationship between the average wear thickness and testing time of the three kinds of protective coatings is shown in Fig. 6. It can be seen that the 351 pure polyurea wears slowest and has the optimal abrasion resistance.

    Fig. 6 Relationship between average wear thickness and testing time

    4.3 Influence of hardness on abrasion resistance

    The test of three kinds of polyurea materials indicates that the 351 pure polyurea has better abrasion resistance than the aliphatic polyurea and high-level hardness pure polyurea. In fact the 351 pure polyurea and high-level hardness pure polyurea are only different in hardness. To further examine the relationship between the hardness and abrasion resistance of pure polyurea, five kinds of pure polyurea specimens with different Shore hardness, i.e., D25, D30, D40, D50, and D60 from soft to hard, hereinafter referred to as the Shore D25, Shore D30, Shore D40, Shore D50, and Shore D60 polyurea, were subjected to anti-abrasion performance testing with the basalt abrasive. Three specimens were made for each kind of hardness, and the results were obtained by computing their average values. The abrasion resistance parameters are listed in Table 5.

    Table 5 Abrasion resistance parameters for pure polyurea of different hardness

    As shown in Table 5, the average mass loss of pure polyurea specimens increased with the abrasion time, demonstrating a linear relationship. The abrasion resistance presented a decreasing trend with the increase of the hardness of pure polyurea. The relationship between the average wear thickness and Shore hardness of pure polyurea is plotted in Fig. 7. The Shore D25 and the Shore D30 polyurea specimens have smaller wear volumes, and their abrasion resistances are almost the same, with that of the Shore D30 polyurea specimen being slightly better.

    Fig. 7 Hardness influence on abrasion resistance of pure polyurea

    The scanning electron microscope was used to observe the micro-morphology of specimens for study of the wear features of pure polyurea with different levels of hardness. The surface and inner micro-morphologies of pure polyurea before testing are shown in Fig. 8. The coating surface was flat and smooth before abrasion, and there were many inner bubbles with diameters of several tens of micrometers. The surface micro-morphologies of the three kinds of pure polyurea materials with the Shore hardness of D25, D40, and D60, after 96 hours of abrasion, are presented in Fig. 9. It can be clearly found that wear of different degrees occurs on the surface of all the specimens, and that the wear features of pure polyurea of different levels of hardness are different. The softest Shore D25 polyurea showed little wear loss but had the roughest surface. Pits appeared at the site of inner bubbles, and regular fish-shaped wear marks appeared at the other sites after the abrasion test. The surface smoothness of the Shore D40 polyurea was significantly better than that of the Shore D25 polyurea. Some etch pits appeared at the site of inner bubbles. The wear feature presented significant directivity, and part of the bubble surface was still left without complete abrasion. Slight wear marks also existed on the other smooth area and were not as serious as those of the Shore D25 polyurea. The Shore D60 polyurea showed the most wear loss, but the abraded surface was very smooth, and few etch pits or wear marks appeared.

    Fig. 8 Surface and inner micro-morphologies of pure polyurea before testing

    Fig. 9 Surface micro-morphologies of pure polyurea with different levels of hardness after 96 hours of abrasion

    It can be concluded that the hardness has significant influence on the abrasion resistance of pure polyurea. The soft polyurea material has a high degree of toughness and will deform and absorb most of the energy under impacting, cutting, and friction effects of the abrasive.The brittleness of pure polyurea increases with the hardness. Thus, the abrasion resistance decreases, and the wear surface becomes smooth with the increase of hardness. Of the five kinds of pure polyurea materials with different levels of hardness, the Shore D30 polyurea has the best abrasion resistance. If the wear thickness is considered the evaluation index, the abrasion resistance of the Shore D30 polyurea is 60 to 70 times that of abrasion-resistant concrete.

    5 Conclusions

    The abrasion resistance of a variety of polyurea elastomer protective materials was examined in this study, and the following conclusions can be made:

    (1) The traditional underwater ball method is not suitable for the abrasion resistance evaluation of flexible protective materials, while the proposed basalt abrasive method is effective for simulation of the abrasion effect of the bed load flow on the polyurea elastomer protective material.

    (2) The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the abrasion time. The abrasion resistance of the protective material is far superior to high-performance abrasion-resistant concrete. The abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea.

    (3) If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is over five times that of high-performance abrasion-resistant concrete under the abrasion by the suspended load flow and about 50 times under the abrasion of the bed load flow.

    (4) Overall, the abrasion resistance of pure polyurea shows a decreasing trend and the wear surface varies from rough to smooth with increasing hardness. Of the five kinds of pure polyurea materials with different hardness, the Shore D30 polyurea has the best abrasion resistance, which is 60 to 70 times that of abrasion-resistant concrete. Therefore, it is recommended in anti-abrasion protection of hydraulic structures.

    More attention should be paid to the interfacial adhesion effect between protective materials and the concrete substrate. Especially for wet concrete, the adhesion quality is the most important factor in hydraulic structure protection with the surface coating of protective materials.

    Aly, K. I., and Hussein, M. A. 2010. New polymer syntheses, part 45: Corrosion inhibition behavior of novel polyurea derivatives based on diarylidenecycloalkanone moieties in the polymers backbone. Journal of Polymer Research, 17(5), 607-620. [doi:10.1007/s10965-009-9349-9]

    Chen, G. X. 2006. New development of abrasion-resistant materials under high-velocity water flow. Water Power, 32(3), 56-59. (in Chinese). [doi:10.3969/j.issn.0559-9342.2006.03.018]

    Chen, L., Han, W., Li, Z., and Wang, Z. Q. 2011. Preparation of polyurea-dam protection materials and theirconstruction technology. Journal of Yangtze River Scientific Research Institute, 28(3), 63-67, 71. (in Chinese). [doi:10.3969/j.issn.1001-5485.2011.03.014]

    Dai, H. C., and Xu, W. L. 2009. Research flood releasing safety of flood discharge structure with high-head and large-discharge. Water Power, 35(1), 14-17.

    Gao, X. X., Cai, Y. B., and Ding, J. T. 2011. Influencing factors of abrasion of hydraulic concrete based on underwater method. Journal of Hydroelectric Engineering, 30(2), 67-71. (in Chinese)

    Grujicica, M., Pandurangana, B., Hea, T., Cheeseman, B. A., Yen, C. F., and Randow, C. L. 2010. Computational investigation of impact energy absorption capability of polyurea coatings via deformation-induced glass transition. Materials Science and Engineering, Ser. A, 527(29-30), 7741-7751. [doi:10.1016/j.msea.2010.08.042]

    Guo, Y. J., Yin, J., He, J. X., Hu, B. L., Hu, H., and Huang, W. J. 2011. Debacle and abrasion of on elastic coating of a hydraulic turbine. Journal of Vibration and Shock, 30(2), 155-158. (in Chinese). [ doi:10.3969/j.issn.1000-3835.2011.02.030]

    Henningsen, J. 2002. Polyurea: Leading a revolution in coating technology. Paint and Coatings Industry, 18(1), 58-63.

    Roland, C. M., and Casalinj, R. 2007. Effect of hydrostatic pressure on the viscoelastic response of polyurea. Polymer, 48(19), 5747-5752. [doi:10.1016/j.polymer.2007.07.017]

    Sarva, S. S., Deschanel, S., Boyce, M. C., and Chen, W. N. 2007. Stress-strain behavior of a polyurea and a polyurethane from low to high strain rates. Polymer, 48(8), 2208-2213. [doi:10.1016/j.polymer. 2007.02.058]

    Sun, Z. H., Guan, Y. S., and Bao, Z. Q. 2006. Spray technology of polyurea elastomer and its application in Nierji project. Water Power, 32(9), 31-33. (in Chinese). [doi:10.3969/j.issn.0559-9342.2006.09.009]

    Sun, Z. H., Xia, S. F., Fu, Y. Q., and Zhen, L. 2009. Application of the single-polyurea in hydropower project. Water Resources and Hydropower Engineering, 40(1), 71-72. (in Chinese). [doi:10.3969/j.issn.1000-0860.2009.01.016]

    Vegas Merino, S. R., Salazar, J. R., and Schexnayder, C. J. 2005. Use of rock blocks to protect the downstream zone of a hydraulic discharge structure. Practice Periodical on Structural Design and Construction, 10(1), 63-69. [doi:10.1061/(ASCE)1084-0680(2005)10:1(63)]

    Wang, X., Luo, S. Z., Hu, Y. A., Yuan, Q., Wang, H. S., and Zhao, L. H. 2012. High-speed flow erosion on a new roller compacted concrete dam during construction. Journal of Hydrodynamics, Ser. B, 24(1), 32-38. [doi:10.1016/S1001-6058(11)60216-3]

    Wu, H. G. 2005. Study on spraying polyurea elastomer abrasion-resistant coatings technology applied in hydraulic concrete structures. Journal of China Institute of Water Resources and Hydropower Research, 3(1), 42-46. (in Chinese). [doi:10.3969/j.issn.1672-3031.2005.01.008]

    Xia, Y. C. 1988. Comprehensive analysis of some prototype observation results on high speed flow of discharge structure. Water Resources and Hydropower Engineering, (11), 14-22. (in Chinese).

    Zhong, P., Peng, E. G., and Li, J. 2007. Study of erosion behavior of polyurethane-urea coating. Tribology, 27(5), 447-450. (in Chinese)

    (Edited by Ye SHI)

    ——

    This work was supported by the National Natural Science Foundation of China (Grants No. 51109143 and 51209144), the Natural Science Foundation of Jiangsu Province (Grant No. BK2011109), and the Foundation of Nanjing Hydraulic Research Institute (Grant No. Y113004).

    *Corresponding author (e-mail: xwang@nhri.cn)

    Received Oct.16, 2012; accepted Sep. 16, 2013

    日韩av不卡免费在线播放| 熟妇人妻不卡中文字幕| 99热6这里只有精品| 久久久久精品性色| 中文字幕精品免费在线观看视频 | 女人十人毛片免费观看3o分钟| 免费大片18禁| 91精品伊人久久大香线蕉| av不卡在线播放| 免费在线观看成人毛片| 狠狠精品人妻久久久久久综合| 国产亚洲一区二区精品| 如何舔出高潮| 97在线人人人人妻| 少妇熟女欧美另类| 晚上一个人看的免费电影| videos熟女内射| a级一级毛片免费在线观看| 亚洲人成网站在线观看播放| 久久久久久久久久成人| 免费av不卡在线播放| 身体一侧抽搐| av播播在线观看一区| 久久久久久伊人网av| 男女边吃奶边做爰视频| 深爱激情五月婷婷| 18禁裸乳无遮挡免费网站照片| 丝袜脚勾引网站| 日本黄色片子视频| 国产91av在线免费观看| 久久国产精品大桥未久av | 久久综合国产亚洲精品| 美女视频免费永久观看网站| 高清视频免费观看一区二区| 精品国产乱码久久久久久小说| 天美传媒精品一区二区| 中文字幕免费在线视频6| 99国产精品免费福利视频| 只有这里有精品99| 亚洲精品国产色婷婷电影| 国产黄色视频一区二区在线观看| 熟女av电影| 亚洲精品视频女| 一级a做视频免费观看| 成年人午夜在线观看视频| 亚洲第一av免费看| 亚洲精品日韩在线中文字幕| 18禁在线播放成人免费| 免费看日本二区| 国产探花极品一区二区| 搡女人真爽免费视频火全软件| 久久国产亚洲av麻豆专区| 欧美 日韩 精品 国产| 亚洲久久久国产精品| 久久99蜜桃精品久久| 我要看日韩黄色一级片| 久久人人爽人人片av| av视频免费观看在线观看| 亚洲av欧美aⅴ国产| 欧美精品国产亚洲| 亚洲精品第二区| 赤兔流量卡办理| 中文字幕av成人在线电影| 黑人高潮一二区| 国产综合精华液| 美女内射精品一级片tv| 亚洲va在线va天堂va国产| 毛片女人毛片| 少妇猛男粗大的猛烈进出视频| 免费观看无遮挡的男女| 97热精品久久久久久| 毛片女人毛片| 亚洲欧美日韩另类电影网站 | 成人高潮视频无遮挡免费网站| 免费观看在线日韩| 久久99蜜桃精品久久| 777米奇影视久久| 精品少妇久久久久久888优播| 插阴视频在线观看视频| 久久人人爽人人片av| 涩涩av久久男人的天堂| 日日摸夜夜添夜夜添av毛片| 亚洲成人av在线免费| 国产极品天堂在线| 十分钟在线观看高清视频www | 精品人妻熟女av久视频| 伊人久久精品亚洲午夜| 在线观看一区二区三区| 一本一本综合久久| 国产午夜精品一二区理论片| 美女主播在线视频| 一区二区三区乱码不卡18| 国产色爽女视频免费观看| 亚洲第一区二区三区不卡| 久久久久视频综合| 三级国产精品片| 成人美女网站在线观看视频| 欧美亚洲 丝袜 人妻 在线| 一级毛片久久久久久久久女| 天堂俺去俺来也www色官网| 欧美激情国产日韩精品一区| 菩萨蛮人人尽说江南好唐韦庄| 天天躁日日操中文字幕| 在线观看人妻少妇| 亚洲精品日韩在线中文字幕| 在线观看免费高清a一片| 99久久人妻综合| 美女脱内裤让男人舔精品视频| 色吧在线观看| 最近的中文字幕免费完整| 国产精品不卡视频一区二区| 免费播放大片免费观看视频在线观看| 最近手机中文字幕大全| 日韩在线高清观看一区二区三区| 视频区图区小说| 一本久久精品| 免费看不卡的av| 亚洲精品日韩av片在线观看| 大片免费播放器 马上看| 少妇精品久久久久久久| 中文字幕av成人在线电影| 天堂8中文在线网| 久久久久久久大尺度免费视频| 一个人看视频在线观看www免费| 99热国产这里只有精品6| 欧美成人a在线观看| 乱码一卡2卡4卡精品| 两个人的视频大全免费| av一本久久久久| 美女高潮的动态| 欧美人与善性xxx| 久久久久精品久久久久真实原创| 久久久久精品性色| 黄色一级大片看看| 一级片'在线观看视频| 亚洲人与动物交配视频| 久久久久久久久久成人| 精品午夜福利在线看| 97精品久久久久久久久久精品| 欧美+日韩+精品| 亚洲av成人精品一二三区| 我要看黄色一级片免费的| 在线观看免费视频网站a站| 黄片无遮挡物在线观看| 男男h啪啪无遮挡| 色视频www国产| 在线播放无遮挡| 亚洲真实伦在线观看| 国语对白做爰xxxⅹ性视频网站| 特大巨黑吊av在线直播| 尾随美女入室| 日韩一本色道免费dvd| xxx大片免费视频| 美女cb高潮喷水在线观看| 亚洲精品456在线播放app| 国产成人一区二区在线| 亚洲欧美精品专区久久| 色视频在线一区二区三区| 国产精品国产三级国产专区5o| 国产午夜精品一二区理论片| 色5月婷婷丁香| 国产真实伦视频高清在线观看| 高清av免费在线| 男人爽女人下面视频在线观看| 国产一区有黄有色的免费视频| 免费av不卡在线播放| 亚洲国产精品专区欧美| 亚洲av电影在线观看一区二区三区| 成年人午夜在线观看视频| 欧美97在线视频| av在线蜜桃| 久久精品国产自在天天线| 91精品伊人久久大香线蕉| 亚洲人成网站在线播| 在线精品无人区一区二区三 | 成人影院久久| 精品人妻熟女av久视频| 成年女人在线观看亚洲视频| 免费观看在线日韩| 美女国产视频在线观看| 国产高清有码在线观看视频| 中文字幕免费在线视频6| www.av在线官网国产| 2022亚洲国产成人精品| 国产亚洲午夜精品一区二区久久| av国产精品久久久久影院| 亚洲av福利一区| 色婷婷久久久亚洲欧美| 成人综合一区亚洲| 亚洲欧美精品自产自拍| 国产免费一区二区三区四区乱码| 亚洲成人一二三区av| 不卡视频在线观看欧美| 精品国产三级普通话版| 精品少妇久久久久久888优播| 99热这里只有精品一区| 久久久久久久久久久免费av| 久久精品人妻少妇| 有码 亚洲区| 黄色视频在线播放观看不卡| 中文在线观看免费www的网站| www.av在线官网国产| 精品少妇黑人巨大在线播放| av线在线观看网站| 亚洲三级黄色毛片| 全区人妻精品视频| 99久久中文字幕三级久久日本| 日韩免费高清中文字幕av| 免费少妇av软件| 国产高潮美女av| 有码 亚洲区| av不卡在线播放| 小蜜桃在线观看免费完整版高清| 男人舔奶头视频| 欧美一区二区亚洲| 男人和女人高潮做爰伦理| 99久久人妻综合| 精品久久久久久久末码| 嘟嘟电影网在线观看| 亚洲国产精品999| 寂寞人妻少妇视频99o| 一本—道久久a久久精品蜜桃钙片| 综合色丁香网| 夜夜骑夜夜射夜夜干| 少妇被粗大猛烈的视频| 日韩三级伦理在线观看| 18禁在线播放成人免费| 简卡轻食公司| 午夜免费观看性视频| 男人舔奶头视频| 国产精品一区二区在线不卡| 国产亚洲精品久久久com| www.色视频.com| 观看美女的网站| 日韩一区二区三区影片| h视频一区二区三区| 老司机影院毛片| 亚州av有码| 在线免费十八禁| 国产精品人妻久久久久久| 男人舔奶头视频| 国产精品精品国产色婷婷| 久久久久性生活片| 色5月婷婷丁香| 哪个播放器可以免费观看大片| 热99国产精品久久久久久7| 亚洲,欧美,日韩| 大片电影免费在线观看免费| av黄色大香蕉| 一区二区av电影网| 嘟嘟电影网在线观看| 男的添女的下面高潮视频| 久久国产亚洲av麻豆专区| 蜜桃在线观看..| 亚州av有码| 欧美极品一区二区三区四区| 国产成人freesex在线| 亚洲av男天堂| 亚洲精品第二区| 香蕉精品网在线| 一个人免费看片子| 亚洲人成网站在线观看播放| 精华霜和精华液先用哪个| 欧美zozozo另类| 久久精品国产a三级三级三级| 国产日韩欧美在线精品| 日本与韩国留学比较| 国语对白做爰xxxⅹ性视频网站| 人妻一区二区av| 国产精品国产三级专区第一集| 午夜老司机福利剧场| 大又大粗又爽又黄少妇毛片口| 日本午夜av视频| 亚洲va在线va天堂va国产| 国产伦理片在线播放av一区| 少妇人妻一区二区三区视频| 亚洲,一卡二卡三卡| 美女中出高潮动态图| 日日摸夜夜添夜夜爱| 欧美+日韩+精品| 日本色播在线视频| 日本av手机在线免费观看| 欧美丝袜亚洲另类| 久久久精品免费免费高清| 在线观看av片永久免费下载| 伦理电影免费视频| 一本一本综合久久| 国产精品三级大全| 国产精品一区www在线观看| 赤兔流量卡办理| 老熟女久久久| 国产综合精华液| 成年人午夜在线观看视频| 赤兔流量卡办理| 国产一区二区在线观看日韩| 国产在视频线精品| 极品教师在线视频| 夜夜看夜夜爽夜夜摸| 我要看日韩黄色一级片| 亚洲不卡免费看| 寂寞人妻少妇视频99o| 97在线视频观看| 国产无遮挡羞羞视频在线观看| 亚洲av二区三区四区| 欧美精品国产亚洲| 丰满少妇做爰视频| videos熟女内射| 欧美激情极品国产一区二区三区 | 99久久精品热视频| 国产精品久久久久久精品电影小说 | 亚洲不卡免费看| 中文天堂在线官网| 国产av国产精品国产| 国产精品麻豆人妻色哟哟久久| 日本免费在线观看一区| 久久99热这里只有精品18| 亚洲精品乱码久久久久久按摩| 黑人高潮一二区| 大片免费播放器 马上看| 又爽又黄a免费视频| 欧美三级亚洲精品| 成人18禁高潮啪啪吃奶动态图 | 啦啦啦中文免费视频观看日本| 亚洲av在线观看美女高潮| 成人毛片a级毛片在线播放| 天美传媒精品一区二区| 丝袜喷水一区| 国产一区二区三区av在线| 王馨瑶露胸无遮挡在线观看| 久久这里有精品视频免费| 少妇被粗大猛烈的视频| 老司机影院成人| 成年女人在线观看亚洲视频| 精品国产乱码久久久久久小说| 久久久久精品性色| 大香蕉久久网| 国产男女内射视频| 色视频www国产| 午夜福利在线观看免费完整高清在| 亚洲国产精品一区三区| 久久久久久久久久久丰满| 亚洲精品自拍成人| 亚洲成人手机| 男女无遮挡免费网站观看| 精品久久久久久久久亚洲| av女优亚洲男人天堂| 国产成人freesex在线| 九色成人免费人妻av| 欧美 日韩 精品 国产| 国产女主播在线喷水免费视频网站| 国精品久久久久久国模美| 亚洲美女搞黄在线观看| 亚洲欧美一区二区三区黑人 | 国产男女内射视频| 久久精品国产亚洲av天美| 国产女主播在线喷水免费视频网站| 日韩欧美精品免费久久| av视频免费观看在线观看| 久久久久久伊人网av| 亚洲成人一二三区av| 人体艺术视频欧美日本| 久久影院123| 亚洲第一av免费看| 亚洲欧洲国产日韩| 熟女人妻精品中文字幕| 另类亚洲欧美激情| 日本午夜av视频| 国产片特级美女逼逼视频| 在线播放无遮挡| 亚洲精品色激情综合| 国产黄色视频一区二区在线观看| 一个人看的www免费观看视频| 亚洲内射少妇av| 欧美成人午夜免费资源| 男人舔奶头视频| av国产久精品久网站免费入址| 在线播放无遮挡| 一本色道久久久久久精品综合| 日本黄色片子视频| 国产免费福利视频在线观看| 久久99热这里只频精品6学生| 日本欧美视频一区| 久久精品久久久久久噜噜老黄| 免费观看的影片在线观看| 人妻一区二区av| 黑人高潮一二区| 热re99久久精品国产66热6| 欧美日韩一区二区视频在线观看视频在线| 一级毛片电影观看| 久久人人爽人人片av| 国产黄片美女视频| 国产精品一区二区在线不卡| av在线app专区| 亚洲成人中文字幕在线播放| 久久久久国产精品人妻一区二区| 精品国产一区二区三区久久久樱花 | 亚洲aⅴ乱码一区二区在线播放| 国产伦精品一区二区三区四那| 丰满人妻一区二区三区视频av| a级毛色黄片| 男女免费视频国产| 卡戴珊不雅视频在线播放| 久热这里只有精品99| 亚洲欧美成人综合另类久久久| 久久精品夜色国产| 全区人妻精品视频| 久久97久久精品| 久久毛片免费看一区二区三区| 大码成人一级视频| 久久精品国产鲁丝片午夜精品| 少妇被粗大猛烈的视频| 国产精品伦人一区二区| 日韩av在线免费看完整版不卡| 亚洲av免费高清在线观看| 久久久久久久久久人人人人人人| 一区二区三区四区激情视频| 国产精品不卡视频一区二区| 国产爱豆传媒在线观看| 在线观看免费高清a一片| 国产在线男女| 十分钟在线观看高清视频www | 亚洲欧美日韩无卡精品| 亚洲精品日本国产第一区| 国产精品不卡视频一区二区| 国产精品三级大全| 中文字幕久久专区| 亚洲av成人精品一二三区| 一级av片app| 只有这里有精品99| 国产精品一区www在线观看| 国产熟女欧美一区二区| 色视频在线一区二区三区| 久久久精品免费免费高清| 自拍欧美九色日韩亚洲蝌蚪91 | 精品一区二区三卡| 久久久久精品久久久久真实原创| 免费在线观看成人毛片| 成人毛片60女人毛片免费| 六月丁香七月| 黄色配什么色好看| 91久久精品国产一区二区三区| 国产成人a区在线观看| 99热国产这里只有精品6| 久久精品国产亚洲网站| 寂寞人妻少妇视频99o| 欧美xxxx黑人xx丫x性爽| 欧美日本视频| 国产亚洲欧美精品永久| 国产大屁股一区二区在线视频| 成人黄色视频免费在线看| 狂野欧美白嫩少妇大欣赏| 成年美女黄网站色视频大全免费 | 日本av免费视频播放| 久久久久久久国产电影| 亚洲综合色惰| 久久精品熟女亚洲av麻豆精品| 国产精品爽爽va在线观看网站| 99re6热这里在线精品视频| 99久久综合免费| 99精国产麻豆久久婷婷| 国产黄色视频一区二区在线观看| 免费观看a级毛片全部| 尤物成人国产欧美一区二区三区| 久久人妻熟女aⅴ| 久久国产亚洲av麻豆专区| www.av在线官网国产| 欧美zozozo另类| 成人高潮视频无遮挡免费网站| 嫩草影院新地址| 亚洲久久久国产精品| 视频中文字幕在线观看| 亚洲久久久国产精品| 久久综合国产亚洲精品| 亚洲国产精品999| 久久ye,这里只有精品| 青春草视频在线免费观看| 国产精品国产三级国产av玫瑰| 伊人久久国产一区二区| 精品国产三级普通话版| 久久久久久久大尺度免费视频| 91aial.com中文字幕在线观看| 国产精品久久久久久精品电影小说 | 观看av在线不卡| 干丝袜人妻中文字幕| 日日啪夜夜撸| 国产视频内射| 中文字幕av成人在线电影| 国产精品99久久99久久久不卡 | 一区二区三区免费毛片| 久久久久久久久久久免费av| 女人十人毛片免费观看3o分钟| 不卡视频在线观看欧美| 黄色怎么调成土黄色| 大香蕉久久网| 男人爽女人下面视频在线观看| 纵有疾风起免费观看全集完整版| 久久久久网色| 亚洲精品aⅴ在线观看| 亚洲四区av| 久久久久久久久久人人人人人人| 欧美成人一区二区免费高清观看| 国产成人精品福利久久| 日韩成人av中文字幕在线观看| 欧美人与善性xxx| 国产综合精华液| 国产探花极品一区二区| 日本av手机在线免费观看| 欧美激情国产日韩精品一区| 欧美日韩视频高清一区二区三区二| 91狼人影院| 国产综合精华液| 免费看光身美女| 天美传媒精品一区二区| 十八禁网站网址无遮挡 | 大片免费播放器 马上看| 亚洲经典国产精华液单| 六月丁香七月| 国产av码专区亚洲av| 男男h啪啪无遮挡| 免费av不卡在线播放| 日韩欧美精品免费久久| 国产精品久久久久久久电影| 我要看黄色一级片免费的| 制服丝袜香蕉在线| 简卡轻食公司| 亚洲精品乱码久久久久久按摩| 少妇 在线观看| 国产亚洲5aaaaa淫片| 亚洲av综合色区一区| 少妇人妻一区二区三区视频| 一级av片app| 婷婷色综合大香蕉| 午夜精品国产一区二区电影| 在线观看一区二区三区| 日日啪夜夜爽| 我的女老师完整版在线观看| 97在线人人人人妻| 国产欧美另类精品又又久久亚洲欧美| 欧美一级a爱片免费观看看| 国产国拍精品亚洲av在线观看| 日韩一区二区视频免费看| a级毛片免费高清观看在线播放| 国产精品国产av在线观看| 噜噜噜噜噜久久久久久91| 亚洲在久久综合| 国产精品久久久久久av不卡| 精品国产一区二区三区久久久樱花 | 老司机影院成人| 22中文网久久字幕| 久久精品国产亚洲网站| 精品人妻视频免费看| 香蕉精品网在线| 亚洲伊人久久精品综合| 国产亚洲av片在线观看秒播厂| 丰满人妻一区二区三区视频av| 国产淫语在线视频| 国产精品一区二区在线不卡| 不卡视频在线观看欧美| 99久久综合免费| 免费观看av网站的网址| av女优亚洲男人天堂| 日日啪夜夜撸| 国产欧美日韩一区二区三区在线 | 人妻制服诱惑在线中文字幕| 精品久久久久久久末码| 高清午夜精品一区二区三区| 婷婷色综合www| 成人毛片a级毛片在线播放| 99热全是精品| 看非洲黑人一级黄片| 97在线人人人人妻| 国产亚洲91精品色在线| 人妻 亚洲 视频| 天堂8中文在线网| 看十八女毛片水多多多| 午夜福利影视在线免费观看| av网站免费在线观看视频| 久久99热6这里只有精品| 日韩伦理黄色片| 我的老师免费观看完整版| 日韩免费高清中文字幕av| 欧美精品一区二区大全| 久久精品久久久久久久性| 久久99热这里只有精品18| 亚洲av成人精品一区久久| 中文精品一卡2卡3卡4更新| 少妇的逼水好多| 国产黄片视频在线免费观看| 美女脱内裤让男人舔精品视频| 丝袜脚勾引网站| 黄片无遮挡物在线观看| 尤物成人国产欧美一区二区三区| 高清av免费在线| 99久久精品一区二区三区| 激情五月婷婷亚洲| 亚洲国产日韩一区二区| 亚洲高清免费不卡视频| 三级国产精品欧美在线观看| 国产精品一二三区在线看| 最新中文字幕久久久久| 亚洲第一av免费看| 久久影院123| h日本视频在线播放| 在线 av 中文字幕| 国产极品天堂在线| 国产深夜福利视频在线观看| 亚洲精品色激情综合| 日韩成人伦理影院| 久久韩国三级中文字幕| 国产免费福利视频在线观看| 久久99热6这里只有精品| 国产精品秋霞免费鲁丝片| 亚洲人成网站高清观看| av一本久久久久| 久久久久国产网址|