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1、Hot rolled asphalt （HRA）（热压沥青混凝土） is a gap graded （间断级配）material with less coarse aggregate（粗集料）. In fact it is essentially a bitumen/fine aggregate（细集料）/filler（填料） mortar（胶浆） into which some coarse aggregate is placed. The mechanical properties are dominated by those of the mortar. This material ha

2、s been extensively used as the wearing course on major road in the UK, though its use has recently declined as new materials have been introduced. It provides a durable（耐久的、耐用的） layer with good resistance to cracking and one which is relatively easy to compact（压实）. The coarse aggregate content is lo

3、w （typically 30%） which results in the compacted mixture having a smooth surface. Accordingly（因此）, the skid resistance is inadequate and precoated（预浇） chippings （石屑）are rolled into the surface at the time of laying to correct this deficiency（不足）. In Scotland, HRA wearing course remains the preferred

4、 wearing course on trunk roads（干线道路） including motorway（高速公路、汽车专用公路） but， since 1999 thin surfacings have been the preferred option in England and Wales. Since 1999 in Northern Ireland, HRA wearing course and thin surfacings are the preferred permitted options. Porous asphalt （PA） is a uniformly gra

5、ded（单一级配） material which is designed to provide large air voids（空隙率） so that water can drain to the verges （路肩、边缘）within the layer thickness. If the wearing course is to be effective, the basecourse（基层） below must be waterproof （防水的）and the PA must have the ability to retain its open textured （构造、纹理

6、）properties with time. Thick binder films（吸附沥青膜） are required to resist water damage（水损害） and ageing（老化） of the binder. In use, this material minimizes vehicle spray（水雾）, provides a quiet ride and lower rolling resistance to traffic than dense mixtures（密级配混合料）. It is often specified（指定） for environm

7、ental reasons but stone mastic asphalt （SMA）（沥青玛蹄脂碎石） and specially thin surfacings are generally favoured in current UK practice. There have been high profile instances where a PA wearing course has failed early in its life. The Highways Agency（公路局） does not recommend the use of a PA at traffic lev

8、els above 6000 commercial vehicles（载重车） per day.Asphaltic concrete（沥青混凝土） and dense bitumen macadam （DBM） （密级配沥青碎石）are continuously graded mixtures（连续级配混合料） similar in principle to the DBMs used in roadbases（基层） and basecourses but with smaller maximum particle sizes（最大粒径）. Asphaltic concrete tends

9、to have a slightly（稍微） denser grading and is used for road surfaces throughout the world with the excepting of the UK. It is more difficult to meet UK skid resistance Standards（抗滑标准） with DBMs than HRA, SMA or PA. This problem can be resolves by providing a separate surface treatment but doing so ge

10、nerally makes DBM economically unattractive.Stone mastic asphalt （SMA） material was pioneered（开辟、开路） in Germany and Scandinavia and is now widely used in the UK. SMA has a coarse, aggregrate skeleton（碎石骨架）, like PA, but the voids are filled with a fine aggregate/filler（填料）/bitumen mortar. In mixture

11、s using penetration grade bitumen（石油沥青） , fibres（纤维） are added to hold（吸收、吸附） the bitumen within the mixture （to prevent “binder drainage”）. Bitumen oil bitumen（ earth oil） natural bitumen Tar Where a polymer modified bitumen （聚合物改性沥青）is used, there is generally no need for fibres. SMA is a gap-grad

12、ed material with good resistance to rutting and high durability（耐久性）. modified bitumen SBS SBR PEEVA It differs from HRA in that the mortar is designed to just fill the voids in the coarse aggregate whereas, in HRA, coarse aggregate is introduced into the mortar and does not provide a continous ston

13、e matrix（矿质骨架）. The higher stone content HRAs ,however, are rather similar to SMA but are not wide used as wearing courses in the UK, being preferred for roadbase and basecourse construction. A variety of thin and what were called ultra（超的、极端的） thin surfacings （nowadays, the tendency is to use the t

14、erm thin surfacings for both thin and ultra thin surfacings ） have been introduced in recent years, principally as a result of development work concentrated（集中） in France. These materials vary in their detailed constituents（成分、要素、组成部分） but usually have an aggregate grading similar to SMA and often i

15、ncorporate（联合、结合、加入） a polymer modified bitumen. They may be used over a high stiffness roadbase and basecourse or used for resurfacing（翻修路面） of existing pavements. For heavy duty pavements （i .e those designed to have a useful life of forty years）, the maintenance philosophy（哲学、哲理） is one of minimu

16、m lane occupancy（占用）, which only allows time for replacement （替换）of the wearing course to these long life pavement structures. The new generation of thin surfacings allows this to be conveniently achieved. The various generic（种类的） mixture types described above can be compared with respect to their m

17、echanical properties and durability characteristics by reference（参考） to Fig.12.1. This shows, in principle, how low stone content HRA, asphaltic concrete, SMA and PA mixtures mobilize resistance（流动阻力） to loading by trafficAsphaltic concrete （Fig.12.1a） presents something of a compromise（和解、折衷方案） whe

18、n well designed, since the dense aggregate grading can offer good resistance to the shear stresses（剪切应力） which cause rutting, while an adequate binder content will provide reasonable resistance to the tensile stresses（拉应力） which cause cracking. In general, the role of the aggregate dominates. DBMs t

19、end to have less dense gradings and properties which, therefore, tend towards good rutting resistance and away from good crack resistance.HRA （Fig.12.1b） offers particularly good resistance to cracking through the binder rich mortar between the coarse aggregate particles. This also provides good dur

20、ability but the lack of coarse aggregate content inhibits（防止、制止） resistance to rutting.SMA and PA are shown in the same diagram （ Fig.c） to emphasis the dominant role the coarse aggregate. In both case, well coated stone is used. In PA, the void space remains available for drainage of water, whilst

21、in SMA, the space is occupied by a fine aggregate/ filler/ bitumen/ fibre mortar. Both materials offer good rutting resistance through the coarse aggregate content. The tensile strength of PA is low whilst that of SMA is probably adequate but little mechanical testing data have been reported to date

22、.13 Provision of adequate drainage（排水 ） is important factor in the location（定位） and geometric （几何学的、几何图形的） design of road and airports. Drainage facilities （排水设施 ） on any highway, street and airport should adequately provide for the flow of water away from the surface of the pavement to properly des

23、igned channels. Inadequate drainage will eventually（最后、终于） result in serious damage to the structure. In addition, traffic may be slowed by accumulated water（积水） on the pavement, and accidents may occur as a result of hydroplaning（水滑现象） and loss of visibility from splash（喷溅） and spray（喷洒、喷雾）. The im

24、portance of adequate drainage is recognized in the amount of highway construction dollars allocated（分配、分派） to drainage facilities. About 25 percent of highway construction dollars are spent for erosion（冲刷、侵蚀） control and drainage structures, such as culverts（涵洞）,bridges, channels, and ditches（明）沟、渠）

25、. Highway Drainage Structures（公路排水结构物） One of the main concerns of the highway engineer is to provide an adequate size structure, such that the waterway opening（过水孔径） is sufficiently large to discharge（放、排出） the expected flow of water. Inadequately sized structures can result in water impounding（集水、

26、蓄水）, which may lead to failure of the adjacent（邻近的） sections of the highway due to embankments（路堤） being submerged（浸没、浸入水中） in water for long periods. The two general categories of drainage structures are major and minor. Major structures（大型结构物） are those with clear spans（净跨（径） greater than 20 feet,

27、 whereas minor structures are those with clear spans of 20 feet or less . Major structures are usually large bridges, although multiple-span culverts（多孔涵洞） may also be included in this class. Minor structures include small bridges and culverts. Emphasis is placed on selecting the span and vertical c

28、learance（净空） requirements for major structures. The bridge deck（桥面） should be located above the high water mark（高水位线） .The clearance above the high water mark depends on whether the waterway is navigable（可通行的、可通航的）. If the waterway is navigable, the clearance above the high water mark should allow t

29、he largest ship using the channel to pass underneath（在下面） the bridge without colliding with（碰撞） the bridge deck. The clearance height（净空高度）, type, and spacing of piers（桥墩） also depend on the probability of ice jams（冰块拥塞） and the extent（程度） to which floating logs（漂浮的圆木） and debris（垃圾） appear on the w

30、aterway during high water. An examination of the banks（堤（岸） on either side of the waterway will indicate the location of the high water mark, since this is usually associated with signs of erosion（冲刷、侵蚀） and debris deposits（沉淀物、沉积物）. Local residents, who have lived near and observed the waterway dur

31、ing flood stages（洪水期间） over a number of years, can also give reliable（可靠的） information on the location of the high water mark. Stream gauges（水文站） that have been installed in the waterway for many years can also provide data that can be used to locate the high water mark. Minor structures, consisting of short-span bridges and culverts, are the predominant（占优势的、主要的） type of drainage structures on highways.