Porous Low-noise Asphalt Concrete Pavement Applied Research

The highway system of our country has made considerable development in recentyears. Since the completion of the first highway in 1988, the total length ofavailable highways in this country has reached beyond 30,000 kilometers, amongwhich Shandong province takes a portion of 10 percent, about 3000 kilometers.Meanwhile the Chinese highway system will grow steadily upward in the future.The building of highway system has greatly encouraged the national economicdevelopment, but it has as well brought noise pollution to the residents alongside,which harmed their health physically and mentally, and affected their normal lifeand word unfavorably.With the aim to reduce the major source of traffic noise on the highways—thenoise produced by the mutual function between the tire and the pavement—thepaper make a technical research on the porous asphalt pavement. Based on theacoustic study of less noise on the asphalt pavement, and study of factors that mayshift the noise-reducing effects of the porous asphalt, and the experimental select ofthe raw materials for porous asphalt pavement, also a comparison between thegradation of the traditional mixed mineral material for asphalt pavement and thatput forward by the NO 99-3 study of American NCAT, the paper adopts animproved method in designing the materials for asphalt pavement, and applies it onthe 1500-meter long experimental section on the freeway between Jinan andLiaocheng (K24~k25+500). The paper also conducts a spot monitor of thepavement of this experimental section, the test of its operating effect, and the trafficnoise produced accordingly. The study aims to provide reliable theories andapplicable techniques for design and construction of modern pavements that havean ideal effect in reducing noises, and thus promote the highway construction andenvironment protection for a sustained development.The research of the factors that influence the noise-reducing effect of the porousasphalt concrete shows that the 60mm thick porous asphalt mixtures of 5% (densegradation) and 20% (open gradation) porosity have better acoustic absorptionfunction. The two samples of 60mm thick asphalt mixture fit the following formula:a p =0.042Vc – 0.053. The two asphalt mixture samples of 15mm and 10mmmaximum granule diameter also have similar frequency and coefficient in acousticabsorption under the condition of similar thickness and porosity. Though it ispossible to improve the asphalt mixture's capability of acoustic absorption byincreasing its connective porosity, yet the hardness and wearability of the pavementwill also be reduced accordingly. Out of this consideration, the paper set the initialporosity as 20%.The hardness and basicity of basalt and its easy conglutination with asphalt makeit the selected material for coarse and fine aggregates (stone chips, sands). To pavethe skid-proof wearing layer of open gradation, the best material is modified asphalt,which can solve the problem of semi-rigidity of Shangdong base course, and theproblems of thin asphalt layer like water damage, fissure and the rapid attenuationof its skip-proof capability, thus can prolong the longevity of the asphalt pavement.Yet the cost of the modified asphalt is relatively high. Through experiment we findthat addition of SBS and MAC modifier would increase the cost by 20% and 18%separately compared with normal asphalt. The major problem confronting highwayconstructors and domestic manufacturers is to resolve the conflict between the highcost and the good performance of SBS and MAC. In order to improve the loose-proof capability of the porous asphalt, and considering the pollution and harm ofmineral fiber—asbestos cement, also the high cost of polymer chemical fiber, thepaper adopt loose wood fiber, in accordance with the present experience andapplication of domestic situation.Ensuring the high porosity and anti-loose capability and reliable mechanicalstrength is the key technique of designing porous asphalt concrete pavement. Thematerial selected for this experimental is basalt, whose conglutination with asphalt,polished stone value, and apparent density are all above the standard level, whilewhose values of needle-shaped aggregates content, Los Angeles abrasion, crushingstrength and the drinking rate are all under the standards. When basalt is used asfine aggregates, no matter the chips or sands, its angularity, sand equivalent andapparent density are all above the normal standards. The porosity of the mixturereduces with the increase of the content of fine aggregates, while the porosity ofporous asphalt is required to surpass 20% in order to reduce noises. Then the paperdesign the proportion of materials as basalt 1(10~15mm): basalt 2(5~10mm): scraps:gravel: mineral powder= 53: 24: 10: 8: 5. The density of SBS asphalt is 1.033, andits penetration, ductility, softening point, recovery of the elasticity, and solubility ofchloral reach above the normal standards, while its movement viscosity andeduction value under the normal standards. This indicates the SBS asphalt has goodcryogenic effect, with strong conglutination and wearability. The best content ofasphalt is 4.5%, and is often adopt as a standard of designing mixture in traditionalproportion scope, with a drift loss around 13%.The improved proportion of minerals is basalt(10~15mm)43%, basalt(5~10mm)47%, scraps 4%, gravel 3%, asphalt 6.1%, fiber 0.4%, and the loss ofmajor controlled variables is around 6%. In the improved design of low-noiseasphalt pavement, the proportion of hot aggregate bin is 1#24%, 2# 58%, 3# 12%,4# 3%, mineral power 3%. According to the design, a 1500m experimental sectionhas been paved on Jinan-Liaocheng freeway (K24~K25+500). The experimentshows that the drift loss of major controlled variables has reduced from traditional13% to 6%, and the loose-proof capability of the low-noise asphalt pavement hasbeen improved, which further increases the wearability of the pavement. Thesection designed with porous asphalt technique, has an overall consideration of thewearability, noise-reducing effect, cost and other technical factors, and sets thereasonable porosity of the pavement as 20%, thickness of 40mm, and uses the SBSor MAC asphalt with an ideal percent around 6%.Through monitoring of the noiseson the experimental section, the traffic noise (A degree) has been confirmed toreduce by 4.2dB when there are 243 vehicles per hour.The porous asphalt pavement with low noise can reduce the traffic noise from thesource and shows better capability in noise-reducing, water drainage, and protectsfrom skidding, dazzling light and splashing water. This can safeguard the sustainingdevelopment of road construction and environmental protection and has a brightfuture for wide appliance. But there still needs extensive research for problems likeendurance of road surface, block up of gaps and water damage.