Present Status of Porous Elastic Rubber Surface (PERS) in Japan Kazuyuki Kubo 1 1 Public Works Research Institute (PWRI) 1-6, Minamihara Tsukuba, Ibaraki 305-8516 JAPAN ABSTRACT Porous Elastic Rubber Surface (PERS) was developed in 1991 in Japan in order to reduce traffic noise. Around 1990, porous asphalt pavement had become popular as low noise pavement, while the effect did not last no more than 3 years. In order to improve this effect, PERS was developed by changing its aggregate from stones to rubber chips. While noise reduction effect was quite well, there were some troubles in its durability and skid resistance. PERS has been developed in its construction methods, aggregate type and so on. This paper shows its history of development and improvement. Keywords: Traffic Noise, Porous Asphalt Pavement, Rubber, Low Noise Pavement 1. GENERAL INFORMATION ABOUT PERS Traffic noise is one of the most critical problems in Japan, especially in urban areas. In order to improve acoustic environment, drainage asphalt pavement (DAP) has become popular. Figure-1 shows the growth of DAP in expressways, and more than 20% of national highways in urban areas have been paved by DAP. Figure 1 Drainage Asphalt Pavement in Expressways While DAP can reduce traffic noise in about 3 db comparing with conventional asphalt pavement with dense-graded asphalt concrete at its surface, its effect cannot last longer than 3years. There have been several trials to maintain DAP s performance, such as two layer DAP and 1 k-kubo@pwri.go.jp 1
cleaning system using high-pressure water and vacuum. However, the results were not so good. In 1991, Dr. Meiarashi, Public Works Research Institute, developed the idea of PERS by replacing stone aggregates by rubber chips. Figure-2 shows the concept of PERS and comparison with dense-graded asphalt concrete and porous asphalt concrete. Figure 2 Concept of Porous Elastic Rubber Surface (PERS) Photo-1 shows Road Acoustic Checker, which is usually used to evaluate DAP s noise reduction performance. This machine has fifth tire at the center of its body and measure the noise near the fifth tire. Figure -2 shows the typical result of noise measurement. Comparing with general asphalt pavement (dense-graded asphalt concrete), DAP can reduce about 10dB. Numbers such as (5) mean the maximum size of coarse aggregate. In Japan, most popular size is 13mm, and it is regarded to be effective to use smaller size coarse aggregate to reduce traffic noise. Comparing with DAP, PERS can reduce about 5dB more. Of course these values are based on tire noise, their effect on traffic noise might be less than these. In real roads, DAP is said to reduce about 3dB. In this reason, PERS is expected to reduce about 5 db or more. Photo 1 Road Acoustic Checker (RAC), standardized by Japan Road Association [1] 2
Figure 2 Comparison of Noise reduction effect between PERS and other Pavements [2] 2. DEVELOPMENT HISTORY OF PERS Development of PERS was started in 1991. The first prototype is 1m * 1m square panel and its thickness is 5cm, which aimed to replace porous asphalt concrete layer by these PERS panels. This panel contains no stone aggregate, and skid resistance in rainy days was under 0.3. This very prototype PERS was actually constructed in a real road, and because of its slippery characteristics, it was removed in less than a year. Another problem of this prototype is durability of adhesion interlayer. Photo-2 shows a construction work at national highway. In this case, PERS panels were fixed by epoxy resin on newly constructed asphalt pavement. There were several test pavement sites using this adhesion method, and have been found that asphalt pavement base with epoxy resin is not a suitable combination. Photo 2 PERS Construction at National Highway In order to improve its skid resistance and adhesion durability, it was made to be a rule to add sand as an aggregate, and semi rigid pavement was recommended as a base course material. According to this improvement, skid resistance became around 0.5. Durability of adhesion was also improved, but there had come another problem. PERS has many small air voids, and easily retain water inside. Retained water in PERS panel caused stripping of asphalt from aggregate in lower layer, semi rigid pavement, in two or three years. Adding to say, the thickness of PERS panel had been revised from 5cm to 3cm in order to cut its cost and improve construction process. Another problem relating to panel type is construction period. The whole process, 1)construct 3
new base semi rigid pavement, 2)spread epoxy resin and 3)lay PERS panels, requires too much time. In order to save time, prefixed glue sheet type PERS was developed. This PERS shown in Photo-3 is the third generation. Both second and third generation PERS panel have trench in their bottom to avoid water retain. Merits to use glue sheet are to assure water impermeability to lower layer and to be fixed to existing asphalt pavement. Glue sheet is expected to behave as water impermeable layer and leveling layer. Photo 3 Third generation PERS panel with glue sheet During improvement of panel type PERS, research and development of on-site construction type have been continued. In the beginning, this type PERS had no stone or sand aggregates neither. Actually this type of rubber pavement is popular in golf course to protect spiked shoes. Since it seemed to have the same problem as the prototype panel PERS, this prototype on-site PERS had been never used in traffic roads. There have been mainly two improvements for this prototype. One is to add sand to improve skid resistance. The ratio in weight is sand=70% and rubber=30%. Fortunately, this revision did not decrease the effect of noise reduction so much. The other is to polish surface of semi-rigid pavement to reveal flat aggregate face. In case of on-site construction, glue sheet can t be utilized. Therefore epoxy resin has been chosen as a binder between PERS and lower layer. In order to assure adhesion, flat aggregate surface is necessary. (a) Polishing semi-rigid pavement surface (b) Pave PERS by finisher Photo 4 On-site PERS construction process 3. RECENT RESEARCH ON PERS Through past research stated above, there are left two possible types of PERS as follows; 1) Panel type with glue sheet on asphalt pavement 4
2) Panel of on-site construction type with epoxy resin on semi-rigid pavement In order to examine their durability and other performance, test pavements were constructed in Pavement Test Field in Public Works Research Institute. Photo-5 shows Pavement Test Field and Loading Vehicle. Table-1 shows the type of each test pavement, and Figure-3 shows cross section of test pavements. Photo 5 Pavement Test Field and Loading Vehicle [3] Table 1 Test Pavement Sections Section ID Section Content On-site On-site Construction Type A-1 Panel Type A with epoxy resin B-1 Panel Type B with epoxy resin C-1 Panel Type C with epoxy resin A-2 Panel Type A with glue sheet C-2 Panel Type C with gluie sheet Dense-Graded Convensional Asphalt Pavement Figure 3 Test Pavements Cross Section 5
Figure-4 shows the monitored data of rut depth at each test section. Except C-2, panel type PERS C with glue sheet, their durability seems to be similar with usual asphalt pavement (Dense- Graded section). PERS panels were removed at C-2 section after loading test, and glue sheet were found to be flowed partially from wheel pass. Figure 4 Rut Depth of Each Test Pavement Figure-5 shows monitored data of skid resistance measured by DF Tester [4]. B-1, panel type PERS B with epoxy resin, has become slippery to be rehabilitated after loading test. Skid resistances of other panel type PERS sections have been also dropped gradually. These are caused by removal of sand aggregate during loading test. The trend of skid resistance at On-site section is similar to that of Dense-Graded section, and enough amount of sand might harden PERS and keep skid resistance longer than other PERS sections. Figure 5 Skid Resistance of Each Test Pavement 4. CONCLUSION AND FUTURE WORKS After 20 year research and development, PERS has become enough practical in terms of skid resistance and durability. The other problems seem to cost and construction time. 6
Especially cost is quite severe problem because we must pay more than ten times as much as drainage asphalt pavement (DAP). However, if we regard this technology as a traffic noise countermeasure, we don t have to build noise barrier and PERS may become enough attractive technology for road managers. Construction time is also hard problem to be solved. Because PERS requires to be fixed by resin binder, the construction time may become much longer than DAP, while PERS should be constructed in urban areas in order to solve traffic noise problem. There are some possibilities to shorten construction time as shown in Photo-6. This technology has been developed in Netherlands to construct this DAP quickly on site. If PERS can collaborate with this technology, the construction time will be shorten drastically. PERS is one of the most possible countermeasures to solve traffic noise problem in urban areas. Future works on cost reduction and construction methods is strongly expected to make this technology practical. Photo 6 Rollpave [5] REFERENCES [1] Japan Road Association, Evaluation methods for Pavement Performance, (2006, Japanese only). [2] Japan Road Association, Guidebook for Eco-Friendly Pavement Technologies, (2009, Japanese only). [3] Kawakami and Kubo, Accelerated loading test on durability of cool pavement in PWRI, the 3 rd International Conference on Accelerated Pavement Testing 2008 [4] Watanabe, Terada and Kubo, Evaluation methods of road surface performance in Japan, the 3 rd International Road Surface Friction Conference 2011 [5] Naus, Bhairo, Voskuilen and Montfort, Rollpave, a prefabricated asphalt wearing course, the 11 th International Conference on Asphalt Pavements 2010 7