A DURABLE JET FUEL RESISTANT PAVEMENT LAYER

Transcription

1 P.O. Box 1 Phone ZG Avenhorn Fax The Netherlands Internet Research & Development ir. C. Plug, ir. A. Srivastava, dr.ir. A.H. de Bondt A DURABLE JET FUEL RESISTANT PAVEMENT LAYER WITH THE USE OF A POLYMER MODIFIED ASPHALT EMULSION prepared for Third International Symposium on Asphalt Emulsion Technology Washington DC, USA October 2004

2 A durable jet fuel resistant pavement layer with the use of a polymer modified asphalt emulsion Paper prepared for: Third International Symposium on Asphalt Emulsion Technology ISAET 04 Washington DC, USA October 2004 Authors : PLUG Cees P. ; SRIVASTAVA Anil and DE BONDT Arian H. Mailing address : P.O. box 1, 1633 ZG Avenhorn, The Netherlands ( kplug@ooms.nl) Abstract The surface of airfield pavements suffers extremely from the spillage of jet fuel, the use of de-icing chemicals and the removal of remaining rubber from the surface. To protect the surface, usually a chemical resistant friction course is applied. Unfortunately the currently used friction courses often contain coal tar. Because of the carcinogenic character of coal tar, the usage of this material will be prohibited in future. For better skid resistance and to protect the asphalt layers from jet fuel, a special tar free jet fuel resistant durable anti-skid pavement layer (DAPL) was developed. This pavement layer consists of two layers. An ultra thin very open graded hot mix asphalt (HMA) under layer and a special designed micro-surfacing top layer, both consisting of jet fuel resistant material. This paper will present the development of the DAPL system and the performance of the system at different trial sections. Furthermore, a laboratory study will be presented on the performance under different simulated weathering and polishing conditions. Finally, an evaluation will be given of the DAPL system with respect to proposed design requirements for anti-skid top layers by the Dutch airport authorities.

3 1. Introduction The use of asphalt (in Europe: bitumen) emulsions in road applications is well known. A new field of application is the use of asphalt emulsions as a protective top layer on airfields. The surface of airfield pavements suffers extremely from the spillage of jet fuel, the use of de-icing chemicals and the removal of remaining rubber from the surface at the touch down zone. To protect the surface, usually a chemical resistant friction course is applied. Unfortunately, the friction courses often contain coal tar. Because of the carcinogenic character of coal tar, the usage of this material will be prohibited in future. Furthermore, the traffic on airfields is totally different from that on normal roads. There is no compacting of the emulsion mixture due to traffic. To solve this problem, a 2-layer system has been developed. In this paper the progress in the development of this durable anti-skid pavement layer (DAPL) system will be presented. 2. Description DAPL-system The pavement layer consists of two layers. An ultra thin very open graded hot mix asphalt (HMA) under layer and a special designed 0-3 mm graded micro-surfacing top layer, both consisting of jet fuel resistant material. DAPL slurry Thin layer HMA Fig.1: Schematic representation DAPL-system The under layer is a stone rich ultra thin asphalt concrete layer (thickness approximately 15 mm), which is normally used as top layer in the Netherlands and can be layed down rapidly. In road construction conventional (modified) asphalt is used, but for this application, jet-fuel resistant material has to be applied. This is important, because in case of severe spillage of jet fuel, the under layer will eventually be penetrated by jet fuel. This will also happen with the use of a tar rich surface dressing. The micro-surfacing top layer also has to be jet-fuel resistant. For this reason a suitable polymer modified binder had to be developed, which could be emulsified. An SBS modification in combination with additives to obtain jet-fuel resistance was chosen [1]. An SBS modified binder presents good elastic properties, which will improve the cracking resistance, while maintaining rutting resistance [2,3]. In combination with the resistance against jet-fuel spillage, a long lasting cost-effective pavement can be made [1,2]. In hot mix applications, this special modification was used for the Kuala Lumpur Airport (1995/1996); Cairo Airport (1997); Aden Airport (1999/2000) and St. Maarten Airport (2001) [1,4]. The combination of the 2 layers and the used modification will result in a stable system, which will increase the lifetime of the pavement. This is due to the embedding of the top layer into the open under layer.

4 3. Trial sections and test procedures The first step was to develop a suitable binder for the emulsion. Therefore a jet fuel resistant polymer modified binder was prepared. For the binder a naphtenic asphalt was used, which was modified with an SBS polymer and additives. The properties of this binder were tested according to the ASTM test methods. After this, the binder was emulsified under pressure, due to the high viscosity of the binder. With the emulsion a standard mix design was made in the laboratory. The used aggregate was 0-3 mm Porphyry and Basalt. With the 0-3 mm gradation, the experience is that the desired specifications for texture depth and friction can be met [5]. Basalt was chosen as aggregate for the DAPL system, because of the better resistance against de-icing chemicals and frost over a long period of time. The jet fuel resistance was tested with an internal test method [6]. The performance over a long period of time was simulated with the wet track abrasion test (WTAT, ISSA TB 100). Therefore, WTAT samples were treated in an oven at 85ºC for 5 days and in water at 25ºC for 1 hour, respectively 6 days. After this the WTAT was carried out. The loss of material was determined and the texture depth was analyzed with the sand patch test [7]. The first trial sections were made at the airfield of Bierset (Liege, Belgium). Here the emulsion was mixed with a gradation of 0-3 mm Porphyry and applied as a normal microsurfacing. After curing, the surface was rolled with a pneumatic tired roller. The location of the sections was near fuel stations and tanks, so the deterioration of the pavement due to spillage of jet fuel could be examined. Fig. 2 Trial section at Bierset The second trial sections were made in Amsterdam according to the described DAPLsystem. Out of this section, 250 mm diameter cores were drilled. These cores were subjected to different simulated weathering conditions. After this the loss of material was tested with the WTAT.

5 The WTAT samples from Bierset were aged in water at 25 C and in an oven at 85 C for several time periods. The aging in water gives an indication of the durability of the system during wet conditions and the oven test simulates the conditions after excessive use of the surface. During treatment at 85 C, the asphalt will soften and react with the oxygen in the atmosphere. This will give an indication of the surface after several years under traffic. 4. Results 4.1 Modified Emulsion The first step in the development of the pavement system was to find a high quality modified binder, which could be emulsified. It was found that there were limitations with the viscosity and production temperature in the manufacturing plant. The properties of the selected binder that could be emulsified are given in table 1. Table 1: Properties modified binder. Test Softening point Penetration 180 C Properties 85 C 94 dmm 295 mpa.s PG-Grade Prepared was a cationic slow-setting emulsion with a water content of approximately 37%. 4.2 Laboratory tests Marshall samples were prepared with a normal emulsion and with the jet-fuel resistant emulsion. After 24-hour treatment in jet-fuel, the samples prepared with the normal emulsion showed severe deterioration and the samples with the jet-fuel resistant emulsion were still intact. The weight loss of the samples were 7.4% and 0.9%. Normal emulsion Jet fuel resistance Fig. 3 Effect of soaking in Jet-fuel.

6 WTAT samples were made with the DAPL micro-surfacing mix, according to the standard mix design procedure. Used was 0-3 mm Basalt and 20% (wt/wt) emulsion. Table 2 shows the texture depth of the laboratory test samples before and after aging and wet track abrasion. Table 2 : Surface texture analysis after WTAT. Aging Macro texture depth Loss of weight None 1.7 mm - 5 days in oven at 85 C 1.7 mm 87 gr/m 2 1 hour in water at 25 C 1.4 mm 54 gr/m 2 6 days in water at 25 C 1.2 mm 76 gr/m 2 The results show a very good resistance against aging. The loss of material is much lower than the recommended values for the micro-surfacing mix design procedure [8]. 4.3 Trial sections The curing of the slurry took more time than a normal micro-surfacing overlay. The cause of this may be the open structure of the HMA under layer. Furthermore, the initial cohesion of the slurry was lower than expected. The cause of this may be the thickness of the top layer or the high modification of the emulsion [9]. More research has to be done to increase the initial cohesion of the modified emulsion. A faster setting of the emulsion will increase its usability. Nevertheless the trial sections where in good shape after 4 months. The cores drilled from the DAPL section, were tested with the WTAT. The results of these tests are found in table 3. Table 3 : Durability DAPL system after WTAT. Aging Loss of weight 1 hour in water at 25 C 316 gr/m 2 7 days in water at 25 C 510 gr/m 2 7 days in oven at 85 C 20 gr/m 2 14 days in oven at 85 C 20 gr/m 2 7 days oven + 7 days water 20 gr/m 2 The results show a high deterioration of the surface after soaking in water for a long period of time, when the micro-surfacing is not properly compacted. After proper compaction, as simulated with the oven test, the deterioration is much lower. After compaction the cohesion of the mixture will improve. So the compaction of a microsurfacing is very important. Normally, the compaction due to traffic loading will be sufficient. In cases in which there is in fact a lack of traffic, such as airports, additional compaction methods have to be used.

7 Furthermore, it is important that the used materials are compatible with each other. This will prevent the surface from early deterioration. For each new material selection, a new mix design has to be carried out. 5. Evaluation In the Netherlands, The National Information and Technology Centre for Transport and Infrastructure (CROW) has published a draft report about the way in which alternatives for anti-skid containing tar at runways can be evaluated [10]. In this report some alternative solutions were compared with each other. Furthermore, recommendations were given for test specifications for the anti-skid. The most critical specifications can be found in table 4 [10]. Table 4: Design requirements for anti-skid runway top layers. Aspect Requirements Remarks Skid resistance Depends on used equipment ICAO* and FAA* regulations Texture depth > 1.0 mm 2.0 mm target at construction Environment 10 PAHs < 75 mg/kg of dry material No tar allowed External bond Average bond stress > 1.35 MPa Pull-off test Internal bond A minimum of raveling Raveling tester / WTAT Resistance to chemicals Loss of mass < 0.1% Jet-fuel, de-icing chemicals *] Airport authorities For the DAPL system friction measurements were carried out in the laboratory according to the Wehner / Schulze test in Germany [11]. For this test, cores with a diameter of 300 mm drilled from an ultra thin very open graded hot mix asphalt, which was laid down with the regular paving equipment were treated in the laboratory with the DAPL slurry containing respectively 13 and 14% (wt/wt) emulsion, mixed with 0-3 mm graded Basalt. With the Wehner / Schulze test, the development of the friction of the surface can be simulated during the service life of the pavement. During the Wehner / Schulze test, the surface was polished during load repetitions of 0.40 MPa and sand blowing afterwards, which was followed by another load repetitions of polishing. During the polishing treatment, the friction of the wet surface (µ PWS ) was continuously measured with a contact pressure of 0.20 MPa. The results can be found in figure 4.

8 Fig 4: Development of friction during second load repetitions. During the treatment, the friction of the surface is decreasing and will become lower than desired. For this method a µ PWS = 0.42 is recommended for heavy used roads. In this test, the mixture with the lowest emulsion content gave the best results. However, lowering the emulsion content will affect the durability of the system. The used aggregate in the top layer, will determine the surface friction. So, a better aggregate type has to be selected for the system. Furthermore, the texture depth of the tested samples was measured during the polishing treatment. The results can be found in table 5. Table 5: Texture depth during polishing process. Step 13% emulsion 14% emulsion Original 0.91 mm 1.00 mm load repetitions 0.65 mm 0.53 mm + sand blowing 0.95 mm 0.79 mm load repetitions + sand blowing 0.79 mm 0.62 mm Unfortunately, the obtained values were lower than desired. An optimum texture depth after lay down will be around 2.0 mm, because then the texture depth can be expected to be above 1.0 mm during the entire service life. To meet the specifications for both friction and texture depth, the used aggregate for the DAPL system needs more optimization. In the summer of 2004, a larger trial section of the DAPL system will be constructed. This section shall be evaluated according to the (new) CROW specifications and compared with other available anti-skid systems.

9 6. Conclusions and recommendations Using carefully selected materials, it is possible to produce a high quality (jet fuel resistant) tar free polymer modified asphalt (bitumen) emulsion. In a micro-surfacing application, a durable anti-skid friction course seems to be possible, which will meet the international airfield specifications for jet fuel resistance. More research has to be carried out to improve the skid resistance (and texture depth) of the DAPL system. 7. References [1] Van Rooijen, R. and De Bondt, A.H.; Performance evaluation of jet fuel resistant asphalt for airport pavements; 4 th International Conference on Road & Airfield Pavement Technology; China; April [2] Srivastava, A.; Polymer, rubber and resin modified binders; The Netherlands; [3] World Road Association (PIARC); Use of modified bituminous binders, special bitumens and bitumens with additives in pavement applications; International workshop modified bitumens; Roma, June [4] Khan, S.; Sealoflex for airport construction and rehabilitation; Sealoflex seminar Benelux [5] NPC; Alternatives for anti-skid containing tar at runways (in Dutch); report ; Utrecht; The Netherlands; [6] Ooms Avenhorn Holding bv; Resistance to jet fuel; Internal test method OV 15. [7] CROW; Standaard RAW Bepalingen 2000; (Dutch specifications); test 111. [8] AEMA / ISSA; Recommended performance guidelines; second edition; USA. [9] Glet, W.; A five stage model for the bitumen emulsion setting and its importance for formulation and application of such emulsions; Second World Congress on Emulsions; Bordeaux; 1997; France. [10] CROW; Alternatives for anti-skid containing tar at runways (in Dutch); Extended draft version of NPC report [5]; Ede; The Netherlands; [11] Asphalt-labor; Friction measurements (in German); report 9332/03; Wahlstedt; Germany.