Annotated Literature Review for NCHRP Report 640 (2009)

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48 The clogging from debris and fines leads to the reduction in the permeability of the surface over a period of time. 1.11 Tolman, F. and F. van Gorkum, Mechanical Durability of Porous Asphalt, Eurobitume, 1996. 1.11.1 General In this paper Tolman and Gorkum present the results of a study carried out to evaluate the cyclic tensile test to differentiate mixes with different degrees of aging. The specimens were obtained from pavements constructed with porous mixes at different times in the Netherlands. First a set of “conventional” tests were conducted, and some specimens were aged in the laboratory. These tests produced results with a significant amount of scatter and could not be reliably used to differentiate mixes with different degrees of aging. The authors then provided the results of cyclic tensile testing and mention that the minimum creep rate model, with a relationship between slope of the secondary part of the creep versus time curve and failure time, could differentiate the mixes with different degrees of aging quite well. They pointed out the need for availability of visual survey data and project data to analyze the results further, and the need to draw more meaningful conclusions to interpret the results from the cyclic tensile tests. 1.11.2 Benefits of Permeable Asphalt Mixtures No information has been provided on benefits. 1.11.3 Materials and Design Tolman and Gorkum provide the description of a porous asphalt that has been developed as a result of the study of field sections constructed between the seventies and nineties. This mix, along with standard mix, is described in Table 22. Table 22: Standard and Proposed New Porous Mix Mix Description Gradation Sieve Size Dutch standard 0/16 Dutch standard 0/11 Proposed new mix C 16 C11.2 C 8 C 5.6 2 mm 63 mm Percent Passing 0.0-5.0 15.0-30.0 50.0-65.0 70.0-85.0 85.0 95.5 Percent Passing --- 0.0-5.0 60.0-85.0 80.0-85.0 85.0 95.5 Percent Passing 0.0-5.0 18.8-28.5 50.0-70.0 70.0-90.0 --- --- Asphalt binder content, percent 4.5 4.5 5.5 Fiber, percent --- --- 0.3-0.7 1.11.4 Construction Practices

49 No information has been provided on construction practices. 1.11.5 Maintenance Practices No information has been provided on maintenance practices. 1.11.6 Rehabilitation Practices No information has been provided on rehabilitation practices 1.11.7 Performance In the introduction, Tolman and Gorkum mention that durability of porous asphalt can be expressed in terms of mechanical and functional durability. They list a set of damage conditions, as shown in Table 23. Table 23: Problems with Porous Mixes Type of Problem Specific Problems Functional Clogging of pores – decreased noise reduction and discharge of water from road surface, surface polishing, unevenness caused by either loss of aggregate or deformation of underlying layers, icing in winter Mechanical Concentrated stress – such as due to rim of flat tire, high shear stress, such as in sharp bends, gradual loss of aggregates leading to raveled surface and/or potholes. Tolman and Gorkum presented the results of a partial study that was started in 1990, to study the loss of aggregate and resulting damage in porous asphalt. They mention that 19 sections were built with different materials and mix types on A10 Motorway around Amsterdam. This motorway had 3 lanes and an average traffic volume of 96,000 vehicles per day (as reported in 1995). Table 24 shows the different mixes used in the study, which include sections on A10 as well as on A12 (with 3 lanes, and 72,000 vehicles per day traffic in 1995). In addition, four other test sections were monitored – one in Belgium (N5) and three in Netherlands (A16 and two on A28).

50 Table 24: Mixes used in the Test Sections around Amsterdam Materials/Mixes Number of sections Sections on A10, each section of 250 m length Standard Dutch PA 0/16, with pen 80/100 asphalt binder 1 section Standard Dutch PA 0/16, with 4.5 % SBS modified binder 2 sections Standard Dutch PA 0/16, with 5.5 % SBS modified binder 2 sections Standard Dutch PA 0/16, with 4.5 % EVA modified binder 2 sections Standard Dutch PA 0/16, with 5.5 % EVA modified binder 2 sections Standard Dutch PA 0/16, with 4.5 % tire rubber scrap modified binder 2 sections Standard Dutch PA 0/16, with 4.5 % tire rubber scrap modified binder 2 sections Standard Dutch PA 0/16, with pen 160/200 asphalt binder 2 sections Standard Dutch PA 0/16 with changed gradation and asphalt content of 5.5% 2 sections Standard Dutch PA 0/16 with cellulose fibers 1 section Standard Dutch PA 0/16 with mineral fibers 1 section Sections on A12, each section of 500 m length Standard Dutch PA 0/16 1 section Standard Dutch PA 0/16 with a resin modified binder 1 section Standard Dutch PA 0/16 with a multigrade binder 1 section Standard Dutch PA 0/16 with a high asphalt binder content, with smaller size and uniformly graded aggregates and mineral fibers 1 section Sections monitored periodically- details of materials and mixes not provided N5 in Belgium Heavy traffic section on A16 (built in 1985) 1 section Section on A28 (built in 1977) 1 section Section on A28 (built in 1985) 1 section To simulate long term aging, and then compare the aged laboratory samples to the aged field samples, the authors conducted some review and then selected the following process (in the following sequence): 16.25 hours open air at a temperature of 50oC, 4 hours sprinkling of water containing sodium chloride at 40oC, 1 hour of rain water at 20oC, and then finally 2.75 hours of frost at -20oC. The authors could confirm the aging process from the reduction in penetration of the recovered binder. Tolman and Gorkum then mention that several tests were carried out to discriminate the different mixes, all of which failed to provide reliable results. Table 25 shows the lists of problems encountered with the specific tests. Table 25: Problems with Tests Test Problem Recommendation Constant displacement rate indirect tensile test - Too much scatter in the data - Not enough theoretical background --- Cantabro test - Too much scatter in the data - Not enough theoretical background Provide strict control of temperature during test to reduce scatter Wheel tracking test - Too much scatter in the data - Not enough theoretical background Circular track preferable to “to and fro” tracks, which suffer from end effects

51 The authors mention that results from the above tests did not correlate well with results of visual condition surveys of the different sections. Some observations, as presented by the authors, are shown in Table 26. Table 26: Observations from Condition Survey Section Observation Cause/Inference A10, A12 No damage Relatively young sections N5 Loss of aggregates Asphalt binder content less than 4.5 %; high binder content reduces loss at the cost of functional properties A18 (1977 section) Rough surface Loss of aggregates Tolman and Gorkum mention that the drawbacks of the above tests were overcome with the use of a cyclic tensile test, with the use of minimum rate of the creep curve or the time to failure parameters. They contend that this test produced results which were able to differentiate binders at different stages of aging. Tolman and Gorkum then proceeded to provide details of the cyclic test carried out on cores for the different test sections. The details of the test are provided in Table 27. Table 27: Details of Cyclic Tensile Test Sample/Variable Type Cores 40 mm high, 100 mm diameter Loading Repeated; frequencies Stresses to cause failure in binder film Tensile stress Temperature Increasing damage at lower temperatures Test conditions (2) 20 oC, 1 Hz, 100-800 N 0oC, 30 Hz, 100-6,000 N Tolman and Gorkum mention that the minimum creep rate model using results from cyclic tensile tests under the different conditions showed good relationship between the slope of the secondary part of the creep curve and the failure time. They indicate that mixes with different stages of aging were found to produce straight lines, in log-log scale (creep rate versus failure time), which were parallel to each other, with a characteristic slope of -1.15. Tolman and Gorkum mention that in terms of damage in porous mixes, a deviation from the average level (for any durability parameter) seems to be more important that a decrease in average level, and that damage increases rapidly once a specific damage level is reached. They also mention that it is impossible to qualify and quantify durability parameters on the basis of one method. Tolman and Gorkum end by stating that the cyclic direct tensile test seems to be the only method capable of discriminating mixes with different degrees of aging and that it offers significant scope of testing with respect to obtaining modulus and phase angle.