MATERIALS AND METHODS
DGA 4.7 DGA 4.7
4.2 The Simplified State of RAP based on Bigger Variation Degree of Gradation In this paper, the influence of high content of RAP on gradation design was also
experimentally studied. According to "Technical Specifications for Construction of Highway Asphalt Pavements", AC13 was still taken as the target gradation. Then respectively synthesized the gradations by using the RAP screening result of pre-extracting and post-extracting at the content of 50% RAP, and the results could be seen in Figure 6.
Fig.6. The change of composite gradation of recycling mixture of 50% RAP
From Figure 6 we can see, when the content of RAP is 50%, the mixture gradation obtained by using the RAP pre-extracting is close to the Lower limit. As well the distance between the “Pre-extracting” and the “Post-extracting” is far, suggesting the
“variation degree of gradation” is also large.
Marshall Test was adopted to determine the optimal asphalt content. And then tested the high temperature performance of the two mixtures (Yang, L.Y. 2012), the comparison results could be seen in Table 1, and the appearance of the specimens could be seen in Figure 7.
Table1. The high temperature performance of mixture based on the two methods of gradation design
Dynamic Stability
（time/mm）
the description of test phenomenon
Post-extra cting
7102 1.the depth of rutting was about 2mm;
2.the specimens not only the Marshall but also the rutting could be looked normal from the appearance;
Pre-extrac ting
3013 1.the depth of rutting was about 4mm;
2.the Marshall specimens looked normal from the appearance, but the rutting specimens could not have enough texture depth, especially in initial, they had larger rutting depth;
Fig.7. The appearance comparison diagram of mixture based on the two methods of gradation design
It can be seen from Table 1 and Figure 7, when the content of RAP is 50%, the rutting specimens don’t have enough texture depth, especially in initial, they have larger rutting depth, and so the high temperature stability of the mixture can’t meet the requirements. Therefore, when the “variation degree of gradation” is bigger, adopting the post-extracting is more feasible.
5 CONCLUSIONS
(1)The different simplified state of RAP will lead to the uncertainty of the warm recycled asphalt mixture gradation, and this uncertainty can be quantified by
“variation degree of gradation”. It is related to the content of RAP, when the content is bigger, the gradation difference will become obvious.
Post-extracting Pre-extracting
(2) When the content of RAP is smaller (less than 20%), the gradation design can adopt the pre-extracting, that is to say, the state of RAP is simplified to black aggregate state.
(3) When the content of RAP is bigger (more than 50%), adopting the post-extracting to design gradation is more feasible, that is to say, the state of RAP is simplified to complete mixing state.
ACKNOWLEDGEMENTS
This research was sponsored by Shanghai Pujing Program and Shanghai Science and Technology Commission, China (project number: 12231201100). The authors gratefully acknowledge its financial support for allowing them the opportunity to perform the present study.
REFERENCES
Chen, H. M. (2001). Manual of petroleum asphalt products, Beijing, Petroleum Industry Press, 215-210.
Dinis, A. M., Castro, G.J.,Antunes, M.D. (2012). Mix design considerations for warm mix recycled asphalt with bitumen emulsion, Construction and Building Materials, v 28, n 1, p 687-693.
Deniz, D., Tutumluer, E., and Popovics, J.S. (2009). Expansive characteristics of RAP materials for use as aggregates in the pavement substructure layers, Bearing Capacity of Roads, Railways and Airfields - Proceedings of the 8th International Conference on the Bearing Capacity of Roads, Railways and Airfields, v 2, p 1187-1196.
Hossiney, N., Tia, M., and Bergin, M.J. (2010). Concrete containing RAP for use in concrete pavement, International Journal of Pavement Research and Technology, v 3, n 5, p 251-258.
Liu, X. M. (2003). The construction technology and quality control of hot in plantrecycling,The national highway asphalt pavement recycling technology and equipment of conference proceedings at 2003, Guangzhou.
Lin, H., Zhuang, Y. and Hu, G. W. (2014). Influence of RAP Content on Pavement Performance of Hot Plant Recycling Asphalt Mixture, Applied Mechanics and Materials, v 522-524, p 830-3.
Ministry of Transport of the People's Republic of China. (2004). Technical Specification for Construction of Highway Asphalt Pavements.
Ministry of Transport of the People's Republic of China. (2006). Specifications for Design of Highway Asphalt Pavement
Ministry of Transport of the People's Republic of China. (2008). Technical Specifications for Highway Asphalt Pavement Recycling.
Ministry of Transport of the People's Republic of China. (2011). Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering.
Mucinis, D., Cygas, D. and Oginskas, R. (2008). The possibility of using Reclaimed Asphalt Pavement (RAP) in hot mix asphalt in Lithuania, 7th International Conference on Environmental Engineering, ICEE 2008 - Conference Proceedings, p 1199-120.
NCHRP Report 452. Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician’s Manual. Washington D.C.,2001.
NCHRP Project 9-12 Report. Incorporation of Reclaimed Asphalt Pavement in the Superpave System. National Research Council, National Cooperative Highway Research Program, Transportation Research Board, Washington D.C.,2001.
The Traffic Department of Transportation Planning Division. (2012). Statistics of highway and waterway transportation industry.
Wu, Y. B., Guo, Y. F., and Zhang, X.L. (2011). Performance evaluation of recycled asphalt mixture using warm mix asphalt technology, Geotechnical Special Publication, Emerging Technologies for Material, Design, Rehabilitation, and Inspection of Roadway Pavements-Proceedings of the 2011 GeoHunan International Conference, n 218 GSP, p 26-34.
Wang, Q. Z., Liu, S. Y., and Li, X. L. (2013). Research on application of warm mix asphalt technology in central plant hot recycled engineering, Applied Mechanics and Materials, Sustainable Cities Development and Environment Protection, v 361-363, p 1635-1639.
Wei, L. (2013). RAP percentage and warm mix additive influence on regenerated asphalt mixture performance, Applied Mechanics and Materials, v 251, p 437-41.
Yang, L. Y., Tan, Y. Q., Liu, H., and Li, E. G. (2012). Research and application of warm recycled asphalt mixture, Advanced Materials Research, Trends in Civil Engineering, v 446-449, p 2412-2417.
Yang, L. Y., Tan, Y. Q., Dong, Y. M. and Li, E. G. (2012). Rutting resistance property of warm recycled asphalt mixture, Applied Mechanics and Materials, Progress in Industrial and Civil Engineering, v 204-208, p 3749-3753.
under Heavy Traffic Loading
H. Li, Ph.D., P.E., M.ASCE 1,2,*; R. Wu, Ph.D., P.E.3; D. Jones, Ph.D.4; J. Harvey, Ph.D., P.E., M.ASCE5; and D. R. Smith, P.E., M.ASCE6
1Research Scientist, University of California Pavement Research Center, Dept. of Civil and Environmental Engineering, University of California, Davis, CA 95616. E-mail: [email protected]
2Professor, Key Laboratory of Road and Traffic Engineering of the Ministry of Education; School of Transportation, Tongji University; Shanghai 201804, China. E-mail: [email protected]
3Professional Researcher, University of California Pavement Research Center, Dept. of Civil and Environmental Engineering, University of California, Davis, CA 95616. E-mail: [email protected]
4Research Scientist, University of California Pavement Research Center, Dept. of Civil and Environmental Engineering, University of California, Davis, CA 95616. E-mail: [email protected]
5Professor, University of California Pavement Research Center, Dept. of Civil and Environmental Engineering, University of California, Davis, CA 95616. E-mail: [email protected]
6 Technical Director , Interlocking Concrete Pavement Institute, 14801 Murdock St., Suite 230, Chantilly, VA 20151. E-mail: [email protected]
* E-mail: [email protected]
Abstract: Although permeable pavements are becoming increasingly common for stormwater management across the world, they are mostly used in parking lots, basic access streets, recreation areas, and landscaped areas, all of which carry very light, slow moving traffic. Very little research has been undertaken on the behavior of permeable interlocking concrete pavement as a surface and structure to support more heavy trucks. To understand how permeable interlocking concrete pavements (PICP) perform under heavy traffic loading, a research project was conducted at the University of California Pavement Research Center (UCPRC) with funding from the interlocking concrete pavement industry. The results of this project were used to develop a mechanistic-empirical (M-E) design method for PICP. This method is based on mechanistic analysis and was partially validated with accelerated pavement testing (APT) results. This paper presents a summary of the structural performance of PICP under heavy traffic loading with a Heavy Vehicle Simulator (HVS). The results include the rutting performance of PICP sections with three different thicknesses of subbase layer (reservoir layer) under dry, wet, and drained conditions and with different load levels. The rut development with loading repetitions in the surface, base, and subgrade layers is discussed.
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INTRODUCTION
Although permeable pavements are becoming increasingly common for stormwater management across the world, they are mostly used in parking lots, basic access streets, recreation areas, and landscaped areas, all of which carry very light, slow moving traffic (Jones, Harvey, Li, Wang, Wu and Campbell, 2010, Jones, Li and Harvey, 2013, Li, Jones and Harvey, 2010, Li, Jones, Wu and Harvey, 2013, Li, Jones, Wu and Harvey, 2014). Only very limited research has been undertaken on the mechanistic design and long-term performance monitoring of permeable pavements carrying higher traffic volumes and heavier loads, and previous work has focused primarily on permeable pavements with open-graded (porous) asphalt or (pervious) portland cement concrete surfacing (Jones, Harvey, Li, Wang, Wu and Campbell, 2010, Jones, Li and Harvey, 2013, Li, Jones and Harvey, 2010, Li, Jones, Wu and Harvey, 2013, Li, Jones, Wu and Harvey, 2014, Metcalf, 1996, Smith, 2011, Ullidtz, Harvey, Basheer, Jones, Wu, Lea and Lu, 2010). Most of the previous work was also emphasized on laboratory studies such as resilient modulus of saturated and unsaturated materials (Chow, Mishra and Tutumluer, 2014, Huang, Tutumluer and Dombrow, 2009, Kim and Tutumluer, 2006, Thompson, Gomez-Ramirez and Bejarano, 2002, Tutumluer, Kim and Santoni, 2004, Tutumluer and Seyhan, 1999, Wnek, Tutumluer, Moaveni and Gehringer, 2013). Very little research has been undertaken on the field behavior of permeable interlocking concrete pavement surfacing and structure for heavy trucks on ports, highway shoulders, rest areas, and maintenance yards, etc.
To understand how permeable interlocking concrete pavements (PICP) perform under heavy traffic loading, a research project was conducted by the University of California Pavement Research Center (UCPRC) and coordinated through the Interlocking Concrete Pavement Institute (ICPI) and the Concrete Masonry Association of California and Nevada with additional support from the California Nevada Cement Association (Jones, Li and Harvey, 2013, Li, Jones, Wu and Harvey, 2013, Li, Jones, Wu and Harvey, 2014). The final report (Li, Jones, Wu and Harvey, 2014) details the research undertaken to develop revised design tables for permeable interlocking concrete pavement using a mechanistic-empirical design approach. The study included a literature review, field testing of existing projects and test sections, estimation of the effective stiffness of each layer in permeable interlocking concrete pavement structures, mechanistic analysis and structural design of a test track incorporating three different subbase thicknesses (low, medium, and higher risk), accelerated pavement testing (APT) on the track with a Heavy Vehicle Simulator (HVS) to collect performance data to validate the design approach using accelerated loading, refinement and calibration of the design procedure using the test track data, development of a spreadsheet based design tool, and development of revised design tables using the design tool. Rut development rate as a function of the shear strength to shear stress ratios at the top of the subbase and the top of the subgrade was used as the basis for the design approach. This approach was selected given that low shear strengths of saturated and often poorly compacted subgrades are common in permeable pavements and that higher allowable ruts are usually tolerated due to the
absence of ponding on the surface during rainfall. The alternative approach of using a vertical strain criterion was considered inappropriate for permeable pavements.
The objective of the entire project was to produce thickness design tables for permeable interlocking concrete pavement (PICP) based on mechanistic analysis and partially validated with accelerated pavement testing (Li, Jones, Wu and Harvey, 2014). This paper only summarizes the main results from APT testing and reveals the structural performance of PICP under heavy traffic loading.
METHODOLOGY
Mechanistic design for structure
The test track design was developed using the results from the mechanistic analysis described in references (Li, Jones, Wu and Harvey, 2013, Li, Jones, Wu and Harvey, 2014). The theoretical optimal design base thicknesses (combined bedding, base, and subbase layers) for the three different subgrade shear stress/strength ratios (0.8, 0.5 and 0.2) under dry conditions were approximately 500 mm, 800 mm and 1,300 mm (20 in., 32 in., and 51 in.), respectively. In wet conditions, the theoretical optimal design thicknesses increased to 600 mm, 1,000 mm and 1,400 mm (24 in, 40 in., and 56 in.), respectively.
Based on the results of the mechanistic analysis, three subbase (i.e., coarse aggregate [ASTM #2]) thicknesses of 450 mm, 650 mm, and 950 mm (18 in., 26 in., and ~38 in.), were selected for the HVS test track design to provide high, intermediate (similar to the thickness determined using the PICP design process), and low risk scenarios (Fig. 1). The bedding layer (#8 stone) and base layer (#57 stone) thicknesses were fixed at 50 mm and 100 mm (2 in. and 4 in.), respectively, equating to total structure thicknesses of 600 mm, 800 mm, and 1,100 mm (24 in., 32 in., and 44 in.) for the three subsections. These subbase layer thicknesses are mostly thinner than the theoretical optimal design thicknesses discussed above and were selected to ensure that the performance and behavior of the test track structure could be fully understood within the time and budgetary constraints of the project.
The HVS test section layout, test setup, trafficking, and measurements followed standard UCPRC protocols (Jones, 2005).
Test track and HVS test section layout
Three HVS test sections were demarcated on the test track, the first for testing under dry conditions, the second for testing under soaked conditions (i.e., water level maintained at the top of the subbase), and the third for testing under drained conditions (i.e., wet subgrade, but no water in the subbase). Test sections were evenly distributed across the test track. The test section numbers were allocated in order of testing sequence as follows (HC refers to the specific HVS equipment used for testing):
• Section 678HC: Dry test
• Section 679HC: Wet test
• Section 680HC: Drained test
An extended HVS test section is 15.0 m (49.2 ft) long and 1.0 m (3.3 ft) wide. A schematic in Fig. 1 shows an HVS test section along with the stationing and coordinate system. Station numbers (0 to 30) refer to fixed points on the test section and are used for measurements and as a reference for discussing performance.
Stations are placed at 0.5 m (1.6 ft) increments. A sensor installed at the center of the test section would have an x-coordinate of 7,500 mm and a y-coordinate of 500 mm.
Thermocouples (0 and 25mm) Thermocouple 80mm Paver 50mm Bedding Layer
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
y
x
Station Number (unit: 0.5m) 0.2 m
0.2 m 1 m
Subgrade
N
Legend
NOT TO SCALE
Permanent deformation Road surface deflectometer Thermocouple
Surface profile measured at every station between Station 3 and Station 27 15 m
Subbase
Pressure cell
Top View
Cross Section
100mm Base
450mm 650mm 950mm
Fig. 1: Proposed pavement structure for PICP test track and schematic of an extended HVS test section.
Test section instrumentation and measurements
Measurements were taken with the various equipment and instruments for the following variables: pavement and air temperature, water level in the pavement, surface permanent deformation (rutting), permanent deformation in the underlying layers, and surface deflection, vertical pressure (stress) at the top of the subbase and top of the subgrade, and jointing stone depth. Instrument positions are shown in Fig.
1. Only some of the measurement results (mainly total permanent deformation or