COMPARISON BETWEEN LABORATORY AND FIELD MEASURED RESILIENT MODULUS FOR FLEXIBLE PAVEMENT

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 10, October 2018, pp , Article ID: IJCIET_09_10_057 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed COMPARISON BETWEEN LABORATORY AND FIELD MEASURED RESILIENT MODULUS FOR FLEXIBLE PAVEMENT A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob Institute for Infrastructure Engineering and Sustainable Management (IIESM), Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia ABSTRACT Resilient modulus, a measure of material stiffness, is a fundamental parameter used in the mechanistic pavement design procedure. Laboratory testing of pavement materials and in-situ field testing of constructed pavements can be used to determine the resilient modulus. This paper details a study undertaken to analyse and compare the relationship between resilient modulus values obtained from laboratory tests and the back-calculated elastic modulus values obtained from the FWD tests. Two newlyconstructed pavement sections of 150 m length were identified and tested using the Falling Weight Deflectometer (FWD) equipment. Materials obtained from the same quarry were tested in the laboratory for their resilient modulus values. Both values were then compared and analysed. The modulus values obtained using FWD are almost similar to the resilient moduli obtained from laboratory testing of reconstituted samples for asphaltic concrete and laboratory-derived models for the base and subbase materials. Key words: Resilient Modulus, Pavement Materials, Falling Weight Deflectometer, Flexible Pavement Design, Mechanistic Pavement Design. Cite this Article: A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob, Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement, International Journal of Civil Engineering and Technology (IJCIET) 9(10), 2018, pp INTRODUCTION Resilient modulus is one of the two main parameters needed to characterize pavement materials in the mechanistic design procedures. The other parameter, Poisson s ratio, are usually assumed based on previous research and experience as the test procedures are complex and also because of the fact that there is very small influence of Poisson s ratio on the analysis results of flexible pavements [1]. The Public Works Department of Malaysia recently issued a Manual on Flexible Pavement Design [2] based on the mechanistic design procedure and requires the determination of traffic loadings and the resilient modulus of pavement materials and subgrade [3],[4],[5],[6],[7]. Laboratory testing using available editor@iaeme.com

2 Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement standards (such as ASTM D4123 for asphaltic concrete and AASHTO T307 for base and subbase) and field testing (using Falling Weight Deflectometer) can be used to determine the resilient modulus. A number of researchers have attempted to compare the resilient moduli obtained from the laboratory tests and those obtained from backcalculation using FWD deflections. The AASHTO Design Guide 1986/93 permits both the measurement of resilient modulus from laboratory tests and from backcalculation of deflection basins obtained from the FWD tests [8]. The AASHTO guide suggests that the FWD back calculated subgrade moduli are approximately 3 times higher than the lab-determined moduli. According to Von Quintus and Killingsworth [9], the backcalculated moduli is not a true material property itself but a property governing the load-response characteristic of the overall pavement structure. Therefore, it is an equivalent modulus representative of the surrounding material, thickness variations and defects (cracks) in the pavement. Houston, Mamlouk & Pereira [10] concluded that the moduli obtained from the FWD tests are more appropriate for mechanistic pavement design because it has better quality and takes into account of the heterogeneity of the actual material. It also does not posses the effects of sample disturbance as in the laboratory measured moduli. There are conflicting results on the comparison made between the laboratory-measured resilient moduli and FWD backcalculated modulus. Significant differences were found between the laboratory resilient moduli and FWD backcalculated moduli in the WesTrack experiment in Northern Nevada [11]. However, FWD tests performed on existing pavements in Washington found that field and laboratory values compared well for the subgrade soil [12]. Chen and Bilyeu [13] found that the resilient modulus values obtained from laboratory testing for subgrade samples of in-service pavements to be two times higher than the FWD backcalculated moduli. Flintsch et al. [14] found strong correlation between the field backcalculated and the laboratory-measured resilient moduli for granular subbase. However, a shift of about 100 MPa exists between the two values, causing the laboratory-measured moduli to be higher than the FWD-backcalculated moduli. Von Quintus and Killingsworth [9] found that backcalculated moduli for asphaltic concrete are consistently higher than laboratory values suggested that mid-depth temperature of the asphaltic layer to be used and the following correction ratios (Table 1) are to be applied to the laboratory-measured resilient modulus values for the asphaltic concrete, in order to match the elastic modulus backcalculated from the FWD deflection tests. Table 1 Correction ratios for laboratory-measured resilient modulus values of asphaltic concrete [9] Temperature o C ( o F) Ratio of Backcalculated (FWD) to Laboratory Measured Values 5 (41) (77) (104) 4.0 Jenkins and Bredenhann [15] used FWD to determine the stress dependant parameters of the granular pavement layers (using constitutive models) by testing pavement at four different load levels and backcalculating the layer moduli for each load level. However, they suggested that the use of backcalculated material parameters from the FWD tests should not replace laboratory testing but should augment the laboratory work editor@iaeme.com

3 A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob As there were conflicting results of resilient modulus obtained from laboratory tests and in-situ tests using the FWD, a study was carried out to investigate both methods to measure the discrepancies between the results obtained. The objective of this study is to analyse and compare the relationship between resilient modulus values obtained from laboratory tests and the back-calculated elastic modulus values obtained from the FWD tests. 2. METHODOLOGY Resilient modulus values were obtained using the repeated load test on asphaltic concrete wearing and binder course, unbound granular base and sub-base materials. The tests were carried out using the UTM-5P testing machine while the Falling Weight Deflectometer (FWD) was used to determine the in-situ modulus values. The laboratory and field values were then compared to determine whether these values were similar or not Laboratory Testing of Pavement Materials In this study, UTM-5P servo-pneumatically controlled testing machine (equipped with an environmental chamber) was used for the resilient modulus testing of asphaltic concrete, base and subbase materials. The resilient modulus values for the asphaltic concrete layers were determined in accordance to ASTM 4123 [16] by testing reconstituted Marshall samples made in the laboratory based on the gradation curve obtained from the proposed design mix report by the contractor. The aggregates were obtained from the same quarry (Negeri Roadstone quarry) that supplied the asphalt mix for the project. A haversine-shaped load pulse was set at 0.1 seconds and the rest period was 0.9 seconds. The samples testing was carried out at a temperature of 35 o C, which is the pavement temperature at one-third depth of the asphaltic concrete layer thickness, based on the average Malaysian air temperature of 27 o C.The samples were then conditioned and testing was repeated whereby the maximum test load and Poisson s ratio were set as as shown in Table 2. Table 2 Testing Load and Poisson s Ratio Setting Temperature 35 o C Load (N) 975 Poisson s ratio 0.40 The resilient modulus (in MPa) was determined from the following formula: Total Resilient Modulus, E RT = P( ν RT +0.27) / tδht where: P = repeated load (N) t = thickness of specimen (mm) ν RT = total resilient Poisson s ratio ΔHT = total recoverable horizontal deformation (mm) A universal triaxial cell capable of testing 100mm diameter x 200mm high specimens is used for repeated load test of base and subbase materials. For each type of sample, the optimum moisture content was first determined using modified proctor test (4.5 kg rammer). Each of the 100 mm diameter x 200 mm high specimen was prepared using a split sand former, using a 0.3 mm thick rubber membrane over it. The specimens were tested for resilient modulus using the UTM-5P machine at the deviator stress and confining pressures as per AASHTO T test [17]. The repeated load was set at a duration of 0.1 seconds with a rest period of 0.9 seconds. Resilient modulus tests were then carried out at the required editor@iaeme.com

4 Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement confining pressures and deviator stress (15 cycles) for 100 repetitions. The average of the last five readings for each cycle is taken as the resilient modulus for the particular cycle. The data obtained for the 15 cycles were then plotted based on the following relationship for the base/subbase materials [5]: where M R ( psi) k 1 k 2 = Stress invariant or Bulk stress (psi)= ( ) = ( d ). 1 = Major principal stress (psi). 2 = Intermediate principal stress (psi). 3 = Minor principal stress/confining pressure (psi). d = Deviator stress (psi). k 1, k 2 = Regression constants from repeated load resilient modulus tests Field Determination of Modulus using FWD A site (Road B11-B15 in Puchong District) consisting of two separate flexible pavement sections of 150 m in length was identified for the field testing (Figure 1). The site was identified having materials similar to those tested in the laboratory. Construction documents showed that the pavement design layer thickness consists of 50 mm wearing course (ACW20), 60 mm binder course (ACB28), 300 mm base course and 300 mm subbase course (Figure 2). The pavement layer thicknesses were derived from JKR AT5/85 (Pavement Design Manual) and were designed for 5 million ESALs. Figure 1 Road B11-B15site in Puchong District editor@iaeme.com

5 A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob ACW 20 ACB 28 BASE 50 mm 60 mm 300 mm SUBBASE 300 mm SUBGRADE Figure 2 Pavement Cross-Section The purpose of the field work is to determine the elastic modulus of each pavement layer obtained by backcalculation of deflections obtained from the FWD tests. This can then be compared with the resilient moduli obtained from laboratory testing. The resulting in-situ moduli are expected to be within the range of values for those measured in the laboratory since all materials used in laboratory testing as well as in construction are as per the PWD Malaysia s Specification for Road Works. The field tests were carried out as follows: Falling Weight Deflectometer tests (Figure 4) at 25 m intervals. Extraction of asphaltic concrete cores (Figure 5) at 50 m intervals for thickness measurement. Dynamic Cone Penetrometer tests (Figure 6) at the same core holes (50 m intervals) to determine the thickness of base, sub-base layers and CBR strength of the subgrade. The 50-m intervals were selected by the Public Works Department of Malaysia s site representatives to minimise damage to the newly constructed pavement due to coring of the asphaltic concrete layer. Figure 3 shows the schematic diagram of the various tests to be carried out. Chainage: 0 m 25 m 50 m 75 m 100 m 125 m 150 m x x x x x x x FWD1 FWD2 FWD3 FWD4 FWD5 FWD6 FWD7 dcp1 dcp2 dcp3 dcp4 Note: x Test Location FWD Falling Weight Deflectometer dcp Coring and Dynamic Cone Penetrometer Figure 3 Schematic diagram showing the position of the various tests to be carried out The deflection basin obtained from the FWD tests at each test point was used in a backcalculation computer programme to determine the resilient modulus of each pavement layer. The elastic modulus of each pavement layer obtained using FWD was then compared editor@iaeme.com

6 Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement with the resilient modulus of the pavement materials prepared and tested in the laboratory to determine how similar or dissimilar these values are. Figure 4 Falling Weight Deflectometer Figure 5 Coring the asphaltic concrete layer prior to DCP test editor@iaeme.com

7 A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob Figure 6 Dynamic Cone Penetrometer 3. RESULT AND DISCUSSION This section presents the results, analysis and discussion of both laboratory and field resilient modulus tests carried out on the asphaltic concrete wearing and binder courses, base and subbase materials. The results of elastic modulus values for each pavement layer were obtained by backcalculation using the FWD deflection data. The field values were then compared with the resilient modulus values obtained from the laboratory tests Laboratory Derived Resilient Modulus Values The laboratory CBR test was carried out on the soil sample and the CBR value was found to be 11.8%. The following equation [18] was used: M R (psi) = 2555*(CBR) 0.64 = 2555* (11.8) 0.64 = 12,399 psi = 85.6 MPa The fines content of the base and subbase materials were determined to be 1% and 6% respectively. Therefore the fines content for both layer materials was within the MID-25% gradation line. The following equations were used [4],[6]: Subbase Material (MID - 25%): M R (psi) = 6,589.1 θ = 6,589.1 (7.5) = 20,619.9 psi = MPa Base Material (MID-25%): M R (psi) = 8,841.1 θ (Table 4.8, page 103) M R (psi) = 8,841.1 (15) = 32,603.5 psi = MPa editor@iaeme.com

8 Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement The resilient modulus values for the asphaltic concrete layers were determined by testing reconstituted Marshall samples made in the laboratory based on the gradation curve obtained from the proposed design mix report by the contractor. The values are shown in Table 3 for wearing course ACW20 and Table 4 for binder course ACB28. Table 3 Resilient Modulus Values of ACW 20 (Wearing Course) Sample Resilient Resilient Average Modulus at 0 o Modulus at 90 o Resilient Modulus (MPa) (MPa) (MPa) 1 1,501 1,386 1, ,437 1,506 1, ,449 1,425 1, ,505 1,454 1, ,341 1,320 1, ,460 1,403 1,431.5 Average 1,432.3 Table 4 Resilient Modulus Values of ACB 28 (Binder Course) Sample Resilient Resilient Average Modulus at 0 o Modulus at 90 o Resilient Modulus MPa MPa MPa 1 2,290 2,298 2, ,171 1,980 2, ,076 2,250 2, ,241 2,315 2, ,072 2,173 2, ,173 2,124 2,148.5 Average 2,180.3 Using the average values for wearing and binder courses, the combined value of the asphaltic layers are as follows [5]: 1/ 3 1/ 3 3 h1 E1 h 2E2 1 E eq h h 3 = 50(1432.3) 1/3 + 60(2180.3) 1/ = 1,814.3 MPa 3.2. Field Derived Elastic Modulus Values from FWD The elastic modulus values were obtained by backcalculation using the FWD deflection basin. PENDOS, a customised back-calculation software was used for the determination of the modulus. The results were then used to estimate the average values. The FWD results for the two sections are shown in Table editor@iaeme.com

9 A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob Table 5 Average values of FWD Elastic Modulus Elastic Modulus (MPa) Section Asphaltic Base Layer Subbase Subgrade Concrete Layer 1 2 1,587 2, Average 1, Overall Comparison of Field and Laboratory Derived Values The summary results of the analysis using FWD and laboratory resilient is shown in Table 6. Table 6 Comparison between FWD Elastic Modulus and Laboratory Resilient Modulus values Pavement Layer Backcalculated Modulus Values (MPa) Correlated/ Lab. Modulus Values (MPa) % Difference From Lab. Values Asphaltic Concrete 1,860 1, Base Subbase Subgrade From Table 6, it could be seen that the resilient modulus values obtained from laboratory testing (for asphaltic concrete) and calculated using models developed from the laboratory data (for base and subbase materials) differs slightly from the modulus values obtained from the FWD test. The asphaltic concrete value from the laboratory testing is 2.5% lower than the value obtained from FWD test. The laboratory base and subbase values are 13.3% and 6.9% higher than the backcalculated values. Also, the subgrade soil value obtained from the laboratory testing is 13.6% higher than the value obtained from FWD test. It is possible that the increase in asphaltic concrete modulus from FWD (i.e. stiffer material) lowers the stresses in base, subbase and subgrade resulting in lower backcalculated modulus values for the base, subbase and subgrade. Another possible reason for the discrepancy between the backcalculated modulus and resilient modulus obtained from laboratory test is due to the differences in the aggregate gradation lines, the assumed temperature used in asphaltic concrete calculations and differences in moisture profiles of the base and subbase materials. It is possible that subgrade modulus have the largest discrepancy due to material variability as soil is a natural material and therefore, is not controlled compared to base and subbase materials. Overall the discrepancies in the values of the resilient modulus obtained is not large and therefore it is reasonable to say that the modulus values obtained using FWD are similar to the resilient moduli obtained from laboratory testing of reconstituted samples for asphaltic concrete and laboratory-derived models for the base and subbase materials. 4. CONCLUSIONS The relationship between the resilient modulus values from the laboratory tests and the backcalculated resilient modulus values obtained for the FWD tests is not direct but can be investigated. For example, from the field test carried out in this study, the asphaltic concrete value calculated from the laboratory developed models is 2.5% lower than the value obtained from the FWD test while the laboratory-derived base and subbase values are 13.3% and 6.9% higher than the FWD values. This difference may be due to the non-homogeneity of the materials and also the variability of the thicknesses of the different layers of pavement editor@iaeme.com

10 Comparison between Laboratory and Field Measured Resilient Modulus for Flexible Pavement materials along the test sections. It can be concluded that FWD tests can be used to determine the modulus required for pavement design, but laboratory tests should also be undertaken in conjunction to the FWD test to verify the reasonableness in value of the modulus. ACKNOWLEDGEMENTS Special thanks to the Research Management Institute (RMI) of Universiti Teknologi MARA for providing the financial support under Lestari fund. The authors would like to thank the Faculty of Civil Engineering, Universiti Teknologi MARA Malaysia for providing the experimental facilities and to all technicians at Highway and Traffic Engineering Laboratory. REFERENCES [1] Vinson, T.S., Fundamentals of Resilient Modulus Testing. In: Proceedings of the Workshop on Resilient Modulus Testing (FHWA-TS ). McLean, VA: Federal Highway Administration, [2] PWD Malaysia, Manual for the Structural Design of Flexible Pavement (ATJ 5/85 rev.2013). Kuala Lumpur: Public Works Department of Malaysia, [3] Arshad, A.K., Shaffie, E., Ismail, F., Hashim, W., Mat Daud, N.L. and Abd Rahman, Z. Comparative Evaluation of Soil Subgrade Strength Using Laboratory and In-Situ Tests, International Journal of Civil Engineering and Technology, 9(7), 2018, pp [4] Arshad, A.K., Shaffie, E., Ismail, F., Hashim, W. and Abd Rahman, Z., Evaluation of Subbase Materials for Mechanistic Pavement Design. International Journal of Civil Engineering and Technology, 9(8), 2018, pp [5] Arshad, A.K., Shaffie, E., Ismail, F., Hashim, W. and Abd Rahman, Z., Asphaltic Concrete Evaluation for Mechanistic Pavement Design. International Journal of Civil Engineering and Technology, 9(8), 2018, pp [6] Arshad, A.K., Ahmad, Shaffie, E., Hashim, W. and Abd Rahman, Z. Resilient Modulus of Crushed Granite Aggregate Base for use in Mechanistic Pavement Design. International Journal of Civil Engineering and Technology, 9(9), 2018, pp [7] Arshad, A.K., Harun, M.S., Jasmi, N., Yaacob, S. and Haron, H.A. Effect of Heavy Vehicles Tyre Pressure on Flexible Pavements. International Journal of Civil Engineering and Technology, 9(9), 2018, pp [8] AASHTO, Guide for Design of Pavement Structures. Washington D.C.: American Association of State Highway and Transportation Officials, [9] Von Quintus, H.L. and Killingsworth, B.M., Analysis Relating to Pavement Material Characterizations and Their Effects on Pavement Performance (Publication No. FHWA- RD ), McLean VA: Federal Highway Administration, [10] Houston, W.N., Mamlouk, M.S. & Perera, W.S., Laboratory versus Nondestructive Testing for Pavement Design. ASCE Journal of Transportation Engineering, 118 (2), pp , [11] Mikhail, M.Y., Seeds, S.B., Sirous, H.A. and Weston, C.O., Evaluation of laboratory and Backcalculated Resilient Moduli from WesTrack Experiment, Transportation Research Record 1687, pp ; Transportation Research Board,

11 A. K. Arshad, M.S. Harun, N. Jasmi, S. Yaacob [12] Newcomb, D.E., Van Deusen, D.A. & Burnham, T.R., Characterization of The Subgrade Soils at the Minnesota Road Research Project (Report No. MN/RD 94/19). St. Paul: Minnesota Department of Transportation [13] Chen, D. & Bilyeu, J., Comparison of Resilient Moduli Between Field and Laboratory Testing: A Case Study. In: Proceedings of the 1999 Annual Meeting of the Transportation Research Board. Washington D.C.: Transportation Research Board, [14] Flintsch, G.W., Al-Qadi, I. L., Park, Y., Brandon, T.L. & Appea, A., Relationship Between Backcalculated and Laborator-Measured Resilient Moduli of Unbound Materials. Paper presented at the 85 th Annual Meeting of the Transportation Research Board, Washington D.C, [15] Jenkins, K.J. & Bredenhann S.J., Determination of Stress-Dependant Material Properties with the FWD, For Use in the Structural Analysis of Pavements Using Finite Element Analysis Techniques. In: Proceedings of the 8 th Conference on Asphalt Pavements for Southern Africa (CAPSA 04), Sun City, South Africa, September 12-16, [16] ASTM. Annual Book of ASTM Standards (Vol Road and Paving Materials; Vehicle-Pavement Systems). West Conshohocken, PA: American Society for Testing and Materials, [17] AASHTO. Standard Specifications for Transportation Materials and Methods of Sampling and Testing (20 th ed.). Washington D.C.: American Association of State Highway and Transportation Officials, [18] National Cooperative Highway Research Project. NCHRP Project 1-28A - Harmonized Test Methods for Laboratory Determination of Resilient Modulus for Flexible Pavement Design, Washington D.C.:Federal Highway Adminstration, editor@iaeme.com