Paper Number 11-2029

RESILIENT MODULUS, REPEATED LOAD PERMANENT DEFORMATION AND PLATE LOAD TESTING OF A MECHANICALLY STABILIZED CRUSHED MISCELLANEOUS BASE MATERIAL

Accepted for presentation by the Transportation Research Board, 90 th Annual Meeting, Washington, D.C.

by

Mark H. Wayne, Ph.D., P.E. (Corresponding Author) Application Technology Manager Tensar International Corporation 2500 Northwind Pkwy, Suite 500 Alpharetta, Georgia 30009 Tel: (770) 344-2164 Fax: (770) 344-2084 [email protected]

Jayhyun Kwon, Ph.D., P.E. Senior Pavement Engineer Tensar International Corporation 2500 Northwind Pkwy, Suite 500 Alpharetta, Georgia 30009 Tel: (770) 344-2133 Fax: (770) 344-2084 [email protected]

Rick Boudreau, P.E. Boudreau Engineering, Inc. c/o Testing, Engineering & Consulting Services Inc. 235 Buford Drive Lawrenceville, Georgia 30046 Tel: (404) 388-1137 [email protected]

Word Count: 3276 + 3250 (13*250) = 6526

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Resilient Modulus, Repeated Load Permanent Deformation and Plate Load Testing of a Mechanically Stabilized Crushed Miscellaneous Base Material

ABSTRACT

In March 1995, the City of Los Angeles passed a motion requiring that road base in all city projects include "crushed miscellaneous base" (CMB) with 100 percent recycled asphalt, concrete, and other inerts, except when site conditions or standards require another specification." In accordance with California Department of Resources Recycling and Recovery, recycled aggregate can save money for local governments and other purchasers, create additional business opportunities, save energy when recycling is done on site, and conserve diminishing resources of urban aggregates. Current AASHTO road design requires either use of layer coefficients or resilient modulus values for each pavement layer. In the spring of 2010, CMB was utilized as part of a repaving project for the China shipping port located at the Port of Los Angeles (POLA). Since the CMB is a man made material, the geogrid manufacturer recommended that a series of tests be performed to characterize its behavior for future use. Laboratory testing consisted of resilient modulus, repeated load permanent deformation on unbound and a geogrid mechanically stabilized CMB, and image analysis. Field testing involved plate load testing along with physical and mechanical characterization of both the subgrade and CMB. Resilient modulus curves for unbound and mechanically stabilized specimen were similar; however, repeated load permanent deformation curves were dramatically different. A relationship was shown to exist between small diameter field plate load tests and resilient modulus of the CMB.

INTRODUCTION

As reported in an earlier paper, a great deal of resilient modulus research work has been completed recently, mostly as part of the Long Term Pavement Performance (LTPP) study (1). This work has resulted in the adoption of the resilient modulus test procedure, T307-99, as published in the current release of the American Association of State Highway and Transportation Officials (AASHTO) Tests ( 2). Neither the test procedure nor the current design guideline addresses how to verify that laboratory resilient modulus test values are achieved in the field. In addition, natural and man-made aggregate commonly used for base and subbase layers within a pavement are generally nonlinear inelastic materials, thus their stiffness is highly dependent upon the stress condition they are subjected to in the field. Recognizing these facts, the research program presented in this paper characterizes the behavior of the crushed miscellaneous base (CMB) aggregate in a mechanically stabilized, through use of a geogrid, and unbound condition. This information is compared to plate load tests conducted during reconstruction of a shipping dock located at the Port of Los Angeles.

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FIELD RESEARCH PROGRAM

The evaluation reported in this paper was performed on a CMB. The CMB was utilized as part of a repaving project for the China shipping port located at Berth 102 at the Port of Los Angeles (POLA). The POLA is underlain by hydraulically placed fill comprised of fine silty sand with good pavement support characteristics owing to the fact that it is well consolidated. An R-Value of 72 was determined for the subgrade material and an R-Value of 79 was determined for the CMB. The planned pavement section consists of 3 inches of asphalt concrete, underlain by 12 inches of roller compacted concrete over 12 inches of CMB. The CMB was mechanically stabilized with one layer of a triangular aperture geogrid exhibiting a junction efficiency of 93%, aperture stability of 3.6 kg-cm/deg @ 5.0 kg-cm torque and a radial stiffness of 20,580 lb/ft @ 0.5% strain. The geogrid was installed within the middle of the CMB, which was 6-inches above the subgrade.

Engineering Properties of Subgrade and CMB

Laboratory tests were performed to evaluate selected engineering properties of the subgrade and CMB materials. The grain size analysis, Atterberg limits, maximum density and optimum moisture content were determined for both materials in accordance with the appropriate ASTM test. Results for the subgrade are summarized in Figure 1. Engineering properties for the CMB are summarized in Figure 2.

100%

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30% Percent Passing Weight Passing by Percent 20%

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U.S. Standard Sieve Size

UNIFIED SOIL Classification: SM Atterberg Limits

Description Silty Sand Liquid Limit 16

R-Value per California Test 301 72 Plasticity Limit NP

Maiximum Density 110.3 lb/ft 3 at 12.5% moisture Plasticity Index NP and Optimum Moisture Content FIGURE 1 Test results for the subgrade material.

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30% Percent Passing Weight Passing by Percent 20%

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U.S. Standard Sieve Size

UNIFIED SOIL Classification: Well Gradede Sand with Gravel Atterberg Limits

Description Crushed Miscellaneous Base Liquid Limit 16

R-Value per California Test 301 79 Plasticity Limit NP

Maiximum Density 127.4 lb/ft 3 at 9.3% moisture Plasticity Index NP and Optimum Moisture Content FIGURE 2 Test results for the Crushed Miscellaneous Base (CMB).

FIELD PLATE LOAD TESTING

Field plate load tests were performed at the locations shown on Figure 3. The exposed surface at each test location was leveled prior to testing. A 5-inch diameter steel bearing plate was then placed on the leveled ground surface. The smaller plate is used in field plate load testing to limit the load influence depth such that k values are for the geogrid stabilized layer alone. A total of 2 dial gauges accurate to the nearest 0.001 inch were located near each extremity of the bearing plate to measure the ground deformation. A seating load of 200 pounds was then applied, released and reloaded, and the dial gauges were then set at their zero mark. Loads were then applied at a moderately rapid rate to the plate with a 10-ton hydraulic ram at uniform increments of 1,100 pounds. After each increment of load was applied, its action was allowed to continue until a rate of deflection of not more than 0.001 inches/minute was maintained for 3 consecutive minutes. The plate load test was performed at the following pavement section elevations and locations:

Subgrade elevation: Locations 8, 9 and 10;
CMB elevation located approximately 6 inches above the subgrade: Locations 5 and 6;
Final CMB elevation: Locations 1, 3, and 4

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Plate load testing was conducted at different locations due to the fact that testing was not allowed to interfere with construction activities on the site. The results of the plate load tests are presented in Figures 4 through 6.

FIGURE 3 Small diameter plate load test locations.

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0.9 Bearing Failure Observed 0.8

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0.5 Location 8

0.4 Location 9

Location 10 0.3

Ground Deformation (inches) GroundDeformation 0.2

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0 0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Force (lbs)

FIGURE 4 Load-deformation curves at the subgrade layer.

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1

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0.7 Bearing Failure 0.6 Observed Location 5 0.5 Location 6 0.4

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FIGURE 5 Load-deformation curves at the mid-level of the CMB layer without geogrid.

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0.6 Location 1 0.5 Location 3 0.4 Location 4 0.3

0.2 Ground Deformation (inches) Deformation Ground

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FIGURE 6 Load-deformation curves at the top of the Mechanically Stabilized Layer.

The results presented in Figures 4 through 6 can be used to calculate the modulus of subgrade reaction for each of the pavement section elevations. The modulus (k) was calculated in accordance with the “ Interim Advice Note 73/06 Revision 1 (2009), Design Guidance for Road Pavement Foundations (Draft HD25).” (3) The Interim Advice Note provides guidance on

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correlating the results from smaller sized plates to those obtained with the standard 30-inch diameter plate as shown in Figure 7.

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0.2 Conversion Factor to obtain k obtain to Factor Conversion

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FIGURE 7 Conversion factors for smaller plate sizes ( 3)

Plate load test results were converted from the 5” diameter plate size using a factor of 0.233 based on the correlation found in Figure 7. The results from this conversion are presented in TABLE 1.

TABLE 1 Modulus of Subgrade Reaction 0.05 inches of 0.1 inches of 0.2 inches of deformation deformation deformation Elevations K762 Percentage K762 Percentage K762 Percentage (pci) Improvement (pci) Improvement (pci) Improvement Finished Base Elevation 1664 84% 1117 57% 832 40% 12 inches from subgrade

Middle Base Elevation 903 12% 713 0% 594 0% 6 inches from subgrade

Subgrade Elevation 808 - 713 - 594 -

Note – Percentage improvement is in relation to the middle base elevation.

Although useful for rigid pavement and foundation design, the results in TABLE 1 require correlation to resilient modulus as determined through laboratory testing discussed later in this paper. As such, subgrade resilient modulus values are estimated using the AASHTO conversion

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of modulus (k) to resilient modulus (M R) using the conversion of k=M R/19.4. With CMB alone (no geogrid) over subgrade, one would expect the composite, ‘k’ on top of subbase, in a plate- load test such as this, to be higher than ‘k’ for subgrade alone. This increase in composite k with 12 inch thick CMB alone (no geogrid) over subgrade are estimated from Figure 3.3 presented in 1993 AASHTO Guide for Design of Pavement Structures (4). The estimated composite modulus values ( k∞) are compared to the measured modulus (with geogrid in middle base) in TABLE 2.

TABLE 2 Modulus of Subgrade Reaction 0.05 inches of 0.1 inches of 0.2 inches of Composite Modulus of deformation deformation deformation Subgrade Reaction k∞ Percentage k∞ Percentage k∞ Percentage (pci) Improvement (pci) Improvement (pci) Improvement

Measured k @ 12 1,664 85% 1,117 40% 832 39% inches from subgrade

Estimated k @ 12 900 - 800 - 600 - inches from subgrade Subgrade Resilient 15,682 13,837 11,531 Modulus (psi)

Apparent in TABLE 2 is the fact that even for a firm subgrade, the inclusion of Geogrid increases the modulus of subgrade reaction (‘ k∞’) approximately 40 to 85%.

RESILIENT MODULUS RESEARCH PROGRAM

The resilient modulus and repeated load triaxial testing reported in this paper was performed. As reported earlier, the CMB possessed a maximum dry density of 127.4 pcf at an optimum moisture content of 9.3% as determined by the Modified Proctor test described in ASTM D1557. Laboratory specimens were targeted to reflect construction specification density (95% of the maximum dry density) at the optimum moisture content.

Repeated Load Triaxial Tests

In order to determine the effects of placing a geogrid within the CMB, a test combination including AASHTO T307 Determining the Resilient Modulus of Soils and Aggregates and NCHRP 598 1 Repeated Load Permanent Deformation (Shear Strength of Aggregate by the Repeated Load Triaxial Test) was conducted on each test specimen; 1) Unbound, and 2) Geogrid mechanical stabilized layer (MSL) ( 2,5). It is noted that both of these tests were conducted in series - first the AASHTO T307, then NCHRP 598 - for each test specimen fabricated (remolded to a specified dry density and moisture content).

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TEST RESULTS

Resilient Modulus (AASHTO T307)

The resilient modulus test was conducted in accordance with procedures contained within the referenced test standard. The specimen is subjected to a series of load pulses at a variety of axial stresses and confining pressures (15 specific combinations of stress levels), and recoverable deformation resulting from these load pulses are measured. Although the test standard specifies a tabular summary of results (as shown in TABLE 3), this summary is not terribly useful to a pavement designer. Rather, the data is used to fit a constitutive model, where resilient modulus can be predicted for any level of stress the pavement designer wishes to consider in his/her design.

There are several constitutive models that can be used to predict the resilient modulus. Each considers the stress regime (vertical and horizontal) as independent variables (either separately – Sc = cyclic stress and S 3 = confining pressure, or combined - θ = bulk stress estimated as S c + 0.5 2S 3 and τoct = octahedral shear stress estimated as S c x 2 /3), and resilient modulus (M R) as the dependent variable. These take the following forms:

K2 K5 SHRP Model: MR = K1(S C) (S 3)

K2 Bulk Stress Model: MR = K1 ( θ)

K2 K3 Universal Model: MR = K1p a ( θ/p a) (( τoct /p a)+1)

TABLE 3 Summary of AASHTO T307 Test Results Control Mechanically Stabilized Layer Confining Load Pressure Cyclic Bulk Resilient Cyclic Bulk Resilient Sequence (psi) Stress Stress Modulus Stress Stress Modulus (psi) (psi) (psi) (psi) (psi) (psi) 1 3 2.64 8.64 15,738 2.60 8.60 15,619 2 3 5.36 11.36 17,515 5.28 11.28 17,133 3 3 8.16 14.16 19,725 8.06 14.06 19,416 4 5 4.54 14.54 21,374 4.46 14.46 20,726 5 5 9.19 19.19 24,541 9.06 19.06 24,137 6 5 13.81 23.81 26,512 13.60 23.60 26,387 7 10 9.23 29.23 31,885 9.11 29.11 31,643 8 10 18.40 38.40 36,668 18.17 38.17 35,928 9 10 27.37 47.37 38,900 27.20 47.20 38,179 10 15 9.27 39.27 35,711 9.11 39.11 37,127 11 15 13.87 43.87 38,555 13.66 43.66 39,662 12 15 27.52 57.52 46,626 27.28 57.28 45,636 13 20 13.91 53.91 43,821 13.66 53.66 45,621 14 20 18.47 58.47 47,711 18.24 58.24 48,220 15 20 36.63 76.63 55,774 36.35 76.35 54,520

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Each model produces widely varied regression constants and coefficients, as seen in TABLE 4. However, these models predict resilient modulus similarly for any given stress regime. It is the data from these predictive models that a pavement designer will utilize for a particular pavement design.

TABLE 4 Summary of Constitutive Model Parameters Model Parameter Control Mechanically Stabilized Layer K1 8,533 8,337 K2 0.2100 0.18828 SHRP K5 0.36200 0.39799 R2 1.00 1.00 K1 4,364 4,197 Bulk Stress K2 0.58052 0.59160 R2 0.99 0.99 K1 1,419 1,451 K2 0.58597 0.63930 Universal K3 -0.02159 -0.19049 R2 0.99 1.00

For this project, it is useful to plot the predictive modulus in graphical form to compare values, in this case, with and without a geogrid. Figure 8 illustrates the test results in graphical form. Although there are a few constitutive models one can use to fit laboratory test data with, the data graphically depicted in Figure 8 is from the Universal Model. The Universal Model is the one currently integrated in the MEPDG.

60,000 0.25 AASHTO AASHTO Layer Coefficient, a 50,000 0.20 40,000 0.15 30,000 Control 0.10 20,000 MSL

Power (Control) 0.05 10,000 Resilient (psi) Mr Modulus, Resilient

Power (MSL) 2 0 0.00 0 20 40 60 80 100 Bulk Stress (psi)

FIGURE 8 Resilient modulus predicted by the Universal Model (AASHTO T307 Results).

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A comparison of values between the unbound (Control) and mechanically stabilized (MSL) layers shows very little stiffness differences between the 2 specimens along the stress regime used for testing.

The data from Figure 8 can be used to estimate a structural layer coefficient by using the formula provided in the 1993 AASHTO Guide for Design of Pavement Structures for granular base layers, a2 ( 4):

a2 = 0.249 LogM R-0.977 (Figure 8)

Each of these materials provides a similar level of pavement support with respect to resilient modulus, or derived layer coefficient. As an example, when evaluating the reinforced and unreinforced materials at a bulk stress of 40psi, a structural layer coefficient of 0.15 for each condition seems reasonable.

Repeated Load Permanent Deformation (NCHRP 598)

The permanent deformation test was conducted in accordance with procedures documented in NCHRP Report No. 598. Each of these specimen were tested immediately following the AASHTO T307 procedure, thus each specimen had been ‘conditioned’ with a specified number and amplitude of loadings, up to 40 psi axial stress.

The results of the NCHRP598 testing are graphically depicted in Figure 9. The NCHRP598 test specifies 1,000 cycles of axial load be applied in a step-sequence of axial stress (10, 20, 40, 60, 80, 100, 120, 140, 160 and 180 psi). This translates into 10,000 cycles of loading to complete the test. During the test, axial strain is monitored. If an axial strain of 10 percent is reached prior to the completing the regimen of 10,000 cycles, the specimen is considered to have failed, and the test is halted. This test is intended to be a ‘torture’ test for aggregate base layers. In the event that a specimen does not exceed 10% strain, the testing is continued at the highest axial stress (180psi) until 10% strain is reached, or an additional 10,000 cycles is achieved, whichever comes first.

Discussion of Repeated Load Permanent Deformation Results

The Control specimen (unreinforced) was able to withstand the 9,619 cycles as prescribed by the NCHRP598 test prior to achieving 10 percent strain. As a comparison, the specimen reinforced with TX160 geogrid was able to withstand the 10,000 cycles as prescribed by NCHRP598 and only strained 4.4%. This same specimen was able to withstand an additional 10,000 cycles at 180-psi axial stress and only reached 6.9% strain, indicating a greater resistance to permanent deformation compared to the same material without reinforcement.

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10 9 8 7 6 5 4

AxialStrain (%) Control 3 2 MSL 1 0

Cycles

Figure 9 Repeated load permanent deformations (Based on NCHRP598 Results).

IMAGE ANALYSIS

Image analysis of the CMB was performed by the University of Illinois Aggregate Image Analyzer (UIAIA). A more detailed discussion about the UIAIA device and the measurements obtained through use of this device can be found in the report developed by Tutumluer et al. (6). For the CMB the average angularity index (AI) was found as 434, Flat and Elongated Ratio of 2.13 and Surface Texture (ST) Index of 0.75. In examining the relationships for angularity index and surface texture for 39 course aggregate material, Pan and Tutumluer, (7) established the fact that uncrushed gravel exhibits a ST index range of 0.5 – 1.20 and an AI range of 250 – 350. In contrast, crushed limestone exhibits a ST index range of 1.20 – 1.80 and an AI range of 400-550. Interestingly, the low ST index value obtained for the CMB may explain why there was little observed difference between the resilient modulus tests performed on an unbound and mechanically stabilized CMB.

SUMMARY AND CONCLUSIONS

A series of laboratory and field tests were performed to characterize a City of Los Angeles CMB aggregate. Results from this research program demonstrated that CMB image analysis results differ from trends previously observed for traditional aggregate with respect to angularity index and surface texture. In this case, angularity index values normally associated with crushed limestone aggregate did not lead to similar values for the surface texture index. This is believed to be due to the nature of the mixing of dissimilar materials (concrete and asphalt) which potentially leads to lubricated surfaces. Although resilient modulus curves for geogrid reinforced and unbound CMB specimen were similar, repeated load permanent deformation curves were dramatically different. Lastly, field plate load testing designed to test thin layers through use of a smaller plate diameter demonstrated the viability of using such testing to determine the in-situ resilient modulus of CMB aggregate. This is possible through use

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of plate diameter conversion and transformation of values through use of AASHTO recommended calculations.

These results highlight the fact that resilient modulus testing can be used to characterize CMB behavior. Image analysis results could be performed to verify angularity and surface texture index values and establish correlations for resilient modulus testing behavior. Small diameter plate load tests can be performed to verify that in-situ resilient modulus meets project design requirements and be used as a quality control measure on future project. Future research on CMB from other states should incorporate the tests presented in this paper to better characterize this material on a regional basis.

ACKNOWLEDGEMENT

The authors would like to thank Garrett Fountain for overseeing the work performed SCS&T. In addition, the authors thank Dr. Erol Tutumluer for the UIAIA analysis of the CMB.

REFERENCES

Boudreau, R. L., “Resilient Modulus – Pavement Subgrade Design Value,” ASTM STP 1437, Resilient Modulus Testing for Pavement Components , G. N. Durham, A. W. Marr, and W. L. De Groff, Eds., American Society for Testing and Materials, West Conshohocken, PA, 2003.

AASHTO T307-99, Determining the Resilient Modulus of Soils and Aggregate Materials Part 2B , 22nd Edition, American Association of State Highway and Transportation Officials, 2002.

Wyn Lloyd, Interim Advice Note 73/06, Design Guidance for Road Pavement Foundations (Draft HD25), Highways Agency, United Kingdom, 2009

AASHTO, Guide for Design of Pavement Structures , American Association of State Highway and Transportation Officials, 1993.

National Cooperative Highway Research Program (NCHRP) Web-Only Document 119: Appendixes to NCHRP Report 598: Performance-Related Tests of Recycled Aggregates for Use in Unbound Pavement Layers

Tutumluer, E., Rao, C., and Stefanski, J.A. Video Image Analysis of Aggregates. Final Project Report, FHWA-IL-UI-278, Civil Engineering Studies UILU-ENG-2000-2015, University of Illinois Urbana-Champaign, Urbana, IL. 2000

Pan, T. and Tutumluer, E. Imaging Based Evaluation of Coarse Aggregate Size and Shape Properties Affecting Pavement Performance, ASCE Geotechnical Special Publication No. 130 , entitled, Advances In Pavement Engineering, Edited by Charles W. Schwartz, Erol Tutumluer, and Laith Tashman, ISBN: 0-7844-0769-X, 2005