An Assessment of Resilient Modulus Testing: Internal and External Deflection Measurements

Transcription

1 Geotechnical Testing Journal, Vol. 35, No. 6, 2012 Available online at doi: /gtj Felipe Camargo, 1 Craig Benson, 2 and Tuncer Edil 3 An Assessment of Resilient Modulus Testing: Internal and External Deflection Measurements REFERENCE: Camargo, Felipe, Benson, Craig, and Edil, Tuncer, An Assessment of Resilient Modulus Testing: Internal and External Deflection Measurements, Geotechnical Testing Journal, Vol. 35, No. 6, 2012, pp. 1 8, doi: /gtj ISSN ABSTRACT: The long-term pavement performance (LTPP) resilient modulus test protocol specifies the use of external linear variable differential transformers (LVDTs) to measure the material s response, whereas the Mechanistic-Empirical Pavement Design Guide (MEPDG) requires input for resilient modulus based on the test results using internal LVDTs. Given this discrepancy of data, the relationship between resilient modulus determined from internal and external measurements was studied for a variety of materials using the NCHRP Project 1-37A resilient modulus test protocol and recording deformation data both with internal and external LVDTs. Resilient moduli determined from internal deformation measurements shows to be higher than those from external measurements, whereas the ratio of external to internal resilient modulus decreases with increasing internal resilient modulus because of an increasing effect of machine compliance as specimens become stiffer. Furthermore, the relationship between internal and external resilient modulus depends on the material type. KEYWORDS: resilient modulus, machine compliance, internal LVDT, external LVDT Introduction The present state of practice of pavement design in the United States is being transformed based primarily on the findings from research conducted under National Cooperative Highway Research Program (NCHRP) Project 1-37A, Guide for Mechanistic Empirical Design for New and Rehabilitated Pavement Structures or simply Mechanistic-Empirical Pavement Design Guide (MEPDG). In the MEPDG, a thorough material characterization is a required input to predict the states of stress, strain, and displacement within the pavement structure when subjected to external loading. These properties include the material s elastic or resilient modulus (E or M r ) and Poisson s ratio (l). The current standard method for determining the resilient modulus of base, subbase, and subgrade materials is described in the National Cooperative Highway Research Program (NCHRP) Project 1-28A, Harmonized Test Methods for Laboratory Determination of Resilient Modulus for Flexible Pavement Design. However, the performance models of pavements in MEPDG were developed based on the Long-term Pavement Performance (LTPP) pavement performances and material properties. The LTPP M r test protocol specifies the use of external Linear Variable Differential Transformers (LVDTs) to measure the material s response, whereas the MEPDG required input for M r based on the Manuscript received October 30, 2011; accepted for publication June 4, 2012; published online September Civil Engineer, Dynatest Engenharia Ltda., São Paulo, SP, Brazil, , felipe.camargo@dynatest.com.br 2 Wisconsin Distinguished Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin-Madison, Madison, WI 53706, chbenson@engr.wisc.edu 3 Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin-Madison, Madison, WI 53706, edil@engr.wisc.edu test results in accordance with NCHRP 1-28A in which internal LVDTs are used. Using internal LVDTs eliminates the errors resulting from machine compliance and end effects. However, it also creates discrepancy between the M r used to develop performance models and M r measured for future pavement design. Therefore, there is a need to evaluate the effects of different test protocols on resilient modulus measurements. In this paper, a direct comparison is made between resilient modulus determined from internal and external measurements for a variety of materials including subgrade soils, natural base aggregate and recycled materials, with and without fly ash stabilization. Additional data was obtained from the Minnesota Department of Transportation (MnDOT) to cover a wider range of materials, with materials ranging from stiff (recycled materials stabilized with self-cementing fly ash) to less stiff materials (subgrade soils). The main objective is to provide a correlation between internal and external resilient moduli for a range of materials. Materials The materials that were specifically tested in this investigation are described below. The properties of other materials from the literature can be found in the references. Conventional Base Material Material meeting the Class 5 specifications for base course in Minnesota (MnDOT 2005) was created by blending pit run gravel obtained from Wimme Sand and Gravel (Plover, WI) with crushed pea gravel obtained from Midwest Decorative Stone and Landscape Supply (Madison, WI). The pit run gravel was sieved past the 25 mm sieve prior to blending with the pea gravel. The Class Copyright VC Copyright by 2012 ASTM by ASTM Int'l (all International, rights reserved); 100 Sat Barr Jan Harbor 5 06:32:03 Drive, EST PO Box 2013 C700, West Conshohocken, PA

2 2 GEOTECHNICAL TESTING JOURNAL 5 base classifies as poorly graded sand with gravel (SP) according to the Unified Soil Classification System (USCS) and A-1-a according to the AASHTO Classification System (AASHTO). Particle size distribution curves for the Class 5 base are shown in Fig. 1. Recycled Materials The recycled pavement material (RPM) was obtained from a roadway reconstruction project in southwestern Madison, WI, near the intersection of Muir Field Rd. and Carnwood Rd. The RPM was a blend of pulverized asphalt and limestone base layer (approximately equal parts) created by removing and pulverizing the existing pavement. The RPM had asphalt content of 4.6 %, as determined by the procedure in ASTM D6307 (2005), and classifies as well-graded gravel or silty gravel (GW-GM) according to the USCS and A-1-a according to the AASHTO. A particle size distribution for the RPM is shown in Fig. 1. The RPM was screened with a 25-mm sieve prior to testing. A road surface gravel (RSG) sample was created by blending Class 5 base with washed limestone fines obtained from Rosenbaum Crushing and Excavating (Stoughton, WI). The Class 5 base was screened past the 19-mm sieve prior to blending with the limestone fines. The RSG meets the AASHTO gradation requirements for surface course materials, as outlined in AASHTO M147, and classifies as silty sand (SM) according to USCS and A-1-b according to the AASHTO. A particle size distribution for the RSG is shown in Fig. 1. Fly Ash Fly ash was obtained from Columbia Power Plant Unit No. 2 in Portage, WI, where sub-bituminous coal is burned in pulverized boilers. The fly ash is collected using electrostatic precipitators. Columbia fly ash is a self-cementing fly ash that classifies as Class C according to ASTM C618. The CaO SiO 2 and CaO (SiO 2 þ Al 2 O 3 ) ratios for Columbia fly ash, which are indicators of cementing potential (Janz and Johansson 2002; Tastan et al. 2011), are 0.8 and 0.4, respectively. Recycled materials were blended using two different fly ash contents (10 % and 15 %) and three curing times (7, 28, and 56 d). Methods The RPM and Class 5 base materials classify as Type I material in NCHRP 1-28A, which requires a specimen 150 mm in diameter and 305 mm in height for resilient modulus testing (NCHRP 2004). For consistency, all specimens were prepared to these dimensions even though smaller specimens could have been used for RSG. Specimens were compacted in six lifts of equal mass and thickness using a split mold 150 mm in diameter. All materials were compacted to 100 % of maximum standard Proctor density at optimum water content. Specimens were compacted to within 1 % of the target dry density and 0.5 % of target moisture content (NCHRP 2004). Similar methods were employed for base materials prepared with and without fly ash. Unstabilized base course aggregates were prepared in a split mold placed directly on the bottom plate of the resilient modulus test cell. A latex membrane was placed inside the split mold and stretched on the inside surface of the mold. After attaching the top cap, a small vacuum was applied to the specimens before removing the split mold until the first cell pressure was applied. Resilient modulus test specimens were instrumented with both internal and external linear variable displacement transducers (LVDTs). Internal LVDTs were mounted on clamps around the specimen and membrane (see Fig. 2), whereas external LVDTs were mounted on the plunger outside the chamber and rested on the cover plate (Fig. 3). Internal LVDTs were placed at quarter points of the specimen to measure deformations over half the length of the specimen, whereas external LVDTs measured deformations of the entire specimen length. Resilient modulus testing was performed in accordance with the NCHRP 1-28A protocol (NCHRP 2004). All base materials were tested under Procedure Ia, which applies to base and subbase materials. All resilient modulus tests were conducted with both internal and external LVDTs for comparison. Clamps for the internal LVDTs were built in accordance with NCHRP 1-28A specifications, having 152 mm (6 in.) in diameter, weighing less FIG. 1 Particle size distributions for Class 5 base, RPM, and RSG. FIG. 2 Internal LVDT clamps mounted on a resilient modulus specimen.

3 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 3 FIG. 3 External LVDTs mounted on a resilient modulus specimen. than 2.4 N (0.55 lb), having a spring force of 44.5 N (10.0 lb), and using two pairs of 12-mm rods to position the clamps in a horizontal plane in the correct location on the specimen (i.e., quarter points along the specimen height). Both the external and internal LVDTs had a measurement range of 65 mm for specimens without fly ash and 61.5 mm for specimens with fly ash. The former had an accuracy of mm, whereas the latter had an accuracy of mm. An MTS Systems Model servo-hydraulic machine was used for top-loading the specimens with a loading pulse having a 0.1 s duration followed by a rest period of 0.9 s. loading sequences, confining and deviator stresses, and data acquisition were controlled by a PC equipped with Labview 8.5 software. Resilient moduli (M r ) from the last five cycles of each test sequence were averaged to obtain the resilient modulus for each load sequence. The resilient modulus data were fit to the power function proposed by Moosazedh and Witczak (1981). A summary resilient modulus (SRM) was also computed, as suggested in Section of NCHRP 1-28A. The summary resilient modulus of a given material is simply the resilient modulus at a given state of stress (the state of stress expected for that material in the field). The advantage of reporting a SRM is that a standard, single value for the resilient behavior of the material is determined and can be used for comparing two or more materials. For base materials, the SRM corresponds to the resilient modulus at a bulk stress of 208 kpa. Results and Analyses The summary resilient moduli (SRM) computed from internal LVDT measurements are higher than those for external LVDT measurements for all resilient modulus tests. A sample graph shows the typical internal and external resilient moduli from sequences 1 5 for a RPM sample (Fig. 4). The ratio of internal to external SRM ranged from 1.2 to 1.4 for the base and recycled FIG. 4 Sample results for a resilient modulus test (load sequence 1 5 for an RPM sample). materials without fly ash and from 4.0 to 18.3 for the recycled materials stabilized with fly ash (Table 1). Jardine et al. (1984) first emphasized the significance of measuring axial strains locally. Others have shown that internal resilient modulus measurements are higher because displacement measurements for external LVDT readings are affected by several external sources of error, such as bedding errors, sample end effects, and machine compliance (Goto et al. 1991; Tatsuoka et al. 1994; Bejarano et al. 2003; Boudreau and Wang 2003; Ping et al. 2003). System compliance may be defined as the deflection of the resilient modulus equipment parts, such as the load cell, top cap, and piston. Barksdale et al. (1997) evaluated the variability and reliability of three different displacement measuring techniques for determining the resilient modulus: two external LVDTs, two or three LVDTs from the top platen to bottom platen, and LVDTs located on clamps at [1=4] points. Two 152-mm (6-in.) diameter by 305- TABLE 1 Summary resilient modulus for base materials with and without fly ash. Materials Fly ash content (%) Curing time (d) Internal SRM (MPa) External SRM (MPa) SRM INT = SRM EXT Class 5 base RPM RSG

4 4 GEOTECHNICAL TESTING JOURNAL mm (12-in) high synthetic elastometer specimens: one having low resilient modulus (54 MPa) and the other having relatively high resilient modulus (350 MPa) were used. LVDTs were also rigidly attached to each specimen for eliminating system compliance deformation as well as the potential for slip and vibration associated with the clamps. Both Anova and Duncańs multiple range tests showed there exists statistical differences at the 95 % confidence level for the mean resilient modulus determined by each measuring technique. Furthermore, the test showed that at 95 % confidence level the resilient moduli measured using the rigidly mounted LVDTs are statistically different from the resilient moduli using the clamp mounted LVDTs at the same location for both the low and high stiffness synthetic specimens. Taking the rigidly mounted LVDTs as reference, the internal clamp mounted LVDTs resulted in a better average resilient modulus (-6 % error) than those for the externally mounted LVDTs (-14 % error) for the stiffer specimen. On the other hand, the externally mounted LVDTs resulted in a better average resilient modulus (2.5 % error) than those for the internal clamp mounted LVDTs (-6 % error) for the low stiffness specimen. The contrasting results were attributed to the fact that low stiffness specimens undergo a large amount of deformation for a given stress compared to a stiff specimen, with system compliance deformations becoming less important in the measuring of the resilient modulus when compared to these large deformations. The system compliance deformations for the stiff specimens; on the other hand, become important because they can be on the same order of the small deformations occurring in stiff specimens. As a result, the external LVDTs show more error for the stiffer specimen. Puppala (2008) summarized the resilient moduli information available in the literature collected from various state DOTs in an extensive study for the National Cooperative Highway Research Program (NCHRP). The majority of the studies conducted resilient modulus testing using either internal or external LVDT measurements, showing certain variations in the resilient moduli measurements. In general, research studies conducted using both internal and external LVDT measurements system yielded higher resilient moduli for internal measurements when compared to external measurements. The higher internally measured resilient moduli were attributed to displacements measurements free from system compliance errors. The resilient modulus results for base and recycled materials without fly ash are similar to those found by Mohammad et al. (1994), Ping and Ge (1996), and Ping et al. (2003). Ping and Ge (1996) conducted resilient modulus tests on lime rock, a weathered limestone base material commonly used in Florida, instrumented with internal and external LVDTs. The ratio of internal to external resilient moduli calculated from the data reported ranges from 0.85 to Ping et al. (2003) conducted resilient modulus tests on granular soils (A-3 and A-2-4) instrumented with internal and external LVDTs. The ratio of internal to external resilient moduli ranged from 1.19 to 1.35 for A-3 soils, whereas the ratio ranged from 1.14 to 1.30 for A-2-4 soils. Mohammad et al. (1994) showed the influence of LVDTs location on the resilient modulus of a blasting sand (A-3) and a silty clay (A-7). The recommended ratio of internal to external resilient moduli ranged from 1.5 to 1.6 for the blasting sand, whereas the recommended ratio for silty clay was approximately The ratio of internal to external SRM for the recycled materials stabilized with fly ash was significantly higher than the ratios for materials without fly ash (ranging from 4.0 to 18.3). The ratio of internal to external SRM also increases with increasing stiffness (Fig. 5). Additional data from Kootstra (2009) and Bozyurt (2011) were obtained for comparison and are included in Fig. 5. Bozyurt calculated the ratio of internal to external SRM for recycled asphalt pavement (RAP) and recycled asphalt concrete (RCA) obtained from different sources in the United States, whereas Kootstra (2009) determined the ratio of internal to external SRM for the RSG and RPM previously described, each blended with 4 % cement (CS-RSG and CS- RPM) as well as with 10 % cement kiln dust (RSG, 10 % CKD and RPM, 10 % CKD). The latter yielded moduli in excess of 2000 MPa, in some cases, with more variability. The increase in ratio with increasing stiffness is attributed to an increase in overestimation of the displacement as the material becomes stiffer (i.e., lower displacements), increasing the difference between external and internal displacement measurements. These results are consisted with the results obtained by Barksdale et al. (1997) for high synthetic elastometer specimens, where externally mounted LVDTs performed poorly for the stiff specimen. Bejarano et al. (2003) also report higher M r from internal readings, with an increase of M r for increasing stiffness because of the greater influence of machine compliance (Bejarano et al. 2003). The measurement accuracy also decreases for very stiff materials at low deviator stresses as the displacements become so small they are at the limit of the LVDT s accuracy, resulting in more variability of the data. Base Materials Additional resilient moduli computed from internal and external LVDT measurements were obtained from the Minnesota Department of Transportation (MnDOT) database (Chadbourn 2007) for FIG. 5 Ratio of internal to external SRM versus internal SRM for Class 5 base, RAP, RCA, and RPM and RSG with and without fly ash, CKD, and cement stabilization.

5 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 5 FIG. 6 Ratio of internal to external M r versus internal M r for base materials (a), and boxplot of ratio of internal to external M r versus internal M r for base materials (b). comparison with the data collected in this study. The procedures used and the data collected in the University of Wisconsin tests were reviewed and confirmed by MnDOT as suitable for their database requirements. Thus, the data used in this study from various sources meet similar quality control and are suitable for comparison. The ratio of internal to external M r was computed for all cycles during resilient modulus testing, except those from the loading phase (Sequence 0). The ratio of internal to external M r as a function of internal M r for base aggregate and recycled materials without fly ash is shown in Fig. 6 along with the corresponding boxplot. The Class 5 base, RPM, RSG, MnROAD Class 6, and MnROAD RPM in Fig. 6 are materials tested at the University of Wisconsin-Madison (UW). The MnROAD Class 6 base and RPM in Fig. 6 were obtained from a research project at the MnROAD facility in Minnesota (Camargo et al. 2009). The Class 6 material is a crushed aggregate conforming to Minnesota s Class 6 specifications (MnDOT 2005), and the RPM is a recycled material containing 50 % RAP. These tests were conducted at MnDOT (MnDOT base, RPM, and reclaimed concrete). MnDOT base materials include gravels, granite, and taconite tailings. The MnDOT RPMs consist of base materials (Class 5, Class 6, and taconite tailings) having RAP contents of 30, 50, and 70 %. There is no apparent trend in the data (Fig. 6(a)). The boxplot shows that the majority of the ratios ranging are between 1.0 and 2.2, with a median ratio of 1.5 for all base and recycled materials (Fig. 6(b)). The relationship between internal (M r INT ) and external resilient moduli (M r EXT ) for base aggregate and recycled materials is shown in Fig. 7. This relationship can be described by M rint ¼ 1:5M r EXT (1) Equation 1 has R 2 ¼ 0.85 (p-value <0.001). This slope of Eq 1 equals the median M r ratio shown in the boxplot in Fig. 6(b). A linear regression analysis was performed to determine if a statistically significant relationship existed between the internal and external resilient moduli. In this analysis, the probability of falsely rejecting the null hypothesis (slope is zero), referred to as the p-value, is determined and compared to the significance level, a. A p-value lower than a indicates the slope is statistically different from zero and the internal resilient modulus is dependent of the external resilient modulus. A significance level of a ¼ 0.05, the significance level commonly used in hypothesis testing (Berthouex and Brown 2002), was used. The corresponding p-value for Eq 1 is < Thus, we reject the null hypothesis and conclude that there was a positive significant relationship between internal and external resilient moduli. The same statistical analysis was performed for the remaining equations. Subgrade Materials Resilient modulus data for subgrade materials instrumented with both internal and external LVDTs were also obtained from the MnDOT database (Chadbourn 2007) and from a previous University of Wisconsin-Madison (UW) study (Sawangsuriya et al. 2009). The ratio of internal to external resilient moduli as a function of internal M r for subgrade materials is shown in Fig. 8. FIG. 7 Internal versus external M r for base materials.

6 6 GEOTECHNICAL TESTING JOURNAL FIG. 8 Ratio of internal to external M r versus internal M r for subgrade materials. FIG. 10 Ratio of internal to external M r versus internal M r for recycled materials stabilized with fly ash. MnDOT subgrade materials include soils such as clay, clay loam, loam, loamy sand, sandy clay loam, sandy loam, silty clay, and silty loam. UW subgrade materials include four subgrade soils from Minnesota classified as ML, CL, and CH according to the Unified Soil Classification System. The ratio of internal to external resilient moduli for subgrade materials increases approximately linearly with increasing internal M r, ranging from 1 to 10. This relationship can be described by M rint ¼ 0:007M rint þ 1:05 (2) M r EXT which has R 2 ¼ 0.87 (p-value <0.001). The relationship between internal and external M r for subgrade materials is shown in Fig. 9. The relationship between internal and external can be described by the power function: M rint ¼ 0:172ðM r EXT Þ 1:627 (3) which has R 2 ¼ 0.86 (p-value <0.0001). Recycled Materials Stabilized with Fly Ash The ratio of internal to external resilient moduli as a function of internal M r for recycled materials stabilized with fly ash is shown in Fig. 10. The ratio increases with increasing internal M r, ranging from 2 to 25. An approximate linear relationship exists between the ratio of internal to external M r and internal M r for the recycled materials stabilized with fly ash: M rint ¼ 0:0014M rint þ 1:195 (4) M r EXT which has R 2 ¼ 0.76 (p-value <0.001). The relationship between internal and external M r for recycled materials stabilized with fly ash is shown in Fig. 11. There is no FIG. 9 Internal versus external M r for subgrade materials. FIG. 11 Internal versus external M r for recycled materials stabilized with fly ash.

7 CAMARGO ET AL. ON AN ASSESSMENT OF RESILIENT MODULUS 7 increasing effect of machine compliance relative to increasing specimen stiffness. The relationship between internal and external resilient modulus depends on material type. Different relationships are provided for unstabilized natural or recycled base course materials, fly ash stabilized recycled base course materials, and natural subgrade soils. Statistical analysis indicated that all relationships are highly significant (p-values <0.0001). FIG. 12 Ratio of external to internal M r versus internal M r for a range of materials. apparent trend in internal to external M r for these materials. The recycled materials stabilized with fly ash have significantly higher stiffness than those without fly ash, which results in less accurate external deformation measurements because of a higher machine compliance effect. This behavior is also observed in Fig. 10, where a larger scatter exists when the internal M r exceeds 6000 MPa. The ratio of external to internal M r for a range of materials (fine-grained soils, crushed natural aggregates, recycled materials, and recycled materials stabilized with fly ash) is shown in Fig. 12. The concrete in Fig. 12 refers to the results for concrete specimens also tested for calibration purposes. To be consistent with the other data in Fig. 12, the data for fine-grained materials were limited to measurements on 150-mm diameter. The ratio of external to internal M r decreases with increasing internal M r. This trend is attributed to the increasing effect of machine compliance as the specimen becomes stiffer, which increases the difference between internal and external M r and therefore decreases the ratio of external to internal M r. Conclusions This study presented the results of a direct comparison between resilient moduli determined from internal and external deflection measurements for a range of granular base course materials including both natural and recycled aggregates. In addition, data from other sources at the University of Wisconsin-Madison and the Minnesota Department of Transportation, including a variety of subgrade soils, were used to investigate the correlations between resilient modulus determined from the internal and external deflection measurements. The tests in the database followed the same procedures albeit different operators. The following conclusions can be drawn: Resilient moduli determined from internal deflection measurements are higher than those from external measurements. The ratio of internal to external resilient modulus increases with increasing internal resilient modulus because of the This difference in resilient moduli depending on test procedure is important to know as the modulus determined from external deflection measurements is used in calibrating field performance based on the Long-term Pavement Performance (LTPP) of highways whereas the design agencies are moving to adopt the new Mechanical-Empirical Pavement Design Guide, which requires use of modulus based on internal deflection measurements. Whereas the difference is less than 50 % for unbound materials and subgrade soils, it is significantly higher for stiff stabilized materials. Acknowledgments This study was sponsored by the Minnesota Local Roads Research Board (LRRB), the Combustion Byproducts Recycling Consortium (CBRC), and the Recycled Materials Resource Center (RMRC). Thanks to the Minnesota Department of Transportation for collaborating with this study. The findings in this report are solely those of the authors. Endorsement by LRRB, CBRC, MnDOT, or RMRC is not implied and should not be assumed. References Applied Research Associates (ARA), 2004, Guide for Mechanistic- Empirical Design on New and Rehabilitated Pavement Structures, NCHRP project 1-37A, National Cooperative Highway Research Program, Washington, D.C. ASTM D6307, 2005, Standard Test Method for Asphalt Content of Hot-Mix Asphalt by Ignition Method, Annual Book of ASTM Standards, Vol , ASTM International, West Conshohocken, PA. Barksdale, R., Alba, G., Khosla, N., Kim, R., Lambe, P., and Rahman, M. S., 1997, Laboratory Determination of Resilient Modulus for Flexible Pavement Design, NCHRP Project 1 28, National Cooperative Highway Research Program, Washington, D.C. Bejarano, M., Heath, A., and Harvey, J., 2003, A Low-cost High-performance Alternative for Controlling a Servohydraulic System for Triaxial Resilient Modulus Apparatus, Resilient Modulus Testing for Pavement Components, ASTM STP 1437, G. Durham, W. Marr, and W. De Groff, Eds., ASTM International, West Conshohocken, PA, pp Berthouex, P. and Brown, L., 2002, Statistics for Environmental Engineers, 2nd ed., CRC Press, Boca Raton, FL. Boudreau, R. and Wang, J., 2003, Resilient Modulus Test Triaxial Cell Interaction, Resilient Modulus Testing for Pavement Components, ASTM STP 1437, G. Durham, W. Marr, and W. De Groff, Eds., ASTM International, West Conshohocken, PA, pp

8 8 GEOTECHNICAL TESTING JOURNAL Bozyurt, O., 2011, Behavior of Recycled Asphalt Pavement and Recycled Concrete Aggregate as Unbound Rd. Materials, M.S. thesis, University of Wisconsin-Madison. Madison, WI. Camargo, F., Wen, H., Edil, T., and Patton, R., 2009, Laboratory Evaluation of Sustainable Materials at MnROAD, 88th Annual Meeting, Transportation Research Board, Washington, D.C. Chadbourn, B., 2007, MN Department of Transportation Pavement Section, St. Paul, MN (personal communication). Goto, S., Tatsuoka, F., Shibuya, S., Kim, Y., and Sato, T., 1991, A Simple Gauge for Local Small Strain Measurements in the Laboratory, Soils Found., Vol. 31, No. 1, pp Janz, M. and Johansson, S.-E., 2002, The Function of Different Binding Agents in Deep Stabilization, Report 9, Swedish Deep Stabilization Research Centre, Linkoping, Sweden. Jardine, R., Symes, M., and Burland, J., 1984, The Measurement of Soil Stiffness in the Triaxial Apparatus, Geotechnique, Vol. 34, No. 3, pp Kootstra, B., 2009, Large Scale Model Experiments of Recycled Base Course Materials Stabilized with Cement Kiln Dust, M.S. thesis, University of Wisconsin-Madison, Madison, WI. MnDOT, 2005, Standard Specifications for Construction, Minnesota Department of Transportation, St. Paul, MN. Mohammad, L. N., Puppala, A. J., and Alavilli, P., 1994, Influence of Testing Procedure and LVDTs Location on Resilient Modulus of Soils, Transportation Research Record 1462, TRB, National Research Council, Washington, D.C., pp Moosazedh, J. and Witczak, M., 1981, Prediction of Subgrade Moduli for Soil that Exhibits Nonlinear Behavior, Transportation Research Record 810, TRB, National Research Council, Washington, D.C., pp NCHRP, 2004, Harmonized Test Methods for Laboratory Determination of Resilient Modulus for Flexible Pavement Design, National Cooperative Highway Research Program Research Results Digest, Transportation Research Board, Washington, D.C., Vol. 285, pp Ping, W. and Ge, L., 1996, Evaluation of Resilient Modulus of Cemented Limerock Base Materials in Florida, Transportation Research Record 1546, TRB, National Research Council, Washington, D.C., pp Ping, W., Xiong, W., and Yang, Z., 2003, Implementing Resilient Modulus Test for Design of Pavement Structures in Florida, Report FL=DOT=RMC=BC (F), Florida Department of Transportation, Tallahassee, FL. Puppala, A. J., 2008, Estimating Stiffness of Subgrade and Unbound Materials for Pavement Design, NCHRP Synthesis 382, Transportation Research Board, Washington, D.C. Sawanguriya, A., Edil, T. B., and Benson, C. H., 2009, Effect of Suction on Resilient Modulus of Compacted Fine-Grained Subgrade Soils, Transportation Research Record 2101, TRB, National Research Council, Washington, D.C., pp Tastan, E. O., Edil, T. B., Benson, C. H., and Aydilek, A. H., 2011, Stabilization of Organic Soils with Fly Ash, J. Geotech. Geoenviron. Eng., Vol. 137, No. 9, pp Tatsuoka, F., Teachavorasinskun, S., Dong, J., Kohata, Y., and Sato, T., 1994, Importance of Measuring Local Strains in Cyclic Triaxial Tests on Granular Materials, ASTM Special Technical Publication 1213, ASTM International, West Conshohocken, PA, pp

9 Erratum Erratum GTJ , An Assessment of Resilient Modulus Testing: Internal and External Deflection Measurements, Felipe Camargo, Craig Benson, and Tuncer Edil, published online September, 2012 and included in Geotechnical Testing Journal (GTJ), Volume 35, Issue 6, November, 2012, pp TABLE 1 Summary resilient modulus for base materials with and without fl y ash. Materials Fly Ash Content (%) Curing Time (d) External SRM (MPa) Internal SRM (MPa) SRM INT /SRM EXT Class 5 base RPM RSG Copyright Copyright by 2012 ASTM by ASTM Int'l (all International, rights reserved); 100 Sat Barr Jan Harbor 5 06:32:03 Drive, EST PO Box 2013C700, West Conshohocken, PA i