High Performance Concrete Pavements
CHAPTER 28. Ohio 4 (US 35, Jamestown)
The Ohio Research Institute for Transportation and the Environment at the Department of Civil Engineering at Ohio University, in conjunction with the Ohio Department of Transportation, have conducted extensive pavement research activities during the past decade. As a part of the TE-30 program, this study has undertaken a comparative evaluation of the available nondestructive test devices for measuring the support of subgrade and aggregate base layers of pavement sections. The study considers the means and results of data measurements of various testing devices, including their application, and ease of use. The test section selected for this project is located on US 35 in Jamestown, Ohio (see Figure 83).
Figure 83. Location of OH 4 project.
Variability in pavement support resulting from variations in subgrade and base layer support values result in significant variation in pavement performance. Deficiencies relative to design assumptions result in reduced pavement performance. Conventional laboratory testing has not been effective in capturing field variation. The use of nondestructive testing methods to assess pavement conditions and to predict pavement performance depends upon the quality and reliability of the data obtained.
The principal objective of the study is to measure the structural characteristics of the subgrade and base layers on a section of US 35 with various NDT devices during construction, and compare the output from the devices in the context of assessing structural conditions and variability. Nondestructive testing was performed using a nuclear density gauge, the Humboldt Stiffness Gauge, the German plate load device, a falling weight deflectometer, and a dynamic cone penetrometer.
Project Design and Layout
A 609.6-m (2000-ft) test section was selected in the eastbound lanes of a 8.5-km (5.3-mi) construction project on US 35 in Jamestown, Ohio. The test location was judged to have relatively uniform topographical and subsurface soil conditions. The pavement consists of a four-lane divided highway with two 3.6-m (12-ft) lanes, a 3-m (10-ft) outside shoulder and a 1.8-m (6-ft) inside shoulder. The pavement cross section consists of 228.6-mm (9-in.) JRCP, a 101.6-mm (4-in.) unstabilized drainable base, and a 152.4-mm (6-in.) dense-graded aggregate base, all over a prepared subgrade.
Subgrade samples were collected and identified as silty clay (AASHTO Classification A-6) with a liquid limit of 22.8 percent, a plastic limit of 16.7 percent, and a plasticity index of 6.1 percent. Laboratory resilient modulus tests were conducted in accordance with SHRP Protocol P-46.
State Monitoring Activities
Initial moisture and density data were collected along the centerline and right wheelpath of the eastbound driving lane at 15.2-m (50-ft) intervals with a nuclear density gauge. Other nondestructive testing was also typically conducted at intervals of 15.2 m (50 ft), except for the German plate load test, whose testing frequency was increased to 30.5 (100 ft) because of the time required to conduct each test.
Laboratory resilient modulus testing was performed on material samples from the project materials to provide a comparison of results. Tests were performed at several confining pressure levels including 20.7, 34.5, 68.9, 103.4, and 137.9 kPa (3, 5, 10, 15, and 20 lbf/in2). The moisture content of the materials is also known to affect the results.
Overall results indicated that each device has a useful function in evaluating subgrade and base uniformity conditions. The laboratory resilient modulus test is limited to materials sampled at specific designated locations. Additionally, the results are very much a function of test conditions. The level of confining pressure used during the testing was found to have an effect on the computed modulus values, as described by Sargand, Edwards, and Salimath (2001).
The nuclear density gauge is limited to a layer thickness measurement of 304.8 mm (12 in.), and greatly affected by nonuniformity within the layers tested. It is a quick means of controlling the uniformity of material density during construction. The density measurements recorded can be correlated with material stiffness.
The DCP is a quick automated field test method for evaluating the in situ stiffness of layers in a highway pavement structure. It measures the strength and stiffness of subgrade and unstabilized base layers. The DCP's ability to penetrate into underlying layers and accurately locate zones of weakness represent its greatest advantage over other tests considered. The automated device includes software for storing and reporting the collected data.
The Humboldt Gauge measures stiffness of the upper 152.4 mm (6 in.) of material by electrical impedance. In this respect, it is quite different from the other NDT devices considered in this study, as the other devices measure the composite response of the upper layer measured, and any supporting layers beneath. The Humboldt gauge was considered effective for monitoring the integrity of individual material layers as they are being placed.
The remaining devices identified significant pavement support variation along the length of the test. Because the Humboldt Gauge only measures to a depth of 152.4 mm (6 in.), its variation represented is much smaller than that indicated by the other devices. Both stiffness and calculated moduli values were evaluated for each device, with sample results provided in Table 44.
Table 44. Stiffness and Modulus Sample Results from OH 4 Testing
|Nondestructive Test||Stiffness, lbf/in.||Modulus, lbf/in2|
|Subgrade (15 stations)|
|FWD, Large load||249,703||22,610|
|FWD, Small load||210,785||19,090|
|German Plate||1st Cycle|
|Composite Base (16 stations)|
|FWD, Large load||252,747||36,220|
|FWD, Small load||257,114||40,970|
|German Plate||1st Cycle|
|FWD = falling weight deflectometer|
The large load FWD represented 2948.3- to 4082.3-kg (6500- to 9000-lb) loads, while the small load represented 1587.6- to 2041.2-kg (3500- to 4500-lb) loads.
The FWD and the German plate load test are considered effective for measuring the total composite stiffness of the in situ pavement structures. Comparisons of the devices, and the Humboldt Gauge, are difficult since each generates load differently, to a different depth, and uses different equations to convert surface deflections to layer modulus. The dynamic loading applied by the FWD typically results in higher material stiffness than static loads used in the German plate test. The Humboldt Gauge produces small excitations, which limits its depth of effectiveness.
The FWD has a definite advantage over the plate load testing because of its speed of testing. The plate load test is much more labor intensive and requires more test time at a single location. The DCP is considered useful for identifying and locating the cause(s) of low stiffness identified with FWD results, which will likely cause premature failure within a pavement structure.
Points of Contact
Ohio Department of Transportation
Office of Pavement Engineering
1980 West Broad Street
Columbus, OH 43223
Ohio Research Institute for Transportation and the Environment
Department of Civil and Environmental Engineering
Athens, OH 45701
Sargand, S. M., W. F. Edwards, and S. Salimath. 2001. Evaluation of Soil Stiffness Via Non-destructive Testing. Final Report. Ohio Department of Transportation, Columbus.