LTPP Specific Pavement Studies (SPS) Materials Action Plan Final Report

Chapter 2. MAP Development

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2.1 Materials testing Needs Analysis

The numbers of required, available, and missing tests presented in this report are based on database queries. It is not always possible to accurately determine from the database if a test is required or possible to run on a layer. For example, the open graded drainage layers on SPS-1 and -2 projects are represented as treated base layers in the database because construction specifications required that they be treated with 2 percent asphalt to add stability during construction. Although they are a treated base layer, it is not possible to extract an intact core of this material because of lack of cohesion.

Thus, the amount of missing tests is a planning number that was expected to be overstated so that resources estimates would be conservative. Because the LTPP database changes as new information is acquired, the basis for the number of required tests can change due to the identification of new material layers in the pavement structure each time a needs assessment is performed.

2.2 Status of SPS Materials Data (2004)

The status of the missing SPS materials data in April 2002 and in April 2004, after 2 years of effort, is summarized in table 1.

Table 1. Status of SPS materials test data, 2002-2004.

Detailed information on these counts is contained in the

• Tabular summaries of percent missing material test data by layer type and by specific test for each SPS experiment.
• Tabular summaries of percent missing material test data by SPS experiment, by layer type, by agency, by specific SPS project, and by specific test.

As table 1 and the appendices indicate, the efforts undertaken by the LTPP program between 2002 and 2004 resulted in a significant reduction in missing SPS materials test data. The number of missing tests was reduced by 4,998 as a result of the addition of 4,060 new data sets and adjustments to the number of required tests. About one third of the materials tests were still missing in 2004-an improvement but still a significant problem.

2.3 Modifications to MS&T Plan Requirements

The FHWA took into consideration recommendations from the Materials ETG and LTPP contractors to establish the following priority material test requirements for the MAP:

• A minimum of three HMA or portland cement concrete (PCC) core examination and thickness (AC01 or PC06) tests per test section.
• A minimum of three HMA bulk specific gravity (AC02) tests per test section.
• A minimum of two PCC thermal coefficient of expansion (PC03) tests per PCC mixture.
• A minimum of three tests per material layer type for other tests.

The following tests were not included as part of the action plan:[1]

• AC05: Moisture Susceptibility-removed because little interest was expressed for test results and to minimize costs.
• AC06: Creep Compliance-removed because test is part of the AC07 test protocol.
• AC08: Field Moisture Damage-removed per Materials ETG recommendation.
• AE01: Abson Recovery-removed to minimize cost and because of limited amount of information provided.
• AE02: Penetration-removed per Materials ETG recommendation.
• AE04: Viscosity at 25 °C (77 °F)-removed per Materials ETG recommendation.
• PC05: PCC Unit Weight-only performed where PCC sampling was required or where agency agreed to proposed new and aging tests.
• PC09: Flexural Strength-removed per Materials ETG recommendation.
• SS04: Classification-removed because test is a computation based on other test results.
• SS05: Moisture-Density Relations-only performed where subgrade sampling was required or where agency agreed to proposed new tests.
• SS06: Plate Bearing Test-removed because test is impractical to perform on existing pavement structure.
• SS08: Unit Weight-only performed where subgrade sampling was required or where agency agreed to proposed new tests.
• SS09: Natural Moisture Content-only performed where subgrade sampling was required or where agency agreed to proposed new tests.
• SS10: Unconfined Compressive Strength-only performed where subgrade sampling was required or where agency agreed to proposed new tests.
• SS11: Permeability-removed to minimize costs.
• SS12: Expansion Index-removed to minimize costs.
• TB03: Resilient Modulus at 77 °F-removed per Materials ETG recommendation.
• UG05: Moisture-Density Relations-only performed where base/subbase sampling was required or where agency agreed to proposed new tests.
• UG08: Classification-removed because test is a computation based on other test results (UG01, UG02, and UG04).
• UG09: Permeability-removed to minimize costs.
• UG10: Natural Moisture Content-only performed where base/subbase sampling is required or where agency agreed to proposed new tests.

Some of these tests were still performed as part of other test protocols, ancillary to other tests, or based on agency participation. For example, classification of unbound soils and base materials (tests SS04 and UG08) are included in this list because they are not tests per se but computations based on other test results.

In general, the Materials ETG's rationale for recommending tests not be included in the plan was usually that the tests were somewhat outmoded and were not likely to provide valuable information in the future.

One or more layers/materials on the following SPS projects were not included as part of the 2004 MAP because they had already been removed or because the project site was out of study and not considered for further testing:

• Arizona SPS-6 project.
• Colorado SPS-5 project.
• Kansas SPS-1 project.
• Michigan SPS-6 project.
• Mississippi SPS-5 project.
• Montana SPS-5 project.
• Nebraska SPS-1 project.
• Nevada SPS-2 project.
• New Jersey SPS-8 project.
• Tennessee SPS-6 project.

Material layers from these sites were not included in the assessment of data needs.

Another assessment of data gaps and needs was performed in 2004 using the new MAP priority test guidelines and the contents of the May 2004 national upload of the LTPP database. Table 2 contains counts by test type and type of material to satisfy the priority test requirements developed for the MAP. Based on the layer structure contained in the database at this time, approximately 12,650 tests were identified as necessary to fill material data gaps. Differences between data needs in table 2 and those reported in table 1 are due to changes in pavement structure data in the database and the more explicit test section-based requirements for the MAP.

Table 2. Required tests by test type to fill data gaps.

AC = Asphalt concrete
PCC = Portland cement concrete
TB-AC = Asphalt concrete treated base
TB-PCC = Portland cement concrete treated base
TB = Treated base

2.4 NEW AND Aging Tests

While addressing the need to resolve material data gaps based on previous criteria, new and aging tests were added to improve materials structure information with little added cost. Aging tests are repeats of previous tests to capture material property aging effects.

New tests included the following:

• Dynamic Cone Penetrometer (DCP)-for unbound layers (also replaced SS06: Plate Bearing Test); three tests per project.
• Specific Gravity of Unbound Materials-for unbound layers; three tests per unique unbound layer.
• Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) (including Direct Tension Test on Binder)-for HMA layers; three tests per HMA layer and mix.
• Petrography-for PCC layers; although originally approved, this test was later cancelled to reduce cost.

Aging tests were only to be performed on HMA or PCC layers, not on material from unbound base, subbase, or subgrade layers nor on treated bases or subbases. They included the following:

• Bulk and Maximum Specific Gravity (AC02 and AC03)-for HMA layers; three tests per HMA layer and mix.
• DSR and BBR (including Direct Tension Test on Binder)-for HMA layers; three tests per HMA layer and mix.
• Resilient Modulus (AC07)-for HMA layers; three tests per HMA layer and mix.
• Compressive, Split Tensile, and Static Modulus of Elasticity (PC01, PC02, and PC04)-for PCC layers; three tests per PCC layer mix type.

Table 3 outlines the 2004 sampling requirements for the new and aging tests by type of SPS experiment.

Table 3. Sampling requirements for new and aging tests.

^a Does not include projects eliminated from the action plan. ^b There are 19 SPS-8 projects; 4 of them have both AC and PCC test sections.

Bulk samples of the unbound base, subbase, and subgrade materials to run the specific gravity test were designated to be obtained from the 12-inch core locations identified in table 3. Where the proper drill rig to cut 12-inch holes was not available, a saw-cut opening was requested to access the underlying unbound materials.

[1] The first two letters of the test designation indicate the material type. AC: asphalt concrete, AE: extracted asphalt cement, PC: portland cement concrete, SS: subgrade soil, TB: treated base, UG: unbound granular base.