Minnesota Department of Transportation

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Road Research

NRRA Rigid Team

Continuous Moisture Measurement during Pavement Foundation Construction

Status: Contract Development

Project overview

Accurate and timely moisture measurement of earthwork during compaction of foundation layers is crucial to proper construction and long-term durability of the pavement structures. Since the traditional methods for measuring moisture are point specific, expensive and/or time consuming, it is desirable to explore new devices that can provide the full coverage of the spatial variation of moisture.

This project will document the current state of knowledge concerning field moisture measurement during pavement foundation construction that also includes case studies that demonstrate cost savings resulting from more effective moisture measurement. This project will also provide critical information regarding the most effective moisture measurement devices suitable for improving compaction near structures such as retaining walls and bridge abutments. Finally, this proposal will demonstrate a prototype device capable of continuously measuring moisture during pavement foundation construction.

Tasks

Task 1: Document current state of knowledge

A substantial review of literature has been carried out in preparing this proposal. In this task, the current state of knowledge related to field and laboratory methods that can measure or estimate material properties used to determine moisture content, degree of saturation and matric suction will be documented. As part of this task, several case studies that demonstrate the technical benefits and the cost savings resulting from more effective moisture monitoring will also be provided. Finally, this task will be concluded with a comprehensive and extended work plan for the smooth and timely execution of this project.

This task also consists of developing an experimental test plan to test up to ten different geomaterials. Based on the interaction with the panel, up to six geomaterials will be selected as a baseline for verification of the outcomes of this study. These materials will be preferably from the home State of the panel members for close interaction and feedback. We will sample adequate amount of materials for laboratory and smallscale studies as described below. Our current thinking is to select two fine-grained soils (CL, CH, ML or MH), two sandy materials (SW, SP, SM or SC) and two coarse-grained materials (GW, GP, GM or GC). These ranges provide a good basis for materials with different characteristics in terms of their interaction with moisture, levels of suction, levels of moduli and their use as compacted geomaterials.

Task 2: Test laboratory prototype

Initial work has been carried out to prototype the devices for laboratory testing. We anticipate that the prototype will be functional by the time that Task 1 is completed. The laboratory work will very closely follow the work that Sotelo (2012) carried out as part of NCHRP Project 10-84 to evaluate the accuracy, precision and applicability of three moisture content devices (soil density gauge, Purdue TDR, Campbell Scientific DOT 600). The laboratory testing on each material selected includes:

  • Conduction of gradation and Atterberg limits tests on soil samples.
  • Development of moisture-density, moisture-CR (using the lab prototype, moisture modulus (using Free-free- resonant column tests), degree of saturation-CR. All these tests will be carried out at five different nominal moisture contents of optimum moisture content (OMC, OMC±10% OMC and OMC±20%OMC). All tests will be carried out in duplicate to assess the repeatability of the results on the same specimens since all tests mentioned are nondestructive.
  • Preparation of small-scale (24 in. high by 18 in. diameter) specimens (at strictly controlled densities and moisture contents placed in 2 in. lifts.
  • Test the specimen with the prototype at least at five horizontal locations at three levels to determine the repeatability.
  • Compare the moisture contents measured by the prototype with those from oven drying to determine the accuracy.
  • Develop a database of all test results.
  • Conduct analysis using statistical and process control tools to develop a preliminary operational tolerance, get a sense for the overall precision and bias of the device.

Task 3: Develop and test field prototype

Concurrent with the laboratory testing, a field version of the tool will be developed. This device will not be ruggedized or professionally packaged for day-to-day use but will be modular for ease of modification.

The last three months of this task will be dedicated to field testing of the field prototype at local sites to debug the system and ensure accuracy. The goals of this activity are the following:

  • to verify the applicability of the results from small-scale and laboratory tests carried out as part of Task 2, and
  • to establish the variability of the prototype under less controlled condition to delineate the equipment variability (established in Task 2) from site variability.

Aside from the tests enumerated in Task 2, we will carry the following activities at each test bed.

  • Sample geomaterial from five points at windrow before compaction
  • Monitor the increase in density and modulus of the layer with number of passes at two points
  • Carry continuous measurement with prototype along five lines three times
  • Graphically summarize field data by mapping the spatial variation of moisture measurements
  • Test ten points at least three times with the device shortly before and after compaction along with one NDG test at each point
  • Retrieve samples for moisture content from ten points to validate the device’s results
  • Analyze field data to ensure that the two goals listed above are met

Task 4: Demonstrate prototype

Upon satisfactory testing of the protype, the device will be demonstrated to the NRRA partners at a site either at MnROAD or any other location selected by the panel. To attract a wide audience, the demonstration can be arranged concurrent with one of the annual meetings of NRRA. This demonstration will be carried out along with an extensive presentation to obtain feedback for future modifications and improvements of the prototype.

Task 5: Communicate results

Upon completion of the project, our team will provide a draft project final report summarizing the results, findings, conclusions, and recommendations of the research. The report will comply with the NRRA requirements for style and organization. The final report will be print-ready and web-publishable formats and will be accompanied by:

  1. An executive summary (5 to 10 pages);
  2. A short video demonstrating the concept, the design and the results of the prototype;
  3. An implementation plan for improving and deploying the products of the research;
  4. A draft specification for compaction of geomaterials and supporting test methods in standard AASHTO format;
  5. An informational webinar to the members of NRRA

Project team

Principal Investigator(s): Soheil Nazarian, Ph.D., P.E., D.GE, University of Texas - El Paso (UTEP), nazarian@utep.edu; Mark Baker, private consultant, bakergrd@cs.com
Project Technical Advisory Panel (TAP) - email the TAP
Contact us to join this TAP

  • Deepak Maskey, Caltrans
  • Kevin Kliethermes, FHWA
  • John Siekmeier, MnDOT 
  • Eyoab Zegeye Teshale, MnDOT

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