KLK574 Evaluation, comparison and correlation between the Idaho IT-144 and AASHTO T-84 methods for determining the Specific Gravity and Absorption Properties of fine aggregate
ITD Research Project 252; Task Order Number UI-16-01
Principal Investigators
- Sunil Sharma
- Emad Kassem
ITD Project Manager
- Mark Wheeler
FHWA Project Advisor
- Kyle Holman
Research Problem Statement
Currently, there are two methods available for determining the Specific Gravity and Absorption properties of aggregates used for the design, testing and volumetric determination of Hot Mix Asphalt (HMA) for use in pavements. The two methods are: (1) Idaho test method IT-144, “Specific Gravity and Absorption of Fine Aggregate using Automatic Vacuum Sealing (CoreLok) Method”, and (2) AASHTO’s standard method of test T-84, “Specific Gravity and Absorption of Fine Aggregate.” Both of these methods require the accurate measurement of the volume of a piece of aggregate and the amount of water that may be absorbed by the dry aggregate.
The AASHTO T-84 method for the determination of fine aggregate specific gravity has encountered ongoing criticism due to the subjective nature of the test. This concerns the reliable determination of a condition known as “Saturated Surface Dry” (SSD), which in turn contributes to variability, especially between laboratories. This variability and the considerable time required to run the test, (15 hour soak time) has led many DOT’s, ITD included, to adopt the CoreLok method. The CoreLok system uses a vacuum chamber and specially designed polymer bags to completely seal field and laboratory samples from water during the bulk specific gravity measurements. This method is quick, reliable, portable, and has been found to provide consistent, repeatable results for compacted asphalt samples (Gmb). However, for highly absorptive aggregates, or aggregates with high rates of absorption, the CoreLok method can lead to significant errors in the calculation of Bulk Specific Gravity of Aggregates (Gsb).
The use of erroneous Gsb values, and absorption rates, for aggregates used in HMA results in errors in mix design volumetrics, especially voids in mineral aggregate (VMA) and asphalt content. The quality of mix designs is further degraded by errors in production paving test results, pay within limits calculations, and contractor pay.
To avoid these errors, there is a need to examine the CoreLok procedures for determining Gsb and absorption and then develop appropriate correlations with results determined according to AASHTO T-84.
Project Objectives
The proposed research will determine the Specific Gravity and Absorption properties of typical aggregates used in Idaho pavements according to the CoreLok and AASHTO testing procedures. The objective of the study is to develop a correlation between the two test methods with a view to improving the accuracy and consistency of reported results. This work will be accomplished according to the tasks itemized below.
Project Tasks
Task 1: Verification of Equipment and Test Procedures
The project team will familiarize themselves with the operation of the CoreLok equipment and verify its accuracy and reliability by testing standard samples. The team will review the AASHTO, ASTM and ITD standards concerning testing procedures for the device. Following this review, and with guidance from the ITD Technical Advisory Committee (ITD-TAC), an appropriate testing procedure will be selected for the project.
Task 2: Literature Review
Perform a literature review of current practice of using the CoreLok procedures for determining Gsb and absorption properties for aggregates. This review will concentrate on studies performed by state DOT’s, FHWA, and other highway agencies. The effort here will concentrate on a thorough review of published laboratory results with a view to identifying the parameters which have a significant influence on the Gsb and absorption properties. A summary of the literature review will be provided to the ITD-TAC.
Task 3: Development of experimental program
With support from ITD Materials Engineers, an experimental program will be established to collect and test sufficient aggregate samples for the development of reliable correlations for use throughout Idaho.
Task 4: Selection of Idaho Aggregates
Work with ITD Pavement Engineers to identify typical aggregates which may be suitable for this study. From this initial list, aggregate samples will be selected for Gsb and absorption testing. These samples will consist of “fresh” aggregate, as supplied by Idaho Transportation Department. The study will also evaluate the characteristics of aggregate extracted from Reclaimed Asphalt Pavements (RAP).
Task 5: Aggregate Testing
This portion of the study will determine Gsb and absorption properties for (1) fresh aggregate, (2) aggregate reclaimed using chemicals, and (3) aggregate reclaimed using ignition oven method. These results will provide a valuable information for designs which use reclaimed aggregate with fresh binder. Additionally, results may also be used to evaluate the ignition or chemical methods in successfully preparing the aggregate for reuse.
Task 6: Data Analysis and Development of Correlations
Use Multiple Linear Regression techniques to model the relationship between Idaho test method IT-144, “Specific Gravity and Absorption of Fine Aggregate using Automatic Vacuum Sealing (CoreLok) Method”, and AASHTO’s standard method of test T-84, “Specific Gravity and Absorption of Fine Aggregate.”
The research will produce best fit prediction models for Bulk Specific Gravity (Gsb) and Absorption (Abs) of fine aggregates currently used in Idaho in the production of Hot Mix Asphalt based on the CoreLok procedure, including Goodness-of-Fit (R²pred.) and predictor variable significance (p-values).
Task 7: Verification and Implementation
In this task, the research team plans to coordinate with ITD district offices (hopefully all will participate), where tests using both methods shall be conducted independently at their labs to verify the correlations developed in Task 4. Results will be compiled and communicated to ITD engineers. A conference shall be held to communicate research results and conclusion, and to prepare procedures for inclusion in the ITD Materials Manual. This will include potential modifications to the CoreLok method as a result of the proposed research.
Task 8: Prepare draft report and submit for review.
Task 9: Submit Final Report to ITD.
Project Communication Schedule
Monthly progress report (ITD form 0771)
A minimum of one project meeting each quarter with the project's Technical Oversight Committee
Needs and Requirements
- Work with ITD Pavement Engineers to identify typical aggregates which may be suitable for this study.
- Request samples of "fresh" aggregate for testing for Gsb and absorption testing at the University of Idaho.
- Request aggregate samples reclaimed from Reclaimed Asphalt Pavements (RAP) using chemical and ignition-oven methods.
- Request "fresh" aggregate samples of the original aggregate material used for the RAP.
Required Outputs/Deliverables
The required outputs and deliverables for this project will include:
- Verification of CoreLok equipment operation and the adoption of appropriate testing procedures.
- Summary of the literature review.
- Assemble a list and description of aggregates selected and delivered to Moscow, ID
- Development of experimental program.
- Results of the laboratory testing.
- Development of correlations.
- Verification and implementation of correlations.
- Prepare and submit draft report to ITD.
- Prepare and submit Final Report to ITD.
Implementation
Results of the proposed study will provide ITD engineers with an accurate assessment of the current ITD and AASHTO procedures used to determine Gsb and absorption properties of typical aggregates used in Idaho pavements through correlations ITD and AASHTO.
Expected Outcomes/Savings to ITD
Correlation of the CoreLok method with AASHTO T-84 will help assure accurate and consistent determination of Bulk Specific Gravity and Absorption of fine aggregates used in the production of HMA. Errors that result from uncorrected Specific Gravity measurements go undetected through the mix design process and cause over or under asphalted roadways. The results of this research will provide a best fit statistical model for use in determining Gsb and absorption using the CoreLok method. This will allow ITD to continue using this method with confidence, and derive such benefits as reducing the subjectivity, time, and cost of testing. Additionally, the research findings will lead to better acceptance specifications for HMA for construction, resulting in improving the overall quality of pavements which should extend the life of Idaho’s highways.
Monthly Progress Reports (ITD 771) and Task Progress Charts
Project status:
Active
Draft report:
Due April 2017
Final report:
Due June 30, 2017