# Presentation: 056156

## Mechanical System VerificationLVDT Calibration

- Use NIST traceable micrometer
- Eight point calibration

-  Acceptance Criteria
-   Near zero intercept
-   R-squared > 0.99

**Notes:**
An LVDT is a device that measures the displacement or deformation of the sample during the test. 
The LVDT calibration verification procedure is straightforward.  
The LVDT is positioned in the micrometer calibrator and run through its full displacement.  
The data is checked to make sure the LVDT is linear and is measuring very close to the micrometer reading.

Shown here is a photo of a micrometer calibrator.

This procedure is documented in section IV of FHWA-RD-96-176.

## Mechanical System VerificationLoad Cell Zero

- Use strain indicator
- Measure load cell zero reading
- Used to determine if load cell has been fatigued or overstrained

-  Acceptance Criteria
-  Zero reading < 1.5 %
-   of full-scale sensitivity

**Notes:**
As the name suggests, the load cell is a device that measures the load imparted to the specimen under test.  
The load cell also controls the movement of the test device.  Simply, load cells are made up of strain gauges mounted within the load cell chassis usually in a Wheatstone Bridge formation. 

This test procedure is intended to ensure that the load cells have not been damaged.  
A strain indicator basically measures the amount of electrical resistance within the Wheatstone bridge.  
This value is then compared against the manufactures specifications.  
A load cell that does not meet this criteria should be sent back to the manufacturer for further evaluation and possible replacement.

This procedure is documented in section IV of FHWA-RD-96-176.

## Mechanical System VerificationLoad Cell Calibration Certificates

- Check laboratory documentation to determine last NIST traceable calibration

-  Acceptance Criteria
-  NIST traceable calibration
-    within one year

**Notes:**
This procedure is self-explanatory.  
The laboratory should have its load cells calibrated yearly or at least bi-annually to ensure that they are in calibration.  This procedure merely verifies that the laboratory is having its load cells calibrated by a qualified outside source.

This procedure is documented in section IV of FHWA-RD-96-176.

## Mechanical System VerificationLoad Cell Calibration Verification

- Requires NIST traceable proving rings
- Utilizes static loading
- Verifies load cell calibration
- Measures unwanted friction
- Measures unwanted bending and deflections

**Notes:**
The load cell calibration verification procedure is used to make sure that the load cells are calibrated correctly. 
A proving ring is a device that measures the load imparted by the machine.  
It is traceable to National Institute of Standards and Technology (NIST – formerly National Bureau of Standards) standards.   
A proving ring is also used for this test because it is a “specimen with known properties.”  
We know what the response of the ring should be.  And since it is a perfectly linear elastic material (unlike a real soil sample), it is repeatable. 

The photo is of the load cell calibration verification taking place in one of the FHWA LTPP contract laboratories.

This procedure is documented in section IV of FHWA-RD-96-176.

## Mechanical System Verification Load Cell Calibration Verification

- Procedure
- Apply static (ramp) load from 10 - 90% of proving ring capacity @ 10% intervals
- Register load cell/LVDT readings with data acquisition system
- Read dial gauge on proving ring

**Notes:**
This slide describes the load cell calibration procedure.  
The picture on the left is a typical loading pattern used to perform the procedure.

## Mechanical System Verification Load Cell Calibration Verification

- Acceptance Criteria
- Proving ring versus load cell value within ± 5% of each other
- Proving ring dial gauge versus LVDT reading within ± 5% of each other

**Notes:**
The proving ring dial gauge versus LVDT reading is only necessary for systems that measure deformation outside the triaxial cell. 
For systems that measure deformation on the sample, this test is not required.  
P46 requires outside LVDT measurements, however AASHTO protocols allow either outside or inside deformation measurement.

## Mechanical System VerificationDynamic Response

- Verify overall equipment ability to conduct Resilient Modulus testing
- Verify data acquisition process
- Verify data format

**Notes:**
This test is used to verify that the machine can perform in a manner that is compatible with P46 dynamic testing specifications.  
This is a very important part of the P46 Startup process.  
Again, the proving ring is used because it is a specimen with a known set of properties.  Thus the deformations obtained from the proving ring are known and can be compared with the machine produced deflections.

This procedure is documented in section IV of FHWA-RD-96-176.

## Mechanical System Verification Dynamic Response

- Procedure
- Remove dial gauge from proving ring
- Use external LVDTs or internally mounted LVDT for displacement measurements
- Apply haversine shaped load pulse (.1 seconds on, .9 seconds off)

**Notes:**
This slide details how the dynamic response is checked.  (See P46 for a definition of a haversine wave form.)   
The picture at left shows the test being performed in one of the FHWA LTPP contract laboratories.  
Note that the dial gauge is out of the proving ring and the LVDTs are measuring the deformation on the outside of the triaxial chamber.

## Procedure (continued)
Apply dynamic load from 10 - 90% of proving ring capacity @ 10% intervals	
Read deformation using data acquisition system

- Apply dynamic load from 10 - 90% of proving ring capacity @ 10% intervals
- Read deformation using data acquisition system

- Mechanical System Verification Dynamic Response

**Notes:**
Similar to the static proving ring procedure, the dynamic response check is performed by applying a dynamic haversine waveform at intervals of 10, 20, 30, 40, 50, 60, 70, 80 and 90 percent of proving ring capacity. 
The data generated is read by the data acquisition system and analyzed using computer software macros.  
Data collected includes time, load, and deformation.

## Acceptance Criteria
Generated haversine close to ideal
Deformation response close to haversine
Deformation within 5% of standard
R-square > 0.99
.002 second or less phase shift between load and deformation
Ymax/Ymin < 1.10 (10%)

- Generated haversine close to ideal
- Deformation response close to haversine
- Deformation within 5% of standard
- R-square > 0.99
- .002 second or less phase shift between load and deformation
- Ymax/Ymin < 1.10 (10%)

- Mechanical System Verification Dynamic Response

**Notes:**
The haversine waveform is checked to make sure that is close to ideal.  This is one of the most important checks of the startup process.  

Since the proving ring is a perfectly linear elastic device, the deformation of the proving ring should follow the load pulse very closely.  This is checked during this step of the procedure.  

Phase shift is the time between when the maximum load is applied and when the maximum deformation is achieved.  Again, since this is a perfect specimen, the maximum deformation should occur exactly when the maximum load occurs or slightly thereafter (due to electronic sampling issues).  Therefore the”phase shift” should be zero or very close to zero.

Ymax is the value of the LVDT that has the higher deformation and Ymin is the value of the LVDT with the lower deformation.  These values are compared to ensure that the LVDTs are in alignment.  If the reading of one of the LVDTs is substantially higher or lower than the other, there is a strong possibility that the specimen is not aligned properly and that true axial forces are not being applied (i.e. specimen is subject to bending moment).  This condition is not suitable for a uni-axial test (where dynamic load is concerned) test.  

## Dynamic sinusoidal tests
Verify overall system electronics  (phase angle measurements)
Detect misalignment problems through the use of phase angle measurements

- Verify overall system electronics  (phase angle measurements)
- Detect misalignment problems through the use of phase angle measurements

- Mechanical System VerificationPhase Angles

-   Acceptance Criteria
-  Phase angle < 2.8 degrees

**Notes:**
As discussed previously, the phase angle check ensures that the electronics are performing as advertised.  
The phase angle for the proving ring should be close to zero.  

The graph on the left is a typical loading pattern for this test procedure.  
The set-up for this check is similar to that for the dynamic response check discussed earlier.  

This procedure is documented in section IV of FHWA-RD-96-176.  
The phase angle calculation procedure is contained in Appendix D of FHWA-RD-96-176.

## Procedure
Use autonomous pressure reading device to verify pressure

- Use autonomous pressure reading device to verify pressure

- Mechanical System VerificationTriaxial Pressure Chamber

-  Acceptance Criteria
-  Gauge readings ± 2.5 % of target values
-  Hold for 10 minutes

**Notes:**
This triaxial pressure chamber check verifies that there are no leaks in the triaxial chamber and that the pressure control system can hold the pressure as specified.  
This is a very important part of the procedure.  
The value of the resilient modulus is highly dependent on the confining pressure.  
If the confining pressure system is not measuring correctly or the prescribed confining pressure cannot be maintained, errors will occur in the resilient modulus values and variability will exist from one test to another.

This procedure is documented in section IV of FHWA-RD-96-176.

## The 3-Phase Startup Process

- Verification of Electronic System
- Verification of Mechanical System
- Verification of Laboratory Ability to Conduct P46 Resilient Modulus Test

**Notes:**
Once the electronic and mechanical systems have been verified to be operating within acceptable limits, it is necessary to make sure that the laboratory can actually perform the resilient modulus test.

##  Laboratory Proficiency Testing

- Focuses on laboratory ability (personnel/equipment)
- Sample preparation
- Operator’s ability to conduct a test
- Proper sequence and magnitude of loading
- Proper data format
- Analysis of raw data to detect any discrepancies
- Investigation of within and between laboratory variability

**Notes:**
To test a laboratory’s proficiency, a resilient modulus test is performed from start to finish for subgrade and base samples.   
The auditor evaluates the performance of the laboratory personnel for adherence to the protocol guidelines, proper operation of the test equipment, and proper handling and analysis of the data.
This step brings together all of the previous experiments to determine if a laboratory is really “up to snuff.”

The photograph illustrates a technician performing the resilient modulus test.

This procedure is documented in section V of FHWA-RD-96-176.

## Laboratory Proficiency Testing

- Acceptance Criteria
- Vertical deformations within 30%
- Approval by Representative based on visual observations
- Conformance to all aspects of the protocol
- Haversine wave form close to ideal
- Deformation response reasonable
- Resilient Modulus relationship reasonable

**Notes:**
This slide shows the acceptance criteria for the proficiency test. 
Many of the criteria shown earlier for the dynamic portion of the procedure are again evident here.  

## PRESENTATION OBJECTIVES

- What is the Resilient Modulus (Mr) Startup Procedure Product Line
- Why Mr  Testing and the Startup Procedure is Important
- Development of the Mr Startup Procedure
- How to Conduct the Mr Startup Procedure
- How to Get Information on the Mr Testing and Startup Product Line

***Who Should Use the M******r****** Testing and Startup Product Line and Why***

**Notes:**
Now that we have walked through the steps in the start-up procedure for resilient modulus, it is worth mentioning who benefits from the procedure and why.

## Who Should Use the Product?

- Any organization performing resilient modulus testing
- State DOT’s
- Universities
- Consultant laboratories
- Can be used for other tests as well
- Complex modulus
- Creep compliance
- Indirect tensile testing, etc.

**Notes:**
Let’s be clear that this is a very flexible procedure and has wide-spread applications beyond merely resilient modulus testing.

## When Should Product Be Used?

- General
- Prior to starting a testing program
- Every year during production testing
- After a period of system inactivity
- Other recommendations
- Verify the operation of older machines for new applications
- When equipment is replaced
- When equipment is moved
- Whenever a suspected overload or malfunction occurs

**Notes:**
This slide is fairly self-explanatory.  The procedure should be used prior to initiating a testing program and any time during production testing when a problem arises or a suspected malfunction has occurred.

## Uncover and Avoid Problems Electronics

- Over-ranged load cell
- Inadequate filters
- Amplitude roll off: 2 Hz - 50 Hz
- Unmatched filters
- Excessive time delay (phase angle) between channels
- Filters on and off

**Notes:**
There are many reasons why the start-up procedure should be implemented.  
This and the following slides show a partial list of the problems that have been found (and therefore, avoided) by using the procedure.  
This is no joke!   
If the startup procedure was not performed, these problems most likely would have gone unnoticed.  

I cannot stress enough how important it is to perform the startup procedure prior to embarking on a resilient modulus testing program.  
A startup procedure has not been completed yet without a significant problem being discovered that would have potentially affected the test results significantly.

## Uncover And Avoid Problems Software

- Software not controlling the load adequately
- Inadequate sampling rate
- Raw data with no units
- Automatic gain control, error range too big
- Lack of gain control adjustment during testing
- Improper raw data format - command values were saved rather than the feedback values

**Notes:**
More problems. 
Look at the last one, the command (input) values were saved rather than the real test results.  
Those results would have been perfect every time!

## Uncover And Avoid Problems Mechanical

- System not fast enough to apply proper haversine loads - complete upgrade of signal conditioning and control
- Oversize servo-value
- Friction in servo-value piston
- Friction in triaxial cell seals
- Misalignment caused by improperly designed triaxial cell fixture
- Excessive deformation, up to 76% of total deformation due to bending of triaxial cell base plate

**Notes:**
And even more problems found.  
Again, the last bullet is an eye-opener.  
76% of the deformation read by the LVDTs was caused by the triaxial cell, not the sample. 
Needless to say, this would have resulted in very large errors in the test results and subsequently (potentially) very conservative pavement designs.

## Uncover And Avoid Problems  Mechanical (continued)

- Excessive deformation due to unrestrained triaxial cell
- Slippage of LVDT holders
- Lack of control of pressure transducer
- Malfunction of air pressure regulator

**Notes:**
And just when you thought there could not be any more, here are more potential pitfalls that can be discovered using the procedure.

## Benefits of Use

- Provides guidelines for standardization of test process
- Provides a benchmark performance standard for equipment
- Minimizes equipment and operator variability
- Promotes greater confidence in resilient modulus testing and resulting pavement design

**Notes:**
This slide describes the benefits of using the procedure. 
As shown on the previous slides, this procedure is worthwhile insurance against obtaining wrong test results.

## Current Status of Product

- P46 test procedure established
- Videos produced and distributed
- Startup procedure published
- Startup procedures completed
- FHWA
- Kansas
- North Carolina
- Minnesota
- University of Rhode Island
- Consultant laboratories

**Notes:**
The P46 and the startup procedure were developed by the LTPP team headed by Aramis Lopez.
The videos were produced in cooperation with the Minnesota Department of Transportation by the FHWA LTPP 
Implementation team, affectionately known as the “Dirt Squad” – Max Grogg, Keith Herbold and Don Peterson.  
The startup procedure has been rolled out at three state DOT laboratories.
North Carolina and Kansas DOTs performed the startup procedure with grants from FHWA.  
Minnesota DOT performed the procedure (currently underway February 2000) with their own resources; as did University of Rhode Island.  
The consultant laboratories mentioned were those laboratories under contract to FHWA for the LTPP program.

## PRESENTATION OBJECTIVES

- What is the Resilient Modulus (Mr) Startup Procedure Product Line
- Why Mr  Testing and the Startup Procedure is Important
- Development of the Mr Startup Procedure
- How to Conduct the Mr Startup Procedure
-  Who Should Use the Mr Startup Procedure and Why

***How to Get Information on the Mr Startup Procedure?***

**Notes:**
You are probably wondering where you can get the documentation about the resilient modulus testing and startup as well as the videos.

## Get and Use Mr Testing and Startup Procedure Product Line

- Download procedure manuals from
-    LTPP homepage at **www.tfhrc.gov**
- Order procedure manuals/videos:
- Through LTPP homepage
- Through LTPP customer service
- (Tel Number:  865-481-2967)

**Notes:**
I would encourage you to get, review and use the resilient  modulus products mentioned in this presentation.  
They contain vital information that will help you ensure that you obtain good resilient modulus test results.  

[NOTE TO SPEAKER:  Make sure you have the correct customer service number.]