106.3.2.64 TM-64, Void Detection and Undersealing Verification Testing of Concrete Pavement with a Falling Weight Deflectometer: Difference between revisions

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This method determines pavement deflection when undersealing, in accordance with the specifications. This test is normally performed by the contractor, using contractor equipment, in the presence of the MoDOT engineer.
==106.3.2.64.1 Apparatus==
 
A falling weight deflectometer (FWD) shall be employed for performing void detection testing.  The FWD shall have:


==106.3.2.64.1 Apparatus==
:1) A guided falling weight system capable of generating a peak force of 9000 lbf,
:2) A 12 in. diameter load plate capable of uniformly distributing the falling weight impact force on the pavement surface,
:3) A deflection sensor in the center of the load plate,
:4) A load cell to measure the applied load of each impact,
:5) Data processing and storage equipment to accurately record the peak load with a resolution of 50 lbf or less and peak deflection with a resolution of 0.04 mils or less,
:6) A distance measuring instrument (DMI) or global positioning system (GPS) to record test locations.


1) Gauges: Four gauges on two gauge mounts, two gauges per mount, that are capable of detecting slab movement of 0.001 in.
The FWD shall have a reference calibration of the load and measurement systems performed in accordance with the manufacturer’s recommendations within one year prior to testing on the MoDOT project.


2) Test Vehicle: Vehicle having a dual-tire single axle with an 18,000 pound single axle load.
The FWD shall have a relative calibration of the deflection sensors performed in accordance with the manufacturer’s recommendations within one month prior to testing on the MoDOT project.
[[image:106.3.2.64.1.jpg|center|500px|thumb|<Center>'''Falling Weight Deflectometer'''</center>]]


==106.3.2.64.2 Procedure==
==106.3.2.64.2 Procedure==


Position one set of gauges as shown in Fig. 106.3.2.64.
In this test method deflection testing at concrete corner slab joints and cracks serves one of the following two purposes:
 
:* To identify voids under slabs that require undersealing
:* To verify slabs have been successfully undersealed.
 
<u>'''Void Detection'''</u>
 
Deflection testing shall occur when the ambient temperature is ≤ 70º F.  The following steps shall be used for void identification under a slab:
 
:'''Step 1.''' The load plate shall be placed as close as possible to the outside corner of the driving lane approach slab without passing over the joint or crack edge.
[[image:106.3.2.64.2 load.jpg|center|600px|thumb|<Center>'''Load Plate'''</center>]]
 
:'''Step 2.''' An approximate 9000 lbf shall be applied to the load plate five consecutive times.  The first two drops will seat the plate and their deflections will not be counted.  The final three drops will be averaged to determine the deflection under the load plate.


Zero both gauges to the pavement surface with no load on the slab on either side of the joint or crack.
[[image:106.3.2.64.2 falling.jpg|center|500px|thumb|<Center>'''Falling Weights'''</center>]]


Slowly move the test vehicle into position and stop it when the center of the test axle is one foot behind the joint and the outside test wheel is one foot from the pavement edge, as shown in Fig. 106.3.2.64.
:'''Step 3.''' The load plate shall then be moved as close as possible to the outside corner of the driving lane leave slab without passing over the joint or crack edge.


[[image:106.7.64.gif|center|775px|thumb|<center>'''Fig. 106.3.2.64'''</center>]]
:'''Step 4.''' The test will proceed with load drops as in Step 2.
[[image:106.3.2.64.2.jpg|center|800px]]


Read both gauges and record the results.
:'''Step 5.''' The normalized deflection (Δ) for each drop shall be calculated using the following equation:


Slowly move the vehicle across the joint and stop it when the center of the test axle is one foot past the joint, as shown in Fig. 106.3.2.64.
::::Δ = (D)(9000)/(P)


Read both gauges and record the results.
:where, 
:::D = actual peak deflection (mils)
:::P = actual peak load (lbf)


Repeat this procedure at every transverse joint and designated crack or pavement repair patch.
:'''Step 6.''' The differential deflection (DD) shall be calculated using the following equation:


A MoDOT inspector will be responsible for reading and recording the gauge results.
::::DD = Δ<sub>L</sub> - Δ<sub>A</sub>


==106.3.2.64.3 Deflection Testing Before Undersealing==
:where,
:::Δ<sub>L</sub>  = average of three normalized deflections on leave side (mils)
:::Δ<sub>A</sub>  = average of three normalized deflections on approach side (mils)


When required by contract, the contractor shall test each joint, crack and pavement repair patch in accordance with this test procedure.
:'''Step 7.''' ''The slabs at the test location shall be undersealed if one of the following occurs:''


Any joint, crack or pavement repair patch that has a joint efficiency of 65 percent or more, and (a) a loaded slab corner deflection of 0.0175 in. or more, or (b) which ejects water when loaded or (c) which displays indications of past pumping, shall be undersealed.
:::a. Δ<sub>L</sub> ≥ 20 mils
:::b. DD ≥ 15 mils


When directed by the engineer, any joint or crack that has a joint efficiency of 64 percent or less and any of the conditions required for undersealing as described above shall be removed and repaired in accordance with [http://www.modot.mo.gov/business/standards_and_specs/Sec0613.pdf Sec 613].


To determine action to be taken, the highest loaded slab corner deflection and the lowest joint efficiency at each joint or crack shall be used. Joints or cracks with deflection measurements of 0.005 or less on both sides of the joint or crack will be considered to have a joint efficiency of 65 percent or better, regardless what the calculated joint efficiency is. Joint efficiency (JE) will be calculated as follows:
<u>'''Undersealing Verification'''</u>


::%JE = 100 x (Unloaded Slab Corner Deflection) / (Loaded Slab Corner Deflection)
The following steps shall be used for verification of successful undersealing after the undersealing material has reached its recommended set time:


==106.3.2.64.4 Deflection Testing After Undersealing==
:'''Step 1.''' Steps 1 through 6 from Void Detection shall be conducted.


Twenty-four or more hours after grouting and prior to acceptance, each stabilized joint, crack and pavement repair patch shall be re-tested for deflection. Slabs that deflect 0.0175 in. or more shall be re-grouted and re-tested as directed. Any slab that continues to show movement in excess of that specified after two properly performed groutings may be accepted or the slab may be removed and replaced as directed by the engineer.
:'''Step 2.''' ''The slabs at the test location shall be considered successfully undersealed if one of the following occurs:''


:::a. Δ<sub>L</sub> ≤ 15 mils
:::b. DD ≤ 10 mils




[[Category:106.3.2 Material Inspection Test Methods]]
[[Category:106.3.2 Material Inspection Test Methods]]

Latest revision as of 11:54, 8 October 2013

106.3.2.64.1 Apparatus

A falling weight deflectometer (FWD) shall be employed for performing void detection testing. The FWD shall have:

1) A guided falling weight system capable of generating a peak force of 9000 lbf,
2) A 12 in. diameter load plate capable of uniformly distributing the falling weight impact force on the pavement surface,
3) A deflection sensor in the center of the load plate,
4) A load cell to measure the applied load of each impact,
5) Data processing and storage equipment to accurately record the peak load with a resolution of 50 lbf or less and peak deflection with a resolution of 0.04 mils or less,
6) A distance measuring instrument (DMI) or global positioning system (GPS) to record test locations.

The FWD shall have a reference calibration of the load and measurement systems performed in accordance with the manufacturer’s recommendations within one year prior to testing on the MoDOT project.

The FWD shall have a relative calibration of the deflection sensors performed in accordance with the manufacturer’s recommendations within one month prior to testing on the MoDOT project.

Falling Weight Deflectometer

106.3.2.64.2 Procedure

In this test method deflection testing at concrete corner slab joints and cracks serves one of the following two purposes:

  • To identify voids under slabs that require undersealing
  • To verify slabs have been successfully undersealed.

Void Detection

Deflection testing shall occur when the ambient temperature is ≤ 70º F. The following steps shall be used for void identification under a slab:

Step 1. The load plate shall be placed as close as possible to the outside corner of the driving lane approach slab without passing over the joint or crack edge.
Load Plate
Step 2. An approximate 9000 lbf shall be applied to the load plate five consecutive times. The first two drops will seat the plate and their deflections will not be counted. The final three drops will be averaged to determine the deflection under the load plate.
Falling Weights
Step 3. The load plate shall then be moved as close as possible to the outside corner of the driving lane leave slab without passing over the joint or crack edge.
Step 4. The test will proceed with load drops as in Step 2.
Step 5. The normalized deflection (Δ) for each drop shall be calculated using the following equation:
Δ = (D)(9000)/(P)
where,
D = actual peak deflection (mils)
P = actual peak load (lbf)
Step 6. The differential deflection (DD) shall be calculated using the following equation:
DD = ΔL - ΔA
where,
ΔL = average of three normalized deflections on leave side (mils)
ΔA = average of three normalized deflections on approach side (mils)
Step 7. The slabs at the test location shall be undersealed if one of the following occurs:
a. ΔL ≥ 20 mils
b. DD ≥ 15 mils


Undersealing Verification

The following steps shall be used for verification of successful undersealing after the undersealing material has reached its recommended set time:

Step 1. Steps 1 through 6 from Void Detection shall be conducted.
Step 2. The slabs at the test location shall be considered successfully undersealed if one of the following occurs:
a. ΔL ≤ 15 mils
b. DD ≤ 10 mils
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