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August 2017 LBR Technician Release 10, Module 4‐1

Florida Department of

TRANSPORTATION

Limerock Bearing Ratio Technician Training Course

Module 4: Compaction

- This section will cover the compaction of materials for LBR testing. Thephysical compaction of LBR samples is identical to AASHTO T 180 section 11 (in method D), but there are exceptions/differences outlined in FM 1-T 180 section 7 that are specific to compacting of LBR samples.

- This section will discuss the differences between modified Proctor compaction (per AASHTO T 180) and LBR compaction (per FM 1-T 180). It will be assumed technician are already familiar with AASHTO T 180 compaction, therefore an in depth discussion of that procedure will not be covered.

Module 4- Compaction

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LBR Technician Course

August 2017



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Compaction: Equipment Differences

AASHTO T 180 section 11 (method D):• Follow section 9, method C compaction

• 18” drop height, 10 lb. rammer

• 5 lifts, 56 blows/lift

FM 1‐T 180 section 7: • Mold meeting AASHTO T 180 section 3.1.2 except:

• Height: 6.00 ± 0.026 inches (152.40 ± 0.70 mm)

• Volume: 0.0982 ± 0.001 ft³ (0.00278 ± 0.001 m³)

• Baseplate: 28 open holes, 0.06 ± 0.03 inches (1.6 ± 0.8 mm) in diameter

• Produces a sample volume within 1.2% of 0.0750 ft³

- All compaction equipment is the same with the exceptions noted in FM 1-T 180 section 7.

- Method D requires a 6 inch diameter mold but instead of the standard 4.584 inch height, FM 1-T 180 section 7 requires a 6 inch tall mold and uses a spacer disk to reduce the sample height. The purpose of this is to give a height of mold above the top of the soil when being soaked and penetrating so that the soil is not expressed out the top of the mold due to swelling or upward pushing of material by the piston. It is also designed to retain the surcharge weights and spacer disks within the appropriate areas of the mold/sample.

- The baseplate must have 28 holes to allow for free drainage of water from the soil during the draining and penetration portions of the test. Modified Proctor molds are standard with a solid baseplate.


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FM 1‐T 180 section 7: • Spacer Disk:

• 5.938 ± 0.031 inches (150.8 ± 0.8 mm) diameter• 1.41 ± 0.026 inches (35.80 ± 0.70 mm) height• Plane to 0.005 inches (0.13 mm)

AASHTO T 180 ‐ Note 2:• Using alternative mold assemblies

• CBR molds are acceptable

• Must meet all requirements

• Must produce the same sample volume

- Spacer disk is used to create that space above the top of the soil and the top of the mold once mold is inverted.

- Spacer disk acts as the temporary baseplate of the mold and therefore must meet the same planeness requirements as the modified Proctor baseplates.

- Note 2 of AASHTO T 180 applies to allow the use of alternative mold assemblies. CBR molds are allowed as long as they produce a sample with the dimensions and volume required by this method (FM 1-T 180).


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FM 1‐T 180 section 7:

• Compaction Rammer:• Meets the requirements of AASHTO T 180 sections 3.2.1 or 3.2.2

• For mechanical rammers:• Sector faced rammer is required:

• Length of 2.90 ± 0.02 inches (73.70 ± 0.51 mm)

• New sector face shall have area of 3.14 ± 0.03 in² (2025.80 ± 19.2 mm²)

• Used sector face shall have area greater than

3.09 in² (1996.6 mm²)

- The physical compaction rammers (manual and automatic) are identical to those used in the AASHTO T 180 method. Section 3.2.3 of AASHTO T 180 allows the use of rammer faces other than circular as long as they meet the area requirements of a 50.8 mm circular faced rammer. The sector (pie) faced rammer used for LBR meets those requirements as long as the length is in tolerance.

- The most likely wear spot on the rammer face is on the center of the back portion (curved edge of the face). Measurements for length should be taken at various spots on the face including this wear spot.


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Compaction of Soaked PortionsFM 1‐T 180 section 7.3:

• Begin approximately 3% below optimum moisture

• Each specimen shall increase in moisture by no greater than 1.5%

• Compacted points shall represent points below, at or near, and above the optimum moisture content

FM 1‐T 180 section 7.4:• Compact specimens in accordance with AASHTO T 180 method D

FM 1‐T 180 section 6:• Ensure each of the 5 layers is 1.1 ± 0.5 inches in height after compacting

- The purpose of starting 3% below optimum is so there are two points below the optimum moisture. This defines the left side of the curve.

- Ideally each moisture points should be about 1% in difference. In the event the moisture starts several percent below optimum the technician can elect to go 1.5% between points, however if they should be consistent with whichever method they use. All points should have approximately equal moisture between them.

- AASHTO T 180 method D is the method to follow for compaction. FM 1-T 180 directly references this method for compaction.


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Compaction Review

•Apply Note 6:• Obtain moisture content sample from mixing bowl• Perform moisture content in accordance with AASHTO T 265

•Mold tare mass:• May be obtained with OR without spacer disk.

• If spacer disk is inserted the post‐compaction mass must be obtained after trimming but before inverting the specimen (preferred method).

• If spacer disk is not inserted the post‐compaction mass must be obtained after the specimen is inverted (FM 5‐515 section 4.1).

- Note 6: “When developing a compaction curve for free-draining soils, such as uniform sands and gravels, where seepage occurs at the bottom of the mold and base plate, taking a representative moisture content sample from the mixing bowl may be preferred to determine the amount of moisture available for compaction.”

- Because we are not removing the sample from the mold after compaction we CANNOT take a moisture sample from the center of the pill. Therefore we MUST apply Note 6 in all case for LBR samples. This should be accounted for when preparing the sample. If the technician needs a 12 lb. sample to compact they should add an extra 1 lb (543.6g) so material is available for a moisture content without impacting the amount of material available for compaction.-

- Spacer Disk: Determining the mass of the soil in the mold should be done so that the equipment used to obtain the tare mass is identical to the equipment used to obtain the soil mass. In other words, if the mold tare weight is taken with the spacer disk in the mold then the soil mass should be taken with the spacer disk still in the mold (i.e. after trimming the soil but before inverting the sample and removing the spacer disk). If the mold tare weight was taken without the spacer disk the soil mass should be taken after inverting and removing the spacer disk.

- The second method is not preferred because inverting the sample and removing the spacer disk is part of the FM 5-515 LBR method. The soil mass should be obtained during the FM 1-T 180 modified Proctor method, which ends before the sample is inverted. Therefore the preferred method is to obtain the tare weight with the spacer disk in place.


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Compaction Review• Attach collar and lock into base frame.

• Compact 5 equal lifts, 56 uniformly distributed blows per lift.

• Remove mold from frame, remove collar.

• Trim soil with straightedge and patch holes with smaller sized material (minus #4 size recommended).

• Weigh sample (if tare weight was obtained with spacer disk in mold).

Procedure should be repeated for remaining prepared portions. Produce a minimum of 4 specimen (for non‐cohesive well drained soils, A‐1, A‐3, A‐2‐4 non‐plastic) representing two points below optimum moisture, one at optimum and one past optimum.

- This procedure is identical to that of AASHTO T 180 except when compacting non-cohesive well drained soils (A-1, A-3, A-2-4 non-plastic). It is advised to have 5 points minimum on your compaction curve per AASHTO T 180, however for these non-cohesive Florida soil types studies have shown 4 points are acceptable. If you start 3% below optimum then you will end one point above optimum. The third point should be at optimum moisture. If the curve is drawn such that the optimum moisture is not at a point the technician should review the data and the curve and determine if an additional point should be compacted at the optimum moisture (to verify the curve).


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Compaction Review

Compaction results should be recorded in the appropriate fields

of a compaction worksheet.

Highlighted fields should be obtained during physical testing.

- Yellow fields are hand recorded data completed during physical testing.- White fields are calculated data performed once all physical testing is

completed and hand recorded data obtained.


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Compaction Review

Moisture Content:

• Maximum particle size 3/4 inch for base materials, minimum sample size 500g.

• Maximum particle size #4 sieve (4.75 mm) for subgrade materials, minimum sample size 100g.

• Dry overnight (15 hr. minimum) at 230 ± 9oF (110 ± 5oC) or until constant mass.

- Moisture content performed in accordance with AASHTO T 265, as required in the AASHTO T 180 and FM 1-T 180 methods.

- Minimum sample size can change based on the maximum particle size. If performing LBR on a sand/clay material with a maximum particle size of a No. 4 sieve (4.75 mm) the required minimum sample size is 100 g.

- Refer to the table in section 5.1 of AASHTO T-265 for required minimum moisture sample size.


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Calculation Review

10

101

25.47

17.65

7.82

C5

584.25

75.26

536.26

- Rows in Yellow are the fields that will have data recorded into them. White rows are fields that will be calculated.

- The Wet Mass is the amount of water and soil in the mold. Subtract the Mold Mass (after tare weight) from the Wet Mass & Mold (soil and mold mass) obtained immediately after compaction.


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Calculation Review

C5

584.25

75.26

536.26

10

101

25.47

17.65

7.82


- The Wet Unit Mass is the weight of the wet soil divided by the volume it occupies. Because the mold is within the tolerances outlined in section 7 of FM 1-T 180 we can use the assumed mold volume of 0.0750 ft3. The technician should use the actual mold volume for each mold determined in accordance with AASHTO T 19 (per AASHTO T 180 section 3.1.2).


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August 2017



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Calculation Review

10

101

25.47

17.65

7.82

104.26

C5584.25

75.26

536.26


- In order to determine the Dry Unit Mass, the moisture content must be known. The Water Added (%) field in the top table is an estimated amount of moisture in the specimen. The actual must be calculated in accordance with AASHTO T 265.

- The Water Mass is the amount of water removed from the soil during oven drying. It is the Dry Soil plus Can Mass (tare) minus the Wet Soil plus Can masses.


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August 2017



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Calculation Review

10

101

25.47

17.65

7.82

104.26

C5584.25

75.26

536.26


- The Dry Soil Mass is the Dry Soil & Can mass minus the Can Mass. Use the same mass determination for each Moisture Content, that is, if you had a lid on for the tare it must be on for the final dry soil mass. If you didn’t have a lid on it must be removed before final mass is obtained.


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August 2017



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Calculation Review

10

101

25.47

17.65

7.82

C5584.25

75.26

536.26

Water Added = 10%


- The Moisture Content is the Water Mass divided by the Dry Soil Mass converted to a percent.

- Notice the value is not exactly 10% (Water Added (%) from top table). This is the ACTUAL moisture content including hydroscopic moisture.


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August 2017



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Calculation Review

10

101

25.47

17.65

7.82

C5

584.25

75.26

536.26

Wet Unit MassMoisture Content + 100

X 100 = Dry Unit Mass

104.26(10.41 + 100)


- The Dry Unit Mass is the Wet Unit Mass with the moisture content removed, calculated as shown in the equation.

- The Dry Unit Mass is the reported value for Proctor testing.- All Proctor results are reported to the tenths place. Rounding should

not be performed until the final values are determined. Rounding early can throw off your results.


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Maximum Density: 103.1 lb/ft3

Optimum Moisture: 12.4%

Moisture/Density Curve Review

93.0

94.0

95.0

96.0

97.0

98.0

99.0

100.0

101.0

102.0

103.0

104.0

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0

Moisture (%)

Dry Unit Mass (lbs/ft3)

- The table shows all the data for five points on a compaction curve. Each point is plotted Dry Unit Mass vs. Moisture Content and a smooth curve is drawn through the points. The curve can be computer aided or hand drawn. If using a computer aided curve the technician should observe the curve and identify if it is the best curve to represent the data. If not, the technician should hand draw a curve free-hand or with the use of a French curve.

- The Optimum Moisture Content is where the curve peaks at the Maximum Dry Unit Mass (Density).

- For the data in the table the maximum density is not a physical point but on the curve close to the point. Points do not always exactly represent the maximum density. The technician should observe how close the curve maximum is to the nearest recorded point. Additional points may be needed to better define the curve.


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August 2017



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Compaction Review

Retain compacted specimens for immediate continuation in FM 5‐515, Limerock Bearing Ratio.

Reporting:

•Maximum Density: tenths place (103.1 lb/ft³)

•Optimum Moisture: tenths place (12.4 %)

- This ends the compaction portion per FM 1-T 180. For LBR testing the technician should immediately continue on to the FM 5-515 method (or hand the specimen(s) off to the technician who will be performing that test. It is critical to immediately continue and not wait as drying out of the compacted specimen can effect the LBR result.

- All compaction results should be reported to the tenths place.


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August 2017



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ANY QUESTIONS?

LBR Technician Course Module 4- Compaction

4-18August 2017

limerock bearing ratio technician training course js.pdflimerock bearing ratio technician training...

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