Strength gain of lime stabilized plastic clays used in Pavements.

The role of QC Procedures.

April 2015 Alejandro Fernandez Moreira

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Contents of the presentation

1. Introduction to Lime Stabilization.

2. North Tarrant Expressway project.

3. The role of Lime Stabilized Soil in Pavement Design.

4. The Mix Design.

5. The Specification or QA/QC Protocol.

6. The Quality Control.

7. Conclusions.

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1. Introduction to Lime Stabilization

• The lime stabilization phenomena comprises complex physical processes and chemical reactions.

• There are three key concerns when lime stabilization is applied in a construction project:

a) A correct mix design completed at design phase.

b) A concise specification to follow for construction.

c) An effective quality control during the works.

• This presentation deals mainly with points b) and c).

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2. The role of LSS in Pavement Design.

2. North Tarrant Expressway project

12 mi (20Km)

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3. The role of LSS in Pavement Design.

• Lime Stabilized Soil (LSS) is usually considered as a subbase layer underneath the Granular Base.

• Pavement Design at the North Tarrant Expressway project followed AASHTO93 guidelines.

• Pavement Design also complies with TxDOT Standards regarding “Potential Vertical Rise” (PVR).

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3. The role of LSS in Pavement Design.

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4. The Mix Design.

• The mix design typically comprises two phases:

1. Testing in the natural soil.

2. Testing in lime stabilized soil with tentative lime contents.

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5. The specification or QA/QC Protocol.

• Definition of Specification:

• “A detailed, exact statement of particulars, especially a

statement prescribing materials, dimensions, and quality of work for something to be built, installed, or manufactured”.

• TxDOT publication: “Standard Specifications for Construction and Maintenance of Highways, Streets and Bridges. 2004”.

• Item 260. LIME TREATMENT (ROAD-MIXED) specifies the lime stabilization procedure.

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• Item 260 is a good starting point but not sufficient due to the following reasons:

• It has been created without considering that the Lime Stabilized Soil (LSS) can contribute to the bearing capacity of the pavement to a minimum degree.

• Does not assess the assumptions considered in the design for vertical movements of the natural subgrade.

• Does not consider secondary chemical reactions like the formation of ettringite and thaumasite.

5. The specification or QA/QC Protocol.

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• The Specification can follow the same structure that Item 260:

1. Description.

2. Materials.

3. Equipment.

4. Construction.

5. Measurement.

6. Payment.

• An additional key section should be added: “Quality Control / Quality Assurance”.

5. The specification or QA/QC Protocol.

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6. The Quality control

• As a minimum the following tests shall be part of the Lime stabilization Quality Plan.

Element Test Frequency

Soluble sulfates See Table 1

1 per 500 linear ft in cuttings.

At the criterium of the geotechnical

manager in the fills

Plasticity Index See Table 1 1 per lot

Passing 75 µm sieve See Table 1 1 per lot

Lime See Item 260 Chemical analysis for each source

Water See Item 260 Approved source

Depth of lime treatment

Tex-140-E Digging test holes and

spraying a non-hazardous color

sensitive indicator solution on

the soil exposed

Spot check at the Engineer criteria

(QLL)

Moisture Tex-103-E 1 per lot

Density Tex-115-E 3 per lot

Gradation See Item 260 1 per lot

Surface level See Item 260 1 control every 50ft

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• In the Continual Testing the lots would be further sub-divided into 3 sublots for UCS testing.

• UCS testing:

• Samples should be collected directly behind the rotary mixer and transported to the lab in a seal bag.

• The material should be compacted following Tex-113-e.

6. The Quality control

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• The specimen should be placed in the oven during 7 days at 104ºF (40ºC).

• The specimen is then placed in a porous stone for capillarity soak during 24h.

• Unconfined compressive strength is then carried out.

6. The Quality control

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Compaction of the

material following

Tex-113-e.

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Compaction of the

material following

Tex-113-e.

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Weighting of the specimen

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Extrusion of the

specimen.

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Sealing the specimens for curing period

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Specimens placed in the oven for curing

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Porous stone for 24h capillarity soaking

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Specimens during capillarity soaking

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Unconfined

compressive

strength test.

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Detail of

unconfined

compressive

strength test.

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Completion of

unconfined

compressive

strength test.

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• The mid and long term gain strength of the Lime Stabilized Soil can (“or should”) be incorporated into the Pavement Design for an optimized solution.

• That sentence implies:

1. A more exhaustive testing to complete the mix design.

2. A more comprehensive and effective Quality Control during the construction.

7. Conclusions

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• The final product is a roadway with a subbase exhibiting a very high modulus and therefore with a longer life compared to a road with a thinner and softer subbase layer.

7. Conclusions