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FAQs - Construction

Our customer service department answers many questions regarding our lime products for all the industries we serve. The questions range from lime applications and use to storage, shipping and handling. As a resource to our customers and website viewers, the listing below represents the most frequently asked questions.

 

How is soil tested to determine the proper amount of lime needed for stabilization?

Two ASTM procedures apply – ASTM D-6276, “Standard Test Method for Using pH to Estimate the Soil-Lime Proportion Requirement for Soil Stabilization” and ASTM C-977 (Appendix A). The amount of lime, as a percentage of the soils bulk dry density, needed to maintain a pH level of the moistened soil-lime mixture of at least 12.4 for one hour is determined. Strength tests, generally unconfined compressive tests (ASTM D-5102) are then used to evaluate the long-term and weather resistance properties of the lime-stabilized soil.

 

How are soils classified?

Two systems are generally used to classify soils:

  • American Association of State Highway and Transportation Officials (AASHTO) Standard M145.

  • American Society for Testing and Materials (ASTM) D-2487. This is commonly called the Unified Soil Classification System.

Particle size, fraction passing the No. 200 sieve (0.074 mm), and plasticity characteristics are the chief characteristics used to classify soils. The AASHTO Classified System groups the soils into seven basic groups, designation A-1 to A-7, with subgroups in some of the groupings. The Unified Classification System groups soils into four major divisions – gravels, sands, silts and clays with liquid limit less than 50, silts and clays with liquid limit 50 or more. These divisions are further separated into 11 groups represented by two letter symbols. For instance, a soil described as “silty sand, sand-silt mixture” would be classified as SM. In addition to the AASHTO M145 and ASTM D-2487 standards, most soils engineering textbooks provide a good reference for more information.

 

What soils are appropriate for lime stabilization?

Experience has shown that lime will react with medium, moderately fine and fine grained soils. Generally speaking, those soils classified by the Unified System as CH, CL, MH, SM, GC, SW-SC, SP-SC, SM-SC, GP-GC or GM-GC are potentially capable of being stabilized with lime. The extent to which the soil-lime pozzolanic reaction proceeds is influenced primarily by the natural soil properties. As a general guide, lime stabilization should be considered for soils that have plasticity indices of 10 or greater along with 25% or more of the soil smaller than the number 200 sieve. Particles smaller than the No. 200 sieve (0.074 mm) are considered to be silt (0.002 to 0.06 mm) or clay (< 0.002 mm). Lime is generally the stabilizer of choice for soils that have plasticity indices above 30 and greater than 25% material passing the number 200 sieve.

 

Can lime be used with soils containing soluble sulfates?

Particular attention must be paid to the sulfate content of soils when considering lime stabilization. Caution must be used when using lime or any calcium-based stabilizer with soils containing more than 10% clay and 0.2% soluble sulfates when the sulfates are extracted from the soil in a 10 parts water to 1 part soil solution. For more information, see “Technical Memorandum: Guidelines for Stabilization of Soils Containing Sulfates” available from the National Lime Association www.lime.org

 

What types of lime are used for soil stabilization?

Both hydrated lime and quicklime are used. Quicklime will consume more of the soil's moisture as it hydrates, then reacts with the soil. Lime kiln dust is also used, but may require more quantity as it typically consists of 20-25% CaO, while high calcium quicklime consists of about 90% CaO. When using lime kiln dust the quality should be checked regularly.

 

How should lime being used for soil stabilization be specified?

Lime should meet the requirements of ASTM C-977, “Standard Specification for Quicklime and Hydrated Lime for Soil Stabilization" or AASHTO M 216, “Lime for Soil Stabilization.”

 

Can lime be combined with fly ash for soil stabilization?

The addition of fly ash can significantly increase the compressive strength of a lime stabilized soil. The fly ash provides additional alumina and silica to the mixture made soluble at high pH, reacting with the calcium from the lime to form calcium aluminates and calcium silicates for the pozzolanic cementitious action. This is particularly beneficial for lower plasticity soils with higher silt content. With proper material selection and proportioning, virtually any granular soil can be stabilized with lime-fly ash.

 

Where can I find information on lime stabilization construction practices?

The National Lime Association's publication “Lime Stabilization Construction Manual” can be ordered through the NLA's website www.lime.org

 

What technical references and resources are available to help design lime-stabilized soils for long-term strength and durability?

The National Lime Association's (NLA) website www.lime.org

describes a number of technical publications available on lime stabilization from the NLA. “Evaluation of the Structural Properties of Lime Stabilized Soils and Aggregates”, Volumes 3 and 4 are particularly informative.

 

Can dolomitic lime be used for soil stabilization?

Yes. ASTM C-977, “Standard Specification for Quicklime and Hydrated Lime for Soil Stabilization”, allows for the use of dolomitic lime. Both material are effective for soil drying, modification (plasticity reduction) and stabilization. Certain basic chemical and physical differences exist between high calcium lime and dolomitic lime that may affect lime-soil reactivity.

  • Pound for pound, high calcium lime provides more free calcium or available calcium (Ca), making it somewhat more effective.

  • In some cases, slightly more dolomitic lime may be required for soil stabilization. However, this is very dependent on the soil properties. In many cases, lime quantities do not need to be increased if dolomitic lime is used for soil stabilization.

  • When soil stabilization (rather than drying or modification) is the goal, laboratory procedures to determine the mixture proportions should be done using the type of lime that will be used on the job. Such testing will often show that equal quantities of dolomitic and high calcium lime will effectively stabilize a reactive soil.

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