Soil Lime/Cement Mix Design

Observations & Lessons From The School Of Experience Soil Stabilization With Lime

While not the solution to every soil subgrade problem, the proper application of lime or cement to a problem soil can yield outstanding results. In this Lessons Learned, we would like to pass along some instructive information regarding what benefits you receive when adding lime to soils. To avoid confusion between their uses and results, cement will be the topic of a future Lessons Learned. While lime and cement both affect the soils apparent wetness, each alters the soil in very different ways.

Observations & Lessons From The School Of Experience Soil Stabilization With Lime

While not the solution to every soil subgrade problem, the proper application of lime or cement to a problem soil can yield outstanding results. In this Lessons Learned, we would like to pass along some instructive information regarding what benefits you receive when adding lime to soils. To avoid confusion between their uses and results, cement will be the topic of a future Lessons Learned. While lime and cement both affect the soils apparent wetness, each alters the soil in very different ways.

What Is Lime Stabilization

While lime, like cement, is frequently seen as the quick answer to very wet soils, lime stabilization is the alteration of inherently weak or plastic soils, that may also be wet, into a much improved material whose physical engineering properties are significantly altered. The changes to the soil include increasing its strength, decreasing its water sensitivity, and volume change as the moisture content is altered.

When To Use It

While lime will have a positive effect on a broad range of soils, it is most effective with clay bearing soils, with which it can react both chemically and physically to alter the clays physical properties, and to produce a radically new material. As long as sufficient clay is present, the remainder of the soil can be silts, sands, or gravels. Organic contamination is to be avoided.

What Is Lime Stabilization

While lime, like cement, is frequently seen as the quick answer to very wet soils, lime stabilization is the alteration of inherently weak or plastic soils, that may also be wet, into a much improved material whose physical engineering properties are significantly altered. The changes to the soil include increasing its strength, decreasing its water sensitivity, and volume change as the moisture content is altered.

When To Use It

While lime will have a positive effect on a broad range of soils, it is most effective with clay bearing soils, with which it can react both chemically and physically to alter the clays physical properties, and to produce a radically new material. As long as sufficient clay is present, the remainder of the soil can be silts, sands, or gravels. Organic contamination is to be avoided.

What Is Lime?

There is a lot of confusion about what is lime. Lime which is used for soil stabilization should be either quicklime or hydrated lime. Both of these are the product of limestone (calcium carbonate) which is burnt, heated to a very high temperature, and ground to powder. This results in quicklime (calcium oxide), or hydrated lime (calcium hydroxide), which is made by slaking quicklime with a controlled amount of water. Most frequently the confusion over lime is the inclusion of pulverized agricultural limestone as lime. The latter has no beneficial effects in stabilizing soils, although it still will dry a wet soil by absorbing moisture.

What Is Lime?

There is a lot of confusion about what is lime. Lime which is used for soil stabilization should be either quicklime or hydrated lime. Both of these are the product of limestone (calcium carbonate) which is burnt, heated to a very high temperature, and ground to powder. This results in quicklime (calcium oxide), or hydrated lime (calcium hydroxide), which is made by slaking quicklime with a controlled amount of water. Most frequently the confusion over lime is the inclusion of pulverized agricultural limestone as lime. The latter has no beneficial effects in stabilizing soils, although it still will dry a wet soil by absorbing moisture.

Application Method

The steps are simple: pulverize the clayey soil into walnut sized particles, thoroughly mix in the lime, add water, mix again, allow to mellow, and then perform final compaction of the new altered soil.

Application Difficulties

  • Quicklime, because of its higher reactivity, is the more difficult to control, and its use in populated areas is very problematic. The rapid hydration of the calcium oxide produces heat, causing the water present to sputter and to be driven off as steam, carrying with it lime which can cause chemical burns of the skin.
  • Hydrated lime, because part of its water demand has already been satisfied, is less aggressive in its reaction to added or available water, but to a lesser extent the same conditions exist as with quicklime.
  • Dust control and inhalation protection are necessary whenever lime is applied to the soil.

Application Method

The steps are simple: pulverize the clayey soil into walnut sized particles, thoroughly mix in the lime, add water, mix again, allow to mellow, and then perform final compaction of the new altered soil.

Application Difficulties

  • Quicklime, because of its higher reactivity, is the more difficult to control, and its use in populated areas is very problematic. The rapid hydration of the calcium oxide produces heat, causing the water present to sputter and to be driven off as steam, carrying with it lime which can cause chemical burns of the skin.
  • Hydrated lime, because part of its water demand has already been satisfied, is less aggressive in its reaction to added or available water, but to a lesser extent the same conditions exist as with quicklime.
  • Dust control and inhalation protection are necessary whenever lime is applied to the soil.

Beneficial Effects Of Lime Stabilization

The changes in the soil are two fold, one relatively quickly, within a few days, and the other occurring over a longer period of time. First is the textural change of the soil as the fine clay particles are aggregated into larger, coarser (silt or sand size) particles as the clays bond together by base exchange. Second is the chemical reaction of the silica and alumina in the clays with the lime to produce a cementing together of the particles. The reaction benefits are permanent, and the strength of the cementing increases with time.

Beneficial Effects Of Lime Stabilization

The changes in the soil are two fold, one relatively quickly, within a few days, and the other occurring over a longer period of time. First is the textural change of the soil as the fine clay particles are aggregated into larger, coarser (silt or sand size) particles as the clays bond together by base exchange. Second is the chemical reaction of the silica and alumina in the clays with the lime to produce a cementing together of the particles. The reaction benefits are permanent, and the strength of the cementing increases with time.

In summary, while lime or cement can be added to almost any soil to dry it for immediate use, the stabilization of soil by the addition of lime should be a planned construction process intended to permanently alter the soils index properties and engineering properties, making it a more stable, even excellent material suitable for engineered fills and roadway subgrade construction. Unfortunately, there is not enough space on this page to fully explore the finer details of this subject, so should you have any questions regarding soil stabilization or, for that matter, any other soils issues, please feel free to contact the Geotechnical Engineering staff at our local office in your area.

In summary, while lime or cement can be added to almost any soil to dry it for immediate use, the stabilization of soil by the addition of lime should be a planned construction process intended to permanently alter the soils index properties and engineering properties, making it a more stable, even excellent material suitable for engineered fills and roadway subgrade construction. Unfortunately, there is not enough space on this page to fully explore the finer details of this subject, so should you have any questions regarding soil stabilization or, for that matter, any other soils issues, please feel free to contact the Geotechnical Engineering staff at our local office in your area.