Does chemical soil stabilization work on Oklahoma clay?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

In short: Oklahoma highway research shows lime can sharply cut swelling in ordinary clay, but it can cause severe heave in soils high in sulfate. Kiln dust raised swelling in every soil tested in one study because the dust itself carried sulfate. Two acid-based additives tested on Oklahoma clays did not reduce swelling or meaningfully raise strength.

Why does this research matter to homeowners?

Chemical soil stabilization means mixing or injecting a material into clay to reduce its tendency to swell and shrink. Most published Oklahoma testing was done for roads by the Oklahoma Department of Transportation (ODOT) and the University of Oklahoma, so it measures mixed-in treatment of subgrade soils rather than injection under a house ¹². The results still show how Oklahoma clays respond to common chemicals. For how treatment is used around foundations, see chemical soil stabilization.

The common additives are:

Lime: hydrated lime or quicklime, calcium-based.
Fly ash: a byproduct of burning coal; Class C fly ash contains calcium.
Cement kiln dust (CKD): fine dust collected from cement plants.

What did lime, fly ash and kiln dust tests show?

A University of Oklahoma study (FHWA-OK-08-10) measured three-dimensional swell after curing for three Oklahoma soils ¹.

Soil	Sulfate	Untreated swell	3% lime	15% fly ash	15% kiln dust
Kingfisher (lean clay, LL ~39, PI ~21)	none detected	6.1%	swell cut about 95%	swell cut about 54%	swell up 98% ¹
Vernon (lean clay, PI ~11 to 15)	15,400 ppm	not stated	swell up 1,237%	swell cut about 145%	swell up 593% ¹
Carnasaw (fat clay, LL ~58, PI 29)	267 ppm	not stated	nearly eliminated swell	swell cut about 32%	swell up 113% ¹

Additional findings from the same study:

At 9% lime, Kingfisher soil averaged negative 2.8% swell, meaning it shrank slightly ¹.
Lower fly ash doses on Vernon soil (5% and 10%) reduced swell by about 40% and 75% ¹.
The kiln dust tested carried about 28,133 ppm soluble sulfate, and the report says soil-kiln dust mixes above 2,000 ppm can cause sulfate heave ¹.

What sulfate heave is

When calcium from lime, fly ash or kiln dust reacts with sulfate in soil and water, it can form ettringite, a mineral that takes up a large volume as it grows ¹. The researchers confirmed ettringite in treated samples with electron microscopy and X-ray methods ¹.

Sulfate in Oklahoma soils ranges widely. Borings at one McClain County site tested between 38 and 1,300 ppm, and that report stated that levels below 3,000 ppm pose a low risk of harmful reactions in lime stabilization ⁴. Vernon soil, at 15,400 ppm, is far above that ¹. Gypsum is a calcium sulfate mineral, and gypsum-rich soil was behind the highway failure described below ³ (see Permian gypsum units and gypsum karst and sinkholes).

A field failure: SH-412 near Woodward

In 2004, several miles of State Highway 412 near Woodward failed from sulfate-induced heave ³. The subbase soil had been lime-treated and came from a borrow source with a large amount of gypsum; the lime reacted with the gypsum to form ettringite, which swelled the subbase and ruined that section of road ³.

Do acid-based additives work?

A 2013 University of Oklahoma study for ODOT (FHWA-OK-13-06) tested two commercial acid-based liquid additives, described as sulfonated oil products mixed with acid, on three Oklahoma clays: Lela clay (Kay County), Renfrow clay (Logan County) and Vernon soil ². They were compared with hydrated lime and Class C fly ash ².

Measure	Finding
Strength	No substantial increase in unconfined compressive strength in any soil; neither additive met ODOT's stabilization criteria ²
Plasticity	Little effect; Renfrow cured PI was 27.2 untreated vs 27.4 and 25.7 with the two additives ²
Swell	No reduction in swelling potential in any soil; lime clearly reduced swell in Lela clay ²
Sulfate soil	The additives did not cause the adverse swelling that lime and fly ash produced in Vernon soil ²

What are the limits of the research?

These studies tested road subgrade mixing and lab samples, not injection beneath existing houses ¹².
Results vary by soil; a treatment that works on low-sulfate Kingfisher soil behaved very differently on Vernon soil ¹.
Measured soil properties for many Oklahoma soils are listed in soil lab values.

Common questions

Does lime reduce swelling in Oklahoma clay?

On low-sulfate soil it can. In Oklahoma research on Kingfisher soil, 3% lime cut swelling by about 95%, and 9% lime produced slight shrinkage instead of swell.

Can lime make clay swell more?

Yes, in sulfate-rich soil. Vernon soil from western Oklahoma, with 15,400 ppm sulfate, swelled 1,237% more after 3% lime was added, because the lime and sulfate formed the expansive mineral ettringite.

Do acid-based soil stabilizer products work on Oklahoma clay?

A 2013 University of Oklahoma study for the state DOT tested two acid-based additives on three Oklahoma clays and found no substantial strength gain, little change in plasticity and no reduction in swelling potential.

Has sulfate heave happened on an Oklahoma project?

Yes. In 2004, several miles of State Highway 412 near Woodward failed when lime-treated soil from a gypsum-rich borrow source heaved as ettringite formed.

Sources

Engineering Properties of Stabilized Subgrade Soils for Implementation of the AASHTO 2002 Pavement Design Guide (FHWA-OK-08-10) Oklahoma Department of Transportation
Report FHWA-OK-13-06 (ODOT SP&R Item 2242), University of Oklahoma Oklahoma Department of Transportation / U.S. DOT ROSA P
Calcium-Based Stabilizer Induced Heave in Oklahoma Sulfate-Bearing Soils (FHWA-OK-11-03) Oklahoma Department of Transportation / U.S. DOT ROSA P
Subsurface Exploration, New ODOT Maintenance and Residency Facilities Oklahoma Department of Transportation

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