3125
Heaving Mechanisms in High Sulfate Soils
Mécanismes de soulèvement dans les sols à contenu élevé en sulfates
Puppala A.J.
Professor, Department of Civil Engg. University of Texas at Arlington
Talluri N., Gaily A., Bhaskar, Chittoori C.S.
Doctoral Student, Doctoral Student and Faculty Research Associate, Department of Civil Engg., University of Texas at
Arlington
ABSTRACT: Pavement distress caused by chemically treated sulfate soils are considered as major maintenance problems to highway
agencies. In view of this, researchers across the world have conducted studies on heave mechanisms in chemically treated sulfate
soils. Many of these studies are focused on soils with soluble sulfate contents below 10,000 parts per million (ppm). Heave
mechanisms in soils with sulfate contents above 10,000 ppm still need to be understood as sulfate measurements indicate that the soil
sulfate levels of certain regions are well above 10,000 ppm and may exceed 50,000 ppm in some cases. In order to understand the
behavior of treated soils containing sulfates above 10,000 ppm, a research study was initiated. Two soils with different soil
classification are studied. Lime is used as a chemical stabilizer for these soils. Chemical and mineralogical tests as well as engineering
swell tests were conducted to compare the changes in swelling, mineralogical and chemical compositions of the soils from the lime-
sulfate reactions. Results will explain the need to look for replace the classical treatments by alternate ones for these high sulfate soils
for civil infrastructure projects.
RÉSUMÉ : La dégradation des chaussées causée par les sols à contenu de sulfates traités chimiquement sont considérés comme des
problèmes d'entretien majeurs par les agences routières. Compte tenu de cela, les chercheurs du monde entier ont mené des études sur
les mécanismes de soulèvement dans les sols à contenu de sulfates traités chimiquement. La plupart de ces études portent sur des sols
à teneurs en sulfates solubles en inférieures à 10.000 parties par million (ppm). Les mécanismes de soulèvement dans les sols à
teneurs en sulfates supérieures à 10.000 ppm doivent encore être étudiés car des mesures de taux de sulfates indiquent que les niveaux
de sulfates du sol de certaines régions sont bien au-dessus 10.000 ppm et peuvent même dépasser 50.000 ppm dans certains cas. Afin
de comprendre le comportement des sols traités à contenu de sulfates supérieurs à 10.000 ppm, une étude a été lancée. Deux sols
réputés différents selon la classification des sols ont été étudiés. De la chaux a été utilisée comme stabilisant chimique de ces sols. Des
tests chimiques et minéralogiques ainsi que des tests d'ingénierie du gonflement ont été menés pour comparer les gonflements, et la
composition minéralogique et chimique des sols à la suite des réactions chaux-sulfate. Les résultats exposés expliqueront la nécessité
de chercher des traitements alternatifs aux traitements classiques pour ces sols à contenu élevé en sulfates dans les projets
d'infrastructures civiles.
KEYWORDS: Sulfate, Swell, Mellowing, Ettringite, Expansive Soil
1 INTRODUCTION
Chemical stabilization of expansive soils using lime and cement
has been a favourite option for practitioners over the years
(Hausmann, 1990). In last few decades, premature failure of
roads, highways and infrastructure facilities around several
parts of the globe lead to question the validity of calcium based
stabilization. It was reported that when soils contain sulfate
minerals such as gypsum (CaSO
4
.2H
2
O) and sodium sulfate
(Na
2
SO
4
) in their natural formation and are treated with calcium
based stabilizers, adverse reactions occur causing heave and
pavement distress. (Mitchell 1986, Hunter 1988, Puppala et al.
1999, 2003, 2012). These adverse reactions are attributed to the
formation of expansive minerals such as Ettringite
(Ca
6
.[Al(OH)
6
]
2
.(SO
4
)
3
.26H
2
O)
and
Thaumasite
(Ca
6
.[Si(OH)
6
]
2
.(SO
4
).(CO
3
)
2
.24H
2
O). This phenomenon is
termed as “Sulfate Induced Heave” in literature. Repair and re-
construction of the the failed infrastructure is costing millions
of dollars to the tax payers. Under favourable moisture,
humidity and temperature conditons these minerals grow
causing further swell. Lime/cement treatement of sulfate soils
can be regarded as the man made expasive soil problem.
In view of the past sulfate induced failures researchers have
developed “Threshold Sulfate Levels” beyond which calcium
based stabilization is to be cautioned. Berger et al., 2001 stated
that sulfate levels below 0.3 percent can be safely treated with
calcium stabilizers. Sulfate levels between 0.3 percent to 0.8 are
to be handled with caution and sulfate levels greater than 0.8
percent should be avoided. Puppala et al., 2003 indicated that
sulfate levels below 1000 ppm are of no concern and soils with
sulfate levels between 1000-2500 ppm can be treated with
additional amount of lime. Sulfate levels above 2,500 ppm are
to be completely avoided. Harris et al., 2004 confirmed that in
soils with sulfate levels greater than 7,000 ppm lime
stabilization is not a viable option. There is no conclusive
agreement between the threshold sulfates since in most cases of
sulfate induced failures sulfate contents varied from as low as
320 ppm to as high as 43,500 ppm.
Based on previous recommendations researchers have
studied heave mechanisms and developed alternative
stabilization techniques for treating sulfate soils. Many of these
studies were focused on soils with sulfate contents below
10,000 ppm. However, a further understanding about the soils
with sulfate contents above 10,000 ppm and higher is needed.
Researchers named these soils as “High Sulfate Soils”. In view
of this aspect the current study focuses on heaving mechanisms
and remedial options for high sulfate soils. Two soils from the
state of Texas with sulfate contents above 20,000 ppm are
considered in the current study. These soils were lime stabilized
using mellowing technique and various engineering and
mineralogical tests were conducted to understand the swell
shrinkage characteristics of chemically stabilized high sulfate
soils. Based on test results and analysis recommendations about
