Archive for October, 2009

Sulfates in Soil, Part II

Last week was the first post in a series about sulfates in soils.  This week I will talk about soil stabilization chemicals and their relationship to sulfate soils.


Chemical modification of soil involves mixing soil with a chemical additive such as lime, Portland cement, flyash, cement kiln dust, or a combination of any of the four.  Soils treated with chemicals may expand to an even greater extent if chemical modification is used in soils which contain high levels of sulfates, organic matter, or salts. 



Lime is the most common chemical additive for treating highly plastic clay soils.    When treating soils, lime can be used in two different forms: quicklime or hydrated lime. 

Quicklime, or calcium oxide, is the most reactive form of lime.  In the presence of moisture, it is corrosive to equipment and to human skin.  When mixed with water it produces heat and swells.  Lime mixed with water is hydrated lime, also known as slaked lime.  Slaked lime comes as a fine powder or mixed in a slurry, where quicklime is coarse powder (Hausmann, 1990).  Quicklime is more cost-effective because it takes less to react with the soil, but slaked lime is often used instead.  More and more communities in Oklahoma have regulations against using quicklime because of its corrosive nature and ability to travel in windy conditions. 

Quicklime reacts with moisture in the clay soils and generates heat and expands, consolidating the soil.  This is especially effective when the lime is injected or placed in layers, as opposed to simple soil mixing (Hausmann, 1990).

Slaked lime, used in a slurry, can be more costly to transport, but is safer for the contractors, equipment, and persons down-wind of the project.

In either the quicklime or slaked form, when lime is mixed with clay, two pozzolanic chemical reactions occur.  These reactions are cation exchange and flocculation-agglomeration.  In the cation exchange reaction, calcium ions are exchanged with the adsorbed cations attached to the montmorillonite surfaces.  The flocculation-agglomeration reaction causes the clay particles to flocculate and agglomerate into large clumps.  This decreases the liquid limit and increases the plastic limit, which decreases the plasticity index (Das, 2004).  The strength, shrinkage limit and workability of the soil are also increased.   In addition to decreasing the plasticity index, increasing the shrinkage limit, increasing the workability and improving the strength of high plasticity index soils, lime treatment also increases a soil’s permeability and optimum water content and decreases its dry density (Hausmann, 1990). 

Cation exchange and flocculation-agglomeration are immediate reactions when soil is mixed with lime.  A secondary reaction causes cementation of the soil by removing the silica and alumina from the clay’s crystal lattice structure.  This increases the strength of the clay soil, both immediately and long-term (Hausmann, 1990). 

Lime stabilization is the most common form of chemical stabilization for high plasticity index soils.  Lime can be used when sulfates are present in low levels and at higher levels if the conditions are tested and monitored correctly.

Portland Cement

Portland cement is the most commonly used additive for general soil stabilization.  Cement stabilization is effective for a wide variety of soil types, including expansive clays, but is usually used to increase strength in soils.  Cement has the same effects on sulfate rich soils as lime does.

With cement stabilization of soils, cementation occurs between the soil and the calcium silicate and aluminate hydration products (Gromko, 1974).  Cement treatment of soils generally increases the maximum dry density and reduces the plasticity index of an expansive soil.  A small addition of cement to an expansive subgrade material can often reduce the shrink/swell potential below 1 percent (Hausmann, 1990). 

Cement stabilization is a viable option for treating expansive soils.  As with lime, it can be used when sulfates are present in low levels and at higher levels if the conditions are tested and monitored correctly.

Fly Ash

Fly ash is a waste product created by coal combustion.  It is a fine-grained dust primarily composed of silica, alumina, and various oxides and alkalies (Das, 2004). Fly ash is usually combined with lime to stabilize soils.  Therefore, it poses the same risk to sulfate rich soils as does lime and cement.

Class F fly ash is produced when anthracite or bituminous coal is burned.  It has pozzolanic properties and can react with hydrated lime to produce cementitious products (Hausmann, 1990).  Class C fly ash is produced when subbituminous or lignite coal is burned.  It contains up to 25 percent free lime, which means it can produce cementitious reactions without the addition of manufactured lime (Das, 2004).  Additive mixtures of fly ash and lime contain 10 to 35percent fly ash and 2 to 10 percent lime (Hausmann, 1990). 

As with lime and cement, flyash can be used when sulfates are present in low levels and at higher levels if the conditions are tested and monitored correctly.

Cement Kiln Dust

Cement kiln dust (CKD) is a byproduct of Portland cement rotary kiln operations.  It is a fine powder that is chemically similar to Portland cement.  It is used in the same fashion as Portland cement.

Because CKD has many of the same properties as Portland cement it too has negative effects on sulfate rich soil.  But as the other products, it can be used when sulfates are present in low levels and at higher levels if the conditions are tested and monitored correctly.

Red Rock Consulting in Daily Oklahoman

Red Rock Consulting was featured in the Edmond section of the Daily Oklahoman on Wednesday, October 21, 2009.

Read the article

Crossword – ODOT

Okay, I haven’t figured out how to link the crossword directly to the post, but I am working on it.  Click the link to fill out the ODOT-themed crossword puzzle.  You may even be in it! 

Email me when you have it figured out.  If you’re the first, I’ll put you in the Crossword Hall of Fame.  Have fun and let me know if it is too easy.  🙂

ODOT Crossword – for newer browsers click here

ODOT Crossword – for older browsers click here

Drill, Baby

Bailey’s first experience on a drill rig was at East Texas Baptist University in September. 


ETBU 09-04-09

ETBU 09-04-09


Ethics – Bribery

The September issue of ASCE News included an article about an ASCE member who allegedly bribed a county official by gifting goods and services which helped the official to build a vacation home.  In exchange (supposedly), the engineer was awarded no-bid engineering projects from the county which the official supervised.  What do you think?  Is it a question of ethics or a friendly construction project? 

Read the Article

Sulfates in Soil


Naturally sulfate rich soils can be found in the southern, western and southwestern regions of the United States.  Sulfate rich soils that are stabilized with calcium based chemicals can result in what is called sulfate-induced heave.  Calcium based stabilization chemicals include lime, cement, and their derivatives.

Lime, cement, flyash, or cement kiln dust can react with clay soil and the sulfates in the clay to form expandable minerals, such as ettringite, which can expand up to 250 percent of its original size when exposed to moisture.  This can create large hills of soil, destroying roadways and foundations.  Sulfate-induced heave causes millions of dollars in damage each year to roads, highways, runways, parking lots, buildings, and other earth structures created by treating sulfate rich soils with cement or lime products (Puppala, Griffin, Hoyos, Chomtid, 2004). 

Simple laboratory testing may be performed on soil samples to determine on-site sulfate levels.  With proper awareness and testing, sulfate-induced heave can be prevented.

Sulfates, stabilization chemicals, sulfate-induced heave, heave prevention, and alternative treatments will be discussed through a series of posts with an emphasis on Oklahoma and Texas.



What is a Sulfate?

Sulfates are salts of sulfuric acid.  The sulfate ion is an anion, SO4 2-.  It consists of one central sulfur atom surrounded by four equivalent oxygen atoms.  The sulfate ion carries a negative two charge and is the conjugate base of the hydrogen sulfate ion, HSO4, which is the conjugate base of sulfuric acid, H2SO4.


3-D Rendering of a Sulfate Ion

3-D Rendering of a Sulfate Ion


Sulfate compounds are created when cations, such as calcium, combine with the sulfate anion.  Sulfate compounds include the sulfate minerals gypsum, ettringite and thaumasite, which are the culprits in sulfate induced heave.


Sulfates in Soil
Vertical heave during construction of US 67 near Midlothian, TX (Harris, Sebesta, Scullion, 2004)

Vertical heave during construction of US 67 near Midlothian, TX (Harris, Sebesta, Scullion, 2004)


Sulfate problems resulting from lime and cement stabilization in soils have been reported since 1962, but were not paid much attention to until the mid-1980s(Harris, Sebesta, Scullion, 2004).    Sulfates occur naturally in soils and have been reported in Oklahoma, Texas, Nevada, Louisiana, and Kansas (Puppala, Griffin, Hoyos, Chomtid, 2004). 


Sulfates in soils alone do not pose a problem for roadways and structures.  When sulfate rich soils are treated with calcium-based stabilizers and subjected to moisture, however, results can be devastating.  Sulfate ions in the soil combine with calcium from lime or cement stabilizers, aluminum from stabilizers and/or the clay minerals in the soil and water to generate sulfate heave.


Sulfate levels in soil can vary greatly in an area.  Seams of high concentrations of sulfates can be found on a project site.  It is important to determine where these seams are and to either remove them or properly mix them with non or low sulfate soils.  The amount of sulfates in soil can be tested by collecting a soil sample and testing it in a laboratory.  These laboratory tests will be discussed further in an upcoming post.