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Improvements in Design and Construction Procedures
for Cement-Treated Soils
Principal Investigator: Tom Scullion
Background
Calcium-based stabilizers (lime, cement, type-C fly ash) are currently
used to modify the characteristics of clay soils through an ion-exchange
process. This modification process improves the constructability
of a clay soil by reducing the plasticity and improving the compaction
characteristics. The use of lime for soil modification is sometimes
preferred because of the higher amounts of available calcium hydroxide,
as compared to cement. However, specific laboratory tests on highly
plastic soils have shown that the same treatment dosage of cement
and lime will result in similar modification of the soil. A better
understanding of the chemistry involved in the ion-exchange process
is needed, particularly with regard to how the dosage of cement
and lime affect the modification of highly plastic soils.
In the past few years contractors have developed construction procedures
that allow the application of cement slurries for soil stabilization.
The application of cement in a slurry form has the benefit of not
generating any dust, and ensures that all the cement particles are
completely hydrated. However, procedures are not available to determine
the best cement-to-water proportions for slurry applications, and
construction specifications have not been developed so that agencies
and owners can monitor the proper construction methods. Recommendations
need to be developed for slurry mixing and construction procedures.
Objective
Part A. Understanding the Chemistry of Cement Modified Soils.
Part A will better define the chemistry that occurs with cement
modification of clay soils. This will improve the understanding
of proper cement contents for ion-exchange, and explain the treatment
of clay soils in comparison to the modification of soils using lime.
Part B. Development of Construction Specifications for Cement
Slurries.
Methods of mixing and placing cement slurries will be evaluated
with the objective of developing recommendations for construction
specifications. This will include the evaluation of different cement-to-water
proportions and how different types of equipment might be used to
uniformly apply the slurry. Test methods will be developed for design
and construction specifications.
Market Significance of Project
Part A will improve the understanding of how cement can be used
for soil modification, particularly in comparison with the use of
lime. This will help to explain to agencies and consulting engineers
how to select the proper stabilizer, and how to determine the proper
dosage.
Part B will contribute to the use of cement slurries, which will
reduce the associated problems with dust that develops as a result
of applying dry cement for soil stabilization.
Utilization of Results
The results from this project will be utilized through improved
procedures for designing and construction of cement-treated soils.
Project Description
Part A: Evaluate the chemistry of the ion-exchange process in soil
modification, and develop methods to determine the proper cement
dosage.
Part B: Develop procedures to determine cement-to-water mixing
ratios, and construction specifications, for cement slurry mixes.
Delivery Date
The project will be completed over a 2-year period, beginning in
November 2006. The final project deliverables and documentation
will be completed by December 2008.
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