CTB Research In Progress
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Development
of Procedures to Evaluate Cement Stabilization of Difficult Soils
(Click here)
Improvements
in Design and Construction Procedures for Cement-Treated Soils (Click
here)
Effect of Laboratory Conditioning and Compaction
Characteristics on Projects Specifications for Cement-Treated Materials
Principal Investigator: W. Spencer Guthrie, Ph.D.
Project Description
Both laboratory and field project specifications have a tremendous
impact on the selection and use of materials on soil stabilization
projects. However, performing an adequate evaluation of alternative
materials is often difficult because they are not tested and specified
in the same manner. For example, lime and fly-ash mixes are evaluated
for freeze-thaw durability using American Society for Testing and
Materials (ASTM) C 593 (Standard Specification for Fly Ash and Other
Pozzolans for Use with Lime for Soil Stabilization), which requires
conditioning using a vacuum-saturation method. Cement-treated materials
are evaluated using ASTM D 559 (Standard Test Methods for Wetting
and Drying Compacted Soil-Cement Mixtures) and ASTM D 560 (Standard
Test Methods for Freezing and Thawing Compacted Soil-Cement Mixtures),
which include far more rigorous laboratory conditioning. Evaluating
these different materials on a common basis is therefore difficult.
Designs for stabilized materials are typically based on the results
of laboratory tests; however, different types of specimen-conditioning
protocols are often employed by different agencies for different
materials and stabilizers. Because the results of strength and durability
tests depend to a large degree on the conditioning to which specimens
are subjected, selection of a particular conditioning protocol can
directly impact the choice of stabilizer type and content.
This research will evaluate the relative severity of some commonly
used conditioning methods, such as freeze-thaw cycling, wet-dry
cycling, vacuum saturation, water submersion, and others. Understanding
the effects of different conditioning practices on strength and
durability test results will enable more objective selection of
conditioning protocols by design engineers and facilitate more meaningful
comparisons of data obtained for different stabilizer treatments
using different conditioning methods. Different materials, such
as lime, lime-fly ash, and calcium chloride, will be evaluated in
comparison to cement so that a better understanding of the relative
strength and durability of these materials under different types
of conditioning can be achieved.
A separate, but related, specification for cement-treated materials
involves the amount of time allowed for working and compacting the
material after mixing. Current construction specifications often
require that contractors compact and finish cement-treated materials
within two hours after adding cement. While this specification has
been widely adopted, the actual limitations associated with compaction
characteristics of cement-treated materials have not been thoroughly
investigated. For example, temperature, relative humidity, wind
speed, cement content, and soil or aggregate type can all influence
the rate of hardening. In particular, given that the great majority
of pavement construction is performed during hot summer months,
the loss of moisture from cement-treated materials between mixing
and compaction can play a significant role in the compaction characteristics
of the material. This research will quantify the individual effects
of moisture and other environmental and materials factors and investigate
interactions between them. Understanding the effects of these factors
will enable engineers and contractors to optimize segmentation and
sequencing of pavement construction operations utilizing cement
stabilization and better understand the importance of the construction
specifications. In addition, this project will provide useful data
regarding the relative efficacy of various instruments for monitoring
pre-cracking of cement-treated base materials during construction.
Market Significance of Project
Regarding the research on laboratory conditioning, market significance
will be derived from the ability to perform more accurate comparisons
among different types of stabilizers. The benefits of cement can
be better demonstrated if laboratory conditioning procedures are
similar for different stabilizing agents.
Research on factors affecting the time frame in which cement-treated
materials must be compacted will have market significance through
development and implementation of improved construction specifications.
Having better definitions of the effects of different field conditions
will allow contractors to construct cement-treated materials more
efficiently and produce higher-quality final products for the industry.
Utilization of Results
The results from work on laboratory conditioning will provide guidelines
for direct comparisons of different stabilizing agents with cement.
The effect of various conditioning procedures will be better understood,
and proper test procedures for strength and durability will be recommended.
The results of the compaction study will be utilized through development
of better construction specifications that more accurately reflect
the effect of various construction variables.
Completion of this project is expected to result in five master
of science (M.S.) theses and at least five journal articles. Publication
of the research in well respected and widely circulated media will
not only benefit the pavement industry nationwide, but it will also
provide recognition to PCA for sponsoring the research.
Project Organization
The project will be conducted in three phases as follows:
Phase I: Evaluate and compare various
laboratory conditioning protocols for stabilized materials.
Phase II: Evaluate factors
influencing compaction characteristics of cement-treated materials
and recommend construction specifications.
Phase III: Evaluate the utility of specific
field instruments for assessing the progression of pre-cracking
of cement-treated base materials during construction.
Work Plan
Phase I
Task 1. Conduct Literature Review on Laboratory Conditioning Protocols
Used for Stabilized Materials
A comprehensive review of the literature will be conducted to identify
laboratory conditioning protocols utilized for testing stabilized
soil and aggregate materials. Test methods will be documented in
detail, and the extent of their use will be reported where possible.
Published research results pertaining to this project will also
be summarized if available.
Task 2. Perform Laboratory Testing to Investigate Different Types
of Conditioning
Laboratory testing will be conducted in the Highway Materials Laboratory
at Brigham Young University (BYU). Unconfined compressive strength
(UCS), stiffness, or other response variables will be measured before
and after specific types of conditioning are performed to assess
the sensitivity of different types of stabilizers to different types
of conditioning. Examples of possible conditioning types include
freeze-thaw cycling, wet-dry cycling, vacuum saturation, and water
submersion, while examples of possible stabilizer types include
cement, lime, lime-fly ash, and calcium chloride. Specific soil
or aggregate types to be utilized in the research will be selected
in consultation with Portland Cement Association (PCA) personnel,
and material donations will be solicited from agencies interested
in supporting the project. Experimental design methodologies will
be applied so that the relative effects of soil or aggregate type,
stabilizer type, stabilizer content, and conditioning type can be
quantified.
Task 3. Analyze Data and Prepare Report on Laboratory Conditioning
A comprehensive report will be produced from the information collected
during the course of this research. The results of the literature
review will be documented, and the laboratory findings will be fully
described.
Phase II
Task 4. Conduct Literature Review on Factors Affecting Compaction
of Cement-Treated Materials
In preparation for the laboratory testing to be completed in this
phase of the project, the literature will be searched to identify
factors affecting compaction of cement-treated materials. Specifically,
factors such as temperature, relative humidity, wind speed, cement
content, soil or aggregate type, and compaction delay time will
be investigated. Published articles describing the effects of these
factors on compaction specifications will also be summarized if
available.
Task 5. Perform Laboratory Testing to Investigate Factors Affecting
Compaction of Cement-Treated Materials
For this laboratory work, a parametric study will be designed to
systematically assess the relative effects of factors such as temperature,
relative humidity, wind speed, cement content, soil or aggregate
type, and compaction delay time. Selected factors identified in
the literature review will be incorporated in a test program conducted
in the BYU Highway Materials Laboratory, which includes a computer-controlled
environmental chamber that allows specific temperature and relative
humidity settings. Cement-treated soil or aggregate samples will
be prepared at different cement contents and subjected to various
environmental conditions during the mixing process. UCS, stiffness,
density, or other response variables will then be measured following
compaction of the samples. As with the laboratory work to be conducted
in Phase I of this project, specific soil types to be included in
the research will be selected in consultation with PCA personnel.
Task 6. Analyze Data and Prepare Report on Compaction
A detailed report will be produced to document findings from the
literature review and the laboratory testing program. The potential
influence of each factor on compaction specifications will be described.
Phase III
Task 7. Conduct Literature Review on the Use of Pre-Cracking of
Cement-Treated Base Materials
A review of the literature will be performed to identify publications
describing pre-cracking practices and associated project details.
Information about individual field devices potentially useful for
monitoring the progression of pre-cracking will also be documented.
Task 8. Perform Field Testing to Evaluate Sensitivity of Specific
Instruments to Pre-Cracking
Field testing of cement-treated base layers will be scheduled with
local or regional agencies willing to specify pre-cracking on upcoming
projects. At least two sites will be included. The testing will
include evaluations of the Clegg impact soil tester, soil stiffness
gauge, and portable falling-weight deflectometer, at minimum, for
assessing the progression of pre-cracking during construction. Projects
utilizing applications of both dry cement powder and cement slurries
will be sought. Statistics principles will be followed in the experimental
design to ensure the collection of an appropriate quantity of data.
Where possible, the spatial variability in structural properties
of cement-treated base layers constructed using different methods
will be evaluated. Materials sampled in the field will be returned
to the BYU Highway Materials Laboratory for classification.
Task 9. Analyze Data and Prepare Report on Pre-Cracking
When all of the data have been analyzed, a final report describing
the results of the literature review and field and laboratory testing
will be produced.
Delivery Date
The project will be completed over a 3-year period, beginning in
June 2006. The final project deliverables and documentation will
be completed by June 2009.
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