Technical Papers and Articles
»Loss Prevention QA
From the Loss Prevention Seminar 2003
Soil Stabilization Using Chemical Treatment
control is essential to assure that the final product will be adequate
for its intended use. Additionally, it must assure that the contractor
has performed work in accordance with the plans and specifications.
quality control plan attempts to identify those control factors that
are most important in soil stabilization construction with quicklime,
quicklime/pozzolans, and cement products. Inspection and testing
requirements, for each of those factors, will also be discussed.
of laboratory methods for soil stabilization will be of little value if
the results of these methods cannot be successfully applied in the
field. The success, at least in part, is more likely if some plan is
available to assure the quality of the final product. The engineer or
technician in the field encounters highly variable conditions such as
climate, efficiency of equipment and soil type. These items can be a
major impact during construction. Therefore, field personnel must be
aware of those factors that control the quality of the final product.
The use of quicklime, quicklime/pozzolan, and cement products in soil
stabilization can present significant problems, unless the field
engineer has some familiarity with those factors which must be
controlled to assure that an investment of time and money will not be
The quality of stabilized mixtures, as produced and
placed, must be monitored on a continuing basis to ensure a quality
product. The general tests normally conducted on these materials are
listed below in their order of importance or frequency of testing.
1. In-place density (ASTM D 1557, Cal Test 216, and AASHTO T 238-73)
2. Stabilizer content - (Quicklime, Quicklime/pozzolan, and cement products – ASTM)
3. Gradation (ASTM D 136-71)
4. Moisture content (ASTM D 2216-71)
Quicklime Treatment - Quality Control and Guide Specifications
procedures have been identified for soil-quicklime construction. The
factors most important to control during construction are:
1. Lime content,
3. Pulverization, gradation
4. Uniformity of mixing
5. Time sequence of operations
material to be treated shall contain no rocks or solids other than soil
clods larger than 4 inches in any dimension. Removing and disposing of
said rocks or solids larger than 4 inches will be paid for as extra
Prior to placement of reagent,
engineer or technician should determine the soil weight being used to
determine spread rate. With this information, a determination can be
made on the reagent weight per square foot. The amount of lime is a
percentage by weight of the treated material’s PCF dry weight.
lime is applied to soil, the spread rate can be determined by placing a
3 square foot pan on the ground in front of spreader truck. After the
lime has been spread, weigh the reagent in the pan to determine the
rate of spread in pounds per square foot.
The engineer will
determine the depth of treatment. Lime shall be spread by equipment
capable of uniformly distributing the required amount of lime for the
full depth and width of treatment.
The spread lime shall be
prevented from blowing by suitable means selected by the contractor.
The spreading operations shall be conducted in such a manner that a
hazard is not present to construction personnel or the public. All lime
spread shall be thoroughly mixed into the soil the same day lime
spreading operations are performed.
No traffic other than the
mixing equipment or other related construction equipment will be
allowed to pass over the spread lime until after completion of mixing.
This includes the spreader, mixer, and water truck.
equipment shall be equipped with a visible depth indicator showing
mixing depth, an odometer or footmeter to indicate travel speed and a
controllable water additive system for regulating water added to the
Mixing equipment shall be of the type that can mix the
full depth of the desired thickness and leave a relatively smooth
bottom of the treated sec-tion. Mixing and re-mixing, regardless of
equipment used, will continue until the material is uniformly mixed,
free of streaks or pockets of lime, moisture is at approximately 3-5%
over optimum and all material other than rock or aggregate complies
with the following requirements:
For Sieve Size = l", Percent Passing = 98 Min.
For Sieve Size = No. 4, Percent Passing = 60 Min.
Lime treated material shall not be mixed or spread while the atmospheric temperature is below 35°F or below 1.67 C.
first and final mixings shall not be performed on the same day. The
entire mixing operation shall be completed within 7 days of the initial
mixing of lime, unless otherwise permitted by the engineer.
of color reaction when the treated material, exclusive of one inch or
larger clods, is tested with the standard phenolphthalein alcohol
indicator, will be considered evidence of inadequate mixing.
The lime treated soils shall be compacted to a relative compaction determined by the engineer.
maximum compacted thickness of a single layer may be any thickness the
contractor can demonstrate to the engineer that his equipment and
method of operation will compact to the required density throughout the
The sample of lime treated soil used for determining
the maximum dry density will be a composite of 5 samples taken at
random from the area to be tested and obtained after all mixing
operations have been completed.
Initial compaction shall be
performed by means of sheepsfoot or segmented wheel roller. Final
rolling shall be by means of steel-tire or pneumatic-tire rollers.
Areas inaccessible to rollers shall be compacted to the required compaction by other means satisfactory to the engineer.
finish compaction, if the treated material is above the grade tolerance
specified in this section, uncompacted excess material may be removed
and used in areas inaccessible to mixing equipment. After finish
compaction and trimming, excess material will be removed and disposed
of. The trimmed and completed surface shall be rolled with steel- or
pneumatic-tire rollers. Minor indentations may remain in the surface of
the finished material as long as no loose material remains in the
After a part-width section has been completed, the
longitudinal joint against which additional material is to be placed
shall be trimmed approximately 3 inches into treated material, to the
neat line of the section, with a vertical edge. The material so trimmed
shall be incorporated in the adjacent material to be treated.
acceptable alternate to the above construction joints, if the treatment
is performed with cross shaft rotary mixers, is to actually mix 3
inches into the previous day's work to assure a good bond to the
The surface of each
compacted layer of lime treated material shall be kept continually
moist until covered by a subsequent layer of lime treated or other
material or by applying a curing seal immediately following final
trimming and rolling of the lime treated layer.
A curing seal
will be required only for the top layer of lime treated material if
treatment is to be exposed for more than 3 days. The curing seal shall
consist of SS or CSS grade asphaltic emulsion and shall be furnished
and applied in accordance with the provisions in Caltrans
Specifications Section 94, "Asphaltic Emulsions".
shall be applied at a rate between 0.10- and 0.20- gallon per square
yard of surface, the exact rate to be determined by the engineer. The
curing seal shall be applied as soon as possible after the completion
of final rolling and before the temperature falls below 35°F or 1.67 C.
National Lime Association provides specifications for hydrated lime and
information on storage and handling requirements. Field personnel
should assure that the lime used in the treatment process has not been
rendered non-reactive through improper storage and handling.