lime only. Consequently, the same factors involved
checking the specific gravity of the slurry, either
for quality control are suggested.
by a hydrometer or volumetric-weight procedure.
5-5. Bituminous Stabilization. The factors that
c. Uniformity of mixing. The major concern is to
seem most important to control during construc-
obtain a uniform lime content throughout the
tion with bituminous stabilization are surface
depth of treated soil. This presents one of the most
moisture content, viscosity of the asphalt, asphalt
difficult factors to control in the field. It has been
content, uniformity of mixing, aeration, compac-
reported that mixed soil and lime has more or less
tion, and curing.
the same outward appearance as mixed soil with-
a. Surface moisture content. The surface mois-
out lime. The use of phenolphthalein indicator
ture of the soil to be stabilized is of concern.
solution for control in the field has been recom-
Surface moisture can be determined by conven-
mended. This method, while not sophisticated
tional methods, such as oven-drying, or by nuclear
enough to provide an exact measure of lime con-
methods. The Asphalt Institute recommends a
tent for depth of treatment, will give an indication
surface moisture of up to three percent or more for
of the presence of the minimum lime content
use with emulsified asphalt and a moisture con-
required for soil treatment. The soil will turn a
tent of less than three percent for cutback asphalt.
reddishpink color when sprayed with the indicator
The gradation of the aggregate has proved to be of
solution, indicating that free lime is available in
significance as regards moisture content. With
the soil (pH = 12.4).
densely graded mixes, more water is needed for
d. Compaction. Primarily important is the
mixing than compaction. Generally, a surface
proper control of moisture-density. Conventional
moisture content that is too high will delay com-
procedures such as sand cone, rubber balloon, and
nuclear methods have been used for determining
soils require higher moisture contents.
the density of compacted soil lime mixtures. Mois-
b. Viscosity of the asphalt. The Asphalt Institute
ture content can be determined by either oven-dry
recommends that cold-mix construction should not
methods or nuclear methods. The influence of time
be performed at temperatures below 50 degrees F.
between mixing and compacting has been demon-
The asphalt will rapidly reach the temperature of
strated to have a pronounced effect on the proper-
the aggregate to which it is applied and at lower
ties of treated soil. Compaction should begin as
temperature difficulty in mixing will be encoun-
soon as possible after final mixing has been com-
tered. On occasion, some heating is necessary with
pleted. The National Lime Association recom-
cutback asphalts to assure that the soil aggregate
mends an absolute maximum delay of one week.
particles are thoroughly coated.
The use of phenolphthalein indicator solution has
c. Asphalt content. Information can be provided
also been recommended for lime content control
to field personnel which will enable them to
testing. The solution can be used to distinguish
determine a satisfactory application rate. The as-
between areas that have been properly treated and
phalt content should be maintained at optimum or
those that have received only a slight surface
slightly below for the specified mix. Excessive
dusting by the action of wind. This will aid in
quantities of asphalt may cause difficulty in com-
identifying areas where density test samples
paction and result in plastic deformation in service
should be taken.
during hot weather.
e. Curing. Curing is essential to assure that the
d. Uniformity of mixing. Visual inspection can
soil lime mixture will achieve the final properties
be used to determine the uniformity of the mix-
desired. Curing is accomplished by one of two
ture. With emulsified asphalts, a color change
methods: moist curing, involving a light sprinkling
from brown to black indicates that the emulsion
of water and rolling; or membrane curing, which
has broken. The Asphalt Institute recommends
involves sealing the compacted layer with a bitu-
control of three variables to assure uniformity for
minous seal coat. Regardless of the method used,
mixed-in-place construction: travel speed of appli-
the entire compacted layer must be properly pro-
cation equipment; volume of aggregate being
tected to assure that the lime will not become
treated; and flow rate (volume per unit time) of
nonreactive through carbonation. Inadequate
emulsified asphalt being applied. In many cases,
sprinkling which allows the stabilized soil surface
an asphalt content above design is necessary to
to dry will promote carbonation.
assure uniform mixing.
5-4. Lime-Fly Ash (LF) and Lime-Cement-Fly
e. Aeration. Prior to compaction, the diluents
Ash (LCF). The nature of lime-fly ash and lime-
that facilitated the cold-mix operation must be
cement-fly ash stabilization is similar to that for
allowed to evaporate. If the mix is not sufficient-