Lesson 1/Learning Event 2
in Table 1. However, portland cement may be considered for heavier clays if the clay is first treated
with lime or fly ash.
Relatively small amounts of portland cement may be used to modify the plasticity index and swell
characteristics of the soil. Test for desired improvement by Atterberg limits and swell tests.
Stabilization with Lime
Fine grained soils, clays and silts with a plasticity index of 12 or greater with at least 12 percent of the
material passing a #200 sieve are considered potentially capable of being stabilized by lime. However,
certain clay minerals will behave differently in the presence of lime making laboratory tests necessary to
determine the effectiveness of the lime treatment. The plasticity index and swell potential of the soil
may be reduced by addition of one to six percent hydrated lime by weight. If quicklime is used, the
amount required may be reduced by 25 percent. It should be noted, however, that quicklime is highly
caustic and hazardous to handle. Use Atterberg limits and swell tests to determine the amount of lime
Lime may also be used to dry out wet soils. Quicklime is especially advantageous for this purpose as
heat of hydration is generated on exposure to moisture.
The use of lime requires adequate equipment and special construction practices which must be followed
very carefully if uniform results are to be obtained. Lime is normally mixed with the pulverized soil and
then allowed to "cure" or mellow for from three to 14 days prior to repulverizing, mixing, and
compaction. For highly plastic soils it may be more advantageous to apply half the lime during the
initial mixing and the balance during final mixing.
Stabilization with Bitumen
In general, soil with a plasticity index of less than 10 with not more than 30 percent passing the #200
sieve can be stabilized with liquid bitumen or emulsion. The tendency in recent years has been to use
emulsions in preference to liquid asphalts for mixed-in-place stabilization.
The bitumen content should be sufficient to provide a firm, stable foundation for operation of
construction equipment. You can obtain preliminary estimates of the percent of bituminous materials
required from the following: