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Introduction
Cement-treated or cement-stabilized soils have been used in pavement
base, subbase, and subgrade construction since 1915 because
cement has been effective in improving the engineering
properties of a wide variety of soils, including granular materials,
silts, and clays
PCA 1992. Usually, cement-treated soils are
mixed with low cement dosages with or without a targeted
strength, depending on their functions, whereas the cementstabilized
soils are mixed with high cement dosages with a targeted
strength.
The durability of cement-treated or stabilized soils is another
concern for the mix design of cement stabilization under wetting–
drying or/and freezing–thawing cycles. Due to the long testing
period of durability tests
about six weeks, many state highway
agencies currently require a minimum 7-day unconfined compressive
strength
UCS with typical values varying from 1.4 to
5.2 MPa
from 200 to 750 psi, in lieu of the durability test
Little
et al. 1999, assuming the intrinsic correlation between the
strength and durability will secure the required durability. However,
this approach may have a problem for the cement stabilization
with a low strength target
1.03 MPa because it does not
assure the durability. Yet, moisture’s influence on the durability of
cement-treated base or subbase materials is currently not directly
addressed by most state highway agencies.
Assuming all other conditions are the same, untreated and
cement-treated or stabilized materials with less free moisture are
expected to perform better in the long term than those with more
free moisture. Therefore, Scullion and Saarenketo
1997 and
their associates
Saarenketo 2000; Syed et al. 2000, 2003 recently
developed a new method, tube suction
TS test, to characterize
water resistance of untreated and treated or stabilized
base and subbase materials. A capacitance probe, which measures
the dielectric value
DV of materials, is used in this test to indirectly
but quantitatively assess the amount of free water content
in aggregate base materials. Based on their successful preliminary
studies, they proposed a maximum DV criterion for assessing the
quality of base materials: good base aggregates have the maximum
DV less than 10; marginal base aggregates have the maximum
DV ranging from 10 to 16; and poor base aggregates have
the maximum DV exceeding 16
Scullion and Saarenketo 1997.
Scullion and Saarenketo
1997 also suggested that TS tests be an
alternative to the traditional wetting-drying durability test as
water affinity is a good indicator for both water sensitivity and
durability of materials. Table 1 summarizes the three testing procedures
that are discussed herein and their respective criteria.
Although the TS test seems promising as an alternative to the
traditional wetting–drying durability test, most works on the TS
test so far have been confined to aggregates and little information
has been reported on cohesive soils, such as silts and clays that
constitute subbase or subgrade materials in many areas.
Few studies have ever been reported in the literature about the
comparison of durability prediction based on these three procedures,
especially with respect to any influence on soil-cement mix
design caused by following them. Therefore, the authors conducted
a study that a problematic subgrade soil often encountered
in Louisiana is selected to investigate such influence. TS, 7-day
UCS, and wetting–drying durability tests were performed in this
study, with an emphasis on water susceptibility and durability of
the stabilized soil. The results provide an experimental basis to
understand, evaluate, and compare durability prediction from
these three testing procedures, and assist pavement designers in
designing cost-effective and good-performing soil cement.