Assessing the Quality of Soils Modified with Lime Kiln Dust
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Assessing the Quality of Soils
Modified with Lime Kiln Dust
Measuring Electrical Conductivity with
Time Domain Reflectometry
Radha Krishna Daita, Vincent P. Drnevich, Daehyeon Kim,
and Renpeng Chen
By-product materials such as lime kiln dust (LKD), cement kiln dust, throughout the United States. Traditional chemical admixtures include
and fly ash are used for modifying pavement subgrades. It is insufficient quicklime, hydrated lime, and cement. Recently, however, a number
to use density and water content measurements for compaction quality of by-product materials recycled as chemical additives have been
control on modified soils where chemical reactions occur because the used as stabilizers, including lime kiln dust (LKD), cement kiln dust,
properties of the modified soil differ from those of the parent materials. and fly ash. Use of chemicals such as LKD makes stabilization of
The amount of lime, the clay mineralogy, the soil water content, and the subgrades economical and has the added advantage of recycling a
percentage fines in the soil are important parameters that affect the com- by-product. LKD is being extensively used in the state of Indiana as
paction behavior and subsequent properties of the modified soil. Hence, the chemical additive for the modification and stabilization of sub-
they should be considered for effective quality control. The behavior of grades. The addition of lime to soil involves chemical reactions that
soils modified with LKD is more complex than that of soils modified with have been studied extensively by past researchers. The chemical
lime because of the presence of various compounds besides lime in LKD. reactions are classified into short-term (modification: hydration and
Research indicates that the electrical conductivity of soil is strongly flocculation) and long-term (stabilization) reactions. Usually, engi-
affected by chemically modifying soils and tracks the chemical reactions neers and researchers study only the changes in physical and engi-
with time. Time domain reflectometry (TDR) technology using the Pur- neering properties of chemically modified soils. Monitoring chemical
due TDR apparatus measures the electrical conductivity of soil and is changes with time by direct or indirect means has significant merit for
feasible for use in the laboratory and in the field. This paper describes the study of chemically modified soil. Generally, chemical changes
the electrical conductivity behavior of an LKD-modified soil for various in a system are associated with simultaneous changes in its electri-
compaction conditions. The variation of electrical conductivity with cal properties. This paper describes the behavior of LKD-modified
time for a given cohesive soil is shown to depend on the amount and type soils in terms of their compaction characteristics and electrical prop-
of LKD and the water content. A hyperbolic-type model is proposed to erties. The electrical conductivity and dielectric constant of a mod-
capture the change in electrical conductivity with time for different ified soil were measured with a Purdue TDR apparatus. Attempts
amounts of LKD. Test results indicate that electrical conductivity also were made to take the past research on chemically modified soils a
can be correlated to the penetration resistance of modified soil, which is step further by testing the potential of the TDR method as a possi-
an indicator of shear strength. Compared with conventional test methods, ble quality control method for modified subgrades. The work also
TDR is expected to provide better understanding of the rate and extent explored the potential of using TDR to determine the amount of
of chemical reactions between chemical modifiers such as LKD and soil LKD present in a soil from electrical conductivity measurements.
and be useful for compaction quality control.
BACKGROUND
When field conditions are not favorable for compacting subgrades,
soil improvement is frequently employed to facilitate the construc- The chemical reactions that occur when lime is added to soil consist
tion of pavements and enhance the engineering properties of the of time-dependent short-term and long-term reactions (1). The short-
soil to improve subgrade performance. Improving soil by adding term reactions primarily constitute hydration of CaO to Ca(OH)2 and
chemical admixtures is a technique that continues to be widely used the agglomeration–flocculation of clay particles as a result of cation
exchange. These short-term changes are rapid and are sometimes
referred to as modification because they modify the soil to a relatively
R. K. Daita, H. C. Nutting Company, 611 Lunken Park Drive, Cincinnati, OH 45226.
workable state when compared with its original state. These short-
V. P. Drnevich, School of Civil Engineering, Purdue University, 550 Stadium Mall
Drive, West Lafayette, IN 47907-2051. D. Kim, Indiana Department of Transporta- term reactions result in a high pH environment, which facilitates the
tion Research Division, 1205 Montgomery Street, P.O. Box 2279, West Lafayette, dissolution of aluminum and silicon from clay minerals present in
IN 47906-2279. R. Chen, Department of Civil Engineering, Zhejiang University, the soil. These elements react with calcium to form pozzolanic com-
38 Zheda Road, Hangzhou, 310027, China. pounds; namely, calcium silicate hydrate (CSH) and calcium alu-
Transportation Research Record: Journal of the Transportation Research Board,
minate hydrate (CAH). These compounds are cementitious in nature
No. 1952, Transportation Research Board of the National Academies, Washington, and crystallize to bind the structure together, providing long-term
D.C., 2006, pp. 101–109. strength. The improvement in the properties of lime-stabilized soil
101102 Transportation Research Record 1952 depends on various factors, including time and temperature. Various researchers have reported on the effects of time on strength, com- paction behavior, and permeability (2–5). Because the improvement process involves chemical reactions, it must be temperature dependent. The long-term and short-term reactions discussed so far corre- spond to the addition of quicklime (CaO). LKD is mainly composed of CaO but also contains varying amounts of CaCO3, CaSO4, fly ash, and limestone (6 ). The reactions of LKD with soil will be complex because of the presence of these various other compounds along with available lime in the form of both quicklime and hydrated lime. It can be assumed, however, that the reactions between soil and the available free lime would be similar to the reactions between soil and quicklime. Recent research on chemically stabilized soils has concentrated on studying the changes in the electrical properties, such as electri- cal conductivity and dielectric constant with time. The idea is based on the application of electrical measurements in concrete technol- ogy to monitor the hydration of cement and a simultaneous increase FIGURE 1 Purdue TDR apparatus. in strength. Beek and Hilhorst characterized the microstructural changes in young concrete based on the dielectric measurements using microwave frequencies (7). They found that with time, as the conductivity and surface conductivity; however, the apparent dielec- strength of the concrete increased, its electrical conductivity decreased. tric constant is relatively independent of the conductivity. Based on These observations enabled them to develop a nondestructive way measurements of dielectric constant and electrical conductivity, the of testing strength development in concrete based on conductiv- water content and dry unit weight of the soil can be determined fol- ity measurements. Like concrete, lime-stabilized soils also involve lowing either of two methods: the two-step TDR method (ASTM D hydration reactions and changes in properties with time. Boardman 6780-02) and the one-step TDR method (13). et al. found that the electrical conductivity of a lime-modified soil is Yu and Drnevich showed that electrical conductivity was an higher than that of the natural soil and that it decreases with time (8). accurate and effective indicator of the progress of hydration in lime- They explained that the initial increase in electrical conductivity is stabilized soils at the I-70 Relocation Project in Indianapolis (14). caused by Ca+2 ions in the system and that as these ions form the The ultimate goal of this research is to develop a field quality con- complex pozzolanic compounds CAH and CSH, the conductivity trol procedure for chemically modified subgrades based on the mea- decreases. They concluded that effective quality control of lime- surements of electrical properties. The developed procedure(s) should stabilized subgrades can be achieved by electrical conductivity mea- not only provide information related to engineering properties of the surements. However, they did not develop or propose a procedure subgrade but also take into account the various factors affecting the for performing in situ monitoring. process of stabilization. The developed procedure should not only test Research on one-dimensional electromagnetic wave propagation in both the short-term and long-term performance of the subgrade, but soils introduced time domain reflectometry (TDR) technology to geo- also provide details on the amount of stabilizer, the depth of stabi- technical engineering (9–12). TDR involves propagating transverse lization, and the uniformity of mixing, all of which affect performance electromagnetic waves through soils by means of special soil probes. of the stabilized soil. During propagation through the medium, the electromagnetic wave encounters impedance mismatches, and a portion of the wave energy is reflected back to the TDR device while the remaining portion is EXPERIMENTAL PROGRAM transmitted. Some of the energy is dissipated within the soil. Figure 1 shows the Purdue TDR apparatus. The test can be per- The experimental program had the following objectives: formed both in the lab and in situ, and the configuration requires a coaxial cable with a center probe to transmit the electromagnetic • Characterize the chemical composition of LKD, wave. A standard Proctor compaction mold can be used in the lab- • Examine the effects of the amount of LKD on the compaction oratory, where the mold acts as the shield in a coaxial cable and a behavior of a stabilized soil, steel rod driven through a template acts as the center lead. In the • Study the time-dependent behavior in electrical properties of field, four spikes are used: Three spikes are driven in a pattern so as stabilized soil, and to simulate a shield, and the center spike acts as the center lead of a • Examine the feasibility of developing a method to estimate the coaxial cable. A multiple rod probe (MRP) head placed over this amount of LKD in the modified soil. coaxial “cable” allows an electromagnetic wave to be propagated through the soil to the depth of the probe. In either the lab or field case, the dielectric medium between the center rod and the shield is soil Materials whose dielectric constant (Ka) can be calculated based on the time elapsed between the portion of the signal reflected from the soil sur- The research project used several locally collected soils. Tests with face and another portion reflected from the end of the probe. Voltage one of the soils, Orchard clay, will be featured in this paper. It was measurements of the applied and reflected signals allow the bulk tested for basic index properties of grain size distribution, Atterberg electrical conductivity (ECb) of the soil to be determined. The appar- limits, compaction characteristics, and pH following the relevant ent dielectric constant and the electrical conductivity of a soil are ASTM standards. Two LKDs, Buffington LKD (BLKD) and South strongly affected by the water content and dry unit weight of the soil. Chicago LKD (CLKD), provided by Mount Carmel Sand and Gravel, The bulk electrical conductivity is strongly affected by the pore fluid were used. LKD was added by dry weight of soil solids and the opti-
Daita, Drnevich, Kim, and Chen 103
mum amount of stabilizer was determined following the standard this supposition, the surface of the 4%L_OMC2 and 4%L_OMC3
ASTM D 6276-99 pH test. Table 1 provides the chemical composi- specimens were sealed with wax and were monitored for 28 days.
tion of the LKDs used in this research. The BLKD has more available The conductivity was measured every hour for the first week, and
lime than the CLKD. As shown in Table 1, the chemical composition thereafter every day for 28 days. The second specimen prepared in
of LKDs is not detailed; hence, X-ray diffraction experiments were each trial was used to find the penetration resistance just after com-
performed on both the LKDs in their natural and hydrated states. paction, 24 h after compaction, and 1 week after compaction. Only
These experiments helped to characterize the chemical composition one trial was performed for tests with water contents ±2% OMC. Sim-
and to study the hydration products of LKD. Diffraction patterns ilar tests were conducted on Orchard clay modified with 2% BLKD
were obtained with a PANalytical X’Pert PRO MPD X-ray dif- at its OMC and 6% BLKD at water contents equivalent to OMC and
fraction system equipped with a PW3050/60 θ-θ goniometer and OMC+2%. These specimens were monitored for only 1 week.
a Co-target X-ray tube operated at 40 KeV and 35 mA. For testing
hydrated specimens, LKD was initially mixed with water and air-dried
for 2 days. The samples were pulverized, and powdered specimens RESULTS AND DISCUSSION
were prepared and tested in a similar way as those in the natural state.
Material Properties
Tests on LKD-Modified Soils Table 2 presents the basic engineering properties of Orchard clay.
From Table 2 we can observe that LMO with CLKD is higher than
Compaction Tests that with BLKD, which proves again that BLKD has a greater
amount of available lime than does CLKD. The X-ray diffraction
In the field, the mixing procedure of LKD and natural subgrade soil patterns for BLKD in both its dry and hydrated forms are pre-
is not very uniform, and hence it is possible that the stabilized sub- sented in Figure 2. The chemical composition of the LKD based
grade may contain varying amounts of stabilizer at different loca- on the d-values of diffraction peaks is also shown in Figure 2. In
tions and different depths. To account for this variability and also Figure 2 that intensity of the quicklime peaks (peaks 1) decreased
to study the compaction behavior of stabilized soil with different in hydrated specimens, whereas the peaks of Ca(OH)2 (peaks 2)
amounts of LKD, Orchard clay was modified and compacted with increased at the same time and indicates that the hydration of avail-
varying amounts of BLKD and CLKD. BLKD was mixed in even- able quicklime. X-ray diffraction tests performed with CLKD also
numbered percentages (i.e., 2%, 4%, 6%, 8%), and CLKD was mixed yielded similar results.
in odd-numbered percentages (i.e., 3%, 5%, 7%, 9%). The lime mod-
ification optimum (LMO) for BLKD is 4%, and for CLKD, 7%. The
electrical conductivity and the dielectric constant of the compacted Compaction Behavior
specimen were determined using the Purdue TDR apparatus just
after compaction. Figure 3 shows the compaction behavior of Orchard clay modified
with various amounts of BLKD. From Figure 3 we can observe that
the addition of 2% and 4% of BLKD resulted in an increase in OMC
Monitoring Tests and a decrease in γdmax when compared with the natural soil. With the
addition of 6% BLKD, the OMC decreased back toward the OMC of
A test program was planned to study the changes in the electrical the natural soil, and the dry unit weight further decreased. On addi-
properties of an LKD-modified soil with time in both short- and tion of 8% BLKD, a significant additional decrease in OMC occurs,
long-term conditions. Orchard clay modified with the LMO amount and there is an increase in dry unit weight when compared to 6%
for BLKD (4%) at three different water contents—optimum mois- BLKD. Tests conducted on Orchard clay modified with various
ture content (OMC) and ±2% of OMC—was compacted in a stan- amounts of CLKD yielded similar results. It can be concluded from
dard Proctor mold. Two specimens were prepared for every test. The these observations that the compaction behavior of modified soils is
first specimen was used for monitoring the electrical properties with a function of the amount of LKD.
time, and the second specimen was used to test penetration resis- The OMC of the soil is affected by the fraction of clay-sized par-
tance with the apparatus described in ASTM C 403-05. The test with ticles. The larger the fraction of these particles, the higher the OMC
water content equal to OMC was repeated three times (4%L_OMC1, becomes. The soil tends to behave more like a granular soil with the
4%L_OMC2, and 4%L_OMC3). The surface of the 4%L_OMC1 addition of lime as a result of hydration, flocculation, and agglom-
specimen was not sealed and was monitored for 1 week. Specimen
drying was thought to contribute to the observed behavior. To validate
TABLE 2 Properties of Orchard Clay
TABLE 1 Chemical Composition of BLKD and CLKD as Provided Property Orchard Clay
by Supplier
Particle size analysis Sand = 28%, silt = 47%, clay = 25%
Buffington South Chicago Liquid limit 35
LKD Characteristic % Value % Value
Plasticity index 19
Available lime 32.2 11.3 AASHTO classification A-6 (11)
Ca(OH)2 —calculated 42.52 14.94 USCS classification Lean clay (CL)
Magnesium 1.65 27.73 Compaction characteristics γdmax = 113 lb/ft3, OMC = 16.5 %
Hydroxide equivalent 3.03 50.98 Soil pH In distilled water = 7.74; in 0.01M CaCl2
Total equivalents as Ca(OH)2 30 – 45.55 65.92 LMO BLKD = 4%, CLKD = 7%104 Transportation Research Record 1952
40000
BLKD_1
Ca C O3
Ca O; Ca Mg (C O3)2
30000
Ca Mg (C O3)2
20000
Ca C O3; Ca S O4
Ca Mg (C O3)2; Ca S O4
Ca O
Ca C O3; Si O2
Ca C O3; Ca S O4
Ca (OH)2
Ca Mg (C O3)2
Ca S O4
Ca C O3
Ca (OH)2
10000
Ca S O4
Si O2
Ca S O4
Ca S O4
Counts
BLKD_Hydrated-Cycle1
Ca C O3
40000
Ca (OH)2
Ca (OH)2
Ca Mg (C O3)2; Ca S O4 !2 H2 O
Ca C O3; Si O2; Ca S O4 !2 H2 O
Ca C O3; Ca S O4 !2 H2 O
Ca C O3; Ca S O4
Ca (OH)2; Ca S O4
20000
20 30 40 50
Position (°2Theta)
FIGURE 2 X-ray diffraction patterns for dry and hydrated BLKD.
eration. With the addition of small amounts of LKD, the reactions the higher pH environment in the modified soil changes the surface
between LKD and the clay particles are not complete. The increase of charge distribution in the clay soil particles, resulting in an increase
effective particle size (flocculation and agglomeration) is not signifi- in repulsion between particle layers. This, along with changes in the
cant, but the addition of LKD increases the fraction of fine particles, particle size distribution, causes a decrease in maximum dry density.
causing the OMC to increase. With further addition of LKD, the reac- From the plots in Figure 3, it is clear that the use of density and
tions between LKD and soil are more pronounced, the effective par- water content measurements for compaction quality control on mod-
ticle size changes are significant, and the soil tends to behave more ified soils is insufficient because the properties of the modified soil
like a granular soil and causes the OMC to decrease. In addition, are different from those of the parent materials.Daita, Drnevich, Kim, and Chen 105
114
113 0%LKD
2%LKD
0%LKD 4%LKD
112
6%LKD
8%LKD 2%LKD 8%LKD
111
Dry Unit Weight, γd (lb/ft3)
4%LKD
110 6%LKD
109
108
107
106
105
1 lb/ft3 = 0.16 kN/m3
104
10 12 14 16 18 20 22
Water Content, w (%)
FIGURE 3 Compaction behavior of BLKD-modified Orchard clay.
Electrical Properties ing amounts of LKD. The hydration of LKD provides more free ions
in the pore water, which increases the electrical conductivity of the
TDR measurements were conducted after compaction. Figure 4 soil. The higher the amount of LKD, the higher will be the electrical
shows the electrical conductivity measured just after compaction conductivity.
for different water contents of Orchard clay modified with various The initial conductivity will decrease with time as a result of the
amounts of BLKD. The electrical conductivity increases with increas- physicochemical reactions shown in Figure 5, where the variation
200 8% LKD
0%BLKD
y = 13.11x - 84.92
180 4%BLKD 6% LKD
R2 = 0.96
6%BLKD
y = 14.79x - 84.39
160 8%BLKD
R2 = 1.00
Electrical Conductivity, ECb (mS/m)
140
4% LKD
120
y = 10.53x - 55.31
R2 = 0.96
100
80
60 0% LKD
y = 2.96x + 5.68
40
R2 = 0.88
20
0
10 12 14 16 18 20 22
Water Content, w (%)
FIGURE 4 Linear regressions between electrical conductivity measured immediately after compaction
and water content for BLKD-modified Orchard clay.106 Transportation Research Record 1952
200
6%_19%w 4%L_OMC1
180
4%L_OMC2
6%L_OMC
4%L_OMC3
160
4%L_19%w 4%L_15%w
Electrical Conductivtiy, ECb (mS/m)
140 4%L_OMC2 4%L_19%w
4%L_OMC3 2%L_OMC
120 4%L_15%w
6%L_OMC
2%L_OMC 6%L_19%w
100
80
60
40
20
4%L_OMC1
0
1 10 100 1000 10000 100000
Time, t (min)
FIGURE 5 Variation in electrical conductivity with time for LKD-modified Orchard clay.
in electrical conductivity is plotted versus the log of time for all the apparent dielectric constant agrees well with the measurement of
specimens tested. It is evident from Figure 5 that electrical conduc- oven-dried water content. There is no decrease in water content for
tivity at any time is a function of both water content and the amount sealed specimens before and after monitoring.
of LKD. The electrical conductivity decreases with time for all the
modified specimens. The data for the 4%L_OMC1 specimen without
any wax seal decrease faster in comparison with data for other sealed Strength Increase
specimens with the same initial water content and amount of LKD.
The difference can be explained by the drying of the soil specimen The plot between the penetration resistance obtained from the needle
during monitoring. penetrometer test ASTM D1558-04 and the electrical conductivity
The electrical conductivity of the natural soil at similar water con- for all the specimens tested is shown in Figure 7. From Figure 7 we
tents, as seen in Figure 4, is very low (about 40 to 60 mS/m) and observe that the curve between resistance and conductivity is linear
does not change with time. The decrease in the electrical conduc- for high electrical conductivities (which corresponds to times shortly
tivity with time for modified soils is caused by both short-term reac- after compaction) and then flattens as the rate of increase in strength
tions (flocculation and cation exchange) and long-term reactions. decreases with time. For 4% BLKD-modified Orchard clay, at a
Figure 6 shows a plot between normalized net decrease of electrical given value of electrical conductivity, the penetration resistances fall
conductivity and time, where the normalized net change of electri- within a narrow range of values. In comparison, the penetration resis-
cal conductivity is defined as ΔECb(t) = [ECb1 − ECb(t)]/ECb1 where tance of specimens with 2% and 6% BLKD at a given value of elec-
ECb1 is the initial electrical conductivity (the first measurement after trical conductivity are lower and higher than that of specimens with
compaction) and ΔECb(t) is the electrical conductivity measured 4% LKD. With the knowledge of the amount of LKD, this graph
with time. The net change in electrical conductivity appears to be a works as a tool for estimating the penetration resistance of modi-
measure of the pozzolanic activity of a modified soil at any given fied Orchard clay from the measured values of electrical conduc-
time. From Figure 5 we observe that plots of specimens with 4% LKD tivity. Further testing on other soils should check whether a unique
all follow the same trend and merge into a single curve. The plots for relationship exits between electrical conductivity and penetration
2% and 6% LKD follow different paths. For the same amount of resistance.
LKD, the pozzolanic activity of a soil with a higher percentage of
fines would be significant in comparison with that of a soil with a
very small amount of fines. Estimate LKD Percentage with
The apparent dielectric constants of all the specimens with the Electrical Conductivity
same water content are very close to each other. The apparent dielec-
tric constant decreases slightly, but not significantly during monitor- The percentage of LKD in the soil is important for quality control in
ing. Apparent dielectric constant measured by TDR is an indicator the field. The results of the monitoring tests indicate that electrical
of free water in the soil. The curing process in stabilized soil appar- conductivity can be used to estimate the amount of LKD present in
ently does not change the free water content. The observation of a modified soil. Generally, field quality control testing will be doneDaita, Drnevich, Kim, and Chen 107
Time, t (min)
1 10 100 1000 10000
0
0.1
4%L_OMC2
Normalized ECb = (ECbt=0-ECbt)/ECbt
4%L_OMC3
0.2
4%L_15%w
4%L_19%w
0.3 2%L_OMC
6%L_OMC
0.4 6%L_19%w
0.5
0.6
0.7
FIGURE 6 Normalized electrical conductivity of BLKD-modified Orchard clay with time.
within 1 or 2 days after chemical modification. The conductivity where ECb(t) is the conductivity at time t after the first measurement,
measured in the compacted specimens with time was fitted with the and B and A are fitting constants.
hyperbolic equation Figure 8 shows how A and B vary with the amount of LKD. The
calibration constant B denotes the maximum decrease of electrical
Bt conductivity, and B/A denotes the initial gradient of the decrease of
ECb (t ) = ECb1 − (1)
A+t conductivity. B increases with the amount of LKD. The mean value
7000
6%L_OMC
4%L_15%w 4%L_OMC2
4%L_OMC3
6000 4%L_OMC3
4%L_OMC2 4%L_15%w
Penetration Resistance (psi)
4%L_19%w
5000
2%L_OMC
6%L_OMC
4%L_19%w
4000
3000
2%L_OMC
2000
1 lb/in.2 =6.89 kN/m2
1000
60 80 100 120 140 160 180
Electrical Conductivtiy, ECb (mS/m)
FIGURE 7 Penetration resistance and electrical conductivity for LKD-modified Orchard clay.108 Transportation Research Record 1952
100 is dependent on the parent soil and characteristics of the LKD used.
The validation of the method needs to be verified with other soils
B: mS/m
and types of chemical stabilizers.
80 A: hours
A and B Value
60 SUMMARY AND CONCLUSIONS
X-ray diffraction tests identified the chemical composition of LKD
40 and also justified its use as a chemical modifier. The compaction
behavior of LKD-modified soils is dependent on the amount of LKD,
20 the water content of the modified soil, and various other factors. From
the results of the long-term monitoring tests, the relationship between
normalized electrical conductivity and time validate that electrical
0 conductivity measured with a TDR apparatus is directly correlated to
0 1 2 3 4 5 6 7 both the amount of LKD and the water content. In addition, electri-
LKD Percent, % cal conductivity is strongly correlated with the needle penetration
FIGURE 8 Fitting constants for electrical conductivity with time. resistance of an LKD-modified soil. Dynamic cone penetration tests
should be performed along with TDR tests in the field to develop
similar correlations between electrical conductivity and penetration
of A is 5.56 with a deviation of 1.0. Normalizing Equation 1 with B resistance for field quality control.
and A results in The test results presented here validate that electrical conductiv-
ity is dependent on various key parameters affecting the properties
T of modified soils. Therefore, simple electrical conductivity measure-
ΔECb (T ) = (2)
1+ T ments can be used for field quality control of chemically modified
soils. The authors are currently working on extending these obser-
where ΔECb(T) = (ECb1 − ECb(T))/B and T = t/A. vations to various soils by testing subgrades modified with LKD.
The normalized curves are plotted in Figure 9. The hyperbolic Future research will attempt to develop a model that relates the elec-
function fits all the curves very well and is quite independent of the trical conductivity, time, and amount of lime or LKD of a modified
amount of LKD in the soil. soil based on the field test results.
Because the B value is strongly related to the LKD percentage in
the soil, it can be used to estimate the LKD percentage. If two TDR
measurements are taken at the same place and at different times after ACKNOWLEDGMENTS
construction in the field and assume that A = 5.56, the initial electri-
cal conductivity and the B value can be calculated with Equation 1. This work was supported by the Joint Transportation Research Pro-
With the B value and the calibration plot (e.g., Figure 8), it is possi- gram administered by the Indiana Department of Transportation and
ble to find the percentage of LKD. The calibration plot of the B value Purdue University. The authors are grateful to the FHWA–Indiana
1
0.8 4%L_OMC2 4%L_OMC3
4%L_15%w 4%L_19%w
0.6 2%L_OMC 6%L_OMC
ΔECb(T)
T/(1+T)
0.4
0.2
0
0 2 4 6 8 10 12 14 16 18 20
T
FIGURE 9 Hyperbolic model fit for normalized electrical conductivity with time.Daita, Drnevich, Kim, and Chen 109
Department of Transportation–Joint Transportation Research Proj- tion Research Record: Journal of the Transportation Research Board,
ect for supporting this research. They appreciate the input of the No. 1757, TRB, National Research Council, Washington, D.C., 2001,
pp. 3–13.
Study Advisory Committee members: Nayyar Zia Siddiqui, P. A.;
9. Benson, C. H., and P. J. Bosscher. Time-Domain Reflectrometry (TDR)
Ron Heustis; Greg Pankow (INDOT); Mark Behrens (Schneider in Geotechnics: A Review, Nondestructive and Automated Testing for Soil
Corp.); Doug McPherson (Mt. Carmel Sand and Gravel); and Val and Rock Properties. ASTM SPT 1350 (W. A. Marr and C. E. Fairhurst,
Straumins (FHWA). The authors acknowledge the assistance pro- eds.). American Society for Testing and Materials, West Conshohocken,
vided by lab manager Janet Lovell, Adam Prochaska, Joon Ho Penn., 1999.
10. Noborio, K. Measurement of Soil Water Content and Electric Con-
Hwang, and Uma Shankar Balunaini in this research.
ductivity by Time Domain Reflectrometry: A Review. Computers and
Electronics in Agriculture, Vol. 31, 2001, pp. 213–237.
11. Drnevich, V. P., X. Yu, J. Lovell, and J. K. Tishmack. Temperature
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