Advances in Civil Engineering Materials

Advances in Civil Engineering Materials J. Gudimettla1 J. Tanesi,2 G. Crawford,3 and A. Ardani4

DOI: 10.1520/ACEM20160028

Evaluation of the Specimen Saturation Criterion for the AASHTO T336 Test Method VOL. 6 / NO. 1 / 2017

Advances in Civil Engineering Materials

doi:10.1520/ACEM20160028

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Vol. 6

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No. 1

/

2017

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available online at www.astm.org

J. Gudimettla1 J. Tanesi,2 G. Crawford,3 and A. Ardani4

Evaluation of the Specimen Saturation Criterion for the AASHTO T336 Test Method Reference Gudimettla, J. Tanesi, J., Crawford, G., and Ardani, A., “Evaluation of the Specimen Saturation Criterion for the AASHTO T336 Test Method,” Advances in Civil Engineering Materials, Vol. 6, No. 1, 2017, pp. 119–133, http://dx.doi.org/10.1520/ACEM20160028. ISSN 2165-3984

ABSTRACT Manuscript received May 17, 2016; accepted for publication January 4, 2017; published online April 7, 2017. 1

2

3

4

Federal Highway Administration/ ATI, E73-105C, HIAP-10, 1200 New Jersey Ave, SE, Washington, D.C. 20590 (Corresponding author), e-mail: [email protected] http://orcid.org/0000-00019898-325X SES Group and Associates, LLC, Turner-Fairbank Highway Research Center/FHWA, 6300 Georgetown Pike, McLean, VA 22101 Federal Highway Administration, E73-438, HIAP-10, 1200 New Jersey Ave, SE, Washington, D.C. 20590 Concrete Research Studies, Turner-Fairbank Highway Research Center/FHWA, 6300 Georgetown Pike, McLean, Virginia 22101

Realizing the importance of coefficient of thermal expansion (CTE) in concrete pavement design, the Federal Highway Administration conducted a ruggedness study for the AASHTO T336 test method in 2012. Of the seven variables that were evaluated as part of the ruggedness study, specimen saturation criterion was found to be one of the significant variables that warranted further investigation. This paper documents a follow-up study performed to specifically evaluate the effect of specimen saturation criterion on the measurement of CTE using the AASHTO T336 test method. CTE tests were conducted on multiple specimens from five concrete mixtures (two field and three laboratory prepared) at different levels of saturation in water: T336 criterion, 4 days, 7 days, 14 days, 28 days, and vacuum saturation. Data analysis from this study indicated that there is no statistical difference in CTE measurement after 28 days of water saturation versus T336 criterion, 4 days, 7 days, 14 days, and vacuum saturation. Based on this limited study, it appears that the current saturation criterion outlined in AASHTO T336 is adequate. Keywords coefficient of thermal expansion (CTE), concrete saturation, vacuum saturation, linear variable differential transducer (LVDT)

C 2017 by ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959 Copyright V

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GUDIMETTLA ET AL. ON SPECIMEN SATURATION CRITERION

Introduction A number of studies over the past 10 years have well documented the importance of the coefficient of thermal expansion (CTE) as a key input to characterize concrete behavior in mechanistic-empirical pavement design [1–3]. With the release of the American Association of State Highway and Transportation Officials (AASHTO) Pavement ME DesignV software in 2011, there is a greater emphasis on measuring CTE of concrete due to its significance on pavement design [4]. For example, in 2014, 37 state highway agencies, 61 private sector companies, 18 universities, 2 local agencies, 10 international agencies, and 4 Canadian provinces licensed the AASHTO Pavement ME DesignV software. There is also interest in using CTE as a Quality Assurance test [5]. California currently requires contractors to test the CTE of concrete during production and the Texas Department of Transportation (DOT) has put a maximum limit on the CTE of aggregates used for continuously reinforced concrete pavement projects. The most widely used test method to measure the CTE of concrete is the AASHTO T336-15 [6]. The concrete CTE is a relatively new test method and was first accepted as an AASHTO provisional test method (AASHTO TP 60) in 2000 [7] and became a standard test method (AASHTO T336-09) in 2009 [8]. R

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Background Realizing the importance of CTE in pavement design, the Federal Highway Administration (FHWA), over the past several years, has worked with AASHTO to improve the CTE Test Method. Some of the activities performed as part of this work included (1) identifying a major erroneous assumption in the test method regarding the calibration of the test frame, (2) conducting two interlaboratory studies to obtain an understanding of the variability of the test method, (3) introduction of certified calibration and verification specimens, (4) identifying materials that could be used as calibration and verification specimens, (5) addressing linear variable differential transducer (LVDT) temperature effects, (6) analysis of CTE variability based on several field projects, and (7) update of the CTE data in LTPP database, etc. Results from some of these studies have been incorporated in the various versions of the test method [6–9]. References to the publications documenting the various activities mentioned above are listed in Gudimettla et al. [9]. In addition to those listed previously, in 2012, FHWA completed a ruggedness study [10] for the AASHTO T336 test method in order to evaluate the most likely variables to affect the test results. The ruggedness study comprised 2 mixtures (either with gravel or limestone coarse aggregate) with CTEs ranging from approximately 6.3 l-strain/ C and 11.3 l-strain/ C, 4 laboratories, and two different types of commercially available equipment. In this study, seven factors pertaining to the AASHTO T336 test method were evaluated at two levels: time at temperature extremes (T336 criterion or 2 extra hours after it), water level (same water level used for calibration or 0.51 mm above it), position of the LVDT (LVDT positioned either on paste or on coarse aggregate), number of segments (necessary to achieve T336 requirement or extra 2 segments after that), saturation criterion (T336 or saturated since demolding), specimen length (175.30 or 177.8 mm), and temperature of the Advances in Civil Engineering Materials


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first segment (10 or 50 C). The results from the ruggedness study indicated that saturation criterion factor had a statistically significant impact on the CTE test results in eight out of the ten cases evaluated (five CTE units times two concrete mixtures with different aggregates). It is important to clarify that although statistically different, the CTE differences between specimens saturated either according to T336 or in continuous saturation (never left to dry or resaturated) were very small: 0.1 l-strain/ C in 4 out of the 10 cases, 0.2 l-strain/ C in 4 out of the 10 cases, 0.3 l-strain/ C and 0.4 l-strain/ C. This paper documents a follow up study that exclusively focused on evaluating the impact of specimen saturation criterion on the AASHTO T336 test results.

Literature Review Significant research was performed in the 1940s and 1950s to study and quantify the effect of the cement paste relative humidity or moisture content on its coefficient of thermal expansion. Some of the original work on this topic was performed by Meyers [11,12], and Powers [13]. Powers called the shrinkage and swelling of cement paste and concrete that does not involve gain or loss of water as hygrothermal volume change. According to Powers, the entropy of gel water is different from that of capillary water in cement paste. If equilibrium exists between water in the gel pores and that in capillary pores at a given temperature, a change of temperature will disturb the equilibrium and will require the water to move to or from the gel to restore equilibrium. The significant consequence of hygrothermal volume change is that paste and, as a result, concrete do not have a constant thermal coefficient over different levels of moisture content. Fig. 1a [14] shows the relationship between moisture content and thermal coefficient of cement paste based on studies performed in the 1950s. According to Fig. 1a, cement paste has the maximum coefficient of thermal expansion when its moisture content is around 70 %, where the CTE at 100 % saturation was nearly half of what it was at 70 % saturation. In a more recent study, Yeon et.al [15] found that for the same saturation levels, the difference in paste CTE was only about 10 %–12 % (Fig. 1b).

FIG. 1

Effect of moisture content and RH on the CTE of cement paste.


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FIG. 2 Effect of RH on the CTE of concrete.

Work on concrete also indicated that thermal expansion of concrete changes with the change in moisture content or relative humidity (Fig. 2). However, the effect of moisture content on concrete CTE was found to be less pronounced since the volume of cement paste in concrete is significantly less, and aggregates do not experience similar changes in thermal expansion with change in relative humidity. For Powers [13] (Fig. 2a), the CTE at 100 % saturation is about 70 and 87 % of the maximum for two concretes with limestone aggregate and quartz aggregate, respectively. Yeon et al. [15] found a lower CTE difference (only about 3 %) between 80 and 100 % relative humidity (Fig. 2b). Some of the divergences on the magnitude of the effect of the moisture content on the CTE when comparing studies over the years (Figs. 1 and 2) may have been partly due to the fact that the deformations measured are very small and the accuracy of the instruments used for the displacement and relative humidity measurements may have evolved considerably during this time period. Other aspects that may have influenced these divergent results are the use of different methodologies, the number of replicates, and the mixtures proportions (w/c ratio and aggregate contents) used. Neverthless, the studies mentioned previously evaluated the effect of a wide range of relative humidities on the CTE, but were unable to provide information on the appropriateness of the T336 saturation criterion. Only a study by Kohler et al. [16] reported testing concrete specimens between 97 and 100 % and found little differences in CTE (Fig. 3). It should be noted that relative humidity and moisture content are both related to degree of saturation but are not interchangeable terms. Relative humidity refers to the ratio of the water vapor present to the amount present in a saturated atmosphere at a given temperature, while moisture content refers to the ratio of the water mass in a material to its total dry mass [17]. Degree of saturation represents the ratio of the absolute volume of absorbed water to the total volume of pores (i.e., the total volume of water that can be absorbed by concrete) [18]. The terms used in this document represent the original terms used in the references cited. Advances in Civil Engineering Materials


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FIG. 3 Degree of saturation versus CTE on a concrete specimen.

Degree of Saturation Criterion in the AASHTO T336-15 Test Method The saturation criterion in the current version of the AASHTO T336-15 test method states that, “The specimens shall be conditioned by submersion in limewater in a water storage tank at 23 6 2 C (73 6 4 F) for not less than 48 hrs and until two successive weighings of the surface-dried sample at intervals of 24 hrs show an increase in weight of less than 0.5 %.” It typically takes 2-3 days for dry concrete specimens or cores to meet the current AASHTO T336-15 saturation criterion described above. The T336 standard was designed to be a relatively simple test method: (a) CTE is obtained through temperature cycling with the use of a simple water bath; (b) although CTE is not maximum at 100 % saturation, this level of saturation is much easier to be reached and maintained than 70 %, especially because specimens are submerged in water during testing; and (c) it is also much easier to measure mass change over time to indirectly access saturation level than to directly measure it. Nevertheless, the previously mentioned ruggedness study showed that there was a statistically significant difference on CTE values between samples saturated according to T336 and samples saturated for 28 days or longer, which indicated that samples saturated as per T336 may not be completely saturated, as assumed by the standard.

Objective The objective of this study was to identify the most appropriate saturation criterion for the AASHTO T336 test method in order to obtain consistent results. Advances in Civil Engineering Materials

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The approach taken was to identify the shortest saturation time for concrete specimens that yields statistically the same CTE as that of companion concrete specimens that are saturated for 28 days because from a testing stand point, saturating a specimen up to 28 days is practical and implementable, but anything beyond that would make the test method more cumbersome. Due to this reason, in this research, 28 days of saturation in water was assumed as the benchmark degree of saturation and was used for comparison with other saturation criteria. In order to further evaluate the saturation process, the vacuum saturation procedure outlined in ASTM C1202-12 [19] was also evaluated as an option in this research. The vacuum saturation process for this work involved putting 102 by 203 mm concrete specimens in a vacuum chamber for 3 h. The specimens were vacuum saturated for 1 h and allowed to soak in water for 18 h. ASTM C1202 is designed to saturate a much smaller specimen (102 mm diameter by 51 mm thick) than a 102 by 203 mm specimen. However, it is anticipated that the vacuum saturation on a standard specimen (102 by 203 mm) per ASTM C1202 would increase saturation compared to standard T336 saturation.

Materials and Test Matrix This study involved testing the CTE of five different concrete mixtures, as shown in Table 1. Both laboratory cast specimens and cores were included in the study since the AASHTO T336 test method covers the determination of CTE of both. LABORATORY CAST SPECIMENS

Specimens from three of the mixtures were cast at the FHWA Turner-Fairbank Highway Research Center (TFHRC) laboratory: one of them used gravel coarse aggregates (producing a high CTE concrete), one of them used limestone coarse aggregates (producing a low CTE concrete), and the third one used a high absorption limestone aggregate (absorption ¼ 2.1 %) from Kansas. FIELD CORES

Cores (102 mm diameter cores) were obtained by the FHWA Mobile Concrete Laboratory (MCL) from two recently built concrete pavements in North Carolina and Ohio.

TABLE 1 Mixture design of specimens. Laboratory Cast Specimens Testing Laboratory Mixture ID Cement, lbs Coarse Aggregate, lbs Fine Aggregate, lbs w/c or w/cm

Field Cores

MCL

TFHRC

MCL

MCL

MCL

Gravel

Limestone

Kansas High Absorption Limestone

North Carolina Cores

Ohio Cores

650

580

564

560

550

1700 (Gravel) 1263 (Natural Sand) 0.46

1570 (Limestone) 1521 (Crushed Fine Agg) 0.55

1737 (HA Limestone) 1310 (Natural Sand) 0.42

2050 (Granite) 1175 (Crushed Fine Agg) 0.49

(1670) (Limestone) 1320 (Natural Sand) 0.43



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TABLE 2 History of the lab cast specimens and cores. Laboratory Cast Specimens

Field Cores

Testing Laboratory

MCL

TFHRC

MCL

Gravel

Limestone

HA Limestone

NC

Ohio

Month When Specimens were cast/Month When Paving occurred Age of specimens when they were Oven Dried

Sep 2010 22 months

Sep 2010 23 months

Aug 2012 3 months

Dec 2012

May 2013

33 Days

38 Days

27 Days

Age of concrete when the cores were taken from the pavement Duration the cores were left out in the DOT lab

2 months 1 months

2 months 14 months

Age of concrete in the cores at the start of the study

3 months

16 months

Mixture ID

Approximate number of days to reach 4 % weight loss

MCL

MCL

TEST MATRIX

For the laboratory cast specimens, fifteen 102 by 203 mm concrete specimens were prepared from each mixture according to AASHTO R39-07 [20] (18 specimens for gravel aggregate mixture). The time frame of when these specimens were cast is listed in Table 2. After the specimens were kept in water for a minimum of three months (to ensure even saturation in all the specimens), they were sawed to 178 mm (12 mm was cut from each side of the specimen). The specimens were maintained wet between removal from the soak and saw cutting to ensure that no drying took place. The 15 specimens each from the mixtures containing limestone or high absorption limestone aggregate were then each divided into five sets of three specimens. The 18 specimens from the mixture containing gravel aggregates were divided into six sets of three specimens. After water saturation for extended periods of time (Table 2), all the specimens in each set were kept in an oven at 50 C until the mass loss of the specimens was equal to or smaller than 4 %. This was performed so a saturation baseline could be established. The 4 % mass loss was selected based on previous experience with drying specimens during the CTE ruggedness study. The drying temperature was limited to 50 C in order to avoid specimen damage due to higher temperatures and based on the fact that the specimens are exposed to 50 C during the CTE testing (AASHTO T336). Table 2 shows the average time needed for each of the laboratory mixtures to reach this criterion. After all the specimens reached 4 % mass loss, four sets of specimens for the mixtures containing limestone and high absorption aggregates and five sets for the mixture containing gravel aggregate were placed in water at the same time. Three specimens from each mixture were tested after they met the following criteria: AASHTO T336 degree of saturation (in general 2 days), 4 days, 7 days, 14 days and 28 days of saturation. The set that was not put in water was vacuum saturated per the ASTM C1202 criterion [19] and then tested for CTE. This procedure is outlined in Table 3. The number three in Table 3 indicates that three specimens were tested for CTE at each criterion. Since only 5 sets were available for the limestone mixture (second mixture in Table 1) and Kansas high absorption limestone mixture (third mixture in Table 1), these were not used in vacuum saturation and 4-day saturation criteria, respectively. Advances in Civil Engineering Materials

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TABLE 3 Example test matrix for saturation study for laboratory mixture (for one mixture).

Set A Set B Set C

Day 0

Day 2 (T336)

Day 4

Day 7

Day 14

Day 28

Conditioning

Mon

Wed

Fri

Mon

Mon

Mon

Oven Dry until all specimens reached 4 % mass loss

Put Specimens in Water

3 3a 3

Set D

3

Set E Set F a

Vacuum Saturation

3 3b

Not carried out in concrete specimens containing high absorption limestone aggregate. Not carried out in concrete specimens containing limestone aggregate.

b

The field cores were also tested in the same way as the laboratory specimens. However, the field cores from North Carolina and Ohio were not oven dried to 4 % mass loss to be more representative of how cores could be potentially treated in the field. These cores, after being taken from existing pavements, were stored at the DOT materials laboratories, on racks and left to air dry (Table 2). After the FHWA MCL received these cores, they were first cut to 178 mm in height and then air dried again for a week before being immersed in water. Each set of three specimens was conditioned according to the saturation criterion outlined in Table 3.

Testing Four of the five mixtures were tested for CTE by the FHWA MCL and the fifth mixture (Limestone) was tested by the concrete laboratory at the FHWA TFHRC. In the case of the MCL, for each set of three specimens, two were tested concurrently in a CTE unit that had submersible LVDT (that had two CTE frames) and one was tested in a CTE unit that has non-submersible LVDT. In the case of TFHRC, all three specimens from each set were tested in a single unit with submersible LVDT (that had three CTE frames) at the same time. CTE was determined according to AASHTO T336, with the exception of the saturation criterion. Based on a past interlaboratory study [9], there is no statistical difference in CTE data between units than use submersible or non-submersible LVDTs

Results CTE results for specimens from the various saturation conditions are presented in this section. EFFECT OF DAYS OF SATURATION ON CTE Fig. 4 shows the average CTE at different periods of saturation for the five mixtures used in the study. The error bars indicate 61 standard deviation for the three replicate test results. The variability of the CTE results includes inherent test variability, variability between replicate specimens, and also reflects the variability between frames since data from three frames is included in each data set.



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FIG. 4 Measured average CTE for various saturation conditions.

Visually, there appears to be a “u” shaped trend between the various saturation conditions and CTE of the specimens. This trend appears to be similar in all the cases except for the cores from Ohio. A two sample unpaired t-test was conducted between the CTE measurements of specimens saturated for 28 days and each of the different saturation criteria for the five mixtures. Table 4 shows the statistical significance information at 95 % confidence level. It also shows that, except for the 14 day saturation in the limestone mixture, in all other cases, there was no statistical significant difference in CTE measured after 28 days of saturation versus those measured after 2, 4, 7, and 14 days of saturation. Previously, in the ruggedness study [10], a statistical significant CTE difference between specimens saturated for a minimum of 28 days versus those saturated per AASHTO T336 criterion was found. In some ways, the results from the two studies could be construed as contradictory; however, this is not the case. As mentioned previously, in the ruggedness study, data from each CTE unit (obtained by a single frame) is analyzed individually compared to this study, where data at each saturation criterion is obtained by combining data from three individual frames. In other words, the between frame CTE standard deviation is greater than the differences in CTE associated with change in saturation criteria. EFFECT OF VACUUM SATURATION ON CTE

It was anticipated that vacuum saturation would help with the saturation process. Figs. 5a–5d show the CTE values for four of the mixtures after 28 days of saturation, AASHTO T336 saturation criterion, and vacuum saturation. A two sample unpaired t-test was conducted between the CTE measurements of specimens saturated for 28 days, and CTE measurements of specimens that were vacuum saturated. Table 5 shows the statistical significance information at 95 % confidence level. Fig. 5 shows that the average CTE of the three specimens that were vacuum saturated was slightly lower compared to the CTE of the 28 day and the AASHTO T336 criterion saturated specimens. However, based on Table 5, there is statistically no difference in CTE between the vacuum saturated and 28 day water saturated specimens. Advances in Civil Engineering Materials

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TABLE 4 CTE statistical significance information for various saturation criteria.

Concrete Gravel Concrete

Limestone Concrete

High Absorption Aggregate Kansas

Cores from North Carolina

Cores from Ohio

Days of Saturation

AVG l-Strain/ C

STD l-Strain/ C

p-value

Statistical Significance With 28 Day Data Saturation Data?

28 2

11.33 11.34

0.15 0.04

0.91

No

4

11.22

0.11

0.37

No

7 14

11.20 11.24

0.05 0.06

0.21 0.40

No No

28 2

6.24 6.06

0.05 0.15

0.18

No

4

6.03

0.22

0.18

No

7 14

5.99 5.93

0.13 0.13

0.05 0.03

No Yes

28

7.58

0.24

2

7.52

0.13

0.70

No

4 7

7.50

0.26

0.69

No

14

7.57

0.43

0.96

No

28

9.04

0.08

2

9.10

0.12

0.60

No

4 7

9.02 8.92

0.10 0.03

0.80 0.08

No No

14

8.93

0.19

0.42

No

28

7.70

0.02

2

7.67

0.16

0.73

No

4 7

7.69 7.60

0.16 0.23

0.92 0.49

No No

14

7.76

0.23

0.68

No

EFFECT OF DAYS OF SATURATION ON THE NUMBER OF SEGMENTS TO COMPLETE THE CTE TEST

shows a graph from a typical CTE test. The graph plots temperature and specimen length change data during the test. Per the AASHTO T336 test method, the CTE is calculated by averaging the CTE of the last two individual segments from a CTE test, provided the difference between the two segments is lower than 0.3 l-strain/ C. A segment is defined as the measured length change for a given heating (from 10 to 50 C) or cooling change (from 50 to 10 C). An example of a segment is show in Fig. 6. Table 6 shows the average number of individual CTE segments required to complete a CTE test. Typically, the expansion CTE (obtained when heating specimen) is slightly higher than the contraction CTE (obtained when cooling specimen). However, this difference gets narrower as the number of segments increases. Based on Table 6, the general trend is that, as the number of days of saturation increases, the number of segments required to complete the CTE decreases. In other words, if the concrete specimens are saturated in water for a longer time, the Fig. 6



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FIG. 5 Measured average CTE for various saturation conditions.

difference between expansion and contraction segments becomes smaller than 0.3 l-strain/ C in a fewer number of segments. Typically, if a specimen is close to 100 % saturation, the CTE test is completed within two segments. Interestingly, the vacuum saturation process did not offer any additional advantage since it took about the same or higher number of segments to complete a test as that for the AASHTO T336 criterion. This is potentially due to the fact that during the vacuum saturation process, more water is forced into the air voids of the specimen than what would typically occur in a water bath immersion type of saturation, requiring longer time (or more segments) for the specimen to reach equilibrium (redistribution of water).

TABLE 5 CTE statistical significance information for 28 day and vacuum saturation.

Concrete Gravel Concrete Limestone Concrete

Days of Saturation

AVG l-strain/ C

STD l-strain/ C

28

11.33

0.15

Vacuum Saturation

11.2

0.06

28

Cores from North Carolina Cores from Ohio

Statistical Significance With 28 Day Data Saturation Data

0.30

No

6.24

0.05

28

7.58

0.24

Vacuum Saturation

7.47

0.26

0.62

No

28 Vacuum Saturation

9.04 9.01

0.08 0.11

0.72

No

28

7.70

0.02

Vacuum Saturation

7.59

0.15

0.25

No

Vacuum Saturation High Absorption Aggregate Kansas

P value

Did not perform testing


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FIG. 6 Raw data from a typical CTE test.

Discussion As mentioned previously, it is well documented that in the mechanistic-empirical pavement design, the predicted concrete pavement performance is very sensitive to CTE. Recently, McCarthy et al. [21], using the AASHTO Pavement ME DesignV software and Level 1 input data from several geographical regions pavement projects, performed analytical work to quantify the effect of CTE precision. The study indicated that to minimize the error in required pavement design thickness to 12.5 mm or less (error in pavement design thickness based on precision of measured CTE), the precision of the CTE test should be within 60.5 l-strain/ C. From a non-statistical standpoint, the data in Tables 4 and 5 show that the maximum nominal difference in average CTE within a mixture, for the six saturation conditions presented, was 0.34 l-strain/ C. This is much lower than the McCarthy et al. [21] criterion of 60.5 l-strain/ C, implying a negligible impact on the predicted performance based on the current CTE test method. Cores that are typically obtained from the field are stored in moisture cure rooms, saturated in water, or left outside. Data from this study clearly shows that irrespective of how the specimens are stored, if they meet the minimum criterion of saturation listed in AASHTO T336, their CTE would be statistically similar. The AASHTO T336 test method does not explicitly mention saturation criteria for concretes with highly absorptive aggregates. Based on the CTE test results from the Kansas high absorption limestone aggregate mixture from this study, it appears R

TABLE 6 Average number of segments at different level of saturation. Mixture

T336

4 Day

7 Day

14 Day

28 Day

VS

Gravel

4.0

3.0

3.3

2.0

2.0

3.7

Limestone HA Limestone

4.3 4.0

3.3

2.0 5.6

3.7 3.3

2.0 3.3

— 4.0

NC Cores

2.7

2.7

2.3

2.0

2.0

3.7

OH Cores

4.3

4.3

4.0

3.3

2.7

5.0



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that the current AASHTO T336 saturation criteria is adequate for concrete mixtures with high absorptive aggregate as well.

Conclusions Based on the concrete specimen saturation study that was conducted for the AASHTO T336 test method, the following can be concluded: •

•

•

•

Except for one case, there was no statistically significant difference in CTE values when testing specimens that were saturated in water for 28 days versus those saturated based on AASHTO T336 criterion, 4 days, 7 days, and 14 days. For the five mixtures tested in this study, there was no statistically significant difference in CTE value of specimens saturated in water for 28 days versus specimens that were vacuum saturated per the ASTM C1202 criterion. When testing concrete specimens that were dry, saturating them in water for longer periods of time (beyond the AASHTO T336 requirement) could reduce the number of segments required to complete the CTE test. However, the CTE of specimens is statistically the same irrespective of the number of days the specimen is saturated (between 2 and 28 days). The differences in CTE obtained in this study for the various saturation conditions are expected to have a negligible impact on the predicted performance based on the AASHTO Pavement ME DesignV software. Based on the results from this study, the current saturation criterion in the AASHTO T336 test method to measure CTE appears to be adequate for both laboratory specimens as well as field cores. R

•

ACKNOWLEDGMENTS

The writers would like to acknowledge the contribution of Nicolai Morari and Senaka Samaranayake for performing the CTE tests for this study. The authors would also like to thank Richard Burley and Nilesh Surti with North Carolina DOT and Craig Landefeld, Prasad Kudlapur and Daniel Miller with Ohio DOT for providing the concrete cores.

References [1] Schwartz, C., Li, R., Kim, S., Ceylan, H., and Gopalakrishnan, K., “Sensitivity Evaluation of MEPDG Performance Prediction,” National Cooperative Highway Research Program Research Results Digest RRD 372, National Research Council, Washington, D.C., 2013. [2] Mallela, J., Abbas, A., Harman, T., Rao, C., Liu, R., and Darter, M., “Measurement and Significance of the Coefficient of Thermal Expansion of Concrete in Rigid Pavement Design,” Transp. Res. Rec., Vol. 1919, 2005, pp. 38–46, http://dx.doi.org/10.3141/1919-05 [3] Kohler, E. and Kannekanti, V., “Influence of the Coefficient of Thermal Expansion on the Cracking of Jointed Concrete Pavements” Pavement Cracking: Mechanisms, Modeling, Detection, Testing and Case Histories, I. L. AlQadi, T. Scarpas, and A. Loizos, Eds., London, CRC Press, 2008, pp. 69–78. Advances in Civil Engineering Materials

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