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New AASHTO 336-09 Coefficient of thermal expansion test method: how will it affect you?  Article  in  Transportation Research Record Journal of the Transportation Research Board · November 2010 DOI: 10.3141/2164-07

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New AASHTO T336-09 Coefficient of Thermal Expansion Test Method How Will It Affect You? Jussara Tanesi, Gary L. Crawford, Mihai Nicolaescu, Richard Meininger, and Jagan M. Gudimettla The principle of TP60 is quite simple. simple . It measures the length change of a saturated concrete specimen placed vertically in a metal frame sub jected  jec ted to a spe specific cific temp temperat erature ure cha change nge.. A con control trolled led temp temperat erature ure wat water er bath is used to vary the temperature range r ange specified by the test method. Deformation of the frame is taken into account by measuring the length change of a specimen of known CTE, normally a 304 stainless steel specimen. TP60 states that the CTE of a 304 stainless steel specimen is 17.3 × 10−6 / °C (9.6 × 10−6 / °F). This is the value normally reported in the literature (8–11) and used by most of the state and university laboratories that perform TP60.

Although many papers were published during the past decade on the coefficient of thermal expansion (CTE) and its impact on concrete pavement design, an error was recently discovered in the AASHTO TP60-00 about the calibration of the testing equipment and, consequently, determination of the concrete CTE. The new AASHTO T336-09, even though based on the TP60-00, rectifies this calibration issue. This paper presents differences between the two test methods and implications for the Long-Term Pavement Performance database and for the Mechanistic the  Mechanistic –Empirical   Pavement Design Guide and for its implementation by state departments of transportation. Recommendations are provided for improvements to

Won proposed a new method to calculate CTE of concrete based on modifications to TP60 (12). The remainder of this paper refers to this new method as the Texas method. The principal and testing equipment proposed in this method is similar to that of TP60. It is based on the same principles and also assumes ass umes that the CTE of the 304 stainless steel specimen is 17.3 × 10−6 / °C (9.6 × 10−6 / °F). The difference between the Texas method and TP60 is that the former calculates the concrete CTE as the slope of the deformation versus temperature curve, while in AASHTO TP60, the CTE is calculated as the length change over a temperature change after the specimen achieves thermal equilibrium. Both TP60 (or new AASHTO T336) and the Texas method can be carried out with the same equipment. Equipment may be a custommade unit (manual or automated versions) or an automated commercially available unit. See Figure 1 a through 1d. TFHRC has been evaluating three commercial units over the past 2 years, but it has

the AASHTO T336-09 test method.

The Turner-Fairbank Highway Research Center (TFHRC) of FHWA was one of the pioneers in carrying out coefficient of thermal expansion (CTE) tests of concrete pavements over the past 10 years. It has tested more than 2,200 specimens, mostly cores for the LongTerm Pavement Performance (LTPP) database. The LTPP CTE test results were originally used to calibrate Version 1.0 of the  Mechanistic–Emp  Mechani stic–Empirical irical Pavemen Pavementt Design Design Guide (MEPDG) models. Interest in CTE testing has increased significantly in the past few years because it was observed obse rved to be one of the most important inputs of the MEPDG for pavement design (1–7 ). ). In the past 5 years alone, more than 20 papers have been published on CTE and its effect on the MEPDG.

not published onstill specific Two of them are commercially available, and data one is underunits. evaluation. The U.S. Army Corps of Engineers has its own CTE test method, CRD-C 39-81, which has some similarities to TP60 but does not employ a frame; consequently, no calibration specimen is required for the test. Instead, it uses a length comparator. Preliminary tests at TFHRC using this procedure showed higher variability of test results than with others. The Bureau of Reclamation has test method USBR 4910-92, which does not require the use of a calibration specimen. Other test methods have been proposed but are not widely used (13–15), including test methods that mea sure the CTE of the aggregates and calculate the CTE of the concrete ( 16 ). ).

 AVAILABLE COEFFICIENT  AVAILABLE COEFFICIENT OF THERM THERMAL AL EXPANSION TESTS FOR CONCRETE

Several test methods are available for determining the CTE of concrete. The most widely used is the AASHTO TP60-00, the basis for all the LTPP CTE testing. This test method was recently modified and approved as the new AASHTO T336-09. This is the test tes t method used by all the state departments of transportation except Texas, which uses a local version of the test method. J. Tanesi and M. Nicolaescu, Global Consulting, Inc., and R. Meininger, TurnerFairbank Highway Research Center, FHWA, 6300 Georgetown Pike, McLean, VA 22101. G. L. Crawford, FHWA, FHWA, Room E73-438, HIPT-20, HIPT-20, and J. M. Gudimettla, Global Consulting, Inc., FHWA Mobile Concrete Laboratory, Room E73-105C, HIPT-20, 1200 New Jersey Avenue, SE, Washington, DC 20590. Corresponding author: J. Tanesi, [email protected].

REFERENCE MATERIALS FOR RUGGEDNESS TEST

Transportation Research Record: Journal of the Transportation Research Board,  No. 2164, 2164, Transportation Research Board of the National Academies, Washington, D.C., 2010, pp. 52–57. DOI: 10.3141/2164-07

TFHRC, as part of the CTE equipment evaluation study and in preparation for ruggedness and precision studies of equipment and laboratories, obtained additional reference materials (other than 52

 

Tanesi, Crawford, Nicolaescu, Meininger, and Gudimettla

53

(a )

(b)

(c)

(d)

FI GU GU RE RE 1 E xam xampl ples es of CTE CTE uni unitt s: s: ( a ) manual custom-built units, ( b ) automated commercially available unit (Pine), ( c ) automated commercially  available unit (Gilson), and ( d ) unit under FHWA evaluation not commercially available (InstroTek).

the 304 stainless steel calibration used for obtaining the correction factor in all initial TFHRC manual custom-built CTE testing of LTPP portland cement concrete pavement cores). The new reference specimens consist of a variety of materials with a range of CTE values typically within the range of the concrete specimens that have been tested previously by TFHRC. Materials obtained were as follows: •

Alumina bisque. According to the literature, its CTE is 5.5 × 10  / °C (3.1 × 10−6 / °F) (11). In the case of alumina bisque, the specimen is a very porous ceramic and needs to be saturated before testing. Careful is necessary when handling handling the specimen, for the material can be easily broken. • Titanium 6 – aluminum 4 – vanadium (Ti-6Al-4V). According to the literature, its CTE is 9.2 × 10−6 / °C (5.1 × 10−6 / °F) (11). • Meanwhile, the FHWA Mobile Concrete Laboratory (MCL) obtained another reference material, 410 stainless steel. According to the literature, its CTE is 10.5 × 10−6 / °C (5.8 × 10−6 / °F) ( 8). −6

The 410 stainless steel has a weak magnetic field that could affect the linear variable differential transformer (LVDT) during tests. Preliminary evaluations did not show any effect on the CTE units at FHWA’s TFHRC or MCL.

THIRD-PARTY TESTING

The reference material specimens were tested at TFHRC using manual custom-built units and one of the commercially available units following TP60. As can be seen in Table 1, CTE values obtained for the alumina bisque, titanium alloy, and 410 stainless steel CTEs did not coincide with the values reported in the literature. They were about 1 × 10−6 / °C (0.6 × 10−6 / °F) higher than the values reported in the literature. Possible reasons for the differences were that the alumina bisque, titanium alloy, and 410 stainless steel s teel obtained by the TFHRC laboratory and MCL laboratory were not not exactly the same materials for which values are reported in the literature, or the

 

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 TA BL BLE E1

Transportation Research Record 2164

CTE CT E Re Repo po rte d in Li ter at ur e an d Te Test st Re Resu su lts (A ASH TO TP 60 an andd AST M E2 28) AASHTO TP60 ASTM E228 Litera Lite ratu ture re Re Repo port rted ed CTE Value × 10−6 / °C (× 10−6 / °F)

Manual Manu al Un Unit it CTE × 10−6 / °C (× 10−6 / °F)a

Commer Comm erci cial al Un Unit it CTE × 10−6 / °C (× 10−6 / °F)a

Specimen ID

Material

Third-Party Laboratory 1 CTE × 10−6 / °C (× 10−6 / °F)b

A

Alumina bisque

5.5 (3.1)

6.5 (3.6)

6.7 (3.7)

5.4 (3.0)

T

Titanium alloy

9.2 (5.1)

10.0 (5.6)

10.2 (5.7)

8.9 (4.9)

S

410 stainless steel

10.5 (5.8)

11.8 (6.6)

11.5 (6.4)

10.4 (5.8)

SS743

304 stainless steel—manual Calibration Specimen 2

17.3 (9.6)

Not applicable

Not applicable

15.8 (8.8)

M1

304 stainless steel—Manufacturer 1 calibration specimen

17.3 (9.6)

Not applicable

Not applicable

15.9 (8.8)

M2

304 stainless steel—Manufacturer 2 calibration specimen

17.3 (9.6)

Not applicable

Not applicable

16.2 (9.0)

a

Average of two tests. Single test result. ASTM E228 precision is 0.8% for the temperature range of 25 °C to 400°C (77°F to 752°F).

b

LVDTs were being affected by temperature change or moisture, or both, during the test cycling. This difference led to the exploration of options for verification of the CTE by an independent third-party laboratory. As a result, the reference specimens were sent to be tested at a laboratory specializing in the CTE testing of metals for the aerospace

value of 17.3 × 10−6 / °C (9.6 × 10−6 / °F). So if the specimens are tested, the CTE result would be 17.3 × 10−6 / °C (9.6 × 10−6 / °F). Results obtained according to TP60 were much higher than those obtained according to ASTM E228. Moreover, other than the 304 stainless steel specimens, results reported by the thirdparty laboratory are in general agreement with the values reported

industry. The tests were carried out following a modified version of the ASTM E228-06 test method, to accommodate 18-cm 18- cm long × 8-cmor 10-cm (7-in. × 3-in. or 4-in.) diameter specimens and the same temperature range as TP60, 10°C to 50°C (50°F to 122°F). In addition to sending of the newly obtained reference specimens, several 304 stainless steel specimens used for calibration of the FHWA manual custom-built unit and two of the commercial units were sent to the same laboratory for verification. In the ASTM E228 test method, a push-rod dilatometer is used to measure linear thermal expansion. The differential expansion between the sample and a known standard standard reference material is measured as a function of temperature. The expansion of the sample is computed from this differential expansion and the expansion of the standard. Measurements are made under computer control, and linear expansion is calculated at preselected temperature intervals. Table 1 shows the CTE reported in the literature and test results

in the literature. The 304 stainless steel CTE test result was lower than the reported 17.3 × 10−6 / °C (9.6 × 10−6 / °F) for all three of the specimens. After analysis of results received from the independent laboratory, another reason for the higher TP60 results arose: the values of CTE of 304 stainless steel used for f or the calibration of the units might not be correct for the temperature range during CTE testing. Of emphasis is that the CTE value of 17.3 × 10−6 / °C (9.6 × 10−6 / °F) is used by most laboratories running TP60 and the Texas method, whether a custom-built or a commercially available unit is used. If the 304 stainless steel calibration specimen CTE values used as an input for the determination of the correction factor (according to TP60) were not correct, the resulting CTE values for the materials tested would not be correct, either. As a proof of concept, a new correction factor was obtained using 15.8 × 10−6 / °C (8.8 × 10−6 / °F) as the CTE for 304 stainless steel (TFHRC manual custom-built unit).

obtained at TFHRC at the independent laboratory. As can be seen, results obtainedand at TFHRC following TP60 are much higher than those obtained at the third-party laboratory following ASTM E228. No need existed to test the 304 stainless steel in the manual and commercial units, for they are calibrated with the assumed CTE

With the new correction factor, reported in Table were recalculated (Table 2). The CTE the testsCTE in Table 2 were carried1out in the TFHRC manual custom-built units. When the correction factor is determined using the TP60 suggested default value for 304 stainless steel, the CTE of alumina bisque, tita-

 TA BL BLE E 2 Comp Co mpar ar is ison on of CT CTE E O bt ai ne nedd at Th ir d- Par ty La bo bora rato tory ry an d at TF HR C  Assu  As su min g Tw o CTE CT E Va Valu lues es fo r Ca Calili br ati on Sp Spec ec im en Third Thi rd-P -Par artty Laboratory 1 CTE × 10−6 / °C (× 10−6 / °F)

 

Man anu ual Uni nitt CT CTE E −6 −6 × 10  / °C (× 10  / °F) (Cf a b  ased on 304 SS of 15.8 × 10−6 / °C)

 

Manua Man uall Un Unii t CTE −6 −6 × 10  / °C (× 10  / °F) a (Cf   based on 304 SS of 17.3 × 10−6 / °C)

Specimen ID

Material

A

Alumina bisqueb

5.4 (3.0)

5.0 (2.8)

6.5 (3.6)

T

Titanium alloy

8.9 (4.9)

8.5 (4.7)

10.0 (5.6)

S

410 stainless steel

10.4 (5.8)

10.3 (5.7)

11.8 (6.6)

a

Cf = correction factor as determined by AASHTO TP60. The difference between TFHRC and the third-party laboratory test result was partially due to the fact that the thirdparty laboratory was unable to keep the specimen saturated and alumina bisque is very porous. b

 

Tanesi, Crawford, Nicolaescu, Meininger, and Gudimettla

55

 TA BL BLE E 3 Co mpa ris on Be Betwe twe en CT CTE E Te Test st Re su sult lt s Ob tai ne d by Tw o Th ird -P ar ty La bo bora ra to tori ri es (ASTM E228)

Specimen ID

Material

T

Titanium alloy

S SS743 M1

Third-Party Laboratory 1 CTE × 10−6 / °C (× 10−6 / °F)

Third-Party Laboratory 2 CTE × 10−6 / °C (× 10−6 / °F)

8.9 (4.9)

9.2 (5.1)

410 stainless steel

10.4 (5.8)

10.2 (5.7)

304 stainless steel—manual Calibration Specimen 2

15.8 (8.8)

15.9 (8.8)

304 stainless steel—Manufacturer 1 calibration specimen

15.9 (8.8)

15.7 (8.7)

NOTE: CTE values based on temperature range of 10°C to 50°C (50°F to 122°F).

nium alloy, and 410 stainless steel are higher than expected, but when the correction factor is determined determined using the measured measured CTE value for 304 stainless steel obtained by the third-party laboratory, the CTE of alumina bisque, titanium alloy, and 410 stainless steel are much closer to the expected values. It seemed that the differences were not due to the impact of the temperature change or moisture on the LVDT readings. Rather, they were due to the use of an inappropriate CTE for the 304 stainless steel calibration specimen as an input to calculate the correction factor and consequently the CTE of the reference materials. To confirm the CTE of the 304 stainless steel specimens, TFHRC

independent laboratory. The small differences observed can be attributed to test variability. The CTE test results shown in Table 3 represent the CTE values over the same temperature range as for TP60 and do not include the full temperature range used by the laboratory. Figure 2 shows the mean CTE for the entire temperature range used during the test by the second independent laboratory. It can be seen that the CTE value changes with temperature. The material that presented the most stable CTE over the temperature range of −40°C to 300°C (−40°F to 572°F) was the titanium alloy. It is also clear that at around 300°C (572°F), the CTE test results for the 304 stainless steel specimens approach the value reported in the literature of 

sent specimens to a second independent laboratory. Since another laboratory was not found that was capable of running a modified ASTM E228 on 18-cm long × 8-cm- or 10-cm (7-in × 3-in. or 4-in.) diameter, small samples of each of the specimens previously sent to the first independent laboratory were cut off. The samples, also called 1 coupons, were approximately 5.1 × 5.1 × 0.6 cm (2 × 2 ×  ⁄  4 in.). Because it was not possible to obtain coupons out of all the specimens previously tested by the first independent laboratory without damaging the specimens, only four specimens were tested by the second independent laboratory. This laboratory measured the CTE over a much wider temperature range of −40°C to 300°C (−40°F to 572°F) than did the previous laboratory. Table 3 shows clearly that results received from the second independent laboratory were in agreement with results obtained from the first

17.3 × 10  / °C (9.6 × 10  / °F).

−6

−6

IMPACT OF RECENT FINDINGS ON NEW T336 COEFFICIENT OF THERMAL EXPANSION TEST METHOD

In light of new findings about the CTE of the 304 stainless steel calibration specimen, the recently approved T336 has incorporated incorpor ated language that cautions the reader on the use of assumed CTE values regardless of the material used. The differences between the TP60 and the new T336 are as follows: •

Third-party testing. While TP60 states in the nonmandatory appendix that the CTE of the 304 stainless steel is 17.3 × 10−6 / °C

20    ) 18    C    °    /

   6   -

   0 16    1   x    (    E 14    T    C   n 12   a   e    M

T 336 temperature range

10 8 -50

0

50

100

150

200

250

300

350

Temperature (°C) M1

S

SS743

T

FIGURE 2 Mean CTE CTE over wide range range of tempera temperature ture (CTE (CTE calculate calculatedd with reference temperature of 20  C: M1  304 stainless steel of commercial unit; S  410 stainless steel; SS743  304 stainless steel of manual units; and  T   tit an aniu iu m al lo loy) y)..

 

56

(9.6 × 10−6 / °F), T336 requires the CTE of any calibration specimen to be determined by a laboratory possessing ISO 9001 or equivalent certification. • Determination of CTE of the calibration specimen. The CTE has to be determined by a third-party laboratory, according ac cording to ASTM E228 or ASTM E289. Moreover, the CTE determination has to be conducted over the same temperature range as with T336: 10 °C to 50°C (50°F to 122°F). • CTE certificate. The calibration specimen has to have a certificate issued by the third-party laboratory, including the lot number of  the specimen tested. The CTE has to be determined on the same specimen or on a specimen from the same lot, since the CTE of materials may change by lot. • MEPDG cautionary note. Models in Version 1.0 of the MEPDG software were calibrated using the LTPP database on CTE, obtained according to TP60. Since the values obtained according to TP60 and T336 may differ considerably depending on the calibration specimen used and assumed CTE value, the CTE obtained according to T336 should not be used as an input in Version 1.0 of the MEPDG software, to prevent pavement thickness from being underestimated.

Transportation Research Record 2164

impact on the predicted design thickness. For example, based on a sample design, not adjusting the models would result in less conservative designs of approximately 1.3 cm (0.5 in.) thinner pavement for low CTE values and 2.5 cm (1.0 in.) thinner pavement for higher CTE values. A national recalibration of MEPDG concrete models based on revised CTE values (NCHRP 20-7 Task 288) has been initiated.

OTHER IMPLICATIONS

Numerous highway agencies have started characterizing the material properties of their typical mixtures in advance of MEPDG implementation. The CTE values stored in these databases are still valid. However, the recorded values will need to be adjusted by the difference in the assumed CTE value of the calibration calibrat ion specimen and the CTE value obtained according to ASTM E228. As noted, these adjusted adju sted CTE values should be used for design purposes with the MEPDG software only after the models have been recalibrated. Some states have already developed typical pavement designs and design tables based on the MEPDG and CTE. In that case, once the MEPDG is recalibrated, the tables should be verified and changed as necessary.

IMPACT OF RECENT FINDINGS ON LONG-TERM PAVEMENT PERFORMANCE DATABASE SUGGESTED CHANGES FOR T336

The current LTPP database of CTE values is the result of extensive testing of thousands of cores from pavements throughout the country over a 10-year period. The test method used to obtain the CTE was the TP60, which assumes an improper CTE for the calibration specimen for the temperature range at which the test is carried out. As a result, the CTE values in the LTPP database are higher than they should be for the expected temperature range and needed to be adjusted accordingly. Since the divergence on the CTE of the calibration specimens was discovered, TFHRC has worked to backcalculate all the test results, substituting the 17.3 × 10−6 / °C (9.6 × 10−6 / °F) by the CTE value of  the specific calibration specimens used for each specific unit, including several manual custom-built units and the commercial units. units . The LTPP database Version 24, released in January 2010, contains the adjusted CTE values.

IMPACT OF RECENT FINDINGS ON MECHANISTIC–EMPIRICAL PAVEMENT DESIGN GUIDE

Several studies in the past few years have identified CTE as one of  the most significant inputs or classified as extremely sensitive input in the MEPDG for designing concrete pavements (1–7 ). ). The CTE of  the concrete determines the magnitude of the pavements curling stresses, joint movement, and load transfer efficiency that affect the overall pavement design. In continuously reinforced concrete pavements, the CTE determines the crack spacing and crack width, which affects the crack load transfer efficiency and ultimately punchouts. Since the various distress models in the MEPDG use CTE data from the LTPP database, these models need to be adjusted based on the corrected data (using the right CTE for the calibration specimen). Because the current models in the MEPDG software are based on the higher CTE values included in the LTPP database, a lower CTE value should be used only after the models have been recalibrated, either through a global recalibration of the models or through a local calibration process. If this issue is not addressed, it could have a negative

Although the approval of a full standard dedicated to measuring the CTE of concrete has been a great achievement, some modifications would further improve the procedure. The following recommendations are based on TFHRC extensive testing and research experience: •

Correction factor. T336 already presents a procedure for the determination of the correction factor. Nevertheless, it is in a nonmandatory appendix to the test method. Since determination of the correction factor is mandatory, it should be moved to the body of  the standard. Moreover, in the current T336, no discussion is provided for the calibration specimen. To obtain accurate results, it is suggested that the length of the calibration specimen be within 2 mm (0.1 in.) of  the concrete specimens to be tested. The diameter of the calibration specimen should be a suitable diameter to firmly rest on support buttons of the frame. • Addressing the water level. When the water level in the controlled temperature water bath affects the CTE, especially if the water level changes during the test or if the water level during concrete testing is different from the water level during calibration. This is because when the water level changes, the length of the frame and the LVDT shaft that is submerged or exposed to the ambient air will change. Therefore, based on TFHRC research, the water level should not depart from the last calibration’s water level by more than 13 mm (0.5 in.). • Equipment verification. With use of LVDTs in contact contac t with water and at high temperatures, the electronics can be affected. To verify proper functioning of the LVDT and overall equipment operation, it is suggested that the setup be verified monthly by testing a reference specimen of known CTE, other than the calibration specimen. The reference specimen should have a CTE value at least 5 × 10−6 / °C (2.8 × 10−6 / °F) different from that of the calibration specimen. specimen. It will ensure that readings are consistently good, for any discrepancies would be easily discovered. A suggestion is that the reference specimen should be composed of a material that is noncorroding, nonoxidizing, nonporous, and nonmagnetic. Also, it should have a thermal coefficient coef ficient close to that

 

Tanesi, Crawford, Nicolaescu, Meininger, and Gudimettla

of concrete within the temperature range of 10 °C to 50°C (50°F to 122°F). The CTE of the reference material should be determined determined by an independent laboratory, the same as with CTE of the calibration specimen. In this study, the titanium alloy (Ti-6Al-4V) was found to be a suitable material. After verification, if the CTE of the reference specimen is found to differ by more than 0.3 × 10−6 / °C (0.2 × 10−6 / °F) from the certified value, the correction factor should be determined again using the procedure described in T336. • Calibration of LVDTs. The current T336 requires a micrometer be used for calibrating the LVDT. Nevertheless, it does not provide any guidance on calibration, nor on the frequency of calibration. A calibration every 6 months is believed to be adequate. • Specimen end condition. The end condition of the concrete specimen may be a source of some test error. T336 should provide guidance on the minimum requirements. It is suggested that the same requirements from AASHTO T 22-07 on compressive strength be applied. • Number of specimens to be tested. The CTE of a mixture should not be determined based on a single test result. Guidance on the number of specimens to be tested should be provided. It is suggested that a minimum of two specimens be tested and the average value reported, to characterize a mixture.

CONCLUSIONS AND RECOMMENDATIONS

In an effort to finalize the work on CTE, FHWA discovered that the CTE of the 304 stainless steel specimen, a calibration specimen normally used to test the CTE of concrete according to AASHTO TP60, is not 17.3 × 10−6 / °C (9.6 × 10−6 / °F) for the temperature range of the TP60. Of importance is that the CTE value of 17.3 × 10−6 / °C (9.6 × 10−6 / °F) is employed by most laboratories running TP60 and the Texas method. One cannot overemphasize the impact this finding may have. A new test method was approved (AASHTO T336). It is based bas ed on the provisional test method TP60 but does not assume any value for the calibration specimen. However, it requires that the CTE of the calibration specimen be determined by a certified independent laboratory. The CTE values in the LTPP database were determined based on TP60 and need to be adjusted for the difference in CTE values of the calibration specimen. The January 2010 LTPP database (Release (Rele ase 24.0) already contains the adjusted values. The MEPDG models were developed based on the LTPP data. Since the LTPP database needs to be adjusted, the MEPDG models need to be recalibrated. With use of MEPDG Version 1.0, the CTE values must be determined according accord ing to TP60 and not T336, to prevent an inaccurate pavement design. Some improvements to the new T336 have been suggested, in regard to the water level, correction factor, equipment verification, LVDT calibration, specimen end condition, and number of specimens to be tested. The following recommendations are made: 1. All laboratories laboratories that conduct conduct CTE tests should should determine the CTE value of the calibration specimen measured according to ASTM E228. 2. A reference specimen specimen with with a known CTE CTE value according according to ASTM E228 should be obtained and used to verify correct operation oper ation of the CTE equipment. 3. Once the models in the MEPDG software have been recalibrated, highway agencies will need to adjust their CTE test results

57

to account for the difference between assumed and actual CTE value of the calibration specimen.

 ACKNOWLEDGMEN  ACKNOWL EDGMENT T

The authors thank William Luecke of NIST for his expertise on metal properties and the invaluable contributions provided.

REFERENCES

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The Properties of Concrete Committee peer-reviewed this paper.