Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Protocol P63
Test Method for The Determinationof The Coefficientof Thermal Expansionof PCC (Pc03)

This LTPP protocol covers the test method for determination of the coefficient of thermal expansion (CTE) of hardened PCC. This protocol is based on a test method and apparatus developed by the FHWA at the Turner-Fairbank Highway Research Center.

The test described herein may be performed on concrete cylinders or cores drilled from field structures.

The following definitions will be used throughout this protocol:

1. Core: An intact cylindrical specimen of a concrete structure which is removed from the structure by drilling in accordance with AASHTO T24 (ASTM C42).
2. Cylinder: An intact cylindrical specimen of concrete fabricated in accordance with AASHTO T23 or AASHTO T126 (ASTM C31 or ASTM C192).
3. Test Specimen: That portion of a core or cylinder which is used in this test. Test specimens should be 175-mm (7-inches) long with a nominal diameter of 100 mm (4 inches).

NOTE: The apparatus used in this test will allow use of specimens 175 to 200 mm (7 to 8 inches) long with nominal diameters of 100 to 150 mm (4 to 6 inches); however, for ease of testing and for consistency it is recommended that a consistent specimen length and diameter be used whenever possible. Use of different lengths and/or diameters will require adjustment of the apparatus and recalibration.

1. SCOPE

1.1 This test method covers determination of the CTE of hydraulic cement concrete cores or cylinders. Since it is known that the degree of saturation of concrete influences its measured CTE, the moisture condition of the concrete specimens must be controlled. For this test procedure, the specimens must be in a saturated condition.

1.2 The values stated in SI units shall be regarded as the standard.

2. APPLICABLE DOCUMENTS

2.1 AASHTO Standards:

T23 Making and Curing Concrete Test Specimens in the Field.
T24 Obtaining and Testing Drilled Cores and Sawed Beams of Concrete
T126 Making and Curing Concrete Test Specimens in the Laboratory.

2.2 ASTM Standards:

C31 Making and Curing Concrete Test Specimens in the Field.
C42 Obtaining and Testing Drilled Cores and Sawed Beams of Concrete.
C192 Making and Curing Concrete Test Specimens in the Laboratory.

2.3 LTPP Protocols:

P66 Visual Examination and Thickness of PCC Cores

3. SUMMARY OF TEST METHOD

3.1 This method determines the CTE of a cylindrical concrete specimen, maintained in a saturated condition, by measuring the length change of the specimen due to a specified temperature change. The measured length change is corrected for any change in length of the measuring apparatus (previously determined), and the CTE is then calculated by dividing the corrected length change by the temperature change and then the specimen length, as described in the section on calculations.

4. SIGNIFICANCE AND USE

4.1 Measurement of the CTE permits assessment of the potential for length/volume change of concrete due to a uniform temperature change, and the potential deformation of a concrete structure due to a temperature gradient through the concrete. As an example, for pavement slabs on grade, uniform temperature change will affect the openings at joints, and a temperature gradient through the thickness of these same slabs will produce curling of the slabs. Using the results of this test, better estimates of slab movement and stress development due to temperature change can be obtained.

5. EQUIPMENT

5.1 Concrete saw, capable of sawing the ends of a cylindrical specimen perpendicular to the axis and parallel to each other.

5.2 A scale or balance having a capacity of 20 kg (44 lb), and accurate to 0.1% over its range.

5.3 Caliper, comparator or other suitable device to measure the specimen length to the nearest 0.1 mm (0.004 in).

5.4 A controlled temperature water bath with a temperature range of 10 to 50° C (50 to 122° F), capable of controlling the temperature to 0.1° C (0.2° F).

5.5 A rigid support frame for the specimen to be used during length change measurement. The frame should be designed to have minimal influence on the length change measurements obtained during the test, and support the specimen such that the specimen is allowed to freely adjust to any change in temperature. A suitable support frame is described in detail in Appendix A.

5.6 Four submersible temperature measuring devices with a resolution of 0.1° C (0.2° F) and accurate to 0.2° C (0.4° F).

5.7 A submersible LVDT gauge head with excitation source and digital readout, with a minimum resolution of 0.00025 mm (0.00001 in), and a range suitable for the test (for ease in setting up the apparatus, a range of ± 3 mm (0.1 in) has been found practical).

NOTE: LVDT with the appropriate associated electronic actuating and indicating apparatus appear to give the best results with respect to stability, sensitivity, and reliability. Multichannel recording of outputs has been found to be practical and efficient. As an alternate, a data logger can be used to excite the LVDT and record the LVDT and both temperature and time outputs. The data can be stored directly in a personal computer for graphing of test results.

5.8 A micrometer, or other suitable device for calibrating the LVDT over the range to be used in the test, and with a minimum resolution of 0.00025 mm (0.00001 in).

6. TEST SPECIMENS

6.1 Test specimens shall consist of drilled 100-mm (4-in) nominal diameter cores sampled from the concrete structure being evaluated, or 100-mm (4-in) nominal diameter cylinders. Cores shall be obtained in accordance with AASHTO T24. Cylinders shall be cast in accordance with AASHTO T23 or T126. The specimens shall be sawed perpendicular to the axis at a suitable length. A length of 180 ± 2 mm (7.0 ± 0.1 in) has been found acceptable. The standard reference material used for calibration (see Appendix) shall be the same length as the test specimen so that the frame does not have to be adjusted between calibration and testing. The sawed ends shall be flat and parallel.

7. PROCEDURE

7.1 Specimen conditioning

The specimens shall be conditioned by submersion in saturated limewater at 23 ± 2° C (73 ± 4° F) for not less than 48 hours and until two successive weighings of the surface-dried sample at intervals of 24 hours show an increase in weight of less than 0.5%. A surface dried sample is obtained by removing the surface moisture with a towel.

7.2 Test Procedure

7.2.1 Place the measuring apparatus, with LVDT attached, in the water bath and fill the bath with cold tap water. Place the four temperature sensors in the bath at locations that will provide an average temperature for the bath as a whole. To avoid any sticking at the points of contact with the specimen, put a VERY THIN film of silicon grease on the end of the support buttons and LVDT tip.

7.2.2 Remove the specimen from the saturation tank and measure its length at room temperature to the nearest 0.1 mm (0.004 in). After measuring the length, place the specimen in the measuring apparatus located in the controlled temperature bath, making sure that the lower end of the specimen is firmly seated against the support buttons, and that the LVDT tip is seated against the upper end of the specimen.

NOTE: The desired range of travel is the linear range of the LVDT over which it has been calibrated. The LVDT travel during the test should remain well within this range to insure accurate results.

7.2.3 Set the temperature of the water bath to 10 ± 1° C (50 ± 2° F). When the bath reaches this temperature, allow the bath to remain at this temperature until thermal equilibrium of the specimen has been reached, as indicated by consistent readings of the LVDT to the nearest 0.00025 mm (0.00001 in) taken every ten minutes over a one-half hour time period. Also at this time, check that the specimen is firmly seated against the support buttons, as confirmed by the LVDT reading.

7.2.4 Record the temperature readings from the four sensors to the nearest 0.1° C (0.2° F). Record the LVDT reading to the nearest 0.00025 mm (0.00001 in). These are the initial readings.

7.2.5 Set the temperature of the water bath to 50 ± 1° C (122 ± 2° F). Once the bath has reached 50 ± 1° C (122 ± 2° F), allow the bath to remain at this temperature until thermal equilibrium of the specimen has been reached, as indicated by consistent readings of the LVDT to the nearest 0.00025 mm (0.00001 in) taken every ten minutes over a one-half hour time period.

7.2.6 Record the temperature readings from the four sensors to the nearest 0.1° C (0.2° F). Record the LVDT reading to the nearest 0.00025 mm (0.00001 in). These are the second readings.

7.2.7 Set the temperature of the water bath to 10 ± 1° C (50 ± 2° F). When the bath reaches this temperature, allow the bath to remain at this temperature until thermal equilibrium of the specimen has been reached, as indicated by consistent readings of the LVDT to the nearest 0.00025 mm (0.00001 in) taken every ten minutes over a one-half hour time period.

7.2.8 Record the temperature readings from the four sensors to the nearest 0.1° C (0.2° F). Record the LVDT reading to the nearest 0.00025 mm (0.00001 in). These are the final readings.

8. CALCULATIONS

8.1 Coefficient of Thermal Expansion - Calculate the CTE of one expansion or contraction test-segment of a concrete specimen as follows (reported in micro strains/° C):

(1)

where: ?L_a= actual length change of specimen during temperature change, mm (see equation 2)

L_o = measured length of specimen at room temperature, mm

?T = measured temperature change (average of the 4 sensors),° C (increase is positive, decrease is negative)

(2)

where: ?L _m = measured length change of specimen during temperature change, mm (increase = positive, decrease = negative)

?L_f = length change of the measuring apparatus during temperature change, mm (see equation 3)

(3)

where: C_f = correction factor accounting for the change in length of the measurement apparatus with temperature, in^-6/in/° C (see appendix A.2)

8.2 For the expansion test segment, the initial and second readings are used in the calculations. For the contraction test segment, the second and final readings are used in the calculations.

8.3 The test result is the average of the two CTE values obtained from the two test segments provided the two values are within 0.3 microstrain/° C (0.2 microstrain/° F) of each other. If the two values are not within 0.3 microstrain/° C (0.2 microstrain/° F) of each other, one or more additional test segments are completed until two successive test segments yield CTE values within 0.3 microstrain/° C (0.2 microstrain/° F) of each other. The test result is the average of these two CTE values.

(4)

NOTE: Differences in successive CTEs greater than the required value sometimes occur during the first few cycles of temperature change due to minor misalignment, or lack of proper initial seating of the specimen. This is usually self-correcting during the first few temperature cycles. However, it does point out the importance of carefully positioning the specimen at the start of the test.

9. REPORT

The following information is to be recorded on Form T63:

9.1 Sample identification shall include: SHRP ID, Laboratory Identification Code, State Code, Layer Number, Field Set Number, Sample Area Number, Sample Location Number, LTPP Sample Number.

9.2 Test identification shall include: LTPP Test Designation, LTPP Protocol Number, LTPP Laboratory Test Number, Test Date.

9.3 Correction Factor Measurements

9.3.1 Description of material type calibration specimen.

9.3.2 Length of calibration specimen in millimeters (to the nearest millimeter).

9.3.3 Diameter of calibration specimen in millimeters (to the nearest millimeter).

9.3.4 CTE, a_c, of calibration specimen, mm/°C.

9.3.5 Average C_f, average correction factor, mm/°C (from the results of three tests).

9.4 Test Results

9.4.1 Description of specimen, including type of specimen, diameter, coarse aggregate type, age.

9.4.2 Length of specimen (L) in millimeters (to the nearest 0.1 mm).

9.4.3 Initial temperature (T_i), in °C, to the nearest 0.1°C.

9.4.4 Initial LVDT reading, in volts, to the nearest 0.001 volts.

NOTE: Some LVDT signal conditioning equipment gives output directly in units of length rather than in volts. Such equipment is also acceptable and would eliminate the need to convert a voltage reading to units of length.

9.4.5 Final temperature (T_f), in °C, to the nearest 0.1°C.

9.4.6 Final LVDT reading, in volts, to the nearest 0.001 volts.

9.4.7 LVDT calibration factor, in volts/mm.

9.4.8 CTE, a_c, of PCC specimen, mm.

9.5 Comments shall include LTPP standard comment codes, as shown in Section 4.3 of this Guide and any other notes as needed.

APPENDIX A STANDARD TESTING EQUIPMENT

A.1 Specimen Measuring Apparatus

The measuring apparatus consists of two primary components: a frame and a length change measuring device.

A.1.1 Frame

Figure A.1 shows a schematic of a suitable measuring frame. Any specimen measuring frame should be constructed with the following features in mind:

Because the frame will be submerged in water throughout the test, components should be made of a non-corroding material. In so far as possible, the portions of the frame which directly affect measurement over a change in temperature, should be constructed of invar and protected from corrosion as necessary.

The frame may be designed to be adjustable to accommodate different sample lengths; however, calibrations will be required after each adjustment.

A.1.2 Length Change Measurement Devices

The sample length change may be measured using any suitable apparatus which can be submerged in water, has sufficient resolution, and gives reproducible results. The FHWA apparatus uses a submersible spring-loaded LVDT gauge head for length change measurement.

Appropriate signal conditioning equipment will be required if an LVDT or other electronic transducer is used for length change measurements. A voltmeter or a computer and data acquisition software may also be required if the signal conditioning equipment does not have a digital readout. The LVDT will require calibration using a micrometer to relate the digital readout output (which may be in volts or arbitrary units) to actual length changes.

The contact tip (at the point of contact between the measuring device and the specimen) must be attached to the length change measuring device with a suitable adhesive to prevent loosening during a test.

A.2. Reference Test for Determination of Correction Factor

The test procedure described in Section 7.2 is used to determine a correction factor to account for expansion of the measuring apparatus during the test. A specimen with a known CTE is used. The specimen should be composed of a material which is essentially linearly-elastic, non-corroding, non-oxidizing, and non-magnetic and have a thermal coefficient as close as possible to that of concrete (304 stainless steel, which has a CTE of 17.3 × 10^-6/°C (9.6 × 10^-6/°F), is a suitable material). The reference material sample should also be of the same nominal dimensions as the test samples, so that no adjustment of the frame and/or the LVDT is necessary between calibration and testing.

A.2.1 Calculation of the correction factor

Assuming that the length change of the apparatus varies linearly with temperature, the correction factor C_f is defined as:

(A.1)

where: ?L_f = length change of the measuring apparatus during temperature change, mm (see equation A.2)

L_cs = measured length of calibration specimen at room temperature, mm

?T = measured temperature change, ° C (increase = positive, decrease = negative)

(A.2)

where: ?L_a = actual length change of calibration specimen during temperature change, mm (see equation A.3)

?L_m= measured length change of calibration specimen during temperature change, mm (increase = positive, decrease = negative)

(A.3)

where: a_c = CTE of calibration specimen, /° C (known)

NOTE: It is recommended that at least 3 calibration tests be performed, and that the average of the correction factors calculated for each test be used for calculations on actual concrete test.

BASEPLATE DIA. @ 10"
FRAME HEIGTH @ 10"

Figure A.1 Schematic of Suitable Measuring Frame.

LTPP LABORATORY MATERIAL HANDLING AND TESTING

LABORATORY MATERIAL TEST DATA
DETERMINATION OF THE COEFFICIENT OF THERMAL EXPANSION

LAB DATA SHEET T63-A

PORTLAND CEMENT CONCRETE

TEST DESIGNATION PC03/PROTOCOL P63

LABORATORY PERFORMING TEST:______________________________________________________________

LABORATORY IDENTIFICATION CODE: __ __ __ __

REGION _________________ STATE ___________________ STATE CODE __ __

EXPERIMENT NO _____ SHRP ID __ __ __ __

SAMPLED BY: ______________________________________________ FIELD SET NO . __

DATE SAMPLED: __ __-__ __-__ __ __ __

1. LAYER NUMBER __

LTPP LABORATORY MATERIAL HANDLING AND TESTING
LABORATORY MATERIAL TEST DATA

DETERMINATION OF THE COEFFICIENT OF THERMAL EXPANSION

APPARATURS CORRECTION FACTOR

LAB DATA SHEET T63-B

PORTLAND CEMENT CONCRETE

TEST DESIGNATION PC03/PROTOCOL P63

LABORATORY PERFORMING TEST:______________________________________________________________

LABORATORY IDENTIFICATION CODE: __ __ __ __

REGION _________________ STATE ___________________ STATE CODE __ __

1. CALIBRATION SPECIMEN MATERIAL _________________________________