Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Protocol P61
Test Method for Determinationof Compressive Strengthof PCC Cores/Cylinders (Pc01)

This LTPP protocol covers the determination of the compressive strength of PCC cores and molded cylinders. The test shall be carried out in accordance with AASHTO T22-88I, as modified by the following. Only sections of the referenced standard which have been modified are included below. In all other sections the standard (AASHTO T22-88I) shall be followed as written. The test shall be performed on PCC cores obtained from LTPP projects. The specimens to be tested are as shown on the materials testing plans developed for each project.

For PCC pavement cores consisting of multiple layers, the test shall be conducted separately on the core specimens consisting of each of the concrete overlay layers and the original concrete pavement layer from each specified location after assigning proper layer numbers. Layer numbers shall be assigned using the field layer number information from Field Operations Information Form 2 of the field data packet or lab sheet L04. The following definitions will be used throughout this protocol.

a) Core: An intact cylindrical specimen of the pavement material that is removed from the pavement by drilling at the designated location. A core can consist of, or include, one, two or more different layers.

b) Layer: That part of the pavement produced with similar material and placed with similar equipment and techniques. The material within a particular layer is assumed to be homogeneous. The layer thickness can be equal to or less than the core thickness or length.

c) Test Specimen: That part of the layer which is used for the specified test. The thickness of test specimens cored from the pavement can be equal to or less than the layer thickness.

1. SCOPE

1.1 This test covers the determination of the compressive strength of concrete cores or molded cylinders obtained from a SPS or GPS pavement project.

2. APPLICABLE DOCUMENTS

2.1 AASHTO Standards: As listed in AASHTO T22-88I.

2.2 ASTM Standards: As listed in AASHTO T22-88I.

2.3 LTPP Protocols: P66 - Visual Examination and Thickness of Portland Cement Concrete Cores.

3. SUMMARY OF METHOD

3.1 This method consists of applying a compressive axial load to test specimens at a rate which is within a prescribed range until failure occurs. The compressive strength of the specimen is calculated by dividing the maximum load attained during the test by the cross-sectional area of the specimen.

4. SIGNIFICANCE AND USE

4.3 Delete

6. TEST SPECIMENS

6.1 The length of the specimen when capped, shall be as nearly as practicable twice its diameter. Follow Section 6.2 of AASHTO T24-86 for specimen end preparation. The test specimen shall be prepared to achieve the desired length to diameter (L/D) ratio of 1.94 to 2.10 by sawing and/or grinding the bottom and top ends of the core of a PCC layer. Exceptions are: (a) thin PCC overlay layers and (b) the need for reduction in length because of sawing off concrete with embedded steel.

6.2 Neither end of test specimens when tested shall depart from perpendicularity to the axis by more than 0.5° (approximately equivalent to ? inch in 12 inches [3 mm in 305 mm]). The test specimens shall always be capped at both ends by following AASHTO T231-87I procedures for capping hardened concrete specimens.

6.3 The diameter (D) used for calculating the cross-sectional area of the test specimen shall be determined to the nearest 0.01 inch (0.25 mm) by averaging two diameters measured by a caliper at right angles to each other at about the mid-height of the specimen.

6.4 Measure the length of the specimen before capping (L_O) and measure the length of the capped specimen (L) prior to testing to the nearest 0.1 inch (2.5 mm). The length shall be determined by averaging four measurements equally spaced around the specimen.

6.5 Use the length of the capped specimen to compute the L/D ratio. This ratio is required to be reported. If the ratio exceeds 2.10, the specimen shall be further reduced in length. Specimens within the ratio of 1.80 to 2.10 require no correction in the measured compressive strength.

6.6 If the L/D ratio is less than 1.80, apply the correction factor shown in the following:

Values not given in the table shall be determined by interpolation.

6.7 Care shall be exercised during sample preparation so that the length of a specimen is not reduced to the extent that L/D ratio becomes less than 1.0. However, if for any reason the L/D ratio is less than 1.0 the test shall be performed, the actual L/D ratio reported and a special comment (see Section 9.4) included in the report that explains the reason for the low value of the L/D ratio. Apply a correction factor of 0.87 to a specimen with a L/D ratio less than 1.0.

6.8 PCC cores (obtained from the pavement) shall be stored flat side down, fully supported and at between 5 ° C (40 ° F) and 38 ° C (100 ° F) in an environmentally protected storeroom.

PCC cylinders (molded in the field) shall be moist cured during storage prior to testing at 23 ± 1.7 ° C (73.4 ± 3 ° F). As applied to the treatment of demolded specimens, moist curing means that the test specimens shall have free water maintained on the entire surface at all times. The moist room shall meet the requirements of AASHTO Specification M201. Specimens shall not be exposed to dripping or running water.

Prior to performing the test, the cores or cylinders shall be submerged in lime-saturated water at 23 ± 1.7 ° C (73.4 ± 3 ° F) for at least 40 hours immediately prior to performing the test.

9. REPORT

The following information is to be recorded on Form T61:

9.1 Sample Identification shall include: Laboratory Identification Code, Region, State, State Code, SHRP ID, 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, Laboratory Test Number, Test Date.

9.3 Test Results
Report the following:

1. Diameter (D) to nearest 0.01 inch.
2. Length before capping (LO), Length after capping (L), to the nearest 0.1 inch.
3. Length to diameter (L/D) ratio.
4. Cross-sectional area, in square inches to the nearest 0.01 inch.
5. Maximum load, in pounds-force.
6. Compressive strength (CS), calculated to the nearest 10 psi after applying the appropriate correction factor.
7. Type of fracture (see Fig. 2 of AASHTO T22-88I and described as follows).

9.4 Comments shall include LTPP standard comment code(s), as shown in Section 4.3 of this Guide and any other note, as needed. Additional codes for special comments associated with the testing are given below.

9.5 Use Form T61 (Test Sheet T61) to report the above information (Items 9.1 to 9.4).

LTPP LABORATORY MATERIAL HANDLING AND TESTING
LABORATORY MATERIAL TEST DATA
COMPRESSIVE STRENGTH OF PCC CORES

LAB DATA SHEET T61

PORTLAND CEMENT CONCRETE

TEST DESIGNATION PC01/PROTOCOL P61

LABORATORY PERFORMING TEST:______________________________________________________________

LABORATORY IDENTIFICATION CODE: __ __ __ __

REGION _________________ STATE ___________________ STATE CODE __ __

EXPERIMENT NO _____ SHRP ID __ __ __ __

SAMPLED BY: ______________________________________________ FIELD SET NO. __

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