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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-07-052
Date: September 2007

Long Term Pavement Performance Project Laboratory Materials Testing and Handling Guide

Protocol P66
Test Method for Visual Examination and Thicknessof PCC Cores (Pc06)

This LTPP protocol covers the visual examination and determination of thickness (measurement of length) of PCC cores. The visual examination shall be performed prior to the conduct of other designated tests. The test shall be carried out in accordance with the following procedure, unless otherwise directed by LTPP.

If an AC core is bonded with the PCC core and/or the underlying layer of treated base/subbase is bonded with the PCC core, then the PCC portion will be sawed off from other bonded layers in the laboratory. The participating laboratory is required to paint the same arrow or other traffic direction symbol on the top of the surface of each PCC core as that marked on the surface of the overlying AC core after sawing.

PCC cores from pavement sections are marked with an arrow or other symbol to show the direction of traffic. Any underlying bonded layer of treated base and/or subbase (including asphaltic treated base, lean concrete, econocrete, or cement treated aggregate layers) are required to be removed from the PCC cores in the field or in the participating laboratory by sawing. Layer thicknesses shall be measured prior to sawing.

For PCC pavements cores consisting of multiple PCC layers, the test shall be conducted separately on the test specimens from the concrete overlay layer and the original concrete pavement layer from each specified location after assigning proper layer numbers. The traffic direction symbol marking shall be transferred to the underlying bonded original concrete pavement layer surface by the Laboratory Contractor following the procedure in paragraph 2. This rule does not apply to specimens designated for LTPP Protocol P67, Interface Bond Strength Test. The following definitions will be used throughout this protocol.

  1. 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.
  2. 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.
  3. Test Specimen: That part of the layer which is used for the specified test. The thickness of the test specimen can be equal to or less than the layer thickness.

In this protocol the use of the term core implies the entire length of the core.

When assigning the layer number in the laboratory to the PCC cores, the field layer number information provided on Field Operations Information Form 2 of the field data packet and/or lab sheet L04, should be carefully examined and the following rules shall be followed.

RULE #1: If only one field layer number is assigned to the overlay concrete layer and the original concrete pavement layer of the PCC core, then this field layer number shall be assigned to the underlying original concrete pavement core, and the next layer number shall be assigned to the overlay. These layer numbers shall be used on Form T66 and included on the sample tags/labels.

RULE #2: If two different field layer numbers from Field Operations Information Form 2 or two different layer numbers from lab sheet L04 have been assigned to the two bonded concrete layers within the PCC core or to the two separated PCC cores from the same location on the pavement, then these layer numbers shall be retained for use on Form T66 and included on the sample tags/labels.

RULE #3: In all other cases when a PCC core consists of only one PCC layer from a given location from the PCC pavement, then the field layer number from Field Operations Information Form 2 (or the layer number assigned on lab sheet L04, if different from the field layer number) shall be retained by the participating laboratory on Form T66 and on the sample tags/labels.


1.1 This method covers the visual examination of the entire PCC core and measurement of the length of the entire PCC core in the laboratory.


2.1 AASHTO T148-86, Measuring Length of Drilled Concrete Cores.

2.2 ASTM C856-83, Petrographic Examination of Hardened Concrete.


3.1 The apparatus shall be a calipering device that will measure the length of axial elements of the core.

3.2 The apparatus shall be so designed that the core will be held with its axis in a vertical position by three symmetrically placed supports bearing against the lower end. These supports shall be short posts or stubs of hardened steel, and the ends that bear against the surface of the core shall be rounded to a radius of not less than 6.4 mm (¼ in.) and not more than 12.7 mm (½ in.).

3.3 The apparatus shall provide for the accommodation of cores of different nominal lengths over a range of at least 25 to 250 mm (1 to 10 in.).

3.4 The calipering apparatus shall be so designed that it will be possible to make a length measurement at the center of the upper end of the core and at three additional points spaced at equal intervals along the circumference of a circle of measurement whose center point coincides with the center of the core and whose radius is approximately one-half of the radius of the core.

3.5 The measuring rod or other device that makes contact with the end surface of the core for measurement shall be rounded to a radius of 3.2 mm (? in.). The scale on which the length readings are made shall be marked with clear, definite, accurately spaced graduations. The spacing of the graduations shall be 2.54 mm (0.1 in.) or a decimal part thereof.

3.6 The apparatus shall be stable and sufficiently rigid to maintain its shape and alignment without distortion or deflection of more than 0.25 mm (0.01 in.) during all normal measuring operations.


4.1 If the PCC pavement core is bonded with a treated base or subbase layer and/or AC layer (as shipped to the laboratory) then the PCC portion of the core shall be carefully removed by sawing after measuring layer thicknesses. If two PCC layers are bonded within the PCC core then these should be separated by sawing after measuring layer thickness. In all cases, the arrow or other traffic direction symbol marking on the top surface shall be transferred to the top of the sawed surface of the core as explained in the beginning (paragraph 3) of this protocol.

4.2 The core shall be free of any conditions not typical of the pavement surface. If a core is found damaged or shows abnormal defects then it shall not be used for length measurement and its condition shall be recorded during the visual examination described in Section 6.

4.3 If a core drilled from a pavement includes particles of the aggregate material bonded to the bottom surface of the core, then the bonded particles shall be removed by wedging, or by chisel and hammer, so as to expose the lower surface of the PCC core. If during the removal of the bonded aggregate the concrete is broken so that the instructions of Section 5.4 cannot be followed, the core shall not be used for length measurement and its condition shall be recorded during the visual examination described in Section 6.

4.4 Care shall be exercised in preserving the marked arrow or other symbol, if present on the top surface of the core. The arrow or the other symbol marking indicates the direction of traffic on the pavement.


5.1 Before any measurements of the core length are made, the apparatus shall be calibrated with suitable gauges so that errors caused by mechanical imperfections in the apparatus are known. When these errors exceed 0.25 mm (0.01 in.), suitable corrections shall be applied to the core length measurements.

5.2 The core shall be placed in the measuring apparatus with the smooth end of the core, that is, the end that represents the upper surface of the pavement placed in the down position so as to bear against the three hardened-steel supports. The core shall be placed on the supports so that the central measuring position of the measuring apparatus is directly over the mid-point of the upper end of the core.

5.3 Four measurements of the length shall be made on each core, one at the central position and one each at three additional positions spaced at equal intervals along the circumference of the circle of measurement described in Section 3.4. Each of these measurements shall be read to the nearest 2.5 mm (0.1 in.) either directly or by interpolation.

5.4 If, in the course of the measuring operation, it is discovered that at one or more of the measurement points the surface of the core is not representative of the general plane of the core because of a small projection or depression, the core shall be rotated slightly about it axis and a complete set of four measurements made with the core in the new position.

5.5 The individual measurements shall be recorded to the nearest 2.5 mm (0.1 in.) and the average of four measurements, expressed to the nearest 2.5 mm (0.1 in.), shall be reported as the average thickness of the core.


6.1 Cores are to be visually examined for general condition, deterioration distresses and defects such as cracks, voids, staining, honeycombing, layer separation, aggregate distribution, general type and shape of aggregate such as rounded gravel, angular crushed stone, etc. The field logs should be reviewed prior to the visual examination in order to be aware of and confirm or reject any notations made in the field.

6.2 The bottom surface of the core shall also be examined and any condition affecting the length measurements such as uneven surface due to removal of underlying bonded aggregates from the aggregate base or subbase course (as described in Section 4.3) , shall be recorded.

6.3 Follow the instructions provided in Section 4.2 (especially 4.2.1, 4.2.2, 4.2.3, 4.2.5, 4.2.6, 4.2.7, 4.2.10, 4.2.11), Section 10.2 and Table 1 of ASTM C856-83 standard for further visual examination. Petrographic and stereo microscopic examinations are not required.

6.4 Results of visual examination shall be based on LTPP standard codes, as described in Appendix "A" to LTPP Protocol P66.


The following information is to be recorded on Form T66.

7.1 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.

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

7.3 Test Results:

  1. Average Thickness of Core (L) to the nearest 0.1 inches.
  2. Comments based on Visual Examination. Use standard visual examination result codes listed in Appendix A to LTPP Protocol P66 and a note, if needed, not exceeding 25 characters.

7.4 Comments shall include: LTPP standard comment code(s) in Section 4.3 of this Guide and any other note as needed.

7.5 Use Form T66 (Test Sheet T66) to report the above information (Items 7.1 to 7.4).

7.6 Test results of PCC cores from only one PCC layer (with the same layer number) shall be reported on the same test sheet (Form T66). Test results of the PCC cores from the second PCC layer, if present, shall be reported on a separate test sheet (Form T66).


This attachment to LTPP Protocol P66 describes a series of two-digit codes for reporting the results of visual examination of PCC cores.

Code Description
51 Intact core; excellent condition; suitable for testing.
52 Hairline cracks on the surface of the core; suitable for testing.
53 Cracks and/or voids visible along the side of the core; core is suitable for testing.
54 Badly cracked or damaged core; unsuitable for testing.
55 Ridges on the sides of the cores; (Identify by placing a straightedge along the side of the core when the distance between the straightedge and core face is 1/16 inch [1.6 mm] or greater); such a condition should be recorded if the core is used for any other test.
56 Very rough and uneven bottom surface of the core. Place the core on a level surface. Identify with this code when less than 75% of the surface area is in contact with a level surface when the core is perpendicular to the surface.
57 Core extremely damaged from sampling, shipping, or laboratory handling; unsuitable for testing. Core thickness cannot be measured.
58 Core was sawed in the laboratory to remove the core from the underlying bonded layer of base, subbase, or AC.
59 Core consisted of two or more PCC layers. Core was sawed in the laboratory and appropriate layer numbers were assigned to each PCC layer.
60 One or more PCC layers have become separated, appropriate layer numbers were assigned to each PCC layer.
61 Segregation of coarse and fine aggregate is observed over 25% or more of the surface area of the core.
62 Voids in the matrix of the PCC mixture are observed along the sides of the core.
63 Voids due to loss of coarse and fine aggregate are observed along the sides of the core.
64 Core is missing significant portions and cannot be considered a coherent cylindrical core; unsuitable for testing.
65 Coarse aggregate along the face of the core contains 50% or more of crushed materials with fractured faces.
66 Coarse aggregate along the face of the core is a mixture of uncrushed gravel and crushed gravel or stone.
67 The exposed aggregates along the face of the core are lightweight aggregate.
68 More than 10% of the surface area of the core contains soft and deleterious aggregate particles or clay balls. Soft aggregates are defined as those aggregates that can be easily scratched with a knife.
69 Cracks are generally across or through the coarse aggregate.
70 Cracks are generally around the periphery of the coarse aggregate.
71 Cracks are associated with embedded steel.
72 Rims are observed on aggregate.
73 Fine aggregate is natural sand.
74 Fine aggregate is manufactured sand.
75 Fine aggregate is a mixture of natural and manufactured sand.
76 Steel is present in the core (give type size and location of steel in a separate note).
77 Steel is corroded.
78 Core indicates D-crack - cracking is defined as a series of closely spaced crescent-shaped hairline cracks that appear at a PCC pavement surface and often curve around the intersection of longitudinal joints/cracks and transverse joints/cracks.
79 Core indicates deterioration due to freeze-thaw cycles.
80 Core indicates sulfate attack.
81 Core indicates alkali silica reactivity. It is shown by the expansion of reactive aggregates. As expansion occurs, the cement matrix is disrupted and cracks. It appears as a map cracked area.
82 Skewed core. A core is considered skewed when either end of the core departs from perpendicularity to the axis by more than 0.5° or ? inch in 12 inches (3 mm in 305 mm), as tested by placing the core on a level surface.
99 Other comment (describe in a note).

Any six codes from the above list can be used to report the results of the visual examination. A note may also be recorded (the note shall not be more than 25 characters long).




LABORATORY PERFORMING TEST:______________________________________________________________


REGION _________________ STATE ___________________ STATE CODE __ __

EXPERIMENT NO _____ SHRP ID __ __ __ __

SAMPLED BY: ______________________________________________ FIELD SET NO. __

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


2. SAMPLING AREA NO. (SA-) __ __ __ __ __ __ __ __ __ __ __ __
3. LABORATORY TEST NUMBER __ __ __ __ __ __
4. LOCATION NUMBER __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __
5. LTPP SAMPLE NUMBER __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __
6. AVERAGE THICKNESS (L), INCHES __ __.__ __ __.__ __ __.__ __ __.__ __ __.__ __ __.__
      (a) CODE ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
      (Section 7.3(b), Protocol P66) ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
      (b) NOTE ___________ ___________ ___________ ___________ ___________ ___________
___________ ___________ ___________ ___________ ___________ ___________
___________ ___________ ___________ ___________ ___________ ___________
      (a) CODE ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
(Section 7.4, Protocol P66) ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___
      (b) NOTE ___________ ___________ ___________ ___________ ___________ ___________
___________ ___________ ___________ ___________ ___________ ___________
9. TEST DATE ___-___-___ ___-___-___ ___-___-___ ___-___-___ ___-___-___ ___-___-___
GENERAL REMARKS:___________________________________________________________________________


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