ASTM C856 - 14

    Standard Practice for Petrographic Examination of Hardened Concrete

    Active Standard ASTM C856 | Developed by Subcommittee: C09.65

    Book of Standards Volume: 04.02


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    Abstract

    This practice outlines the standard procedures for performing petrographic examination of hardened concrete samples. The samples examined may be taken from concrete constructions, that is, all sorts of objects, units, or structures that have been built of hydraulic cement concrete. They may also be concrete products or portions thereof, or concrete or mortar specimens that have been exposed in natural environments or simulated service conditions, or subjected to laboratory tests. This practice applies to samples of all types of hardened hydraulic-cement mixtures, including concrete, mortar, grout, plaster, stucco, terrazzo, and the like. The equipments generally used for specimen preparation are diamond saw, cutting lubricant, horizontal lap wheels, free abrasive machine, polishing wheel, hot plate or oven, prospector's pick and/or bricklayer's hammer, abrasives, plate-glass squares, suitable media, and microscope slides. For specimen examination, the equipments needed are stereomicroscope, dollies, petrographic or polarizing microscope, metallographic microscope, eyepiece micrometer, stage micrometer, microscope lamps, needleholders and points, bottles with droppers, assorted forceps, lens paper, refractometer, and immersion media. Appropriate procedures for the sampling, preparation, and examination of specimens are detailed methodically.

    This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

    1. Scope

    1.1 This practice outlines procedures for the petrographic examination of samples of hardened concrete. The samples examined may be taken from concrete constructions, they may be concrete products or portions thereof, or they may be concrete or mortar specimens that have been exposed in natural environments, or to simulated service conditions, or subjected to laboratory tests. The phrase “concrete constructions” is intended to include all sorts of objects, units, or structures that have been built of hydraulic cement concrete.

    Note 1: A photographic chart of materials, phenomena, and reaction products discussed in Sections 8 – 13 and Tables 1-6 are available as Adjunct C856 (ADJCO856).

    TABLE 1 Visual Examination of Concrete (1)5

    Coarse Aggregate

    + Fine Aggregate

    + Matrix

    + Air

    + Embedded Items

    Composition:

     

     

     

     

     Maximum dimension,A in. or
      mm, in the range> d>

     

     

     

     

     Type:

    Type:

    color, by comparison with
     National Research
     Council Rock Color
     Chart
    (1963)

    more than 3 % of total,

    Type, size, location; kinds of metal; other items

      1 Gravel

     1 Natural sand

     

     predominantly in spherical

     

      2 Crushed stone

     2 Manufactured sand

    color distribution:

     voids?

     

      3 Mixed 1 and 2

     3 Mixed

     1 mottled

    less than 3 % of total,

     

      4 Other (name)

     4 Other (name)

     2 even

     abundant nonspherical

     

      5 Mixed 1 + /or 2 + /or 4

     5 Mixed 1 + /or 2 + /or 4

     3 gradational changes

     voids?

     

     If Type 1, 2, or 4, homogeneous
      or heterogeneous

    If Type 1, 2, or 4,
     homogeneous or
     heterogeneous

     

    color differences between
     voids and mortar?

     

    Lithologic types
    Coarse aggregate more than 20,
     30, 40, or 50 % of total

     

     

    voids empty, filled, lined, or
     partly filled

     

     

     

     

     

     

    Fabric:

     

     

     

     

     Shape
     Distribution
     Packing
     Grading (even, uneven,

    Equation C0856-14_1

     as per-
     ceptible

    distribution

    shape
    distribution
    grading (as perceptible)
    parallelism of long axes of

    voids below horizontal
     or low-angle
      reinforcement

      excess, or deficiency of

     

     

     

     irregular voids or sheets

     

      size or sizes)

     

     

     

     of voids: with each other;

     

     Parallelism of flat sides or
      long axes of exposed

     

     

     

     with flat sides or long
     axes of coarse aggregate

     

      sections, normal to

     

     

     

     

     

      direction of placement

     

     

     

     

     

       + /or parallel to formed and

     

     

     

     

     

      finished surfacesB

     

     

     

     

     

     

    Condition:
     Does it ring when hit lightly with a hammer or give a dull flat sound? Can you break it with your fingers? Cracks? How distributed?
     Through or around coarse aggregate? With cores or sawed specimens, did the aggregate tear in drilling or sawing? Crack fillings?
     Surface deposits? If air dry, are there unusually wet or dry looking areas? Rims on aggregate?

    clean or corroded?
    Are cracks associated
     with embedded
      items?

    (A) A substantial portion of the coarse aggregate has maximum dimensions in the range shown as measured on sawed or broken surfaces.
    (B) Sections sawed or drilled close to and parallel to formed surfaces appear to show local turbulence as a result of spading or rodding close to the form. Sections sawed in the plane of bedding (normal to the direction of placement) are likely to have inconspicuous orientation. Sections broken normal to placement in conventionally placed concrete with normal bond tend to have aggregate knobs abundant on the bottom of the upper piece as cast and sockets abundant on the top of the lower piece as cast.

    TABLE 2 Outline for Examination of Concrete with a Stereomicroscope (1)

    Note 1: Condition—When it is examined at 6 to 10× under good light, the freshly broken surface of a concrete in good physical condition that still retains most of its natural moisture content has a luster that in mineralogical terms is subtranslucent glimmering vitreous.A Thin edges of splinters of the paste transmit light; reflections appear to come from many minute points on the surface, and the quality of luster is like that from broken glass but less intense. Concrete in less good physical condition is more opaque on a freshly broken surface, and the luster is dull, subvitreous going toward chalky. A properly cured laboratory specimen from a concrete mixture of normal proportions cured 28 days that has shown normal compressive or flexural strength and that is broken with a hammer and examined on a new break within a week of the time that it finished curing should provide an example of concrete in good physical condition.

     Under the same conditions of examination, when there is reasonable assurance that the concrete does not contain white portland cement or slag cement, the color of the matrix of concrete in good physical condition is definitely gray or definitely tan, except adjoining old cracks or original surfaces.

    Coarse Aggregate

    Fine Aggregate

    Matrix

    Voids

    Lithologic types and mineralogy as percep-

    Lithologic types and miner-

    Color

    Grading

    tible

     alogy as perceptible

    Fracture around or through aggregate

    Proportion of spherical to nonspherical

    Surface texture

    Shape

    Contact of matrix with aggregate:

    Nonspherical, ellipsoidal, irregular, disk-

    Within the piece:

    Surface texture

     close, no opening visible on sawed

     shaped

     Grain shape

    Grading

      or broken surface; aggregate not

    Color change from interior surface to

     Grain size extreme range observed, mm

    Distribution

      dislodged with fingers or probe;

      matrix

     Median within range _ to _ mm

     

      boundary openings frequent,

    Interior surface luster like rest of ma-

     Textureless (too fine to resolve)

     

      common, rare

     trix, dull, shining

     Uniform or variable within the piece

     

     Width

    Linings in voids absent, rare, common,

    From piece to piece:

     

     Empty

     in most, complete, partial, colorless,

     Intergranular bond

     

     Filled

     colored, silky tufts, hexagonal tab-

     Porosity and absorptionB

     

    Cracks present, absent, result of spec-

     lets, gel, other

    If concrete breaks through aggregate,

     

     imen preparation, preceding spec-

    Underside voids or sheets of voids un-

     through how much of what kind?

     

     imen preparation

     common, small, common, abundant

    If boundary voids, along what kind of

     

    Supplementary Cementitious MaterialsC

     

     aggregate? All? All of one kind? More

     

    Contamination

     

     than 50 % of one kind? Several kinds?

     

    Bleeding

     

    Segregation

     

     

     

    (A) Dana, E. S., Textbook of Mineralogy, revised by W. E. Ford, John Wiley & Sons, New York, N. Y., 4th ed., 1932, pp. 273–274.
    (B) Pore visible to the naked eye, or at × _, or sucks in water that is dropped on it.
    (C) Dark solid spheres or hollow-centered spheres of glass, or of magnetite, or some of glass and some of magnetite, recognizable at magnification of × 9 on sawed or broken surfaces. Other mineral admixtures with characteristic particles visible at low magnification are recognizable. Ground surface of concrete containing portland blast-furnace slag cement are unusually white near-free surfaces but retain greenish or blue-greenish patches, and slag particles can be seen with the stereomicroscope or polarizing microscope.

    TABLE 3 Effects of Fire on Characteristics of Concrete

    Characteristic

    Causes and Effects

    Ways of Investigation

    Surface hardness


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    C125 Terminology Relating to Concrete and Concrete Aggregates

    C215 Test Method for Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of Concrete Specimens

    C227 Test Method for Potential Alkali Reactivity of Cement-Aggregate Combinations (Mortar-Bar Method)

    C342 Test Method for Potential Volume Change of Cement-Aggregate Combinations

    C441 Test Method for Effectiveness of Pozzolans or Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction

    C452 Test Method for Potential Expansion of Portland-Cement Mortars Exposed to Sulfate

    C457 Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete

    C496/C496M Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens

    C597 Test Method for Pulse Velocity Through Concrete

    C803/C803M Test Method for Penetration Resistance of Hardened Concrete

    C805 Test Method for Rebound Number of Hardened Concrete

    C823 Practice for Examination and Sampling of Hardened Concrete in Constructions

    C1012 Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution

    C1260 Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method)

    E3 Guide for Preparation of Metallographic Specimens

    E883 Guide for Reflected-Light Photomicrography

    ASTM Adjuncts

    AdjunctC856(ADJCO856 A chart of 27 photos Available from ASTM International Headquarters. Order Adjunct No. . Original adjunct produced in 1995.


    ICS Code

    ICS Number Code 91.100.30 (Concrete and concrete products)

    UNSPSC Code

    UNSPSC Code 30111500(Concrete and mortars)


    DOI: 10.1520/C0856-14

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