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  • ASTM C856-17

ASTM C856-17

Standard Practice for Petrographic Examination of Hardened Concrete

ASTM International, 01/01/2017

Publisher: ASTM

File Format: PDF

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Published:01/01/2017

Pages:14

File Size:1 file , 180 KB

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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).

(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.
(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.
(A) Secondary ettringite can sometimes be recognized by crystal habit and silky luster.
(B) Fly ash can be detected by color and shape when dark spheres are present. In concrete that has not oxidized the presence of slag may be inferred from the green or blue color of the paste.
(C) Ettringite and calcium hydroxide in voids may be recognized by their crystal habits.
(D) Magnesium oxide and calcium oxide should be identifiable in polished section.
(A) The literature and private reports include data on many unidentified secondary compounds in concrete; these are not included in the tabulation. Indexes of refraction of common mineralogic types are taken from standard works on mineralogy.
(B) Higher and lower indexes of refraction have been recorded for naturally occurring ettringite (13) and thaumasite (12), but it is not known that the naturally occurring minerals and compounds found in hydrated cement are of the same composition.

1.2 The petrographic procedures outlined herein are applicable to the examination of samples of all types of hardened hydraulic-cement mixtures, including concrete, mortar, grout, plaster, stucco, terrazzo, and the like. In this practice, the material for examination is designated as “concrete,” even though the commentary may be applicable to the other mixtures, unless the reference is specifically to media other than concrete.

1.3 The purposes of and procedures for petrographic examination of hardened concrete are given in the following sections:

 

Section

 

Qualifications of Petrographers and Use of Technicians

 4

Purposes of Examination

 5

Apparatus

 6

Selection and Use of Apparatus
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