More C 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. 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.
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Does it ring when hit lightly with a hammer or give a dull at sound? Can you break it with your ngers? How distributed? Are cracks associated Through or around coarse aggregate?
With cores or sawed specimens, did the aggregate tear in drilling or sawing? Crack llings? If air dry, are there unusually wet or dry looking areas? Rims on aggregate? 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. In some cases, gates for Radiation-Shielding Concrete2 the petrographer will have had experience adequate to provide C Test Method for Penetration Resistance of Hardened detailed interpretation of the materials performance with Concrete2 respect to engineering and other consequences of the observa- C Test Method for Rebound Number of Hardened tions.
In others, the interpretation will be made in part by Concrete2 engineers, scientists, or others qualied to relate the observa- C Practice for Examination and Sampling of Hardened tions to the questions to be answered. Concrete in Constructions2 3.
Request adjunct No. A Thin edges of splinters of the paste transmit light; reections 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 exural strength and that is broken with a hammer and examined on a new break within a week of the time that it nished 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 denitely gray or denitely tan, except adjoining old cracks or original surfaces. All of one kind? Several kinds? Bleeding Segregation A Dana, E. C Dark solid spheres or hollow-centered spheres of glass, or of magnetite, or some of glass and some of magnetite, recognizable at magnication of 3 9 on sawed or broken surfaces.
Other mineral admixtures with characteristic particles visible at low magnication 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.
Pertinent background information, including results of 4. If the petrographer is was or was not as specied. In this case, other tests may be highly experienced, his advice and judgment should be sought required in conjunction with petrographic examination.
In such a case, the purchaser and the consultant ture, the nature of the hydration products, adequacy of curing, should together determine the kind, extent, and objectives of and unusually high water - cement ratio of the paste.
The agreement may stipulate bonate reactions, or cement - aggregate reactions, or reactions specic determinations to be made, observations to be re- between contaminants and the matrix have taken place, and ported, funds to be obligated, or a combination of these or other their effects upon the concrete.
Purposes of Examination jected to and affected by sulfate attack, or other chemical attack, or early freezing, or to other harmful effects of freezing 4. The probable usefulness of petrographic examination in specic instances 4. Paste expands with thermal concrete is probably normal if it has not undergone coefficient effect and then shrinks, cracks, decrepitates, color change. Establish by coring for compressive and becomes soft 4. Cracking Perpendicular to the face and internal, where heating or Examination of the surface, ultrasonic tests, coring, cooling caused excess tensile stresses.
In some new petrographic examination 4. Color changeWhen concrete has not Concrete made with sedimentary or metamorphic Color change is the factor most useful to the spalled, observe depth of pink color to aggregates shows permanent color change on heating.
Color normal to C; goes from pink to red from to temperature of about C occurred 5. For temperatures up to about C temperature distribution is little affected by using carbonate rather than siliceous aggregate 5. At C low quartz inverts to high with 0. Spalling over steel to expose one fourth of the bar at C; white powdered decomposed hydration products at C.
Surface crazing about C; deeper cracking about C. Aggregate behaviorAggregate behavior Aggregates differ in thermal diffusivity, conductivity, Changes on heating are often accompanied by affects strength, modulus, spalling, coefficient of expansion. Heat transmission decreases volume change 4. Spalling Occurs subparallel to free face; followed by breaking off saucer-like pieces especially at corners and edges 4. Note: Compressive strength and elastic Reduction in strength of concrete containing siliceous Determinations by compressive tests and static modulus.
For concrete at least 1-year gravel after heating, then cooling and testing: modulus of cores; Test Method C for old, strength will increase after cooling Heated to Temperature qualitative determination; Test Method C 4.