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Publication Number: FHWA-HRT-04-150
Date: July 2006

Appendix E. Examplesof Reasons Petrographic Services Are Requested and Corresponding Plans for Analysis

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Situation: Concrete submitted failed test for required compressive strength.

Situation: Mixture was harsh and workability was very poor.

Situation: Inspector reported that contractor added water because workability was poor.

Situation: Inspector reported that tines used for surface texturing seemed to tear concrete surface rather than produce usual continuous lands and grooves.

Situation: Inspector reported that vibrating screed failed to operate and the concrete was handscreeded.

Situation: Air-meter test showed that mixture had low air content; however, contractor placed mixture anyway.

Situation: There was a driving rainstorm during placement of concrete.

Situation: Specimens are from a test mixture employing a new material or construction practice.

Situation: A crack system is developing in a pavement (or bridge deck) soon after placement.

Situation: Placement developed a severe crack system over many portions of the surface. Deterioration is becoming worse at an ever-increasing rate, and concrete is requiring constant work from maintenance crews. (Obviously, the younger the placement, the more mystifying and crucial the problem. However, even when a pavement’s life has surpassed its planned life cycle, the need for extensive repairs can seem to be a disaster to a transportation department&s budget.)

Situation: Shortage of a material from one source necessitated use of an unapproved material.

Situation: Concrete telephone conduit (or drainage ditch lining) in contact with soil was distressed by some mechanism that seems to be dissolving it.

Client’s question: What is this slick-looking coating (or this dark coating or this white coating) that we find near the cracks in the placement? Does it indicate serious problems?

Client’s question: Why is this concrete such a funny color? Does it mean the concrete was made from the wrong materials? How durable is this sort of concrete?

Client’s question: Why is there a peculiar dark blue-green color so unevenly distributed in this concrete? Does it mean that the mixing was not sufficient? Are there weaker and stronger places in this concrete? (Suspected: Ground granulated blast-furnace slag (GGBFS) was used in the mixture.)

Client’s question: Why didn’t this concrete that was placed 3 weeks ago ever set? The concrete can be shoveled like gravel and is almost dry.

Client’s question: What material is in these stalactites found hanging under this concrete bridge? Or, What is this white (gray, beige, etc.) material occurring as a coating on this concrete? What do they mean concerning the durability and strength of the bridge?

Situation: This concrete set much faster than expected.

Situation: This concrete had a very high slump and a runny consistency.

Situation: Pavement is pushing out and causing humps in adjacent bituminous concrete.

Client’s question: How deep are these cracks? Will they cause corrosion of the reinforcing rods?

Concrete researcher’s question: Can you (the petrographer) actually see a difference between concrete with a low chloride ion permeability and that with a high permeability (see ASTM C 1202)?

Concrete researcher’s request: Measure these cracks (depth and width at 25-mm intervals) and give me the data so that we can calculate the volume of the crack.

Concrete researcher’s request: Compare these two beams subjected to testing for resistance to freezing and thawing and report any internal differences.

Concrete researcher’s request: Compare the bond in these different types of overlay (or different methods of achieving overlay bond) and report the location of any cracking or debonding.

Client’s question: “Why is this concrete so good?” (Only once in the more than 35 years of our experience was any HCC submitted with this request.)

 

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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