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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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