Concrete Pipe Spec for allowable cracking

[jgailla]

I'm writing a concrete pipe spec and am planning on including the following language.
I would like opinions on whether the specification is too stringent or too lax. Any comments would be appreciated on this topic and also concerning the clarity of the spec.

"One hundred percent of all reinforced concrete concrete pipe
installations shall be checked using a remote controlled camera
for joint separations, soil migration through the joint, cracks
greater than 0.01 inches, settlement, and alignment.

Replace pipes having cracks greater than 0.1 inches in width or
deflection greater than 5 percent deflection. The Engineer
shall evaluate all pipes with cracks greater than 0.01 inches
but less than 0.10 inches to determine if any remediation or
repair is required. RCP with crack width less than 0.10 inches
and located in a non-corrosive environment (pH 5.5) can
generally be repaired by installing a lining. The pipe shall be
replaced if visible circumferential cracking is greater than 20%
of the circumference or longitudinal cracking is greater than
10% of the pipe segment length."

 

[dicksewerrat]

What do you mean by 'deflection', joint deflection or ovality of the pipe? New RCP should be very close to 0% ovality. And CIPP lining can go from pH of about 3 to 10 with out going to a more expensive resin.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[jgailla]

Thanks for the response, dicksewerrat.
Good catch on the ovality. I had copied some stuff from another spec and that was in reference to PVC.
I'll also be taking out the pH reference.

I've had some issues in the past with vague storm sewer post-construction inspection specs and this is my first chance to write one from scratch.

 

[Ron]

jgailla....a remote camera cannot discern the width of cracks to the criterion you have given. About the best they can do is locate cracks, not measure them.

The 0.01" crack width is a design parameter, intended to be measured physically with a crack comparator or feeler gauge. Since reinforced concrete pipe is designed to crack, such cracks are of no consequence. If the cracks are wider than that, they should be sealed to prevent rebar corrosion, but the only way to know that is to measure them directly....a difficult proposition for "in-service" pipe.

As for the pH, corrosion of the rebar can occur with neutral pH...that's not the reason for the corrosion. In fact, rebar corrosion will typically occur up to a pH of about 9.5, after which there is sufficient passivation to mitigate corrosion. You are correct to remove the pH reference.

You might consider requiring compliance with
ASTM C76 "Standard Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe"

ASTM C497 "Standard Test Methods for Concrete Pipe, Manhole Sections, or Tile"

And

ASTM C1628 "Standard Specification for Joints for Concrete Gravity Flow Sewer Pipe, Using Rubber Gaskets"

for starters.

 

[jgailla]

Thanks Ron. The other parts of the specification do require compliance with the three ASTM standards you state.

The main reason for this part of the specification is to provide an objective, measurable basis for acceptance or rejection of the RCP after installation. Granted that the CCTV method will not allow accurate measurement of the cracks, but you can tell the difference between "large" and "small" cracks. A 0.01" crack is barely visible on the TV, while a 0.1" crack has a visible separation between the crack edges.

Perhaps I could put something in the specification that the contractor can, at his expense, use a direct method of measuring cracks if he disagrees with the Engineer's assessment of pipe to be repaired or replaced.

 

[cvg]

I would inspect the pipe delivered to the site. I have not seen CCTV inspection done after installation except on dams. generally not considered to be necesssary due to the bullet proof nature of RCP.

 

[Ron]

jgailla...good idea on the contractor responsibility if he disagrees. You're right...you can distinguish large from small.

cvg...some authorities in jgailla's area require video of installed stormwater infrastructure before project close-out and acceptance....and with good reason. I've viewed hours and hours of stormwater video showing all the things that jgailla is trying to prevent in his design.

 

[jgailla]

cvg, good comment on inspecting the pipe when delivered. I don't have that in the spec yet.

One of the reasons I am in favor of CCTV for storm systems after installation is it helps to keep site contractors in line in the absence of full time inspection.

As Ron notes, video is becoming popular in my region.

Several years ago, I was involved in several projects in a row with the same site contractor. On one project, the regulating authority required televising of storm sewers, which at the time I had not thought of doing. It so happened that the site contractor did not know of the requirement until most of the storm sewer was installed.

A bunch of the pipe had to be replaced or lined to satisfy the regulating authority. On the next project, the same site contractor knew of the requirements and there were zero defects.

 

[cht13er]

Where I work, 100% of storm and sanitary sewers are CCTV inspected after installation...lots of "dirty videos" as the sanitary is often in use already by the time the CCTV is done!