CFRP & Concrete Utility Poles

01The Problem: Reinforced Concrete VS Road Salt

Take a walk down any street where concrete poles and road salt meet every winter and what might you see (picture beside)

In most cases the typical concrete utility pole will experience a certain amount of deflection by way of wind loading.  This repetitive action eventually causes the pole to develop cracks quite often within the lower 1/3 of the pole.  This is the area where the damage becomes its worst, the area where salty snow and slush make its way into the cracks and attacks the steel reinforcement we call “rebar”

There is a very technical explanation for this process that can be found on various websites across the internet but for ease of explanation it comes down to this: the rebar starts corroding (rusting) and swells.  This action in turn pushes against the surrounding concrete and makes it fall off as seen in the picture to the right.  As this scenario continues to occur the bottom of the pole begins to lose some of its structural integrity and if left too long will eventually fail.

Feasibility

In determining the feasibility of repairing a concrete pole with a carbon fiber wrapping method one must take into account a number of variables.  Variables such as pole size, structural integrity (original strength), reinforcement properties, load carrying capacity, mounting type, damage type and total area affected.

Before a pole can be repaired it must be inspected by H&N Fiberworx in order to determine whether it can be repaired using our carbon fiber wrapping procedure.  As a general rule of thumb we can say that if the pole’s damage/degradation is limited to the bottom 1/3 of the overall height above grade and does not protrude into the pole’s wall more than half it’s original thickness and is not degraded more than half of its circumference chances are good that it can be repaired at a price that can be justified.

Guidelines

When looking at a concrete pole in need of repair and the methodology that H&N Fiberworx provides we can honestly say that the end result will meet or exceed the original manufacturer’s specifications.  The deciding factors that are involved in moving forward with a repair are two fold – The first one being the level of damage and the second being price justification – should it be repaired or replaced.

Level of Damage: Because we are dealing with different manufacturers, pole designs and mounting configurations there are different levels of damage or degradation seen on concrete poles.  Below are some examples:

01

In most cases the damage is limited to the bottom 1/3 of the pole exposed to the atmosphere (approx. 8-10 feet above grade at most) and typically appears on the outer surface not protruding more than half way through the wall of the structure.

Repair vs. Replace: Determining whether a concrete pole should be repaired or replaced can ultimately come down to price but when factors such as available man hours, public safety and liabilities come into the picture it takes on a whole new meaning.

If a pole has degradation beyond those basic parameters it is likely that the cost to repair it may outweigh the cost of replacement but should not be overlooked as it depends on the severe ness of the damage itself.  A proper inspection should be performed to properly assess the damage and determine whether it is feasible to repair or not.  If man hours are not available to replace a pole that is determined non-repairable in a reasonable timeframe a temporary repair may also be considered in order to prolong replacement.

Repair Classification: Due to the wide spectrum of damage/degradation that can occur to concrete poles we have broken down our repair kits to specific categories in order to accommodate and pin point the required repair.

box04Category 1: Minor cracking where steel rebar has not yet been exposed – minor signs of rust may be appearing on the outer surface of the pole – damage can range from 2 to 10 feet above grade.
box05Category 2: Minor spalling & cracking has occurred and in some cases the steel rebar can be seen but is not exposed in its entirety. Damage can be located from 2 to 10 feet above grade.
box06Category 3: Major spalling has occurred and the circumference of the steel rebar is ½ or more exposed to the atmosphere.  Cracks emanate from the exposed area allowing for more severe spalling to take place if pole is not repaired.  Damage is anywhere from grade level to the 10 feet above grade.

Why Consider Carbon Fiber Wrapping?

Having a concrete pole repaired using a carbon fiber wrap will leave you with a pole that:

  • Is as strong or stronger than originally supplied
  • Will resist salt water & other environmental damage
  • Will increase pole life for up to an additional 20 years or more
  • Can be painted to simulate concrete
  • Can save you 25% to 75% in replacement costs