By:
Gregory J. Livingston 
Vice President, Technical Sales, PCSI
 

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Figure 2

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Stand and look at telephone poles that have been in place for more than ten years. One of the most notable observations is that many of these "stationary" objects are in constant state of movement. Many are out of alignment and in extreme cases are leaning severely enough to pose a danger. Not only are above ground structures being effected by this movement. but below ground structures like sewer pipes and manholes are also being moved around. As with ground structures, the implication of these movements range from benign to severe. The Nations infrastructure is constructed from very rigid materials such as; concrete, brick and iron. The rigidity of the system does not allow for much resistance to these creep forces. The micro-movement of the local topography is technically called "creep". The impact of creep can result in everything from local health issues resulting from contaminated drinking water to the loss of literally hundreds of millions of tax dollars spent on treatment of clean groundwater that infiltrates the system through the consequent breaks in the rigid infrastructure.

Unfortunately, when the resulting breaks are repaired. or the entire structure is replaced, the repair method often used is the same materials that originally failed; concrete, brick and iron, thereby setting up the next generation for costly infrastructure repairs.

In 1991, we introduced a new class of materials to the infrastructure repair industry. The major benefit of this new family of polymeric materials called polyurea, was that we could actually formulate a "shock-absorber" right into the material. The internal flexibility acts to absorb and dissipate the creep forces. When properly formulated, polyurea hardness can range from soft (Shore A 60) to hard (Shore D 50) elastomers. Therefore, depending on the severity and type of forces that will be encountered in service, the polyurea rehabilitative coating can be tailor made to achieve the optimum balance between structural enhancement and force dissipation.

We must not lose sight of the fact that creep forces are only the cause of the problem and that the impact of the problem are breaks in the system. Spray applied polyurea forms a monolithic coating which seals breaks in the infrastructure segment.

To illustrate my point, let's look at a severe example. In Figure 1, we are using a high pressure water jet (2000 psi) to clean a brick manhole wall. Brick construction has the highest degree of failure because the mortar around each brick potentially may be broken down. Note that in Figure 1, the picture was taken in winter, January to be specific. One of the benefits of polyurea coatings is that there is no catalyst. Catalyzed systems such as urethanes and many of the epoxy based systems are temperature dependent to achieve full cure. Since polyurea has no catalyst, the cure is not temperature dependent which allows application at any temperature, including winter. The significance of this, is that it first extends your contracting season to year round and, second it allows a company to retain skilled labor without having seasonal "lay-offs" due to the operational  inadequacies of your materials. Because of corrosive conditions of many infrastructure environments, many concrete based materials such as mortar and concrete itself , show signs of corrosion.  In Figure 2, we can see evidence of such corrosion on the bottom or "bench" of the manhole, where the concrete has eroded away exposing the aggregate. In this case, we need to rebuild the area, as we are doing in Figure 3. Because of this corrosion, the mortar between bricks, the bottom as we discussed and the un-observable area under the rim at the top, all experienced some corrosion. These corroded areas are weak and, when under stress may break and become an active infiltration site. The areas of infiltration are sites where clean ground water can enter the system, it must be cleaned at the treatment plant.  More importantly, especially to the industrial community these breaks are site of exfiltration where process effluent leaks out of the plant infrastructure system, and can contaminate ground water. Figure 4 is the prepared manhole prior to polyurea application. The preparation phase is very important, as with any coating operation. Also, n the case of polyurea manhole rehabilitation, it is the most time consuming phase.                                

To summarize, the surface of the earth is constantly moving. The amount of movement varies with location, and is technically called "creep". Creep effects both above and below ground structures such as telephone poles and sewer infrastructure respectively. Creep and other forces cause a misalignment of these systems and, with regard to infrastructure, may cause breaks in the system. These breaks are site of infiltration, where groundwater can gain entry to the system. Once in the treatment system, the clean water must be treated in local water plants. The cost to taxpayers of this needless remediation is hundreds of millions of dollars per year. Infrastructure breaks at industrial facilities are site of both infiltration and. more importantly, exfiltration. The danger of exfiltration is ground water contamination, which is a Federal offense, heavily fined and costly to remediate.  

Manhole after polyurea coating. PCS-355 polyurea ,cured in 6 seconds. Manhole took 1.5 hours to complete.

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