Protective Coatings Industry Interview: Structural Linings for Manhole Rehabilitation
In this interview, John Manijak, Director of Technical Training and Technical Support, discusses how we can help our customers save time and money with structural solutions. For the video version, click here.
What do you do?
In my role as Director of Training and Technical services I concentrate on rehab services for pipes. We perform UV curing, traditional cured in place pipe (CIPP), pressure pipe lining, spray in place pipe (SIPP), cleaning and televising, grouting, geopolymer lining and manhole rehabilitation.
Let's put some things into perspective. For example, how many manholes are there approximately in Chicago?
The EPA estimates that there are around 21 million manholes in the U.S. In a city like Chicago, we have 9 million feet of sewer. If a typical section of sewer is 250 feet long, in between manholes that would equate to about 36,000 manholes in the city. That’s not counting the suburbs, the Metropolitan Water Reclamation District, who has 175 municipalities also feeding into it.
Why do manholes need rehabilitation?
Our sewer systems are getting old. The early structures were constructed of brick or block, and the mortar they used to hold it together eventually breaks down and begins to crumble over time. When that happens, the bricks start to become loose and fall out, compromising the integrity of the pipe. This ultimately leads to a collapse.
Newer manholes are constructed of pre-cast concretes and we often see problems caused by hydrogen sulfide (H2S) in those structures. H2S is a naturally occurring gas in sewers, responsible for lowering the pH levels in the concrete walls. When the pH level falls, the biological colonization of Thiobacillus bacteria begins. It’s a big fancy word but basically bacteria start to take over and in, the presence of oxygen, the bacteria have a unique ability to convert hydrogen sulfide gas, which is in the sewers, into sulfuric acids which eat away at the concretes. In later stages, the acids also begin to corrode the cement binders of the concretes, converting to gypsum, a non-load bearing material that makes the structures start to fall apart and collapse.
Obviously these manholes are in a very aggressive, hostile, destructive environment. What are some of the typical solutions used for sewer manhole rehabilitation?
The most common material for both construction as well as manhole rehab is concrete. By applying a half inch to 2 inches of concrete to the inside of a manhole wall, we will rebuild and replace the integrity of the structure.
We use two types of concrete; the first is a micro silicate mortar (MSM), a Portland-based concrete infused with tiny fiberglass rods that provide a higher strength material when cured. The MSM does not have a lot of resistance to hydrogen sulfide so it should be limited to structures serving storm or other systems with very little hydrogen sulfide present.
The second type of concrete that we use in manhole rehab is calcium aluminate mortar (CAM). These concretes are infused with aluminum dusts that provide additional protection against hydrogen sulfide. This is the type we should be using in sanitary systems.
A third type of material that we use to rehab manholes are epoxies. In sewer systems that have very high levels of hydrogen sulfide – for example lift stations and manholes located closer to lift stations and treatment plants – we coat those manholes with about 125 mils of epoxy on the inside. Sometimes we first have to rebuild the structure walls with the concretes, but then we do put a top coat of epoxy on afterwards.
The newest type of manhole rehab material that we use is geopolymer. This is a really cool, specialized, manufactured rock. The polymers within the geopolymer material react with one another, creating a kind of mesh to give it a higher flexural strength than standard concretes. When you spray concrete on concrete, you get a cold joint, but with geopolymers you don’t. The polymers react to one another and create one solid piece of rock.
When it comes to spray/hand-applied polymer linings, what surface preparation is typically conducted?
Surface prep is everything. First, you have to remove all of the debris in the manhole. Next, you have to wash the entire surface down with at least a 4k power washer. Then, you remove any materials (loose concrete, bricks) and patch up the large holes. Once you’ve done all of this, you have to stop any and all groundwater or infiltration that’s coming into the structure. If you don’t remove it, then it’s going to wash out the material that you’re trying to put on the walls. Finally, you have to check the pH level of the surface that you’re trying to coat and, if it is acidic, you need to neutralize it.
Another important factor to consider are the outside temperatures at which we’re working in. Spring and fall are usually ideal times because there are typically not extreme temperatures. If you’re working in the summertime with high temperatures, the material will set off way too quickly so you have to protect the material you’re applying from getting warm in the sun. Then there is the other extreme; in the wintertime when it’s too cold, the material just won’t cure at all. The epoxy materials are highly sensitive to temperature changes; there is a very specific temperature range that the materials need to be before you apply them, otherwise they will never set at all.
So in the aspect of applied linings, I would imagine that craft workers and inspectors in manhole rehabilitation projects need specialized training. Is this the case based on your experience? What skills do they need to be trained and certified in?
Manhole workers need to possess a high work ethic. The people I’ve worked with take a lot of pride in their work; the finished product that they leave behind is their signature. Usually there are three people in a crew. The top man or woman sets the stage. They need to be in top physical shape as they are going to be lifting 60-pound bags of concrete all day long. They also have to know how to properly mix the concrete; if you add too much water its going to be too wet and if there is not enough water its going to be too dry. The crew has to know the proper consistency of that concrete. They also have to know the equipment inside and out. Concrete setup is time sensitive, so if something goes wrong, we need to get it fixed right away. The leader is also responsible for the safety of the person in the hole, so they have to know confined space entry, how to ensure their crew member is safe, and how to get them out of there if there is a problem.
The person in the manhole has to be a jack of all trades: top physical shape, unafraid to be in a confined space for a long time, has to know how to prep the walls properly by washing them down, fixing the holes, stopping all type of infiltration. They also need to have an understanding of what structural integrity is and how to rebuild it before putting a covering over the wall surfaces. Finally, they also need to have the skills and experience to know how to properly apply the materials.
There is not a national training program out there for people on manhole rehabilitation. The training is left to the contractors. Some manufactures have certifications, some don’t. What I think is the most exciting thing coming up is the Society for Protective Coatings (SSPC) rehab certification program for manhole rehab. SSPC is a wonderful organization that has a long history of training and certifying coding applicants. Not only do they certify, they also follow up on the work of the certified individuals.
Is there anything we did not talk about that you wanted to cover?
It’s important to have a good contractor with a solid history of quality work. You get what you pay for. A lot of times contractors will come in inexpensively, and then I get the calls from the city asking me how to fix the project that they just paid someone else to do. Don’t be afraid to check into your contractors, check their backgrounds, make the phone calls to the municipalities, and check out their work.
Want to talk more protective coatings? Contact John today.