February 2022 Vol. 77 No. 2
Rehab Technology
Coating Materials Contribute to Rebuilding Wastewater Collection Systems
By Gerhard P. Muenchmeyer, P.E., Principal, Muenchmeyer Associates
As the aging underground, pipeline collection system continues to deteriorate, replacement and/or rehabilitation become major issues for municipalities, industrial/commercial complexes and other utility owners. The deterioration includes sewer mains, lateral pipes and manholes. The need to re-construct the pipeline system is driven by corrosion, structural failure, and leaking and surcharged pipes conveying unwanted infiltration and/or inflow.
To better understand this continuing deterioration, a condition assessment of the collection system must be undertaken to determine existing conditions and the cause. Assuming dig-and-replace is not an option, rehabilitation technologies are a key alternative. Available products can be evaluated, leading to the best approach for rehabilitating the system.
System components, options
Options for a system’s main and lateral pipelines include coating, lining and replacement products. Rehabilitation using lining technology, starts with the concept that the existing or old pipeline will serve as the form or mold for creating a new pipe within the existing pipe. The condition, however, must be reviewed to determine if the existing pipe will provide the basis for installing a new pipe that will meet the contract requirements. Occasionally, the existing pipe may be repaired or rebuilt so that the liner, after installation, is a long-term, properly designed pipe within a pipe, meeting contract requirements.
A system’s main and lateral pipelines can be replaced by pipe bursting technology. This involves using either a pneumatic or static bursting tool that causes the existing pipe to be broken into small pieces, while an expander cone presses the broken pipe into the surrounding soil matrix and new pipe material is pulled into the created and expanded void. The technique not only provides for installing a new pipe, but a pipe that can be a larger diameter than the one being replaced.
Coating materials, though very effective for some collection system components, are not as frequently used in either lateral or main wastewater pipelines.
Manholes, a critical component of the collection system for inspection, maintenance cleaning and repair of the main and lateral pipelines, can be effectively rehabilitated with both lining techniques and coating products. Also, unlike main and lateral pipelines, manholes are constructed of multiple components, some of which can readily be replaced, rather than rehabilitated.
As a general rule, manhole walls are designed to provide structural stability against earth, hydrostatic and live loads that may affect the long-term design of the structure. Additional wall thickness is typically added, by the manhole manufacturer, to protect it during transportation to the job site and against field installation stresses. Since total structural failure of a manhole is rare, the use of coating materials can effectively rebuild walls, prevent infiltration and inflow, and prevent corrosive environments from causing the ultimate failure of a manhole.
Inspection, assessment
Regardless of which technology and associated products are selected for rehabilitation, an evaluation process, including condition assessment, best rehabilitation approach, technology and product selection, application requirements, inspection and testing requirements, should be specified, in detail, in the contract documents.
The condition of a manhole must be inspected, and all existing conditions documented. There are standard programs such as the Pipeline Assessment Certification Program (PACP) and the associated Manhole Assessment Certification Program (MACP) offered by NASSCO. These programs define all structural defects, in standard industry language. This information, together with a visual inspection, should provide the engineer with sufficient data to determine the existence of any structural, leakage and/or corrosion issues that may exist.
Once the condition of the manhole has been assessed, the engineer must determine the best and most cost-effective approach for replacing/rehabilitating its components. This may require some replacement/repair, and rehabilitation of other components.
The technology selection may be as simple as digging up the manhole and replacing it with a new one. This occurs when the existing manhole has partially or totally collapsed, its shape is significantly distorted, or it has essentially lost all function and structural characteristics.
Based on the existing defects documented, the type and best-suited rehabilitation technology should be selected. Manholes can be rehabilitated using a variety of methods. In each case, the manhole is cleaned and prepared for new product application.
The collection system may simply suffer from old age and deterioration or from structural damage; other cases, corrosion or leakage may be causing the problem. It is very important to select products that have a verifiable, proven history of application success and product longevity, for projects with similar conditions. Verified design life means the material is still in place after its projected life has expired. Verified service life means it’s functioning, as intended, after its expiration.
Product specification
Products can include cementitious, polymer, CIPP, composite liner, panel liners, inserts, and many variations of each. Individual, or combination of, products should be evaluated to verify its history for effectively protecting a specific manhole material for the longevity required. Products may be designed to mechanically bond, forming a homogeneous application, or simply form a separate, non-bonded, protective coating to the structure. Project reference and third-party test reports should be consulted to satisfy the product’s capabilities to perform, particularly as it concerns long-term protection.
All applicable product and application data must be specifically identified in the contract documents. These performance specifications must include clearly defined installer requirements and the obligation to provide a product that meets the contract requirements. Specific quality control requirements must also be clearly defined, including installer obligations and inspector verification responsibilities during product delivery, installation, and final quality delivery. In addition, inspection specifications and required documentation must be included.
Product application varies.
A variety of products can be hand-applied, including cementitious, polymers, and composites.
Some products can be spray-applied or spun-cast, so that the product mechanically bonds to the structure’s surfaces.
Lining products may be prefabricated to the specific dimensional configuration of the manhole structure or designed as an in-place, one-size, material that, when expanded during installation, will tightly conform to all aspects of the existing manhole wall.
Installation, inspection
In accordance with a performance specification, the contractor/installer must submit a Performance Work Statement (PWS), detailing the installation means and methods, before any work proceeds. The PWS covers labor, materials and installation procedures to be followed by the contractor/applicator while performing the contract work. Any revisions to the procedures require submittal of a revised PWS.
Products to be furnished and applied by the installer, are typically submitted to the engineer for review/approval prior to any work proceeding. Further inspection and verification must be performed on all contract materials, to be incorporated into the product delivery, for compliance with the engineer’s review/approval.
Prior to product application, manhole cleaning and preparation is a common requirement for all coating technologies. The manufacturer will typically furnish detailed instructions on proper preparation, for its particular product, to achieve a quality, long-term application. Preparation of the coating application is highly critical to achieving long-term product design and service life.
During the selection process, a key element to evaluate is whether the product is intended to bond to the host structure or not. For a material to bond, the host structure must be properly prepared to ensure a surface area that is clean, and structurally sound.
Product installation requirements may vary for different service requirements. For instance, a system can be cleaned and properly prepared, but in a matter of hours, a grease-laden wastewater environment will re-contaminate the manhole, requiring re-cleaning before product application to effectively provide a clean bonding surface. It is recommended therefore, that these products be applied in strict compliance with the manufacturer’s preparation and application requirements.
Whether hand-applied, sprayed-on or lined with a fabric tube, inspections must be performed to verify correct product installation. In addition to visual inspections, which are common to all product installations, specific evaluations and measurements, by type of product, include thickness during application, material mix ratios, and temperature and humidity.
In addition to verifying material quality, quantities and application procedures before and during installation, quality control testing must be performed before final acceptance of the applied product. This usually includes detailed visual inspections, adhesion testing to verify the bonding characteristics between the structure and the coating, spark testing to identify the location of pinholes or voids in the coating, core removal for testing, and vacuum testing.
Conclusion
Successful coating applications follow specific application requirements and understand the existing manhole conditions, the effects of the wastewater environment and the preparation requirements. Product expectations must be clearly defined in the contract, emphasizing performance capabilities for structural, corrosion and/or leakage solutions, and verified by required inspections, enforced testing and documented by trained inspectors.
Comments