Enhancing Infrastructure Resilience: Combating Corrosion in Manholes

Municipal infrastruc­ture forms the backbone of urban areas. Sewer systems ensure the efficient transport and treatment of wastewater. However, the longevity and functionality of these systems are often threatened by corrosion, struc­tural degradation, and environ­mental factors. Manholes, in particular, play a crucial role in infrastructure yet are often overlooked.

 One large Northeastern util­ity company recognized the critical importance of proactive maintenance and embarked on a comprehensive rehabilitation project for its municipal manholes in New Jersey. This case study explores the challenges posed by corrosion in sewer infrastructure, the significance of manhole rehabilita­tion, and the successful application of advanced materials and techniques.

Understanding Corrosion in Sewer Infrastructure

Corrosion, a natural process driven by chemical reactions between materi­als and their environment, poses a significant threat to sewer infrastruc­ture integrity. In wastewater environments, the primary driver of structural deterioration and water infiltration is microbiologically induced corrosion (MIC). This occurs when hydrogen sulfide gas, which is always present in a municipal wastewater stream, is ingested as a food source by the thiobacillus bacteria found in wastewater. The bacteria metabolize the hydrogen sulfide gas and secretes highly corrosive sulfuric acid that readily attacks Portland cement-based concrete and mortars, as well as many of the metals found in wastewater structures such as manholes. The corrosive nature of municipal wastewater, coupled with the presence of abrasive solids, leads to the degradation of the surfaces within manholes, necessitating timely intervention and rehabilitation.

Manhole Rehabilitation: Importance and Challenges

Manholes serve as critical access points for maintenance and inspection within sewer networks, facilitating the flow of wastewater and providing ven­tilation. However, prolonged exposure to corrosive gases and moisture renders manholes susceptible to structural fail­ure, infiltration, and exfiltration leading to more widespread problems. Corro­sion-induced defects, including cracks, spalling and delamination, compromise the integrity of manhole structures, undermining the hydraulic efficiency of sewer systems — thus increasing operational costs. Furthermore, these problems stemming from corrosion pose risks to public health, environmen­tal quality and infrastructure resilience.

Rehabilitating manholes presents multifaceted challenges, ranging from identifying corrosion hotspots to select­ing suitable materials and techniques for repair and protection. Traditional rehabilitation methods often involve labor-intensive processes resulting in prolonged downtime, traffic disrup­tions, and escalating costs. Address­ing these problems necessitates the adoption of innovative approaches, advanced materials, and collaborative partnerships to optimize efficiency, du­rability, and sustainability in manhole rehabilitation projects.

Project Overview

The county utility authority man­hole rehabilitation project repre­sents a proactive response to the corrosive challenges confronting sewer infrastructure. Prior to reha­bilitation, the municipal manholes showed signs of surface deteriora­tion, corrosion on cementitious ma­terials, and infiltration in multiple locations. Led by the utility author­ity and supported by contractors and suppliers, the project aimed to enhance the resilience and longevity of the municipal manholes through targeted rehabilitation measures.

The rehabilitation process com­menced with the meticulous removal of existing coal tar epoxy coatings through abrasive blasting. This method ensured a clean and recep­tive substrate for subsequent repair and protection measures. A critical aspect of the rehabilitation effort involved addressing numerous active leaks within the manholes, which were sealed by hand using Instaplug Hydraulic Cement F-180. This versatile material effectively halted water infil­tration, mitigating the risk of further structural deterioration and corro­sion propagation.

To restore degraded surfaces and provide long-term corrosion protec­tion, the application of advanced materials such as high-strength, rapid-set substrate resurfacer and a MIC-resistant, epoxy lining was employed. The substrate resurfacer, applied using the wet shotcrete method, facilitated uniform coverage and surface restoration. A trowel and broom finish were then applied to reach the correct surface profile for optimal adhesion and bond strength between the substrate and coating system. This approach enhanced the structural integrity and hydrau­lic performance of the manholes, mitigating the risk of infiltration and exfiltration.

Following the restoration of the substrate, SewerGard 210XHB, ahigh-performance coating system, was applied in a single coat to achieve a dry film thickness of 60 mils, providing ro­bust corrosion resistance and chemical protection against harsh wastewater environments. The spray application method ensured consistent coverage and adhesion to substrate surfaces, enhancing the durability and service life of the rehabilitated manholes.

Furthermore, the application of Chimney Seal, a hand-applied elasto­mer, effectively sealed the chimney areas of the manholes, preventing water ingress. This additional protec­tive measure further bolstered the watertightness and structural integrity of the rehabilitated manholes, ensuring reliable performance and longevity in service.

Outcome and Impact

The successful completion of the municipal manhole rehabilitation project signifies a significant mile­stone in the ongoing effort to enhance the resilience and sustainability of sewer infrastructure in New Jersey. By addressing corrosion-induced defects, sealing active leaks, and ap­plying advanced materials, the project has fortified the structural integrity, hydraulic performance, and service life of these manholes. Furthermore, the risk of ground and surface water contamination was mitigated by ensuring future regulatory compliance.

The rehabilitation of manholes represents a critical component of cor­rosion management strategies, safe­guarding public health, environmental quality, and community resilience. Understanding the underlying mecha­nisms and manifestations of corrosion in manholes, empowers municipali­ties to implement targeted interven­tions, materials selection criteria, and corrosion-resistant design practices to mitigate risks, optimize performance, and extend the service life of critical infrastructure assets.

This rehabilitation project exem­plifies the efficacy of collaborative partnerships, innovative approaches, and advanced materials in addressing the challenges posed by corrosion in sewer infrastructure. Moving forward, the lessons learned from this project underscore the importance of proac­tive maintenance, strategic investment, and sustainable practices in ensuring the longevity and functionality of municipal infrastructure in the face of evolving environmental and operational pressures.