Case Studies in Polyurea Wastewater Infrastructure Rehabilitation

The performance of polyurea coatings in wastewater infrastructure applications is best understood through documented field experience across diverse operating conditions and structure types. The following case studies describe representative rehabilitation projects that illustrate the range of applications, the scale of infrastructure that polyurea technology can address, and the performance outcomes that sustained service experience has documented.

Case Study 1: Municipal Collection System Manhole Rehabilitation Program

Context: A mid-sized North American city with a collection system constructed primarily between 1940 and 1970 identified approximately 400 manholes in moderate-to-severe condition through a comprehensive NASSCO MACP inspection program. The city’s engineering staff had observed progressive deterioration in the highest-risk structures over multiple inspection cycles, with some structures showing active concrete loss exceeding 2 inches of section thickness at the crown. The traditional response of patch repair with Portland cement mortar had proven ineffective, with repaired areas typically showing renewed deterioration within 18-24 months.

Approach: The city specified a polyurea rehabilitation program requiring high-pressure water jetting to International Concrete Repair Institute (ICRI) surface preparation profile CSP 5-6, chemical grouting of all active infiltration points, repair of structural defects with calcium aluminate cement mortar, and application of 125-mil aromatic polyurea to all interior surfaces using heated plural-component equipment. A post-application inspection protocol required holiday detection testing, minimum 80% dry film thickness compliance with the 125-mil specification, and pull-off adhesion testing at 5% of structures.

Outcome: The program was completed over three construction seasons with a two-crew mobilization, averaging 8-12 manholes per day. Post-application inspection found a 94% first-pass acceptance rate across the program. Flow monitoring in the rehabilitated service areas documented a 32% reduction in wet-weather I/I peaks over the two years following program completion. Re-inspection of the first-season manholes at 5 years post-application found all coating systems intact, with no evidence of delamination, blistering, or visible deterioration. The city’s engineering staff estimated the program had deferred approximately $18M in manhole replacement costs within the next 15-year capital plan horizon.

Case Study 2: Force Main Transition Structure Rehabilitation

Context: A regional wastewater authority experienced accelerated deterioration at the receiving manhole of a 16-inch force main serving a dense residential development with high sulfate concentrations in the wastewater. Crown corrosion in the receiving manhole had progressed to a depth of 4 inches at the highest-exposure zone within 12 years of construction, exposing aggregate and creating a structural risk. The annual repair cost for this single structure had exceeded $8,000 using traditional patch repair methods, with no improvement in deterioration rate.

Approach: The authority engaged a specialty coating contractor to perform comprehensive rehabilitation using a two-component system: calcium aluminate cement structural restoration to rebuild lost section to the original dimensions, followed by a 250-mil polyurea coating application over the entire interior surface. The thicker specification was selected to provide additional service life margin and to accommodate the elevated deterioration rate expected at this location based on the wastewater chemistry and force main discharge conditions.

Outcome: The structure has remained in service for 11 years since rehabilitation without requiring any additional maintenance. The 250-mil polyurea specification has shown no degradation in the annual visual inspections conducted by the authority’s collection system crew. At the projected inspection interval, the authority anticipates the coating will reach its 20-year service life without re-application, representing a total avoidance of approximately $88,000 in annual patch repair costs compared to the pre-rehabilitation maintenance pattern.

Case Study 3: Wastewater Treatment Plant Primary Clarifier Rehabilitation

Context: A regional wastewater treatment authority managing a 40 MGD plant identified deterioration in two of four primary clarifiers dating from the facility’s 1968 construction. Chloride-induced reinforcement corrosion and biogenic acid attack in the above-waterline zone had produced widespread cracking and spalling, with rebar exposure at multiple locations in the effluent launder and inlet baffle areas. The authority required rehabilitation of both clarifiers within a single 6-month period to minimize treatment process disruption.

Approach: The authority specified a multi-system rehabilitation approach: cathodic protection using a titanium mixed metal oxide anode system installed in drilled holes and embedded in repair mortar for the submerged and tidal zones; epoxy injection grouting for structural cracks with widths exceeding 0.010 inches; cementitious polymer-modified repair mortar for all spalled and deteriorated concrete areas; and a dual-coat polyurea system (2-mil primer plus 125-mil topcoat) for all interior surfaces. The dual-coat system was specified to address the challenging adhesion conditions presented by the polymer-modified repair mortar, which had been evaluated and found incompatible with direct polyurea application without primer.

Outcome: Both clarifiers were rehabilitated within the specified schedule, with each structure out of service for 14 and 17 days respectively. Post-application inspection achieved 100% first-pass acceptance for both structures. The authority has maintained the clarifiers in full service for 8 years since rehabilitation with no coating-related maintenance events. The cathodic protection systems are functioning within design parameters based on reference electrode monitoring. The combined rehabilitation was determined by the authority’s engineering staff to have extended the service life of both clarifiers by a minimum of 25 years, deferring replacement capital estimated at $4.2M per structure.