This page defines the method and material for the rehabilitation of sanitary sewer structures (manholes, wet wells, lift/pump stations, large diameter concrete pipe, etc.) utilizing the SewperCoat® rehabilitation system. The intent is to obtain a dense and durable concrete lining that is resistant to minimum inhibitory concentration (MIC). The items discussed include labor, equipment, and materials necessary to accomplish the rehabilitation of a wastewater structure.
The lining material is SewperCoat®. SewperCoat® is a prepackaged 100% calcium aluminate mortar that includes all cement, aggregates, and any required additives. The only additional thing required to add is the proper amount of potable water so as to produce a mortar suitable for spray application. Do not add Portland cement, other aggregates, or any admixtures whatsoever to SewperCoat®.
SewperCoat® is available in a "pumpable grade" formulation. It is designed to be applied with low-pressure, wet spray equipment. The material is mixed with water and conveyed through a hose with a progressive cavity (rotor-stator), a piston type (swing tube) pump system or with a peristaltic type pump. There is an atomizing nozzle on the hose that uses air pressure to propel the wet material, spraying it onto the surface at a low velocity. Spinning head application techniques can also be utilized.
SewperCoat® is also available as a "dry-gunite" formulation. It is designed to be applied with high-velocity, dry-gunite equipment. The material is blown dry through a hose with high pressure air. There is a nozzle on the hose that contains a water ring, which injects water into the dry material as is passes through. The SewperCoat® is mixed as it hits the sub-surface. The nozzleman uses a circular application pattern that shears the material and mixes it through displacement.
Regardless of the application method, careful attention should be given to surface preparation to ensure proper bond strength development. The typical sub-surface for structural wastewater applications is generally composed of Portland cement concrete. There are several industry guidelines available regarding surface preparation for concrete repair materials. In general, all sub-surfaces should be clean and free of laitance, loose material, residue and all existing coating and lining materials. Inflow and infiltration prevention measures should also be undertaken.
(For a detailed explanation of the surface preparation requirements please see ACI RAP-3 "Spall Repair by Low Pressure Spraying". ACI 546R "Concrete Repair Guide", chapter 2 also provides a good reference for important considerations for repairing concrete surfaces using mortar.)
A newly cast Portland cement concrete structure may require a significant amount of surface preparation to achieve the desired degree of surface roughness. A severely corroded existing structure may be well in excess of desired degree of surface roughness at the time of rehabilitation and may require only high-pressure water cleaning. Regardless, SewperCoat® must be applied to clean, sound, rough, damp surfaces. Any unsound concrete or contaminated surface materials must be removed and all active and potential leaks must be addressed prior to installation. SewperCoat® is generally applied at an installation thickness ranging from ½" to 1" (15 to 25mm), but can be installed up to a 4" (100mm) thickness (or even more if appropriate) depending upon the application.
It should also be noted that corroded Portland cement mortars and concretes that have been cleaned down to a sound subsurface may still be damaged chemically by the biogenic corrosion process. The presence of efflorescence, scale, carbonation, or precipitates after wet cleaning may be an indication that this process is not completed and that further washing or surface removal may be necessary. The use a phenolphthalein indicator is helpful in determining the condition after cleaning.
One key property with SewperCoat®'s resistance to biogenic corrosion is the chemical composition of both the calcium aluminate cement portion as well as the synthetic aggregates. Both have the same chemistry and mineralogy
|Al2O3||CaO||FeO + Fe2O3||SiO2|
|Compressive Strength (ASTM C109)||> 5,500 psi||24 hours|
|Flexural Strength (ASTM C348)||> 900 psi||24 hours|
|Splitting Tensile Strength (ASTM C496)||> 550 psi||24 hours|
|Slant Shear test (ASTM C882)||> 2,500 psi||28 days|
|Shrinkage at 28 days (ASTM C157)||< 0.04%|
|Freeze/Thaw after 300 Cycles (ASTM C666)||< 102|
A recognized independent testing laboratory is generally used to test SewperCoat® installed on a project. Typical field testing includes compressive strength testing, generally performed at 24 hours.
Work Crew responsibilities prior to application of SewperCoat® typically include the following:
Typically a foreman will operate the mixing/placing equipment and direct the work of mixing crew personnel, while the work crew maintains proper line pressures throughout the mixing/placing equipment to ensure the necessary consistent nozzle velocity.
Equipment is of the spray type. There are numerous equipment manufacturers that supply both low-pressure, wet-spray equipment (progressive cavity rotor-stator pumps) and traditional dry-gunite equipment (N series or rotary guns). All installation equipment should be kept in operating condition and good repair.
The intent is to ensure that the substrate is clean and free of laitance, loose material, residue and all existing coating and lining materials.
For detailed explanation of the required surface preparation see ACI RAP-3 "Spall Repair by Low Pressure Spraying" page 2. ACI 546R "Concrete Repair Guide", chapter 2 also provides a good reference for important considerations for repairing concrete surfaces using mortar. Sub-surfaces should be thoroughly saturated with water prior to the application of SewperCoat®. SewperCoat® should not be applied in an area where running water exists. The substrate should be saturated and free of any running water just prior to installation - or SSD, "saturated surface dry condition." To achieve this condition it may be necessary to presoak the sub-surface.
If inflow or infiltration is observed within the structure after surface preparation is complete, a rapid setting crystalline enhanced hydraulic cement product specifically formulated for infiltration control is generally used to stop minor infiltration flows. Where infiltration flows are more severe, pressure grouting may be required.
SewperCoat® should not be applied to a frozen surface or to a surface that may freeze within 24 hours of application. Typically the sequence of application is from bottom to top or vice versa if rebound is properly removed.
The nozzle should be held an angle as nearly perpendicular to the surface as practicable, with the nozzle held at least 1 foot (for wet spray) from the working sub-surface (except in confined space conditions). Care should be taken to ensure that the air velocity at the nozzle is uniform and does not cause the cement to separate from the aggregate at the nozzle.
If successive installation layers are requires, the time between successive layers of SewperCoat® should be sufficient to allow "tackiness" to develop but not final set.
Construction joints within a manhole should be avoided if possible. If joints are necessary, the leading edge should be thoroughly cleaned as necessary, then moistened and scoured with an air jet prior to the placement of the adjoining material.
After the body coat has been placed, the surface should be trowelled to remove high areas and expose low areas. Low areas should be filled with additional SewperCoat® to ensure a true, flat finished surface. After troweling to a uniform thickness, a brush/broom finish can be done if wanted.
For manhole applications, the minimum thickness of SewperCoat® is ½-inch (15mm for Aus. ½" is 12.5mm) cover over all surfaces. For other larger structures (lift stations, wet wells, treatment plant structures, etc.), the minimum thickness of SewperCoat® is generally a 1-inch (25mm) cover over all surfaces.
Once SewperCoat® has been applied, curing is critical. Moist/humid curing is ideal. If moist curing is used, it should be implemented just after the notice of uniform heat generation of the SewperCoat®. Moist curing can consist of the use of soaker hoses, water sprinklers, or vapor/misting machines. Regardless of delivery method, moist curing should continue overnight.
The use of curing compounds is also acceptable. Curing compound should be applied to all coated surfaces. Curing compound should be a commercially available product that meets the requirements of ASTM C309.
Overall, SewperCoat® is a bloody durable solution, as said by François.
Guideline for SewperCoat® lining installations in corrosive municipal sewer environments