Wastewater Clarifier Trough Rehabilitation, City of West Palm Beach – concrete resurfacing and coating

City of West Palm Beach, Public Utilities – West Palm Beach, FL, USA
Concrete repair, rebuild, and coating of clarifier troughs (#1-#8)
East Central Regional Water Reclamation Facility
2009 – 2010
(Epoxytec certified contractor:
Service Painting of Florida)
The City of West Palm Beach consulted with Epoxytec to assist in the design of a proper specification for the rehabilitation of concrete wastewater clarifier troughs.

Outdoor concrete troughs require restoration at times, and must include the utilization of high performance coatings to combat the effects of corrosion.

Although most wastewater clarifiers, especially those found in the secondary process, do not typically pose a threat due to high chemical attack, such as sulfuric H2S, they do however come with a variety of other considerations to address. Because of the ultraviolet rays coupled with treated sewage or reclaimed water beating down onto porous concrete – breeding of excessive algae is a constant issue. Algae roots into the concrete, deep and annoyingly. When attempts to remove the excess microbial growth, often times maintenance crews find that chunks of concrete comes out with it. In time, the algae and continuous water trickling through the weirs begin to erode and weaken the concrete binder.

Prior to any rebuilding or coating, the concrete must be assessed and prepared. To avoid any sand entering the clarifier itself, and possibly harming the pumping operation, water blasting was specified via the use of ultra-high pressure water jetting (UHP).

UHP water jetting not only removes all the algae; at 40,000 psi, the ultra-high pressure water also removed any previous coatings, eliminated all loose or weakened concrete binder and aggregate, etched the concrete, and cleaned/decontaminated all-in-one-shot.

Concrete should be clean, sound, and etched before applying any reparative or protective materials.

As per NACE and SSPC standards, follow-up inspection after blasting is highly encouraged. Here a NACE/SSPC certified inspector checks the pH level in the concrete after blasting to ensure neutral to alkaline concrete has been exposed after blasting. This is one method to gain confidence that decontaminated concrete has been eliminated, for wastewater corrosion typically keeps the contaminated surfaces acidic, and therefore that acidic surface most be removed.

The selection of a high build, ultra-high density mortar was specified – Epoxytec MortarTec Silicate.

Epoxytec MortarTec Silicate is a perfect selection for this project because it provides the applicator the right amount of pot life to mix and trowel, yet it is designed for top coating as it cures within 24 hours without harmful curing agents often problematic to top coating, and to a density near 10,000 psi compressive strength in a matter of a hours.

Mortar had to be utilized in this application, because the concrete was so badly deteriorated by the rooting algae that large aggregate was exposed leaving a near impossible substrate to coat without a resurfaced underlayment.

After troweling the mixed resurfacing mortar, a 24 hour cure was required before protective coatings were applied.

After the final cure of the Epoxytec MortarTec Silicate, a light water blast took place to remove any laitance or dust. With a uniform and resurfaced profile and filling of any bugholes or voids, the surface can now be coated.

Before coating, the City specified Epoxytec CPP Gel to fill and seal between the mortar rebuild and the original clarifier weirs, as a highly adhesive joint sealant to anchor the weir and fill the gap.

The coating is now applied, Epoxytec Uroflex (urethane-modified-epoxy) coating system for wastewater (with algae and chemical resistance exhibiting self-leveling properties, UV tolerance, high gloss, and flexibility).

The Uroflex coating is a great option for confined places or areas difficult to mobilize. Because it can be rolled or sprayed it offers an application crew options and various mobilization logistics depending on this situation.

Because the Uroflex is an epoxy, but modified with urethane it gains an ultra-high glossy sheen because of the urethane, making the surface (even after cure, as it is seen here) a very non-porous, smooth and leveled top coat in order to prevent algae from rooting. And therefore it also facilitates any cleaning methods the plant so chooses, whether brush sweepers or chlorinated spray – it will withstand and assist the algae cleaning effort with no rooting making it easy to come off and controls the algae from growing excessively, aggressively or long.

The Epoxytec Uroflex coating is also suitable to the outdoors, unlike other epoxy-only systems. Ultraviolet (UV) is known to breakdown epoxies, however, because Uroflex has urethane modified within its matrix, it is UV stable and does not degrade in an outdoor immersed environment such as in clarifier troughs and therefore, stays impermeable and durable throughout its life expectancy.

The coating system is repairable, never looses its recoat window and can be applied in multiple lifts because of it. Here we built a 60 mil system. The mileage was selected high build enough to properly fill and cover all the peaks and valleys of the substrate, yet stay semi-structural, allowing a durable liner with enough movement and flexibility to conform with the outdoor expansion and contraction requirements. Uroflex has 38% elongation, unlike typical 1% – 6% of solid epoxies.

After holiday testing (spark testing) was completed, a final visual inspection was conducted and signed off. The warranty was delivered to the owner, backed by Epoxytec and their certified applicator.

The installation of clarifier trough renewal systems and protective coatings was successful.

Resurfacing: Epoxytec MortarTec Silicate @ 1/2″ – 1″
Weir anchoring and sealing: Epoxytec CPP Gel
Coating system: Epoxytec Uroflex @ 60 mils

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