Project: Repair of Joint Sealant in Equalization Holding Basins Santa Rosa Waste Water Treatment Plant, Santa Rosa, CA

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1 Project: Repair of Joint Sealant in Equalization Holding Basins Santa Rosa Waste Water Treatment Plant, Santa Rosa, CA Background In mid-1990 s, Concrete Science, Inc. was hired by City of Santa Rosa to perform condition assessment and provide repair recommendations to three very large Effluent Equalization basins and a Holding Basin. The basins were about 9 years old and had expansion joints at about 18 to 23 feet on center. The joint width varied from ¾-inch to 1.25 inch and the joints were filled with a greyish color joint sealants. The sewage effluent filled the basins as seen in Photograph 1. Within five years from installation of the joint sealant, the sealant started deteriorating. Vegetation began to grow out of the joints. Photographs 1 through 5 show the observed conditions. City s Primary Concern & Objectives The City s primary concern and repair objectives were as follows: 1. How to avoid seepage of effluent into the soil which had potential to contaminate the local ground water, and 2. Install long lasting joint sealant. Concrete Science, Inc. performed condition survey of the existing sealant in the basins, reviewed drawings and specifications, evaluated chemical make-up of the sewage contained in the effluent, reviewed commercial available sealants and its suitability to the application, and design a repair to meet Owner s objectives. Challenge to Concrete Science, Inc. The biggest challenge to us was to identify a joint sealant product that not only adhered

2 well to concrete, withstand the constant wetting & drying, but also resist deterioration due to exposure to UV rays. Construction Details The drawings & Specifications dated April 1988, specified 4-inch wide, center bulb type elastomeric, waterstop at the mid-depth of the 8-inch thick concrete slab at the expansion joints. Alternative option for the waterstop was, a 6-inch wide galvanized waterstop with a 12-inch overlap secured with self-tapping sheet metal screws. A polyurethane sealant was to fill the ½-inch wide expansion joint to ¼-inch depth. The affluent sewage was alkaline in nature with a ph of 7.6. Repair Challenge Concrete Science, Inc. reviewed joint sealant literature from 10 major manufacturers including Euclid, Master Builders, W.R. Meadows, Sika, and Fosrock Chemicals. The majority of the sealants were conventional types where existing failed sealant will have to be removed, concrete re-saw-cut to get clean sides and then installing the sealant. This approach was time consuming and expensive. The City wanted to use their own un-skilled crew to perform this work. We had to come up with a product that is easy to install, yet meet the project requirements for longevity of repair under harsh conditions. Repair Recommendations Concrete Science, Inc. recommended installation of a 4-inch wide pre-manufactured sealant tape which did not need removal of the existing sealant. Several thousand linear feet of expansion joint sealants were repaired using this innovative and State-of-the-Art repair method. We saved thousands of dollars from City s budget. At the time, this was one of the first largest application of such a sealant system in the United States. The existing

3 sealant also acted as a back-up waterproofing system. Repair Mr. Brad Kamin from Sika Corporation did mock-up and also trained City employees on installation of the sealant tape system called the Sikadur Combiflex System, The installation included shot blasting both surfaces along the expansion joint and then bonding the Combiflex tape with the Sikadur epoxy adhesive to the clean concrete surface to span across the existing joints. The installation steps are shown in Photographs 6 through 10. The City performed this large repair project using its in-house labor force and saved thousands of dollars. Repair Evaluation Recently in February 2017, about 20 years later, we visited the site to observe performance of the Combiflex. The observations are shown in Photographs 11 through 13. The Combiflex was in excellent condition after nearly 20 years in a harsh and challenging conditions.

4 Photograph 1. A portion of the equalization basins filled with Effluent.

5 Photograph 2. A portion of the Equalization basin without effluent. The joints were at about 23 feet on center. Photograph 3. Typical failed joint sealant.

6 Photograph 4. Failed joint sealant with vegetation growth. Photograph 5. A close-up of vegetation growth through the joint.

7 Photograph 6. Shot blasting machine used for the surface preparation machines used at the project. Photograph 7. Shot blasted surface along the joint ready for the Combiflex joint installation.

8 Photograph 8. Brad Kamin from Sika Corporation performing a demonstration of Combiflex installation. Photograph 9. A completed demonstration of Combiflex installation.

9 Photograph 10. A completed installation of Combiflex in one of the three large Equalization Basins. Photograph 11. About 20 years later, the Combiflex in one of the three large Equalization Basins is still in excellent condition.

10 Photograph 12. About 20 years later, the Combiflex in one of the three large Equalization Basins is still in excellent condition.

11 Photograph 12. A close-up of the condition of Combiflex after nearly 20 years. Photograph 13. A close-up of the condition of Combiflex after nearly 20 years.