Concrete Tanks and Distribution Boxes: Watertightness and Corrosion Claude Goguen, PE Director of Technical Services National Precast Concrete Association

Introduction Onsite Wastewater System Basics Watertightness - Manufacturing Corrosion of Concrete – How does it work? Conclusion Watertightness - Installation Outline

Introduction Estimated 26.1 million of total U.S. housing units were served by septic systems in In 2007, 22 % (1.6 million) of all housing units less than 4 years old used septic systems. 50 % of total housing units with septic systems in the United States were in rural areas, 47%were in suburbs, while 3% were found in central cities. 46% of occupied housing units with septic systems were located in the southern region of the US followed by the Midwest with 22%

Introduction More than 800,000 onsite sewage disposal systems are currently used in Indiana

Introduction How important is it to have a good quality onsite wastewater system? Value for homeowner Avoids contamination

Introduction The risk of contamination Pollutants can reach surface waters in hours, days, months or years The EPA standard for nitrate in drinking water is 10 mg/L Nitrogen (nitrates) is the most common contaminant How do we get rid of nitrates? So, a proper system and drainfield is important but if it’s not watertight …it doesn’t matter.

Watertightness Watertightness of precast concrete is defined as the ability of concrete to hold back or retain water without visible leakage. Permeability refers to the amount of water migration through concrete when the water is under pressure. Generally, the same properties of concrete that make it less permeable also make it more watertight.

Watertightness Paste (Cement And Water) Aggregates (Coarse And Fine) Air

Watertightness Type I Water / Cementitious Material Ratio W/C Ratio

Watertightness Curing

Watertightness Strength of concrete 4000 PSI or greater

Watertightness Pipe connectors Drain Plugs Joint Sealant Risers Installation Testing

Watertightness Pipe Connector Must conform to ASTM C1644 – Specification for Resilient Connectors Between Reinforced Concrete On-Site Wastewater Tanks and Pipes.

There are plastic risers and concrete risers Watertightness

Very important to make sure drain hole in bottom of septic tank is plugged.

Watertightness Joint Sealant Must conform to ASTM C990 – Standard Specification for Joints for Concrete Pipe, Manholes, and Precast Box Sections Using Preformed Flexible Joint Sealants

Watertightness Different applications depending on nature of tank

Watertightness Recommended Practice

Watertightness Testing Two methods permitted by ASTM C Standard Specification for Precast Concrete Tanks Vacuum Testing

Watertightness Testing Two methods permitted by ASTM C Standard Specification for Precast Concrete Tanks Water-Pressure Testing

Watertightness General appearance of tank

Watertightness Cracks

Watertightness ACI 224 – Control of Cracking of Concrete Structures

Watertightness Honeycombing

Watertightness Cold Joints

Corrosion

Bacteria

The Process

Corrosion

Factors: Temperature Low Velocity BOD Low pH High Sulfates

Corrosion How do we mitigate this issue? #1 – GOOD QUALITY CONCRETE

Low w/c ratio.45 is significantly more resistant to MIC than.48 In moderate to severe conditions,.40 or lower

Dense Mix Good aggregate gradations to allow for minimal void spacing S CM’s Good consolidation

High strength At least 4000 PSI

Adequate Curing This is often overlooked but can’t be overstated Cement not fully hydrated Shrinkage cracks

Products or actions to prevent or repair MIC damage Sealers Liners Nanomaterials Calcareous aggregates Coatings Concrete Additives Corrosion

Conclusion

Questions? If you have any questions about this presentation or anything about precast concrete onsite wastewater structures, please contact: Claude Goguen, PE. LEED AP Director of Technical Services Phone: Web:

THANK YOU!