concrete tanks and distribution boxes: watertightness and corrosion claude goguen, pe director of...
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TRANSCRIPT
Concrete Tanks and Distribution Boxes: Watertightness and Corrosion
Claude Goguen, PEDirector of Technical ServicesNational 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 2007.
• 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
• We Can Also Segment the Image to Try to See Each of These More Clearly 150 mm
• Recipies Can TellUs What to Use
Paste (Cement And Water)
Aggregates (CoarseAnd Fine)
Air
Watertightness
Type IType IType 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 ConnectorMust 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
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
WatertightnessDifferent applications depending on nature of tank
Watertightness
Recommended Practice
Watertightness
TestingTwo methods permitted by ASTM C1227 - Standard Specification for Precast Concrete Tanks
Vacuum Testing
Watertightness
TestingTwo methods permitted by ASTM C1227 - Standard Specification for Precast Concrete Tanks
Water-Pressure Testing
Watertightness
General appearance of tank
Watertightness
Cracks
WatertightnessACI 224 – Control of Cracking of Concrete Structures
Watertightness
Honeycombing
Watertightness
Cold Joints
Corrosion
Corrosion
Bacteria
The Process
Corrosion
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
Porosity
Str
eng
th
High
Low
Low
High
Dense Mix
• Good aggregate gradations to allow for minimal void spacing
• SCM’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: 317.582.2328Email: [email protected]
Web: www.precast.org
THANK YOU!