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: cgoguen@precast.org

Web: www.precast.org

THANK YOU!