fabricating a watertight precast concrete septic tank
TRANSCRIPT
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Fabricating a Watertight PrecastConcrete Septic Tank
Dan Wagner – Milan Vault, Inc.
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SEPTIC TANK QUALITIES
What qualities do we want in a septic tank?
COST BENEFIT
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DEPENDABLE
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ECONOMICAL
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Barney buys a concrete septic tankhttp://www.youtube.com/watch?v=kW3JkVaAZEc&feature=related
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Components of Watertightness
• Engineering and Design
• Manufacturing
• Quality Assurance and Testing
• Installation
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The septic tank must:• Withstand all loading conditions
– Surface Surcharge
– Concentrated wheel loads
– Lateral Loads
– Soil Bearing Capacity
Design Considerations
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Click to edit the outline text formatSecond Outline
Level Third Outline
LevelFourth
Outline Level Fifth
Outline Level
Sixth Outline Level
Seventh Outline Level
Eighth Outline Level
• Ninth Outline LevelClick to edit Master text styles
– Second level
• Third level
– Fourth level
» Fifth level
NO TRAFFIC / NO LOADS
240 psf
180 psf avg. 180 psf avg.
415 psf
2' Cover
5' 4' x 8' Tank
(Earth + Tank Weight)
(Earth Weight)
Assume soil at 120 lb/ft3
(Assume 7,000 lbs.)
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ASTM C 1227 LOADS
240 p sf
180 ps f avg . 180 p sf avg .
715 p sf
2 ' C o ver
5 ' 4 ' x 8 ' Tan k
(Earth , T an k W eig h t, L ive L o ad s )
(Earth W eig h t)
A ssu m e so il a t 120 lb /ft3
(A ssu m e 7 ,000 lb s .)
(L ive L o ad s )300 p sf
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LIGHT TRUCK TRAFFIC
325 psf
220 psf avg. 220 psf avg.
500 psf
2' Cover
5' 4' x 8' Tank
(Earth + LL + Tank Weight)
(Earth + LL Weight)
Assume soil at 120 lb/ft3
(Assume 7,000 lbs.)
2,250 lbs. wheel load
LL = 85 lb/ft2
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Click to edit the outline text formatSecond Outline
Level Third Outline
LevelFourth
Outline Level Fifth
Outline Level
Sixth Outline Level
Seventh Outline Level
Eighth Outline Level
• Ninth Outline LevelClick to edit Master text styles
– Second level
• Third level
– Fourth level
» Fifth level
The septic tank must not be buoyant; it must not float
Design Considerations
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Design Specifications
Tanks should be designed at least to:
• ASTM C1227
– Stdandard Specification for Precast Concrete Septic Tanks
• ASTM C890
– Standard Practice for Minimum Structural Design Loading for Monolithic or Sectional Precast Concrete Water and Wastewater Structures
• Local Codes, CSA B66, IAPMO/ANSI
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Manufacturing and Installation
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NPCA Design Recommendations• Minimum concrete thickness for conditions
• Clean forms in good conditions
• Proper reinforcement placement
• Prepour and post pour inspections
• A well designed concrete mix
• Proper finishing and curing
• Lifting inserts designed with S.F. = 4 min.
• Properly Sealed joints and fittings
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The Manufacturing Process
Raw Materials
Mix Design
Reinforcement
Production Practices
(Seals, Fittings, and Joints)
Post-Pour Operations
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Raw Materials
Use quality, certified materials• Aggregates
• Cement
• Water
• Admixtures
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Mix Design for Watertightness• Low Water/Cementitious Ratio!
– A maximum of 0.45 • (weight of water / weight of cement and pozzolans)
• Minimum 4,000 psi strength at 28 days– Minimum strength when shipped?
• Quality materials, well graded aggregates• Volumetric proportioning (ACI 211)• Air entrainment
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WATER
STRENGTH POROSITY
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Aggregates
• Comprise of about 70% of the total volume
• Conform to ASTM C 33
• Clean and well graded
• Free from deleterious substances
• Moisture content checked daily
• Properly handled and stored
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Entrained Air = Desirable Improves freeze/thaw resistance, ASR resistance, sulfate
resistance Improves workability
Entrapped Air = Non-desirable Bugholes Released through adequate vibration
Air Content
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Purpose of Reinforcement
• Concrete is strong in compression but weak in tension
• Reinforcement supplies strength to withstand tensile and shear forces experienced by concrete
• Sometimes tanks experience greatest forces during stripping, handling, and transporting
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Non-reinforced Concrete Behavior
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Reinforced Concrete Behavior
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Reinforcement Requirements
• Meet ASTM requirements (A615 or A706)
• Designed to withstand all loading conditions
• Provide adequate cover to protect from corrosion (1” min. ASTM C1227)
• Spaced properly, not touching formwork
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REBAR SHOWING
Visible problems
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Click to edit the outline text formatSecond Outline
Level Third Outline
LevelFourth
Outline Level Fifth
Outline Level
Sixth Outline Level
Seventh Outline Level
Eighth Outline Level
• Ninth Outline LevelClick to edit Master text styles
– Second level
• Third level
– Fourth level
» Fifth level
Rebar Touching Form
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Click to edit the outline text formatSecond Outline
Level Third Outline
LevelFourth
Outline Level Fifth
Outline Level
Sixth Outline Level
Seventh Outline Level
Eighth Outline Level
• Ninth Outline LevelClick to edit Master text styles
– Second level
• Third level
– Fourth level
» Fifth level
What it should look like
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Pre-Pour Operations• Pre-Pour activities include:
– Setting of formwork
• Forms must be cleaned and inspected after each use
– Positioning of steel reinforcement
– Positioning of Blockouts
– Positioning of embedded items (i.e. lifting apparatus)
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Casting Concrete
• Placement of concrete is important
• Consolidating Concrete
– Insufficient vibration leads to poor consolidation, excessive vibration causes segregation
– Proper vibration techniques lead to smooth, dense surfaces that promote impermeability
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CuringProper curing is important in developing strength, durability, and watertightness
Two critical elements in curing Maintaining Correct Moisture Maintaining Concrete Temperature
Note: ACI 305 Hot Weather Concreting ACI 306 Cold Weather Concreting
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Post Pour Practices• Sufficient Strength for stripping
• Handle to reduce or eliminate damage
• Perform a post poor inspection
• Mark the casting with all required information
• Store product to prevent damage in storage
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TANK SEAM / JOINT SEAL
• 3/8” maximum gap between two mating joint surfaces BEFORE sealant is applied.
• ASTM C 1227-05 Section 10.3
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PROOF TESTINGASTM C 1227-10a• 9.1 Proof testing is used to demonstrate the strength of the
tank to resist anticipated external and internal loads.
• 9.1.1 Proof testing, when required by the purchaser, shall be performed in such a way as to simulate the actual anticipated loads.
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PROOF TESTING
• Calculate for anticipated actual loads
– Internal and external
– Soil loads, lateral earth loads
– Weight of tank
• Use live load at the surface of 300 lb/ft2 unless heavier loads are anticipated.
• Proof test to 150% of the anticipated actual loads
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Proof Testing - VacuumWith 300 psf Live Load from ASTM C-1227
240 psf
180 psf avg. 180 psf avg.
715 psf
2' Cover
5' 4' x 8 ' Tank
(Earth, Tank W eight, Live Loads)
(Earth W eight)
Assum e soil at 120 lb /ft3
(Assum e 7,000 lbs.)
(Live Loads)300 psf
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Proof Testing - Vacuum
Top Loads • (540 psf) x 150%
= 810 psfFloor Loads• (715 psf) x 150%
= 1,073 psfWall Loads• (180 psf) x 150%
= 270 psf Since the floor load is the highest load force, it can be used for vacuum testing.
1,073 psf = 14.9” Mercury
With 300 psf Live Load from ASTM C-1227
240 psf
180 psf avg. 180 psf avg.
715 psf
2' C over
5' 4' x 8' Tank
(Earth , Tank W e ight, L ive Loads)
(Earth W eig ht)
A ssum e so il a t 120 lb /ft3
(Assum e 7 ,000 lbs.)
(L ive Loads)300 psf
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Alternative Loads
• Typical loads for a septic tank are:
– Soils
– Internal fluids
– External soil / saturated soils
– Weight of tank
– Incidental loads from a vehicle
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Proof Testing - VacuumWith a concentrated wheel load of 2,250 pounds
325 psf
220 psf avg. 220 psf avg.
500 psf
2' Cover
5' 4' x 8' Tank
(Earth + LL + T ank W eig ht)
(Earth + LL W eig h t)
A ssum e so il at 120 lb /ft3
(A ssu m e 7,000 lb s.)
2,250 lb s. wh eel lo ad
L L = 85 lb /ft2
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Proof Testing - Vacuum
Top Loads • (325 psf) x 150%
= 488 psfFloor Loads• (500 psf) x 150%
= 750 psfWall Loads• (220 psf) x 150%
= 330 psf Since the floor load is the highest load force, it can be used for vacuum testing.
750 psf = 10.4” Mercury (Better)
With a concentrated wheel load of 2,250 pounds
325 psf
220 psf avg. 220 psf avg.
500 psf
2' C over
5' 4' x 8' Tank
(Earth + LL + Tank W eight)
(Earth + LL W eight)
Assum e soil at 120 lb/ft3
(Assum e 7,000 lbs.)
2,250 lbs. wheel load
LL = 85 lb/ft2
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Proof Testing - Alternative
• Place tank on a bed of sand (about 3”-4”)
• Vacuum test for the wall loads
– 330 psf or 4.6” of mercury
• Add weight to the top to simulate the additional live and soil loads
– (750 psf) – (330 psf) = 420 lbs/ft2
• Add 1,680 lbs. (4 ft2 x 420 lbs/ft2) on a 2’ x 2’ area in center
• Voluntary proof testing in Ohio - approved by ODH
– 4” mercury + 2,000 lbs. on a 2’ x 2’ area
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Area for Additional Weight
2' x 2' Footprint2’ x 2’ Footprint
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Testing in Action
Vacuum
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Testing in Action
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Watertight Testing
Vacuum Testing
4” of Mercury (Hg), for 5 minutes, must hold 100% to pass certification.
Per ASTM C 1227-10a
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Vacuum Testing
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Watertight Testing: In-Plant
Vacuum Test
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Watertight Testing: In Field
Vacuum Test
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Watertight Testing
• Water Test– Fill the tank
– Let stand for 24 hours
– Refill the tank
– Tank passes if water level does not drop within 1 hour
Sealing a Watertight Septic Tank
http://www.youtube.com/watch?v=MaMb4Epo_2A
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Watertight Testing: In-Plant
Water Test
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Watertight Testing: In Field
Water Test
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Installation• Site and Excavation
– Locate buried utilities
– Safe and free of hazards
• Trees
• Overhead power lines
– Sloped or shored excavation if entry is required
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Installation• Bedding
– Minimum of 4” of sand or granular bedding
– a firm uniform base
– Void of large boulders or rock edges
– Design to resist flotation in high water table
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Installation
• Placement of Tank– Confirm orientation
– Inspect the bedding
– Check level of tank
– Slope should meet local plumbing and building codes
– Use safe lifting devices designed for the load
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Installation• Sealing On-site
– Use a high quality joint sealant
• Should conform to ASTM C 990
• Should be compressible for the temperatures expected
• Molded into one continuous band
– Joint free of loose debris
– Remember to seal risers and lids also
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Installation• Backfilling
– Uniform layers of less than 24” thick
– Free of large stones (>3” in diameter)
Don’t damage the tank!
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Commitment to Excellence
• Adopt a good quality control program
• Have management committed to program
• Have trained QC personnel and production crew
• Design to standard specifications as minimum
• Plan for quality finished products
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