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Fabricating a Watertight Precast Concrete Septic Tank

Fabricating a Watertight Precast Concrete Septic Tank

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Fabricating a Watertight Precast Concrete Septic Tank

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  1. Fabricating a Watertight PrecastConcrete Septic Tank Dan Wagner – Milan Vault, Inc.

  2. SEPTIC TANK QUALITIES What qualities do we want in a septic tank? BENEFIT COST

  3. DEPENDABLE

  4. ECONOMICAL

  5. Barney buys a concrete septic tank http://www.youtube.com/watch?v=kW3JkVaAZEc&feature=related

  6. Components of Watertightness • Engineering and Design • Manufacturing • Quality Assurance and Testing • Installation

  7. Design Considerations • The septic tank must: • Withstand all loading conditions • Surface Surcharge • Concentrated wheel loads • Lateral Loads • Soil Bearing Capacity

  8. NO TRAFFIC / NO LOADS

  9. ASTM C 1227 LOADS

  10. LIGHT TRUCK TRAFFIC

  11. The septic tank must not be buoyant; it must not float Design Considerations

  12. 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

  13. Manufacturing and Installation

  14. 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

  15. The Manufacturing Process Raw Materials Mix Design Reinforcement Production Practices (Seals, Fittings, and Joints) Post-Pour Operations

  16. Raw Materials • Use quality, certified materials • Aggregates • Cement • Water • Admixtures

  17. 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

  18. WATER STRENGTH POROSITY

  19. 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

  20. Air Content • Entrained Air = Desirable • Improves freeze/thaw resistance, ASR resistance, sulfate resistance • Improves workability • Entrapped Air = Non-desirable • Bugholes • Released through adequate vibration

  21. 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

  22. Non-reinforced Concrete Behavior

  23. Reinforced Concrete Behavior

  24. 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

  25. Visible problems REBAR SHOWING

  26. Rebar Touching Form

  27. What it should look like

  28. 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)

  29. 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

  30. Curing • Proper 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

  31. 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

  32. TANK SEAM / JOINT SEAL • 3/8” maximum gap between two mating joint surfaces BEFORE sealant is applied. • ASTM C 1227-05 Section 10.3

  33. PROOF TESTING • ASTM 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.

  34. 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

  35. Proof Testing - Vacuum With 300 psf Live Load from ASTM C-1227

  36. Proof Testing - Vacuum With 300 psf Live Load from ASTM C-1227 • Top Loads • (540 psf) x 150% = 810 psf • Floor Loads • (715 psf) x 150% = 1,073 psf • Wall 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