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

SEPTIC TANK QUALITIES What qualities do we want in a septic tank? 2 A variety of loading conditions: manufacture, transportation and installation, testing, service (full or empty) SEPTIC TANK QUALITIES What qualities do we want in a septic tank? BENEFIT COST

DEPENDABLE

ECONOMICAL

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

Components of Watertightness 8 Components of Watertightness Engineering and Design Manufacturing Quality Assurance and Testing Installation

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

NO TRAFFIC / NO LOADS

ASTM C 1227 LOADS

LIGHT TRUCK TRAFFIC

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

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

Manufacturing and Installation

NPCA Design Recommendations Concrete thickness must be sufficient to meet minimum reinforcement cover requirements and withstand loading conditions w/c < 0.45 reduce permeability, improve durability, increase strength 1616 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

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

Raw Materials Use quality, certified materials Aggregates Cement Water Admixtures

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

WATER STRENGTH POROSITY

2323

2424

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

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

Purpose of Reinforcement 3030 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

Non-reinforced Concrete Behavior

Reinforced Concrete Behavior

Reinforcement Requirements 3333 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

Visible problems REBAR SHOWING

Rebar Touching Form

What it should look like

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)

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

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

Post Pour Practices Sufficient Strength for stripping 4343 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

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

4747 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.

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

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

Proof Testing - Vacuum Top Loads Floor Loads Wall Loads 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

Alternative Loads Typical loads for a septic tank are: Soils Internal fluids External soil / saturated soils Weight of tank Incidental loads from a vehicle

With a concentrated wheel load of 2,250 pounds Proof Testing - Vacuum With a concentrated wheel load of 2,250 pounds

With a concentrated wheel load of 2,250 pounds Proof Testing - Vacuum With a concentrated wheel load of 2,250 pounds Top Loads (325 psf) x 150% = 488 psf Floor Loads (500 psf) x 150% = 750 psf Wall 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)

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

Area for Additional Weight 2’ x 2’ Footprint

Testing in Action Vacuum

Testing in Action

Watertight Testing Vacuum Testing 4” of Mercury (Hg), for 5 minutes, must hold 100% to pass certification. Per ASTM C 1227-10a

Vacuum Testing

Watertight Testing: In-Plant Vacuum Test

Watertight Testing: In Field Vacuum Test

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

Watertight Testing: In-Plant Water Test

Watertight Testing: In Field Water Test

Installation Site and Excavation Locate buried utilities 6565 Installation Site and Excavation Locate buried utilities Safe and free of hazards Trees Overhead power lines Sloped or shored excavation if entry is required

Installation Bedding Minimum of 4” of sand or granular bedding 6666 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

Installation Placement of Tank Confirm orientation Inspect the bedding 6767 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

Installation Sealing On-site Use a high quality joint sealant 6969 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

Installation Backfilling Uniform layers of less than 24” thick 7070 Installation Backfilling Uniform layers of less than 24” thick Free of large stones (>3” in diameter) Don’t damage the tank!

Commitment to Excellence 7171 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