Effective March 24, 2004
Beginning March 24, 2004, construction of confinement operations with a one-time capacity of more than 500 animal units (1,250 hogs weighing more than 55 pounds or 5,000 pigs weighing between 15 and 55 pounds) must meet new minimum concrete standards.
If a DNR construction permit is not required; a structure constructed (defined in Iowa law as excavation for the structure) before March 24, 2004 will be subject to the old concrete rules and a structure constructed on or after March 24 will be subject to the new concrete rules.
If a construction permit is required but has not been issued before March 24, a structure constructed pursuant to the permit on or after March 24 will be subject to the new concrete rules.
If a construction permit is issued before March 24, but no construction on the site has occurred before March 24; a structure constructed on or after March 24 will be subject to the new concrete rules.
If a construction permit is issued before March 24, and one or more structures is constructed on the site pursuant to the permit before March 24; a structure constructed after March 24 pursuant to the issued permit will be subject to the old concrete rules.
The new rules provide two options for liquid manure storage:
The design may be certified by an NRCS or professional engineer (an engineer is required for animal capacities of more than 7,500 finishing pigs, 30,000 nursery pigs, 3,125 sows farrow to wean, and 6,875 sows farrow to finish) meeting specifications in American Concrete Institute 318, 360 or 350; Portland Cement Association EB075, EB001, or ISO72; or Midwest Plan Service 36 or TR-9; and the following standards:
Floors must be 5 inches thick. DNR may require only nondestructive methods to verify floor thickness. These results must show at least 95% of the floor is 5 inches thick with no portion being less than 4 1/2 inches thick.
No wire mesh as primary reinforcement in floors of pits deeper than 4 feet. Wire mesh is allowed as primary reinforcement in the floors of pits less than 4 feet deep. Fiber is not allowed as the primary reinforcement in any pit floor.
If the structure’s is not designed and certified by a professional engineer, the design must meet Midwest Plan Service specifications or specifications in tables in the new rules and the following standards:
- Compacted subgrade to provide a uniform (similar soils) and level base.
- Be constructed above the groundwater table or have a perimeter tile line installed within 3 feet of the footings and covered with at 2 inches of gravel, granular material, or fabric.
- Meet compressive strength standard ASTM C-94 and minimum as-placed psi (pounds per square inch) of 4,000 psi for walls, floors, beams, columns, and pumpouts; and 3,000 psi for footings.
- Cement must be Portland cement meeting ASTM C-150. Blended cements meeting ASTM C-595 are allowed only between March 15 and October 15. Blast furnace slag blended cements must contain 75% Portland cement. Aggregates must meet ASTM C-33.
- Concrete in walls must be consolidated or vibrated in accordance with ACI-309.
- Rebar must be at least 40 grade steel. All rebar must be tied in place before concrete is placed, with the exception of rebar dowels connecting the walls to the footings.
- Wall rebar in below ground storage must have a 2 inch cover from the inside face. Vertical wall rebar should be placed closest to the inside face. Wall rebar placement must meet ACI-318.
- Floors must be 5 inches thick. DNR may require only nondestructive methods to verify floor thickness. These results must show at least 95% of the floor is 5 inches thick with no portion being less than 4 1/2 inches thick. Floors of pits deeper than 4 feet must have primary reinforcement of #4 rebar on 18 inch centers. Floors of pits less than 4 feet deep shall have 6×6-W1.4xW1.4 welded wire fabric for shrinkage reinforcement. All floor slab reinforcement must be placed in the middle of the thickness of the slab.
- Footings must be as thick as the walls but no less than 8 inches thick, and have a width at least twice the thickness of the footing.
- Vertical rebar in walls must be extended into the footings and bent at 90, or a separate dowel installed at least 12 inches into the footing.
- Walls must be placed with forms ñ they cannot be earth-formed.
- Concrete must be cured for at least 7 days meeting ACI-308 by maintaining adequate moisture or preventing evaporation. Curing must be done by ponding , spraying, or fogging water; a curing compound meeting ASTM C-309; or using wet burlap, plastic sheets or similar materials.
- All construction joints in exterior walls must prevent discontinuity of steel and have properly spliced rebar through the joint. Waterstops installed where fresh and hardened concrete meet.
- Backfilling must be free of vegetation, large rocks and debris and cannot start until the slatted floors or permanent bracing has been installed.
- A structure more than 12 feet deep must be designed by a professional engineer.
Dry manure storage, which includes confinement hoop buildings, must meet one of the following two options:
1. The design may be certified by an NRCS or professional engineer (see #1 above for when an engineer is required) meeting specifications in American Concrete Institute 318 or 360; Portland Cement Association EB075, EB001, or ISO72; or Midwest Plan Service 36.
|Above ground:||meet requirements in (1), (3), (4), (5), (6), (8), (12) above.|
|Partially or completely
|meet requirements (1) through (15) above and MWPS-36 or requirements in tables in the rules.|
2. Concrete manure storage structures located in Karst terrain or in an area that drains to a known sinkhole must meet additional requirements as set out in the rules.