STRUCTURAL CONCRETE
PART 1 - GENERAL
1.01 SECTION INCLUDES
Structural concrete and reinforcing for cast-in-place manholes and intakes for sanitary and storm sewer systems, and other structures such as concrete thrust blocks and sewage air release pits as designated by the Jurisdictional Engineer.
1.02 DESCRIPTION OF WORK
A. Construct concrete structures for sanitary and storm sewers.
B. Reference is made to the Iowa Department of Transportation Standard Specifications for Highway and Bridge Construction, Series 2001, and all current General Supplemental Specifications and Materials Instructional Memorandum by the term "Iowa DOT Specifications" and/or "Iowa DOT I.M.".
1.03 SUBMITTALS
A. Submit under provisions of Division 1.
B. Shop drawings of steel reinforcement, showing sizes, lengths, bends, and counts, if required.
C. Concrete mix design, if required by Jurisdictional Engineer.
D. Sample test results and certifications.
E. Certification that materials being provided meet the requirements of these specifications or that alternate materials or substitutions have received written approval of the Jurisdictional Engineer.
F. Project record documents.
G. Upon requests, the Contractor will provide Material Certifications to the Jurisdictional Engineer.
1.04 SUBSTITUTIONS
A. Use only materials conforming to these specifications unless
permittedotherwise allowed by Jurisdictional Engineer.B. Obtain written approval of Jurisdictional Engineer for all substitutions prior to use.
1.05 DELIVERY, STORAGE, AND HANDLING
A. Deliver only materials that fully conform to these specifications and for which submittals have been provided to Jurisdictional Engineer and approved for use.
B. Store and handle materials to avoid damage. Store reinforcing steel only on pallets or lagging. Replace any damaged materials. Remove damaged materials from the site.
C. Follow the aggregate storage and concrete transport requirements in Section 7010, 1.05.
1.06 SCHEDULING
A. Construction Sequence:
Schedule concrete placement to coordinate with other work, such that trenching, backfilling, and other work can proceed in an orderly manner, and to provide the greatest protection for new work.
B. Conflict Avoidance:
1. Expose potential conflicts such as utility lines and drainage structures in advance of construction. Verify elevations and locations and verify clearance for proposed construction.
2. Complete elements of work that can affect line and grade in advance of pipe construction unless noted on the plans.
3. Notify Jurisdictional Engineer of conflicts discovered or changes needed to accommodate unknown conditions.
1.07 SPECIAL REQUIREMENTS
A. Stop Work: Stop work and notify Jurisdictional Engineer immediately if contaminated soils, historical artifacts, or other environmental or historic items are encountered.
B. Conform to local, state, and federal requirements.
C. Restrictions: Restriction on operations shall follow Section 7010, 1.07.
1.08 MEASUREMENT FOR PAYMENT
The cost for concrete and reinforcing in concrete structures and testing, as specified in Section 6010, 3.09, is incidental.
PART 2 - PRODUCTS
2.01 CONCRETE MATERIALS
A. Portland Cement:
1. ASTM C 150, Type I or Type III when specified.
2. Air entrained per ASTM C 260.
3. Iowa DOT Class C concrete, unless otherwise specified in the contract documents.
B. Aggregates:
1. Per ASTM C 33.
2. Follow Section 7010, 2.02 for coarse and fine aggregates.
C. Water: Follow Section 7010, 2.02.
D. Liquid Admixtures for Portland Cement Concrete (PCC):
1. Description:
a. Meet requirements of AASHTO M 154 for air entraining mixtures.
b. Meet requirements of AASHTO M 194 for other liquid admixtures.
c. Submit tests by a recognized laboratory for Jurisdictional Engineer approval.
d. Do not use admixtures containing more than 1% chloride ions, unless approved by Jurisdictional Engineer.
e. Inspection and acceptance of liquid admixtures will be according to Iowa DOT Materials I.M. 403.2. Air Entraining Admixtures: Stir, agitate, or circulate air-entraining admixtures prior to use to ensure a uniform and homogeneous mixture.
3. Retarding and Water Reducing Admixtures:
a. Ensure compatibility with air entraining agent.
b. Introduce into the mixer after all other ingredients:
c. Agitate prior to and during use according to Iowa DOT Materials I.M. 403.
d. Apply dosage reate to both cement and fly ash when used.4. Other Admixtures: Other admixtures may be used with the approval of the Jurisdictional Engineer according to the manufacturer's recommendations.
2.02 CONCRETE QUALITY
A. Compressive Strength: Minimum 4,000 psi at 28 days.
B. Water-Cement Ratio: Follow Section 7010, 2.03.
C. Air Content: The intended air entrainment is 6.0%. To allow for loss during placement, the air content of fresh, unvibrated structural concrete is 6.5%, as a target value, with a maximum variation of ± 1.0%.
D. Slump: Place structural concrete with a slump between 1 inch and 3 inches as a target range, allowing a maximum of 4 inches unless specifically modified by the Jurisdictional Engineer.
E. Admixtures: Per manufacturer’s recommendations.
2.03 REINFORCEMENT
A. Reinforcing Steel:
1. Use deformed bars.
2. Epoxy coated deformed bars apply only when specified.
3. Billet steel: ASTM A 615, Grade 60.
4. Fabricate and bend, per approved submittals or plans.
5. Fabricate all bars prior to delivery to site unless field bends are required.
B. Wire Fabric:
1. Per ASTM A 185.
2. Size and Mesh: As shown on the figures or on the p>lans.
3. Placement: As shown on the figures or on the plans.
4. Joints: Lap no less than 6 inches, or as specified.
2.04 CEMENT MORTAR: Mix in the following portions:
A. Portland Cement: Type I: 10 Parts
B. Mortar Sand: 20 Parts
C. Lime, Hydrated: 3/4 to 1 Part
PART 3 - EXECUTION
3.01 FORMING
A. Form all cast-in-place manholes and structures on both the inside and the outside face above the base. Do not use earth excavation next to the proposed manhole as forming.
B. Use metal or plywood-lined forms for exposed surfaces.
C. Erect and secure forms to true line and grade.
D. Coat forms with non-staining mineral oil before placing reinforcing. Do not apply oil to surfaces to which concrete must be bonded.
E. Use 3/4 inch bevel for exposed corners, unless otherwise required.
3.02 REINFORCING STEEL
A. Remove dirt, scale, and other materials that might impair the concrete bond.
B. Place reinforcement where shown. Space bars properly and secure in position.
C. Support reinforcement for slabs with chairs or bolsters. Do not use wood, bricks, stones, or other foreign materials.
D. Lap bars 36 diameters, except as otherwise shown.
3.03 MIXING (IOWA DOT 2403)
A. Provide accurate control for measuring materials.
B. Mix concrete to a uniform composition and consistency upon discharge. Thoroughly discharge each batch of concrete from the mixer before the next batch is introduced. Upon cessation of mixing for any considerable length of time, thoroughly clean the mixer and flush with water.
C. When using ready-mixed concrete, conform to ASTM C 94.
3.04 PLACING
A. Clean and dampen forms, reinforcing steel, and embedded items.
B. Prevent segregation during placement. Do not allow concrete to fall more than 4 feet from the placement chute to the final position.
C. Place concrete continuously in each section until complete. Do not allow more than 30 minutes between depositing adjacent layers of concrete within each section.
D. Thoroughly compact, puddle, and vibrate concrete into corners and around reinforcing and embedded items. Vibrate sufficiently to work concrete into crevices and around steel. Refer to Comply with Iowa DOT 2403.09.
E. Do not place concrete when the air temperature is less than 40ºF without the approval of the Jurisdictional Engineer. Iowa DOT 2403.11.
3.05 FINISHING
A. Comply with Iowa DOT 2403.21.
B. Use a smooth form finish for exposed surfaces.
C. Use broomed finish for slabs, except as noted on the plans.
3.06 STRIPPING AND CLEANING
A. Remove forms for manhole and intake walls and tops according to Iowa DOT 2403.18.
1. References to culverts include all sanitary and storm structures.2. When allowed by the Jurisdictional Engineer, compressive strengths as six times the stated flexural strengths may be used in determining concrete strength of structure roofs.
B. Chip out and repair any honeycomb areas per direction of the Jurisdictional Engineer.
C. Break back form ties and fill holes with portland cement mortar.
D. Remove flashing and thin webs.
3.07 CURING
A. Comply with Iowa DOT 2403.10.
B. Apply curing system immediately after finishing or stripping of forms, as applicable.
C. For slabs on grade, visible to the public, use only curing compounds meeting ASTM C 309, Type 1-D or Type 2.
3.08 Exterior Loading
A. Restrict loads on concrete, other than the load caused by the weight of the concrete itself, according to Iowa DOT Section 2403.19.
B. When allowed by the Jurisdictional Engineer, compressive strengths at six times the stated flexural strengths may be used.
3.09 TESTING
A. General:1. Provide required testing by a testing service approved by the Jurisdictional Engineer, unless such services are provided by the Jurisdiction.
2. Review and test proposed mix design when required by the Jurisdictional Engineer.
3. Obtain production samples of the job‑delivered concrete mix after any needed water has been added and the concrete has been remixed.
B. Strength Testing: Unless otherwise specified in the contract documents, strength testing will be the responsibility of the Contractor by a certified testing service.
1. Make at least one strength test for each 100 cubic yards or fraction thereof, and at least one test for each structure. Mold and cure three specimens per ASTM C 31 for each strength test. When the total quantity is less than 50 cubic yards, the strength tests may be waived by the Jurisdictional Engineer.
2. Test specimens according to ASTM C 39. Test one specimen at 7 days. Test two specimens at 28 days. Average the compressive strength of the two specimens tested at 28 days. If one of the 28-day specimens manifests evidence of improper sampling, molding, or testing, discard and use the strength of the remaining specimen as the test result.
C. Slump Testing: Unless otherwise specified in the contract documents, testing will be conducted by the Jurisdictional Engineer. Determine the slump of the concrete sample for each strength test and whenever consistency of concrete mix appears to vary, using ASTM C 143.
D. Air Testing: Unless otherwise specified in the contract documents, testing will be conducted by the Jurisdictional Engineer. Determine the air content of the concrete sample for each strength test according to ASTM C 231, ASTM C 173, or ASTM C 138.
END OF SECTION