Environmental Impact Assessment and Mitigation for Dam Construction Projects

 

1. General Description and Scope
   High-performance concrete (HPC) mixes for bridge decks shall be produced to achieve enhanced durability, strength, and resistance to environmental exposures including freeze–thaw cycles, deicing chemicals, and water penetration. The work includes batching, mixing, transporting, placing, finishing, and curing HPC in bridge deck applications. The concrete mix shall be designed to achieve a minimum compressive strength of 60 MPa at 28 days, with low permeability and improved bond characteristics for long-term performance. All operations shall comply with relevant standards such as ASTM C150, ASTM C33, ASTM C39, ASTM C1202, ACI 318, and ACI 363R, or their applicable regional equivalents.

2. Material Specifications
   • Cement: The binder shall consist of Type I Portland cement conforming to ASTM C150 (or IS 8112, if applicable). Where beneficial, supplementary cementitious materials such as silica fume or fly ash may be incorporated in proportions recommended by the mix design to enhance strength and durability.
   • Fine Aggregates: Natural sand shall be clean, well-graded, and free from impurities, in accordance with ASTM C33 or IS 383. The sand shall possess a fineness modulus within the prescribed range to ensure proper workability and bond in the HPC mix.
   • Coarse Aggregates: Crushed stone or gravel shall be used as the coarse aggregate. The aggregate shall be durable, angular, and well-graded per ASTM C33 or IS 383. Maximum size of the coarse aggregate shall be limited to ensure proper compaction and surface finish of the bridge deck.
   • Admixtures: Chemical admixtures, including high-range water reducers (superplasticizers) conforming to ASTM C494 and air-entraining agents (if required), shall be used to achieve the target workability, low water-cement ratio (typically less than 0.35), and to promote a dense, impermeable microstructure.

3. Mix Design Requirements for Bridge Deck Durability
   The HPC mix design shall be developed to meet the following criteria:
   • Compressive Strength: A minimum 28-day compressive strength of 60 MPa shall be achieved.
   • Workability: The mix shall attain a slump of 75–125 mm to facilitate placement and proper consolidation on bridge decks.
   • Water-Cement Ratio: The water-cementitious materials ratio shall not exceed 0.35 to promote high strength and low permeability.
   • Air Content: If air entrainment is incorporated, the air content shall be maintained within 4–6% to balance workability and durability, particularly for freeze–thaw resistance.
   • Durability Enhancements: The inclusion of silica fume at 5–10% by weight of cement (as applicable) shall be considered to refine the pore structure, reduce permeability, and improve resistance to chloride ingress and sulfate attack.

4. Testing Procedures
   Quality control of the HPC mix shall be maintained through systematic testing as follows:
   • Compressive Strength Testing: Cylindrical specimens shall be tested in accordance with ASTM C39 at 7, 28, and 56 days to verify compliance with strength requirements.
   • Permeability Testing: Rapid chloride permeability tests (ASTM C1202) shall be performed to assess the electrical charge passed through the concrete, with limits established to ensure low permeability suitable for bridge deck exposures.
   • Slump and Workability Tests: Workability shall be verified using the slump test in accordance with ASTM C143.
   • Durability Tests: Additional tests, such as freeze–thaw resistance (ASTM C666) and rapid chloride penetration tests, shall be conducted as specified by the Engineer to confirm long-term performance characteristics.

5. Quality Control and Assurance
   • Batch Verification: Each batch of HPC produced shall be sampled and tested for compliance with the specified mix design and performance criteria. Records of batching, material properties, mix proportions, and test results shall be maintained for review.
   • Field Inspections: Regular inspections during placement shall be conducted to verify proper consolidation, finish, and curing practices.
   • Documentation: All test reports, quality control records, and inspection findings shall be submitted to the Engineer for approval and archived as part of the project documentation.
   • Corrective Actions: In the event of non-conformance, corrective measures shall be implemented immediately, and affected batches shall be re-tested before further use.

Sources: ASTM C150, ASTM C33, ASTM C39, ASTM C1202, ACI 318, ACI 363R