MECHANICALLY-STABILIZED EARTH (MSE)
RETAINING WALL PANELS
Approval to furnish Mechanically-Stabilized Earth (MSE) Retaining Wall Panels shall be on the basis of certification from approved sources (approved plant prior to letting) and shall conform to all applicable specifications and design requirements. Approved producers and fabricators are listed in the Materials Approved Products Listing Enterprise (MAPLE).
Plant approval shall be on the basis of certification, approved quality control plant and a recommendation by the District Materials Engineer responsible for the inspection of the plant.
An up-to-date Quality Control Plan that ensures all materials, mix design(s), workmanship and fabrication methods is required and shall be subject to the approval of the engineer.
All aggregates, cementitious materials, admixtures and reinforcing steel, shall be from approved sources and shall comply with the requirements of the Iowa Department of Transportation Standard Specifications.
· Coarse aggregate shall be Class 3 durability (as defined in Article 4115.04). The use of gravel is subjected to the approval of the Engineer, based on past history of deleterious and stain-producing material found in the aggregate source.
· Air content shall be 6.5% as a target value, with a maximum variation of ± 1.0%. When specified, or authorized, approved admixtures for the purpose of improving workability or for retardation may be used with prior approval of the Engineer.
· Mix design is subject to the approval of the Engineer.
· Reinforcement shall be epoxy coated steel meeting the requirements of Article 4151.03.
· Compressive Strength
Acceptance of the concrete face panels with respect to compressive strength will be determined on a lot basis. The lot will consist of all production units (batches of concrete or panels) produced within a consecutive 7 day production period. Production units will be randomly selected according to the production day sample table and tested for compressive strength. Perform compression tests on the test specimens according to Materials I.M. 315.
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Table: Production day samples
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Production Day Quantities |
Sample Size |
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35 cubic yards or less (50 panels or less) |
1 |
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35-70 cubic yards (50-100 panels) |
2 |
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70-100 cubic yards (100-150 panels) |
3 |
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Over 100 cubic yards (150 panels) |
5 |
· A minimum of six test cylinders shall be cast for each production unit sampled.
· Three test specimens shall be tested at 7 days and three at 28 days.
· A test will be the average compressive strength of three cylinders.
A. Lateral position of the strips within 1.0 inch
B. All dimensions within 1/4 inch
C. Angular distortion with regard to the height of the panel shall not exceed 1/4 inch in 5 feet
D. Surface defects shall not be acceptable if objectionable. However, on smooth-formed surfaces defect shall not exceed 1/8 inch in 5 feet. On textured surfaces defect shall not exceed 5/16 inch in 5 feet.
· As soon as practical (after initial set) after casting, but not later than 30 minutes, panels shall be covered with wet burlap and kept wet. Within two hours of the initial covering, water shall be applied to the burlap by means of a continuous pressure-sprinkling system that is effective in keeping the burlap wet during the initial curing period. The initial curing period shall continue until the minimum moving strength is obtained.
· After the initial curing period is completed, panels may be moved from casting beds to a secondary curing area and covered with wet burlap and polyethylene (plastic) 3.0 mil (60 µm) thick, properly secured to retain moisture.
· Concrete face panels shall not be left uncovered longer than 20 minutes during the moving process.
· Curing shall continue until the specified strength is obtained.
· Steam curing may be used and shall be subject for prior approval by the engineer.
· Forms shall remain in place until the moving strength is obtained – 1800 psi.
· Panels shall be acceptable for shipping or for placement when 28-day strengths have been obtained.
1. Failure to meet any of the specified requirements
2. Defects that indicate imperfect molding
3. Defects that indicate honeycomb or open texture concrete
4. Surface defects that exceed 5/16 inch in 5 feet.
5. Chipping, cracking or fractures
· Units shall be handled with care, lifting shall be with padded straps or padded contact areas and shall be stored above ground on wooden or padded supports.
· Support shall be adequate, firm, and shall be placed evenly to prevent sagging.
· Handling shall be minimized.
· Handling, storage and shipping shall be in a manner as to prevent and/or eliminate the causes of cracking, fracturing, damaging and excessive bending stresses.
Leveling pad shall be concrete and shall have a nominal strength of 3500 psi.
REINFORCING & TIE STRIPS
· Tie strips shall be fabricated from hot-rolled steel conforming to the requirements of ASTM A570, Grade 50 or equivalent.
· Galvanization shall conform to the requirements of ASTM A123.
· Tie strips, reinforcing strips and connectors shall be galvanized by an approved galvanizer listed in IM 410.01 Appendix A.
· Reinforcing strips shall be galvanized and shall be made of hot-rolled steel bars meeting the requirements of ASTM A572, Grade 65 and made into the required shape and dimensions. Strips shall be cut to lengths and tolerances as shown on the plans or shop drawings.
· Only plastic supports for reinforcing steel shall be accepted based on approved brands as noted in IM 451.01, Appendix A.
· All reinforcing including tie strips and reinforcing strips and all other steel and iron products and coatings shall meet the requirements of IM 107.
The producer of precast units shall furnish, on each shipment day, a certified bill of materials or invoice which identifies the county, project number, contractor, and number of pieces of each class, size, and length and the plant the precast unit was fabricated. The certification of compliance shall be signed by a designated, responsible company representative and shall be stated as follows:
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"The materials itemized in this shipment are certified to be in compliance with the applicable AASHTO and/or ASTM requirements and Iowa Department of Transportation Standard Plans and Specifications, IMs and meet the Buy America requirements as described in IM 107 for all steel, iron products and coatings." |
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Authorized Signature & Date |
One copy of the above-described document shall be forwarded to the Project Engineer on the day the item is delivered to the project. In addition, one copy shall be sent to the District Materials Engineer
The fabricator shall also provide summary quantity documentation, as shown in Appendix B of IM 445 to the District Materials Office responsible for the project and the project engineer at the completion of the shipments to the project. A designated representative shall sign the certification statement on the summary documentation.