Sample Guide Specifications for Construction of Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS)
SECTION 2. MATERIAL REQUIREMENTS
2.1. CMU FACING ELEMENT
2.1.1. Physical Requirements
- Furnish-facing elements consisting of split-face CMU should meet ASTM C90-11b requirements, with a minimum required compressive strength of 4,000 psi and a maximum water absorption rate of 5 percent after 24 h.(3)
- In areas where repeated freezing and thawing occur, CMU block units shall be tested for freeze-thaw durability in accordance with ASTM C1262-10.(4)
- Specimens used for absorption testing shall not subsequently be used for freeze-thaw testing.
- CMU blocks shall be furnished within the following tolerances:
- The height of each individual block shall be within 1/16 inches of the specified dimension.
- The length and width of each individual block shall be within 1/8 inches of the
specified dimension.
- Hollow CMU units shall have a minimum face shell thickness of 1.25 inches and a web thickness of 3/4 inches.
- The CMU units shall be randomly sampled and tested in accordance with ASTM C140-12.(5) Contractor QC testing shall be conducted at a qualified agency or AASHTO accredited laboratory as described in section 4.4 of this guide.
- Agency acceptance testing of the CMU blocks will be performed on a lot basis.
2.2. BACKFILL MATERIAL
Furnish sound, crushed durable particles, fragments of stone gravel free from organic matter or other deleterious material for the abutment, reinforced soil foundations (RSFs), and integrated approach conform to the following:
2.2.1. Abutment Backfill
Backfill material shall meet the following requirements:
- Quality requirements.
- Gradation (see table 1).
- Angle of internal friction with a minimum of 38 degrees.
- Plasticity Index (PI) with a maximum of 6 (AASHTO T 89-10 and
AASHTO T 90-00).(6, 7)
Table 1. GRS abutment backfill gradation requirements.
Description |
Value |
Well-Graded Material |
Open-Graded Material |
Maximum grain size (inches) |
0.5–2 |
0.5–2 |
Percent passing the No. 200 sieve (percent) (AASHTO T 11-05)(8) |
≤12 |
≤5 |
- Soundness.
- The backfill material shall be substantially free of shale or any other poor durability particles.
- The backfill material shall have a magnesium sulfate loss of less than 30 percent after four cycles or a sodium sulfate soundness loss of less than 15 percent after five cycles (AASHTO T 104-99).(9)
- Well-graded aggregates and open-graded aggregates shall be used as respectively defined in sections 3.3.1.1 and 3.3.1.2 of FHWA-HRT-11-026.(1)
- Open-graded aggregates shall be used if the abutment will be submerged at any point.
2.2.2. RSF Backfill
The backfill for the RSF shall be well-graded material as described in section 2.2.1 of this guide.
2.2.3. Integrated Approach Backfill
Well-graded backfill material shall be furnished as described in section 2.2.1 of this guide for the integrated approach.
2.3. GEOSYNTHETICS
- Geosynthetics consisting of geogrid or geotextile for the GRS abutment should be furnished. Furnish geotextile for the RSF and integrated approach.
- Geosynthetics material may be manufactured from polypropylene, high-density polyethylene, or polyester.
- Geosynthetics can be either uniaxial or biaxial. When a uniaxial type is used, higher-strength axis must be placed perpendicular to the wall face.
- Geosynthetics composed of a minimum ultimate tensile strength of 4,800 lb/ft according to ASTM D 4595-11 for geotextile or ASTM D 6637-11 for geogrid should be furnished.(10, 11) The design requirements may call for a geosynthetic with higher strength.
- Geosynthetic reinforcement strength at 2 percent strain shall be greater than the unfactored required reinforcement strength.
- The geosynthetic shall be evaluated in accordance with XXX Department of Transportation standard procedures (refer to section 3.4 of FHWA-HRT-11-026).(1)
2.4. MISCELLANEOUS MATERIALS
- Concrete block wall fill—Furnish AASHTO class A concrete with a minimum compressive strength of 4,000 psi.(12) Furnishing, placing, finishing, and curing of concrete shall be done according to XXX Department of Transportation specifications.
- Flashing—Flashing, such as 4-inch by 1.5-inch aluminum fascia or equivalent, may be used to serve as a drip edge under the superstructure within the clear space to shed potentially corrosive fluids off of the dry cast block and to prevent animals from burrowing into the abutment.
- Foam board—A durable foam board, such as expanded polystyrene filler or equivalent, having a compressive strength greater than or equal to 10 psi may be used to provide a setback and create a bearing buffer between the superstructure and the wall face.
- Reinforcing steel bar—Deformed #4 (0.5-inch diameter) bars that conform to AASHTO M31M/M31-10 or ASTM A615/A615M-12 shall be furnished.(13, 14) The bars shall be epoxy coated conforming to AASHTO M 284M/M 284-09.(15)
- Asphaltic coating—An asphaltic coating shall be shop installed on the concrete beam when embedded between the GRS abutment and the wing wall to seal the embedded concrete.