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18TH STREET PEDESTRIAN IMPROVEMENTS 3741 RMT July 03, 2024 71 1 8-26.2(2) Cement Concrete Modular Block (CMB) Unit 2 Cement Concrete Modular Block (CMB) Unit: a concrete retaining wall element 3 machine-made from Portland cement, water, and aggregates. 4 5 CMB Units shall conform to the following architectural requirements: 6 7 1. Face color: concrete gray, unless otherwise specified. 8 2. Face finish: sculptured rock face in straight-face configuration. Other face 9 finishes will not be allowed without written approval of Engineer. 10 3. Bond configuration: running with bonds nominally located at midpoint of 11 vertically adjacent units, in both straight and curved alignments. 12 4. Exposed surfaces of units shall be free of chips, cracks or other 13 imperfections when viewed from a distance of 10 feet (3 m) under diffused 14 lighting. 15 16 CMB unit concrete materials shall conform to the requirements of ASTM C1372-17 Standard Specifications for Segmental Retaining Wall Units. 18 19 CMB units shall conform to the following structural and geometric requirements 20 measured in accordance with ASTM C140 Sampling and Testing Concrete Masonry 21 Units, ASTM D6916 Determining the Shear Strength Between Segmental Concrete 22 Units and ASTM D6638 Determining Connection Strength Between Geosynthetic 23 Reinforcement and Segmental Concrete Units: 24 25 1. Compressive strength: ≥3000 psi (21 MPa) 26 2. Absorption: ≤ 8 % for standard weight aggregates. 27 3. CMB Units: Similar to Keystone Standard 21” units or approved alternate. 28 a. Width: 18" (457 mm). 29 b. Depth: 21" (533 mm), not including rough split face. 30 c. Height: 8" (203 mm). 31 d. Weight: 82 - 114 pounds (37 - 52 kg) per unit minimum using 32 standard weight aggregates 33 34 8-26.2(3) Shear Connectors 35 36 Shear connectors shall be 1/2" (12 mm) diameter thermoset isopthalic polyester resin 37 pultruded fiberglass reinforcement rods to provide connection between vertically and 38 horizontally adjacent units with the following requirements: 39 40 1. Flexural Strength in accordance with ASTM D4476: 128,000 psi (882 41 MPa) minimum; 42 2. Short Beam Shear in accordance with ASTM D4475: 6,400 psi (44 MPa) 43 minimum. 44 45 Shear connectors shall be capable of holding the geogrid soil reinforcement in the 46 proper design position during grid pre-tensioning and backfilling. 47 48 8-26.2(4) Unit Drainage Fill 49 Unit Drainage Fill: drainage aggregate that is placed within and behind the CMB units. 50 Unit drainage fill shall consist of clean 1" (25 mm) minus crushed stone or crushed 51 gravel meeting the following gradation tested in accordance with ASTM D422: 52