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SECTION 20 <br /> <br />CONCRETE STRUCTURES <br /> <br />20-01 <br /> <br />20-02 <br /> <br />General; Concrete structures including manholes, inlet aprons, cut-off <br />wall and lateral pipe entries shall conform to the Standard Drawings of <br />the Alameda County Flood Control and Water Conservation District and to <br />the applicable provisions of Section 51 of the Standard Specifications <br />with the modifications and additions contained in this section. <br /> <br />Materials: <br /> <br />Concrete: All concrete structures shall be constructed of Class A <br />concrete with 3/4 inch maximum aggregate as specified in Section <br />90 of Standard Specifications. Admixtures may be used only when <br />approved by the Engineer. <br /> <br />Motar: Mortar shall conform to the applicable provisions of <br />Section 65-1.06A of the Standard Specifications. <br /> <br />Reinforcement: Reinforcement shall conform to the applicable <br />provisions of Section 52 of the Standard Specifications with the <br />following modifications: <br /> <br />1. Reinforcing steel shall be intermediate grade Billet-Steel <br /> Bars only. <br /> <br />2. All bends in reinforcing steel shall be cold bends. <br /> <br />Where concrete is deposited directly against earth the minimum <br />clear distance between the reinforcing steel and the earth <br />shall be three inches (3"). <br /> <br />Manhole Frames and Covers: Manhole frames and covers shall be <br />Gray-Iron Castings conforming to the requirements of ASTM <br />Designation A 48, Class 40, and shall be match marked in pairs <br />with each cover ground or otherwise finished so that it will fit <br />in its frame without rocking. Before leaving the foundry the <br />castings shall be cleaned and coated with asphalt to form a tough <br />non-scaling coating. <br /> <br />Grates: Grates shall be fabricated of structural steel conforming <br />to the requirements of ASTM Designation, A7 and shall be hot- <br />dipped galvanized after fabrication. Grates shall be assembled <br />and made to fit before delivery to the job site. <br /> <br />Crushed Rock or Gravel: Crushed rock or gravel, where used as <br />bedding, shall be uniformly graded with 100% passing a 1-1/2" <br />sieve and not more than 10% passing a No. 8 sieve and shall be <br />hard, sound, and durable and shall not slake or disintegrate in <br />water. <br /> <br />CDS.1.16 20-1 <br /> <br /> <br />