Page - 1511 - in Book of Full Papers - Symposium Hydro Engineering

• Maximum elapsed time from introduction of water to the mix and final compaction is 60 minutes. Lift Joint Conditions: The thickness of the layer shall not exceed 300 mm, and shall be aggressively cleaned before applying bedding mortar and placing next layer. Good lift joint conditions are a vital component of good RCC construction. The underlying goal is to place subsequent RCC lifts before the underlying lift has set, allowing the lifts to bond to each other. Cleaning shall include removal of all loose material, cement paste, fine particles, still and current waters, snow, ice, oil and grease and other detrimental materials. In particular, the surfaces of joints shall be kept free of dust at all times. All horizontal joints shall be prepared for the next lift by removing mortar coating, laitance, or other contaminants by water jet or other approved methods. After this initial preparation, the surface shall be kept damp until receiving the bedding mortar application prior to the next RCC placement. Bedding Mortar: A lift surface is considered a "cold joint" if the surface is damaged by weather or equipment, frozen, Cold joint treatment consists of thorough cleaning of the surface and placement of a layer of bedding mix concrete (bedding mortar) immediately prior to placement of the successive RCC lift. Not more than 15 minutes shall have elapsed after spreading the bedding mortar when RCC is spread on it. Figure 4 shows cleaning of lift Surface and spreading of bedding mortar. Fig. 4 Cleaning of Surface and spreading of bedding mortar (Uma Oya Project) 4.3. COMPACTION AND VERIFICATION Compaction is generally viewed as one of the most important elements in RCC Construction. During construction of the RCC, adequate compaction will have one of the most profound impacts on the quality of the finished RCC dam. In RCC dams, the in-place compaction and water content of the RCC in the lifts are tested using nuclear gauges in accordance with ASTM C1040 and ASTM D1557. The testing shall be performed frequently; Acceptance criteria for in-place density of the RCC require no test less than 98 percent of required compaction. The variation of moisture outside minus 5% and plus 5% of the optimum moisture content shall require aggregate moisture contents testing and control of water contents at the batch plant. Re-compaction of the RCC shall not be allowed 1511