1. Specifications: • The work shall consist of furnishing, mixing, applying, and curing shotcrete. Except as otherwise specified, either a dry mix or wet mix process may be used. 2. Material: • Portland Cement shall conform to the requirements of Material Specification 531, Portland Cement, for the specified type. • Aggregates shall conform to the requirements of Material Specification 522, Aggregates for Portland Cement Concrete, unless otherwise specified. Gradation shall be one of the three options specified by ACI 506R, table 2.1, unless otherwise specified. • Admixtures, if specified, shall meet the requirements indicated. Nonchlorine chemical admixtures shall conform to ASTM C 494. Air-entraining admixtures shall conform to ASTM C 260. Fly ash or pozzolanic material shall con form to ASTM C 618. Calcium chloride shall conform to ASTM D 98 and shall be in flake or pelletform. • Water used in mixing or curing shotcrete shall be clean and free from intrusions amounts of oil, salt, acid, alkali, organic matter, or other deleterious substances. • Curing compound shall conform to the requirement of Material Specification 534, Concrete Curing Compound. 3. Strength and Quality: • The compressive strength of shotcrete at the age of 28 days shall be not less than specified in section 19 of this specification. • Shotcrete shall be uniform and dense, free from "drummy" areas that indicate laminations, voids, sand pockets, or disbanded material. 4. Consistency: • The proportion of water added to the mixture shall be accurately controlled to produce thorough and uniform hydration of the shotcrete. The consistency of the shotcrete shall be such that the surface of the shotcrete in place shall have a rich, glossy appearance and that the shotcrete shall adhere to the supporting surface without flowing, slumping, or sloughing. For application to vertical or overhanging surfaces, the mix proportions shall be adjusted so that the placed shotcrete will adhere to a minimum thickness of 0.75 inch without sagging or sloughing. For adjustment of consistency, fly ash or pozzolanic material can be added to the mixture in amounts of no more than 20 percent (by weight) of cement in the mixture