479 SECTION 623 PNEUMATICALLY APPLIED MORTAR OR CONCRETE (SHOTCRETE)
623.1 -DESCRIPTION : This work shall consist of repair of concrete structures, protection of structural steel, or any other type of work as may be designated on the Plans by applying one or more layers of concrete conveyed through a hose pneumatically projected at a high velocity against a prepared surface in conformity with the dimensions and design shown on the Plans. It shall include removal of all loose, soft, honeycombed, and disintegrated concre te, the preparation of the surface, the furnishing and placing of reinforcing steel including wire fabric, dowels, and any other steel items noted on the Plans, and the mixing and applying of shotcrete as outlined in this sub -section.
623.1.1 -Definiti ons: Dry-mix shotcrete -Shotcrete in which the mixing water is added to concrete materials at the nozzle. Nozzleman -Craftsman on shotcrete crew who manipulates the nozzle, controls consistency with the dry process, and controls final deposition of the m aterial. Shotcrete -This is mortar or concrete conveyed through a hose and pneumatically projected at high velocity onto a surface. Wet-mix shotcrete -Shotcrete in which all the ingredients, including water, are mixed before introduction into the deliver y hose; compressed air accelerates to the material flow at the nozzle.
623.2 -MATERIALS : Materials shall meet the requirements specified in the following Sections, Subsections, o r Standards and other requirements as noted below:
MATERIAL SUBSECTION OR STANDARD Accelerating Admixtures 707.13 Air-Entraining Admixtures 707.1 Coarse Aggregate 703.1, 703.2 Curing Materials 7076. -707.10 Fibers* ASTM C1116 Fine Aggregate 702.1 Portland Cement 701.1, 701.3 Supplementary Cementitious Materials** 707.4 Reinforcing Steel 709.1, 709.3, 709.4 Water 715.7 Water Reducing Admixtures 707.3 Water Reducing, Accelerating Admixtures 707.14 Water Reducing, Retarding Admixtures 707.2 * ASTM C1116, Type II or III. Provide a minimum dosage of 1.5 pounds per cubic yard. Use fibers that are a minimum of ½ -inch length, monofilament or collated -fibrillated microfibers. ** The use of a supplementary cementitious materials will not be permitted when a blended hydraulic cement is used.
480 The aggregate gradation shall comply with the requirements of Table 623.2.
TABLE 623.2 Sieve Size Allowable Percent by Mass Passing Each Individual Sieve in Mix Design Note 1 ½ inch (12.5 mm) 100 ⅜ inch (9.5 mm) 90-100 No. 4 (4.75 mm) 70-85 No. 8 (2.36 mm) 50-70 No. 16 (1.18 mm) 35-55 No. 30 (600 µm) 20-35 No. 50 (300 µm) 8-20 No. 100 (150 µm) 2-10
Note 1 The maximum and minimum ranges of the allowable % by mass passing on each sieve size noted in Table 623.2 shall not be exceeded during production.
CONSTRUCTION METHODS
623.3 -QUALIFICATIONS : 623.3.1 -Crew Qualifications: Contractor: The contractor selected must be an American Shotcrete Association (ASA) Qualified Contractor and must have a current qualification. The contractor will have completed at least five shotcrete projects of similar size, scope, and shotcrete process used (dry or wet - mix). The contractor must provide proper documentation, including full contact information for owner/engineer/construction m anager/general contractor who contracted the contractor to perform the shotcrete work, a project description, scope, and outcome of previous 5 structural shotcrete projects. Superintendent, Project Engineer, or Project Manager: The Project Engineer, Pro ject Manager, or Superintendent will have a minimum of 3 years of relevant experience on structural shotcrete projects. The contractor must provide proof of the previous shotcrete experience. Foreman: The foreman will have a proficiency in all positions . The foreman will be required to have at least two years of experience on structural shotcrete projects. The foreman must provide references of the previous shotcrete projects that can be contacted to verify the experience and outcome of these projects. T he contractor must provide proof of the foreman’s previous shotcrete experience. Nozzleman: The nozzleman will be required to have a current ACI certification as required by the current ACI Shotcrete Nozzleman certification policy in vertical shooting, and if overhead work is included in the scope of work, then an additional ACI overhead certification will be required. The nozzleman will be required to have a current ACI certification in the shotcrete delivery method that is chosen for the project, eit her dry -mix process or wet -mix process. The Nozzleman must have at least 300 shooting hours of verified experience as a nozzleman on projects with a similar application and scope. The contractor must provide proof of the Nozzleman’s previous shotcrete exp erience. The nozzleman will also be able to demonstrate, by test, an ability to satisfactorily perform the required duties and to apply the shotcrete as required by specifications.
481 623.3.2 -Quality Control Personnel: Shotcrete Inspector: Every project in which shotcrete is included is required to have an independent Shotcrete Inspector with a current ACI Shotcrete Inspector Certification. The Shotcrete Inspector must have verifiable work experience in one of the following areas: 1. Testing, inspection, and quality control of shotcrete. 2. Supervision of shotcrete construction work. 3. Design of shotcrete structures. The Shotcrete Inspector is required to be at the place of shotcrete placement while shotcrete placement i s occurring.
623.4 -PROPORTIONING : Unless otherwise specified, the proportioning and mix design of shotcrete shall conform to prevention of Class B concrete in Table 601.3.1.1.1.3. At least 30 calendar days prior to the start of construction, the Contractor shall design and submit, to the Engineer, for approval, the proportions of ma terials, including cement, aggregate, admixtures, fibers, and supplementary cementitious materials, to be used which will result in a mixture conducive to effective shotcreting, and a mixture having the desired properties. A mix design shall be required fo r each different type of shotcrete to be used in the work. The mix design shall be accompanied by a statement giving the source of materials and components used in the mix. All shotcrete mix designs will be accepted based on the results of preconstruction testing. When using the wet -mix process the air content of the concrete must be 7 ± 1% before shooting. Dry-mix shotcrete may be used provided that the in -place air entrainment shall be checked at least once at the beginning of the operation, once in th e middle, and once after restarting the shotcrete process after any breaks each day and found that the in -place mixture has a of 4 ± 1%% air entrainment. The maximum allowable w/c ratio for any shotcrete mix design will be 0.45. Shotcrete shall achieve a minimum compressive strength of 2000 psi in 3 -days and 4000 psi in 28 -days when tested using cores in accordance with ASTM C1140. Compressive strength and plastic air content test results from at least one test panel for each mix design shall be submitte d to the Engineer prior to construction.
623.5 -PRE -CONSTRUCTION TESTING : Prior to the start of construction, the contractor will shoot qualifying test panels. At a minimum, two panels will be shot for every different mix design that is going to be used on the project. Additional test panels may be required at the discretion of the Engineer. The same ACI certified nozzleman, crew, and equipment that will be performing shotcreting operations on the project must be used to shoot the test panels. If during construction the nozzleman is changed, the new nozzleman will be required to shoot additional test panels prior to beginning work. The same shooting positions that will be used in the project must be used in shooting the test panels. All form materials and procedures will comply with ASTM C1140. One of these two test panels will have reinforcement which is the same as the most congested section on the shotcrete project and shall use the same mix design designated for that section of the project. The finish that is selected for the section of the project, which the panel with reinforcement represents, will be applied to the panel with reinforcement, to indicate whether that finish has any effect on the shotcrete encasement around the reinforcement. This will be used to qualify the nozzleman and shotcreting feasibility. The m inimum diameter for the cores taken from the panel with reinforcement will be 3.75 -inches and will be the entire thickness of the panel. The panel with reinforcement will be large enough so that actual project conditions can be