623Pneumatically 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 concrete, 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-Definitions: 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 material. 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. 479 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 manager/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, Project 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. The 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 experience. 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. 480 623.3.2-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 is 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 for 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 submitted 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 481 simulated. The other panel will have no reinforcement and will be used to qualify the properties of the mix design. The size of the panel without reinforcement, for qualifying the mix design, will be such so that cores can be drilled allowing for three (3)-inches diameter and length of 5.5-inches or the thickness of the panel, whichever is greater. This process shall follow the guidelines of ASTM C1604. A WVDOH representative and the Shotcrete Inspector must be present when the test panels are constructed and tested, and the WVDOH representative and the Shotcrete Inspector must inspect the performance of the test panels with reinforcement for quality of shotcrete placement, quality of nozzleman, and encasement. Three cores shall be taken from the test panel with reinforcement and will be visually inspected to ensure proper shotcrete placement and consolidation around the reinforcement. Three cores shall be taken from the test panel without reinforcement and will be tested in accordance with ASTM C1604. Cores that are damaged from drilling must be immediately discarded. If any preconstruction testing panel fails the contractor will be allowed to shoot another test panel with the same nozzleman, equipment, and mix design. If the second panel also fails, the contractor must make changes until the shotcrete panel passes the testing. These changes must be implemented during the entire shotcreting process during construction. If permitted by the Engineer on small projects, where preconstruction testing is cost prohibitive, the requirement for constructing test panels may be waived if the contractor provides results of previous tests with the same nozzleman, materials, mix designs, qualified personnel, and similar project application. The requests must be made to the Engineer and appro ved before pre- construction testing may be omitted. A site on the project must be selected by the engineer to perform a tensile bond strength test between the original concrete, which will be repaired, and the new layer of concrete placed with shotcrete. The contractor will repair the selected site and after curing, a minimum of three tests will be performed following the guidelines of ASTM C1583 (Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of C oncrete Repair and Overlay Materials by Direct Tension (Pull -off Method))The minimum bond strength which the average of the three tests shall meet is 150 psi. If the average of the three tests do not meet this bond strength requirement then changes should be made to mix design, or methods to ensure the specified bond strength. 623.6-TESTING DURING CONSTRUCTION: The Contractor must notify the Engineer at least 48 hours prior to beginning any shotcreting operations. The Contractor shall perform Quality Control Testing as outlined in this sub-section. 623.6.1-Sampling and Testing Methods: Sampling Materials for Shotcrete ASTM C1385 Temperature of Freshly Mixed Hydraulic Cement Concrete ASTM C1064 Testing of Air Content ASTM C231 or AASHTO T 152 Preparing and Testing Specimens from Shotcrete Test Panels ASTM C1140 Obtaining and Testing Drilled Cores of Shotcrete ASTM C1604 623.6.2-Temperature: Testing of the temperature will be performed hourly and shall be within the allowable temperature ranges specified in Section 601.9. 482 623.6.3-Air Content: For wet -mix shotcrete, the air content must be 7 ± 1% when tested prior to placement. The testing frequencies of air content for wet -mix shotcrete, prior to placement, will be as required in MP 601.03.50 Table 1 Section C. A, “as shot shotcrete”, air test shall be performed one per ½ day of operation for both wet- mix and dry-mix shotcrete as follows. The shotcrete nozzleman will shoot a sample of shotcrete into a wheelbarrow or at the wall or floor, then place the shotcrete sample into the air meter using a scoop. The subsequent sample will follow guidelines of ASTM C231 or AASHTO T 152. The air entrainment of the “as shot shotcrete” will be 4.0 ± 1%. 623.6.4-Compressive Strength: During construction, test panels shall be shot for each different mix in the project. The panels will have a minimum dimension of sixteen (16) inches x sixteen (16) inches and have enough depth to allow cores to be 5.5 -inches long. One test panel will be shot for each mix every day or every 50 yd³, whichever produces the greatest number of panels. The panels will then be cured using the procedures in ASTM C1140. Three cores with a diameter of three (3) inches and a length of 5.5 - inches will obtained from each panel and tested for compressive strength following the guidelines of ASTM C1604. The minimum 28-day average compressive strength for each set of cores from each panel shall be 3,500 psi with no single core strength less than 3,000 psi. When testing in-place concrete that has been placed using shotcrete, cores will be obtained at the location specified by the Engineer and tested as outlined in ASTM C1604. 623.6.5-Combined Aggregate Gradation: The aggregate gradation shall be performed by the contractor once for every 50 cubic yards of shotcrete that is produ ced from the same mix design. The aggregate gradation shall meet the requirements of Table 623.2. However, not more than one aggregate gradation test (for each mix design) shall be required per calendar day as long as not more than 400 cubic yards of shotcrete is produced in a single day from the same mix design. In situations when more than 400 cubic yards of shotcrete is produced in a single day from the same mix design, two aggregate gradation tests shall be required (one in the AM and one in the PM) for that mix design. During any calendar week (Sunday through Saturday) in which shotcrete is being produced, a minimum of one aggregate gradation test shall be required (for each mix design from which shotcrete is being produced). This aggregate gradation test shall be conducted on the first day of production of that calendar week. Should the aggregate gradation tests results for any sieve size listed be outside of the limits set forth in Table 623.2 then production shall be discontinued until appropriate corrections are made. Corrections shall be made either in the aggregate proportions in the shotcrete mix (the mix design), the gradation of the aggregates, or the storage and loading of the aggregate, as the Contractor may elect. When the small quantity work condition applies, the aggregate gradation test required after 50 cubic yards of shotcrete production shall be performed on the day that the 50 cubic yard quantity is achieved. All shotcrete produced on that day (the day that the 50 cubic yard quantity is achieved) shall be represented by the previous aggregate aggradation test. The aggregate gradation test conducted on the day that the 50 cubic yard quantity is achieved shall represent the next 50 cubic yards of shotcrete produced, beginning wit h the shotcrete produced on the next day of production. 483 623.7-EQUIPMENT AND TOOLS: The Contractor shall maintain a clean, dry, oil-free supply of compressed air sufficient for maintaining adequate nozzle velocity at all times. The equipment shall be capable of delivering the premixed material accurately, uniformly and continuously throug h the delivery hose. To prevent sagging or sloughing of freshly -applied shotcrete, control must be taken with the application thickness, nozzle technique, air pressure and rate of shotcrete placement. A minimum 600 CFM compressor capable of producing 120 psi air pressure exiting the compressor is required. The internal diameter of the hose shall be at least three times larger than the largest particle in the mixture. For shotcrete containing steel fiber-reinforcement, the internal hose diameter shall be a minimum of 1.5 times the length of the fiber, and for shotcrete containing synthetic fibers, the internal hose diameter shall be a minimum of the same length as the fiber. For all dry-mix applications, a water booster pump must be included in the system adding water to the application. 623.8-HANDLING, MEASURING AND BATCHING OF MATERIALS: The batch aggregate and cement by weight or by volume must be in accordance with the requirements of Section 601 and AASHTO M 157 or ASTM C685. The mixing equipment must thoroughly blend the materials in sufficient quantity to maintain placing continuity. The batch, delivery and placement of shotcrete must b e completed within 90 minutes of mixing. The use of retarding admixtures may extend application time beyond 90 minutes if approved by the Engineer. Dry-mix shotcrete shall be sufficiently damp prior to shotcreting. Site -batched dry-mix shotcrete typically does not need to be pre -dampened, since the aggregate usually contains sufficient moisture. However, pre-bagged dry-mix shotcrete must be pre-dampened. 623.9-CLEANING: All surfaces must be free from damaged material. The surfaces must be clean from dirt, oil, or other contaminants that could inhibit the bond of shotcrete. Concrete or masonry surfaces will be chipped prior to the placement of shotcrete to make surfaces even, sa wcut surfaces must be roughened. In concrete repair work, disintegrated concrete shall first be removed with pneumatic or hand tools. The surfaces shall then be thoroughly blasted to remove all dirt and loose materials, special care being taken in concre te repair work to thoroughly clean exposed reinforcing steel. Any unsound concrete, on which shotcrete will be placed, shall be removed. Prior to applying each layer of shotcrete, the concrete surfaces shall be cleaned and washed with water and dried to a saturated surface dry condition with compressed air. Earth surfaces shall be dug to line and grade. The surface will be dampened prior to the placement of shotcrete. There will be no pools of standing water prior to the shooting of shotcrete.

623.10PLACING REINFORCING STEEL:

Lap adjacent sheets of reinforcing wire or reinforcing bars and install anchors as directed on the Plans. If possible, the splices should be lapped from front to back.

623.11PLACING SHOTCRETE:

Shotcrete shall not be placed if the air temperature is 40°F or lower and falling. The contractor may install shotcrete in temperature less than 40°F if they can prove that they can provide adequate cold weather protection that will not be detrimental to the strength and quality of the concrete, and if it is approved by the Engineer. Shotcrete shall n ot be installed on frozen surfaces or ground. Shotcrete shall be deposited with a material temperature of not less than 50° F 484 or more than 90° F, and unless otherwise stated, shotcrete temperature requirements will comply with Section 601.9. During high wind or rain, unless suitable protective covers, enclosures or wind breaks are installed, shotcrete application shall be suspended. Any newly placed shotcrete that has been exposed to rain making the shotcrete unacceptable shall be removed and replaced. A polyethylene film or equivalent shall be used to protect the work from exposure to adverse weather. When placing shotcrete on an existing concrete surface, the receiving concrete surface must be damp before shotcrete is placed. Care must be taken so that there are no locations of pooled water. Before an admixture or accelerator, which was not included in the initial mix design qualification, is added to the mix a minimum of two preconstruction test panels must be shot before approval. One test panel must contain the most complicated arrangement of steel which is expected with that mix design, as determined by the Engineer. Shotcrete may not be placed during precipitation that will disturb the finish or cause the shotcrete to run. Shotcrete will not be pl aced when wind conditions will disturb the stream of shotcrete before hitting the receiving surface. The Contractor shall maintain the face of the surface on which the shotcrete is to be applied and other surfaces, such as reinforcing steel, clean of loose materials, mud, rebound, overspray or other foreign matter that could prevent or reduce shotcrete bond. Any surface materials that are loosened or damaged should be removed to a sufficient depth. Any material that loosens during application shall be rem oved. The adjacent surfaces shall be protected from overspray during shooting. Water flow shall be diverted and standing water shall be removed so that shotcrete placement will not be affected. The shotcrete shall be applied from the lower part of the ar ea upward to prevent accumulation of rebound. The placement of the nozzle shall be at a distance and approximately perpendicular to the working face so that rebound will be minimal and compaction will be maximized. Rebound shall not be worked back into t he construction. Shotcrete crews must always keep area around nozzleman clean and clear using compressed air to removed impurities and shoveling overspray before that area is shot. A clearly defined pattern of continuous horizontal or vertical ridges or depressions at the reinforcing elements after they are covered with shotcrete will be considered as indication of insufficient reinforcement cover or poor nozzle techniques. In this case, immediately suspend the application of shotcrete and implement corrective measures. Correct the shotcreting procedure by adjusting the nozzle distance and orientation, ensuring adequate cover over the reinforcement and adjusting the water content of the shotcrete mix or other means. Any shotcrete surface defects shall be repaired after placement as soon as possible. Any shotcrete that exhibits segregation, honeycombing, lamination, void or sand pockets, or excessive shrinkage cracking shall be removed and replaced. In -place shotcrete not meeting the specified strength requ irement will be subject to remediation. Possible remediation options include placement of additional shotcrete thickness or removal and replacement, at no additional cost to the Division.

623.12FINISHING SHOTCRETE SURFACES:

The finish shall be completed as per the contract documents. When specified, a pre - construction mockup panel representing the desired finish shall be provided and evaluated by the Division for conformance with the contract documents. When using a troweled or rod finish, the shotcrete must sufficiently set to avoid sagging or sloughing. 485

623.13CURING AND PROTECTING SHOTCRETE:

Unless otherwise specified, s hotcrete shall be cured as outlined in Section 601.12. Immediately after shotcreting and not to exceed 30 minutes after placement, initial curing is to commence. The surface of the concrete must be continually kept moist using a fogging system. Use equipment that produces a fog spray from atomizing nozzles that will uniformly cover the concrete surface. The minimum rate of fog application shall not be less 10.6 gal./h/yd2. The number and placement of nozzles shall be dependent on the discretion of the Engineer. The mist must be fine enough as to not disturb the finished surface of shotcrete. Final curing must be done through fogging, sprinkling, or a combination of burlap sacks with sprinkling or plastic -coated synthetic fabric with sprinkling. The burlap sacks and plastic -coated synthetic fabric must be kept continually saturated with water by sprinkling. Set up fogging equipment to allow complete coverage of the area to be cured. The surface of the concrete must be continuously kept wept from the time of placement and the alternation of wetting and drying of the concrete surface will not be allowed. Perform sprinkling for final curing by using either soaker hoses or lawn sprinklers. The surface of the concrete is to not be eroded by running water. All methods of final curing must be performed for a period of 7 calendar days. If no other curing method is available due to project limitations, curing compounds can be used and must be placed in two coats of different orientations of application one vertical and the other horizontal, to ensure a complete seal. Use of curing compounds is only permitted on the final layer of shotcrete and not between layers of application.

623.14METHOD OF MEASUREMENT:

The quantity of shotcrete to be paid for will be the number of square yards complete in place and accepted.

623.15BASIS OF PAYMENT:

The quantities, determined, as provided above, will be paid for at the contract unit price, and shall constitute full compensation for furnishing and preparing of a ll materials, including reinforcing steel, all items incorporated into the shotcrete work as shown in the Plans such as anchors and bolts, placing, finishing, testing, and curing shotcrete, and all labor, equipment, tools, supplies, and incidentals necessary to complete the work.

623.16PAY ITEMS:

ITEM DESCRIPTION UNIT 623001-* Shotcrete Square Yard * Sequence Number 486