ITEM 520 PNEUMATICALLY PLACED CONCRETE- SHOTCRETE
520.01 Description. This work consists of removing all loose and disintegrated concrete; surface
preparation; furnishing and placing reinforcing steel, welded steel wire fabric, and dowels; furnishing and placing pneumatically applied concrete; and curing for new work, rehabilitation, or repair.
520.02 Materials. Furnish materials conforming to:
Reinforcing steel ................................... 509 Portland cement .......................................... ... 701.01 through 701.05, 701.09, 701.15 Micro-silica ...................................... 701.10 Fly ash .............................................. 701.13 Slag Cement ..................................... 701.11 Fine aggregate ..................... 703.02, 703.03 Air-entraining admixture ................. 705.10 Chemical admixture for concrete ..... 705.12 Welded steel wire fabric .. 709.10 or 709.12 Swedged anchor bolts ...................... 711.10 Use water for concrete mixing free from sewage, oil, acid, strong alkalis, vegetable matter, clay, and loam. Potable water is satisfactory for use in concrete. Non -potable water will meet the requirements of ASTM C1602. Water from a reclaiming system will contain no more than 0.06% chlorides. Test the non-potable and reclaiming system water prior to the start of shotcrete production. Provide certified test data to the Engineer, at least 21 days prior to shotcrete production.
520.03 Shotcrete Mix Design . Only use mix designs accepted by the Department and the
following requirements.
A.Provide a Shotcrete job mix conforming to the following:
1.Compressive strength. Provide a compressive strength, at a minimum, of 2000 psi at 3 days, and 4000 psi at 7 days, or as per plan requirements.
2.Migrating Corrosion Inhibitors. Each admixture shall be accompanied by manufacturer’s written certification meeting ASTM C1582. Dosage rate will follow manufacturer’s recommendations.
B.Provide prepackaged shotcrete materials in accordance with ASTM C 1480 from a single manufacturer. The minimum compressive strength for shotcrete is 2000 psi at 3 days and minimum of 4000 psi at 28 days. Follow the manufacturer’s recommendations for storing the material on site, do not allow the prepackaged materials to beco me wet prior to use. Submit certified test data to the Engineer for approval prior to use that and meets the requirement of Table 520.3.B-1. TABLE 520.3.B-1, SHOTCRETE CONCRETE PROPERTIES Hardened Properties Test Method Requirement Slant Shear Bond Strength @ 28 days ASTM C882 Modified (1) 2000 psi (14 MPa), min. Drying Shrinkage @ 28 days ASTM C157 Modified (2) 0.08%, max. Rapid Chloride Permeability @ 28 days ASTM C1202 (3) / AASHTO T277(3) 750 coulombs, max. Volume of Permeable Voids @ 28 days ASTM C642(3) 10%, max. Freeze-Thaw Resistance @ 300 cycles ASTM C666, Procedure A 95% RDM, min. Flexural Strength @ 28 day ASTM C78 900 psi (6 MPa), min. Compressive Strength @ 3 days ASTM C1604 2000 psi (14 MPa), min. Compressive Strength @ 28 days ASTM C1604 4000 psi (28 MPa), min.
1.No epoxy bonding agent used.
2.ICRI Guideline No. 03733, “A Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces”, 1”x1”x10” prism, air cured
3.Either Rapid Chloride Permeability or Volume of Permeable Voids can be used. Provide dry mix with migrating corrosion inhibitors. Each admixture shall be accompanied by manufacturer’s written certification meeting ASTM C1582. Dosage rate will follow manufacturer’s recommendations.
520.04 Delivery of Materials. Deliver all materials in their original containers bearing the
manufacturer’s label, specifying date of manufacturing, batch number, trade name, and quantity. Each shipment will be accompanied by a Safety Data Sheet (SDS).
520.05 Storage of Materials . Stock and store any material necessary to perform the work to
prevent damage by the elements. Keep the storage space clean and dry per Manufacturer’s recommendations.
520.06 Equipment. Provide shotcrete equipment capable of delivering the premixed material
accurately, uniformly and continuously through the delivery hose.
A.Mixing: Provide dry-mix shotcrete using a rotary type or pressure vessel gun with a continuous - type predampener, capable of thoroughly mixing the shotcrete mixes in sufficient quantity to maintain shotcreting continuity and a moisture range of 3 to 5% prior to d ischarging into the gun. Operate all equipment in accordance with the manufacturer’s recommendations. Provide wet-mix shotcrete using a positive displacement pump (swing tube). Concrete for wet-mix shotcrete placement may be supplied by an approved concrete batch plant and delivered by truck concrete mixers. Supply plant batched concrete and delivery equipment meeting the requirements of ASTM C94. Where the concrete mixture is prepared on -site, use mixing equipment with a calibrated water meter capable of mixing prepackaged shotcrete material. Supply concrete mixes used in shotcrete placement having a W/Cm ratio between 0.35 -0.45. The maximum 90 -minute limit will be implemented for wet-mix shotcrete after the addition of water to the mixture. Use of hydration control admixtures (HCA) may be used to extend the 90 minutes as approved in the job mix approval prior to use.
B.Air Pressure, Dry-Mix Process. Use a compressor capable of delivering a sufficient volume of oil-free air at the pressure shown in Table 520.6.B-1. Maintain steady pressure throughout the placing process. Use a water pump or a water booster pump with the size and capacity to deliver water to the nozzle with a pressure at least 15 psi more than the required air pressure. The values shown in the Table 520.6.B-1 are based on a hose length of 150 feet with the nozzle less than 25 feet above the delivery equipment. Increase operating pressure approximately 5 psi for each additional 50 feet of hose and approximately 5 psi for each 25 feet the nozzle is raised. TABLE 520.6.B-1, COMPRESSOR CAPACITIES Compressor Capacity, CFM Hose Diameter, in. Maximum Size of Nozzle Tip, in. Operating Air Pressure Available, psi 250 1 3/4 40 315 1-1/4 1 45 365 1-1/2 1-1/4 55 500 1-5/8 1-1/2 65 600 1-3/4 1-5/8 75 750 2 1-3/4 85
C.Air Pressure, Wet-Mix Process. Use a compressor capable of delivering a sufficient volume of oil-free air to operate the pump at a line pressure between 100 psi and 300 psi. Use delivery hoses between 1-1/2 inches and 3 inches in diameter. Use mixing equipment capable of thoroughly mi xing the materials in sufficient quantity to maintain continuous placement.
520.07 Submittal Requirements. Submit to the Engineer for review at least two weeks before
beginning the work.
A.Evidence the contractor has successfully executed no less than five projects with similar size and scope over the last five years. The information provided is to include a statement of the type of work, and contact information for Engineer or Owner who have knowledge of the execution of the work and present condition of the work.
B.Documentation and owner references, verifying the qualifications of the nozzlemen. Personnel designated as nozzlemen on the job are required to document a minimum of one year of experience in the application of shotcrete on a comparable project and hold a current certificate for ACI Shotcrete Nozzleman, either dry -mix process or wet -mix process, as corresponds to the process indicated. Certifications for all nozzlemen to be utilized on the job.
C.Documentation the supervisor has experience supervising more than one comparable project including written documentation and owner references, verifying the qualifications.
D.JMF information and a list of materials and quantities. Include list of Admixture literature used. Indicate the admixture type and the manufacturer’s recommendations for mixing the admixtures with JMF.
E.Methods and materials used for Depth control quality measures.
520.08 Removal of Concrete. In areas to be repaired, remove all loose, soft, honeycombed, and
disintegrated concrete, plus a minimum of 1/4 inch (6 mm) to a maximum of 1 inch (25 mm) depth of sound concrete. Remove additional concrete as necessary to permit the placement of the mini mum specified shotcrete thickness of not less than 1 -1/2 inches (38 mm), except on top horizontal surfaces of not less than 3/4 inch (19 mm). Once initial removals are made, undercut all exposed reinforcing bars. Undercutting will expose the full circumfer ence of the exposed reinforcing bar. Provide a clearance of 3/4 inch (19 mm) between the exposed reinforcing bar and the surrounding concrete. Remove all heavy corrosion and scale from the reinforcing bars with wire brush or abrasive blasting. A minor amount or tightly adhered rust may be left in place. Saw cut edge locations to a minimum of 1/2 inch (13 mm). Maintain an edge location depth of not less than the specified minimum depth for all repair areas. Only use pneumatic, hand tools, or hydrodemolition equipment to obtain results satisfactory to the Engineer in the removal of concrete and in preparing and shaping the areas to be repaired. If working around reinforcing steel, avoid loosening the steel, or shattering the concrete around it, beyond the repair area.
520.09 Reinforcement. For existing reinforcing bar that have been cut or having lost 20% or
greater section loss, splice in supplement reinforcing bar of equal bar size. Use mechanical rebar slicing system for supplemental reinforcing bars. Place deformed wire fabric in all vertical surface areas where the thickness of the shotcrete patch is greater than1 1/2 inches (38 mm) or bottom side of horizontal surfaces. Repairs areas on the top of horizontal surfaces do not require deformed wire fabr ic. Reinforce patches with deformed wire fabric meeting either 2 x 2 inches (50 x 50 mm) with wire size number D 0.9 (MD 6), or 3 x 3 inches (75 x 75 mm) with wire size number D 1.4 (MD 9). Cover the entire area of the repair with deformed wire fabric, place the wire fabric no closer than ½ inch (13mm) to the prepared surface and not less than 1 inch (25 mm) from the finished surface. Overlap adjacent sheets of deformed wire fabric by 6 inches (150 mm), and securely tie them together. Carefully pre -bend fabric before installation to fit around corners and into re-entrant angles. Rolled wire fabric is prohibited. Wire fabric held in place by elastic force (spring-loaded) or by friction is prohibited. The deformed wire fabric can be tied to the existing reinforcing bars if there is a 3/4 inch (19 mm) clearance around the bar. The maximum anchor spacing for the deformed wire fabric is 18 inches (46 cm) on center, in all horizontal for vertical surfaces and 12 inches (30 cm) in all horizontal for bottom vertical surfaces, overhead. A minimum of 3 anchors are required for each repair area. Unless specified on plans use 3/8 inch (10 mm) swedged anchor bolts. Embed anchors to manufactures recommendation to develop full capacity of swedge bolt. Use swedge bolt and nut to secure wire fabric.
520.10 Blast Cleaning of Repair Area . After performing 520.08 and 520.09, blast clean all
surfaces to which shotcrete is to bond between 24 and 72 hours prior to placing of the shotcrete. All surfaces to which the concrete is to bond include exposed reinforcing steel, existing concrete, and the work face of any previously placed material. Blast clean all surfaces using high-pressure water blasting with or without abrasives in the water, abrasive blasting with containment, or vacuum abrasive blasting. High-pressure water washing requirements can be defined as a minimum pressure of 4000 psi (28 MPa) and flow of 5.0 gal/min (79 L/min). Maintain a standoff distance (the distance between the nozzle and the surface being cleaned) to a maximum of 12 in. Bring the prepared substrate to saturated surface dry (SSD) with water meeting 520.02, ensure that all prepared substrate maintain a SSD prior to and during the shotcrete placement. The Engineer will approve the preparation and condition of all surfaces immediately before the application of the shotcrete..
520.11 Preconstruction Testing. Before placing any shotcrete on the project, each nozzleman
will need to perform mock -up panels to be accepted by the Engineer . The purpose of the mock -up panel is to demonstrate the nozzleman’s ability to place and finish shotcrete around the reinforcement. A nozzleman shall not perform any work on the structure until the Engineer accepts every mock -up panel. Fabricate mock-up panels using the same personnel, equipment, materials and procedures that will be used on the project. Finish mock -up panels as required by plan, if no finish is required by plan, texture exposed surfaces according to 520.12. Construct mock-up panels no less than 3 ft (0.9 m) square and a minimum of 4 inches (100 mm) deep. Mock-up panel depth will be adjusted if greater than 4 inches (100mm) to match the depth of application shown in the plans. Install reinforcement in the mock-up panel that matches the largest size and tightest spacing found for the reinforcement in the bridge. Orient the mock-up panel for a vertical surface application. If an overhead application is specified in the plan, perform an additional mock-up panel or iented for overhead application. Apply the shotcrete until panel is full and finish exposed surfaces. Age mock-up panels for at least 24 hours before cutting. Cut every mock -up panel in half, transverse to the main reinforcements. There shall be no voids with a maximum dimension greater than 0.25-inches adjacent to the reinforcement bars. If 0.25-inches or greater voids are found, an additional cut is to be performed to prove the debonding does not extend greater than 3 -inches along the length of the reinforcement bar. The shotcrete in the mock -up panel shall not sag nor decrease the bond of the preceding coat for multiple layer application of shotcrete.
520.12 Shotcrete Placing. Place the shotcrete when the ambient temperature is between 50 °F
and 90 °F. Do not place concrete against a surface containing frost, ice, standing water, or when the surface temperature is less than 40 °F. Protect the work from environmental conditions until final curing has been applied. Do not place shotcrete during a rainfall event. Immediately cover previously placed shotcrete, not yet cured. Resume concrete placement after the rainfall stops. Discontinue placement of shotcrete or shield the nozzle stream if wind causes separation of ingredients from the nozzle stream. Apply the concrete using pneumatic equipment that sprays the mix onto the prepared surface. Minimize rebound and produce a compacted dense homogenous mass. Use shooting strips or guide wires to ensure square corners, straight lines, and a plane surface of shotcrete, except as otherwise permitted by the plans or approved by the Engineer. Place shooting strips to keep the trapping of rebound at a minimum. At the end of each day’s work, or similar stopping periods requiring construction joints, cut the work on a 45° angle through the full depth of the section, roughen the surface by stiff broom, racking or scoring for good surface bond when placing subsequent shotcrete layers. In shooting all surfaces, ensure that the stream of flowing material from the nozzle impinges as nearly as possible at right angles to the surface being covered, and hold the nozzle 2 to 4 feet (0.6 to 1.2 m) from the working surface. Finish shotcrete repairs flush with the original masonry or concrete surface, except as noted for areas of exposed reinforcing steel. Do not initiate cutting or finishing until the shotcrete is sufficiently set. If not specified on plan, use rubber/sponge float to finish all exposed surfaces. On vertical and overhead surfaces, the layer thickness is to be establish and demonstrated during the preconstruction testing phase of the project. If a successive coat is applied on shotcrete that has set for more than 2 hours, clean and dampen the shotcrete surface as required in 520.05 for the prepared surface. After shotcrete has been placed to the desired thickness, cut off all high spots with a sharp trowel, or screed them to a true plane as determined by shooting strips or by the original masonry surface, or as directed. If using screeds, apply them lightly t o all surfaces so as not to disturb the shotcrete for an appreciable depth, and work them in an upward direction when applied on vertical surfaces. Shotcrete rebounded outside of the formwork is prohibited from being worked back into the surface and is not to be salvaged and included in later batches. Rebounded shotcrete is the responsibly of the Contractor for removal and disposal.
520.13 Curing. Cover the pneumatically placed shotcrete patches with burlap or cotton mats and
keep them wet for 7 days after placing. If it is not practical to use mats, keep the surface wet by sprinkling for the same length of time. If the Engineer determines that the above curing procedures are impractical because of the inaccessibility of isolated repair areas, the Contractor may cure the final shotcrete surface according to 511.13, Method B, using twice the manufacturer’s recommended coating rate for formed concrete surfaces (equal to a white sheet of typing paper) at the time of application. Protect all shotcrete against cold weather according to 511.12. Do not use curing compounds on any surfaces against which additional shotcrete or other cementitious finishing materials are to be bonded unless positive measures, such as prepare surface per 520.10, are taken to completely remove curing compounds prior to application of such additional materials.
520.14 Inspection and Testing . At a minimum provide one test panel per nozzleman at the
beginning of each day shotcreting occurs. The purpose of the test panel is to determine the compressive strength of all shotcrete placed after test panel per Table 520.3.B-1. Fabricate test panel using the same personnel, equipment, materials and procedures that will be used on the project. Construct a 24 inch x 24 inch x 3.5 inch (610mm x 610mm x 89mm) test panel with no reinforcement. Cure test panel in the same manner used for the structure. Follow ASTM C1140 for panel size and coring, and compressive strength testing as per ASTM C1604. Provide a minimum of six cores, test three cores per test age. Test the cores at an AASHTO Accredited laboratory for compressive strength. After curing and before final acceptance, sound all patched areas. Remove and replace all unsound or cracked areas. In addition to sounding all patches, the Department will base acceptance of the shotcrete on compressive strength tests on cores taken from test panels. Remove, replace, re -inspect, and re -test all defective patches, as determined by sounding, visible cracks, or unacceptable cores. Fill core holes according to 519. Maintain the in-place inspection access equipment employed during the original work activities or provide alternate inspection equipment such as platform lifts, bucket trucks, snooper trucks, or equivalent as approved by the Engineer for testing.
520.15 Method of Measurement. The Department will measure Pneumatically Placed Shotcrete
by the number of square feet (square meters). The Department will measure the area of exposed surfaces of all completed, tested, and approved patches, irrespective of depth or thickness of the patch. If a patch includes corners or edges of such members as beams, columns, or curbs, the Department will include all the exposed surfaces; if a patch extends completely through a member or a slab, the Department will include both exposed surfaces. The Contractor is responsible for all test panels, coring repair of core holes, independent laboratory testing of the cores, replacement of rejected areas, and all previously mentioned work under Pneumatically Placed Shotcrete for payment.
520.16 Basis of Payment. The Department will not pay for additional reinforcement to replace
that damaged by the Contractor’s operations. The Department will not pay for removing, replacing, and re -inspecting of defective patched shotcrete as determined by sounding, visible cracks, or unacceptable cores. The Department will pay for accepted quantities at the contract price as follows: TABLE 520.16-1 SHOTCRETE 28 DAY COMPRESSIVE STRENGTH PAY FACTOR Compressive Strength (psi) Pay Factor (%) >4000 100 3999 –3700 90 3699 – 3520 75 <3520 Remove and Replace Item Unit Description 520 Square Foot Pneumatically Placed Concrete Shotcrete (Square Meter)
Referenced in this section
Get an email when 520 changes
Ohio revises spec sections through supplementals and new editions. We check this one every week and email you the day it changes. Free, no account.
Source: Construction and Material Specifications, 2023 (rev. 7/17/2026) Edition. Pages 424–431 of 892. View official source ↗