53 SHOTCRETE
53-1 General
53-1.01 General
53-1.01A Summary
Reinforcement must comply with section 52.
53-1.01B Definitions
shotcrete: Concrete pneumatically projected at high velocity onto a surface to achieve compaction. dry-mix shotcrete: Dry aggregates and cementitious materials are mixed before entering the delivery hose. Mixing w ater is added at the nozzle. wet-mix shotcrete: Dry aggregates, cementitious materials, and water are mixed before entering the delivery hose. If used, accelerator may be added at the nozzle. rebound: Aggregate co ated with cement paste that ricochets away from the surface against which the shotcrete is being applied.
53-1.01C Submittals
Reserved
53-1.01D Quality Assurance
Air pressure and shotcrete supply at the nozzle must be uniform and provide a steady, contin uous flow of shotcrete. Inspect nozzles and nozzle body components before each work shift. Replace nozzles and components under the manufacturer's instructions.
53-1.02 Materials
Shotcrete must consist of cementitious material, fine aggregate, and water. Cementitious material, fine aggregate, and water must comply with section 90 -1. For dry -mix shotcrete :
1.Thoroughly mix 1 part cementitious material to not more than 4.5 parts fine aggregate in a dry state before charging into the machine. Measurement mus t be either by volume or weight.
2.Fine aggregate must contain not more than 6 percent moisture by weight. For wet -mix shotcrete :
1.Shotcrete must contain at least 675 pounds of cementitious material per cubic yard.
2.You may substitute a maximum of 40 percent coarse aggregate for the fine aggregate . Coarse aggregate must comply with section 90 -1, except section 90 -1.02C(4)(d) does not apply. The gradation for the coarse aggregate must comply with the gradation specified in section 90 -1.02C(4)(b) for the 1/2 inch x no. 4 or the 3/8 inch x no. 8 primary aggregate nominal size.
3.You may add admixtures complying with section 90 -1.02E. If colored shotcrete is described, color shotcrete by mixing a fine ground, sy nthetic mineral oxide into the shotcrete. The synthetic mineral oxide must be specifically manufactured for coloring concrete . The coloring agent must be uniformly and homogeneously mixed with the shotcrete.
53-1.03 Construction
53-1.03A General
Reserved
53-1.03B Preparing Receiving Surfaces
Evenly grade the receiving surface before applying shotcrete. No point on the graded slope may be above the slope plane shown. SECTION 53 SHOTCRETE Thoroughly compact the receiving surface . The receiving surface must contain enough moisture to provide a firm foundation and prevent excess absorption of water fr om the shotcrete. The receiving surface must be free of surface water. Forms must comply with section 51 -1.03C(2). Reinforce, secure, and brace forms to maintain form alignment against distortion from shotcrete operations. Install and maintain alignment co ntrol means at corners or offsets not established by forms or shotcrete operations. Use ground wires to establish thickness, surface planes, and finish lines. Use temporary coverings to protect adjacent surfaces from the nozzle stream.
53-1.03C Applying Shotcrete
Dry-mix or wet -mix shotcrete must be applied by the nozzle . Apply shotcrete using small circular motions of the nozzle while building the required thickness. Direct the nozzle perpendicular to the receiving surface with the nozzle held at such a d istance to produce maximum consolidation and full encapsulation of the reinforcement. Shotcrete must completely encase reinforcement and other obstructions. Apply shotcrete first in corners, voids, and areas where rebound or overspray cannot easily escape. Do not incorporate rebound or overspray in the work. Before applying subsequent layer s of shotcrete:
1.Allow shotcrete to stiffen sufficiently. Remove hardened overspray and rebound from adjacent surfaces, including exposed reinforcement.
2.Use a cuttin g rod, compressed air blowpipe, or other authorized methods to remove all loose material, overspray, laitance, or other deleterious materials that may compromise the bond of the subsequent layers of shotcrete.
3.Bring the receiving surface to a saturated surface -dry condition immediately before applying subsequent layer. For dry -mix shotcrete:
1.Adjust air volume, material feed volume, and distance of the nozzle from the work as necessary to encase reinforcement
2.Maintain uniform water pressure at the nozzle of at least 15 psi greater than the air pressure at the machine
3.Do not use aggregate and cementitious materials that have been mixed for more than 45 minutes For wet -mix shotcrete:
1.Transport shotcrete under section 90 -1.02G(3)
2.Apply gr ound wires at approximately 7 -foot centers
3.Select a slump range that will effectively encapsulate reinforcement within the work but not cause shotcrete to sag or slough during application
53-1.03D Finishing Shotcrete
Apply shotcrete to the line and gr ade shown. Leave finished shotcrete surface as gun finish unless otherwise described. Do not initiate cutting or finishing until the shotcrete has set sufficiently to avoid sloughing or sagging . The finished surface must be smooth and uniform for the type of work involved. Remove and replace loose areas of shotcrete. Cure shotcrete for at least 7 days by any of the methods specified in section 90 -1.03B. If the curing compound method is used for a gun or roughened surface, a pply the curing compound at twice the specified rate. If you add a coloring agent to the shotcrete and you use the curing compound method for curing the shotcrete, use curing compound no. 6. Protect shotcrete under section 90 -1.03C. SECTION 53 SHOTCRETE
53-1.04 Payment
Shotcrete is measured along the slope of areas placed and the thickness shown. The Department does not pay for shotcrete applied outside the dimensions shown or to fill low areas of receiving surfaces.
53-2 Structural Shotcrete
53-2.01 General
53-2.01A Summary
Section 53 -2 includes sp ecifications for applying structural shotcrete . Structural shotcrete must be applied using wet -mix shotcrete .
53-2.01B Definitions
Reserved
53-2.01C Submittals
Submit:
1.QC plan that includes: 1.1. Number and certifications of nozzlemen available to place shotcrete, number of nozzlemen on the job site at any time during shotcrete placement, description of their work schedule, and procedures for avoiding fatigue of any nozzleman 1.2. Proposed method of placing shotcrete, including application rates, details of proposed construction joints and their locations, and methods for achieving the required thickness and surface finish 1.3. Procedures for curing shotcrete surfaces 1.4. Description of any required debris containment system
2.Preconstruction test panels and test results
3.Production test cores and test results
53-2.01D Quality Assurance
53-2.01D(1) General
Reserved
53-2.01D(2) Qualifications
Nozzlemen performing the work must h old current ACI CPP 660.1 -17 certification as a nozzleman for wet-mix shotcrete. Nozzlemen performing overhead shotcrete work must hold current qualifying ACI CPP 660.1 -17 certification in the overhead shooting orientation for wet -mix shotcrete.
53-2.01D(3) Preconstruction Test Panels
Obtain authorization of the QC plan before constructing test panels. Each nozzleman performing the work must c onstruct 1 unreinforced test panel and 1 reinforced test panel for each proposed mix design. The test pan el orientation must match the orientation of the work. Cure the test panels under conditions similar to those in the work. For the unreinforced test panel:
1.Determine the size of the test panel
2.Obtain 3 -inch-diameter cores from the test panel
3.Disca rd cores that show evidence of improper coring
4.Identify each core that is to be tested
5.Test cores for compressive strength
6.Label and submit the test panel and a copy of the test results within 5 days of testing
7.Include the mix design and ambien t temperature in the submittal For the reinforced test panel: SECTION 53 SHOTCRETE
1.Construct a square test panel that has the same (1) thickness, (2) bar size and quantity of bar reinforcement or other obstructions, and (3) positioning of bar reinforcement or obstructions as the most heavily reinforced section of shotcrete to be placed
2.Minimum length of each side must equal 3 times the thickness of the most heavily reinforced section of shotcrete to be placed but not less than 30 inches
3.Break the test panel in the pre sence of the Engineer after a minimum 7 -day cure into pieces no larger than 10 inches in the greatest dimension
4.Surfaces of the broken pieces must be dense and free of laminations and sand pockets and must show that the bar reinforcement or other obstru ctions are completely encased Obtain and test cores for compressive strength under section 53 -2.01D(4)(a). Instead of constructing a separate unreinforced test panel, you may obtain cores from the reinforced test panel to determine the compressive strengt h. If you choose this option, do not break the test panel until it has cured for at least 14 days. Dispose of test panels.
53-2.01D(4) Quality Control
53-2.01D(4)(a) General
Obtain cores for compressive strength testing under ASTM C1604/C1604M. Discard c ores that contain bar reinforcement or other obstructions or show evidence of improper coring. Test cores for compressive strength at 28 days under ASTM C1604/C1604M at an authorized laboratory. The compressive strength is the average strength of at least 3 cores that are free from bar reinforcement or other obstructions. Notify the Engineer at least 24 hours before performing any coring or testing.
53-2.01D(4)(b) Field Quality Control
Obtain at least four 3 -inch-diameter test cores from each 50 cu yd, or portion ther eof, of shotcrete applied. Three cores must be free from reinforcement or obstructions. One core must include reinforcement. The Engineer determines each core location. For soil nail walls, do not core through waler bars. Cores must be both visually inspected and tested for compressive strength. The Engineer performs the visual inspection and you must perform compressive strength testing. Identify each core, including a description of the core location and mix design, and submit the cores immediately after coring. The Engineer will perform the visual inspection and return the cores to you for compressive strength testing within 48 hours.
53-2.01D(5) Department Acceptance
53-2.01D(5)(a) General
The Department accepts shotcrete based on test c ores for visual inspection and compressive strength.
53-2.01D(5)(b) Visual Inspection
Each test core must be dense and be free of laminations and sand pockets. Any core with reinforcement must show reinforcement or other obstructions are completely encase d. Shotcrete represented by an unacceptable core will be rejected unless you submit evidence that the quality of the shotcrete placed in the work is acceptable.
53-2.01D(5)(c) Compressive Strength
If the compressive strength of the shotcrete is below the specified compressive strength:
1.Make corrections to the mix design or fabrication procedures and obtain authorization before you place additional shotcrete.
2.Shotcrete represented by the cores is subject to one of the following: SECTION 53 SHOTCRETE 2.1. If the compressiv e strength is at least 95 percent of the specified strength, $10/cu yd is deducted from the payment for structural shotcrete. 2.2. If the compressive strength is below 95 percent of the specified strength but is at least 85 percent of the specified strength, $15/cu yd is deducted from the payment for structural shotcrete. 2.3. If the compressive strength is below 85 percent of the specified strength, the shotcrete must be removed. If the compressive strength is below the specified strength but is at least 85 percent of the specified strength, the deductions specified above apply unless you obtain and submit evidence that the strength of the concrete placed in the work is greater than or equal to the specified strength and this evidence is accepted by the Engineer. If the compressive strength is below 85 percent of the specified compressive strength, the noncompliant concrete represented by the test must be removed unless you obtain and submit evidence that the strength of the concrete placed in the work is at least 85 percent of the specified compressive strength and this evidence is accepted by the Engineer. If the evidence consists of tests made on cores taken from the work, obtain and test the cores under ASTM C1604/C1604M.
53-2.02 Materi Als
Shotcrete must comply with the specifications for concrete in section 90 -1. Shotcrete must have a minimum compressive strength of 3,600 psi , unless otherwise described. Mortar and alternative filler material must comply with section 60 -3.05B(2).
53-2.03 Construction
For ground anchor and soil nail walls, backfill voids due to the removal of cobbles, boulders, portions of boulders, debris, or other obstructions with shotcrete. Splicing of reinforcing bars no. 7 or larger must be made using a servi ce butt splice. Before applying shotcrete, reinforcement must be:
1.Free from loose rust, oil, curing compound, overspray, or other material deleterious to the bond between concrete and steel.
2.Lapped separated by one of the following: 2.1. Three times the diameter of the largest reinforcing bar . 2.2. Three times the maximum size aggregate . 2.3. Two inches, whichever is least, unless otherwise specified. Lapped bars must be in the same plane and parallel to the shooting direction.
3.Securely tied to min imize movement or vibration. The temperature of reinforcement and receiving surfaces must be below 90 degrees F before applying shotcrete. Apply the wet -mix shotcrete c ontinuously remov ing accumulations of rebound and overspray using a compressed air blow pipe. Ensure the nozzleman and the blowpipe operator work together and the nozzleman does not get ahead of the blowpipe operator. Taper construction joints. Construction joints must comply with section 51 -1.03D(4). Before final set, use air blowpipes to re move rebound, overspray, and other debris from the areas to receive shotcrete. If a finish coat is used, clean the surface before applying the finish coat. W ash receiving surface with an air-water blast to remove all loose material, laitance, overspray, or other material that may compromise the bond of subsequent layers of shotcrete. Remove shotcrete that extends into the space shown for CIP concrete. SECTION 53 SHOTCRETE Cure shotcrete under section 51 -1.03H. The surface finish of the shotcrete must comply with section 51 - 1.03F. Shotcrete must be maintained at a temperature of at least 45 degrees F for 72 hours after placing and at least 40 degrees F for an additional 4 days. After removing field QC test cores, fill the holes with mortar or alternative filler material. If using mortar, apply mortar under section 51 -1.03E(2) . If using an alternative filler material, apply a bonding epoxy before placing the filler material. Apply the alternative filler material under the manufacturer's instructions.
53-2.04 Payment
Payment for ba r reinforcing steel is not included in the payment for structural shotcrete.
53-3 Sculpted Shotcrete
Reserved
53-4 53-9 Reserved
Source: California Standard Specifications, 2024 Edition. Pages 841–846 of 1,372.