Part 1 — General
1.1 Section Includes
A.Shotcrete mix design, application and curing
1.2 Related Sections
A.Section 03055: Portland Cement Concrete
1.3 References
A.AASHTO T 152: Air Content of Freshly Mixed Concrete by the Pressure Method
B.ASTM C 309: Liquid Membrane- Forming Compounds for Curing Concrete
C.ASTM C 1604: Obtaining and Testing Drilled Cores of Shotcrete
1.4 Definitions
A.Dry Mix Process – Shotcrete production process in which most of the water is added at the nozzle.
B.Nozzle Operator – Worker on shotcrete crew who manipulates the nozzle, controls consistency of dry mix shotcrete, and controls final disposition of the material.
C.Rebound – Shotcrete that fail s to adhere to the surface on which the shotcrete is being applied.
D.Wet Mix Process – Shotcrete production process in which cement, aggregate, water and admixtures are first mixed together before introduction into the delivery hose.
1.5 Submittals
A.Shotcrete mix design with mix proportions and test results for approval.
1.The Department approves shotcrete mix designs based on preconstruction test panel results.
2.Include at least the following:
a.Aggregate source and grading
b.Cement type and brand
c.Water source
d.Type and dosage of hydration stabilizing/extended- set admixtures, if used
e.Discharge time limit for wet mix shotcrete
f.Preconstruction test panel test results including at least the following: 1) Sample identification, including mix design and test panel number and orientation. 2) Date and time of core sample preparation including sample dimensions. 3) Date and time of compression test. 4) 28 day compressive strength . 5) Names and signatures of people performing the compression test. 6) Name of nozzle operator who produced test panel. 7) Air content measured at the time of test panel creation (wet mix only) .
B.Written documentation of the shotcrete supervisor’s and nozzleman’s qualifications including proof of ACI Shotcrete Nozzleman certification for review.
1.ACI Shotcrete Nozzleman Certification
2.Experience on at least three comparable projects.
a.Include project names, locations and owners' contact information
C.Production summary reports for each shift
1.Submit for information within 24 hours of completing shift.
2.Include at least the following:
a.Observations of success or problems of equipment operation, application, final product conditions, and any other relevant issues during production and application. 1) Includ e sketches for locations as necessary.
b.Shotcrete batch number(s) if applicable
1.6 Acceptance
A.The Department will perform testing according to Table 1. Table 1 Sampling and Testing Schedule Property or Characteristic Test Methods or Specifications Frequency Sampling Point Air Content (Wet Mix Only) AASHTO T 152 1 per load1 Prior to placement 28 day Compressive Strength ASTM C 1604 1 set per 50 cy; at least one set per day Production test panels 1 When continuous mixing is used, sample every 10 cy. 2 A single compressive strength test result is the average result from three 3- inch diameter core specimens from the same test panel tested according to ASTM C 1604 at 28 days.
B.Shotcrete that fails to meet the strength requirements based on the following will be cause for rejection.
1.Specified 28 day minimum c ompressive strength test result less than 0.85 times the minimum 28 day compressive strength.
2.A single core compressive strength test result less than 0.75 times the minimum 28 day compressive strength.
3.The engineer may accept a 'reject' lot based on engineering analysis. The Department will apply a price reduction on rejected shotcrete allowed to stay in place.
C.Shotcrete that has been damaged by frost, or which lacks uniformity, exhibits segregation, honeycombing, lamination with a shotcrete stage, or shows excessive cracking will be cause for rejection.
Part 2 — Products
2.1 Shotcrete
A.Refer to Section 03055 for material requirements.
B.Conform to the requirements in Table 2. Table 2 Process Air Content Range 28 day Minimum Compressive Strength2 (psi) Dry Mix N/A 4,000 Wet Mix 8% - 10% at the pump 4,000 2 According to ASTM C 1604
C.Use the amount of water required to produce shotcrete of suitable strength, consistency, quality, and uniformity with the minimum amount of rebound.
2.2 Mix Design
A.Design mixes to meet the requirements of this Section and project specific criteria.
B.Preconstruction Test Panels
1.Refer to this Section, Article 3.1.
2.3 Curing Compound
A.Use a curing compound that complies with ASTM C 309 Type 1-D or Type 2, Class A.
Part 3 — Execution
3.1 Test Panels
A.Forms and Construction
1.Construct wood forms for preconstruction and production test panel s at least 3.5 inch thick by 2 ft by 2 ft in size.
2.Construct wood forms with plywood back 0.75 inch thick minimum.
3.Do not include reinforcing steel bars in the test panels
B.Preconstruction Test Panels
1.Produce test panels for each proposed mix design.
a.Include a separate test panel for each anticipated shooting orientation (slab, slopes, vertical, and overhead) , and each proposed nozzle operator.
b.Assign a test panel number and record specific information about the panel required for submittal.
2.Notify the Engineer of the time and location of preconstruction test panel production so that the Engineer may witness the production.
C.Production Test Panels
1.Produce separate panels for each nozzle operator applying shotcrete.
a.Produce production test panels for every 50 cubic yards of material placed, but not less than one panel per day .
b.Shoot test panels in the same manner as that being used on the project, including distance from nozzle, angle and orientation.
c.Include a separate test panel for each mix design used by the nozzle operator and each shooting orientation that mix design was used in (slab, slopes, vertical, and overhead).
2.Cure test panels in similar conditions to what is anticipated in the field and until test specimens are sampled.
D.Compressive Strength Test
1.Use a core drill to remove three, 3 inch diameter samples from the center of the test panel, at least 5 inch clear of the edges.
2.Remove the test specimens at least 21 calendar days and no more than 26 calendar days age.
a.Coordinate timing of specimen removal, delivery and testing with the Engineer.
3.Store cores in watertight plastic bags and label with the project number, test panel number, date of placement, and name of nozzle operator.
4.Deliver cores to the Department for testing immediately after removal .
3.2 Surface Preparation
A.Prepare shotcrete application surface according to the following:
1.Remove loose material, mud, rebound, and other foreign matter.
2.Clear any vegetation or organic material from the surface.
3.Remove curing compound on previously placed shotcrete surfaces by sandblasting.
4.Install depth gages on 4 f t centers longitudinally and vertically to indicate the thickness of shotcrete layers.
5.Dampen natural excavated surfaces immediately before shooting.
a.Remove standing water before shooting .
6.Achieve saturated surface dry condition on shotcrete surfaces.
3.3 Application
A.Limitations
1.Do not apply shotcrete during adverse weather including rain, snow, and high winds without adequate protection authorized by the Engineer .
2.Cease placement operations when the ambient temperature drops below 50 degrees F .
B.Use authorized nozzle operators and approved mix designs.
C.Apply shotcrete in one or more layers.
1.Apply shotcrete within discharge time limit indicated in the approved mix design.
2.Make the surface of each shotcrete layer uniform and free of sags, drips, or runs.
3.Limit the layer thickness to 3 inch per application with no sloughing or sagging.
4.Broom or scarify the applied surface and allow the layer to harden if additional thickness is required.
5.Remove laitance, loose material, and rebound.
a.Promptly remove rebound from the work area.
6.Construction Joints
a.Taper construction joints at an approximately 45 degree angle from the receiving surface.
b.Form joints by cutting plastic shotcrete. Roughen shotcrete in the joint face while it is still plastic.
3.4 Curing
A.Apply curing compound to shotcrete surfaces which are exposed in their final condition.
1.Apply at twice the rate indicated for formed surfaces recommended by the manufacturer .
B.Cure for at least 7 consecutive days or the time necessary to attain 70 percent of the specified 28 day minimum compressive strength, whichever period is less.
1.Immediately repair damage to the curing compound film during the specified curing period by re- spraying.
Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 303–308 of 1,331.