Section 566 — Shotcrete

Description

566.01This work consists of constructing shotcrete on a prepared surface. This work also consists of installing shotcrete drainage systems.

Material

566.02Conform to the following Section and Subsections: Concrete curing material and additives 711 Geocomposite drain 714.02 Hydraulic cement 701.01 Pozzolans 701.03 Reinforcing steel 709.01 Shotcrete aggregate 703.16 Water for cementitious materials 725.01(a)

Construction Requirements

566.03Qualifications. Provide an on- site supervisor and nozzle operators with experience placing shotcrete. A t least 30 days before starting shotcrete work, s ubmit the following for approval:

(a)On-site supervisor. A résumé describing experience on at least five shotcrete projects of similar complexity within the past 5 years. Include project names, locations, and contact information for project owners; and

(b)Nozzle operator. A r ésumé describing experience in shotcrete construction on at least three projects with similar complexity within the past 3 years. Include a n ACI nozzle operator certification in the processes and orientations in which shotcrete will be applied.

566.04Compositi on (Shotcrete Mix Design). Design and produce shotcrete mixtures that conform to Table 566-1 and ACI 506.2, Specification for Shotcrete . Submit the following for approval at least 30 days before preconstruction testing:

(a)Proposed shotcrete mix design with mix proportions and aggregate grading;

(b)Dosage of admixtures. Do not mix chemical admixtures together in a mix unless they are compatible. Provide supporting documentation of compatibility from the manufacturers;

(1)Air-entraining adm ixtures. Entrained air may be obtained with either air -entraining hydraulic cement or air -entraining admixture.

(2)Set accelerating admixtures. Do not use chloride accelerators. Do not use set accelerating admixtures in prestressed concrete applications.

(3)Hydration stabilizing admixtures. Hydration stabilizing admixtures may be used to extend the allowable delivery time for concrete. Determine dosage required to stabilize shotcrete using 577 job site material, field trial mixtures, and admixture manufacturer’s reco mmendations. Changes to dosage rates to meet changing job site conditions is allowed. Include the design discharge time limit. The maximum allowable design discharge time is 3½ hours;

(c)Representative samples of shotcrete material, if requested;

(d)Test results conforming with Table 566-1;

(e)Material certifications;

(f)Fiber samples and method for adding the fibers to the shotcrete, if used;

(g)When an integral color admixture is specified, prepare five 2 - by 2- foot test panels. Construct the test panels using the proposed mix design. Determine coloring agent batch amounts by weight. Provide color charts representing available color selections for shotcrete material in a range of dark, earth -tone colors representative of natural features found in the local landscape. Provide additional mixing time according to the manufacturer’s recommendations. Cure the test panels similar to the structure. Transport the panels to an approved location. Provide at least 2 weeks outside exposure. The CO will select the acceptable test panel. Use the same rate of integral color admixture for the item of work;

(h)Proposed equipment and method for applying shotcrete. Conform to the equipment requirements in ACI 506R, Guide to Shotcrete ;

(i)Proposed methods of shotcrete pla cement, installing depth gauges for maintaining shotcrete thickness, and for properly curing the applied shotcrete layers;

(j)If applicable, the proposed construction method, sequence, and schedule for shotcrete drainage system elements. Include the following :

(1)Proposed weep hole drilling methods and equipment. Include drill rod sizes and bit diameters ;

(2)Catalog cuts, brochures, or other descriptive literature describing the materials and equipment to be used in the installation of shotcrete drainage system elem ents;

(3)Proposed method to access the weep hole locations with the drill equipment; and

(4)Proposed methods for cleaning weep holes, protecting them during shotcrete applications , and reopening them after shotcrete has set.

(k)Other information necessary to verify compliance with ACI 506.2, including steel reinforcement plan for each area, when applicable. Table 566-1 Composition and Property Requirements of Shotcrete Mixtures

Type of

Shotcrete

Mixture Maximum

Water -

Cementitious

Material

Ratio Air

Content

AASHTO T 152 Minimum 28-Day

Compressive

Strength, f 'c, ASTM C1604 , pounds per square inch ,(1) Maximum

Boiling

Absorption,

ASTM

C642, percent Maximum

Permeable

Void

Volume,

ASTM C642 , percent Minimum Core

Quality

Evaluation

ACI 506.6T(2) Maximum

Water -Soluble

Chloride Ion

Content,

ASTM C1218, percent by mass of cement Wet 0.50 – 4000 9 17 Satisfactory 0.15 Wet (AE) 0.45 Grading A 7±1.5%

Grading B

6±1.5% 4000 9 17 Satisfactory 0.15 Dry 0.40 – 4000 9 17 Satisfactory 0.15

(1)Calculate mean compressive core strength as the average strength of at least three individual cores taken from the same n onreinforced test panel. Provide a minimum mean core strength of 0.85 f'c for the arithmetic average of any three consecutive cores with no individual core less than 0.75 f' c.

(2)Use a group of at least three cores taken from the same reinforced test panel to complete evaluation.

566.05Production Start -Up Procedures. Conduct preconstruction shotcrete field trials before starting shotcrete production. Preconstruction test panels are required for each production nozzle operator. Prepare and cure test panels according to ASTM C1140. Construct steel or wood test panel forms contai ning no reinforcement with a width and length of at least 24 inches and a depth matching the design shotcrete thickness with either square or sloped sides. When shotcrete is to be applied over reinforcement or on natural ground and rock, construct addition al steel or wood test panel forms containing reinforcement with a width and length of at least 30 inches and a depth of at least 3 inches with either square or sloped sides. Use reinforcement of the same size and spacing or include the fiber reinforcement required for the project. Demonstrate the procedure for adding fibers with uniform distribution to the shotcrete in the field for approval during preconstruction testing. Shoot test panels using the personnel, material, equipment, operating pressures, and mix designs approved for the project. Produce test panels for each approved mix proportion, each anticipated shooting orientation, and each proposed nozzle operator. When shotcrete is applied over reinforcement, or with reinforcing fibers, evaluate at least three cores from each reinforced test panel according to ACI 506.6T, Visual Shotcrete Core Quality Evaluation, between 14 and 28 days after shooting. Repeat the preconstruction testing process until an acceptable test panel is produced. If a nozzle operator’ s test panel is rejected due to quality evaluation, a second panel may be shot. If the nozzle operator’s second test panel is rejected due to quality evaluation, that nozzle operator is not allowed to shoot shotcrete on the project. Sample material and test according to ACI 506.2 and Table 566-2. Submit reports with the test data and results. Include the following information in the reports:

(a)Date and time of test panel shooting. Include panel dimensions, size and spacing of rei nforcement, when used, and type of curing;

(b)Test panel identification. Include panel number, shooting orientation, mix proportions, and nozzle operator;

(c)Date, time, method of panel coring, number of test samples obtained from each panel and sample preparati on methods;

(d)Test sample identification by panel number, sample number, and sample dimensions; and

(e)Date, time, and types of tests performed. Approval of the nozzle operator and placement operations will be based on preconstruction field trials and test resu lts. Start production only after the test panel is approved. 580 566.06 Shotcrete Construction. Produce shotcrete according to ACI 506.2 and the following:

(a)Surface preparation. If shotcrete is to be placed over existing concrete or rock, remove loose or deteriorated material from the existing surface by chipping with pneumatic or hand tools. Cut shoulders approximately 1 inch deep along the perimeter of repair areas on existing concrete. Remove curing compound on previously placed shotcrete surfaces by sandblasting or other approved method. Maintain prepared surfaces in a clean condition. Install approved depth gauges to indicate the thickness of the shotcrete layers. Install depth gauges on 3- foot centers longitudinally and transversely. When applying shotcrete to soil, thoroughly clean the area of loose material with compressed air and compact the soil to provide a firm face for application. Apply water to surfaces 2 to 24 hours before application to provide a saturated surface dry condition. Remove surfa ce water before placing shotcrete.

(b)Reinforcing. Install reinforcing steel as shown in the plans. Support the reinforcing steel by installing anchor studs or bolts in the existing surface. Do not displace reinforcing steel during shotcrete application. Space supports at no more than 12 inches on overhead surfaces, 18 inches on vertical surfaces, and 36 inches on top of horizontal surfaces. Use at least three supports in each area. Reinforce areas where the planned shotcrete thickness exceeds 1½ inches. Place reinforcement parallel to the proposed finished surface. Support reinforcement at least ½ inch from the existing surface. Provide at least 1 inch cover over steel items including anchors and reinforcement.

(c)Temperature and weather conditions. Conform to Subsection 552.07. Limit expected evaporation rate to less than 0.2 pound per square foot per hour as determined by Figure 552-1. If the ambient conditions (relative humidity, wind speed, air tempera ture and direct exposure to sunlight) cause the shotcrete to develop plastic shrinkage or early drying shrinkage cracking, suspend shotcrete application. Reschedule the work to a time when more favorable ambient conditions prevail; or adopt corrective measures as required by Subsection 552.07(c) . Do not place shotcrete against frozen surfaces. Place shotcrete when the surface and ambient temperature is at least 40 °F and rising.

(d)Shotcrete application. Apply shotcrete according to ACI 506.2 and the following:

(1)Use the same nozzle operator that produced approved test panels.

(2)Apply shotcrete within 45 minutes of adding cement to the mixture unless an approved hydration stabilizer is used. If a hydration stabilizer is appro ved, deliver and place the shotcrete within the approved design discharge time limit, up to 3½ hours maximum.

(3)If fibers are added at the nozzle, uniformly distribute the fibers throughout the shotcrete without isolated concentrations. If fibers are added t o the dry or wet mix process, use a screen having a mesh of 1½ inches to 2½ inches to prevent any fiber balls from entering the shotcrete line unless it is demonstrated that fiber balls are not being formed without a screen. Do not add fibers to the dry or wet mix at a rate faster than can be blended with the other ingredients without forming balls or clumps. Pass bulk fibers that tend to tangle together through a vibrating screen or sift them into the mix, so they enter as individual elements and not as cl umps. 581 (4)Limit the thickness of each shotcrete layer to no more than 2 inches. Thicker layers may be approved if no sloughing or sagging is occurring. If additional thickness is required, broom or scarify the applied surface and allow the layer to harden. Provide a saturated surface dry conditionbefore applying an additional layer. (5)Remove laitance, loose material, and rebound. Promptly remove rebound from the work area. Do not incorporate rebound or slumped shotcrete into final shotcrete.(6)Taper construction j oints to a thin edge over a distance of at least 12 inches. Wet the joint surface before placing additional shotcrete on the joint. Do not use square construction joints.(7)Construct nonreinforced test panels for each mixture, each workday conforming to Table 566-2. Cure test panels according to ASTM C1140 for mixture properties testing. Construct steel or wood test panel forms to a minimum width and length of 24 inches and a depth matching the design shotcrete thickness with either square or sloped sides.(8)Finish shotcrete as shown in the plans. If no method is specified, finish according to ACI 506.2. If penetrating stain is required, apply according to the manufacturer’ s recommendations.

566.07Curing Shotcrete. Cure shotcrete for at least 7 days. Do not use liquid membrane curing compounds for intermediate shotcrete surfaces or if a stained or finished final surface is required. Cure by one of the following methods: (a)Ponding or continuous sprinkling; (b)Covering with an absorptive mat or sand that is kept continuously wet; (c)Covering with impervious sheeting material; or (d)Liquid membrane curing compound. Apply twice the rate for formed surfaces as recommended by manufacturer if the surface is a gun finish.

566.08Production Report. Submit a written report within 24 hours of shotcrete work for each shift. Include the following information: (a)Quantity and location of shotcrete applied. Include photos of areas before and after the shotcrete was placed; (b)Observations of success or problems of equipment operation, application, final product condition, and other relevant issues during production and application; (c)Batch tickets if applicable; (d)Name of nozzle operator; and (e)Name and signature of person performing the observation.

566.09Defective S hotcrete. Repair shotcrete surface defects as soon as possible after placement. Remove and replace shotcrete that exhibits segregation, honeycombing, lamination, voids, or sand pockets. 582 Make changes to the mix, crew, equipment, or procedures, as needed to obtain satisfactory results, before resuming work. Shoot additional test panels and demonstrate that the shotcrete in the panels satisfies the specified requirements.

566.10Shotcrete Drainage Systems. Install strip drains, collector systems, and weep holes as shown in the plans. Provide equipment that can drill straight, uniform -diameter weep holes to the diameter and length shown in the plans. Holes may be advanced by rotary, percussion, down-the- hole hammer, or using other drilling methods suitable for advancing the drill tools to the depth and at the alignment specified. Do not use water or drilling slurry. Drill weep holes to the minimum depths shown in the plans, and within 6 inches of the required location. Adjust weep hole lengths and locations as directed. Drill weep holes perpendicular to rock faces with a minimum inclination of 5 degrees upward unless otherwise shown in the plans, or as directed. Do not drill weep holes within 15 feet (horizontal and vertical) of any grouted rock reinforce ment elements until the grout has set at least 12 hours. Upon completion of drilling, clean drill holes of cuttings, sludge, and debris using compressed air. Drill weep holes after rock reinforcements are installed, if applicable, and before shotcrete is a pplied. Protect weep holes during application of shotcrete and reopen them after the shotcrete has set. Do not drill weep holes through shotcrete. Provide equipment that can install collector systems, including strip drains, as shown in the plans. Install strip drains after installation of rock reinforcement and weep holes and before the application of shotcrete. Provide additional drainage measures, as needed, in addition to the described pattern or adjust the spacing of the weep holes as directed to allow proper drainage of any observed springs or seeps exposed as surface preparation proceeds.

566.11Acceptance. See Table 566-2 for sampling, testing, and acceptance requirements. Material for shotcrete will be evaluated under Subsections 106.02 and 106.03. Submit a production certification with each shipment of hydraulic cement. The shotcrete mixture ’s air content, density, boiling absorption, and permeable void volume will be evaluated under Subsections 106.02 and 106.04. Compressive strength will be evaluated under Subsection 106.05. Construction of shotcrete will be evaluated under Subsections 106.02 and 106.04. Shotcrete drainage system elements will be evaluated under Subsection 106.02.

Measurement

566.12Measure the Section 566 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring shotcrete by the cubic yard, measure in place. When measuring shotcrete by the square yard, measure the plane parallel to the finished shotcrete surface.

Payment

566.13The accepted quantities will be paid at the contract price per unit of measurement for the Section 566 pay items listed in the bid schedule, except the shotcrete contract price will be adjusted according to Subsection 106.05. P ayment will be full compensation for the work prescribed in this Section. See Subsection 109.05. Payment for shotcrete will be made at a price determined by multiplying the contract price by the compressive strength pay fac tor. Table 566-2 Sampling, Testing, and Acceptance Requirements

Material or

Product

(Subsection) Type of

Acceptance

(Subsection) Characteristic Category Test Methods

Specifications Sample

Frequency Point of

Sampling Split

Sample Reporting

Time Remarks

Source

Aggregate

quality (703.16 ) Measured & tested for conformance (106.04 & 105) Quality – Subsection

703.161 per material type Source of material Yes Before producing –

Mix Design

Shotcrete

composition Measured & tested for conformance (106.04) All – Subsection

566.041 per mix design Source of material No Before producing – Production Start -up (Test Panels)

Shotcrete

composition Measured & tested for conformance (106.04 ) Boiling absorption & permeable void volume(2) – ASTM C642(1),(2) 1 set per test panel (unreinforced) Test panels No Before producing – Density – AASHTO T 121 1 per load Shotcrete machine(5) " " –

Compressive

strength – ASTM C1604(1),(3) 1 set per test panel (unreinforced) Test panels Yes 28 days –

Core quality

evaluation – ACI 506.6T 1 set per test panel(4) (reinforced) Test panels No 14 to 28 days after shooting – Table 566- 2 (continued) Sampling, Testing, and Acceptance Requirements

Material or

Product

(Subsection) Type of

Acceptance

(Subsection) Characteristic Category Test Methods

Specifications Sample

Frequency Point of

Sampling Split

Sample Reporting

Time Remarks

Production

Aggregate

(fine & coarse) Measured & tested for conformance (106.04 ) Gradation – AASHTO T 27 & T 11 1 per day Flowing aggregate stream (bin, belt, discharge conveyor belt, or stockpile) Yes, If requested Before batching – Moisture test – AASHTO T 255 " " " " –

Shotcrete Measured &

tested for conformance (106.04 ) Boiling absorption & permeable void volume(2) – ASTM C642(1),(2) 1 set per 50 yd3 but not less than 1 per job Production test panels Upon completing tests – Density – AASHTO T 121 1 per load Per

Shotcrete

machine(5) – " –

Air content

(wet mix only) – AASHTO T 152 " " – " –

Statistical

(106.05) Compressive strength II ASTM C1604(1),(3) 1 set per 30 yd3 but not less than 1 per day Production test panels Yes 28 days –

(1)Core 3- inch diameter samples at least 14 days after the field trial and moisture condition in sealed plastic bags or nonabsorbent containers according to ASTM C1604. As directed, deliver Government cores to the designated laboratory for testing.

(2)Test a t least three samples from each nonreinforced test panel between 14 and 28 days after shooting. Samples may consist of cores or pieces of cores.

(3)Test at least three 3 -inch diameter moisture conditioned cores from each nonreinforced test panel 28 days a fter shooting.

(4)Use a group of least three 3 -inch diameter cores, taken from the same reinforced test panel at least 14 days after shooting, to complete evaluation.

(5)Obtain samples of shotcrete material according to ASTM C1385.