519Shotcrete

519.1 Description

This Work consists of construc ting a pneumatically applied non- structural shotcrete onto rock, soil or structural shotcrete onto formed surfaces in acco rdance with the Contract and as directed by the Project Manager. These Specifications refer to premixed cement and aggregate pne umatically applied by suitable Equipment and competent operators.

519.2 Materials

Structural shotcrete shall have a design strength of 4000 psi at 28 Days. If structural shotcrete is required, the Contractor shall use a shotcrete mix that has been designed and proportioned in accordance with Section 509, “Portland Cement C oncrete Mix Designs” and complies with the designated hardened properties for the class of concrete required in the specifications. All mix consti tuents must comply with Table 51 9.2:1, “Applicable Specification Sections.” The Contractor shall determine all hardened propert ies in accordance with Section

519.2 6, “Acceptance Sampling and Testing.”

Non-structural shotcrete shall have a design strength of 3000 psi at 28 Days. If the shotcrete is non-structural, the non-structural shotcrete mix d esign may be developed in accordance with Section 509, “Portland Cement Concrete Mix Desi gns” without using the special boxes required in Secti on 519.2.6, “Acceptance Sampling and Testing.” All shotcrete mix designs must be reviewed and approved by the State Concrete Engineer before being used on NMDO T Projects. The Contractor s hall use either wet-mix or dry-mix shotcrete. The Contract or shall reinforce shotcrete in accordance with the Contract. The Contractor shall provide Materials and perform constructio n requirements in accordance with the specificati on sections listed in Table 519. 2:1, “Applicable Specification Sections.” Table 519.2:1 Applicable Specification Sections Material/Construction Requirements Section Portland cement Section 509, “Portland Cement Concrete Mix Designs” Fly Ash Section 509, “Portland Cement Concrete Mix Designs” Pozzolans Section 509, “Portland Cement Concrete Mix Designs” Curing Materials and Admixtures Section 509, “Portland Cement C oncrete Mix Designs” Water Section 509, “Portland Cement Concrete Mix Designs” Fine Aggregate Section 509, “Portland Cement Concrete Mix Designs” Coarse Aggregate Section 509, “Portland Cement Concrete Mix Designs” Neat Cement Grout Section 521, “Non-Shrink Mortar” Applicable Specification Sections Material/Construction Requirements Section Bar Reinforcement Section 540, “Steel Reinforcement” Welded Wire Fabric Section 540, “Steel Reinforcement” Surface evaporation Section 512, “Superstructure Concrete”

519.2.1 Fine Aggregate Quality Requirements

The Contractor shall provide fine aggregate with the following properties: 1. A soundness Loss of 12 or less when tested in accordance wit h AASHTO T 104 using magnesium sulfate solution and a test duration of five (5 ) cycles; and 2. A sand equivalent of at least 75 when tested in accordance w ith AASHTO T 176.

519.2.2 Fine Aggregate Gradation Requirements

Fine aggregates shall comply with Table 519.2.2:1, “Fine Aggreg ate Gradation” for either Grading No.1 or Grading No. 2. Table 519.2.2:1 Fine Aggregate Gradation Sieve Size, U.S. Standard Square Mesh Percent by Weight Passing Individual Sieves Grading No.1 Grading No.2 ¾ inch (19 mm) --- --- ½ inch (12 mm) --- 100 3/8 inch (10 mm) 100 90 to 100 No. 4 (4.75 mm) 95 to 100 70 to 85 No. 8 (2.4 mm) 80 to 98 50 to 70 No. 16 (1.2 mm) 50 to 85 35 to 55 No. 30 (600 µm) 25 to 60 20 to 35 No. 50 (300 µm) 10 to 30 8 to 20 No. 100 (150 µm) 2 to 10 2 to 10

519.2.3 Water

The Contractor shall use water in the shotcrete mix that is fre e of elements that could stain the mix and in accordance with Section 509.2.6, “Water.”

519.2.4 Anchor Bars

The Contractor shall provide anchors of appropriate size to hol d reinforcement in place. The Department will allow maximum anchor spacing of 24 inches o n a grid pattern over the entire area for structural applications. Section 519: Shotcrete Page 414 If using “ L”-shaped anchors, the Contractor shall use those that consist o f No. 5 reinforcement bars (or larger) bent into an “ L” shape. The short leg of the “ L” will be at least six (6) inches long and the long leg at least two (2) feet long .

519.2.5 Welded Wire Mesh

The Contractor shall provide non- galvanized eight (8) gauge ste el with a four

519.2.6 Fiber Reinforcement

Synthetic Fibers shall meet the requirements of ASTM C1116. Steel fibers should meet the requirements set forth in ASTM A82 0.

519.2.7 Prepackaged Product

For non-structural shotcrete; a pre-mixed and prepackaged concr ete product, with or without steel fibers, specifically manufactured as a shotcrete product for on-site mixed shotcrete, may be used if approved by the State Materials Burea u. The Material shall meet the requirements of ASTM C1480 and have a minimum strength of 3 ,000 psi at 28 Days for non-structural Shotcrete.

519.2.8 Acceptance Sampling and Testing for Structural and non- structural Shotcrete

The Contractor shall apply shotcrete to approved test panels. The Contractor shall orient the spray nozzle to the test panel in the same position as that used on the actual Project. The Contractor shall provide test panels constructed in accordance with the requirements of ASTM C 1140. The Contractor shall use test panels with the fol lowing characteristics: 1. Minimum dimensions of 30 inch² × eight (8) inch deep; 2. Constructed from wood and sealed plywood; and 3. 45° sloped sides to allow rebound to escape. The Contractor shall use at leas t one (1) pre-construction tria l to do the following: 1. Obtain test cores to confirm compliance with the hardened pr operties of Section 510, “Portland Cement Concrete.” 2. For structural Shotcrete only, pre-qualify the proposed nozz le operator and strike-off persons. The Department will not allow nozzle operators and st rike-off persons who have not been pre-qualified to apply shotcrete on the Project. Each nozzle operator and strike-off person shall shoot pre-construction test panels in the presence of the Project Manager or designated repr esentative. Each nozzle oper ator shall have a minimum of the following qualifications: 2.1. Supervisor, at least one (1) year of experience as a shotc rete nozzle operator and at least two (2) years of exper ience on shotcrete Projects. 2.2. Nozzle operator and delivery Equipment operators, at least one (1) year of apprenticeship on similar applications with the same type of Eq uipment. 2.3. Nozzle operators shall be ACI Certified Shotcrete Nozzle O perators. Section 519: Shotcrete Page 415 The Contractor shall perform curing, coring, and testing of the shotcrete test panels and specimens at a private testing Laboratory approved by the State Materials Bureau for concrete mix designs. The Contractor shall provide one half of the test panels with r einforcement and anchors representative of the same size and spacing required in the Con tract for the actual Work. The Contractor shall provide the remaining panels with no reinforce ment to allow for extraction of shotcrete test cores for compliance testing. Each nozzle operator proposed for use on the Project shall shoo t at least one (1) test panel at each orientation. The Contractor shall obtain the required number of test cores i n accordance with Section 510, “Portland Cement Concrete,” from these test panels for testing at the designated ages for the specified performance parameters. The Contractor shall extract a minimum of three (3) four (4) inch diameter cores from locations of inters ecting reinforcing steel and mesh to check the adequacy of consolidation of shotcrete around and behind the reinforcement. The Contractor shall take at least one (1) core at an anchor lo cation. The State Materials Bureau will evaluate the quality of the ext racted cores and test panels. If the Department rejects a prequalification test pane l, the Contractor shall have the nozzle operator shoot a second test panel. If the Department r ejects the second test panel, the Contractor shall not allow the nozzle operator to shoot on the Project until the operator completes an appropriate training program and prepares an accep table test panel. The Contractor shall transport test panels in the wooden forms with care to not crack or damage the specimens. The Contractor shall place the test panels in a moist room in t he Laboratory that is maintained at a temperature of 73 °F ± 3 °F, and a relative hum idity of 98 ± two percent (2%). After three (3) Days, the Contractor shall remove the test pane ls from the wooden forms and return them to the moist room until testing time.

519.2.8 1 Production Testing for Structural Shotcrete

The Contractor shall shoot two (2) construction test panels for each nozzle orientation and for each nozzle operator each Day of shotcrete production i n the presence of the Project Manager. The Contractor shall shoot one (1) set of panels for each nozzle operator in the morning and one (1) set of panels for each nozzle operator in t he afternoon for a full Day’s production. The Contractor shall produce test panels in accordance with AST M C 1140, a minimum 12 inch² × eight (8) inch deep. The Contractor shall use test panels constructed of wood and sealed plywood with 45° sloped si des to permit escape of reboun d. The Contractor shall provide construction test panels that contain no reinforcement or embedments. The Contractor shall store, handle, and cure construction test panels the same as specified for pre-c onstruction test panels. The Contractor sha ll prepare test specimens the same as specified for pre- construction test specimens. The Contractor shall use compressive strength test specimens th a t a r e f o u r

519.3 Construction Requirements

519.3.1 Equipment

519.3.1 1 Shotcrete Placing Equipment

The Contractor shall apply wet mix shotcrete with one (1) of th e following methods: 1. The “thick-stream” method, which involves the use of a regul ar concrete pump with air addition at the discharge nozzle to pneumatically apply the shotcrete on the receiving surface. The “thick-stream” method usually uses a tw o (2) inch to 2 1/2 inch internal diameter delivery hose. 2. The “thin-stream” method, which normally involves the use of a pressurized chamber to pneumatically send the shotcrete down the delivery h ose to the receiving surface. The “thin-stream” method normally uses a ho se with a maximum 1 1/2 inch internal diameter. The Contractor shall only use the “thin-stream” method for non- structural shotcrete if pre- construction testing confirms the capability to properly consol idate shotcrete, fully encase reinforcing steel, and produce a Material that meets the requir ed hardened properties. The Contractor shall use shotcrete delivery Equipment in accord ance with ACI 506R and that is capable of delivering a steady stream of uniformly mixe d Material to the discharge nozzle at the proper velocity and rate of discharge. The preferred type of the wet-mix shotcrete delivery system use s positive displacement pumps equipped with hydraulic or mechanically powered pistons ( similar to conventional concrete piston pumps), surge -reduction devices, and compressed air added at the discharge nozzle. The Contractor may use pneumatic-feed guns, rotary-typ e feed guns (similar to dry- mix guns), and peristaltic squeeze-type pumps if the Contractor demonstrates that the guns can produce shotcrete in accordance with the performance requir ements and the Project Manager approves. The Contractor shall carefully monitor the air ring at the nozz le for signs of blockage of individual air holes. If non-uni form discharge of shotcrete be comes apparent, the Contractor shall stop shooting and clean the air ring or take other approp riate corrective actions. The Contractor shall thoroughly clean the delivery Equipment at the end of each shift. The Contractor shall remove build-up of coatings in the deliver y hose and nozzle liner. The Contractor shall regularly i nspect the air ring and nozzle and replace as necessary.

519.3.1 2 Auxiliary Shotcrete Equipment

The Contractor shall supply a clean, dry air supply capable of maintaining sufficient nozzle velocity and simultaneous operation of a blow pipe. The Contractor shall use an air supply system with a moisture a nd oil trap. The Contractor shall provide auxiliary shotcrete Equipment, suc h as air delivery hoses, blow pipes, couplings, admixtu re dispensers, and fiber feeders, in accordance with the

519.3.2 Batching and Mixing Shotcrete

519.3.2 1 Wet Mix Process

The Contractor shall batch, mix, and supply wet mix shotcrete u sing one (1) of the following systems: 1. Central Mixing with transit delivery; or 2. Transit mixing and delivery.

519.3.2 1.1 Central Mixing and Supply

The Contractor shall batch and mix ingredients in accordance wi th Section 510, “Portland Cement Concrete.” The Contractor shall provide inspected trans it mixers in accordance with Section 510, “Portland Cement Concrete.” The Contractor may only re-temper the shotcrete once with super plasticizer added directly to the transit mixer during the period of discharge to maintain workability (slump) of shotcrete. The Contractor shall mix the shotcrete for a minimu m period of five (5) min at the rated mixing speed after adding the superplasticizer to the tra nsit mixer. The Contractor shall shoot shotcrete within 90 min of adding mi x water to the batch. The Contractor shall use appropriate shotcrete batch sizes per load to meet this requirement.

519.3.2 1.2 Transit Mixing and Supply

The Contractor shall apply central mixing requirements to trans it mixing, except add ingredients directly to the transit mixer, not the central mixe r. The Contractor shall not charge transit mixers to more than 70% of their rated capacity.

519.3.2 2 Dry Mix Process for Non-Structural Shotcrete

The Contractor shall batch the cement and aggregate by weight d irectly at the Project site within the tolerances requi red in Section 510, “Portland C ement Concrete.” The Contractor shall pre-dampen the dry mix before flow into th e main hopper and immediately after flow out of t he packaging to ensure uniform s hotcrete free of dry pockets. The Contractor shall not use pre-dampened cement/aggregate mixt ures that are more than 90 min old or that are unable to produce the specified har dened properties.

519.3.2 3 Batching and Mixing Steel Fibers

The Contractor shall submit the procedure used for adding steel fibers to the shotcrete to the Project Manager for approval. The Contractor shall demonst rate the procedure in the field to the satisfaction of the Project Manager before starting prod uction operations. If fiber addition takes place at the nozzle, the Contractor sha ll uniformly distribute fibers throughout the mortar matrix with out isolated concentrations (c lumping or balling). If adding fibers to the dry or wet mix during the batching and mixing process, the Contractor shall use a screen with a mesh of from 1 1/2 inch to 2 1/2 inch to prevent fiber balls from entering the shotcrete line. The Department will not requ ire batching through a screen if Section 519: Shotcrete Page 418 the Contractor demonstrates that fiber balls are not forming. The Contractor shall not add fibers to the dry or wet mix too q uickly (so they can be blended with the other ingredients without forming balls or clu mps). The Contractor shall use a vibrating screen or sift to pass bulk fibers (that have a ten dency to stick) into the mix as individual elements and not as clumps.

519.3.2 4 Preparation and Hardware

519.3.2 4.1 Subsurface Preparation

The Contractor shall locate and remove loose, spalled, deterior ated, and delaminated concrete, stone, or other substrate. The Contractor shall use hammer sounding to locate specific de-laminated areas of concrete or rock. The Contracto r shall not damage areas of sound concrete or reinforcing st eel during concrete removal ope rations. The Contractor shall remove concrete using one (1) or more of t he following methods: 1. Chip with light duty pneumatic , or electric, chipping hammer s (not to exceed 15 lb). 2. Scarifiers, scabblers or oth er suitable mechanical means. 3. High-pressure (15,000 psi to 40,000 psi) water jetting. (If using water jetting, do not allow water to collect so tha t surrounding areas are not contam inated or damaged.) If the Contractor exposes corroded reinforcing steel, the Contr actor shall continue concrete removal until there is a minimum 3/4 inch clearance ar ound the exposed, corroded reinforcing bar. The Contractor shall not damage the bond to a djacent non-exposed reinforcing steel duri ng concrete removal. The Contractor shall taper the perimeter of removed concrete ar eas at approximately 45° angles. The Contractor shall sawcut the outer edges of chipped areas to a minimum depth of 3/4 inch to avoid feather edging. The Contractor shall use abrasiv e blast cleaning to remove frac tured surface concrete and traces of unsound Material or contaminants, such as oil, gr ease, dirt, slurry or Materials that could interfere with the bond of the freshly placed shotcr ete. The Contractor shall apply shotcrete to abrasive blast cl eaned areas within 48 h or re-bla st them. The Project Manager may waive t he requirement for abrasive blas t cleaning where the Contractor performed concrete removal with high-pressure water blasting and the prepared surface is free of residual slurr y or other Material detrimenta l to an Acceptable shotcrete bond. The Contractor shall install reinforcement in slope blankets th at do not contain steel reinforcement. Unless otherwise specified, the reinforcement w ill consist of No. 4 steel reinforcing bars placed with maximum spacing of 12 inch for ver tical and horizontal bars. The Contractor shall rigidly attach this reinforcement to the under lying forms or concrete Structure. The Contractor shall remove dust, debris, or laitance generated by this process in accordance with these abrasive bla st cleaning procedures.

519.3.2 4.2 Repair or Replacement of Steel Reinforcement

If the Contractor exposes corro ded reinforcing steel during con crete removal, the Contractor shall remove corrosi on using abrasive grit blasting. The Contractor shall remove and replace reinforcing steel displ aying deep pitting or loss of more than 20% of cross-secti onal area as directed by the Pro ject Manager. If pitting is isolated, the Contractor shall reinforce the stee l by adding appropriately placed reinforcing bars of suitable l ength (the existing reinforcing s teel need not be cut).

519.3.2 4.3 Steel Reinforcement

The Contractor shall use a mini mum lap splice length of reinfor cing steel that is in accordance with the AASHTO LRFD Bridge Design Specification . The Contractor shall place these bars in accordance with ACI 506R, Sections 5.4 and 5.5. In particular, the Contractor shall not bundle bars in lapped splices; place them so the mini mum spacing around each bar is three (3) times the maximum aggregate size to allow for prop er shotcrete encapsulation. The Contractor shall tightly secure intersecting reinforcing st eel bars to each other using 12 gauge or heavier tie wire and adequately support them to min imize vibration during shotcrete placement. The Contractor shall place welded wire mesh fabric in accordanc e with the Contract. The Contractor shall lap sheets of adjoining mesh by at least two ( 2) spaces in both directions at intersections, and securely fasten. The Contractor shall fasten mesh to preset or existing anchors and reinforce using 12 gauge or heavier tie wire on a grid not less than 12 inch 2. The Contractor shall avoid large knots of tie wire that could result in sand pockets and voids d uring shotcreting. The Contractor shall provide a minimum clearance of 3/4 inch be hind installed reinforcing steel or mesh and existing concrete forms or bare rock.

519.3.2 4.4 Structural Anchors

Unless otherwise specified in the Contract, the Contractor shal l place anchor bars (for structural applications) at a max imum spacing of 24 inches on a grid pattern over the entire area. The Contractor shall provide the types of anchors in accordance with the Contract and either mechanically set or grout, as specified. The Contractor shall ensure anchors develop the minimum pullout force in accordance with the Contract. The Contractor shall randomly test anchors at a frequency in accordance with the Contract to verify pullout force. The Department will not accept a pull out force less than 150 lb. If anchors fail to meet the minimum acceptable pu llout value, the Contractor shall remove and replace immediately and take corrective action. Als o, the Contractor shall test the anchors in the same relative location as those that failed. Th e Project Manager will determine the area for corrective measures.

519.3.2 4.5 Non-Structural Anchors

For non-structural applications ( slope blankets, etc.), the Con tractor shall install anchor bars at ten (10) foot centers on a grid pattern over the entire area in one (1) inch diameter holes drilled into the rock or soil approximately 24 inches dee p. The Contractor shall completely fill the drilled hole with neat cement grout using a grout tube extending to the bottom of the hole. The Contractor shall push the anchor bar into the grout-filled hole and center it such that the short leg of the “L”-shaped bar points upward and parallel to the slope and is located Section 519: Shotcrete Page 420 approximately 1 1/2 inches from the rock or soil surface.

519.3.2 4.6 Weep Holes

For slope blankets, the Contractor shall provide weep holes thr oughout the shotcrete mat on maximum ten (10) foot centers, horizontally and vertically. The weep hole drains will consist of two (2) inch diameter Sche dule 40 PVC slotted drainpipe, two (2) feet in length, placed within predrilled hol es and sloped five percent (5%) to drain. The exposed end will extend from one (1) inch to three (3) inch outside the slope. The Department will not allow pr e-drilled holes with diameters larger than three

519.3.2 4.7 Alignment Control and Cover

The Contractor shall implement alignment control (to establish control over line and grade), and maintain the minimum s pecified shotcrete thickness and cover of reinforcing steel. The Contractor shall perform alignment control with shooting wi res (also called ground wires), guide strips, depth gauges, or forms. The Contractor s hall submit the proposed means of alignment control to the Project Manager for review and appr oval. The Contractor shall use shooting wires that are at least “pian o wire”–sized high-strength steel wire combined with a turnbuckle and spring coil. The Con tractor shall remove shooting wires after completion of shotcreting and screeding operations. The Contractor shall not let guide strips and forms impede the ability of the nozzle operator to produce uniform, dense, properly consolidated shotc rete. The Contractor shall not use alignment control Material th at causes the formation of san d-pockets and voids. If using depth gauges for alignment control, the Contractor sha ll space no greater than four (4) ft in a grid pattern. The Contractor shall cut back m etal depth gauges to 1/4 inch below the finished surface. The Contractor shall cover reinforcing steel in accordance with Section 540, “Steel Reinforcement.”

519.3.3 Quality Assurance and Quality Control Testing

519.3.3 1 Quality Assurance

The Department will implement a Quality Assurance Program for t he shotcrete Work. The program will include the following: 1. Review of Contractor submittals; 2. Review of the approval of Contractor-proposed Materials, sup ply, Equipment, and crew. In particular, evaluati on in the pre-construction testin g program of shotcrete nozzle operator and strike-off person proposed for use on the P roject; the Department will allow only nozzle operators and strike-off pers ons approved in writing by the State Materials Bureau to perform Work; Section 519: Shotcrete Page 421 3. Examination and approval (before application of any shotcret e) of areas prepared for shotcreting, including inst allation of anchors, reinforceme nt, and alignment control devices; 4. Provision of Inspectors to m onitor shotcrete installation an d authority to require removal and replacement of defective shotcrete while still plas tic; 5. Regular monitoring of Quality Control testing results; 6. Implementation of a program for in-place evaluation and Acce ptance or rejection, if test results indicate shotcr ete is unacceptable; and 7. Implementation of a program of remedial Work, if the Quality Assurance Program deems it necessary.

519.3.3 2 Quality Control Testing

The Contractor shall provide an independent testing Laboratory to establish and maintain a Quality Control program for the shotcrete Work to ensure comp liance with Section 519, “Shotcrete.” Such a program will include, but not be limited t o, the following: 1. Maintenance of test records for Quality Control operations; and 2. Physical testing in accordance with Section 519.2.6.1, “Prod uction Testing” for the confirmation of compliance wi th the specified hardened shotcret e properties.

519.3.3 3 Safety and Cleanup

519.3.3 3.1 Preparation

The Contractor shall implement a safety program during preparat ion for shotcreting to do the following: 1. Protect the structural integrity of structural elements (by shoring or other suitable means) during concrete and reinfo rcing steel removal operations . 2. Protect personnel from falling debris, blasting grit, and hi gh-pressure water jets during concrete removal processes. The Contractor shall dispose of debris, blasting grit, and hydr o-demolition and water- jetting slurry in accordance wi th Section 107, “Legal Relations , Environmental Requirements, and Responsibility to the Public.”

519.3.3 3.2 Shotcrete Operations

The Contractor shall implement a safety program using hoarding, shrouds, screens, or other appropriate measures to protect personnel and surrounding property from pneumatically applied shotcrete over-spray and rebound Materials during the s hotcrete application process. Personnel working near the shotcreting operation, including noz zle operator, strike-off persons, nozzle operator’s helper s, supervisors, and Inspectors , shall wear appropriate protective Equipment. Such Equipment includes, but is not limi ted to, safety helmet, safety boots, gloves, appropriate clothing, safety glasses with side e nclosures, and dust masks. Nozzle operator’s helpers shall keep a supply of water, cloth o r towel, and backup safety glasses available for the nozzle operator so satisfactory visio n can be maintained during shooting operations. The Contractor shall provide sufficient l ighting so the nozzle operator has a clear view of the Work. The Contractor shall provide readily available eyebaths and was h facilities in the Section 519: Shotcrete Page 422 immediate vicinity of the shot crete application. The shotcrete crew shall apply appropriate skin protection and adopt Work hy giene to protect against cemen t or accelerator alkali burn. The Contractor shall install sufficient lighting and ventilatio n to provide the nozzle operator and helpers with clear, unhindered view of the shootin g area. The Contractor shall terminate Work and adopt correct ive measures if, in the opinion of the Project Manager, visibility is unsuitable for t he safe application of quality sh otcrete.

519.3.4 Shotcrete Application and Finishing

519.3.4 1 Shotcrete Application

The Project Manager will review and approve areas prepared for shotcrete application before application of shotcrete. The Contractor shall flush surfaces with water at least one (1) hour before application of shotcrete. The Contractor shall allow flushed surfaces to dry back to saturated surface-dry condition before application of shotcrete. If necessary, the C ontractor shall use a blowpipe with oil-free compressed air to facilitate removal of surface w ater. For very porous and dry substrates, the Contractor shall saturate the substrate the Day before shotcreting and then re- wet before shooting as described above. The Contractor shall apply shotcrete in accordance with ACI 506 R, except that if using silica-fume modified shotcrete; the Contractor may apply the fu ll thickness of shotcrete in a single layer. The Contractor shall use the minimum number of l ayers required to build up the full thickness of shotcrete without sagging, separation, or slo ughing. Wherever possible, the Contractor shall apply shotcrete to the full thickness in a sin gle layer. If using multiple-layer shotcrete construction, the Contractor shall prepare the first layer with one (1) of the following methods before applying a subsequ ent layer: 1. Broom the stiffening layer with a stiff bristle broom to rem ove loose Material, rebound, over-spray, or glaze, before the shotcrete attains ini tial set. 2. If the shotcrete has set, Delay surface preparation at least 24 h, then prepare the surface by sandblasting or high-pressure water blasting to remo ve loose Material, rebound, hardened over-spray, glaze, or other Material detrimen tal to good bond. When successive layers of shotcr ete are necessary to build up f ull shotcrete thickness, the Contractor shall prevent the first layer from drying out wi th fogging or wetting. The Contractor shall only use curing compound with the approval of the Project Manager. If using a curing compound, the Contractor shall remove it by abrasive b last cleaning or high-pressure water blasting, before application of the next layer of shotcre te. The Contractor shall clean the first layer of shotcrete of surface water and ensure it is in a saturated surface-dry condition when applying the next shotcrete layer. The Contractor shall exercise car e to protect adjacent surfaces from buildup of rebound and over-spray. The Department will not allow rebound and over -spray on the completed Work. The Contractor shall remove rebound and over-spray from surfaces to receive shotcrete while the Material is still plastic, using blowpipes, scrapers, wire brushes, or other suitable tools. The Contractor shall remove hardened rebound a nd overspray with abrasive blast cleaning, chipping hammers, high-pressure water blasting or other suitable techniques before applying additional shotcrete. The Contractor shall provide scaffolding or other devices so th e nozzle operator and helpers have free, unhindered access to the Work area. The Contractor shall apply shotcrete from the nozzle in accorda nce with ACI 506R. The Contractor shall not apply shotcrete during periods of rain or high wind, unless suitable protection is provided. The Contractor shall apply shotcrete in accordance with the Con tract using shooting wires, depth gauges, guide strips, forms, or other suitable dev ices. The Contractor shall apply the minimum cover of shotcrete to reinforcing steel in accordan ce with the Plans. The Contractor shall cut back metal depth gauges to within 1/4 inch of the shotcrete surface, to prevent corrosion staining of the surface. When applying a 3/8 inch maximum aggregate size shotcrete, the Department will allow a final flash coat layer (¼ inch to ¾ inch thick) using ¼ inch ag gregate shotcrete.

519.3.4 2 Shotcrete Finishing

The Contractor shall leave shotcrete in the natural gun finish unless otherwise specified in the Contract. If the Contract requires finishing, the Contractor shall cut ba ck shotcrete to line and grade using cutting rods, screeds, or o ther suitable devices. The Co ntractor shall allow shotcrete to stiffen sufficiently before cutting and trimming, to prevent th e formation of tears, cracks, and delaminations. The Contractor shall remove shooting wires on c ompletion of cutting and trimming. The Contractor shall apply one (1) or more of the following fin ishes if required: 1. Wood float finish, either as a preliminary finish for other surface treatments, or as a granular texture finish. 2. Rubber float finish, applied to either a flash coat or wood float finish, to produce a finer textured granular finish. 3. Brush finish, a fine hairbrush float finish that leaves a fi nely textured, sandy finish. 4. Steel trowel finish that leaves a dense, smooth hard finish. The Contractor shall trim back shotcrete and over-spray from ad jacent non-prepared concrete surfaces. The Contractor shall provide the edges of s hotcrete repairs with a minimum square saw-cut edge 3/4 inch deep; finish shotcrete up to this edge. The Contractor shall not featheredge shotcrete (including flash coats). 519.3.4.3 Curing and Protection On completion of finishing, the Contractor shall immediately pr event shotcrete from drying out by fogging or wetting. If the Contract requires leaving shotcrete with a natural gun f inish, the Contractor shall apply curing compounds at twice the application rate normally s pecified for smooth concrete finishes. The Contractor shall completely remove curing compou nds by abrasive blasting or water blasting (with a pressure of 3,000 psi) before applicatio n of subsequent sealers. Once the shotcrete achieves its f inal set, the Contractor shall keep it continuously moist for at least seven (7) Days. The Contractor shall perform mois t curing using one (1) or both of the following procedures: 1. Wrap the elements in wet burlap presoaked in water for 24 h before installation; Section 519: Shotcrete Page 424 wrap the wet burlap in plastic sheet to slow the drying rate of the burlap. 2. Install sprinklers, soaker hos es, or other devices that keep the shotcrete continuously wet. Do not use intermittent wetting procedures t hat allow the shotcrete to undergo cycles of wetting and drying during the cu ring period.

519.3.4 4 Hot and Cold Weather Protection

The Contractor shall apply shotcrete during periods of hot and cold weather in accordance with ACI 305R and ACI 306R. If it is anticipated that shotcrete will be placed when the amb ient temperature will fall below 35 °F, a Cold-Weather Shotcrete Plan must be prepared and submitted to the Project Manager at least 30 Days before the intended application. The Cold Weather Shotcreting Plan must be reviewed and approved by the State Concrete Engine er before shotcrete is permitted to be placed at temperatures below 35 °F. The Contractor shall monitor the Surface Evaporation of the Sho tcrete in accordance with Section 512, “Superstructure Concrete.” The Contractor shall n ot proceed with shotcrete application if the average rate of surface evaporation of the s hotcrete over any ten (10) minute period exceeds 0.2 lb per square foot per hour, in accordance w ith Section 512, “Superstructure Concrete.” The Contractor shall not allow the prevailing ambient conditions (relative humidity, wind speed, air temperature, and direct exp osure to sunlight) to cause either plastic shrinkage or early drying shrinkage cracking. All cracked Structural shotcrete, regardless of the cause, shal l be removed and replaced at no cost to the Department. Subsequent efforts to prevent further cracking problems shall i nclude, but not be limited to: 1. Rescheduling of the Work to a time when more favorable ambie nt conditions prevail; and 2. Adopt corrective measures, such as installation of sunscreen s, windbreaks, or fogging devices to protect the Work. During periods of cold weather, shotcreting may only proceed if the substrate to which the shotcrete is applied and the air temperature in contact wit h the shotcrete surfaces are both above 50 °F. The Contractor shall maintain the air temperature in contact wi th the shotcrete surfaces at 60 °F or greater for at least four (4) Days after applicatio n of shotcrete. The Contractor shall submit the means of maintaining the air temperature to the Proj ect Manager for approval. The Contractor shall not use unvented heaters. The Contractor shall apply shotcrete at a temperature of betwee n 50 °F and 90 °F. The Contractor shall use cooler mix temperatures during hot-weather shotcrete operations and warmer mix temperatures during cold-weather shotcrete operation s.

519.3.4 5 Inspection and Remedial Work

The Contractor shall sound the surface of the cured shotcrete w ith a hammer to locate unsound areas. The Contractor shall provide Equipment, hardware, and means nec essary to perform the inspection operations. The inspe ction accommodations are subje ct to the approval of the The Contractor shall cut out and replace sags or other defects with another layer. If welded wire mesh reinforcement is damaged or destroyed by such repairs, the Contractor shall repair the damaged area by overlapping and tying addition al wire mesh in accordance with Subsection 519.3.2.4.3, “Steel Reinforcement.”

519.4 Method of Measurement

The Department will measure shot crete using the dimensions sho wn in the Contract or approved modifications.

519.5 Basis of Payment

Pay Item Pay Unit Structural Shotcrete Square Yard Non-structural Shotcrete Square Yard

519.5.1 Work Included in Payment

The following Work and item(s) will be considered as included in the payment for shotcrete and will not be measured or paid for separately: 1. Reinforcement; 2. Anchors; 3. Slotted pipe; 4. Ties; 5. Test molds; 6. Test samples; 7. Submittals; 8. Boring; 9. Cores; and 10. Grouting. Section 520: Post-Tensioned Conc rete Bridge Members Page 426