641Shotcrete

Shotcrete Description

641.01This work consists of constructing pneumatically applied concrete onto designated

surfaces at locations and thicknesses with the lines and dimensions shown on the plans or as designated by the Engineer.

Materials

641.02Shotcrete proportioning and placement shall comply with the requirements of ACI

506.2, "Specifications for Materials, Proportioning and Application of Shotcrete," and the requirements of Section 601 (Class Shotcrete)

Pre-packaged material shall meet the requirements of ASTM C1480 and meet the sulfate resistance requirements listed in the general notes.

The maximum aggregate size in shotcrete shall be 1/2 inch.

When specified, steel fibers shall be incorporated into the mixture. Steel fibers shall conform to the requirements of ASTM C1116, Type I, Section 4.1.1.

When specified, polypropylene fibers shall be incorporated into the mixture. Polypropylene fibers shall have a nominal length of 3/4 inch and shall conform to the requirements of ASTM C1116, Type III, Section 4.1.3.

641.03Submittals. The following documents and shop drawings shall be submitted per

subsection 105.02. Shotcrete shall not be placed on the project before the submittals have been reviewed and approved by the Engineer.

shall indicate dry-mix process or wet-mix process and shall include drawings and notes describing equipment, procedures and sequences for shotcrete production, application, curing plan, and applicable manufacturer's literature and recommendations. The Shotcrete Application Method Statement shall also include written documentation that verifies the qualifications of the nozzlemen that will be performing the work. All nozzlemen shall have had at least one year of experience in the application of shotcrete and hold a current certification for ACI Shotcrete Nozzleman for the methods and orientations to be used.

641.04

with excavation.

shall submit the following for approval by the Engineer before full production:

technical information on the proposed pigment, colorants, or photo-reactive stains.

Construction Requirements

641.04General. Shotcrete shall be applied at the locations and to the thicknesses shown

on the plans. The thickness of shotcrete shall not be less than the dimensions shown on the plans.

Acceptable shotcrete shall consist of a dense and uniform mixture without rebound, inclusions, segregation, or discernible weakness of bond between the rock or structure and the shotcrete. Acceptance will be based on the requirements of subsection 641.06 and the visual inspection and sounding of the shotcrete. Shotcrete that exhibits movement or settlement after placement while still in the plastic state shall be repaired or replaced at the Contractor’s expense. Applications that are deemed by the Engineer to be unacceptable shall also be repaired or replaced at the Contractor’s expense.

For rock and soil cuts, surfaces shall be prepared to the line and grade shown on the plans. The Contractor shall provide documentation, including survey data, to show that the excavated face conforms to the plans so that the minimum thickness is achieved. If the Engineer determines that irregularities are excessive, additional reinforcing may be required. All costs associated with additional shotcrete required to bring an over excavated cut to the proper line and grade shall be borne by the Contractor. The Contractor shall fill all voids, holes, or pits created during the excavation process. Where additional shotcrete in excess of the plan thickness is required to make the final shotcrete face conform to the plans, the Contractor shall provide a plan and method statement for applying the additional shotcrete. The work shall not proceed until the proposed plan and methods have been reviewed and approved by the Engineer.

A light application of water may be used to clean the surface of all dry soil or rock surfaces before application of the shotcrete.

Shotcrete shall not be applied to frozen surfaces. De-icing compounds shall not be used to thaw ice, snow, or frost.

641.05

Before patching concrete structures, loose material shall be removed, and surfaces shall be dampened to a saturated surface dry condition. Before the placement of new shotcrete, the Contractor shall sandblast exposed reinforcing steel clean.

Rebound shall be removed and disposed of by the Contractor. Rebound shall not be worked back into the surface and shall not be salvaged and included in later batches.

Weep holes and the drainage system shall be installed as shown on the plans.

Where reinforcement fibers are required, the fibers shall be uniformly dispersed in the shotcrete. Production shall be suspended when visible fiber clumps are observed.

When multiple layers of shotcrete are to be applied, each layer of shotcrete shall be cleaned. If curing compound is used the curing compound shall be removed by sandblasting or a method approved by the Engineer.

641.05Curing Shotcrete. Curing shall be per subsection 601.13 and shall include the

following:

Film curing with polyethylene sheeting may be used to supplement water curing. The Contractor shall spray the shotcrete surface with water immediately before installation of the polyethylene sheeting. Polyethylene sheeting shall completely cover the surfaces and the Contractor shall overlap the sheeting edges. Joints between sheets shall be sealed. The Contractor shall promptly repair any tears, holes, and other damage. Anchor sheeting shall be installed as necessary to prevent billowing.

The minimum curing period shall be determined by one of the following methods.

shotcrete has met a compressive strength of 80 percent of the required field compressive strength. Compressive strength shall be determined by coring information panels. Information panels shall be constructed by the Contractor on the final portion of a placement and stored as close to the structure as possible. If the information panels are lost, mislabeled, damaged or destroyed in the field, the minimum curing period shall be seven days.

shotcrete has met a compressive strength of 80 percent of the required field compressive strength. The Contractor shall develop a maturity relationship for the shotcrete mix design per CP 69. The Contractor shall provide the maturity meter and all necessary thermocouples, thermometers, wires and connectors. The Contractor shall be responsible for the placement, protection and maintenance of the maturity meters and associated equipment. Locations where the maturity meters are placed shall be protected in the same manner as the rest of the shotcrete. The Contractor shall install the thermocouples at locations designated by the Engineer. The Contractor shall monitor the temperature at intervals acceptable to the Engineer. If the maturity meter malfunctions, the minimum curing period shall be seven days.

All costs associated with curing shall be at the Contractor's expense. The curing period may be stopped when succeeding layers of shotcrete are to be placed.

641.06 When the ambient temperature is expected to fall below 35 °F during the curing period the Contractor shall maintain the shotcrete internal temperature above 50 °F during the curing period. The Contractor shall monitor the internal shotcrete temperature by the use of maturity meters or high/low thermocouples. Maturity meter probes or thermocouples shall be located 2 feet from the edge of the final portion of shotcrete placed for the day and be located at mid-depth of the layer. The Contractor shall determine the necessity for undertaking protective measures. Maturity meters, thermocouples and information panels will not be measured or paid for separately but shall be included in the work. Enclosures with artificial heat sources will be permitted. If enclosures are used the Contractor shall monitor the structural integrity of the enclosure. Artificial heat sources shall not be placed in such a manner as to expose any area of shotcrete to drying due to excessive temperatures. At the end of the curing period, the protection shall remain in place until it can be removed without allowing the shotcrete temperature to fall more than 50 °F in a 24-hour period. Sudden changes of shotcrete temperature shall be prevented. The following procedures shall be followed if the temperature of the shotcrete structure falls below 32 °F before the minimum curing period is complete:

designated by the Engineer.

petrographic examination per ASTM C856.

be borne by the Contractor regardless of the outcome of the petrographic examination.

removed and replaced at the Contractor’s expense.

have been removed.

641.06Acceptance

than 50 cubic yards of a shotcrete mixture has been placed in a day, a test panel shall be produced for every 50 cubic yards or fraction thereof. Test panels shall be produced per ASTM C1140 Standard Practice for Preparing and Testing Specimens from Shotcrete Test Panels. Test panels shall be constructed in the same manner as that being used on the project, including distance from nozzle, angle and orientation. Test panels shall be cured in similar conditions to what is anticipated in the field and shall be field cured until test specimens are taken.

least three test specimens from each test panel per ASTM C1140 and tested at 28 days. The Contractor shall remove test specimens and immediately give them to the Engineer. The Contractor shall remove the test specimens between 25 and 27 days of age. The test specimens shall be stored in watertight plastic bags and labeled with the project number, test panel number and date of placement. If the 28-day compressive strength does not meet the required strength, the Contractor may take additional cores from the test panel to be tested at 56 days. The Contractor shall remove the 56-day test specimens between

641.08

53 and 55 days of age. Shotcrete will be evaluated for acceptance and price reduction per subsection 601.17.

excessive cracking, the following procedures shall be applied:

designated by the Engineer. The shotcrete shall be at least 28 days old. A set of three cores will be taken for each 100 square feet of shotcrete. Cores containing reinforcing steel shall not be tested.

compressive strength. A core that breaks during coring operations such that it cannot be tested per ASTM C1604 will be assigned a compressive strength of 0 psi.

represented by the cores shall be removed and replaced at the Contractor’s expense.

outcome.

have been removed.

Method of Measurement

641.07Shotcrete will be measured by the actual number of square yards applied and accepted

The quantity will be determined by the Engineer. There will be no increase of pay if the thickness exceeds the required minimums shown on the plans.

Initial Shotcrete Facing for soil nail wall, including the shotcrete steel and mesh reinforcement used for the temporary facing, will be measured by the actual square feet of shotcrete that is applied to the depth shown on the plans. Square feet of wall will be determined using the height measured at 20-foot maximum intervals along the wall layout line.

Basis of Payment

641.08The accepted quantities will be paid for at the contract unit price per square yard for

each of the items listed below that appear in the bid schedule:

Pay Item Pay Unit Shotcrete Square Yard Shotcrete Sculpting Square Yard Initial Shotcrete Facing Square Foot

Payment will be full compensation for all work, materials, and equipment. required to complete the item including submittals, test panels, test specimens, samples, pigment, fiber, drainage system and maturity meters. Shotcrete that is sculpted will be measured and paid for as Shotcrete Sculpting. The architectural surface treatment shall include full compensation for furnishing all labor, materials, tools, equipment and incidentals, and for doing all work involved in providing architectural surface treatment complete in place, including the test panels, line layout and all supporting metal bracing and support as specified in the Contract.

641.08 Test panels for shotcrete sculpting will not be measured and paid for separately but shall be included in the work.

Line layout and metal bracing for shotcrete sculpting will not be measured and paid for separately but shall be included in the work.

701.01