1062 If required, the reset reference markers shall be painted as specified on the plans for new reference markers. Markers broken or damaged in removing and resetting shall be replaced at no additional cost to the Dep artment. 911- 4 Method of Measurement: Right -of-way markers will be measured as a unit for each marker, including reference markers. Reset right -of-way markers will be measured as a unit for each marker, including reference marker, removed and reset at the new location. Markers removed but not reset will not be included in the measurement. 911- 5 Basis of Payment: The accepted quantities of right -of-way markers and reset right -of-way markers, measured as provided above, will be paid for at the contract unit price each, complete in place. 912- 1 Description: The work under this section shall consist of furnishing all materials and applying shotcrete on prepared surfaces at the locations and in accordance with the details shown on the plans and the requirements of the specifications. Shotcrete shall be mortar or concrete conveyed through a hose and pneumatically applied using either the dry mix process or the wet mix process. The dry mix process shall consist of thoroughly mixing a proportional combination of dry fine aggregate and Portland cement; conveying the mixture through a delivery hose to a special nozzle where water is added and mixed with the other materials immediately prior to its discharge from the nozzle. The wet mix process shall consist of premixing by mechanical methods a proportional combination of Portland cement, supplementary cementitious material, aggregate , and water required to produce mortar or concret e; conveying the mortar or concrete through the delivery hose to the special nozzle where additional compressed air is added at the nozzle prior to its discharge. TABLE OF CONTENTS INDEX 1063 912- 2 Materials and Equipment: 912- 2.01 Portland Cement and Water: Portland cement and mixing water shall conform to the requirements of Subsection 1006- 2.01 and 1006- 2.02 of the specifications, respectively. 912- 2.02 Aggregate:
Fine aggregate shall conform to the requirements of Subsection 1006- 2.03(B) of the specifications.
Coarse aggregate shall conform to the requirements of Subsection 1006 - 2.03(C) of the specifications, except that it shall conform to the following gradation: Sieve Size Percent Passing 1/2 inch 100 3/8 inch 85 - 100 No. 4 0 - 30 No. 8 0 - 10 No. 16 0 - 5 912- 2.03 Admixtures: Admixtures shall conform to the requirements of Subsection 1006- 2.04 of the specifications. Air-entraining admixtures will be required for shotcrete placed at an elevation of 3,000 feet or above. Air conte nt will be measured in accordance with AASHTO T 152. When the wet -mix process is used, the air content will be measured just prior to pumping, and shall not be less than 7 percent nor more than 10 percent. When the dry- mix process is used, the air content will be measured from the in- place material that has been shot, and shall not be less than 4 percent nor more than 7 percent. 912- 2.04 Reinforcing Steel: Reinforcing steel bars or welded wire fabric shall conform to the requirements of Section 1003 of the specifications. TABLE OF CONTENTS INDEX 1064 912- 2.05 Equipment: Equipment for use with the dry mix process shall be capable of metering the aggr egate- cement mixture into the delivery hose under close control and delivering a continuous smooth stream of uniformly mixed material at the proper velocity to the discharge nozzle. The nozzle shall be equipped with a manually operated water ring for directing an even distribution of water through the fine aggregate- cement mixture. The water ring shall be capable of ready adjustment to vary the quantity of water. Equipment for use with the wet mix process shall be the pneumatic feed type; however, a positive displacement type may be used if permitted in writing by the Engineer. The pneumatic feed type shall be capable of discharging the concrete or premixed mortar accurately, uniformly, and continuously through the delivery hose and to the gunning nozzle. The nozzle shall be fitted with an air ring for injecting additional compressed air into the flow of material . The size of the delivery hose shall be within the rang e of 1- 1/4 to 2- 1/2 inches. 912- 2.06 Air Supply: The air compressor shall have ample capacity to furnish an adequate supply of clean dry air for maintaining sufficient nozzle velocity for all phases of the work while simultaneously operating a blow pipe fo r clearing away the rebound. The air hose shall be equipped with a filter to prevent any oil or grease from contaminating the shotcrete. A constant air pressure of not less than 80 pounds per square inch shall be maintained in the placing machine when usi ng the dry mix process or at the nozzle when using the wet mix process and when the delivery hose length is 100 feet or less. The pressure shall be increased at least 5 pounds per square inch for each additional 50 feet of hose or fraction thereof. 912- 3 Construction Requirements: 912- 3.01 Proportioning and Mixing :
Dry mix material shall consist of one part Portland cement to not more than four parts fine aggregate, measured either by weight or by volume. The fine aggregate shall contain not less than 3 percent nor more than 6 percent moisture by weight. The cement and fine aggregate shall be thoroughly mixed before being charged into the delivery equipment. If the contractor uses a drum -type mixer, the mixing time shall be not less than one minute. The mixed material shall be utilized promptly after mixing . Any unused material that TABLE OF CONTENTS INDEX 1065 stands more than 45 minutes will be rejected and removed from the work site.
Premixed mortar shall consist of not less than 564 pounds of combined Portland cement and supplementary cementitious material per cubic yard, fine aggregate, chemical and/or air -entraining admixtures, and water mixed to a desired consistency, generally to a slump in the range of 1 -1/4 to 4 inches. The material may be mixed at a central mixing plant or at the project site. If mixing is done at the project site, the mixer shall be capable of thoroughly mixing the specified materials in sufficient quantity to maintain continuous placing of the mortar.
The contractor shall determine the mix proportions and shall furnish concrete for pneumatic placement which cont ains a minimum of 658 pounds of combined Portland cement and supplementary cementitious material per cubic yard of concrete and which attains a minimum 28- day compressive strength of 3,000 pounds per square inch, unless otherwise specified. Fine aggregate and coarse aggregate shall conform to the requirements of Subsection 912- 2.02 of the specifications. The total mix shall contain 15 to 20 percent coarse aggregate, by weight . The water/cementitious material ratio shall not exceed 0.50. In no case shall the slump be greater than 4 inches. If ready- mixed concrete is used, it shall conform to the requirements of ASTM C94. 912- 3.02 Preparation of Surfaces: The surfaces on which shotcrete is to be placed shall be finely graded to the lines and grades shown on the project plans or established by the Engineer. The surfaces shall be thoroughly compacted and shall be uniformly moistened so that water will not be drawn from the freshly placed shotcrete. 912- 3.03 Forms and Ground Wires: Forms shall be of plywood sheathing or other suitable material and shall be true to line and grade and sufficiently rigid to resist deflection during placement of the shotcrete. Forms shall be constructed to permit the escape of air and rebound during the gunning operation. TABLE OF CONTENTS INDEX 1066 Ground or gauging wires shall be installed where necessary to establish the thicknesses, surface planes and finish lines of the shotcrete. 912- 3.04 Steel Reinforcement: Steel reinforcement shall be as shown on the proj ect plans and shall conform to the requirements of Section 605 of the specifications. 912- 3.05 Placement of Shotcrete : The velocity of the shotcrete as it leaves the nozzle shall be maintained uniform and at a rate approved by the Engineer for the given job conditions. The nozzle shall be held perpendicular to the working surface and at a proper distance, generally between 2 and 5 feet, to ensure maximum compaction with minimum rebound of the shotcrete. Rebound or previously expended material in the shotcr ete mix shall not be used in any portion of the work. All rebound shall be removed prior to final set and before placement of the shotcrete on adjacent surfaces. Shotcrete shall not be applied during any precipitation which is of sufficient intensity to cause the in- place shotcrete to run. Shotcrete shall not be applied during wind conditions that cause separation of the nozzle flow. Shotcrete shall not be applied when a descending ambient air temperature falls below 40 degrees F nor until an ascending air temperature rises above 35 degrees F. Temperature shall be taken in the shade away from artificial heat. 912- 3.06 Testing: Tests to determine the physical quality of the shotcrete will be performed by the Engineer during the work as required. The contractor shall prepare test panels and obtain cores as specified herein. Test panels at least 12 inches square and as thick as the structure being constructed, but not less than 3 inches thick, shall be prepared by gunning shotcrete mix into a frame which has been placed on a flat piece of plywood. Test panels shall be cured i n the same manner as the production work, as specified in Subsection 912- 3.09 of the specifications. The contractor shall obtain three cores from each test panel in accordance with Arizona Test Method 317. The cores shall have a minimum diameter of 3 inches and a length to a diameter ratio (L/D) of at least 1.00. The cores must be obtained under the observation of an ADOT representative. TABLE OF CONTENTS INDEX 1067 The cut surfaces of the cores will be carefully examined for soundness and uniformity of the material and shall be free from laminations and sand pockets. The three cores will be tested by the Engineer for 28- day compressive strength in accordance with Arizona Test Method 317. Unless otherwise specified, the cores shall have an average compressive strength of at least 3, 000 pounds per square inch. 912- 3.07 Construction Joints: Construction joints shall be tapered to a shallow edge of 1 inch thick over a width of 1 foot, except where the joint will be subjected to compressive loading . If such is the case, or if joints are at slab intersections, full depth vertical joints shall be constructed and special care taken to avoid or remove trapped rebound at the joint. The entire joint shall be thoroughly cleaned and wetted prior to the application of additional shotcrete. 912- 3.08 Finishing: After the shotcrete has been placed as nearly as practicable to the required thickness and shape outlined by forms and ground wires, the surface shall be checked with a straightedge and any low spots or depression shall be brought up to proper grade by placing additional shotcrete in such a manner that the finished surface shall be smooth and uniform. Unless otherwise specified, the surface of th e shotcrete shall have a natural gun finish. 912- 3.09 Curing: The shotcrete surfaces shall be kept continuously moist for at least seven days, beginning immediately after finishing, by means of either a water spray or fog system capable of being applied continuously or by liquid membrane- forming compound or by polyethylene sheeting conforming to the requirements specified in ASTM C171. If polyethylene sheeting is used, it shall be white opaque and adjoining sheets shall overlap at least 12 inches and the laps secured to provide an airtight and windproof joint. If liquid membrane- forming compound is used it shall be Type I conforming to the requirements of ASTM C309 and the application rate shall be 1 gallon per 100 squar e feet. 912- 4 Method of Measurement: Shotcrete will be measured by the square yard of surface areas placed to the required thickness. TABLE OF CONTENTS INDEX