1、Section 24 PNEUMATICALLY APPLIED MORTAR 24.1 DESCRIPTION This work shall consist of the furnishing and placing of pneumatically applied mortar for the construction of portions f structures, repairing concrete structures, texturing concrete surfaces, encasement of structural steel members, lining dit
2、ches and channels, paving slopes and for other miscellaneous work, all as shown on the This work also includes the preparation of surfaces to receive the mortar and the furnishing and placing of any reinforcing steel and anchors for reinforcement. Pneumatically applied mortar shall consist of either
3、 dry mixed fine aggregate and Portland cement pneumati- cally applied by a suitable mechanism, to which mixture the water is added immediately previous to its expulsion from the nozzle, or mortar premixed by mechanical meth- ods and pneumatically applied through a nozzle onto the prepared surface. p
4、lans. 24.2 MATERIALS 24.2.1 Cement, Aggregate, Water and Admixtures Cement, aggregate, water and admixtures, when used, shall conform to the requirements of Section 8, “Concrete Structures.” Aggregate shall be fine aggregate, except that up to 30% coarse aggregate, conforming to AASHTO M 43 for size
5、 Ys inch to No. 8 or No. 16, may be substituted for fine aggregate. Recovered rebound which is clean and free of foreign material may be reused as fine aggregate in quantities not to exceed 20% of the total fine aggregate require- ments. 24.2.2 Reinforcing Steel Reinforcing steel shall conform to th
6、e requirements of Section 9, “Reinforcing Steel.” 65 3 24.2.3 Anchor Bolts Studs Anchor studs used to support reinforcing wire fabric or bars when placing mortar against existing concrete or rock shall consist of Y4-inch minimum diameter expansion hook bolts placed in drilled holes. Each bolt shall
7、have sufficient engagement in sound masonry to resist a pull- out force of 150 lbs. When permitted by the Engineer, driven steel studs of not less than 18 inches, center to center, on vertical surfaces; and 36 inches, center to cen- ter, on top horizontal surfaces. At least three anchors shall be us
8、ed in each individual patch area. The Engineer shall be notified in advance of the date when installation of anchor studs is to begin. The loca- tions of the studs shall be such that damage will not occur to prestressing tendons or conduits embedded in the con- crete. Unless otherwise shown or speci
9、fied, for repair work, all areas where the thickness of the mortar exceeds 1% inches shall be reinforced with a single layer of either 2 X 2-W1 XWlor3 X3-WlSXW1.5weldedwirefab- ric. For areas where the thickness of the mortar exceeds 4 inches, a single layer of wire fabric shall be used to rein- for
10、ce each 4-inch thickness of patch or fractional part thereof. All fabric shall be placed parallel to the proposed finished surface. Each layer of fabric shall be completely encased in mortar which has taken its initial set, before the succeeding layer of fabric is installed. Fabric supported adjacen
11、t to the prepared masonry surface shall be no closer than YZ inch to said surface. Fabric shall be carefully prebent before installation to fit around corners and into re-entrant angles, and shall in no case be sprung into place. All steel items, including anchors, reinforcing bars and wire fabric,
12、shall be no closer than 1 inch to the finished surface of the mortar. 24.5.2 Placement of Mortar Only experienced foremen, gunmen, nozzlemen, and rodmen shall be employed, and satisfactory evidence of such experience shall be furnished when requested by the Engineer. The mortar shall be applied by p
13、neumatic equipment that sprays the mix onto the prepared surface at a high velocity as needed to produce a compacted dense homo- geneous mass. The air compressor and delivery hose lines shall be of adequate capacity and size to provide a mini- mum pressure of 35 psi at the nozzle for 1-inch nozzles
14、and proportionally greater for larger nozzles. The veloc- ity of the material as it leaves the nozzle must be main- tained uniform at a rate determined for the given job con- ditions to produce minimum rebound. Water which is added at the nozzle shall be supplied at a uniform pressure of not less th
15、an 15 psi greater than the air pressure at the nozzle. The mortar shall be applied as dry as practicable to pre- vent shrinkage cracking. Shooting strips shall be em- ployed to insure square corners, straight lines, and a plane surface of mortar, except as otherwise permitted by the plans or approve
16、d by the Engineer. They shall be so placed 24.5.2 DIVISION II-CONSTRUCTION 655 as to keep the trapping of rebound at a minimum. At the end of each days work, or similar stopping periods re- quiring construction joints, the mortar shall be sloped off to a thin edge. Before placing an adjacent section
17、, con- struction joints shall be thoroughly cleaned and wetted as required under Article 24.4. In shooting all surfaces, the stream of flowing material from the nozzle shall impinge as nearly as possible at right angles to the surface being covered, and the nozzle shall be held from 2 to 4 feet from
18、 the working surface. A sufficient number of mortar coats shall be applied to obtain the required thickness. On vertical and overhead surfaces, the thickness of each coat shall be not greater than 1 inch, except as approved by the Engineer, and shall be so placed that it will neither sag nor decreas
19、e the bond of the preceding coat. The time interval between succes- sive layers in sloping, vertical or overhanging work shall be sufficient to allow initial but not final set to develop. At the time the initial set is developing, the surface shall be cleaned to remove the thin film of laitance in o
20、rder to pro- vide for a bond with succeeding applications. Rebound or accumulated loose sand shall be removed from the surface to be covered prior to placing of the orig- inal or succeeding layers of mortar and shall not be em- bedded in the work. Materials that have been mixed for more than 45 min-
21、 utes and have not been incorporated in the work shall not be used, unless otherwise permitted by the Engineer. After curing and before final acceptance, all repaired areas shall be sounded. All unsound and cracked areas shall be removed and replaced. 24.5.2.1 Weather Limitations Pneumatically place
22、d mortar shall not be placed on a frozen surface nor when the ambient temperature is less than 40F; nor shall it be placed when it is anticipated that the temperature during the following 24 hours will drop below 32F. The application of pneumatically placed mortar shall be suspended if high winds pr
23、event proper application, or rain occurs which would wash out the pneumatically placed mortar. 24.5.2.2 Protection of Adjacent Work During progress of the work, where appearance is im- portant, adjacent facilities which may be permanently dis- colored, stained, or otherwise damaged by overspray, dus
24、t or rebound, shall be adequately protected and, if con- tacted, shall be cleaned by early scraping, brushing, or washing, as the surroundings permit. 24.5.3 Finishing After mortar has been placed to desired thickness, all high spots shall be cut off with a sharp trowel, or screeded to a true plane
25、as determined by shooting strips or by the original masonry surface, or as directed. Cutting screeds, where used, shall be lightly applied to all surfaces so as not to disturb the mortar for an appreciable depth, and they shall be worked in an upward direction when applied on vertical surfaces. Unle
26、ss otherwise directed, the finished mortar surface shall be given a final flash coat of about f/s inch of mortar. Special care shall be taken to obtain a uniform appearance on all exposed surfaces. 24.5.4 Curing and Protecting Pneumatically placed mortar shall be water cured in conformance with the
27、requirements of Article 8.11.3.2. The minimum water curing duration shall be 96 hours. The mortar shall be protected from freezing during the curing period. 24.6 MEASUREMENT AND PAYMENT The quantity of pneumatically applied mortar will be measured either by the square foot or by the cubic foot as in
28、dicated in the schedule of bid items. Square foot measurements will be based on measure- ments of the surface area of acceptable mortar placed in the work made along the plane or curve of each surface. Cubic foot measurement will be based on the dimensions of such work shown in the plans or ordered
29、by the Engineer. Pneumatically applied mortar will be paid for by the contract price per square foot or cubic yard. Such payment shall be considered to be full compensation for the cost of furnishing all labor, materials, equipment, incidentals, and for doing all work involved in preparing the surface and installing the mortar, reinforcing steel, anchor studs, head- ers, joint fillers, and other items as shown on the plans or specified.
