1、Section 28 WEARING SURFACES 28.1 DESCRIPTION This work shall consist of placing a wearing surface of durable and impervious material on the roadway surface of bridge decks. It also includes the preparation of the sur- faces of either existing or new decks to receive such an overlay of surfacing mate
2、rial. The type and thickness of the wearing surface shall be as designated on the plans. The materials and installation requirements for wearing surfaces of types other than latex modified concrete shall be as specified in the special provisions. Latex modified concrete wearing surfaces shall be fur
3、nished and installed in accordance with these Specifications. 28.2 LATEX MODIFIED CONCRETE TYPE WEARING SURFACE 28.2.1 General All equipment used to prepare the surface and to pro- portion, mix, place and finish the latex concrete shall be subject to approval by the Engineer prior to use. This ap- p
4、roval will be contingent on satisfactory performance and will be rescinded in the event such performance is not being achieved. Equipment shall be on hand sufficiently ahead of the start of construction operations to be exam- ined and approved. Any equipment leaking oil or any other containment onto
5、 the deck shall be immediately removed from the job site until repaired. A technician who is well experienced in the propor- tioning, mixing, placing and finishing of latex modified concrete shall be employed by the Contractor and shall be present and in technical control of the work whenever these
6、operations are underway. The qualifications of this technician which includes a list of projects on which the technician was employed and the technician?s level of re- sponsibility on each shall be submitted to and approved by the Engineer prior to the start of these operations. Approval by the Engi
7、neer of equipment or technicians shall not relieve the Contractor of any responsibility under the contract for the successful completion of the work. If not otherwise shown on the pians, the minimum thickness of latex modified concrete wearing surfaces shall be 1 */4 inches. 28.2.2 Materials 28.2.2.
8、1 Portland Cement Portland cement shall conform to the requirement of Article 8.3.1 of Section 8, ?Concrete Structures,? except that only Types I or II shall be used. 28.2.2.2 Aggregate Aggregate shall conform to the requirements of AASHTO M 6 for fine aggregate and to AASHTO M 80 for coarse aggrega
9、te. Coarse aggregate shall be graded ?/2 inch to No. 4 per AASHTO M 43. 28.2.2.3 Water Water for mixing concrete shall conform to the requirements of Article 8.3.2. 28.2.2.4 Latex Emulsion Formulated latex emulsion admixture shall be a non- hazardous, film forming, polymeric emulsion in water to whi
10、ch all stabilizers have been added at the point of manufacture and shall be homogeneous and uniform in composition. Physical Properties-The latex modifier shall conform to the following requirements: Polymer Type Stabilizers Styrene Butadiene (a) Latex Nonionic Surfactants (b) Portland Cement Compos
11、ition . Polydimethyl Siloxane Percent Solids . 46.0-49.0 Weight per Gallon (lbs at 25C) 8.4 Color . White 679 680 HIGHWAY BRIDGES 28.2.2.4 A Certificate of Compliance signed by the manufac- turer of the latex emulsion certifying that the material con- forms to the above specifications shall be furni
12、shed for each shipment used in the work. Latex admixture to be stored shall be kept in suitable enclosures which will protect it from freezing and from prolonged exposure to temperatures in excess of 85F. Containers of latex admixture may be stored at the bridge site for a period not to exceed 10 da
13、ys. Such stored con- tainers shall be covered completely with suitable insulat- ing blanket material to avoid excessive temperatures. 28.2.2.5 Latex Modified Concrete The latex modified concrete for use on this project shall be a workable mixture and meet the following requirements. Material or Prop
14、erty Concrete Fine Aggregate (Parts by weight) (Note 3) . Coarse Aggregate (Parts by weight) (Note 3) Latex Emulsion Admixture- (Gals /Bag Cement) . . . . . . . . . . . . . . . . . . Air Content of Plastic Mix, Slump,Inches (Notes 1 and 2) . . . . . . . . . . . Cement (Parts by weight) (Note 3). . .
15、 . . . . . 1 2.5 2.0 3.5 % (AASHTO T 152). . . . . . . . . . . . . . . . . 3-6 3-6 NOTES: Following sampling of the discharged, normally mixed material, the commencement of the slump test shall be delayed from 4 to 5 minutes. Water may be added to obtain slump within the pre- scribed limits. The dry
16、 weight ratios are approximate and should produce good workability, but due to gradation changes may be adjusted within limits by the Engi- neer. The parts by weight of sand may be increased by as much as 0.2 if the coarse aggregate is reduced by an equivalent volume. 28.2.3 Surface Preparation 28.2
17、.3.1 New Decks The surfaces of new decks upon which a wearing sur- face overlay is to be placed shall be finished to a rough texture by coarse brooming or other approved methods. After curing of the deck concrete is complete and be- fore placing the overlay, the entire area of the deck surface and t
18、he vertical faces of curbs, concrete parapets, barrier walls, etc., up to a height of 1 inch above the top elevation of the overlay shall be blast cleaned to a bright, clean ap- pearance which is free from laitance, curing compound, dust, dirt, oil, grease, bituminous material, paint, and all foreig
19、n matter. The blast cleaning of an area of the deck shall normally be performed within the 24-hour period preceding placement of the overlay on the area. The blast cleaning may be performed by either wet sandblasting, high pressure water blasting, blasting grits, shrouded dry sandblasting with dust
20、collectors, or other method ap- proved by the Engineer. Water blasting equipment shall operate with a minimum pressure of 3,500 psi. The method used shall be performed so as to conform to ap- plicable air and water pollution regulations and to applic- able safety and health regulations. All debris,
21、including dirty water, resulting from the blast cleaning operations shall be immediately and thoroughly cleaned from the blast-cleaned surfaces and from other areas where debris may have accumulated. The blast cleaned areas shall be protected, as necessary, against contamination prior to placement o
22、f the overlay. Contaminated areas and areas exposed more than 36 hours after cleaning shall be blast cleaned again as directed by the Engineer at the Contrac- tors expense. Just prior to placement of the overlay, all dust and other debris shall be removed by flushing with water or blow- ing with com
23、pressed air. The prepared surface shall then be soaked with clean water for not less than 1 hour prior to the placement of the latex overlay. Before the overlay is applied, all free water shall be blown out and off, and this procedure shall continue until the surface appears dry or barely damp. The
24、air supply system for blast cleaning and blowing shall be equipped with an oil trap in the air line, and pro- visions shall be made to prevent oil or grease contamina- tion of the surface by any equipment prior to placement of the overlay. 28.2.3.2 Existing Decks The surface of existing decks that h
25、ave become conta- minated by traffic usage or by deicing salts shall be scar- ified to the depth shown on the plans or specified. If no depth is shown or specified, a minimum of Y4 inch of ma- terial shall be removed by scarification. Prior to beginning scarification and until operations are complet
26、ed, all deck drains, expansion joints and other openings where damage could result, as determined by the Engineer, shall be temporarily covered or plugged to pre- vent entry of debris. Scarifying shall be done with power-operated mechan- ical scarifiers, or other approved devices, capable of uni- fo
27、rmly removing the existing surface to the depths re- 28.2.3.2 DIVISION II-CONSTRUCTION 681 quired without damaging the underlying concrete. Ma- chine scarifiers shall not be operated so as to damage hard- ware such as drain grates and expansion joint armor. In areas where machine scarifying cannot r
28、each and in areas of spalling and where steel reinforcement is exposed, scarifying and the removal of deteriorated or unsound concrete shall be accomplished with hand tools. Pneu- matic hammers heavier than nominal 45 pounds shall not be used. No scarifying or chipping will be allowed within 6 feet
29、of a new overlay until 48 hours after its placement. In areas where deteriorated or unsound concrete is en- countered, as determined by the Engineer, the concrete shall be removed to a depth of 3/4-inch below the top mat of reinforcing steel. A minimum of V4-inch clearance shall be required around t
30、he reinforcing steel except where lower bar mats make this impractical. Care shall be exer- cised to prevent damaging the exposed reinforcing steel. All reinforcing steel shall be blast-cleaned. The repair areas are to be filled during the overlay operation. After scarification and removal of unsoun
31、d concrete has been completed, the deck surface shall be blast cleaned and prepared as specified for new decks. 28.2.4 Proportioning and Mixing The Contractor shall submit to the Engineer for ap- proval, 14 calendar days prior to date of placement, the proposed mix design in writing and samples of a
32、ll mix materials in sufficient quantity to produce a minimum of 3 cubic feet of concrete for laboratory mix design testing. Proportioning and mixing equipment shall be of a self- contained, mobile, continuous-mixing, volumetric pro- portioning type mixer. Continuous-type mixers shall be equipped so
33、that the proportions of the cement, natural sand, and coarse ag- gregate can be fixed by calibration of the mixer and can- not be changed without destroying a seal or other indicat- ing device affixed to the mixer. In addition to being equipped with a flow meter for calibrating the water sup- ply po
34、rtion of the mixer, the mixer shall also be equipped with a cumulative-type water meter which can be read to the nearest 0.1 gallon. The water meters shall be readily accessible, accurate to within 1%, and easy to read. Both water meters shall be subject to checking by the Engineer each time the mix
35、er is calibrated. Approved methods for adding the admixture shall be provided. The admixtures shall be added so as to be kept separated as far as is prac- ticable. The continuous type mixer shall be calibrated to the satisfaction of the Engineer prior to starting the work. Yield checks normally will
36、 be made for each 50 cubic yards of mix. Recalibration will be necessary when indicated by the yield checks, and at any other times the Engineer deems necessary to ensure proper propor- tioning of the ingredients. Continuous type mixers which entrap unacceptable volumes of air in the mixture shall n
37、ot be used. The mixer shall be kept clean and free of partially dried or hardened materials at all times. It shall consistently pro- duce a uniform, thoroughly blended mixture within the specified air content and slump limits. Malfunctioning mixers shall be immediately repaired or replaced with ac-
38、ceptable units. Aggregate stockpiles being used should be of uniform moisture content. Mixing capability shall be such that finishing opera- tions can proceed at a steady pace with final finishing completed before the formation of the plastic surface film. 28.2.5 Installation 28.2.5.1 Weather Restri
39、ctions The placement of latex modified concrete shall not be started when the temperature is, or is expected to fall below 45F or rise above SOOF, or when high winds, rain or low humidity conditions are expected prior to final set of the concrete. If any of these conditions occur during placement, t
40、he placement shall be terminated and a straight construction joint formed. Placement at night may be necessary when daytime conditions are not favorable. If placement is performed at night, adequate lighting shall be provided by the Contractor. 28.2.5.2 Equipment Placing and finishing equipment shal
41、l include hand tools for placement and brushing-in freshly mixed latex modified concrete and for distributing it to approximately the correct level for striking-off with the screed. Hand-op- erated vibrators, screeds and floats shall be used for con- solidating and finishing small areas. An approved
42、 finishing machine complying with the following requirements shall be used for finishing all large areas of work: The finishing machine shall be self-propelled and ca- pable of forward and reverse movement under positive control. The length of the screed shall be sufficient to extend at least 6 inch
43、es beyond the edge of both ends of the section being placed. The finishing machine shall also be capable of consoli- dating the concrete by vibration and of raising all screeds to clear the concrete for traveling in reverse. The machine shall be either a rotating roller type or an oscillating screed
44、 type. 682 HIGHWAY BRIDGES 28.2.5.2 Rotating roller-type machines shall have one or more rollers, augers, and 1,500 to 2,500 vpm vibratory pans. Oscillating screed-type machines shall have vibra- tors on the screeds whose frequency of vibration can be varied between 3,000 and 15,000 vpm. The bottom
45、face of the screeds shall be not less than 4 inches wide and shall be metal. Rails will be required for the finishing machine to travel on. Rails shall be sufficiently rigid to support the weight of the machine without appreciable deflection and shall be placed outside of the overlay area. Rail anch
46、orages shall provide horizontal and vertical stability and shall not be ballistically shot into concrete that will not be overlaid. A suitable portable lightweight or wheeled work bridge shall be furnished for use behind the finishing operation. 28.2.5.3 Placing and Finishing 28.2.5.3.1 Construction
47、 Joints Planned construction joints shall be formed by bulk- heads set to grade. Before placing concrete against previ- ously placed overlay material, the construction joint shall be sawed to a straight vertical edge. Sawing of joints may be omitted if the bulkhead produces a straight, smooth, verti
48、cal surface. The face of the joint shall be sand or water blasted to remove loose material. Longitudinal construction joints will be permitted only at the center line of roadway or at lane lines unless other- wise shown on the plans or permitted by the Engineer. In case of delay in the placement ope
49、ration exceeding 1 hour in duration, an approved construction joint shall be formed by removing all material not up to finish grade and sawing the edge in a straight line. During minor delays of 1 hour or less, the end of the placement may be protected from drying with several layers of clean, wet burlap. 28.2.5.3.2 Placing The finishing machine shall be test run over the entire area to be overlayed each day before placement is started to ensure that the required overlay thickness will be achieved. Immediately ahead of placing the overlay mixture, a thin coating of the polymer modified con
