194 SECTION 408 TACK COAT 408.1 -DESCRIPTION : This work shall consist of preparing and treating an existing hot -mix asphalt or concrete surface with asphalt material in accordance with these Specifications and in reasonably close conformity with the lines shown on the Plans or established by the Engineer. 408.2 -MATERIALS : Materials shall conform to the requirements of the following Subs ection of Division 700: MATERIALS SUBSECTION TYPE Asphalt Emulsion 705.4 SS or RS Grades Cationic Emulsified Asphalt 705.11 CSS or CRS Grades Non-Tracking Asphalt Material 705.13 NTSS -1HM or similar* * Refer to MP 401.02.25 for a list of Certified Asphalt Materials. 408.2.1 -Quality Control: Quality control is the responsibility of the Contractor as specified in 106.1. Quality control shall consist of calibrating the distributor to the proper application rate, verifying the volume and temperature measuring devices, and when performed, assuring that the proper dilution rate is maintained. 408.2.1.1 -Acceptance Testing: Approval of asphalt emulsions used for tack coat material will be handled by the Materials Control, Soils a nd Testing (MCS&T) Division. MCS&T maintains a list of all approved asphalt emulsion sources and grades. The local District Materials Section can provide a copy of the latest list. The list is also posted on the MCS&T web page under the heading Approved Source/Product Listing. The use of non-approved material without prior testing by MCS&T may result in nonpayment of the item. CONSTRUCTION METHODS 408.3 -WEATHER RESTRICTION : Tack coat shall be applied only w hen the weather and existing surface are satisfactory to the Engineer and when the temperature of the surface is 40°F or above. When the surface temperature is less than 50°F, care must be exercised to assure that the tack coat “breaks” (Note 1) prior to the application of the hot -mix asphalt. Note 1: Tack coat “break” is the process in which water separates from the asphalt emulsion and the color of the tack coat begins to change from brown to black. The time required for breaking will depend on the type and grade of the emulsion, the application rate, the temperature of the existing pavement surface, and environmental conditions. Tack coat “set” refers to the final stage of the process when water has completely evaporated from the emul sion leaving a thin film of asphalt binder on the pavement. The rate of set depends on the same conditions that control the rate of break of the emulsion. 195 408.4 -EQUIPMENT : Equipment shall include a power broom and powe r blower, a broom drag, equipment for heating asphalt material, and a self -powered asphalt material pressure distributor. Equipment shall also include scrapers, hand brooms, shovels, and other equipment as may be necessary to thoroughly clean the base or surface. Equipment for heating asphalt material to the required temperature shall consist of a retort coil so designed that steam will not be introduced into the material and shall not degradate the emulsion. The distributor shall be so designed, equippe d, maintained and operated that asphalt material at even heat may be applied uniformly on variable widths of surface up to fifteen ( 15) feet at readily determined and controlled rates from 0.05 to 2.0 gal/sy with uniform pressure and with an allowable vari ation from any specified rate not to exceed 0.02 gal/sy. The distributor shall also have a cab -metering system that will automatically adjust the flow of the asphalt material as the speed of the truck changes and allow the operator to adjust the rate of a pplication from the cab of the truck. Distributor equipment shall include a tachometer, pressure gages, and accurate volume measuring devices or a calibrated tank, and a thermometer for measuring temperatures of tank contents. Distributors shall be equip ped with a power unit for the pump, and full circulation spray bars adjustable laterally and vertically. A manifold connection shall be provided and hand - spraying equipment shall be available to cover areas and patches inaccessible to the distributor. 408.5-PREPARING AND REPAIRING BASE OR EXISTING SU RFACES : No tack coat shall be applied until breaks, holes, depressions, and other irregularities in the base or existing surface have been repaired and cured sufficiently to permit the tack coat to be placed in a uniform application. Patching and leveling material shall be plant mixed. Hand patching will be permitted where necessary. 408.6 -CLEANING AND SWEEPING : Immediately before starting construction, the existing surface shall be swept and thoroughly cleaned by the use of tools or machinery as may be required to remove all mud, dirt, dust, and other caked or loose material foreign to the type of surface to be placed. Cleaning shall be done to a minimum width of one foot on each side beyond the width of the surface to be placed excluding the shoulder. 408.7 -APPLICATION OF ASPHALT MATERIAL : Except when required to maintain traffic, the work shall be done on the full width of the section. After the base or surface has been cleaned, when called for, and is in a dry condition, the asphalt material shall be applied by mean s of a pressure distributor. The spray bar shall be raised to a sufficient height so as to uniformly and completely coat the entire surface. The rate of application of asphalt material shall be as recommended in subsection 408.11, or as determined by the Engineer. Application temperatures of the asphalt material shall be within the range specified in Subsection 705 for the particular material being used. With the exception of SS and CSS grades, all emulsion grades used for tack coat shall be applied wit hout dilution. Anionic asphalt emulsion grades SS -1 and SS -1h, and cationic emulsion grades CSS -1 and CSS -1h, may be diluted at a 1:1 ratio by addition water to the e mulsion. The tack coat shall not precede the placement of the subsequent HMA course to s uch an extent that the treated surface will be damaged during the interim. No patching and leveling or 196 surface courses of any type shall be applied to the tacked surface until the asphalt materia l is thoroughly “set” (see Note 1 in Section 408.3) . Tack c oat shall not be applied over newly placed patching and leveling courses. However, to facilitate construction, minor (spot) areas that have been tacked, patched and leveled may be retacked and the quantity so used will be included for payment as part of t he normal tack coat operation. The intent of the two preceding sentences, in conjunction with the next to the last paragraph of subsection 401.13, is (1) to provide one tack coat application on the existing surface, although two applications, one over one under, for minor (spot) patching and leveling area, are permitted as indicated above, and (2) to limit payment for such operations to one application of the tack coat upon the existing surface for the entire project. The surfaces of sidewalks, curbs, oth er structures, and trees adjacent to the area being treated shall be protected in such a manner as to prevent their being spattered or marred. Material used for such protection shall be removed and disposed of in a satisfactory manner. The distributor shall not be cleaned or discharged win the right -of-way, into borrow pits, or so as to pollute or block water courses. 408.8 -APPLICATION OF COVER AGGREGATE : Any tack coat material applied in excess of the requirements shall be removed or covered with a blotter course of dry sand or stone chips as directed by the Engineer. 408.9 -JOINTS : Longitudinal joints shall be treated using an application rate that will tho roughly coat the vertical face without excessive runoff
408.10 Protection of The Pavement and Traffic Control :
The Contractor shall be responsible for the protection of the surface a gainst damage by their equipment and personnel. Traffic shall not be permitted on any part of the work under construction until the treatment has cured sufficiently to prevent raveling or picking up under traffic. The applicable provisions of 636 shall a pply for regulating traffic.
408.11 Quantities of Materials :
The application rates referenced in Table 408.11 shall be used as guide to assure the proper amount of asphalt is distributed over the pavement surface under various pavement conditions. The undiluted application rate refers to the unmodified emulsion that meets all standard specifications of the specified grade. When an SS or CSS grade emulsion is diluted with water at the allowable 1:1 ratio t he residual asphalt content (the amount of asphalt remaining on the pavement surface after all water has evaporated from the emulsion) will be cut in half. Therefore the distribution rate must be doubled in order to obtain the same residual asphalt applic ation as the undiluted emulsion. Unless otherwise specified on the Plans, the recommended application rates for undiluted and diluted asphalt tack coat shall be as specified in Table 408.11. These rates are provided for guidance and may be adjusted as directed by the Engineer to assure a uniform application that covers the entire pavement, and to assure that excessive asphalt does not cause a slippage plane between two pavement courses.