221 SECTION 420 SINGLE / MULTIPLE COURSE MICRO SURFACING
420.1 -DESCRIPTION : This section covers the materials, equipment, construction and application procedures for placing Micro Surfacing material for filling ruts and for surfacing existing paved surfaces. The Micro Surfacing is a mixture of a latex -modified asphalt emulsion, crushed mineral aggregate screenings, mineral filler, water and other additives for control of set time in the field. All ingredients are to be properly proportioned, mixed and spread on the paved surface in accordance with this Specification and as directed by Engineer.
420.2 -MATERIALS : Furnish a Micro Surfacing mixture consisting of a properly designed and proportioned blend of polymerized asphalt emulsion, fine aggregate, Portland cement, water and other additives. All materials must be from a WVDOH approved source. Use materials meeting the following:
420.2.1 -Mineral Filler: Portland cement, hydrated lime, limestone d ust, fly ash, or other approved filler meeting the requirements of ASTM D242 shall be used if required by the mix design.
420.2.2 -Fine Aggregates, 2FA and 3FA: The fine aggregate used shall be suitable for the particular application and shall be a crus hed stone such as granite, slag, limestone, chat, or other high -quality aggregate, or combination thereof. Additionally, on projects with an ADT greater than 3000, the fine aggregate used in the surface course shall also meet the requirements of the WVDOH commercial source list for potential anti -skid aggregate quality specifications. The aggregate shall be passed over a scalping screen immediately (not prescreened) prior to transfer to the micro surfacing mixing machine to remove oversized material.
Tests Requirements Sand Equivalent Value of Soils and Fine Aggregate AASHTO T 176 65 minimum Soundness of Aggregates by Use of Sodium Sulfate MP 703.00.22 15% max. w/ NA2SO4
Material Percent Passing ⅜ in No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 No. 200 2FA(a) 100 90-100 65-90 45-70 30-50 18-30 10-21 5-15 3FA(a) 100 70-95 45-70 28-50 19-34 12-25 7-18 5-15
420.2.3 -Asphalt Emulsion -CSS-1hM or CQS -1hM: Polymer Modified Asphalt Emulsion shall be a CQS -1P or CQS -1hP in accordance with AASHTO M 316 with the following exceptions: the distillation procedure shall be conducted at 175°C with a 20 minute hold perio d. The polymer material shall be processed into the asphalt cement or milled into the asphalt emulsion. Post adding to the asphalt emulsion is not permitted. The minimum polymer solids content will be 3.0% based on the residual of the emulsion.