504 - Micro-Surfacing
Micro-surfacing should be used only for filling rutted pavements. All other applications are inappropriate. However, if called for on the plans or proposal, the following should apply.
The asphalt emulsion must be certified and supplied by an approved supplier. The mix design and quality control testing is the responsibility of the Contractor. The MDOT inspector must ensure that a proper mix design and JMF have been established and that the Contractor is performing the specified quality control testing. The inspector must also ensure that the proper daily documentation is received from the Contractor.
Before placing the mixture, the Contractor shall thoroughly clean the existing surface of all loose materials, vegetation, dirt, dust, mud and other objectionable materials. The Contractor also shall remove all plastic pavement markings using an abrasion method.
Micro-surfacing shall be applied in a manner to fill ruts and minor cracks, and leave a uniform, smooth surface with straight edges. Drainage structures, monument boxes, water shutoffs, etc. shall be protected during the application of the mixture.
A micro-surface mix with 3FA shall be applied with an approved rut box for each wheel path. Each pass of rut filling shall be limited to a maximum depth of 1 inch (25 mm).
Each rutted wheel track shall be slightly over-crowned to allow for some consolidation by traffic.
Standard micro-surfacing shall be applied full lane width in two courses for a total application rate of 25 pounds/square yard (14 kg/m2). The first course shall be 10 pounds/square yard (6 kg/m2); the second course shall be 15 pounds/square yard (8 kg/m2).
The finished surface should be free from excessive scratch marks, tears, rippling and other surface irregularities. The longitudinal construction joints and lane edges shall coincide with the painted lane lines.
Traffic shall not be allowed on the mixture until it has cured sufficiently to prevent pick up by vehicle tires. The new surface shall be capable of carrying normal traffic within one hour after application without any damage occurring.
Placement is not permitted if there is rain, or threatening weather, and temperatures are forecast to be below 32°F (0°C) within 24 hours of completion of the work. The mixture cannot be placed when the air and pavement surface temperatures are below 45°F (7°C).
The mixing machine shall be equipped with a positive connection conveyer belt aggregate delivery system and an inter-connected positive displacement, water-jacketed gear pump to accurately proportion aggregate and asphalt emulsion. The filler feed must be located so the proper amount of filler is dropped on the aggregate before discharging into the pug mill. A minimum of two truck-mounted machines will be required at all times. The Contractor shall cycle these machines so as not to delay mixture production by more than 15 minutes. If at any time this requirement is not met, production should be stopped.
The mixture shall be spread uniformly by a mechanical tube spreader box attached to the mixer and equipped with paddles mounted on adjustable shafts to continually agitate and distribute the mixture. The spreader box shall be equipped with front and rear flexible seals to achieve direct contact with the road surface. When a two-course application is called for, the first pass shall be made using a metal or stiff rubber strike off on the box. The final pass, or surface pass, shall use a secondary strike off to provide a finished smooth surface texture.
The rut filling application shall be achieved with a steel V-shaped configuration screed (rut box) specifically designed to fill ruts. The rut box shall achieve a mixture spread width of 5 to 6 feet (1.5 to 1.8 meters) and have a secondary strike off to control crown and texture.
Hand squeegees, shovels and other equipment shall be provided as necessary to perform the work. Cleaning equipment, such as power brooms, air compressors, water flushing equipment and hand brooms shall be adequate for surface preparation.
The Contractor is responsible for placing a uniform product. This type of work has a 30 day delayed acceptance procedure so that any major problems will be corrected by the Contractor before the project can be accepted. In most cases, the inspector has little to do with the micro-surfacing operation itself, but must ensure that traffic control is conducted properly and that all safety rules are followed.
If the inspector notices a nonuniform application, any traffic control or safety violations, the Contractor must be notified immediately. If the Contractor does not correct the violation, the project should be stopped.