Asphaltic flexible pavement is a common type of road surface layer construction used broadly in the world. Flexible pavement is composed of a bituminous material surface course and underlying base and subbase courses. Flexible pavement materials consist of aggregates such as crushed stone, gravel, and sand bound together using bitumen, a viscous petroleum-based binder that enhances cohesion, waterproofing, and flexibility within the pavement structure. The combination of aggregates and bitumen allows for efficient construction, durability, and adaptability to different soil types and climates, making flexible pavement a versatile choice for road infrastructure projects.
Before laying the asphaltic base or wearing course, preparation of the base surface is very important to achieve the desired result. Therefore, the following procedure should be adopted:
Prime Coat: It is the application of a low viscosity liquid asphalt product to an absorbent surface. It is used to prepare an untreated base for an asphalt surface. The Prime penetrates into the base and plugs the voids, hardens the top, and helps bind it to the overlying asphalt course. It is to be applied on Aggregate Base Course as well as WBM Base Course.
Tack Coat: It is a light application of asphalt, usually asphalt emulsion diluted with water. It is used to ensure bond between the surface being paved and the overlying course. It is to be applied on Asphaltic Base Course and on concrete surface.
Seal Coat: It is a thin asphalt surface treatment used to waterproof and improve the texture of an Asphalt Wearing surface. Depending on the purpose, Seal Coat may or may not be covered with aggregate. The main types of seal coats are aggregate seals, fog seals, emulsion slurry seals, and sand seals.
The requirements cover Coarse Aggregate, Fine Aggregate, Filler, and Bituminous material. Material requirements of the Asphaltic Base Course layer are given in the tables:
When the combined grading of the Coarse & Fine aggregate is deficient in material passing Sieve # 200, additional Filler material shall be added which will conform to the table given below:
Asphaltic binder to be mixed with the aggregate to Asphaltic base shall be AC having penetration grade 40/50, 60/70, or 80/100 as specified and shall meet the AASHTO M-20 requirements, provided in the table given below:
The table given below shows the limits for Asphaltic Base Course (Plant-Mix) material.
JMF should be established at least one week prior to production, JMF shall be established by the Marshall Method of Mix Design according to the Asphalt Institute Manual series # 2 (MS-2), latest revision or as specified by the designer.
Variation in Passing %age of materials as given below is allowed with respect to the gradation adopted for JMF.
Construction Requirements of laying Asphaltic Base Course layer is as under:
