Asphalt mix design is a complex issue with a lot of variables involved. It is a mixture of course aggregate, fine aggregate, mineral filler and bitumen. Well graded aggregates, mineral filler and optimum quantity of bitumen results a mix with maximum density and very high stability. Marshall Mix design is the most popular method that widely been used in road industry.
Function of Base (or Subbase):
1) Drainage purpose
2) Reduce the effect of subgrade volume change on concrete layer
3) Prevent pumping of fines through joints & edges
4) Increase "K" modulus of subgrade reaction Rigid Pavement Characteristics: - Can resist unlimited loading - Minor defects are not reflected. - More skid resistance, safe. - More economical for same projects at certain location. - Concrete layer is less thickness than other layers.
The design procedure recommended by the American Association of State Highway and Transportation Officials Important Variables used in AASHTO Design Method
1- Pavement Serviceability Index
2- Reliability
3- Standard Deviation
4- Resilient Modulus
5- Drainage Coefficient
6- Layer Coefficient
7- Equivalent Single Axle Load
8- Structural Number
Types of Pavements:
• Rigid pavement (Concrete Slab) The wearing surface of a rigid pavement is usually constructed of Portland cement concrete such that it acts like a beam over any irregularities in the underlying supporting material.
• Flexible pavement (Asphalt Concrete) The wearing surface of flexible pavements is usually constructed of bituminous materials such that they remain in contact with the underlying material even when minor irregularities occur.
HIGHWAY CROSS-SECTION ELEMENTS
Continuous curve showing the relationship between the accumulated algebraic sums of corrected earthwork volume and distance for the purpose of minimizing the cost of excavating hauling & damping the materials (Soil).
The next step in the determination of the LOS is the computation of the peak hour factor.
The determination of level of service for a multilane highway