About Asphalt Concrete
Asphalt, also known as bitumen, is black or brown petroleum-like material that has a consistency varying from viscous liquid to glassy solid. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Asphalt consists of compounds of hydrocarbons.
|Phase at STP||solid|
|Ultimate Tensile Strength||1.2 MPa|
|Young’s Modulus of Elasticity||8 GPa|
|Melting Point||167 °C|
|Thermal Conductivity||0.75 W/mK|
|Heat Capacity||900 J/g K|
Composition of Asphalt Concrete
Asphalt concrete mixes are typically composed of 5% asphalt cement and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, asphalt cement must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The components of asphalt binder include four main classes of compounds: Naphthene aromatics (naphthalene); polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material; saturated hydrocarbons and asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
Applications of Asphalt Concrete
The primary use (70%) of asphalt is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Asphalt concrete consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.
Mechanical Properties of Asphalt Concrete
Strength of Asphalt Concrete
In mechanics of materials, the strength of a material is its ability to withstand an applied load without failure or plastic deformation. Strength of materials basically considers the relationship between the external loads applied to a material and the resulting deformation or change in material dimensions. In designing structures and machines, it is important to consider these factors, in order that the material selected will have adequate strength to resist applied loads or forces and retain its original shape.
Strength of a material is its ability to withstand this applied load without failure or plastic deformation. For tensile stress, the capacity of a material or structure to withstand loads tending to elongate is known as ultimate tensile strength (UTS). Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. In case of tensional stress of a uniform bar (stress-strain curve), the Hooke’s law describes behaviour of a bar in the elastic region. The Young’s modulus of elasticity is the elastic modulus for tensile and compressive stress in the linear elasticity regime of a uniaxial deformation and is usually assessed by tensile tests.
See also: Strength of Materials
Ultimate Tensile Strength of Asphalt Concrete
Ultimate tensile strength of Asphalt Concrete is 1.2 MPa.
Yield Strength of Asphalt Concrete
Yield strength of Asphalt Concrete is N/A.
Modulus of Elasticity of Asphalt Concrete
The Young’s modulus of elasticity of Asphalt Concrete is 8 GPa.
Hardness of Asphalt Concrete
In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Brinell hardness test is one of indentation hardness tests, that has been developed for hardness testing. In Brinell tests, a hard, spherical indenter is forced under a specific load into the surface of the metal to be tested.
The Brinell hardness number (HB) is the load divided by the surface area of the indentation. The diameter of the impression is measured with a microscope with a superimposed scale. The Brinell hardness number is computed from the equation:
Brinell hardness of Asphalt Concrete is approximately N/A.
See also: Hardness of Materials
Thermal Properties of Asphalt Concrete
Asphalt Concrete – Melting Point
Melting point of Asphalt Concrete is 167 °C.
Note that, these points are associated with the standard atmospheric pressure. In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium. For various chemical compounds and alloys, it is difficult to define the melting point, since they are usually a mixture of various chemical elements.
Asphalt Concrete – Thermal Conductivity
Thermal conductivity of Asphalt Concrete is 0.75 W/(m·K).
The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.
The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:
Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.
Asphalt Concrete – Specific Heat
Specific heat of Asphalt Concrete is 900 J/g K.
Specific heat, or specific heat capacity, is a property related to internal energy that is very important in thermodynamics. The intensive properties cv and cp are defined for pure, simple compressible substances as partial derivatives of the internal energy u(T, v) and enthalpy h(T, p), respectively:
where the subscripts v and p denote the variables held fixed during differentiation. The properties cv and cp are referred to as specific heats (or heat capacities) because under certain special conditions they relate the temperature change of a system to the amount of energy added by heat transfer. Their SI units are J/kg K or J/mol K.
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