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engineering materials use-case

By adminpanel In Engineering, Industry, nigeria, Tower, University On September 3, 2022

A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil subgrade, whose primary function is to distribute the applied vehicle loads to the subgrade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light-reflecting characteristics, and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced so that they will not exceed the bearing capacity of the subgrade.
Two types of pavements are generally recognized as serving this purpose, namely flexible pavements and rigid pavements. This chapter gives an overview of pavement types, layers, and their functions, and pavement failures. Improper design of pavements leads to early failure of pavements affecting the riding quality. Requirements of a pavement

An ideal pavement should meet the following requirements:  Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grad soil, structurally strong to withstand all types of stresses imposed upon it,  Adequate coefficient of friction to prevent skidding of vehicles, Smooth surface to provide comfort to road users even at high speed, Produce least noise from moving vehicles,  Dust proof surface so that traffic safety is not impaired by reducing visibility, Impervious surface, so that sub-grade soil is well protected, and  Long design life with low maintenance cost.

Failure of flexible pavements The major flexible pavement failures are fatigue cracking, rutting, and thermal cracking. The fatigue cracking of flexible pavement is due to horizontal tensile strain at the bottom of the asphaltic concrete. The failure criterion relates allowable number of load repetitions to tensile strain and this relation can be determined in the laboratory fatigue test on asphaltic concrete specimens. Rutting occurs only on flexible pavements as indicated by permanent deformation or rut depth along wheel load path. Two design methods have been used to control rutting: one to limit the vertical compressive strain on the top of sub grade and other to limit rutting to a tolerable amount (12 mm normally). Thermal cracking includes both low-temperature cracking and thermal fatigue cracking. The major flexible pavement failures are fatigue cracking, rutting, and thermal cracking.

Requirements of a pavement  An ideal pavement should meet the following requirements:  Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil,  Structurally strong to withstand all types of stresses imposed upon it,  Adequate coefficient of friction to prevent skidding of vehicles,  Smooth surface to provide comfort to road users even at high speed,  Produce least noise from moving vehicles,  Dust proof surface so that traffic safety is not impaired by reducing visibility,  Impervious surface, so that sub-grade soil is well protected, and  Long design life with low maintenance cost.

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