TABLE OF CONTENTS Bitumen has been in use as an essential construction material for thousands of years due to its binding and waterproofing nature. Above 100 C, bitumen is a highly viscous liquid. It hardens at lower temperatures, tending to become hard and ultimately brittle at sub-zero temperatures.
In most highway applications, paving grade bitumens do a perfectly good job in meeting the demands of the UK's busy road network, though there will be situations where the use of polymers is preferred. This may be required, for example, to improve asphalt's resistance to permanent deformation at elevated service temperatures, to improve the asphalt's ductility to reduce the risk of thermal cracking at low temperatures, to improve binder aggregate adhesion to reduce risk of aggregate stripping, or to lay asphalt surface courses in very thin layers (<25 mm) whilst maintaining texture retention, durability and delivering higher levels of traffic noise reduction. Today, more than 5 million tonnes of PMB is used by the global roads' industry per year.
Since polymers used to modify asphalt behaviour are effectively modifying the bitumen component in the mixture, it is appropriate for bitumen to be discussed briefly with some discussion of how polymers actually modify bitumen properties.
Bitumen is derived from crude oil by subjecting it to a controlled distillation process that removes the light fractions (distillates), leaving bitumen as a heavy residue. Bitumen is a viscoelastic material and is particularly temperature sensitive. It is also prone to permanent deformation under...
