FAQ >> Use of aggregates for asphalts around the world

Use of aggregates for asphalts around the world

A wide range or aggregates is usea arouna me woria to manuiacwre asphalts. However, it is beyond the scope of this Chapter to discuss these in detail, other than to mention some of the main factors involved. Obviously, ease of availability is the single most important factor in dictating usage. For example, Northern Ireland has approximately 100 hard rock quarries whilst Holland has none. Contrast Iceland, where the only available rock type is basalt, with the UK which is endowed with almost every type of rock spanning geological time. Factors such as availability, distance of source to market, climatic conditions, national specification requirements and choice of asphalts all combine to make the selection of aggregate around the world a complex subject. Europe may he broken up into a number of distinct areas.

  • Possibly due to its Atlantic climate, the UK has a wide range of available rock types. Historically, great importance has been placed on skid resistance. This combination has favoured the use of high PSV gritsione and sandstone aggregates as surfacing aggregates with a minimum level of PSV specified for all other asphaltic materials.
  • Scandinavian countries, with a combination of very cold winters and the need to use studded tyres, have favoured the use of very hard igneous and metamorphic aggregates to withstand these climatic and trafficking conditions.
  • Mediterranean countries possess, as their main rock type, limestones with poor strength and low levels of skid resistance. Heavy traffic and warm conditions coupled with the use of limestone in dense asphalts of low texture depth and skid resistance has resulted in surfacings which are extremely dangerous when wet.
  • France and Germany tend to favour the use of hard wearing aggregates in thin rut-resistant surfacing mixtures.

It can be seen from the short description above that the availability of aggregates. their properties and local conditions have affected the use and choice of asphalts across Europe. A similar picture occurs across the world. North America has a vast highway structure in which local materials are used一the import of aggregates. as in the south east of England, would be too costly. The main types of aggregate used include limestones. basalts. dolerites. granites and sandstones. Their selection has typically been assessed using the Los Angeles Abrasion Value. Unlike the UK. in the USA there was little, if any, interested in skid resistance characteristics.

One of the most economically active areas in Asia is Hong Kong However, it has problems with its aggregate supplies. The main rock type is granite, which tends to suffer from alteration and weathering problems Indeed, being able to secure a source of aggregate for a large construction job is a major benefit when tendering. Many countries within tropical areas suffer from deep weathering and alteration of potential aggregate sources due to their climate. In southern Australia and New Zealand, alteration of basalt and greywacke aggregates is also a problem and has prompted considerable research into the understanding of this process Research into 'local' problems has resulted in the development of many commendable test methods which can highlight aggregates which may have problems. However. the opposite can also be the case. The use of UK or US specifications and methods in developing countries may not take due account of local materials and conditions.

Despite the geological diversity of aggregates around the world an engineer who is aware of inherent problems associated with particular rock types and approaches the selection process by predicting the likely in-service performance should avoid costly premature failure.

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