Multigrade bitumens

Multigrade bitumen is a special binder that, for the same level of penetration as conventional bitumen, is not as susceptible to temperature changes. This means that it is more consistent at high temperatures and less fragile at low temperatures. In fact, multigrade bitumens have higher penetration index values than conventional bitumen. 

The asphalts produced with this type of bitumen provide better resistance to rutting and better performance to low-temperature fatigue cracking, in comparison to those produced with the same-grade conventional bitumen. 

Multigrade bitumens are manufactured at the refinery by means of a special refining process. The process involves the chemical reaction, under tightly controlled conditions, of oxygen and hydrocarbons. Additives, aromatic components and others (not polymers) may be used depending on the feedstocks. 

Multigrade bitumens come with trade names such as Multiphate, Multibit, Bitrex, Biturox, KNB-MGB, to name a few. They are normally used for the production of high-stiffness 

Experimental measurements carried out in 2009-2011 on the use of multigrade bitumens in chip sealing (surface dressing) did not show any advantage for multigrade bitumens compared to standard binders with a similar 25°C penetration value (Herrington et al. 2011). Multigrade bitumens do not replace polymer-modified bitumens. 

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A European specification is going to be developed for multigrade bitumen (prEN 13924-2 under approval). 

Herrington P., M. Gribble, and G. Bentley. 2011. Multigrade Bitumen for Chipsealing Applications. NZ Transport Agency Research Report 460. Wellington, New Zealand NZ Transport Agency. 

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