Cellulose SMA Fibers
Description & Benefits
Bitubind Fibres are used in the manufacture of Stone Mastic Asphalt (SMA) and Open Graded Pourous Aphalt (OGPA).
Bitubind Fibres can be added directly to the bitumen with the low melt bags that dissolve readily into the binder or directly into the asphalt plant.
An additive rate of 0.3% of the total SMA mix is all that is required to prevent binder drain down and to produce a high performing SMA.
Stone Mastic Asphalt is a strong performing asphalt that works well in heavily trafficked areas because of the larger single size aggregate that can be used with the increased bitumen content. The stone on stone contact along with the increased binder content makes for a high performing asphalt with the benefits of reduced noise, better skid resistance (especially in the wet) and reduced wheel rutting.
An interesting observation is that SMA asphalt has better performance in the field than lab tests indicate because of the increased strength the pavement is able to harness from the stone on stone contact. As a vehicle passes over SMA the downward force is spread over a wider area as the matrix of interconnecting stones is able to share the load unlike tradition asphalt mixes which absorb all the downward pressure directly under the tyre.
More bitumen generally creates a stronger asphalt. However too much bitumen and the asphalt will flush to the surface and create a skidding hazard and eventually asphalt failure and too little bitumen and you have a weak brittle mix which will unravel and fall apart. Cellulose fibers help to get the most amount of bitumen into the mix without it draining through and 'flooding' the asphalt.
Excessive drain down or flooding occurs when either too much bitumen is being used, bit enough fiber has been added or the fiber is not of a significant quality to absorb and hold the bitumen in suspension within the mix design. Excessive drain down produces poor quality asphalt and unhappy truck drivers who will have to spend hours cleaning out a thick carpet of bitumen from the bottom of their truck decks. Any Project Manger would prefer to spend a little more on a quality fiber rather than deal with the wrath of angry truck drivers.