Binders: types
Paving grade bitumen (complying with EN 12591)
Components of Bitumen Mastic Straight-run bitumen types are mostly used in Mastic Asphalt mixtures. Bitumen is defined as the residual product from distillation of crude oil in petroleum refining. Bitumen is produced to specification directly by refining or by blending. Bitumen characteristics are generally deter-mined by the principal properties:
– rheological characteristics
– cohesion
– adhesive power on minerals
– aging
For the use of mastic asphalt the different types of bitumen are characterised by
– penetration
– softening point
The denomination of the types of bitumen is based on the typical character of these proper-ties. Paving grade bitumen used normally for mastic asphalt is less than 50 mm penetration.
Hard Grade Industrial bitumen (complying with EN 13305) and Hard Paving Grade bitumen (complying with EN 13924)
Although straight-run bitumen is most often used, hard bitumen (obtained through mild oxi-dation of bitumen / air rectified bitumen with PI ≤ +2.0) is used for certain mastic asphalt ap-plications (e.g. indoor applications).
Hard bitumens are characterised according to the limits of the softening point values. These are bitumen showing hard and brittle characteristics at ambient temperature. Therefore they are only used for indoor applications. A typical grade is H 90/100.
Synthetic pigment-able binder
A synthetic pigmentable binder is a synthetic binder, which is easily pigmentable. With this kind of binder you can add a small amount of pigment to the binder to obtain a wide range of coloured asphalts.
The binder is either modified with polymers or not. It is mainly used for small infrastructures such as footpaths, bicycle roads, for aesthetic or safety reasons.
Binders: contents
The binder content of mastic asphalt is depending on the end use. It is so adjusted to the void content in the mineral aggregate that voids are completely filled and can vary between 6 up to 12 percent, but can be increased for special applications.
Binders: additives
Addition of polymers (complying with EN 14023)
During the past years polymer modified bitumen (i.e., elastomers or plastomers) has also been used more often. This makes it possible to adapt certain characteristics of the base bitumen to the projected application.
Generally, this results in the following:
– superior visco-elasticity
– improved cohesion
– increased adhesive power
Addition of natural asphalt
Natural asphalts are naturally-occurring mixture of bitumens and mineral matter formed by oil seepages in the earth’s crust. Natural asphalts include Trinidad Lake, Rock, Gilsonite, Sele-nice and others. There are not refined bitumens.
In some cases so-called «natural asphalt» has been added for many decades in small quan-tities (1 to 2 per cent of the final mixture). It is mostly the natural asphalt known as Trinidad-Epuré (EINECS: 310-127-6, CAS: 999999-99-4), which consists of approximately 54 % natural bitumen and approximately 46 % limestone filler. This natural asphalt is mined at the surface on the island of Trinidad (in the Caribbean). The Mastic Asphalt Industry – A Global Perspective
Another type of natural asphalt comes from the USA (Utah) and is known as Gilsonite (CAS number 12002-43-6). The bitumen content of this bitumen is approximately 92 %.
Components of Bitumen Mastic In Europe, production of the Selenizza-asphalt (origin Albania) was resumed. The bitumen content of this asphalt is also approximately 90 %.
Finally, it must also be mentioned that in the past (at present only to a very limited extent) natural asphalt powder was mined in a number of distinctive mountainous areas in Europe (France, Spain, Switzerland).
Addition of wax derivatives
Other additives are aimed at influencing viscosity. Although this is a direct function of the temperature, a number of products were developed that increase the workability at a certain temperature.
As a consequence of the tendency during the last years in which the emission of bitumen fumes is kept as low as possible, these additives can thus also provide the same workability at a lower temperature of the mastic asphalt mixture. These additives belong to the so-called wax derivatives.
Addition of pigments
Some efforts have been made to colour mastic asphalt (mostly for aesthetic reasons) and this in spite of the limited possibilities to colour the straight-run bitumen (amongst other things, because of the content). The most used pigment is certainly iron oxide, which gives a rather red brownish colour. However, to obtain reliably coloured paving, other binders must be used (see above).
Addition of fibers (in combination with the addition of natural asphalt)
In the past, recourse was sought (mainly in Germany) in the addition of natural fibres (mostly of vegetable origin / cellulose fibres). The purpose was to improve the stiffness (particularly) during and (to a lesser extent) after the placing, e.g., in cases of a sloping subsurface.
Fillers
This is the smallest mineral fraction and contains all particles with a maximum diameter of 0.063 mm (or: passing the 0.063 mm sieve).
For mastic asphalt, crushed limestone is used in most cases.
In acid-resistant mixtures, the usual limestone filler (not acid-resistant!) is replaced by a sili-ceous filler, which, on the contrary, is considered as acid-resistant.
Components of Bitumen Mastic To obtain a mastic asphalt mixture with a suitable processing temperature (during manufac-turing!) it is advised to heat the filler in a device specially provided for that purpose. This makes it possible to introduce the filler at a temperature of approximately 150 to 180 °C (in-stead of the normal ambient temperature of, e.g., 20 °C). The Mastic Asphalt Industry – A Global Perspective
Mineral aggregates
Fine aggregates (former sand)
A distinction must be made between
– natural sand, this is found in natural locations (with a round shape) and
– crushed sand which is obtained by crushing (in a crusher) of rock particles (with a cubical shape).
This refers, basically, to the mineral particles between 0.063 and 2 mm. Of course, the origin of the source rock from which the sand fraction is obtained is of great importance.
In the case of underlayers, e.g., (such as waterproofing layers), what is referred to as “soft” aggregates, are more readily accepted, while what is referred to as “hard” aggregates, will be required for wearing courses. Regarding stability, crushed sand is considered to provide a higher level of security than natural sand, because the cubical structure of crushed sand gives better “anchorage” than is the case with the round particles of natural sand.
Limestone Fine Aggregate
Limestone fine aggregate consists of crushed naturally occurring limestone with a calcium carbonate content of not less than 80 %. A substantial proportion is retained on a 0.063 mm sieve and most passes a 2 mm sieve. Limestone fine aggregate may be used as an alterna-tive to, or in conjunction with fillers and/or sand.
Coarse aggregates
This refers to all mineral aggregates with a diameter > 2 mm.
There are two sieve-sets in the standard – different form country to country. In the case of mastic asphalt, aggregates with the following particle size are mostly used:
– 5.6 or 4 mm for layers with a thickness up to 20 mm
– 8 or 6.3 mm for layers with a thickness up to 30 mm
– 11.2 or 10 mm for layers with a thickness up to 40 mm
The origin of the mineral particles determines, just as is the case for the “sand fraction”, to a certain extent the use:
– «soft» for base layers
– «hard» for surface layers
The classification of aggregates is based on a number of typical characteristics:
– frost resistance
– shape of the particle
– shock resistance
– abrasion resistance
– density
– water absorption
– etc.
The minerals are usually of natural origin, (from stone quarries); but sometimes «synthetic» minerals are used (e.g. expanded clay) with the purpose of reducing the specific gravity. Currently, there is also a tendency to increasingly use reclaimed mastic asphalt in the production of mastic asphalt (= recycling).
Components of Bitumen Mastic For acid-resistant mixtures, the mineral fraction must, of course, also have the same characteristic.
