Low temperature bitumens

Los ligantes BT (Baja Temperatura) de Cepsa permiten reducir la temperatura de fabricación de las mezclas asfálticas manteniendo la trabajabilidad necesaria para su extendido y compactación.

La temperatura de fabricación se puede reducir normalmente entre 20 y 40 ºC respecto a la mezcla en caliente original, dependiendo del tipo de mezcla, tipo de áridos, condiciones de la obra, etc.

Utilizando el ligante BT adecuado, se puede fabricar mediante la tecnología semicaliente prácticamente cualquier tipo de mezcla asfáltica, incluidas las que incorporan material de fresado (mezclas recicladas). En este caso, los ligantes BT ayudan a su incorporación y a la fabricación de la mezcla.

Los ligantes BT se pueden utilizar en todo tipo de plantas asfálticas, no requieren ningún tipo de modificación en la instalación.

-  El PG3 en vigor (Orden FOM/2523/2014) permite la utilización de mezclas semicalientes en los artículos 542, 543 y 544 (este artículo según la O.C 3/2019) para los tráficos T1 a T4. En la práctica, consideramos que también se podrían aplicar con éxito para tráficos más pesados y en otros tipos de mezclas no recogidos en la normativa actual.

- También aparecen explícitamente en los pliegos de obras de algunas comunidades autónomas y diputaciones.

In these mixtures, the heating temperature of the aggregates, which account for approximately 95% of the mass of the asphalt mixtures, is considerably lowered, enabling fuel consumption to be reduced by 25 to 35%. This leads to:

• A considerable reduction in atmospheric greenhouse gas (GHG) emissions.
• Significant economic savings by reducing the fuel required to heat the aggregates.
• Improved working conditions for personnel, mainly on site, due to lower paving temperatures.
• Easier incorporation of milled material, especially in conventional plants, since excessive overheating of the virgin aggregates is not necessary to achieve an adequate mixing temperature.

• It allows traffic to be opened quickly, which is of particular interest to airport runways, roads with high traffic intensity, tunnels, etc.
• It increases the workability time of the mixture by allowing for a lower minimum compacting temperature. Using CEPSA BT bitumens at the standard temperatures for hot mixtures is very useful for:

• Construction projects with a long transportation time between the plant and the construction site.
• Worksites with slow execution times, such as streets, potholes, tunnels, etc.
• Worksites in adverse weather conditions, such as cold and wind.

We have a complete range of binders for semi-hot mixtures. The ones that are most used are:

• Cepsasfalt BT 35/50 and BT 50/70: Low-temperature asphalt binders that comply with the specifications of conventional bitumens B35/50 and B50/70 of article 211 of PG-3 and those included in the National Annex of UNE standard EN 12591. They have CE marking. 
   
• Cepsasfalt BT: Asphalt binder specially formulated with waxes to allow the manufacture and application of asphalt mixtures to be carried out at temperatures below normal, through viscosity reduction at high temperature. 

• Elaster BM-3c BT: Low-temperature binder modified with high-performance elastomeric polymers that meets the requirements of PMB 45/80-65 defined in PG-3 and in the UNE standard EN 14023. This bitumen has a high softening point, above 65ºC, high cohesion, and storage stability. Recommended for all types of mixtures, especially open and discontinuous mixtures and those used on roads with the most demanding traffic. It has CE marking. 

• Elaster RAF BT (PMB 45/80-75) High-performance binder modified by a chemical reaction with elastomeric polymers. It allows special and high-performance mixtures to be produced at low temperature, such as anti-cracking treatments, draining mixtures with high void content, mixtures with high resistance to shear stress, SMA, and anti-rut mixtures. It complies with the specifications set forth in article 212 of PG-3 and in the UNE EN standard 14023. It has CE marking  

• Flexodur BC 35/50 BT y BC 50/70 BT: Binders that have been enhanced with rubber from tires at the end of their useful life, additivated for low-temperature mixture manufacturing. They are manufactured in a modified bitumen plant using the wet process technique. They can be used as a substitute for conventional bitumen of the same penetration, even in discontinuous, draining, and SMA mixes in T2 and lower traffic.

• Flexodur BMC-3b BT: Binder modified exclusively with rubber from tires at the end of their useful life, additivated for low-temperature mixture manufacturing. It is manufactured in a modified bitumen plant using the wet process technique. According to PG3, it can be used as a substitute for PMB 45-80/60C in semi-hot mixture manufacturing.

•  Flexodur BMC-3c BT: Hybrid binder modified with elastomeric polymers and rubber from end-of-life tires, additivated for low-temperature mixture manufacturing. It is manufactured in a modified bitumen plant using the wet process technique. According to PG3, it can be used as a substitute for PMB 45-80/65C in semi-hot mixture manufacturing.

The design criteria for semi-hot mixtures are similar to those of their hot counterparts, although, due to the lower compacting temperatures, special attention should be paid to aspects such as:

• Void content and density
• Sensitivity to water
• Resistance to plastic deformation
• Stiffness modulus

Due to the compacting method used in the laboratory, it is possible that the densities obtained with BT binders are lower than those of their equivalents for hot mixtures. In our experience, this is not a problem on site, since compacting is much more energetic. 

To facilitate handling and wrapping, these binders are used at a temperature similar to that used for conventional binders. Therefore, when manufacturing the mixture, the reduced aggregate heating temperature is what results in the lower final temperature of the mixture. In the case of binders made with waxes, the handling and wrapping temperature can be reduced due to their lower viscosity.

In any case, at laboratory scale, it is advisable to keep the manufactured mixture in the oven for the time necessary to ensure that compacting is carried out at the desired temperature.

For a more detailed analysis of the work formula, it may be advisable to carry out a compactability study of the mixture in a gyratory compactor, and to analyze the workability of the mixture.

It should be taken into account that the type of compacting, at laboratory scale, and reduced ageing of the binder due to the lower manufacturing temperature of the mixture have an effect on the result of some tests, such as the track test (UNE-EN 12697). The results are relatively often lower than those obtained with similar hot mixtures, although, according to our experience, this has never led to plastic deformation on site, due to the higher compacting energy applied. In addition, semi-hot mixtures have the advantage of greater durability due to the lower degree of ageing of the binder.

In any case, it should be remembered that low-temperature mixtures require a specific design, meaning that adjustments in binder content and grain size may be necessary and beneficial with respect to conventional reference mixtures to ensure the best possible performance.

For the definition of manufacturing and on-site temperatures, apart from the binder, factors such as the type of aggregates, their grain size, the binder and fines content, the climate, as well as the means of manufacturing and on site use must be taken into account. In general terms, the following aspects are important:

• Selecting the manufacturing temperature while taking into account transport time and weather conditions to obtain an adequate compacting temperature.
• The type of compacting will be similar to that used for equivalent conventional mixtures, but it is advisable that it be somewhat more energetic, bringing the rollers as close as possible to the paver and making additional passes if necessary, especially in cold and windy weather conditions.

It should be kept in mind that when manufacturing these types of mixtures, only the aggregate heating temperature is reduced, which is the predominant temperature for the whole mixture. For this reason, it is advisable to perform previous tests to adjust the asphalt plant, verifying the temperature of the aggregates and the perfect combustion of the burner.

We have experience in semi-hot mixtures in worksites with different types of BT binders. Some examples are:

• GI 4141 Highway (Asteasu) with Cepsasfalt BT
• Gandesa through road N-420 (Tarragona) with Cepsasfalt BT 35/50.
• Medina de Rioseco - Villafrechós CL 612 (Valladolid) with Cepsasfalt BT 50/70,
• A 62, Magaz de Pisuerga (Palencia) with Elaster BM-3c BT

• C-12 km 185 (Lleida) with Elaster RAF BT (high-performance binder)

Other techniques exist for manufacturing semi-hot mixtures, but they require modifications to the mixing plant or significantly reduce its performance. For the foaming technique, our range of low-temperature bitumens (BT) can be a perfect addition for better performance.

Warm mixtures are another low-temperature technique option and are based on the use of a bituminous emulsion as a binder. Cepsa has a complete range of emulsions to manufacture different types of warm mixtures. Consult our range of emulsions in the following link.