Improvement of Asphalt Workability

Pawma is used to increase the workability in Bituminous Hot Mix (BSK) or Warm Mix Asphalt (IKA) production. Since the mid-1990s, various techniques have been developed to improve workability in BSK production or to reduce energy consumption by lowering mixing and laying temperatures. Several techniques are employed to enhance the workability of asphalt mixtures:

Techniques for Improving Asphalt Workability:

PE waxes, amide waxes, or paraffin waxes
Foaming technique and zeolites: Istanbul Technical is the distributor of the synthetic zeolite Aspha-min in Turkey.
Amin-based liquid chemicals: Istanbul Technical has developed the amin-based chemical Pawma.

There are two main application areas:

Bituminous Hot Mixes (BSK)

1a. Due to climate conditions in many regions of our country, the asphalt road construction season is quite short. According to the Highways Technical Specification, the minimum ambient temperature for laying asphalt mixture is 5°C in the shade. When the climate conditions are not suitable for asphalt road construction, the asphalt layer laid on the road quickly begins to cool and solidifies before compaction is completed, making it impossible to compact.

Naturally, the asphalt layer laid under these conditions cools rapidly. However, since the workability of the asphalt mixture with PAWMA continues until the temperature drops to a certain level, additional time is gained for the rollers to complete their compaction work.

Thus, it enables the extension of the asphalt road construction season.

1b. Additionally, if the distance between the asphalt plant and the road to be laid is long, or if there is a possibility of waiting and delays for trucks loaded with asphalt, the asphalt will lose heat, causing the laying temperature to drop. By increasing the workability of the asphalt with PAWMA, it becomes possible to safely transport the asphalt over longer distances.

1c. The workability and compaction of SBS-modified asphalt become challenging. When modified asphalt is laid on the road, it begins to cool rapidly, solidifying in a short time and becoming uncompactable. When PAWMA is used in SBS-modified asphalt, the workability of the asphalt increases, allowing for more comfortable and secure compaction.
Warm Mix Asphalt (IKA)

2a. As the name suggests, Warm Mix Asphalt (IKA) is produced at lower temperatures.

In warm mix asphalt applications, the aggregate temperature is reduced by approximately 30°C. The bitumen is heated to its normal design temperature, which is around 140°C - 150°C. If the bitumen temperature drops, its viscosity will increase, and its fluidity will decrease; therefore, the bitumen temperature should not be lowered.

When the aggregate temperature is lowered, PAWMA should be used to ensure that the bitumen can adequately coat the less heated aggregate. There will be no extension in the mixing time during asphalt production in the plant with PAWMA.

Asphalt consists of two primary components: aggregate and the binder, bitumen. Including fillers, aggregate makes up approximately 95% of the total asphalt weight. The majority of the energy spent on heating the asphalt mixture is used for the aggregate. By lowering the aggregate temperature, significant energy savings can be achieved.

Considering the high energy costs in our country, significant savings can be achieved through the warm mix asphalt technique in the production of millions of tons of asphalt. Additionally, many advantages listed below can be gained. The aging (oxidation) of bitumen mainly occurs due to the heating in asphalt production. Producing asphalt at low temperatures will reduce the aging of bitumen and extend its lifespan.

2b. Ventilation conditions inside tunnels are often insufficient. Especially in long tunnels, the gases emitted during asphalt laying pose a health hazard for workers in the tunnel.

As described above, when asphalt is produced with reduced aggregate temperature, the gases and smoke effects generated are significantly lowered. Thus, the likelihood of tunnel personnel being adversely affected by the gases decreases.

In some countries, it is mandatory to lay asphalt using the IKA technique inside tunnels.

Application

The PAWMA chemical additive developed by Istanbul Technical is used by mixing it into the bitumen beforehand. The usage amount is between 0.2% and 0.4% of the weight of bitumen. Therefore, approximately 150 grams of Pawma is sufficient for 1 ton of asphalt mixture.

The dosage of the additive should be determined in the field according to the type of application, whether the asphalt is modified or not, and environmental conditions such as ambient temperature and wind. Several batches should be produced using different amounts of PAWMA to determine the dosage in the field. Since each application is different from the others, there is no standard dosage table, and the amount to be used should be determined according to local conditions.