Hot-mix asphalt is used for the majority of paving worldwide. In the U.S. and Canada alone, approximately 33 million tons of asphalt are used in paving each year, of which about 90 percent is applied by hot-mix paving methods. A key factor in determining strength and durability of paving is the ability to compact the mix to the desired densities. A mix that is not properly compacted lacks strength and is prone to various pavement stresses. The temperature of the mix has a big influence on the ability to compact. Various grades of asphalt are used in hot-mix and some are more viscose or harder than others. The more viscose or harder the asphalt, the higher the temperatures needed for more efficient compaction.

However, the use of higher temperatures substantially increases the amount of asphalt fumes produced during manufacture and at the site of road construction, causing significant concern for the environment, as well as for the health of personnel. These days there is a major impetus by the asphalt industry and by regulatory agencies to minimize the asphalt fumes to advance environmental stewardship. The hot-mixes that can be produced and paved at temperatures lower than normal temperatures are known these days as warm-mix applications.

Akzo Nobel’s Rediset™ WMX solutions:

Akzo Nobel Asphalt Applications group has been doing research in this area and has recently developed cost effective and novel solutions that enable hot-mix paving at lower temperatures. Warm-mix asphalts which are made at lower temperatures are especially prone to moisture damage as the aggregates may not be totally dry. Rediset™ WMX products not only lower mixing and paving temperatures but also directly addressed the issue of moisture damage associated with hot-mix asphalt. In this respect our innovation has clear advantages over the other warm-mix solutions that are being offered to the market. A patent application based on this innovation has just been filed.

On November 13th a field trial was conducted with Rediset™ WMX additive in Chico California in co-operation with Knife River Companies, Kent’s Oil and Baldwin Contracting Company. In the trial using Rediset™ WMX it was possible to reduce mixing and paving temperatures by 50-60oF and still get better compaction compared to the control. Almost no fumes were observed with the warm-mix with Rediset™ WMX in 240oF warm-mix compared to the control mix at 300oF where significant amount of fumes were very visible.

The following are actual comments from personnel from Baldwin Contracting Company.

• “…extremely positive characteristics at significantly less than standard mixing and placement temperatures”
• “At lower temperatures studied in this trial (240oF and 270oF) compaction efforts were minimized to achieve desired densities … substantial impact on placement costs … Could in fact increase the durability and life of the paved surface.”
• “…operational costs including those incurred by fuel consumption should be lowered”

In summary our Rediset™ WMX warm-mix additives reduces asphalt fumes to a great extent and at the same time significantly improves the moisture resistance properties of the asphalt mix. In addition, it has all the warm-mix benefits such as reduced fuel costs, reduced operational costs due to ease of mixing and compaction, ability to pave in non-attainment areas, paving in cool weather, extending the asphalt paving season and able to haul the mix to longer distances. Several asphalt hot-mix producers and asphalt suppliers have shown significant interest in our Rediset™ WMX solutions and further field trials are being planned. Akzo Nobel Asphalt Applications group is planning to launch this product globally.

Figure 1: Rediset™ WMX pastilles.

Figure 2: Densification Test Results with Vibratory Compactor

Figure 3: Warm-Mix with Rediset™ WMX at 240-250ºF

Figure 4: Control Mix at 300-310ºF