A foamed additive

RECLAMATION WITH EXPANDED ASPHALT

With crude oil prices soaring to 20-year record highs, it would seem logical that low cost alternatives for total reconstruction of asphalt roads would he actively pursued However, this is not always the case, especially when it comes to recycling or reclaiming the road.

Dale Cronauer, vice president of Blount Construction Company ofMarietta, Georgia, USA, is a huge proponent of cost-effective road reclamation, and he sees where the challenges lie in expanding the process. "We reclaim existing roads and deliver as durable of a final product for approximately 50% the cost of new or reconstruction. However, we have trouble selling this process as a viable alternative because engineering schools and firms have little or no formal training or experience with reclamation," claims Cronauer.

Yet it is Blount's work with a relatively new and durable additive that may help the industry to recognise reclamation as a long-term solution to deteriorating roadways.

A FOAMED ADDITIVE

Blount travels the southern United Slates reclaiming asphalt roads with its two CMI RS-600 and oneRS- 800 reclaimers/ stabilisers from Tегех Roadbuilding. They are capable of recycling the existing road surface with the base at depths reaching 41 cm. A mid-mounted cutter design utilises the full weight of the reclaimers to prevent the rotor from riding out of the cut.

With every reclamation application, Cronauer recommends using stabilising additive. "If you are going to the expense of upgrading a road, you should always use an additive, it's only a minor portion of the overall expense, but the added strength and durability benefits are three to four times the cost."

Even with a number of different additive alternatives available, Cronauer prefers, and has had a great deal of success with, expanded (or foamed) asphalt. The company has been using and perfecting reclamation with expanded asphalt for the past four years.

When working with the additive, the process begins with the same type of hot binder that is used in hot mix asphalt. Cold water is injected into the 176 °С liquid asphalt, causing the binder to expand to about 15 times the original volume in the reclaimer's mixing chamber. At this point, the asphalt is much thinner and less viscous.

Foaming temporarily changes the surface tension in the asphalt improving its adhesive properties and greatly improving ability to coat material. Once the expanded asphalt is sprayed in the reclaimer's mixing chamber, the foam adheres to the finer particles which then act as a mortar for the larger particles. According to Cronauer: " After compaction the newly stabilised base is often three times the structural number of the original road."

Recent modifications to computer controls and on-board heating systems, which make the process more accurate and efficient have been instrumental in producing quality foamed asphalt mixes. The fully automatic microprocessor control on Blount's CMI reclaimer/ stabilisers manages the flow of expanded asphalt into the reclaimed material.

Aninternal gear pump offers a flow rate of 511 litres per minute, while a three way asphalt valve on the system allows for fluid transfer between asphalt trucks. The system's patented single point water injection process ensures uniform asphalt cement/water mix throughout the spray bar to all nozzles.

From the control console, the operator sets the application width and desired mix design specs, consisting of percent weight of asphalt, injection water and compaction water. The microprocessor takes inputs from machine speed, elevation and application width to modulate the low of asphalt andwater.

Sample flow rates taken once реr second by the microprocessor ensure consistency and any necessary adjustments to the mix are automatically made. "Іf there are any changes to depth, application width or machine speed, the pump speed automatically adjusts, keeping a consistent percentage mix based on bulk relative density" comments George Denny, vice president, mobile division for Terex Roadbuilding.

A new heating system on Blount's CMI reclaimers makes working with the expanded asphalt much more user friendly. With early asphalt injection system designs any binder remaining in the reclaimer's system would have to be cleared on a daily basis Contractors would run about 50 gallons (nearly 190 litres) of diesel fuel through the injection system to fully clear the lines,"' says Denny.On top of being costly andcumbersome, this practice was not very environmentally friendly.

With the CMI heating system, reclaiming crews canleave the hot asphalt binder in the injection system. The next day, the crew simply turns on system heaters and the asphalt binder in the lines is liquefied andheated to appropriate mixing temperatures.

The automated process and heating system is said to make working with expanded asphalt more user -friendly

"If road reclamation is done properly with the correct additive, the new road will last as long as, if not longer, than new construction," says Cronauer. With lower costs andthe same durability, the industry will not he able to ignore reclamation forever.

Дата добавления: 2015-11-14