WLB 10 Mobile Lab Gives Foamed Asphalt Users Look Ahead At Performance

A mobile, laboratory-scale foamed asphalt plant gives contractors and other users of foamed asphalt an advance look at how foamed asphalt will perform with a variety of materials and liquid asphalts.

Wirtgen's WLB 10 lets contractors or state DOTs pre-test materials and determine what's needed to get optimum foaming before bidding on a job or preparing a proposal. Some find it indispensable.

"We use the WLB 10 laboratory to establish foamed asphalt mix designs," said Chad Nansteel, reclamation superintendent, Intercounty Paving Associates, Hackettstown, N.J. Intercounty recently applied foamed asphalt technology to a privately owned network of roads near Hackettstown. "We bought Wirtgen's mobile lab for our lab, so we'd have the proper facilities to do the mix designs. Wirtgen's the only firm we know that provides it."

"A contractor or DOT using a WLB10 can use actual samples from the road requiring rehabilitation to determine the most suitable mix design under lab conditions," said Mike Marshall, product specialist, Wirtgen GmbH. "The WLB10 simulates what will happen during the recycling process to eliminate any suprises during construction."

The lab can help an agency determine the in-place materials preclude foamed asphalt base reclamation. "When considering options, the use of the WLB10 can provide a DOT with the information it needs to determine whether foamed asphalt recycling is a viable option," Marshall said. "This gives the DOT a greater range of rehabilitation options per road and, of course, the security in knowing the foam process will work for their project."

Finally, the WLB 10 can help keep costs in check. "With oil prices anywhere from $150 to $200 per ton, it’s essential to accurately determine the optimum amount of oil to be used in the recycling process," Marshall said. "The WLB10 enables you to determine exactly the amount of oil or other materials required, so there is no guesswork."

"Foamed" or "expanded" asphalt is created by carefully injecting a predetermined amount of cold water into hot penetration-grade asphalt in the mixing chamber of a pavement remixing unit, and offers a cost-effective alternate for road base stabilization.

Since the end of the 1980s, Wirtgen has been developing machines for the reclamation of road base courses with high load-bearing capacity. Wirtgen has been a major player in development of foamed asphalt (bitumen) technology, in which foamed hot asphalt is used to stabilize and improve existing road materials, producing highest quality base courses and cold mixes at lowest cost.

These materials can be processed in-place by milling and crushing the existing pavement structure -- while incorporating foamed asphalt -- using the WR 2500 Recycler from Wirtgen. Alternatively, cold mix can be produced by adding foamed asphalt to reclaimed asphalt pavement (RAP) -- or new mineral fractions -- in the KMA 150 mobile cold recycling mixing plant from Wirtgen.

Precise addition of water allows control of the rate of asphalt expansion and of the amount of expansion. The expanded asphalt has a resulting high surface area available for bonding with the aggregate.
While expanded asphalt doesn't completely coat all aggregate surfaces, it does form a mortar or glue which bonds the particles together. The expanded asphalt has an affinity for finer particles of 75 microns or less. This effective coating of finer particles increases the available surface area of the expanded asphalt for bonding with the coarser particles of material.

But considerations in the life cycle of the expanded asphalt, measured in its half-life, and the time the asphalt remains expanded vs. its ability to coat aggregate, require pre-application testing in the lab. That's where the Wirtgen WLB 10 is useful in precisely controlling the manufacture of expanded asphalt in the laboratory.

Because the stability of a mixture of materials essentially is dependent on the granulometric composition of the minerals, addition of certain aggregate fractions -- even including fines -- may be necessary to improve the final mechanical properties of the stabilized course. Wirtgen's WLB 10 laboratory system can help determine these properties of the foamed asphalt mix, and thus the optimum asphalt (in Europe, bitumen) foam.

The WLB 10 permits accurate testing of the foaming properties of the liquid asphalt grades to be used.
In order to determine the optimum liquid asphalt foam (half-life and expansion), a technician can conduct a series of tests in which he or she varies the asphalt temperature (140 to 200 deg C, or 284 to 392 deg F), water content (1 to 5 percent), and air input (1 to 10 bar).

The technician's goal is to determine the percentage of water needed to produce the best mix properties for a particular type of liquid asphalt. Two properties are measured: expansion ratio, and half-life. The technician wants to develop a mix with the largest expansion ratio, and the longest half-life.

Preliminary work using Wirtgen's WLB 10 foamed bitumen laboratory system permits the exact definition of the quality of the mixes to be produced for a proposed job, making reports of attainable material properties -- such as the load-bearing capacity -- possible before the start of the work.

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