What is the typical road that can be recycled in place?

Good candidate — If the road has any alligator or longitudinal cracking, or low spots or need for profiling, it is a good candidate, as long as it has sound base and adequate drainage. 

What is a bad candidate for HIPAR?

A less than perfect candidate is a road that has some of the following:  

  • Excessive amounts of sub base failures
  • Mat thickness of less than 2” (50 mm)
  • Wide cracking
  • Poor or soft aggregates
  • Large aggregates larger than ¾” (20 mm)
  • Low oil content — less than 4%


However, some recent projects completed that exhibited some of the above characteristics have been corrected with proper engineering and workmanship.

How can we determine what is a good candidate?

  • Visual observation
  • Drill cores — check aggregate and oil content
  • Review records to determine the type of materials that were previously used to make original road

Ninety-five per cent of time it all works out.

How can all this be true?

How can we recycle 100 per cent of the existing asphalt pavement and restore a 10- to 15-year-old road to a like new condition with a level profile from centerline to edge?

By adding a 3% rejuvenating oil and 15% to 25% new material.

Can HIPAR be used in cities where there are lots of tight turns, manholes, casting, water valves and curbs?

Typically HIPAR has been reserved for major highways, but it is now being used more in the city. In fact, city work is where people notice the benefits immediately.  We offer minimal traffic and retail inconveniences. We are able to heat, soft mill, add a rejuvenate and virgin materials, remix and relay at a rate of about 20 feet-a-minute. Thus, the new surface can be driven on approximately one hour after the train has passed.   

The traveling public is often impressed with the process (which reflects well on the governments that chose this method).

Typically we do 2 to 3 kilometres per day in the city. When operating, we always have a continuous flow of traffic beside the equipment, only stopping traffic for truck changes, which happens about every 40 minutes, depending on the percentage we are adding at the time.

Does the recycled road need to be overlaid?

No. Many roads throughout British Columbia have not been overlaid and we are still driving on them. However, depending on the climate, volume of traffic and existing asphalt thickness it may be a good idea to top lift. In addition, instead of mill and dispose, HIRAP can be used to provide stable and uniform platform for an overlay.

Does admix always have to be utilized?

No. But if the road has sunken or fallen we recommend adding 15% to 20% new asphalt to the recycled material to bring the road back up to grade. Also it will create a much smoother road, and smoothness is synonymous with asphalt longevity.

Are there weather limitations?

We can work as long as the temperature is about 45 C (5 C) and rainwater is not accumulating on the road.

What widths do you operate?

HIPAR is normally done in 12’ (3.65m) or 13’ (3.65m) widths.

How deep do you typically soft mill the old road asphalt down?

We typically soft mill 40 mm to 50 mm (2”) and the measured thickness behind the screed prior to roller compaction is slightly greater than the milled depth because we are adding 20% new material.

Why do you mill in two-stages?

We use 2 separate milling machines in our operation because asphalt is inherently a poor conductor of heat. By heating and then picking up millings, and then heating and milling again, we minimize aggregate degradation. In our opinion, the aggregate distribution, size and shape were originally engineered for strength. If we were to remove one milling unit we would not be able to get sufficient heat penetration and, consequently, we would be splitting or fracturing the existing aggregate in the bottom inch of the road.

Can you recycle the road at night?

Yes, however production rates slow down because when the ambient air temperature is lower it is harder to get sufficient heat penetration.

How much does HIR cost with 20% new hot mix material and 3% rejuvenate?

Pricing fluctuates depending on proximity to asphalt plant location and climate. But typically, a single lane mile 12’ wide and 2” deep will cost approximately $70,000 and $80,000.00. In metric, a single lane km 3.65 metres wide and 50 mm deep will cost between $50,000.00 and $60,000.00.

What is minimum size project you would bid?

This is not an easy question. It depends on many factors, in particular distance to transport equipment. It would need to be at least 30,000 meters squared, before the process becomes cost effective. There are occasions when we can work on smaller projects if we are already working in an adjacent area. If we are moving our equipment into a different country or region then the minimum size would be about 170,000 square meters. 



Does heating up the old asphalt in the road degrade the asphalt oil content?

This is one of the biggest fallacies. By reheating the old oil in the road and adding a rejuvenating agent it will increase the quality of the old oil and in effect bring it back to life.

Recycling asphalt is like recycling an old car. It will be an inferior end product, right?

When project selection is good a recycled road will last as long as a road made with all new material. We know have 20 years of empirical data to back this up.

Governments only choose to recycle asphalt in place because that way they can say they are forward thinking and environmental.

This is simply not true. The government of British Columbia chooses to recycle asphalt because it is cost effective. Current life cycle costing does not include the long-term environmental benefits. If our decisions makers employed holistic life cycle costing whereby the entire life of the asphalt was evaluated from initial construction to disposal, then HIPAR would be everywhere.