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Task 4.1: Production of RA



Aim of the study

The original aim of Task 4.1 of the RE-ROAD project as defined in the Annex 1 of the Grant Agreement, is “to assess the present level of technology and identify the influence of different milling operations on the crushing of the large aggregate and on filler production in the RA together with the influence from polished old surface aggregate in thin surfacings to future reuse”.

It is also specified that “in order to quickly verify the physical and geometrical characteristics of aggregates, after milling, the videogranulometer can be used with the specific methodology for RA, worked out in the work package 1.”

This program was slightly modified and adapted in agreement with the RE-RAOD beneficiaries. It was defined that the intention now was to relate the characteristics of recycled aggregates (obtained from former asphalt bound layers) to milling settings for the purpose of possibly improving milling operations.

Short overview of cold milling

The first experience on concrete or asphalt pavement was approximately 40 years ago when a grade trimmer was upgraded to mill asphalt pavement. It first occurred in the US but the technique was rapidly extended to the rest of the world, and Europe in particular.
One of the first uses of large milling machine in France (source: LCPC)
Eventually, the manufacturers developed more powerful machines. The latest progress concern the productivity of the machines, their safety, reliability and serviceability.


Coring the N164 highway

Principle of the field monitoring

The intention is to compare the same road material, but taken before and after the milling operation so that the aggregates could be cleaned and then compared for possible evolution of their geometry (dimensions, shape).

Several milling parameters (machine forward speed, cooling water flow) are taken to assess their possible impact on the aggregate evolution. A total of 6 sets of parameters are finally selected.

First, cores are extracted from the road before the milling operation. Cores are 16cm of diameter and are cut at a depth corresponding to the eventual milling depth. The quantity of material is hence, quite low and the core edges present aggregates with cut faces. This point is of importance when eventually analysing the aggregates changes before and after miling.

Cores are then cleaned of the binder (bitumen) and aggregates are tested according to the relevant European norms (grading, flakiness index, LA, MDE…).

Each set of milling parameter is applied on an identified section of the road whose length approximately corresponds to the quantity that can be loaded on a semi-trailer truck. The milled products (reclaimed Asphalt Pavement, RAP) are then sampled (30kg each time). Water content and grading tests are performed on the RAP and the material is then bitumen-stripped.






The semi-trailer, the milling machine and the mechanical sweeper

The cutting tools mounted on the drum

Sampling on the stock


The same aggregate tests as the ones done on cores aggregates are also performed on RAP stripped aggregates. The results of each set of results can be compared to each other.