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(Automatic translation)

Influence of milling conditions on the grading of the recycled material

Michel Froumentin
Head of Section Geotechnical and building materials.
Experimentation Center Road of Rouen (France)

Jean BAUER
Head of Studies.
Highway Department.
Laboratoire des Ponts et Chaussées Regional Rouen (France)

ABSTRACT
The principal documents on the technique of cold recycling in situ recommend that the diameter of the particles coarser milling should not exceed 37,5 mm, leading a grading curve as continuous as possible in which the material passing through the sieve 25 mm is between the 90 and 100%. The particle size of the recycled material determines the laying of the mixture and, in fact, involved in obtaining good mechanical properties of the recycled material in the medium and long term.

This article presents the studies controlled within the SCORE Project in order to analyze the influence of milling conditions on the grading obtained location. The experiment, conducted at the Centre for Road Experimentation of Rouen, was carried out on 15 test sections divided into 2 types of structural section, especially studying the effect of the depth of milling, the feed rate of the machine and of adhesion.

It has been observed in all cases the percentage of fine particles is constant and the presence of mineral dust is negligible. The milling process always results in a rather discontinuous granulometric curve, preventing compaction. The decrease in speed milling involves a significant reduction in size of the coarser particles and increased the finer particles. When mixing the layers are adhered old firm, the grading curves are fairly similar for all milling speeds. In the case of unbonded layers, a small increase in speed means the appearance of large particles (biscuits), as the cutting depth is close to the interface between unbonded layers. This phenomenon, which is a function of speed, is appreciable at intermediate speeds of the order of 5 8 to m / min and it becomes very important for speeds over 10 m / min. Regarding the influence of the degree of compaction of the milled mixture, thicker granulometry are obtained if the compactness of the material is higher strawberry.

Overall the study undertaken shows that the characterization phase of the damaged road, necessary in every work of recycling in situ, is relevant to the adequacy of the means that will be required in the works. In particular, the degree of adhesion of the layers to recycle allows assess the maximum allowable milling machine to meet the limits of gradation speed recycled material.

KEYWORDS:
Milling, Recycling, Cold recycling, SCORE, Milling speed, Milling Grit.

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