Practical experience with Stone Mastic Asphalt

The restrictions for Stone Mastic Asphalt 0/11 S and 0/8 S which were newly regulated, are explicitly spelled out in the section "Technical Regulations". These restrictions were taken from "Modifications and Additions", which was issued 1998 together with the Supplementary Technical Conditions of Contract, Specifications and Guidelines for the Construction of Pavement Courses Using Asphalt. There was skepticism and even a total lack of understanding from many experts in the field regarding the significant increase in the lower threshold value for the chippings content up to a minimum of 75 wgt.%.

Using mix design tests, it was discovered, as expected, that this lower threshold value of 75 wgt.% was unsuitable for many regions and for some types of aggregate because it was just too high.

Unfortunately these objections were initially ignored. A compromise was suggested to put the range between 73 and 78 wgt.%. This suggestion took the objections those with practical experience into account, but was not accepted.

It was an obvious step therefore to ask the experts "at the front" about their experiences after a two year trial period during which they produced and processed the mixtures using the new regulations.
In the section entitled Commentary you can find a brief summary of most important comments of those questioned.