Every year in Switzerland about 5 million tons of bituminous mix are used for the construction and reconstruction of roads. This process is harmful to the environment in two ways: Firstly, additional land is necessary to deposit the old bituminous mix. Secondly, the use of new resources of quarrying natural gravel is not possible without interfering with the environment. In order to protect scarce resources and to reduce the amount of land fills old pavement materials should be re-used in new pavements. Due to the facts that it is impossible to use all the old bituminous - bound materials in their initial layers, and because of the increasing scarcity of new natural materials and due to environmental problems, one has to look for new areas to re-use old pavement materials. This research deals with the possibilities to use cement - treated granulate asphalt in bound foundation layers. The constructional and mechanical Properties of this material have been tested with more than 800 laboratory specimens and about 100 cores under different conditions. Quality control tests and strength experiments showed that granulate asphalt cannot be compacted the same way as natural gravel with low compaction energy (Proctor standard); it needs to be compacted according to Proctor modified. The bituminous binder complicates the compaction: A major part of the compaction energy is absorbed by deformation. Only with a higher energy level (Proctor modified) it is possible to reach an acceptable degree of compaction. Granulate asphalt contains only a small amount of fine fractions or none at all. The small particles are bound together by the bituminous binder. The shortage of fine fractions < 0.06 mm further complicates the compaction. The optimal water content for compaction does not coincide with the highest density but with the highest compression strength. The frost-thaw and the water absorption experiments showed that cement bound granulate asphalt is completely resistant to climate. This was to be expected due to the very small amount of fine fractions. The experiments showed as well, that the granulate asphalt may be considered as watertight if the dry density is higher than 2 t/m3. The material possesses a dynamic modulus of elasticity of about 6000 N/mm². Its heat conductivity is very low. In summer one has to reckon with high temperatures in layers of cement - treated granulate asphalt. In addition, the experiments have shown that the specimens with high cement contents have a higher compression strength only in an early stage. The compression strength of the specimens with a lower cement content continues to increase during the course of the time. After a year specimens with 5, 7 and 9% cement content showed compression strengths of the same magnitude. Due to the bituminous binder the mechanical properties of cement bound granulate asphalt are a function of temperature. This temperature - dependency has been investigated above all with long - term experiments. About 400 laboratory specimens and cores have been subjected to fatigue and creep experiments at 5 different temperatures. The results of these experiments showed that this material exhibits a better long - term behaviour at lower as well as at higher temperatures as compared to its behaviour at room temperature (ca. 220 C). In the case of a decrease in temperature the bituminous binder may contribute to the load transfer process. In the case of a rise in temperature cracks will open later than at room temperature. For comparison purposes experiments with cement - bound natural sand - gravel were carded out. They showed that cement - bound granulate asphalt basically may be used in bound foundation layers, however compaction must take place at a considerably higher level of energy as compared to e. g. gravel. From the results of the long - term experiments for pavement design according to AASHTO a material coefficient (a-value) of 0.1 9 for granulate asphalt with 5% cement content is suggested. For granulate asphalt with 7% cement, an a-value of 0.21 is recommended. Finally this research proposes a reduced set of quality tests. (A).
Samenvatting