Iwański M., Mazurek G. (2012): Durability of SMA pavement with hydrated lime additive.
Article prepared for the 5th Eurasphalt and Eurobitume Congress in Istanbul June 2012.
Road surface roughness plays an important role in ensuring the safety of traffic on moisture surface, especially in the initial phase of rain, while on the layer surface usually creates a tin film of the water which starts a skid effect and causes forming a “aquaplaning” effect. To prevent this undesirable phenomenon as soon as there is a need to drain a water from the pavement. For this reason, it is advisable to use such asphalt technologies that allow to perform wearing course layer with high expanded texture, and hence ensure quick drainage of water from the surface and ensure proper contact between the tread of the tire and the surface. An application in the 90’s XX century stone mastic asphalt mix marked as SMA could be accounted for this type of technology. Except of SMA to this group belong a technologies such as porous asphalt and hot rolled asphalt for very thin layers. Researches of potential usability of this technologies in Polish conditions revealed that they are effective. It provide the required surface roughness in the initial period of its operation, ie for the first three – four years and appropriate durability [1, 2, 3]. Depending on the type of aggregate and mineral mix design in the following years the phenomenon of reducing or increasing of anti-skid resistance may take place. That why in the long period of operation of roads the essential role in ensuring its roughness plays a mineral material factor.
The primary criterion for assessing the desirability of aggregates in terms of anti-skid properties is its resistance to abrasion in the Los Angeles drum, according to EN 1097-2 and polishing expressed by using of an polished stone value index PSV according to EN 1097-8. The resistance of aggregate to the polishing has to bear with providing the surface to required macrotexture, which plays an important role in the initial period of its operation. On the other hand the resistance to the polishing is connected with a microtexture that ensuring a wearing course layer a good anti-skid properties in long term operation.
In Poland the quartzite sandstone could be accounted for the most resistant aggregate to abrasion and polishing process, which the one of the largest deposits is located on area of Kielce, near the Swietokrzyskie mountains. An important advantage of the quartzite aggregates is its bright color in comparison with the color of the basalt aggregate, which is used as the standard aggregate in asphalt mixes. The use of the quartzite aggregates in asphalts causes significant brightening of the wearing course surface, which is important from the point of view of ensuring road safety at night. Also contributing to reduce the amount of electricity needed to provide the required stationary lighting on sections of pavement. Despite the advantages, which is characterized by the quartzite aggregates there are some disadvantages. Due to the high silica content up to 95% of its composition, it shows week affinity with the bitumen, which in some way, makes difficulty to use of this aggregates in asphalt mixtures. This property for some technological reasons from the beginning of 90’s last century, limited the applicability of this aggregate. The studies that started of this period reveled that there aren’t barriers to the use of this type of the mineral aggregate in asphalt mixtures. It was posed that it is necessary to apply the adhesives agent to improve the covering effect of this type of aggregate by bituminous binder.
The most commonly adhesion agents ranks fatty amines. Unfortunately, they may cause an adverse effect on the bitumen parameters such the softening point that it may be reduced. Consequence of this influence of the adhesive agent is a decrease of the resistance to forming ruts. It is necessary using other adhesive agents that don’t play a such important role regarding bitumen properties. Another type of adhesive agent is hydrated lime, which has been used in the Central and the Eastern Europe in the 60’s of the twentieth century [7, 8]. However, due to technological difficulties in dispensing during production process into the bitumen, application of this adhesion agent was abandoned. The development the road technique on XX and XXI century contributed that the earlier problems had stopped to exist. In 1999, due to the renovation of Zelazna street in Kielce (Poland) which is the main communication street, the wearing coarse layer was built by application into SMA the composition of the quartzite aggregate. The second purpose of application of this type of aggregate was ensuring a high anti-skid resistance. In order to ensure proper affiliation between the bitumen and aggregate the hydrated lime was used. The fatty amine was used as a reference adhesive agent.