According to earlier research projects in Sweden and Japan, the poroelastic road surface (PERS), a pavement made of rubber granules and stone or sand aggregates, bound with a flexible polymer like polyurethane, is capable of reducing tyre/road noise by substantially more than any other type of surfacing. Earlier attempts to develop this concept into a low noise pavement ready for application in full scale and meeting reasonable requirements regarding safety and durability have failed. Reasons for the failures have been different in various experiments, but durability and/or safety have been the major problems. Never-theless, this project team had the idea that working together in a large European cooperation project and utilizing all kinds of pavement engineering specialists would be the way forward. In 2009, the European Commission accepted a proposal named PERSUADE (PoroElastic Road SUrface for Avoiding Damage to the Environment) to make a serious attempt to turn the concept and earlier practical experience into an implementable noise reducing product. The PERSUADE project has the intention to develop the PERS concept into a durable, highly noise reducing, safe and cost effective pavement which can provide exceptional traffic noise reduction under certain traffic and road conditions and thus provide European road and environmental authorities with a new tool for managing hotspots in noise exposed areas. The following pages summarizes the project work and results with focus on technical issues. Mix development The first step to achieve the goal is to develop an appropriate PERS mix formulation. The properties that had been defined as targets for the mix optimization included: • durability and stiffness of the material in the field • frictional properties during the service life and under various climatic conditions • noise absorption and noise generating properties in the interaction with tyres • drainage properties • rolling resistance • emissions of particulate matter and hazardous materials to the environment To this end, a number of laboratory experiments were conducted to explore the mentioned properties of several interesting mixes. Regarding the stiffness, the results indicated that all the PERS mixes, regardless of the different compositions of each type, behaved similar in that the first cycle always was partly non-elastic (higher deformation incurred) after which, during the next consecutive cycles, the samples were stable against higher hysteresis losses. Under real traffic scenarios, one can expect that the higher the rubber content, the less the plastic (or non-elastic) deformation incurred. Comparison of dynamic moduli was undertaken between the PERS mixtures and a typical asphalt concrete mix showed that the asphalt mix had about 200 up to about 1000 times higher dynamic modulus than two types of PERS which were later tested on the road. This showed that PERS mixes were much softer in nature, which could provide a potential for less noise produced in contact with rolling tyres. As for polishing resistance and friction after some time of polishing, it was concluded that the evolution of friction with polishing on PERS could be studied without major difficulties. The main conclusions of the laboratory experiments are: • The maximum friction value increases with the proportion of hard aggregates in the mix. • The PERS mixes developed and intended for later field testing show first an increase and then a quite constant value of friction as they are polished. At the initial states, the maximum friction of PERS is smaller than maximum values on common French road surfaces, but the friction of some PERS mixes becomes close to DAC 0/10 or VTAC 0/10 surfaces after 50 000 cycles of polishing. These results are encouraging for implementing a safe and durable PERS surface in terms of skid resistance. Next, research should focus on the increase of the initial and maximum friction value of PERS surfaces, possibly by adding sand to the polyurethane (PU) binder. The optimization of the poroelastic mix to improve its ravelling resistance, on the other hand, turned out to be a real challenge and required the study of a lot of various mixes in the PERSUADE project. Most of the testing utilized the Aachener Ravelling Tester (ARTe). To evaluate the perfor¬mance of the mixes in a large scale production; some of them were sampled from production in field tests, to come one step closer to reality. The results show significant differences in terms of ravelling resistance between the tested mixes, sampled from different test sections. It is not possible to give a definite explanation why the results from the different test sections differ so much. For example, the results for the mix used in the Belgian test section laid at the end of the project fulfilled the objective for the ravelling resistance at the beginning, as described in the results section. The on-site properties in terms of ravelling resistance have to be studied in future experiments to confirm the results of ARTe testing, since the trials in PERSUADE could not be continued as long time as desired. Experiments to study the wear under simulated traffic were carried out in the VTI circular road simulator and led to the following conclusions • The wear and ravelling resistance of the best performing PERS material tested is equal to the wear resistance of a high quality SMA with 16 mm maximum chipping size. • The factors that greatly influence the wear resistance are:  Fraction of aggregate (lower is better)  Air void content (lower is better) • The type of aggregate has some influence on wear resistance (Jelsa granite performed 20 % better than the Skärlunda granite or Forserum diabase) • For factory produced material the wear resistance is not improved if the binder content is raised from 9 to 11 %. A comprehensive risk analysis was carried out concerning the risks related to the exposure to emissions produced from PERS. It was found that there is an adequate control of the risks associated with production and scrapping of PERS for the workers and the general population. This is the case for both planned operations and the non-recommended operations such as placing hot poured asphalt on remnants of PERS. An experiment was set up to study the particle emission from the interaction of studded tyres with PERS compared to conventional pavements and it was concluded that: • A number of PERS variants resulted in 10-20 times lower PM10 production and about 90 times lower number concentration (at 70 km/h) than a standard asphalt (SMA16) with granite. • The mass size distribution was bimodal with peaks at 2-3 and >8 µm, and in mean size slightly coarser than from the reference asphalt, but indicates that the source is dust from wear of pavement rocks. • Number size distributions show that ultrafine particles are produced during the test and that these are fewer and smaller than the ultrafine particles formed when wearing the reference asphalt. The number concentration, though, is very low and comparable to normal background values. An extensive test was carried out to assess the durability under “harsh” real life-like conditions with multiple influences, comprising brine, water, freeze-thaw cycles and UV exposure, combined with the interaction of the tyres mounted on a large “wheel-tracking device”. This showed that the tested PERS material had a durability comparable to or better than that of a conventional thin layer asphalt. However, the wheel tracking test additionally showed that the samples submerged in water also resulted in a delamination of the PERS mix from the asphalt concrete mix. Structural design A second important issue was the structural design of roads with a PERS wearing course. A wide range of tests was performed related to this topic, both in–situ and in the laboratory. Due to the typical low stiffness of PERS mixtures compared to the ordinary asphalt mixtures, not all planned tests can be expected to give similar results. The results were used for the calculation of the influence of a PERS wearing course on the durability of the road. Furthermore, the PERSUADE consortium has provided a procedure for the pavement design with a PERS wearing course and to estimate the influence of such a layer on the pavement life. The developed procedure allows for the proper design of the pavement. The following critical phenomena were taken into consideration: • the influence of the PERS wearing course stiffness on pavement design life, and • the influence of bonding between PERS and the base course on the pavement design life All (planned and actually used) full-scale test section locations were tested by means of Falling Weight Deflectometers (FWD), which measure the temporary deflection of roads under heavy tyre loads. The results showed that in most cases the calculated mean deflections at the test section before application of PERS were below 0.5 mm. According to the accepted methodology, it can be concluded that the bearing capacity should be good enough for at least medium traffic category, up to 7.3 millions of standard 100 KN axles in a 20 years design period. This means that these sections did not need to be reinforced before laying a PERS course. In only one case, a planned localization in Denmark, the results of measurements indicated that the thickness of new asphalt layers (upgrade) should be 12-16 cm depending on the location. Finally, but for other reasons, that test site was moved to another location. In Belgium, FWD measurements were performed before and after laying a PERS wearing course. In the “after” measurement, the calculated deflection increased approximately ten times compared to “before” (laying of PERS). According to the nomograph used in Poland the thickness of new asphalt layers (upgrade) should be over 24 cm on the area of the test section. The results show that due to the elasticity of PERS, the calculation of the bearing capacity on the basis of FWD measurements is inappropriate and in reality the road condition is better than estimated. FWD measurements should be performed on the existing pavement without PERS layer and the calculated deflection should be below 0.5 mm. This is the proof that the influence of PERS course will be negligible in order to avoid problems with pavement durability. The so-called Leutner test used to assess the shear strength, yielded a value of 0.4 MPa, which is insufficient to pass Polish requirements, which means that an improved solution should be found. It should be noted that the deflection observed at the maximum force (appr. 5 mm) is three to seven times higher than in case of standard asphalt mixtures. Moreover, a total delamination was not observed in the Leutner test. The hollow cylinder test performed on the hollow cylinder apparatus (HCA) enables torsional simple shear loading, which includes rotation of principal stresses. A hollow cylinder of pavement material can thus be tested by applying a combination of axial and torque loading, subjecting an element of material in the specimen wall to a realistic stress path. Such test reflects to a relatively high degree effects of real traffic on materials used in a road pavement. PERS material is typical elasto-plastic material, and such a behaviour can indeed be observed during cyclic loading. One can see recoverable and irrecoverable strain during loading. Besides the range of strain, stiffness and damping are also very important para-meters for deformation behaviour characterization. So-called hysteresis loops develop during loading. Based on this curve, shear modulus and damping of material were evaluated. Initial perfect elastic behaviour changed in later loops to plastic behaviour. The equivalent shear modulus of PERS material and hysteretic damping ratio were evaluated for various stress conditions. Finally, it was observed that stiffness is decreasing almost linearly with an increase of strain, while on the other hand damping is increasing