Development of Porous Rubber Pavement for the Canadian Climate

Abstract

Permeable pavement usage in North America has increased over the last decade as a viable stormwater management system. Porous Rubber Pavement (PRP) is a new material in this category which has been currently utilized as a pavement surface material for low-traffic areas and pedestrian walkways. This material consists of recycled crumb rubber aggregates, granite aggregates and polyurethane as a binder and is proportioned to attain a very high percentage of interconnected air voids (up to 45%). As a new pavement material in North America, the properties and performance of PRP are not thoroughly understood for cold climate conditions. This research aimed to understand the properties and performance of PRP and improve its performance as a pavement surface material for the Canadian climate. This objective is achieved through an evaluation of existing sites and mixes, developing new mixes through an experimental design process, and evaluating new mixes in the laboratory facilities. Some of the mixes were selected to apply in the trial section to assess field performance. Finally, recommendations and guidelines are developed for this climatic zone. Through the experimental design, four new mixes were developed using different proportions of stone aggregates, rubber aggregates and polyurethane binder. Also, using the proportion of the Control Mix, four polyurethane binders were used to make four different mixes to determine the different binder effects in PRPs. In the next stage of research, two trial sections were constructed using selected mixes along with the Control Mix. In addition, samples were also prepared from the field mixes to test their properties in the laboratory. Then the field performance of the various mixes was evaluated over a series of months. They were initially tested immediately following construction before fully opening for traffic. Then three weeks after construction and after seven months when the sections had experienced their first winter. Preliminary field investigations showed that with the current commercial mix, the achieved elastic modulus of PRP surfaces ranged between 37 MPa and 33 MPa. Besides, frictional values ranged between 57 BPN and 74 BPN. Higher IRI values were calculated for both sites, ranging between 7.56 m/km to 15.77 m/km. The average infiltration rate for the pavement surface areas was found to be 30836 mm/hr.

The mechanical properties and durability of the Control Mix and newly developed mixes were investigated. The tensile and compressive strength of the mixes were found to be higher when the percentages of stone aggregates and binders were increased in the mixes. Additionally, an increase in air voids in the samples reduced the materials' tensile and compressive strength. Concerning the types of binder and sources, the obtained results showed no considerable influence of different types of binder in compressive strength test results, whereas binder sources influenced the tensile strength of the PRP materials. PRP samples with varying compositions retained more than 70% of their tensile strength after conditioning with five freeze-thaw cycles. However, due to the variety of binders used, retained tensile strength for PRP samples varied, and some showed retained tensile strength below 70%.

The durability study showed that the granite stones that were used for all the sample preparation were not strong enough to withstand higher abrasion loss. However, PRPs with different compositions showed good rutting resistance, ranging from 0.3mm to 2.8mm in different mixes. Moisture-induced damage, stripping related abrasion was also found to be very small in PRP mixes, ranging from 2.6% to 0.1%. Also, the use of different binders from different sources showed that the B2—aliphatic binder could withstand more rutting than other binders. A Los Angeles abrasion tester tested unconditioned and conditioned samples to determine the materials' ravelling resistance. The result showed that abrasion loss increased in the samples after conditioning with five freeze-thaw cycles. However, it was consistent with the mix types. On the other hand, abrasion loss of samples with different binders occurred differently in the conditioned and unconditioned situations and was inconsistent in the mixes.

Subgrade samples were collected from sites A and B during the trial section construction. The bearing capacity of subgrade soil for Site B was found to be higher than that of Site A. Subsequently, the performance of the mixes in the sections was evaluated through a series of field testing. The LWD results showed that the stiffness modulus differed for the same mixes at Site A and Site B. Besides, all the mixes showed higher stiffness in the 2nd field test than the 1st since compaction occurred on the pavement after opening for traffic. Nevertheless, after experiencing their first winter, a reduction in stiffness was observed for all mixes in the 3rd test. The BPT test revealed that a higher frictional value of PRP mixes was associated with a higher percentage of rubber aggregates and a lower percentage of binder in the mixes. At the same time, a reduction in BPN values was observed in the 2nd test than in the 1st since the sections were further compacted and polished after opening for traffic. In addition, the surface ravelling and transported loose particles affected the frictional values in the 3rd test, increasing the BPN numbers. Initial rut depths on Site A for different mixes ranged from -7.0 mm to -8.7mm, and the range was -5.8 mm to -10.7mm for Site B. However, after fully opening for traffic, greater rut depths were observed on each section due to the additional compaction under the wheel paths. The permeability of the PRP sections ranged from 28368 mm/h to 45605 mm/h, which is higher than the highest rainfall rate in Canada (298.8 mm/h). However, most of the sections showed higher permeability in the 2nd test. After the first winter, the permeability of some of the sections was found to be further increased, whereas others were found to be decreased due to the influence of site surroundings. In the 1st and 2nd field tests, no visible surface distress was observed at Site A and Site B. A small amount of surface distress was observed after the first winter (seven months after the construction), which included a slight loss of coarse aggregate, minor ravelling, small cracking, and rutting. Throughout the trial section construction process, it was also observed that by improving the construction methods and making slight modifications during the construction process (like increased compaction), the performance of PRPs could be further enhanced.

Finally, a set of recommendations and guidelines were developed for using the PRP in the Canadian climate.