Polymer-Modified Asphalt Pavements in Ontario: Performance and Cost-Effectiveness

Abstract

Two trial sections were constructed to investigate the rutting resistance and low temperature performance of different polymer-modified asphalt (PMA) mixes at sites representative of highways experiencing rutting as a result of heavy traffic loading in cold climatic regions. The two-way average annual daily traffic for both sites was >35,000 (6,000 vehicles per day). Modified asphalts used in the trial sections include engineered bitumen type 306, premium asphalt, reprocessed polyethylene (Novophalt), Neoprene, scrap tire rubber, Vestoplast-S, Kraton 4460, Styrelf, and polyethylene. Representative test samples of aggregates, asphalt cement, modified asphalts, and hot mixes were taken for routine testing during production. In situ quality control tests were done by taking plate samples while laying the mix and by coring after compaction. Additional laboratory tests were done at temperatures ranging from 0°C to —35°C to evaluate the materials’ low temperature cracking resistance. Field performance of trial sections was monitored yearly by crack mapping and measuring transverse profiles at 30-m spacing on each test section. Levels were taken at 100-mm intervals by using a dipstick. A computer program was written to process the data and calculate the rut depths for each wheelpath. Crack mapping was done to assess the crack growth in each test section. The performance of the sections was compared with respect to average rut depth and crack growth. The following are described: (a) the modified mix design chosen specifically to produce accelerated test results, (b) the experience gained in the construction of trial sections, (c) the results of laboratory testing to evaluate the low temperature performance of the PMAs, (d) the field performance evaluation with respect to rutting and cracking, and (e) the life cycle cost analysis. Average rut depth measurements 5 to 7 years after construction show that PMA pavement sections are performing better than conventional asphalt with respect to rutting. With regard to cracking, polymers with 85 to 100 penetration (pen) base asphalt did not perform better than control sections. However, there is an indication that PMA, which has a soft grade (150 to 200 pen) base asphalt, tends to improve low-temperature performance comparable to the control section. In other words, PMA generally performs better than conventional asphalt, provided it contains a soft grade (150 to 200 pen) base asphalt. Life cycle cost analysis indicates that PMA is cost-effective in extending pavement life by 2 to 3 years if the cost of polymer modification does not exceed the cost of conventional asphalt by 100 percent.