Asphalt pavements will inevitably begin cracking and require maintenance to preserve an adequate level of service. However, preemptively sawing and sealing roads at prescribed locations can reduce cracking and improve maintenance predictability. To help the state’s transportation agencies better manage pavement deterioration, the Local Road Research Board sought to compare the performance of a lower-cost unmodified asphalt binder using the saw-and-seal method with that of a higher-cost polymer-modified asphalt binder without using saw and seal.
What Was the Need?
Sawing and sealing asphalt pavements is a preventive crack-control strategy that has been used by cities and counties across Minnesota for decades to reduce random cracking, maintain ride quality and create predictable locations for future crack treatment.
The effectiveness of this approach in Minnesota depends on numerous factors, including cracking resistance, thermal contraction in cold weather, joint construction, moisture conditions, freeze–thaw susceptibility and base and subgrade support. This project provides MnDOT and local agencies with an updated evaluation of the strategy by comparing a lower-cost unmodified Binder B pavement combined with sawing and sealing against a higher-cost polymer-modified Binder C pavement without sawing and sealing.
What Did We Do?
A literature review synthesized current practices and prior research and incorporated findings from a 2022 local agency survey documenting the use and performance of saw-and-seal techniques within the asphalt paving community. Investigators then compiled pavement condition data from four Minnesota local agencies to evaluate saw and seal performance.
Next, mechanistic–probabilistic modeling related road surface cracking behavior to material tensile strength, foundation support and joint spacing to provide guidance for selecting joint spacing based on cracking risk.
Finally, a life-cycle cost analysis compared Binder B pavements with saw and seal against Binder C pavements without saw and seal. The analysis considered four asphalt tensile-strength levels, multiple saw-and-seal joint spacings and different project lengths. Roads constructed to MnDOT Traffic Levels 3 and 4 specifications were evaluated. Traffic Level 4 roads had two asphalt layers consisting of 4 inches of wearing course over 4 inches of non-wearing course, while traffic level 3 roads had a single 4-inch wearing course.
“The results confirmed current joint spacing practices used by metro cities and offered insight on the trade-offs associated with higher initial costs and future maintenance needs,” said Tom Wesolowski, Public Works Director for the City of Shoreview.
What Did We Learn?
The literature identified sawing and sealing as an effective approach for extending pavement service life and improving long-term performance, especially on low-volume roads, when implemented properly with adequate joint preparation and sealant installation. Survey respondents indicated that saw and seal is a preferred strategy because it creates cleaner crack lines, maintains better ride quality and simplifies maintenance on streets with numerous utilities.
The four local agencies reported that saw-and-seal sections generally performed well. One agency reported very good performance with little cracking between planned joints, while another reported a wider range of outcomes, with streets exhibiting good, fair and poor joint conditions. These differences suggest that local factors such as site conditions, mixture properties and moisture susceptibility affect performance.
Modeling results showed that performance depends heavily on factors such as joint spacing and construction and maintenance practices. Specifically, base and subgrade support, drainage conditions and moisture, and freeze–thaw susceptibility significantly affect joint performance and maintenance needs.
The life-cycle analysis found that using the saw-and-seal strategy with Binder B pavements can improve cost-effectiveness, although the degree of benefit depends on traffic level, mixture quality, joint spacing and project length. For example, joint spacings between 30 and 40 feet were found to be the most cost-effective. In addition, while Binder C mixtures have a 34% higher initial construction cost than Binder B mixtures at Traffic Level 3, the initial cost at Traffic Level 4 was only 9% higher. Once a project reaches approximately 60 miles in length at Traffic Level 3, the unit costs for Binder B with saw and seal and Binder C become comparable.
What’s Next?
Overall, project findings indicated that saw and seal is a practical crack-control strategy, especially for lower-volume asphalt pavements when applied to appropriate candidates and constructed correctly. Investigators also identified new technologies for assessing pavement conditions. One option can provide comprehensive, continuous information along an entire road segment, while another uses vehicle onboard data to assess pavement quality.
Crossroads 