Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/291564
RoadScience 8 April 2014 Better Roads in the air or water as a result of equipment leaks. The saw cut must be absolutely clean if the joint sealer is to adhere to the side walls of the cut." A backer rod may then be inserted into the clean saw cut and pushed down to the correct depth, WisDOT says, to form a base for the joint sealant. The backer rod should be tight against the sides of the cut and selection of the right size of rod be used. "When cold-poured silicone joint material is used, the joint must be completely dry," the state spec says. "If there is any moisture present in the joint at the time of sealing, a skin will form on the sides of the sealant, preventing adhe- sion to the concrete. Following rain or damp weather, all of the moisture must be removed from the joint before sealing. The contract special provisions will specify which type seal- ant is to be used. The plan may also contain a special detail drawing." Cold-poured silicone is most frequently used. "Although cold-poured silicone is an improvement over the old hot- poured sealers, frequent failures are experienced," WisDOT says. "Most of these failures can be attributed to inadequate cleaning and drying of the joint or faulty installation proce- dures." A check of many joints sealed with cold-poured silicone indicates the sealant has adhered to only the upper edge of the joint and not to the sides, the spec says. Dirt or moisture on the sides of the joint prevents adhesion. Also, it is likely that insufficient pressure was used during the extrusion of the sealant into the joint to ensure full contact with the sides of the joint. To ensure positive contact, the joint must also be carefully "tooled" after extrusion. The surface of the sealant after tooling must be concave upward and lie about 1/4 inch below the pavement surface. Researching joint seals "The need to seal joints may depend on the region," Eilken says. "When you are in a heavy rain/freeze/thaw region, to ensure longer life of our concrete pavements, we do believe that joints should be sealed." Thus, the jury still is out on sealants in arid, warm regions, but Seal/No Seal Group research on bases at the Texas Trans- portation Institute at College Station should clarify that. "Probably the biggest effect of an unsealed control joint is its impact on the road base," Eilken says. "We have many different design permutations of sealed and unsealed joints in various paving structures that are undergoing study right now. Much of that work is ongoing at TTI, where Dan Zollinger there has just concluded the Phase I report of Evaluation of Joint Sealant Effectiveness on Moisture Infiltration and Erosion Potential. They are measuring, testing and establishing a work- shop model that could be shown to industry regarding how much damage is potentially being done to different types of bases with water running through." The tool will indicate that, depending on the type of base installed under a concrete pavement, what kind of erosion may be expected in the base under an unsealed joint. "TTI did testing for us at Seal/No Seal's test site at IL 59 near Joliet," Eilken says. "They now are attempting to vali- date their model, which if successful, will be presented to the Federal Highway Administration. If validated, this could change the entire design guide FHWA uses. They also are traveling to different locations in the country, showing how On a California airport runway, longitudinal joints were routed and filled with hot applied sealant in advance of polymer modified thin overlay. Coring at deteriorated joints helps identify causes of failure. Photo courtesy of IGGA Photo courtesy of IGGA