International Concrete Abstracts Portal

The recently completed Strategic Highway Research Program (SHRP) included two projects that evaluated joint sealants for Portland Cement Concrete Pavements (PCCP). The major effort consisted of the innovative materials research which, among other things, evaluated silicone and hot pour sealant performance in transverse PCCP joints. This experiment provided intensive evaluations at regularly scheduled intervals. These evaluations consisted of the more traditional performance indicators of joint sealant performance such as the extent and severity of adhesive and cohesive failure, incompressibles, etc. Although fault measurements were obtained, no direct measurement of pavement performance or user satisfaction, such as ride comfort, was obtained. Similarly, no deflection testing was performed in this experiment to evaluate load transfer or to detect voids beneath the slab. The second SHRP effort was the Joint Sealant experiment (Specific Pavement Study No. 4 or SPS-4) which consisted of 500 ft sections of sealed and unsealed transverse joints in PCCP. This experiment was designed to evaluate the effect or benefit of sealing joints on pavement performance. The evaluation factors included ride comfort using an inertial profilometer, deflection testing using a falling weight deflectometer (FWD), and distress evaluations. The experiment did not include the traditional joint seal evaluation factors such as adhesive and cohesive failures. the amount of incompressibles, etc.. During discussions at an early SIIRP western regional meeting, it was requested that SHRP consider combining both the SPS-4 and innovative materials experiments pertinent to PCCP joint sealants. Unfortunately, SHRP had already developed and approved all the experiments, so this request could not be accommodated.

The last several years have brought forth a dramatic increase in research, development, and implementation of sliding isolation bearings(1) (referenced SIB in this paper). And although isolation projects in the United States were once the sole domain of elastomeric bearings, expanding isolation needs have recently shifted attention in the direction of sliding isolation bearings with restoring force elements. High damping capabilities, dynamic stability, and reliability of response are among the key reasons for turning to SIBs. Disadvantages of SIBs such as potential high frequency vibration transfer, and lower limit force reductions need to be recognized and considered. The intrinsic potential of SIBS has been recognized for many years. The confluence of potential, equipment, funding, and need, triggered an SIB research boom in the mid 1980's. The lag of implementation from research is dependent upon many factors. including practicality, performance, need, market inertia, fiscal potential, design code state, time, and supplier wherewithal. The first bridge SIB installation in the US (Evansville, IN 1993), postdates by twenty years those of our engineering peers from other countries, such as Japan, New Zealand, Italy, Russia, etc.. Other SIB bridge installations have and are currently being implemented at a steadily increasing rate. Some of these installations and associated seismic details are highlighted.

In July 1986, the Arizona Transportation Research Center coordinated the installation of a joint sealant test site near Flagstaff, on the southbound lanes of Interstate 17. The original project was constructed in 1974, with 8 inches of portland cement concrete pavement over 6 inches of cement treated base. The test site consisted of 200 transverse joints. The objective of the project was to evaluate the performance of five joint sealants: Dow Corning 888, Superseal 888, Allied Koch 9005, Crafco Roadsaver 231, and W.R. Meadows Sof-Seal. The highway sections abutting this test site were also rehabilitated and their pavement joints were sealed with Superseal 444 which, at that time, was a specified sealant in the Arizona Department of Transportation standards. Field evaluations of the joint sealants were conducted periodically. The final evaluation was conducted eight years after construction. The evaluations were based on: (i) sealant flexibility, (ii) length of joint with missing sealant, (iii) adhesive and cohesive failure of sealant, (iv) joint width and sealant depth, (v) joint spatting, (vi) sealant recess, (vii) structural tests made with a Falling Weight Deflectometer, and (viii) slab faulting. After about eight years of service, all five sealants had exhibited comparable performance level. Clearly, all test sealants performed better than Superseal 444.

The Wisconsin Department of Transportation has been studying the effect of PCC joint/crack sealing on total pavement performance for nearly 50 years. The issue has always been very simple: does joint sealing/filling enhance total pavement performance; if so, is it cost-effective; if so, what is the best sealant system. Most research done nationally has focused on the last portion of this issue (the best sealant system) and has totally ignored the primary issue (total pavement performance). In the 1950's and 1960's, Wisconsin engineers noted that the initial filling and refilling of contraction joints had no beneficial effect on total pavement performance. In 1974 a carefully designed joint and sealant study began with sealed joints (which were kept sealed for at least 10 years) and with totally unsealed joints. After 10 years it was concluded that the pavement with unsealed joints had better overall pavement performance (distress, ride, materials integrity) than the pavement with sealed joints. In 1990, after considerably more data verified all the previous findings, Wisconsin passed a policy which eliminated the sealing of PCC pavement joints in new construction and in maintenance. Joints are now sawed 1/8 inch wide during construction and no sealing is ever performed. This has saved Wisconsin at least six-million dollars a year with no loss in pavement quality. This report summarizes ongoing research and verifies that Wisconsin's policy is cost-effective. We believe the burden of proof has now shifted. The challenge, for those who advocate that water and incompressibles must be kept out of the joint, is to prove this position is economically justified. This entire issue must begin to be addressed from a broad perspective so there can be enlightened discussions and so that productive research can pursue.

It is no secret that many of our existing highway bridges that have been constructed after World War II have become maintenance problems. Flawed assumptions regarding the true performance life of many bridge deck components such as decks, piers, substructures, superstructure, etc. are now very much in evidence. The entry point for much of the deleterious water borne chemical runoff is through the expansion joints. Many of these older structures have deck lengths starting at 20 feet and upwards but the great enemy of bridge deck edges and sub-structural components is the leaking expansion joint. In addition to this many well designed expansion joints just do not have the adequate fastening strength to remain in place under the high speed repetitive truck loadings to which they are now exposed. These jointing systems were conceived and produced in previous years where no real performance data existed for making proper judgements with respect to service life. The fairly recent development of non-metallic expansion jointing systems takes into account knowledge learned regarding true service life of formally popular devices and materials.