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.

From shortly before the entry of the U. S. in World War II and to the present, the author has been continuously involved in the design, testing, manufacturing, and observation of the performance of joints of all types, from pavements to bridges, and bearings of all types, from the old rockers to elastomeric, pot, disc, and then to earthquake isolation concepts. Starting out with load transfer devices buried in concrete pavement joints for state highways and airfield pavements to field molded sealants and then compression seals, the design trend in pavements has been from longer 100 ft panels (30 m) to relatively short panels of 15 ft (4.5 m). This has greatly simplified the sealing problem, since the distance changes between joint interfaces of shorter length panels obviously are much less in creep-shrink and thermal volume change. With respect to bridges, the design trend has been reversed, going from relatively short decks of 40 ft (12 m) to longer and longer spans, greatly complicating the sealing problem. It was in this confused design period that the writer worked toward developing sealing and bearing systems for every conceivable type pavement or bridge structure. Some lessons learned during the past 50 or more years are the subject of this paper.

A suitable design of deck joints and bearings in highway bridges should take into account the environmental conditions existing in the location of the bridge. Several authors state that the influence of the thermal effects should never be un derestimated in the design of joints and bearing systems and point out the existence of damages-in bridges due to environmental thermal effects. This paper presents a general method for the prediction of thermal movements in highway bridges located in Spain. It provides design recommendations which allow accurate prediction of thermal movements, depending on the location of the bridge, the longitudinal type of the bridge deck, the cross section type and other factors which significantly affect the thermal response of the bridge. Lastly, the influence of the temperature of settlement of the deck joints is also considered, in order to determine precisely the thermal movements in highway bridges. Such method can be developed and applied to other countries.

The design of a bridge deck joint must be able to withstand the wear and impact of heavy traffic loads, and resistant to roadway oils and chemicals, debris, ultraviolet rays, and other environmental factors. Failure of a joint system can occur from a debonding of the nosing and substrate; a delamination of material layers; severe wearing, cracking or spalling of the nosing; or improper aterial mixing and joint installation. Loose steel armor retainers and leaking joint seals also cause joint system failures. A large scale accelerated testing facility designed and constructed at the University of Central Florida has tested over twenty different bridge deck joints for wear, abrasion, impact loading, and leakage. Many of the aforementioned failure criteria were observed during the course of testing. The testing program also established a simulated life expectancy for each joint system as a result of its performance under full-scale live loading, during a five week test period. This method of testing proved to be a timely, feasible alternative to live bridge applications and monitoring procedures. Test results indicated several areas of deficiency common to many of the joint components and systems and promoted further development of some of these products to enhance their performance.

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.