| | Introduction to Sealers & Rejuvenators To address the problem of asphalt cement hardening in pavements, this study was undertaken to determine the effects of spray applied surface seals on the long-term performance of asphalt pavements. This study is designed to evaluate the effectiveness of this preventive maintenance strategy. Traditionally, these treatments, often called fog or flush seals, are applied to pavements to arrest pitting and raveling, to reduce shrinkage tendencies, to decrease permeability, to decrease traffic and snow plow damage, and to rejuvenate the properties of the existing asphalt cement. They are also sometimes used to improve appearance. Different types of sealers and rejuvenators are available in the marketplace and can be readily attained. Sealers such as SS-1 (Slow Setting emulsified asphalt) or CSS-1 (Cationic Slow Setting emulsified asphalt) are commonly used to “seal” the pavement surface or to “bind” or “lock” cover material or fines in place reducing surface attrition. Rejuvenators, on the other hand, are designed to penetrate into the existing age-hardened asphalt cement, thereby modifying and improving existing chemical and rheological properties. The product selection is dependent upon the problem being solved and the existing pavement type. The most prevalent use of rejuvenator products is on dense graded asphalt surfaces. Sealer products, on the other hand, are more commonly applied on chip seals and friction courses where binding or enrichment is the main purpose. Both product types have been used successfully on all three surface types.  To better understand the process of embrittlement in flexible pavements, it should be remembered that the oxidation of asphalt occurs during both the construction phase and during the service life of the pavement. Asphalt hardening during the construction operation can be predicted, to a large degree, by laboratory aging procedures. Hence, the initial rheology of the binder can be adjusted to account for typical changes expected during hot mix asphalt (HMA) mixing and compaction. The long-term aging of asphalt during the in-service pavement life is much more difficult to control. It is closely linked to the asphalt’s crude source, the environment, and interconnected air voids near the surface through which oxygen and moisture can infiltrate. Sealers and rejuvenators are used in a preventive maintenance strategy to prevent surface asphalt from reaching the limiting stiffness where surface cracks begin to appear. The aging of a pavement can be represented by the diagram. At the time of construction the pavement has an initial stiffness shown as point 1 in the diagram. As the pavement ages, the high temperature stiffness of the binder increases approximately exponentially with time in service. That is, rheological change is relatively slow up to a point, but then hardening occurs much more rapidly. Although such theories form the basis for the Global Aging Effects Model as included in the new Mechanistic-Empirical Design Guide, very recent findings from other research studies suggested a new direction for evaluating aging pavements. At low temperatures where surface cracking is more likely to occur, the binder stiffness does not change much at all, even after severe aging. However, the relaxation or fracture properties of the binder, as might be measured by ductility, m-value, tensile strain at failure or fracture strength, indicate asphalt becomes more brittle as it ages. As cracks develop, aging further accelerates due to infiltration of moisture and oxygen. Preventive maintenance concepts suggest that application of a sealer/rejuvenator should occur before the pavement has reached the critical condition where embrittlement leads to raveling or block-cracking. However, many believe that the intervention point should occur well before the asphalt becomes brittle. Some even suggest sealing the pavement soon after construction. With this concept in mind, rejuvenators were developed in the late 1950s to “turn back time” on the aging process by softening the hardened binder. The use of rejuvenators and sealers has continued since that time. Even though the economic advantages of rejuvenators and sealers have long been recognized, continuing problems with traffic accidents resulting from lowered pavement friction have caused some agencies to put moratoriums on the use of fog seal emulsions, and particularly rejuvenators as applied to traffic lanes. Hence, any evaluation of product effectiveness must include analysis of pavement friction, particularly as the road is initially reopened to traffic. This study was initiated to determine the effectiveness of seals and evaluate the effects and possible mitigation efforts on safety. This project has four main tasks: collecting existing information; placement of several experimental sections within different climates, traffic levels and surface characteristics; evaluation of field and laboratory test methods and data collected from the test sections; and disseminating the lessons learned. Details of the user survey and test results may be found in the Project Library. Field observations may be found in the Photo Gallery. More detailed "Lessons Learned" are can be found on each of the topic pages. | downloadable Documents:
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Sealer & Rejuvenator Overview Annotated Bibliography Caltrans Fog Seal Technical Advisory Guide Project Overview Powerpoint (ppt file) Project Overview Powerpoint (pdf file with speakers notes) Full Project Report |