ASPHALT & SEAL COATING— THE BEGINNING
In the early 50’s there became a concern at US air bases. Asphalt pot holes where appearing in the same locations over and over again. These areas where the result of fuel spillage from the loading of fuel on air craft or the spillage of fuel from pilots checking there fuel tanks for the signs of water. The Army Corp of Engineers and the the United States Air Force requested manufactures to design a product to be applied to the asphalt surfaces at airport parking ramps. This material would need to be fuel resistant for 14 – 21 hours. One company that brought forth a coal tar based material was Koppers Chemical. This material was designed to be a water based material. 40% of water mixed with sand and a additive to promote an hardening effect. The first in “seal coats” It was easy to apply and meet all the requirements that the Army was looking for. The seal coat was applied to the areas and the fuel damage stopped occurring. In the late 70’s this technology came to the commercial market and has been in use ever since. For the past 40 years coal tar seal coats have been used to help protect asphalt surfaces from fuel. What we have learned is that these products seem to enhance the effects of cracks that form on the asphalt surface. As a seal coat is applied to the asphalt surface it is boned mechanically to the surface. As the asphalt surface under goes the natural temperature change from the day time maximum temperature compared to the lower night time temperature difference. The asphalt surface expands and contracts at a different rate compared to the seal coat material. The result is that the seal coat develops cracks in it self. Because the seal coat is bonded to the asphalt surface like paint these cracks propagate into the asphalt surface. (Click Here for the report) A study was undertaken by the The Army Corp of Engineers in the 80’s. The goal of the study was to come up with a mix design that would do away with crack formation in the asphalt surface. The study covered 52 mix designs, if you would 52 different ways to make a cake. The ideal was to set forth and see how the asphalt surface would preform with variations of less or more of each additive in the mix design. In the end each sample failed and cracked the asphalt surface. Click here – Final Report “Criteria For Coal Tar Seal Coats On Airport Pavements”
DEFINING CHARACTERISTICS OF ASPHALT REJUVENATION
The deterioration of asphalt pavements caused by hardening and inherent changes in the physical properties of the asphalt binder in the aging process has been generally recognized throughout the transportation industry. The influence of chemical composition of asphalts on pavement performance was initially advanced from research reported by Rostler and White wherein, it was determined that an asphalt binder consists of five fractional components which govern its behavior. With aging of the asphalt binder, the fractional components are converted from one fractional component to another fractional component in a hierarchy measured by the asphalt binder consistency; thus, with aging, or oxidation process, there is a corresponding increase in the consistency of the asphalt binder. It was reported that “the ratio of chemically more active to less reactive components present in the asphalt binder was a measure of predictive durability. To affect performance, a rejuvenation material must possess characteristics to restore, or partially restore, the original chemical ratio of the asphalt binder components when applied to the pavement surface. For these phenomena to occur, two general rejuvenation criteria must be satisfied, as follows:
First, the rejuvenation material has to contain ingredients with chemically active components to decrease the asphalt binder consistency
Second, the rejuvenation material must penetrate the asphalt binder to effect reaction. Based on these research findings, asphalt rejuvenation products have been developed and used as a pavement preservation technique since the mid 1960s.
1976 – INDEPENDENT EVALUATION OF REJUVENATION PRODUCTS
The U.S. Air Force has a vast worldwide inventory of aging bituminous airfield pavements. Because of the need for pavement preservation and potential for proven rejuvenation products, the U.S. Air Force sponsored the first independent study on the performance of rejuvenation materials. This study was comprised of independent tests to evaluate the rejuvenation characteristics of four different rejuvenation materials and an asphalt emulsion as the control, and was conducted by the U.S. Army Corps of Engineers over the period from 1971 to 1975. The study involved placing test strip applications of the materials at three different Air Force bases and monitoring the performance for three years.
The results of this study were documented by a report in 1976; commonly referred to within the bituminous rejuvenation industry as the 1976 Air Force report. Adjacent pavement areas were treated at the three Air Force bases with four proprietary products available in 1971 [including Bituminous Pavement Rejuvenator (BPR), Reclamite, Petroset, and Gilsabind; and an asphalt emulsion seal as a control application]. The tests were conducted at Williams AFB, AZ, in the dry, hot southwestern part of the United States, Eglin AFB, FL, in the humid, hot southeastern part of the country, and at Malstrom AFB, MT, in the cold north-central part of the country. The objective of the effort was to evaluate the effectiveness of rejuvenation products on existing aged airfield asphalt pavements and to prepare guide specifications for placing these products. Rejuvenation was judged by a reduction in the viscosity or an increase in the penetration of the asphalt binder in the treated pavement.
The study reached the conclusion that BPR, Reclamite, and Petroset products accomplished rejuvenation of the old asphalt binder while Gilsabind and SS-1 Asphalt Emulsion had a hardening effect. The original Corps of Engineers, Unified Facilities Guide Specification for Bituminous Rejuvenation [UFGS 02787] was developed under this study. Other conclusions were reported, including an indication that the viscosity of treated asphalt was a better indicator of the rejuvenation effect of the materials tested than was the penetration test.