Asphalts, chemical properties

With minor exceptions the requirements for the physical and chemical properties of asphalt were essentially the same for the three national specifications and included penetration and ductiUty at 25 °C flash point % loss at 163 °C penetration of residue as a % of original solubiUty in carbon disulfide solubiUty in carbon tetrachloride specific gravity at 25°C and softening point. 

Many physical and chemical properties of substances have been determined by GC. Characterization of complex materials such as asphalts, polymers, and catalysts have been performed. Carbon number and the placement of hydroxyl groups in alcohols as well as vapor pressures of numerous compounds (Table 11.5) have been determined by GC. 

Of all the materials available for use as a supercritical fluid, CO2 has become the material of choice because of its chemical properties. Instruments have been developed to utilize the principles described to effect extractions of compounds from a variety of sample matrices including asphalt, plant material, and soils (Figure 25.1). The supercritical fluid is pumped through the sample, through a filter or column to a trap where the fluid vaporizes and solvent is added to transfer the analyses to a vial for analysis. More recent instruments combine the supercritical fluid extraction system with a variety of columns and detectors to acquire data from complex samples. 

TABLE 1—Physical and chemical properties of selected asphalts [IJ. 

Sulfur is a low cost, high purity, readily available material It exists in many allotropic modifications with interesting physical and chemical properties. In 1970 world consumption of sulfur in all forms totaled 38 million tons. However, only a small percentage of the sulfur consumed depended upon or benefited from its high purity and unique chemical and physical properties, Sulfurization of asphalt, sulfur impregnation of ceramics and paper, and the use of sulfur in construction are a few potential applications which could exploit sulfur s unique properties. The present status and additional research needed to commercialize these potential applications are discussed. 

To simulate the in-service oxidative ageing that occurs in asphalt binders during pavement service. Residue from this conditioning practice is used to estimate the physical or chemical properties of asphalt binders after several years of in-service ageing in the field. 

There have been a number of not particularly successful attempts to correlate asphalt physical properties to chemical properties, including SEC (10,19,35-40). Chollar et al. (41) attempted to relate a number of chemical and physical properties, including percentage LMS, with poor results. Huynh et al. (42) divided asphalt into a number of fractions by preparatory SEC and showed that the glass transition temperature (not precisely defined for asphalts), in moving from one fraction to the next, first decreased with increasing molecular size and then increased. Beazly et al. (43) used SEC and nuclear magnetic resonance (NMR) to estimate asphalt yields and viscosity from crude oil Woods et al. (44) used SEC fractions to study differences in maltenes from tar sand bitumens. 

There have been objections to this approach (16), partly because of the arbitrariness of the procedure in which the percentage of LMS is very much an artifact of the SEC operating parameters. It is also thought that it is the mechanical properties that cause failure, and these do not correlate well with chemical properties, such as SEC thus if ex post facto measurements are to be used, they may as well be the physical properties of the old asphalt. There are several studies that indicate that there is a limiting ductility below which all roads fail (84,85). It has been suggested (86) that penetration at 4X, a good predictor of the limiting stiffness temperature, be used to predict the tendency to crack. 

Attempts to correlate asphalt physical properties with chemical properties have not been particularly successful. This no doubt is primarily the result of the lack of uniqueness in the chemical properties that are used. For instance, a Corbett fraction from one asphalt may have very different physical properties from those of the same fractions from another asphalt. Also, two asphalts with similar physical properties can have radically different SEC chromatograms. 

Asphaltene dispersed in the asphalt can form micelles, supeimicelles, and even giant supermicelles or liquid crystals, depending on the content of asphaltene and resins. All units exist in the asphiit systems but their distributions are different. The micelles and supeimicelles are predominantly sol type asphalts liquid crystal are predominantly gel type asphalts and giant supermicelles are predominantly sol-gel types. For different types of asphalt, the physical and chemical properties are different and, therefore, their uses and applications will differ. 

The physical properties of asphalt are directly related to the quantity of the dispersed phase (asphaltenes) the size of the micellar structures, which depends upon the degree of adsorption of resins the nature of the dispersion medium and maltenes (oils and resins). In heavier fractions of petroleum, single molecules contain Cp, C, and C portions. The aromatic protons near the aromatic ring system can participate in electrophilic reactions, such as nitration, sulfonation, halogenation, and others. The interaction between the molecules will determine the chemical properties of asphalt. 

Asphalt Roofing Components. Asphalt (qv) is a unique building material which occurs both naturally and as a by-product of cmde-oil refining. Because the chemical composition of cmde oils differs from source to source, the physical properties of asphalts derived from various cmdes also differ. However, these properties can be tailored by further ptocessiag to fit the appHcation for which the asphalt will be used. Softening poiat, ductility, flash poiat, and viscosity—temperature relationship are only a few of the asphalt properties that ate important ia the fabricatioa of roofing products. 

Many investigations of relationships between composition and properties take into account only the concentration of the asphaltenes, independendy of any quality criterion. However, a distinction should be made between the asphaltenes which occur in straight mn asphalts and those which occur in blown asphalts. Remembering that asphaltenes are a solubiUty class rather than a distinct chemical class means that vast differences occur in the make-up of this fraction when it is produced by different processes. 

Durability. The term "durable" has several meanings, but in the present context it is used to describe an asphalt that possesses the necessary chemical and physical properties required for the specified pavement performance, being resistant to change during the in-service conditions that are prevalent during the life of the pavement. 

This article discusses traditional hull ding and construction products, ie, not made from synthetic polymers (see Building materials, plastic), including wood, asphalt, gypsum, glass products, Pordand cement, and bricks. The article presents information about each basic material, the products made from it, the basic processes by which the products or materials are produced, estimates of the quantity or doUar value of the quantities produced or used in the United States, and some pertinent chemical or physical properties related to the material. More detailed chemical and physical property data can be found in articles devoted to the individual materials (see Asphalt Cement Glass Wood). 

Elemental sulfur has been modified In an exothermic reaction with commercially available hydrocarbon compounds to produce a pavement binder material that has been successfully utilized to construct several experimental pavement sections on public highways. The engineering properties, the formulation, and the methodology for producing and utilizing this chemically modified sulfur pavement binder, intended as a substitute for asphalt cement, are discussed. 

Terms such as paraffinic, naphthenic, naphthenic-aromatic, and aromatic-asphaltic are used in the several classification methods which have been proposed. These terms obviously relate to the molecular structure of the chemical species most prominent in the crude oil mixture. However, such classification is made difficult because the large molecules usually consist of condensed aromatic and naphthenic rings with paraffinic side chains. The characteristic properties of the molecules depend on the proportions of these structures. 

Test Samples. Main properties of the residual oils used in the present test are represented in Table II. It should be noted in this table that No. 1 is propane deasphalted asphalt Nos. 2 to 7 are petroleum pitches derived from residual oil heat treated under various conditions No. 8 is KRP pitch made by Kureha Chemical Industry from crude oil heat treated with hot steam at temperatures over 1,000°C and Nos. 9 and 10 are both residual oils from coal, No. 9 being solvent refined coal made by NKK and No, 10 being heat treated coal tar pitch. These Nos. 1 to 10 are typical examples of binding material for coke-making in Japan. 

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