Asphalt content

Petroleum asphalts, compared to native asphalts, are organic with only trace amounts of inorganic materials. They derive their characteristics from the nature of their cmde origins with some variation possible by choice of manufacturing process. Although there are a number of refineries or refinery units whose prime function is to produce asphalt, petroleum asphalt is primarily a product of integrated refineries (Fig. 1). Cmdes may be selected for these refineries for a variety of other product requirements and the asphalt (or residuum) produced may vary somewhat in characteristics from one refinery-cmde system to another and even by cut-point (Table 2) and asphalt content (Fig. 2) (5,6). The approximate asphalt yields (%) from various cmde oils are as follows ... 

Propane is usually used in this process although propane—butane mixtures and pentane have been used with some variation in process conditions and hardness of the product. Propane deasphalting is used primarily for cmde oils of relatively low asphalt content, generally <15%. Asphalt produced from this process is normally blended with other asphaltic residua for making paving asphalt. 

The presence of paraffin wax is usually reflected in the paraffinic nature of the constituent fractions, and a high asphaltic content corresponds with the naphthenic properties of the fractions. As a result, the misconception has arisen that paraffin-base crude oils consist mainly of paraffins and asphalt-base crude oils mainly of cyclic (or naphthenic) hydrocarbons. In addition to paraffin- and asphalt-base oils, a mixed base had to be introduced for those oils that leave a mixture of bitumen and paraffin wax as a residue by nondestructive distillation. 

The effect of sulfur and asphalt contents in SAS mixtures on Marshall Stability is shown in Figure 3 [15]. The stability values tend to increase with sulfur content but decrease with asphalt addition. It is interesting to note that without the sulfur and asphalt, sand mixes would have little or no stability. The data also indicate a wide variety of mix designs are possible whose stabilities are consistant with Asphalt Institute suggested values for conventional asphaltic mixes. 

Figure 3. Marshall stability as a function of sulfur and asphalt contents in sand-asphalt-sulfur mixes (15,). Materials used were medium-coarse sand and 150/180 pen. asphalt. All specimens were prepared with 2 hammer blows on one face only.

An examination of the above criteria would indicate that an optimum SAS system would have sulfur and asphalt content between 12 and 14 percent and 5 and 7 percent, respectively. The final decision will be dictated by the air void content and gradation of the aggregate, the latter of which has a bearing on the tear resistance of the mat during placement. For a fine in-depth treatment of the aggregate selection process and SAS construction procedures, the reader is referred to Volume III of Reference 22. 

Figure 5. Fatigue life as a function of sulfur content for a sand-asphalt-sulfur mix. Test temperature 50°F (10°C). Test frequency 60 Hz. Materials medium-coarse sandt and 150/180 pen. asphalt. Asphalt content 6% wt (15),...

The asphalt content of THERMOPAVE mixes is similar to that of conventional asphalt paving mixes for base and wearing courses mixes containing 4-7% asphalt are generally most suitable. In general, the ratio of sulfur to bitumen is at least 1 1 and pre-... 

Commercial value of a petroleum liquid can be estimated quickly through measurement of the following physical characteristics . specific gravity, gasoline and kerosene content, sulfur content, asphalt content, pour point, and cloud point. 

The SA binder is tested for dispersion and particle size prior to mix production with a microscope. The binder level of the mix is constantly measured with a Troxler model 2226 asphalt content gauge. Hot solvent extraction (ASTM D2172) using tetrachloroethylene solvent can also be used to measure the binder content of a SA mix. The sulfur—asphalt ratio of the binder is monitored in the field with the Troxler or by density measurements. Other methods that can be used to measure SA ratios are x-ray fluorescence of solutions of sulfur-asphalt in tetrachloroethylene, liquid chromatography, and differential scanning calorimetry. X-ray fluorescence measures total sulfur, liquid chromatography determines elemental sulfur, and DSC monitors crystalline sulfur. 

Thermopave mix (medium sand)—asphalt content, 6 wt % sulfur content, 13 wt % Plant, Cedarapids capacity, 6000 lb (2722 kg) batch batch size evaluated, 5000 lb (2268 kg) mixing time, 25 sec with sulfur. 

The allowable sulfur concentration in the binder depends on the properties of the asphalt. For example, asphalts A and B (Appendix, Table A-I) exhibit significantly different viscosities at the Marshall test temperature of 60°C. This difference is reflected by differences in mix stability at similar asphalt contents, shown in the Appendix and in Figure 6, i.e., 11120 N and 5960 N for asphalt A and B, respectively, at a content of 6 wt %. Asphalt B yields high-stability mixes and is not as prone to softening by low sulfur concentrations in the binder, whereas asphalt A exhibits the reverse behavior. 

The use of higher amounts of sulfur, above a sulfur/asphalt weight ratio of 1.0, yields pourable mixes with a marked change in physical properties. For example, the sand mixes in Figure 8 exhibit negligible stability without sulfur addition of sulfur permits mix designs to high stability levels at a variety of asphalt contents. Other mix properties are affected in a similar fashion. 

Asphalt used in mix design. Optimum asphalt content, 5.0%. 

Type Aggregate in Mix Asphalt Content (w/o) Sulfur Content (w/o) Resilient Modulus X (psi)... 

Figure I. Variation of resilient modulus with sulfur and asphalt content...

Marshall test specimens of asphalt mixtures were prepared with the asphalt content varying at 0.5 percent intervals within the range of 4.5 to 6.5 percent. Density, stability and flow value of the specimens were measured to calculate the percentage of air void and voids filled with asphalt and to determinate the design asphalt content. 

The relation between design asphalt contect and volume percent of plastic in the mixtures is shown in Fig. 4. The design asphalt content was determined in the range of asphalt contents which satisfied the standards specified in Table 2. 

The design asphalt content of mixtures with the plastic sample-1, which has the low softening temperature as shown in Fig. 1. decreased as the volume percent of plastic was higher. However, it is doubtful whether the low design asphalt content is the optimum value which must be adopted for construction, because the reduction of asphalt content may bring deterioration of durability of the asphalt mixture. That must be require further investigation. 

Table 3 shows the dynamic stabilities of asphalt mixtures with six plastics listed in Table 1, where the asphalt content was 5.5 or 6.0 percent, and the volume percent of plastic was 5 or 10 percent. The all dynamic stabilities, except of the plastic sample-4, were higher than the value of the mixture with no plastic. 

Especially the dynamic stabilities of the mixtures with the plastic sample-1 and 2 were so high as to be over 20 thousands passes per minute in case of 5.5 percent asphalt content. It is assumed that these plastics were of the first sort mentioned in the paragraph 2. and the dynamic stabilities increased remarkably because a part of plastics dissolved in the asphalt. 

Table 2. Standards specified to determine the design asphalt content of a dense-graded asphalt mixture with plastic in this study...

Fig. 4. Design asphalt content determined by Marshall test...

Fig. 5. Relations between bendig strength and temperature (asphalt content 5.5%)...

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