Asphalt penetration

The only exception seems to be the rock asphalt of Buton Island (south of Sulawesi Island) in Indonesia. In this island, the rock asphalt forms hills and mountains. This porous rock contains hard natural asphalt (penetration of 5-10 dmm) at 15%-30% and soft limestone with fossilised shell impurities. The extraction is very simple and cheap, because of low local labour cost thus, it is used locally for the production of bituminous mixtures. 

For asphalt operation, experimental data is necessary, relating asphalt penetration to residual volume. Using this information, distillate volume can be readily established. Units have been built to make asphalt over the penetration range of 85 down to 10 (approximately 7 to 4 degrees API). The asphalt specifications will most often be set by the owner, and it may be necessary to design for more than one grade of product. 

Penetration—Indentation. Penetration and indentation tests have long been used to characterize viscoelastic materials such as asphalt, mbber, plastics, and coatings. The basic test consists of pressing an indentor of prescribed geometry against the test surface. Most instmments have an indenting tip, eg, cone, needle, or hemisphere, attached to a short rod that is held vertically. The load is controlled at some constant value, and the time of indentation is specified the size or depth of the indentation is measured. Instmments have been built which allow loads as low as 10 N with penetration depths less than mm. The entire experiment is carried out in the vacuum chamber of a scanning electron microscope with which the penetration is monitored (248). 

Trinidad asphalt has a relatively uniform composition of 29% water and gas, 39% bitumen soluble in carbon disulfide, 27% mineral matter on ignition, and 5% bitumen that remains adsorbed on the mineral matter. Refining is essentially a process of dehydration by heating the cmde asphalt to ca 165°C. The refined product averages 36% mineral ash with a penetration at 25°C of about 2 (0.2 mm), a softening point (ring and ball method) of 99°C, a flash point (Cleveland open cup) of 254°C, a sulfur content of 3.3%, and a saponification value of 45 mg KOH/g. The mineral matter typically contains... 

Many agents have been proposed and patented including copper sulfate (34), zinc chloride (35), ferric chloride (36), aluminum chloride (36), and phosphoms pentoxide (37) ferric chloride, zinc chloride, and phosphoms pentoxide have been most widely used. The addition of these agents may vary from 0.1 to 3%, depending upon the feedstock and the desired characteristics of the product (Table 5) and all asphalt feedstocks do not respond to catalysts in the same way. Differences in feedstock composition are important qualifiers in determining the properties of the asphalt product. The important softening point-penetration relationship, which describes the temperature susceptibiUty of an asphalt, also varies with the source of the feedstock. Straight-reduced, air-blown, and air-blown catalytic asphalts from the same cmde feedstock also vary considerably. 

This equation is based on the approximation that the penetration is 800 at the softening point, but the approximation fails appreciably when a complex flow is present (80,81). However, the penetration index has been, and continues to be, used for the general characteristics of asphalt for example asphalts with a P/less than —2 are considered to be the pitch type, from —2 to +2, the sol type, and above +2, the gel or blown type (2). Other empirical relations that have been used to express the rheological-temperature relation are fluidity factor a Furol viscosity P, at 135°C and penetration P, at 25°C, relation of (H—P)P/100 and penetration viscosity number PVN again relating the penetration at 25°C and kinematic viscosity at 135 °C (82,83). 

For the asphalt cements produced at that time the adoption of the volatilisation and penetration tests provided some degree of control of excessive changes during plant mixing that might be reflected in more durable asphalts. The adoption of the method for bitumen was intended to provide a means for identifying Trinidad asphalt by observing the amount and color of the insoluble ash. 

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. 

Specifications for paving asphalt cements usually include five grades differing in either viscosity or penetration level at 60 °C (Table 8) (ASTM D496). Susceptibihty of viscosity to temperature is usually controlled in asphalt cement by viscosity limits at a higher temperature such as 135 °C and a penetration or viscosity limit at a lower temperature such as 25 °C. 

Float Test (ASTMD139). The consistency properties of an asphalt at a very low apphed force are indicated by this test. The test is normally used for those asphalts that are too soft for the penetration test. 

Penetration (ASTMD5). This is a commonly used consistency test. It involves the deterrnination of the extent to which a standard needle penetrates a propedy prepared sample of asphalt under definitely specified conditions of temperature, load, and time. The distance that the needle penetrates in units of mm/10 measured from 0 to 300, is the penetration value. Soft asphalts have high penetration values. 

If straight-mn asphalts are reduced to a hardness below 300 penetration (30 mm), they are termed asphalt cements. For hot-mix paving, either the AC-10 viscosity grade or the next harder AC-20 grade is commonly specified. 

Type 1 asphalt is the softest type of mopping asphalt with softening points between 68°C and with penetration at 25°C between 18 and 50 mm /10. It is for roof slopes of less the j in. per ft (0.25 per 12). It is also called dead level asphalt and is not commonly used today because of the porosity of the fiber-glass ply felts and the industry recommendation that roof slope a minimum of j in. per ft. 

Type 11 asphalt is the second most common type of asphalt used because it offers the best compromise between softness and weatherabiHty and lack of fl °C with penetration at 25°C between 18 and 40 mm /10. It is for roof slopes less than 1 per 12 and is also called flat asphalt. If Type 11 asphalt is used on the roof, it cannot be used on flashings. 

Type IV asphalt is not common except in very hot climates. It has softening points between 96 and 107°C with penetration at 25°C between 12 and 25 mm /10. It is for roof slopes greater than 1 per 12, and is also called special steep asphalt. Type IV asphalt is used on flashings and in hot climates to keep the roofing system from sliding off the roof in hot weather. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Membranes are applied directly to the metal or concrete surface to protect from corrosion by any liquor that penetrates the brick lining through pores and cracks. Membranes consist of sheet material bonded to the metal or concrete, e.g., flexible PVC sheet, or it may be formed in situ (e.g., polyester resin reinforced with glass fiber, or synthetic rubber sheet, lead, polyisobutylene, polyethylene and asphalt). 

The float test is used to determine the consistency of asphalt at a specified temperature. One test method (ASTM D139) is normally used for asphalt that is too soft for the penetration test (ASTM D5, D217, D937, D1403 IP 50, 179, 310). 

Fig. 1. Production of asphaltic coatings, primers, and cements. Typical asphalt has 18—100 mm penetration at 25°C typical solvent has a boiling range of...

Their penetration decreases with age, but at a considerably faster rate than experienced with asphalt cements. Unlike asphalt, which hardens primarily through oxidation, Sulphlex binders can under certain circumstances be brought back to near their original penetrations by heating to approximately 120C. 

The results of this program are contained in reference (10) Table II presents a comparison of the selected physicochemical properties of Sulphlex-233 and an AC-20 grade asphalt cement used in the FHWA study. The table indicates that their properties are generally quite different, particularly the specific gravity, penetration, viscosities, and flash and fire points. However, from a practical standpoint, as the materials are used in the field, these differences are not highly significant. 

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