Oxidised bitumen

Oxidised bitumen is mainly used in roofing, waterproofing, adhesives and insulations. 

Essential requirement Surrogate characteristic Test method Unit 0 / Classes 2 3 4 

Source Reproduced from CEN EN 13924, bitumen and bituminous binders - Specifications for hard paving grade bitumens, Brussels CEN, 2006.With permission ( CEN). 

Note NPD, no performance determined NR, no requirement TBR, level or range to be reported by the supplier (it is not used for the purpose of regulatory marking). 

These additional properties are not part of the mandated essential characteristics but have been considered useful in specification of hard paving grade bitumens in some cases. Important - a restricted softening point range, of 5°C about a midpoint, shall be declared by the supplier the overall range shall be within the range in the table. 

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It has been reported earlier that oxidation at higher temperature affects the property of the bitumen in terms of its hardness represented by penetration. Explanation of oxidised bitumen Ccin be considered into two stages oxidation of oils to resins, and conversion of resins to asphaltenes. The first step is a heterogeneous process (Gas-liquid) and the rate depends on the mass transfer area. The second step is a homogeneous process and its rate is expected to be influenced, by temperature only when bitumen is oxidised at 250 C at a fixed air rate, the rate of the first step is relatively lower than of the second step so that oxidation leads to a decrease of resin content, which in turn affects the penetration value. 

The bitumen and bituminous binders may be divided into three general groups (a) the paving grade bitumens, (b) the hard paving grade bitumens and (c) the oxidised bitumens. 

Paving bitumens are bitumens produced from the residue distillation of crude oil, whereas oxidised bitumens are produced from bitumen subjected to a blowing process during which oxidation of bitumen occurs. 

Table 3.7 Properties and test methods of oxidised bitumen ...

Ring-and-ball softening point testing for oxidised bitumens are carried out in glycerol, as the values typically are above 80°C. 

In contrast to paving bitumens, the oxidised bitumen products are graded in reference to a combination of the softening point values, and penetration at 25°C, expressed in multiples of 5. Hence, an oxidised bitumen 85/25 means that the softening point of the product is between 80°C and 90°C and the penetration is between 20 and 30 dmm. 

Per EN 13304 (2009), oxidised bitumens are specified by the rules given in Table 3.7. 

With regard to American specifications for oxidised bitumen (asphalt), information can be found in standards related to particular use, such as ASTM D 2521 (2014) for canal, ditches, pond lining and so on. 

The consistency of the bitumen and the bituminous binders at elevated temperature is empirically determined with the softening point test, also known as a ring and ball (R B) test. Along with the penetration test, the softening point test is used for grading the oxidised bitumens. 

The limiting theoretical values of the penetration index are -10 for bitumens with very high susceptibility to temperature variations, up to +20 for bitumens almost independent of temperature variations. In practice, penetration index varies between -3 and +7 for paving grade bitumens and oxidised bitumens. The smaller the penetration index, the more sensitive the bitumen is to temperature variations. 

Atmospheres polluted by oxidising agents, e.g. ozone, chlorine, peroxide, etc. whose great destructive power is in direct proportion to the temperature, are also encountered. Sulphuric acid, formed by sulphur dioxide pollution, will accelerate the breakdown of paint, particularly oil-based films. Paint media resistant both to acids, depending on concentration and temperature, and oxidation include those containing bitumen, acrylic resins, chlorinated or cyclised rubber, epoxy and polyurethane/coal tar combinations, phenolic resins and p.v.c. 

The moist sulfide readily oxidises in air exothermally, and may reach incandescence. Grinding in a mortar hastens this [1]. The impure sulfide formed when steel processing equipment is used with materials containing hydrogen sulfide or volatile sulfur compounds is pyrophoric, and has caused many fires and explosions when such equipment is opened without effective purging. Various methods of purging are discussed [2], Formation of pyrophoric FeS in bitumen tanks is considered as a cause of spontaneous ignition and explosion in the head space [3], A detailed study of formation of possibly pyrophoric sulphides from rust in crude oil tankers has been made [4],... 

Rubber is vulcanised by treatment with sulphur chloride or by heating with sulphur. In most cases, however, rubber articles are made, not of pure vulcanised rubber, but of the latter mixed with various other substances, organic and inorganic. The organic substances more commonly used are brown and white factis, fatty oils, oxidised oils, waxes, mineral oils, paraffin wax or ceresine, resin or resin oils, bitumens, tar, pitch, starch, and artificial dyes. Very many inorganic compounds may be added either as fillers or to give colour, e.g., talc, kaolin, asbestos, chalk, gypsum, lime. 

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