Bituminous mixture, also known as asphalt mixture, is mainly composed by aggregates and bitumen, an infinite variety of mixtures being possible.
This section lists the equipment required for bitumen testing, including machines to study the rheological properties of bitumen as well as the features of bituminous emulsion. It includes solutions to perform field tests on road surface.
Penetration
The Penetration is the consistency of a bituminous material expressed as the distance in tenths of a millimeter that a standard needle vertically penetrates a sample of the material under known conditions of loading, time, and temperature.
The penetration is measured with a penetrometer by means of which a standard needle is applied to the sample under specific conditions.
The penetration test is used as a measure of consistency. Higher values of penetration indicate softer consistency. The value of penetration obtained is also used to classify the bitume in a range of penetration grade.
Softening Point
Bitumens are viscoelastic materials without sharply defined melting points; they gradually become softer and less viscous as the temperature rises.
The softening point of bitumen can be determined through the use of a ring-and-ball apparatus immersed in distilled water (30 to 80°C) or USP glycerin (above 80 to 157°C). The softening point is reported as the mean of the temperatures at which the two disks soften enough to allow each ball, enveloped in bitumen, to fall a distance of 25 mm (1.0 in.).
The softening point is useful in the classification of bitumens, as one element in establishing the uniformity of shipments or sources of supply, and is indicative of the tendency of the material to flow at elevated temperatures encountered in service.
Ductility and Elastic Recovery
Different bitumen properties can be analyzed thanks to the use of a Ductilometer, a machine capable of applying a sample elongation at a fixed speed.
1) Ductility: The ductility is a measure of tensile properties of bituminous materials.It is measured by the distance to which a bituminous material will elongate before breaking when two ends of a briquet specimen of the material are pulled apart at a specified speed and at a specified temperature. The specimen will be continuously immersed in water, while the two clips are pulled apart at a uniform speed.
2) Elastic Recovery: The elastic recovery of a bitumen is expressed as a percentage of the distance between the ends of the half-threads, which has developed 30 min after the division relative to the elongation length of 200 mm.A bitumen specimen is stretched at a temperature of 25 °C and a constant rate of 50 mm/min to a predetermined elongation (200 mm). The bitumen thread thus produced is cut in the middle to obtain two halves of thread. After a predetermined time for recovery has elapsed, the shortening of the half threads is measured and expressed as the percentage of the elongation length. This value is especially applicable to bituminous binders modified with thermoplastic elastomers.
3) Deformation Energy: The deformation energy is the energy supplied by test pieces, until a certain displacement of the moving element is achieved. For each test specimen, the energy calculation is accomplished from the computerized data of couples force/elongation.
Rolling Thin Film Oven
The manufacturing processes of asphalt mix involves the removal of lighter components of bitumen. This process is called short-term aging and it starts during the asphalt mix production in plant, continues during the transport at site and finishes during laying and compaction phase.
The short-term aging properties of neat bitumen can be investigated using the rolling thin film oven to simulate these aging phases by the use of only one equipment. The empirical tests, which include penetration and softening points, are conducted to ascertain the binder consistency before and after this aging process. The test is conducted at 163 0 C for 70min, 85min, and 100min in function of the standard used. Due to aging the viscosity increases, the binder penetration decreases and the softening point increases compared to the neat bitumen properties.
Viscosity
Based on absolute or kinematic viscosity requirement, the bitumen viscosity can be measured by a variety of devices. The specifications kept for measurement is the absolute viscosity at 60 degree Celsius and a Kinematic viscosity at 135 degree Celsius. Bitumen tend to soften, when subjected to a temperature rise and will harden when the temperature falls.
The vacuum capillary tube viscometer is used to find absolute viscosity. Atmospheric capillary tube viscometer is employed to measure the kinematic viscosity.
Another method to measure the viscosity is the use of a rotational viscometer where a torque required to rotate a spindle at constant speed while immersed in the sample fluid. Dynamic viscosity is proportional to this measured torque.
FRAAS Breaking Point
This apparatus is used to determine the breaking point of semisolid and solid bitumes. It consists in a flexure device with two concentric sliding resin tubes, jaws for the test specimen, flexure system with handle, cooling device with three containers, plate in special harmonic steel, thermometer IP 42C.
Flash Point
Flash point is the lowest temperature at which a liquid can form an ignitable mixture in air near the surface of the liquid, when given an ignition source. The lower the flash point, the easier it is to ignite the material. The flash point tells the critical temperature at and above which suitable precautions are required to be taken to eliminate the danger of fire during heating.
To measure the bitumen flash point, different devices can be used, according to the required standard. The flash point has been commonly determined by the open cup or closed cup method:
- Tag Closed Cup Tester
- Cleveland Open Cup Tester,
- Pensky-Martens Closed Cup Tester
Solubility
The set comprises:
- Gooch crucible complete with funnel and rubber ring
- Filter flask 500 ml capacity with rubber stopper
- Whatman filter fibreglass discs, 25 mm ø (pack of 100)
Superpave
The need to understand the mechanical properties and relation between the material and the damage that occurs during the service life of road pavement (low temperature cracking, fatigue cracks and rutting deformations) was the motivation behind the development of a new classification system known as Superpave: Superpave is an acronym for Superior Performing Asphalt Pavements.
This is a new, comprehensive asphalt mix design and analysis method, under the Strategic Highway Research Program (SHRP) established by U.S Congress in 1987 to improve the performance and durability of roads.
A unique feature of the Superpave system is that the tests are performed at temperatures and aging conditions that more realistically represent those encountered by in-service pavements. SHRP researchers developed new equipment standards as well as incorporated equipment such as DSR, PAV, VDO, BBR, RTFO.
Test on Bitumen Emulsion
Bitumen emulsion is a mixture of fine droplets of bitumen and water. The average range of bitumen mixed is from 40 to 70% on the total weight.
Based upon the time taken by the water to evaporate, bitumen emulsion is further classified into 3 types based on setting time:
- Water content
- Setting time
- Residue on sieving
- Storage stability
Test for Microsurfacing
Bitumen emulsion techniques can maintain the long term serviceability of your pavement. Emulsion techniques are energy-efficient and limit greenhouse gas emissions. The performance of bitumen emulsions makes it possible to obtain cold asphalt mixes with a good macro texture, and adhesion characteristics equivalent to those of hot asphalt mix materials. Micro surfacing protects the underlying pavement by improving impermeability, provides excellent adhesion to the existing road, compensates for small deformations, and has no loose aggregates under traffic.
The most important parameters that can be checked are:
- Cohesion
- Binder adhesion
- Resistance to abrasion
- Consistency
Specimen
PreparationTo complete our range of bitumen test equipment we offer:
- Air bath
- Bacon sampler
