رجب / محمد محمود االسممعروف

21سكشن/

Penetration Test

the penetration test is the oldest asphalt test. In 1888, H.C. Bowen of the Barber Asphalt Paving Company invented the forerunner to the penetration test, the Bowen Penetration Machine (Halstead and Welborn, 1974[1]). It’s basic principle, and the basic principle of the penetration test, was to determine the depth to which a truncated No. 2 sewing needle penetrated an asphalt sample under specified conditions of load, time and temperature. In 1915, ASTM even went as far as specifying the brand of needle (R.J. Roberts Parabola Sharps No. 2) (Halstead and Welborn, 1974[1]).

Basic Procedure

The current penetration test (Figure 1), first published in 1959, describes the following basic procedure:

1. Melt and cool the asphalt binder sample under controlled conditions.

2. Measure the penetration of a standard needle into the asphalt binder sample under the following conditions:

o Load = 100 gramso Temperature = 25 C (77 F)o Time = 5 seconds

The depth of penetration is measured in units of 0.1 mm and reported in penetration units (e.g., if the needle penetrates 8 mm, the asphalt penetration number is 80). Penetration Grading is based on the penetration test.

Standard Test Methods

AASHTO T 49 and ASTM D 5: Penetration of Bituminous Materials

Standard Test Methods

AASHTO T 49 and ASTM D 5: Penetration of Bituminous Materials

Ring and ball Softening Point test

The softening point is defined as the temperature at which a bitumen sample can no longer support the weight of a 3.5-g steel ball.  Although it is commonly used in Europe, it is mostly used for roofing asphalts in the U.S.  Basically, two horizontal disks of bitumen, cast in shouldered brass rings (Figure 2), are heated at a controlled rate in a liquid bath while each supports a steel ball. 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 inch) (AASHTO, 2000).

Standard Test Methods AASHTO T 53 and ASTM D 36: Softening Point of

Bitumen (Ring-and-Ball Apparatus)

Absolute Viscosity test

Asphalt binder viscosity is typically measured at 60 C (140 F) because it approximates the maximum HMA pavement surface temperature during summer in the U.S.

The basic absolute viscosity test measures the time it takes for a fixed volume of asphalt binder to be drawn up through a capillary tube by means of vacuum, under closely controlled conditions of vacuum and temperature (ASTM, 2003 [1]).

Although absolute viscosity is an improvement over the penetration test, it still only measures viscosity at one temperature and thus does not fully characterize an asphalt binder’s consistency over the expected range of construction and service conditions.

Standard Test Methods

AASHTO T 202 and ASTM D 2171: Viscosity of Asphalts by Vacuum Capillary Viscometer

Kinematic Viscosity at 135° C (275° F)

The kinematic viscosity of a liquid is the absolute (or dynamic) viscosity divided by the density of the liquid at the temperature of measurement.  The 135 C (275 F) measurement temperature was chosen to simulate the mixing and laydown temperatures typically encountered in HMA pavement construction.

The basic kinematic viscosity test measures the time it takes for a fixed volume of asphalt binder to flow through a capillary viscometer under closely controlled conditions of head and temperature (ASTM, 2001).

The standard kinematic viscosity test is:

AASHTO T 201 and ASTM D 2170: Kinematic Viscosity of Asphalts (Bitumens)

 

المراجع

http://www.pavementinteractive.org