How To Test Bitumen Products

It is important to test the quality of bitumen to ensure that the specifications of the product are always met. KEBS is the custodian of testing standards of bitumen in Kenya. They approve the specifications within which the quality of all Bitumen and Bitumen products can be tested at any material testing laboratory.

The tests conducted include;

Penetration Test

It is to measure the hardness or softness of bitumen, by measuring the depth in tenths of a millimeter to which a standard loaded needle will penetrate vertically in 5 seconds. The penetrometer consists of a needle assembly weighing 100g and a device for releasing and locking in any position.

Bitumen is softened to a pouring consistency, stirred thoroughly and poured into containers at a depth at least 15 mm in excess of the expected penetration. This is done at 25degrees C.

Specific Gravity Test

The specific gravity of bitumen is the ratio of the mass of a given volume of bitumen of known content to the mass of the equal volume of water at 20 or at 15 degrees centigrade.

This can be measured using either pycnometer or preparing a cube specimen of bitumen in the semi-solid or solid state. The specific gravity of bitumen varies from 0.97 to 1.02.

Softening Point Test

Softening point is the temperature at which the bitumen attains a particular degree of softening under the specifications of test. This test is done with the Ring and Ball apparatus. A brass ring with a test sample of bitumen is suspended in liquid like water or glycerin at a specific temperature.

A steel ball is placed upon the bitumen sample and the liquid medium is heated at a rate of 5 C per minute. Temperature is noted when the softened bitumen touches the metal plate which is at a specified distance below.

Ductility Test

Ductility is the property that allows deformation or elongation. This is the distance in centimeters, to which a standard sample or briquette of the material will be elongated without breaking.

A bitumen sample is heated and poured in the mould assembly placed on a plate, then cooled in the air and then in the water bath at 25 degrees Centigrade temperature. The excess bitumen is cut and the surface is leveled using a hot knife.

The mould with the assembly containing sample is then kept in the water bath of the ductility machine for about 90 minutes. The sides of the moulds are removed, the clips are hooked on the machine and the machine is operated. The distance up to the point of the breaking of thread is the ductility value which is reported in cm.

Viscosity Test in Bitumen Cutbacks

Viscosity can be defined as the measure of liquidity of bitumen, and the measure of resistance to flow. Orifice type viscometers are used to indirectly find the viscosity of liquid binders like cutbacks and emulsions.

The viscosity expressed in seconds is the time taken by a 50 ml bitumen material to pass through the orifice of a cup, under standard test conditions and specified temperature. The viscosity of a cutback can be measured with either 4.0 mm orifice at 25degree C or 10 mm orifice at 25, 40 or 60 degree Celsius.

Water Content Test in Bitumen Emulsions

Bitumen with minimum water content is ideal to prevent foaming of the bitumen when it is heated above the boiling point of water. A known weight of specimen is mixed in a pure petroleum distillate free from water, heated and then distilled of the water to know the water content in bitumen.

The weight of the water condensed and collected is expressed as the percentage by weight of the original sample. The Dean Stark apparatus are usually used for water content in bituminous emulsions.

Flash Point

The flash point is the temperature at which the vapor of bitumen momentarily catches fire in the form of flash under specified test conditions. Depending on the grades of bitumen, materials leave out volatiles at high temperatures.

These volatiles catch fire which is very hazardous and therefore it is necessary to qualify this temperature for each bitumen grade. The fire point can be described as the lowest temperature under specified test conditions at which the bituminous material ignites and burns.

Loss on Heating Test

After heating, bitumen loses the volatility and then hardens. This test is done by heating about 50gm of the sample to a temperature of 163 C for 5hours in a specified oven designed for the test.

After the heating period, the sample specimen is then weighed again and the loss in weight expressed as the percentage by weight of the original sample. Bitumen used in pavement mixes should not indicate more than 1% loss in weight.

Home