The loss on heating (LOH) test is a standard method used to determine the amount of volatiles present in bitumen, a type of petroleum product commonly used in road construction and maintenance. The test involves heating a sample of bitumen to a specified temperature for a set period of time, and measuring the weight loss due to the evaporation of volatile components.
The LOH test is an important quality control measure for bitumen, as the amount of volatiles can affect the performance of the material in road applications. In this article, we will explore the LOH test in more detail, including its procedure, significance, and interpretation of results.
To determine the loss of volatiles present in asphaltic bitumen on heating.
Bitumen is commonly used as a binder in pavements. When it is exposed to the atmosphere, the volatiles present in it evaporates and bitumen hardens.
In the loss of heating of bitumen, the bitumen specimen is subjected to an accelerated ageing process under the conditions specified by the standard.
By carrying out penetration test at the start and finish of the test, the amount by which bitumen hardens can be known.
Read More: Water Content Test of Bitumen | Procedure & Result
Loss on Heating: The loss of volatiles like oil except water on heating the bituminous material to standard temperature and under predetermined conditions is termed as a loss on heating.
The practical works on the below principle:
The volatile materials evaporate when they are subjected to high temperatures. Bitumen is heated to about 163 ° C so that the volatile materials are evaporated.
Apparatus for Loss of Heating of Bitumen Test:
The apparatus used while conducting loss on heating test of bitumen is described below:
1. Hot Air Oven:
The rectangular double-walled oven is taken. Its parts and their dimensions are mentioned below:
- Interior Height from the top of the heating element to the top of the chamber = 292-298 mm
- Chamber is provided in the oven on one side which has a tight-fitted door hinged to it. Chamber section ≮ 100 mm2.
- A glass window is provided at the front for observation.
- Ventilation arrangement- One round vent hole at the top or bottom. Alternatively, one round vent hole at top and bottom is provided on the sides. Diameter of Vent Hole = 12-16 mm
- Electricity is required for heating purposes
2. Perforated Metal Shelf:
It is made up of aluminum and placed in the center of the oven. It is suspended by means of a vertical shaft which is rotated at the rate of 5-6 rev/min. Its diameter is about 250 mm.
It is a cylindrical pan made up of either metal or glass, cylindrical in shape and has a flat bottom. Its internal diameter is 55 mm and its internal depth is 35 mm.
4. Thermometer or Temperature Indicator and Controller:
To measure the temperature of water in the ductility apparatus. It should be graduated in Celcius. The temperature range should be from 155-170 °C. it is supported on the shaft of the perforated shelf so that it can be kept in a vertical position. Distance between the top of the contraction chamber and the bottom of bulb of the thermometer ≯ 41 mm.
5. Weighing Balance:
It should be accurate to 0.1 grams.
6. Other accessory equipment required for conducting Loss on Bitumen Test are as follows:
- Asbestos gloves
- Penetrometer and water bath
- Container to mix bitumen of about 225 gram
- Bituminous material to be tested
The following precautions should be taken while performing the loss on a heating test of bitumen to obtain accurate results:
- The loss on a heating test of bitumen should be conducted in duplicate
- If there is presence of water in the sample, it should be tested in that composition only
- The temperature of the oven should be strictly maintained to 163 °C
- Hot air oven, analytical balance, penetrometer and water bath should be calibrated in a while
- Water content of the sample should be determined in accordance with IS 1211: 1978 as the method of determination of water content specified
- If the sample shows evidence of loss by foaming, that sample should not be considered but rejected
Procedure for Loss on Heating Test of Bitumen:
- Agitate the bituminous material by stirring as received so that a complete mixture is obtained. Heat the sample above its softening point, if necessary.
- Heat the containers at 100-110 °C for about 30 minutes in the oven and then allow them to cool at room temperature and measure the weight of the empty containers.
- Take a portion of the well-mixed material for testing in a container and allow it to cool. Prepare at least 2 such specimens.
- Weigh the sample along with the container to the nearest 0.1 gram and subtract the weight of the container to obtain the weight of the sample- W1. The weight of the sample filled in the container is 50.0 ± 0.5 grams.
- If penetration values are to be compared too, then pour the sample in the penetrometer cup also. Find out the penetration value as specified in IS: 1203- 1978.
- Set the temperature of the oven to 163 ± 1 °C.
- Place the container with the sample on the perforated shelf placed centrally and close the oven.
- Maintain the temperature to 163 ± 1 °C for 5 hours after the oven has achieved the specified temperature. The duration for which the sample is placed in the oven should not be more than 5 hours and 15 minutes.
- Switch on the motor switch to allow the perforated plate to rotate at a rate of 5-6 rev/min.
- Allow the sample in the containers to cool at room temperature.
- Weight the sample to the nearest 0.1 gram- W2.
- Determine the water content for the sample as done in the determination of water content test in accordance with IS: 1211- 1978.
- Calculate the weight loss of volatile materials because of heating from the above-observed values.
- Arrange the containers on the perforated shelf and turn on the oven for 5 minutes at the specified temperature.
- If the penetration test is also to be compared, then mix the sample of the containers and keep the mixture on a hotplate so that it remains in the liquid state. Pour the mixture into a penetrometer cup and determine the penetration value. The value will be less than the previous one.
Following observation is made as the loss on heating test of bitumen is conducted:
The weight of the sample reduces on heating as the volatile materials are evaporated.
Hence, the initial weight of the sample is more while the weight after testing is reduced. The difference in weight is the loss of volatile materials present in the bitumen.
(A sample observation table for loss on heating test of bitumen is drawn below)
|Descriptions||Sample – 1||Sample – 1|
|Initial Weight of Sample in gm ( W1)|
|Final Weight of Sample in gm (W2)|
|Loss on Heating ( W1 – W2) in gm|
|Penetration Value before testing P1 (in mm)|
|Penetration Value after testing P2 (in mm)|
|Reduction in Penetration Value P1 – P2 (in mm)|
(Note: Penetration values are to be noted ONLY when hardening is to be measured along with loss on heating test of bitumen)
Loss in weight on heating = Average value of loss obtained for specimens 1 and 2.
Apply corrections for water loss, if the water is present in the natural conditions of the sample. Water content is determined and is added to the final result.
The values obtained from the loss on heating test of bitumen are recorded as follows:
- Loss in weight on heating (in gram)= average of loss in weight on heating of the two samples
The result is reported as the percentage by mass of the original sample.
Loss in weight on heating (in %) = (Average Weight Loss/ Original Average Weight of Sample) x 100
The loss in weight on heating is compared against the standard values.
- The weight loss on heating of bitumen used for pavement should not be more than 1 % by mass.
- For a sample having a penetration value of 150-200, loss in weight should not exceed 1 % by mass.
- If penetration values are also to be compared, then the penetration test is carried out before and after heating the sample in the oven. The difference in the penetration values is recorded too.
Reduction in Penetration value of the residue after the test has been performed (in %) =
= (Reduction in Penetration Value / Original Penetration Value of Sample) x 100
By performing the loss on heating test of bitumen, we can determine whether the given bitumen sample meets the specification requirements for loss on heating as given in the standards.
The value found out by the practical is compared to the standard value and thus It can be concluded whether the sample meets the criteria.
Loss on heating test of bitumen gives a measure of the number of volatile materials evaporated on heating. It serves as a measure as to how much bitumen will harden after the loss of these materials.
The hardness gained after the loss of volatile materials can be compared to the results of penetration tests.
|The containers are heated in the hot air oven at 100-110 °C for about 30 minutes.|
|The containers are thereafter allowed to cool at room temperature.|
|The empty containers are weighed to the nearest 0.1 gram.|
|The bituminous material is heated above its softening point to obtain a homogenous fluid of the material.|
|The bituminous material filled in the container is allowed to cool and then weighed.|
IF PENETRATION VALUES ARE TO BE COMPARED TOO:
A sample of bituminous material is poured into a penetrometer cup and the penetration test is carried out as per IS: 1203- 1978
|The penetration value of the sample is thus determined by the penetration test,|
|Sample containers are placed in the perforated shelf attached centrally to the oven|
|The motor is switched on so that the perforated shelf rotates at the speed of 5-6 rev/min during the test.|
|The sample in the container is allowed to cool at room temperature.|
The containers are arranged on the perforated shelf again and place in the oven at the specified test temperature of 163 °C for 15 minutes.
IF PENETRATION VALUES ARE TO BE COMPARED TOO:
The bituminous material is poured from both containers in a container of 225 grams.
|The container is placed on a hot plate so that the bitumen remains in a fluid state.|
|The sample is poured into a penetrometer cup.|
|The penetration value of the sample is found as per the procedure described in IS: 1203- 1978.|
|Loss in Weight (in gram)||The average loss of weight of the two containers|
|Loss in weight after the test (in %)||=(Average Weight Loss/ Original Average Weight of Sample) x 100|
|Reduction in penetration value (in %)||= (Reduction in Penetration Value / Original Penetration Value of Sample) x 100|
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