IMPROVING THE SAFETY, SPEED AND COST OF ASPHALT BINDER CONTENT ANALYSIS
The bitumen content of black top is one of the main factors governing its integrity under load. A new procedure for analysing bitumen content brings significant improvements in safety, speed and cost compared with the usual test method.
For the last 40 years the most widely used procedure has involved washing a sample of black top in a known quantity of solvent and weighing the 'clean' stone remaining to determine the quantity of bitumen removed.
A particular disadvantage of this procedure is the use of methylene chloride to remove the bituminous binder, methylene chloride being highly toxic and heavier than air — a potentially lethal combination in a closed environment. A considerable amount of special equipment, including freezer cabinets, stills and evaporation units, is also needed to store the solvent before and after it has been used. Maintaining this equipment presents particular problems, as does disposing of the dirty solvent and solvent containers.
Apart from the capital cost of the special equipment, methylene chloride itself currently costs about £330 a tonne. A single test typically requires about six litres of solvent and takes up to two hours, with a technician present throughout.
RMC Aggregates Ltd at Dove Holes, Derbyshire, which produces a wide variety of coated stone products, is now using a new type of equipment produced by Carbolite, a specialist UK manufacturer of electric ovens and furnaces, to analyse the asphalt binder content of all limestone products. Because a new British Standard covering the loss-on-ignition method is still in draft form, a single duplicate BS test with methylene chloride is performed each day to provide confirmation of results.
Granite macadams and hot-rolled asphalt with sand fines are still tested in the traditional way because of the lack of data for these materials at this stage. When this data is available, the ABA will be used for all materials produced at the Dove Holes plant.
As well as improving safety, the new test method is also quicker and simpler, according to laboratory manager Joanne Phillips. No more than 45 minutes is needed for the loss-on-ignition procedure, and the amount of technician's time required has been greatly reduced.
A wide variety of equipment is also needed for the solvent test, and all of it has to be calibrated regularly to meet British Standard requirements. With the ABA equipment, a balance is the only item requiring calibration.
As the ABA is microprocessor-based, the laboratory has created a software programme for each type of macadam, so only the weight of the sample and sample tray needs to be keyed in. Once started, the whole process is automatic, with a display on the furnace showing the progress of the test — current sample weight, current weight loss in grams and as a percentage, the rate of change of sample weight and the duration of the test.
At the end of the test the binder content of the sample is shown on the display, and a full print-out is automatically produced. Test times range from 20 minutes for 6mm samples to 45 minutes for 40mm samples. Up to 4.5kg are tested in a batch.
The laboratory plans to completely replace the solvent method with the loss-on-ignition procedure as soon as the new British Standards are in force and sufficient data has been collected for the various mixes produced by the plant.
For the last 40 years the most widely used procedure has involved washing a sample of black top in a known quantity of solvent and weighing the 'clean' stone remaining to determine the quantity of bitumen removed.
A particular disadvantage of this procedure is the use of methylene chloride to remove the bituminous binder, methylene chloride being highly toxic and heavier than air — a potentially lethal combination in a closed environment. A considerable amount of special equipment, including freezer cabinets, stills and evaporation units, is also needed to store the solvent before and after it has been used. Maintaining this equipment presents particular problems, as does disposing of the dirty solvent and solvent containers.
Apart from the capital cost of the special equipment, methylene chloride itself currently costs about £330 a tonne. A single test typically requires about six litres of solvent and takes up to two hours, with a technician present throughout.
RMC Aggregates Ltd at Dove Holes, Derbyshire, which produces a wide variety of coated stone products, is now using a new type of equipment produced by Carbolite, a specialist UK manufacturer of electric ovens and furnaces, to analyse the asphalt binder content of all limestone products. Because a new British Standard covering the loss-on-ignition method is still in draft form, a single duplicate BS test with methylene chloride is performed each day to provide confirmation of results.
Granite macadams and hot-rolled asphalt with sand fines are still tested in the traditional way because of the lack of data for these materials at this stage. When this data is available, the ABA will be used for all materials produced at the Dove Holes plant.
As well as improving safety, the new test method is also quicker and simpler, according to laboratory manager Joanne Phillips. No more than 45 minutes is needed for the loss-on-ignition procedure, and the amount of technician's time required has been greatly reduced.
A wide variety of equipment is also needed for the solvent test, and all of it has to be calibrated regularly to meet British Standard requirements. With the ABA equipment, a balance is the only item requiring calibration.
As the ABA is microprocessor-based, the laboratory has created a software programme for each type of macadam, so only the weight of the sample and sample tray needs to be keyed in. Once started, the whole process is automatic, with a display on the furnace showing the progress of the test — current sample weight, current weight loss in grams and as a percentage, the rate of change of sample weight and the duration of the test.
At the end of the test the binder content of the sample is shown on the display, and a full print-out is automatically produced. Test times range from 20 minutes for 6mm samples to 45 minutes for 40mm samples. Up to 4.5kg are tested in a batch.
The laboratory plans to completely replace the solvent method with the loss-on-ignition procedure as soon as the new British Standards are in force and sufficient data has been collected for the various mixes produced by the plant.
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