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The comparison of laboratory and field test results for low density slags

An accelerated expansion test has been developed which gives a good indication of the likely behaviour of low density (LD) slags used as an unbound aggregate. The test produces a result within 24 h. These results were compared with road performance.

3 samples of LD slag were obtained from 2 different works. These were then incorporated into the subbase and roadbase of a road. For comparison 1 panel was laid with limestone aggregate.

The free lime content of the materials was measured, and found to range from 4 to 7%. In an exercise taking samples from each heat, a range of free lime contents of 0.2 to 14.1% was found at one works and 0.2 to 30.8% at the other.

In the accelerated expansion test, which passes steam through the sample, the expansion is mainly the result of the hydration of free lime. However, the measured free lime content of the test slags did not correlate closely with the expansion values. This is because the ethylene glycol used to extract the free lime also extracts calcium hydroxide. Thus a method had been developed for a separate determination of calcium hydroxide using an infrared analyser to measure the water evolved when the sample is heated.

The road surface was then monitored, with profiles measured every 6 months. These showed no change through the duration of the project. The conclusion was that the acceptance of a content of up to 7% free lime, and the value of 5% accelerated expansion (the current German limits), were justified.

Reported by

Forschungsgemeinschaft Eisenhuttenschlacken eV
Bliersheimer Strasse 62
47229 Duisburg
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