Marshall Stability Test – Flow Test is the resistence to plastic deformation of cylindrical specimen of bituminous mixture. This specimen is measured when the same is loaded at the periphery at a rate of 5cm per minute.
Marshall stability is associated with the resistance to distortion, displacement, furrowing, and also shear stresses of bituminous materials. Stability is mainly due to internal stress and cohesion.
Cohesion is the binding force of the binder substance, while the binding and refriction force of the aggregates is internal friction. Since bituminous pavement is subject to heavy traffic, bituminous material should adopte with good stability and fluidity from time to time.
A gear system is provided for lifting up. The upper end of the unit has a 5 ton pre-calibrated test ring, with samples in the test head between the base and the test ring positioned. The loading jack provides a uniform vertical moment of 5 cm per minute. The computer can also reverse its downward momentum. This offers ample space for inspection of a test head device after testing.
The flowmeter is composed of guide, sieve and also a size calculation. With a small amount of frictional resistance, the pin activates the gauge inside the guide sleeve. The minimum count of 0.025mm is appropriate.
The following general equipment is also required in addition to the above:
Hot plate or oven
Thermometers with a range of up to 200 ° C with a 2.5 ° C sensitivity, and mixing and handling instruments etc.
ASTM D6927 – 06 Standard test protocol for Marshall Stability
The unit for the Marshall Stability Test comprises:
Assembly of specimens of moulds with a diameter of 10.16 cm by 6.35 cm, base plate and extension collars.
Extractor specimen for the extraction of the compacted mold specimen. For load transfer from the extension collar to the high proven ring fastener while the specimen is extracted, an appropriate bar is required.
A flat circular padding hammer with a sliding weight of 4.5 kg is built for a free 45 cilometer fall.
Strong pedestal of 20 — 20 — 45 cm wooden block with 30 — 30 — 2.5 cm square metal plate for mould keeping.
Preparation of Test Specimen
The measured and heated oven to the mixing temperature is 1200 grams of aggregate blended to the appropriate proportions. In order that a viscosity of 170 ± centi-stokes at different percentages can be achieved, bitumen is added at the mixing temperature. In a heated jar, the materials are combined with heated mixing instruments.
The mixture is taken back to the oven to the compacting temperature (to achieve 280±30 centi-stoke of viscosity).
The mixture is then positioned with a collar and base in a heated Marshall mold, and the mixture is then spread across the sides of the body. Under the sample and on top of the sample is a filter document.
The mold is mounted on the pedestal of the Marshall Compaction.
The material is compacted with 50 hammer blows (or as stated), and with the same number of blows the samples are reversed and compacted on the other side. The mold is reversed after compaction. The base is extracted by pushing out the extractor by means of a collar on the rim. The sample can cool for a couple of hours.
The sample mass in the air and when dipped in is used to determine the specimen density so that the void characteristics can be measured.
Marshall Stability Test Procedure
Either in a water bath for 30-40 minutes, or in a oven for at least 2 hours, the samples are heated up to 60-± 1 ° C. The specimens are extracted and placed in the lower section of the breaking head from the washer bath or oven. The upper section of the specimen breaker head is installed and the entire assembly is mounted on the test unit. The flow meter is put over one piece and set to zero reading.
A load of 50 mm per minute before the load is read as high as possible.
Newton observes maximum load reading. The flow reported in units of mm was also observed at the same time.