Marshall stability test – flow test on bitumen was developed by the Mississippi State Highway Department and is suited to hot mix design of bitumen and aggregates with a maximum size of 2.5 cm. Marshall Method is often used to create bituminous concrete mixes. This exam is commonly utilised in paving job routine testing programmes. A maximum load carried by a compacted specimen at a standard test temperature of 600C is used to determine the mix’s stability. During a stability test, the flow is measured as the difference in deformation between no load and the maximum load borne by the specimen in units of 0.25 mm (flow value may also be measured by deformation units of 0.1 mm). This test aims to determine the best binder content for the aggregate mix type and application.
Flow Test on Bitumen
The Marshall Stability Test apparatus consists of the following:
1. Specimen mould assembly with 10.16cm diameter and 6.35cm height mould cylinders, base plate, and extension collars.
2. The compacted specimen is extracted from the mould using a specimen extractor. While withdrawing the specimen, a suitable bar is required to transfer load from the extension collar to the top proving ring attachment.
3. A compaction hammer with a flat circular tamping face and a 4.5kg sliding weight with a 45 cm free fall.
4. A 202045 cm wooden block topped with a 30302.5 cm MS plate serves as a compaction pedestal to keep the mould assembly in place during compaction. A mould holder is provided, which is made up of a spring tension device that keeps the compaction mould in place on the compaction surface.
5. Breaking head: this is made up of upper and lower cylindrical segments (test heads) with a 5 cm inside radius curvature. The longer segment is attached to a base with two perpendicular guide rods that make insertion into the holes of the upper test section easier.
6. Loading Machine: It has a gear system that allows it to lift in the upward direction. On the top end of the machine, a pre-calibrated proving ring with a capacity of 5 tonnes is fixed, and the specimen in the test head is put between the base and the proving ring. The load jack generates a 5 cm per minute uniform vertical moment. The machine may also reverse its moment downward. This provides enough space for the test head system to be placed after one.
7. A flow metre is made up of three parts: a guide, a sieve, and a gauge. With a tiny amount of frictional resistance, the gauge’s activating pin slips into the guide sleeve. A minimum count of 0.025 mm is sufficient. The total vertical upward movement from the initial position at zero load to the value at maximum load is referred to as the flow value. The flow meter’s dial gauge should be able to precisely measure the whole vertical moment upward.
Preparation of Test Specimen
1. 1200 grammes of aggregates in the desired proportions are measured and heated to mixing temperature in the oven.
2. At the mixing temperature, bitumen is added in various percentages to produce viscosity of 170 centi-stokes.
3. In a heated pan, the materials are mixed with heated mixing tools.
4. Return the mixture to the oven and reheat it to the compacting temperature (280-30 centi-stokes viscosity).
5. The mixture is then spaded around the sides of a heated Marshall mould with a collar and base. Under the sample and on top of the sample is a filter paper.
6. Insert the mould into the Marshall compaction pedestal.
7. The material is compacted with 50 hammer blows (or as specified), and the sample is inverted and compacted with the same number of blows on the other face.
8. The mould is inverted after it has been compacted. The base is removed with the collar on the bottom, and the sample is extracted by pushing it out the extractor.
9. After a few hours, the sample is allowed to cool.
10. The mass of the sample in air and when submerged is used to calculate the void properties by measuring the density of the specimen.
Procedure for Testing
Specimens are cooked to 60°C for 30-40 minutes in a water bath or for a minimum of 2 hours in an oven.The specimens are taken out of the water bath or oven and placed in the breaking head’s lower section. The upper portion of the specimen’s breaking head is fitted in place, and the entire assembly is placed on the testing machine. The flow metre is adjusted to zero and put over one of the posts. Until the maximum load reading is attained, the load is applied at a rate of 50 mm per minute. The maximum load is measured in Newtons. The flow as measured on the flow metre in the same instant.
The optimal bitumen content is determined by the mix design (wetmix). The dry mix design mentioned in the preceding chapter comes before this. Mix design can be done in a variety of ways, depending on the size of the test specimen, compaction, and other test parameters. The most prominent approach of mix design is the Marshall method, which is detailed further below.Marshall was in charge of the mix. The Marshall stability and flow test is used to estimate how well the Marshall mix design procedure will perform. The maximum load supported by the test specimen at a loading rate of 50.8 mm/minute is measured during the stability section of the test. The specimen is loaded until it fails, and the maximum load is defined as stability. During the loading, a dial gauge attached to the machine measures the pressure.
Marshall Stability Test;
Marshall technique is often used to build bituminous concrete mixes. This test is widely utilised in the paving industry’s routine testing programmes. The maximum load sustained by a compacted specimen at a specified test temperature of 60 degrees Celsius is termed as mix stability. During the stability test, the flow is measured as the difference in deformation in units of 0.25mm between no load and maximum load carried by the specimen (flow value may be measured by deformation units of 0.1mm). The goal of this test is to find the best binder content for the aggregate mix type and traffic intensity. This is a test that allows us to plot Marshall stability vs. bitumen percent. Marshall Stability is defined as the resistance to plastic in this test.
The mix design should prioritise the cost-effective component, with correct aggregate gradation and bitumen proportions, in order to achieve the desired mix attributes of stability, durability, flexibility, skid resistance, and workability. Mix design procedures should try to determine the aggregate and bituminous material qualities that will result in a mix with these properties. Asphalt paving mixture design is a multi-step process that involves selecting binders and aggregate materials and proportioning them to achieve an appropriate compromise among several variables that affect mixture behaviour while taking into account external factors such as traffic loads and weather conditions. Bitumen is used to bind the aggregate together in the creation of flexible pavements by covering the material. It also aids in the improvement of.
Marshal stability test is the performance prediction measure conducted on the bituminous nix.
The Marshall stability and flow test provides the performance prediction measure for the Marshall mix design method.
The basic Marshall test consists essentially of crushing a cylinder of bituminous material.