--- title: "Marshall stability test procedure" subject: "Transportation Engineering I" chapter: 6 key: "semester_6/transportation_engineering_i:marshall-stability-test" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/marshall-stability-test site: BCT Engineering --- # Marshall stability test procedure Transportation Engineering I · Chapter 6: Highway Materials - Asked in: 2077 Chaitra, 8 marks; 2075 Baisakh; 2073 Bhadra, 8 marks (asked 3 times) - Video: [Marshal Stability Test Tutorial](https://www.youtube.com/watch?v=M1vKNrcRtbU) — Shivananda Roy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/marshall-stability-test - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6 ## Question Write down the laboratory procedure of the Marshall Stability test of bitumen mixes, with its significance. ## Short answer Marshall test determines load-carrying capacity and deformation of compacted cylindrical specimens. Procedure: mix aggregate and bitumen at 150-160°C, compact with 75 blows per face (heavy traffic), measure density/voids, immerse in 60°C water bath 30-40 min, load at 50mm/min to failure. Stability (kN) indicates rutting resistance; flow (2-4mm) indicates plasticity; quotient (stability/flow) indicates stiffness. Used for optimum binder content and quality control. ## Answer The **Marshall stability test** finds the load-carrying capacity and deformation of a compacted cylindrical bituminous specimen. It is the basic test of the Marshall mix design method (ASTM D6927, Asphalt Institute MS-2, adopted in NRS 2070). #### Apparatus - Cylindrical mould 101.6 mm dia and 75 mm high, with base plate and collar. - Marshall compaction hammer (4.536 kg, free fall 457 mm) and compaction pedestal. - Breaking head (two semicircular segments of 101.6 mm inside diameter), Marshall testing machine with a proving ring/load cell and a flow dial, loading rate 50 mm/min. - Water bath at 60 degrees C, ovens, mixing bowl, thermometers. #### Procedure 1. Heat aggregates (blended to the specified gradation, about 1200 g per specimen) and bitumen (grade 60/70 or VG-30) to the mixing temperature (about 150-160 degrees C for aggregates, 150 degrees C for bitumen); mix thoroughly. 2. Place in a preheated mould (and a paper disc at the bottom) and compact with **75 blows on each face** for heavy traffic (50 for medium; 35 for light) at about 135-140 degrees C. 3. Cool, extrude, and measure height; find weight in air and in water and calculate the bulk density and voids. 4. Immerse the specimens in the **60 degrees C water bath for 30-40 minutes** (to represent the hottest condition). 5. Remove, place in the breaking head, and put it in the Marshall machine; apply load at **50 mm/min** until the maximum load is reached, then the load drops. 6. Record the **maximum load (Marshall stability, kN)** with correction for the specimen thickness, and the **flow value** (vertical deformation at the max load in 0.25 mm units or mm). The test must be done within 30 seconds after removing from the bath. #### Significance - **Stability** (typically not less than 8 kN for heavy traffic; or as per NRS 2070/IRC:111 for BC) shows the resistance to rutting and shoving. - **Flow** (2 to 4 mm) indicates the plasticity and flexibility; high flow means a plastic mix that tends to rut; low flow means a brittle mix that cracks. - **Marshall quotient** = stability/flow (kN/mm), an indicator of the stiffness of the mix. - Together with density and voids data, the results are used to find the optimum binder content, to check the mix against standards, and for quality control of the plant mix. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are Marshall specimens conditioned before loading? A. Kept in a freezer at 0 degrees C for 24 hours B. Immersed in a 60 degrees C water bath for 30-40 minutes C. Soaked in water at 25 degrees C for four days D. Oven-dried at 105-110 degrees C to constant weight Answer: B. The 60 degrees C bath represents the hottest in-service condition. (Key point: Specimen conditioning) 2. At what rate is the load applied in the Marshall machine, and what is recorded? A. 1.25 mm/min; load at 2.5 mm penetration B. 50 mm/min; the temperature at which the sample softens C. 50 mm/min; maximum load (stability) and flow at that load D. 5 mm/min; the final weight lost Answer: C. Load is applied at 50 mm/min until it peaks; the peak load is stability and the deformation at that load is flow. (Key point: Loading) 3. What does a very high flow value indicate? A. A brittle mix that cracks B. An extremely stiff mix with high stability C. A mix with no air voids D. A plastic mix that tends to rut Answer: D. High flow means plastic; low flow means brittle. (Key point: Flow interpretation) 4. What is the Marshall quotient? A. Stability divided by flow, an indicator of stiffness B. Flow divided by stability, an indicator of density C. Stability multiplied by flow, an indicator of voids D. Bulk density divided by air voids Answer: A. MQ = stability/flow in kN/mm. 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