--- title: "Marshall method of bituminous mix design" subject: "Transportation Engineering I" chapter: 6 key: "semester_6/transportation_engineering_i:marshall-mix-design" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/marshall-mix-design site: BCT Engineering --- # Marshall method of bituminous mix design Transportation Engineering I · Chapter 6: Highway Materials - Asked in: 2081 Chaitra, 8 marks; 2078 Chaitra, 6 marks; 2078 Poush, 5 marks; 2075 Bhadra; 2071 Magh, 8 marks; 2070 Bhadra; 2069 Bhadra; 2064 Poush (old course), 6 marks; 2064 Shrawan (old course), 8 marks (asked 9 times) - Video: [Marshall Mix Design | Lec-9 Part-1 | GATE](https://www.youtube.com/watch?v=wLmXz1Ikx1g) — Unacademy GATE & ESE - Civil & ES - 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-mix-design - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6 ## Question Explain/describe the Marshall method of bituminous mix design procedure (including determination of optimum binder content). ## Short answer Cylindrical specimens are compacted with 75 blows per face at several binder contents and tested for stability, flow, density and void properties at 60°C. The optimum binder content is the average of binder contents giving maximum stability, maximum density and 4% air voids. Mix must meet criteria such as stability ≥8 kN, flow 2–4 mm and air voids 3–5%. ## Answer The **Marshall method** (developed by Bruce Marshall and further by the US Army Corps of Engineers) designs a bituminous mix by testing compacted cylindrical specimens for **stability, flow, density and voids** at different binder contents, and then selects the **optimum binder content (OBC)**. It is the method used in Nepal (NRS 2070, the Asphalt Institute MS-2 and IRC:111). #### Specimen Cylinders 101.6 mm (4 in) in diameter and 63.5 mm (2.5 in) high, made from about 1200 g of aggregate plus bitumen. #### Procedure 1. **Select materials** - aggregates that pass the quality tests, with grading within the specified envelope (for example, BC or DBM), and the bitumen (VG-30/60-70 penetration grade). 2. **Prepare the trial mixes** - at least 5 binder contents in 0.5% steps (for example, 4.5, 5.0, 5.5, 6.0 and 6.5% by weight of mix), with 3 specimens each. 3. **Mixing and compaction** - heat the aggregates to about 150-160 degrees C and the bitumen to 140-150 degrees C; mix; place in a mould at the compaction temperature (about 138 degrees C) and compact with the Marshall hammer (4.5 kg falling 457 mm) with **75 blows on each face** (heavy traffic; 50 for medium). 4. **Density** - cool, extrude, and find the bulk specific gravity $G_b$ (from the weights in air and in water). 5. **Stability and flow test** - immerse the specimens in a 60 degrees C water bath for 30-40 minutes, then load them at 50 mm/min in the Marshall testing head. The maximum load in kN is the **Marshall stability**; the deformation at maximum load in mm is the **flow value**. 6. **Voids analysis** - calculate $V_v$ (air voids), VMA (voids in mineral aggregate) and VFB (voids filled with bitumen), and apply the stability correction for specimen volume/height. 7. **Plot graphs** (binder content on the X-axis): stability, flow, unit weight, $V_v$, VMA and VFB. #### Optimum binder content Take the binder contents corresponding to: - maximum stability ($B_1$), - maximum bulk density ($B_2$), - 4% air voids, the middle of 3-5% ($B_3$). $$ \text{OBC} = \frac{B_1 + B_2 + B_3}{3} $$ The mix is then checked against the criteria (for 75 blows: stability not less than about 8 kN; flow 2-4 mm; air voids 3-5%; VFB 65-75%; VMA as per the nominal aggregate size). If any criterion is not satisfied, the mix is redesigned (by changing the grading or the binder). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are Marshall trial mixes prepared? A. One binder content, one specimen B. At least five binder contents in 0.5% increments, three specimens each C. Ten binder contents in 5% steps D. Only at the expected optimum Answer: B. Specimens are made at several binder contents with 3 specimens each so graphs can be plotted. (Key point: Specimen preparation) 2. What compaction is applied for heavy traffic in the Marshall method? A. 50 blows on one face B. 75 blows on each face with a 4.5 kg hammer from 457 mm C. 25 blows on each face D. 100 blows on one face Answer: B. 75 blows on each face are used for heavy traffic; 50 for medium. (Key point: Compaction) 3. What are Marshall stability and flow? A. Max load in kN and deformation at max load in mm, after 60 degrees C water bath B. Min load and total length C. Density and air voids D. Penetration and softening point Answer: A. Specimens are conditioned at 60 degrees C and loaded at 50 mm/min; the maximum load is stability and the deformation is flow. (Key point: Stability and flow) 4. How is the optimum binder content (OBC) determined? A. The binder content at maximum flow only B. The average of the binder contents at maximum stability, maximum bulk density and 4% air voids C. The lowest binder content tested D. The binder content at 10% air voids Answer: B. OBC = (B1 + B2 + B3)/3 from these three, and the mix is then checked against the criteria. (Key point: Optimum binder content) ## Related in Transportation Engineering I - [Optimum binder content graphs](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Aoptimum-binder-content) — Transportation Engineering I, chapter 6 - [Marshall stability test procedure](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Amarshall-stability-test) — Transportation Engineering I, chapter 6, asked 3× - [Percentage air void in bituminous mix](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3An-80c-air-void) — Transportation Engineering I, chapter 6 ## Related in other subjects - [DoE mix design for fck 35 MPa (numerical)](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adoe-mix-design-fck35-numerical) — Concrete Technology and Masonry Structure, chapter 3 - [DOE method of mix design steps](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adoe-mix-design-steps) — Concrete Technology and Masonry Structure, chapter 3, asked 8× - [ACI method of mix design steps](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aaci-mix-design-steps) — Concrete Technology and Masonry Structure, chapter 3, asked 9× - [Nominal mix and design mix](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Anominal-vs-design-mix) — Concrete Technology and Masonry Structure, chapter 3, asked 4×