**Lecture notes in Transportation Systems Engineering**

**March 19, 2012**

The Marshall stability and flow test provides the performance prediction measure for the Marshall mix design method. The stability portion of the test measures the maximum load supported by the test specimen at a loading rate of 50.8 mm/minute. Load is applied to the specimen till failure, and the maximum load is designated as stability. During the loading, an attached dial gauge measures the specimen's plastic flow (deformation) due to the loading. The flow value is recorded in 0.25 mm (0.01 inch) increments at the same time when the maximum load is recorded. The important steps involved in marshal mix design are summarized next.

Volume of | Thickness | Correction |

specimen | of specimen | Factor |

(cm) | (mm) | |

457 - 470 | 57.1 | 1.19 |

471 - 482 | 68.7 | 1.14 |

483 - 495 | 60.3 | 1.09 |

496 - 508 | 61.9 | 1.04 |

509 - 522 | 63.5 | 1.00 |

523 - 535 | 65.1 | 0.96 |

536 - 546 | 66.7 | 0.93 |

547 - 559 | 68.3 | 0.89 |

560 - 573 | 69.9 | 0.86 |

- Binder content versus corrected Marshall stability
- Binder content versus Marshall flow
- Binder content versus percentage of void () in the total mix
- Binder content versus voids filled with bitumen ()
- Binder content versus unit weight or bulk specific gravity ()

- Binder content corresponding to maximum stability
- Binder content corresponding to maximum bulk specific gravity ()
- Binder content corresponding to the median of designed limits of percent air voids () in the total mix (i.e. 4%)

The stability value, flow value, and are checked with Marshall mix design specification chart given in Table below. Mixes with very high stability value and low flow value are not desirable as the pavements constructed with such mixes are likely to develop cracks due to heavy moving loads.

Test Property | Specified Value |

Marshall stability, kg | 340 (minimum) |

Flow value, 0.25 mm units | 8 - 17 |

Percent air voids in the mix % | 3 - 5 |

Voids filled with bitumen % | 75 - 85 |

The specific gravities and weight proportions for aggregate and bitumen are as under for the preparation of Marshall mix design. The volume and weight of one Marshall specimen was found to be 475 cc and 1100 gm. Assuming absorption of bitumen in aggregate is zero, find , , and ;

Item | A_1 | A_2 | A_3 | A_4 | B |

Wt (gm) | 825 | 1200 | 325 | 150 | 100 |

Sp. Gr | 2.63 | 2.51 | 2.46 | 2.43 | 1.05 |

Bitumen | Stability | Flow | |||

content | (kg) | (units) | (%) | (%) | |

3 | 499.4 | 9.0 | 12.5 | 34 | 2.17 |

4 | 717.3 | 9.6 | 7.2 | 65 | 2.21 |

5 | 812.7 | 12.0 | 3.9 | 84 | 2.26 |

6 | 767.3 | 14.8 | 2.4 | 91 | 2.23 |

7 | 662.8 | 19.5 | 1.9 | 93 | 2.18 |

- Max stability = 5 percent bitumen content.
- Max = 5 percent bitumen content.
- 4% percent air void = 3 percent bitumen content.

- In Marshall stability test, the sample is compacted using a rammer giving
- 50 blows
- 20 blows
- 25 blows
- 75 blows

- The Marshall flow value is expressed in units of
- 25 mm
- 2.5mm
- 5mm
- 3mm

- In Marshall stability test, the sample is compacted using a rammer giving
- 50 blows
- 20 blows
- 25 blows
- 75 blows

- The Marshall flow value is expressed in units of
- 25 mm
- 2.5mm
- 5mm
- 3mm

Prof. Tom V. Mathew 2012-03-19