Marshall mix design

Marshall method mix criteria Surface and other layers  

Voids in mineral aggregate Nominal maximum Minimum VMA (%),for design air  

Source Asphalt Institute MS-2, Mix design methods - For Asphalt concrete and other hot-mix types. Manual Series 2 (MS-2), 6th Edition, Lexington, USA Asphalt Institute. With permission. 

Although the Marshall mix design (Asphalt Institute MS-2) is relatively old, it is currently used by several agencies/organisations because it uses simpler and cheaper laboratory equipment. However, many engineers believe that the way specimens are compacted does not simulate compaction on site. Additionally, the Marshall stability and flow do not adequately assess the asphalt shear strength. These two parameters do not ensure the asphalt resistance in permanent deformation (resistance to rutting). 

The Marshall mix design is used to determine the optimum bitumen content of dense-graded AC with 25.4 mm maximum nominal aggregate size. This method is specified by Asphalt Institute (MS-2), by ASTM D 6926-04 (2010) and by ASTM D 6927-06 (2006) or AASHTO T 245 (2013). 

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According to the Superpave methodology (AASHTO M 323 2013 Asphalt Institute SP-2 2001), which sooner or later will completely replace Marshall mix design, the AC is currently designed with volumetric criteria, once the materials (bitumen and aggregates) have been chosen. 

Modified Marshall mix design for mixtures with maximum nominal aggregate size >25 mm... 

Dense-graded ACs with a maximum nominal aggregate size >25 mm (usually for base layers) cannot be designed with the standard Marshall mix design outlined above. 

The determination of the optimum binder content is achieved with the modified Marshall mix design procedure. 

The procedure is the same as the standard Marshall mix design procedure described above, except for the following differences attributed to mixes composed of large aggregates, that is, >25 mm. 

Regarding the composition of ACs, the European standard for AC mixtures, CEN EN 13108-1 (2008), realising the weakness of the Marshall mix design, has broadened the... 

Figure 6.1 Typical diagrams derived from modified Marshall mix design for dense-graded cold mixtures, (a) Soaked stability vs. bitumen content, (b) Retained stability vs. bitumen content, (c) Total voids vs. bitumen content, (d) Absorbed water vs. bitumen content, (e) Bitumen film thickness vs. bitumen content, (f) Dry bulk density vs. bitumen content.

ANNEX 6.B MODIFIED MARSHALL MIX DESIGN FOR DENSE-GRADED COLD ASPHALT (DGCA)... 

Table 6.6.2 Laboratory form to be used in modified Marshall mix design for cold dense-graded bituminous mixtures... 

Asphalt Institute recommended cold mix method Resistance to plastic flow of bituminous mixtures using Marshall Apparatus Immersion—Marshall method Immersion—Marshall method Superpave mix design... 

The effect of sulfur and asphalt contents in SAS mixtures on Marshall Stability is shown in Figure 3 [15]. The stability values tend to increase with sulfur content but decrease with asphalt addition. It is interesting to note that without the sulfur and asphalt, sand mixes would have little or no stability. The data also indicate a wide variety of mix designs are possible whose stabilities are consistant with Asphalt Institute suggested values for conventional asphaltic mixes. 

The optimum or minimum allowable substitution ratio is then established by means of a series of justification tests at different binder contents. Figure 15 shows a comparison between the Marshall design properties of a conventional mixture using an asphalt binder and a 30 70 SEA binder. As indicated the optimum substitution ratio based on the maximum stability and equivalent air voids is about 1.7 1. Since minimizing the substitution ratio has a direct impact on the economic benefits to be realized by replacing the asphalt with sulfur these justification tests are to be recommended in all mix designs. 

Mix design is the choice of the best combination of aggregate, binder, and compaction effort to produce desirable pavement material properties. The choice has been made normally based on the results of simple indicator and control tests such as the Marshall stability, Marshall flow, Hveem stability, resilient modulus, and indirect tension tests. 

The fundamental difference between the Superpave and the Marshall methodology is the way specimens are compacted. In the Superpave mix design methodology, the specimens are compacted with the gyratory compactor (Table 5.8) (ASTM D 4013 2009) and the relative density... 

Table 5.13 Marshall hot mix design criteria for dense AC mixtures by FAA...

The composition of the bituminous mixture to be used (job mix) is determined using the Marshall hot mix design method, as described in the previous sections. However, the design criteria used by the FAA are slightly different. FAA s criteria for the Marshall hot mix design are given in Tables 5.13 and 5.14. 

The hot mixes are designed by using a standard laboratory compaction procedure to develop a composition reflecting estabUshed criteria for volume percent air voids, total volume percent voids between aggregate particles, flow and stabdity, or compressive strength. Tests such as the Marshall, Unconfined Compression, Hubbard-Field, Triaxial Procedure, or the Hveem stabdometer method are used (109). 

Karihaloo, B. L. (2000) Optimum design of high-performance steel fibre-reinforced concrete mixes, in Proc. Int. Symp. Brittle Matrix Composites 6, A. M. Brandt, V. C. Li and I. H. Marshall eds, Warsaw ZTurek and Woodhead Publishing pp. 3-16. 

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