ASTM D6927-22

4.1.1?Marshall stability and flow are asphalt mixture characteristics determined from tests of compacted specimens of a specified geometry. The Marshall Test can be conducted with two different types of equipment: (1) Method Ausing a loading frame with a load ring and a dial gauge for deformation or flow meter (Traditional Method); or (2) Method Busing a load-deformation recorder in conjunction with a load cell and linear variable differential transducer (LVDT) or other automatic recording device (Automated Method).

4.1.2?Typically, Marshall stability is the peak resistance load obtained during a constant rate of deformation loading sequence. However, depending on the composition and behavior of the mixture, a less defined type of failure has been observed, as illustrated in Fig. 1. As an alternative method, Marshall stability can also be defined as the load obtained when the rate of loading increase begins to decrease such that the curve starts to become horizontal, as shown in the bottom graph of Fig. 1. The magnitude of Marshall stability varies with aggregate type and grading and bitumen type, grade, and amount. Various agencies have criteria for Marshall stability.

4.1.3?Marshall flow is a measure of deformation (elastic plus plastic) of the asphalt mixture determined during the stability test. In both types of failure, the Marshall flow is the total sample deformation from the point where the projected tangent of the linear part of the curve intersects the 4.1.4?The Marshall stability and flow test results are applicable to dense-graded asphalt mixtures with maximum size aggregate up to 1 in. (25 mm) in size. For the purpose of mix design, Marshall stability and flow test results should consist of the average of a minimum of three specimens at each increment of binder content where the binder content varies in one half percent increments over a range of binder content. The binder content range is generally selected on the basis of experience and historical testing data of the component materials, but may involve trial and error to include the desirable range of mix properties. Dense-graded mixtures will generally show a peak in stability within the range of binder contents tested. Stability, flow, density, air voids, and voids filled with asphalt binder may be plotted against binder content to allow selection of an optimum binder content for the mixture. The above test properties may also be weighted differently to reflect a particular mix design philosophy. In addition, a mixture design may be required to meet minimum voids in the mineral aggregate based on nominal maximum aggregate size in the mixture.

4.1.5?Field laboratory Marshall stability and flow tests on specimens made with plant mix laboratory compacted (PMLC) asphalt mixture mix may vary significantly from laboratory design values because of differences in plant mixing versus laboratory mixing. This includes mixing efficiency and aging.

4.1.6?Significant differences in Marshall stability and flow from one set of tests to another or from an average value of several sets of data or specimens prepared from plant-produced mix may indicate poor sampling, incorrect testing technique, change of grading, change of binder content, or a malfunction in the plant process. The source of the variation should be resolved and the problem corrected.

4.1.7?Specimens will most often be prepared using Practice D6926, but may be prepared using other types of compaction procedures as long as specimens satisfy geometry requirements. Other types of compaction may cause specimens to have different stress strain characteristics than specimens prepared by Marshall impact compaction. Marshall stability and flow may also be determined using field cores from Note 1:?The quality of the results produced by this standard are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of Specification D3666 are generally considered capable of competent and objective testing, sampling, inspection, etc. Users of this standard are cautioned that compliance with Specification D3666 alone does not completely ensure reliable results. Reliable results depend on many factors; following the suggestions of Specification D3666 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.