ASTM D6703 Automated Heithaus Titrimetry

Scope:

This test technique aims to determine the colloidal stability of bituminous asphalt and heavy oil residuum in the laboratory. ASTM D6703 and the original Heithaus test determine a colloidal system’s overall compatibility by calculating a parameter called the state of peptization, P.

Procedure:

In ASTM D6703 three reaction vials with a capacity of 40 mL are tared. Each of the three reaction vials received three samples of asphalt weighing 0.400 g, 0.600 g, and 0.800 g. 3.000 mL toluene is added to dissolve asphalt in each reaction vial, yielding three solutions with different concentrations. To encourage the commencement of flocculation, each solution is titrated with isooctane (2,2,4-trimethyl pentane). Titrations are carried out by inserting reaction vials in the device individually. To enable temperature control of the system, each reaction vial is put individually inside a 250 mL water-jacketed reaction vessel. The output signal from the spectrophotometer is collected using a data acquisition system (computer) during titration and a graph is plotted showing the change in percent transmittance (%T) of detected radiation at 740 nm flowing through the quartz cell versus time, t.

Specimen size:

For ASTM D6703, specimen asphalt of weights 0.400 g, 0.600 g, and 0.800 g are used in three reaction vials.

Data:

The flocculation ratio (FR) and the dilution ratio concentration (C) for each of the three samples are calculated as:

FR= V_S/V_S+V_T

C = W_a/ (V_S + V_T)

Where:

W_a = weights of each asphalt sample

V_S = volume of toluene initially used to dissolve each sample

V_T = volume of titrant at onset of flocculation

Conclusion:

ASTM D6703 explains how to calculate three Heithaus compatibility parameters, which measure the colloidal stability of asphalts, asphalt cross blends, and aged asphalt.