A method is described for calculating molecular size distribution (msd) of asphalt cement using ultraviolet (uv) detection. A 5-microm, 500 angstrom phenogel column is used to fractionate a known amount of a whole asphalt sample. Tetrahydrofuran:pyridine (95:5) servesas mobile phase. After passing through the uv detector at 345 nm, the eluent is fractionated at arbitrarily selected intervals. The fractions are collected in weighed petri dishes and left to dry. A computer generates a slice report showing percent material eluting at successive retention times. The injection is repeated and eluting fractions collected in volumetric flasks. After removing the column, a known volume of a given fraction is injected and the maximum absorbance reading for each fraction is recorded. The second set of fractions is then poured into the petri dishes containing the fractions fromthe first injection. Then, the molar absorptivity "a" is calculated. Using astm method d4124-86(b), the percent saturates is determined. The saturates are injected, a differential refractive index detector is used to get an msd value, and a computer generates a slice report. The data generated for the whole asphalt sample are treated mathematically, first, to account for variation of "a" and, second, forundetectability of saturates by uv. For six samples, coparison of data readily available from the slice report with those obtained after treatment reveals differences of up to 65% for some fractions. Reproducibility of the system and of the proposed method proved satisfactory. Excluding the separation of saturates, the proposed method consumes 7 to 8 hr; in series less than 4 hr. This paper appears in transportation research record no. 1269, Asphalt mix materials and mixtures 1990.
Samenvatting