(Purdue University 2003 for South Dakota DOT)
Abstract
This report summarizes the results of an extensive and comprehensive study to evaluate the possibility of contaminating a hot mix asphalt due to the use of alternate fuel types and through poor combustion of the fuel. Eleven different fuels were used, and the plant burner was adjusted to optimum, insufficient oxygen and excess oxygen conditions. Samples of aggregates and of hot mix produced under these combinations of fuel and combustion conditions were collected and tested using a variety of chemical and physical tests. Gravimetric analysis of the heated aggregates did reveal the presence of minute traces of residue at less than 35 ppb by weight of aggregate. This residue was then analyzed using gas chromatography and FTIR, and was shown to be composed of partially decomposed tars and fuel residues. The dynamic shear rheometer, bending beam rheometer and direct tension tests were used to assess whether the residue caused any changes in binder properties; none were detected. Samples of the hot mix produced in the plant were evaluated using gyratory compaction parameters, Superpave shear tests, dynamic modulus, loaded wheel and moisture sensitivity tests. Again, no significant changes in mix properties were observed. Based on these findings, it was recommended that SDDOT expand the list of allowable fuels to include recycled fuel oils and fuels up to No. 6, allowing the use of economical alternates. No. 6 fuel should be evaluated in pilot field projects for possible inclusion in future specifications. Other specification changes and inspection techniques to ensure combustion adequacy and mix performance were recommended.
