Chemical Modification of Asphalts

In-House ReportProminent among the damages occurring to asphalt cement concrete pavements are cracking and rutting. The occurrence of such damage is dependent upon many factors including the properties of the asphalt, which are, in turn, dependent upon its molecular structure. Experiments to test this hypothesis have been performed; these experiments include the modification of asphalt cements by reacting them separately with maleic anhydride, chromium trioxide and furfural in the presence of hydrochloric acid. Six different asphalts were used in these exploratory reactions. The original and chemically modified asphalts were subjected to laboratory tests to obtain such comparative parameters as penetration-viscosity number, penetration index, limiting stiffness temperature, aging index, complex viscosity, storage modulus, loss modulus, complex modulus and tan delta. These data show that the chemically modified asphalts have potential for use in the highway pavements to help avoid cracking and rutting in such pavements. The adhesion to aggregate by the modified Wyoming pedestal test was performed. The chemical modification of asphalts improves the adhesive bond between asphalt and aggregate in an asphalt mixture implying an increased resistance to stripping. The presence of polar and polymerizing groups in the modified asphalts plays a major role in controlling the adhesion to aggregate. The infrared spectra (IR) and high pressure-gel permeation chromatography (HP- GPC) support this hypothesis

Changes Occurring in Asphalt in Drum Dryer and Batch (Pug Mill) Mixing Operations

Staff StudyThis is part of NCP Study No. 2E1A4082.The study was designed (1) to discover whether steam distillation of asphalt takes place in a drum dryer mixer, (2) to compare changes induced by various laboratory conditioning (aging) techniques versus those occurring in drum dryer mixers, and (3) to identify possible differences in asphalts subjected to drum dryer mixing versus batch (pug mill) mixing. Fifty-five virgin asphalts were subjected to various laboratory conditioning experiments including thin film oven exposure (TFO), rolling thin film oven exposure (RTFO), (small) steam distillation (SSD), forced air distillation (FAD), and rolling forced air distillation (RFAD). Various physical and chemical properties of these conditioned samples were measured. These properties were compared with those of the residues recovered from drum dryer operations for each asphalt. By comparing the laboratory conditioned residues to the recovered residues from the drum dryer operation, similarities of the variously exposed asphalts to asphalt recovered from drum dryer mixers were ascertained. This demonstrated that steam distillation does not take place in drum dryer mixers. Eight matched asphalt pairs, one used in a drum dryer mix and one in a batch (pug mill) mix, were identified among 24 virgin asphalts from Georgia by statistically comparing various physical, thermal, compositional, and molecular size properties of the virgin asphalts. Asphalts were then recovered from the mixes in which each of the eight drum dryer - batch (pug mill) asphalt pairs were used. The recovered asphalts were analysed, and the results show the asphalt residues extracted from drum dryer operations to be slightly harder than those extracted from batch operations

Nationally Coordinated Program of Highway Research, Development and Technology: Annual Progress Report, Executive Summary, Fiscal Year 1989

Nationally Coordinated Program of Highway Research, Development and Technology: Annual Progress Report, Executive Summary, Fiscal Year 198