Using Phenol Formaldehyde Resin, Hexamethylenetetramine and Matrix Asphalt to Synthesize Hard-Grade Asphalts for High-Modulus Asphalt Concrete

Abstract

Traditional hard-grade asphalts for high-modulus asphalt concrete (HMAC) are produced by using natural hard-grade asphalt to modify matrix asphalts. However, natural hard-grade asphalts are scarce and expensive. To find a sustainable alternative, this study presented a method to synthesize hard-grade asphalts using phenol formaldehyde resin (PFR), hexamethylenetetramine (HMTA) and matrix asphalts. Infrared radiation (IR) spectra analysis and fraction analysis for the modifiers and synthesize asphalts show that asphalt molecules can be cross-linked into larger polymeric groups by the thermosetting phenol formaldehyde resin (TPFR) which is the reaction product of PFR and HMTA. This process increased the asphaltene and resin fraction in asphalt, thus transforming a matrix asphalt into hard grade. With the dosing combinations of 4% PFR/15~20% HMTA, 6% PFR/8~10% HMTA and 8% PFR/5~5.7% HMTA, dynamic modules of HMAC were 14,000~16,000 MPa, which satisfied the basic application requirements for HMAC. The rutting resistance of the new hard-grade asphalts with the above dosage combinations completely exceeds the traditional product using the Trinidad Lake asphalt as the raw material. Increasing the amount of PFR/HMTA can further improve the rutting resistance. However, to ensure the fatigue and cracking resistance of the HMAC can get a level like the traditional product, the dosages of HMTA should be controlled below 15%.