Polymer-modified asphalts: effects of varied benzoxazine functionalities on polymer-modified asphalt properties

Abstract

This research aims to study effects of benzoxazine functionalities on properties of asphalts modified bybenzoxazine resin. It could be seen that different functionalities of benzoxazine resin coulddevelop chemical, thermal and mechanical properties of asphalt. Polybenzoxazine, phenolic resin based polymer, processes some prominent properties such as easy synthesis, no by-products released upon curing process, low viscosity, low water absorption, and good mechanical properties as well as high thermal stability. Base asphalt (AC 60/70 penetration grade) was mixed with varied benzoxazine functionalities at various concentrations, i.e., 0, 3, 6 and 9 % by weight to prepare benzoxazine resins modified asphalt. The suitable mixing condition was obtained by mechanical mixing at 80 oC for 1 hr at mixing speed of 500 rpm and then immediately cured at 190 oC for 1 hr. Softening point and viscosity of benzoxazine resins modified asphalt increased whereas penetration depth decreased with increasing benzoxazine resins contents. In addition, the ductility, toughness, and tenacity significant were higher than unmodified asphalt. That could contribute to the improvement of aggregate retention and low temperature susceptibility. Thus, 6% by weight of benzoxazine resins used rendered the highest values. In addition, the rutting parameter (G*/sin δ) increased from 1.3 kPa of neat asphalt to 2.6 kPa, representing resistance to permanent deformation. In consideration of the dispersity of two components in a mixture, chemical interaction, thermal and mechanical properties when the number of functional benzoxazine resins increased, morphology of benzoxazine resins modified asphalt showed that small particles of benzoxazine fraction dispersed in asphalt. From the results of FT-IR spectra, the regeneration of main bands of benzoxazine resins modified asphalt were identified and the significant variation was the peak intensity, which represents the chemical bonding between benzoxazine and asphalt matrix. Furthermore, the degradation temperature at 5 % weight loss of benzoxazine resins modified asphalt increased from 362oC of neat asphalt to 396 oC with increasing functionality of benzoxazine resin. Also, the storage modulus increased and the glass transition temperature (Tg) of benzoxazine resins modified asphalt increased from -14.3 of neat asphalt to 4.7oC when functionality of benzoxazine resin increased. The results could indicate that the benzoxazine resins were able to reduce rutting, cracking bleeding, and enhance the ductility as well as toughness and tenacity of asphalt mixtures, which was possible to promote the adhesion between modified asphalt and aggregate.