Design and construction of microcapsules containing rejuvenator for asphalt

Microcapsules containing rejuvenator are a promising chemical powder product applied in asphalt concrete to prolong its service life. However, the size, thermal stability and mechanical properties of microcapsules are strictly demanded to suit the natural instincts and the actual application conditions of asphalt. The objective of this work was to fabricate and characterize the physicochemical properties of novel microcapsules containing rejuvenator by an in-situ polymerization method using methanol–melamine–formaldehyde (MMF) prepolymer as shell material. It was found that the average size of microcapsules could be successfully controlled in the range of 23.5 to 5.0 μm with increasing stirring rates from 1000 to 6000 r·min− 1. The average size was mainly determined by the core material dispersion rates in an oil-in-water emulsion. Shell thickness and shell density were increased by adding more MMF prepolymer in the fabrication process. Thermal stability results indicated that the decomposition temperatures of microcapsule samples (core/shell ratios of 2/1, 1/1, 1/2 and 1/3) were higher than the melting temperature of asphalt (180 °C). Lower prepolymer dropping rate is responsible for the better homogeneity of the sample which results in achieving a correct thermal decomposition as the investigation in this case shows an improvement of the stability. The hardness and Youngʹs modulus results measured by nanoindentation indicated that the MMF-shell microcapsules had an elastic–plastic deformation. The size and shell thickness were two main influencing factors of micromechanical properties of the microcapsules containing rejuvenator.