Experimental investigation of particle size effect on the self-healing performance of microcapsule for cemented coral sand

The Urea-Formaldehyde (UF) microcapsule with in situ polymerization was fabricated with controlled particles size distributions in order to improve the self-healing efficient of cemented coral sand. The particle size distributions of UF microcapsules were examined by correlating with various rotation speeds during synthesis process. Through the laser particle size analyzer, it shown that the particle sizes of UF/epoxy resin microcapsule ranges from 0 to 650 um under synthesized at 150-800 rad/min. Under a specific synthesized speed, the particle sizes of microcapsules were followed a normal distribution. Further analysis indicated that there is a linear relationship between the medium particle size of microcapsule and the rotation speed. Compression tests were carried out to investigate the effects of the particle sizes and volume fractions of microcapsules. It found that the optimization particle size distributions and volume fractions of microcapsules for cemented coral sand specimens are 450 rpm and 3% (i.e. microcapsule content with ratio of cement by mass), respectively. The compressive strength of the specimen was increased by approximately 85% with 3% of microcapsules. Based on the micro-analysis, the particle size distribution of the microcapsules at 450 rpm was match well with the pore distribution of the specimen. The microcapsules with particle size greater than 18 um were broken after compression. Finally, the piezoelectric sensor (PZT) is used to characterize the self-healing efficiency of the microcapsules. The results indicate that the self-healing efficiency of microcapsules synthesized at 450 rad/min with volume fraction of 3% was about 75%. The optical microscope investigation confirmed that the microcapsules can be triggered by the crack or compression of the specimen and react together with the contribution from the healing agent to self-heal the internal cracks. (C) 2020 Elsevier Ltd. All rights reserved.