Microcapsule encapsulated with leuco dye as a visual sensor for concrete damage indication via color variation.

Yao Li,Qing Wang,Yunfeng Li,Jinjin Luan,Xu Zheng

doi:10.1039/c9ra09492j

Abstract

A microcapsule-type visualization sensor for concrete structural damage indication is proposed in this article. Crystal violet lactone, as damage indicator, was microencapsulated within poly(methyl methacrylate) to synthesize the sensor. The successful encapsulation was confirmed by Fourier transform infrared spectrometry. Microcapsules of different diameters and size distributions were obtained by varied stirring speeds. The fabricated microcapsules were embedded into a polymer coating to accomplish the damage indication. When cracks propagated in the coating, the crystal violet lactone in leuco form was released from the ruptured microcapsules. Due to reacting with silicon dioxide in concrete, the released crystal violet lactone turned blue and highlighted the damaged area. It was verified that the visualization performance of the sensor showed good durability in both dry and wet conditions. The proposed microcapsule-type visualization sensor has advantages of easy fabrication, high indication stability, and no special equipment requirements, which will reduce the complexity of concrete structural health monitoring significantly.

Highlights

IntroductionEspecially concrete, are susceptible to forming micro-cracks, which eventually lead to structure failure.[1]
All cementitious materials, especially concrete, are susceptible to forming micro-cracks, which eventually lead to structure failure.[1]
The lactone ring of crystal violet lactone (CVL) can be opened by weak acid or proton donor,[28,29] trace amounts of CVL with already opened lactone ring generates

Summary

Introduction

Especially concrete, are susceptible to forming micro-cracks, which eventually lead to structure failure.[1]. Structural health monitoring (SHM) technologies to monitor damage are applied extensively throughout civil engineering.[2,3] Since micro-cracks are hardly visible to the naked eye, specialized instruments such as optic ber sensors,[4,5] piezoelectric sensors[6,7,8,9] and data processing equipment are required for traditional SHM technology. A series of visual damage strategies based on visualization materials had been developed for damage indication.[10,11,12,13,14] Dye- lled hollow glass ber[15,16,17] was used to indicate mechanic damages for polymers, but it cannot be applied to the surfaces of complex structures because of its slender shape. Because uorescence cannot be captured by the naked eye in daylight, speci c wavelengths of light were required for uorescence observation

Methods

Results

Conclusion