Feasibility and Compatibility of a Biomass Capsule System in Self-Healing Concrete.

Arkabrata Sinha,Jianqiang Wei,Qi Wang

doi:10.3390/ma14040958

Abstract

Cracking can facilitate deteriorations of concrete structures via various mechanisms by providing ingress pathways for moisture and aggressive chemicals. In contrast to conventional maintenance methods, self-healing is a promising strategy for achieving automatic crack repair without human intervention. However, in capsule-based self-healing concrete, the dilemma between capsules’ survivability and crack healing efficiency is still an unfathomed challenge. In this study, the feasibility of a novel property-switchable capsule system based on a sustainable biomass component, polylactic acid, is investigated. Capsules with different geometries and dimensions were studied focusing on the compatibility with concrete, including survivability during concrete mixing, influence on mortar and concrete properties, and property evolution of the capsules. The results indicate that the developed elliptical capsules can survive regular concrete mixing with a survival ratio of 95%. In concrete containing 5 vol.% of gravel-level capsules, the compressive strength was decreased by 13.5% after 90 days, while the tensile strength was increased by 4.8%. The incorporation of 2 vol.% of sand-level capsules did not impact the mortar strength. Degradation and switchable properties triggered by the alkaline matrix of cement were observed, revealing the potential of this novel biomass capsule system in achieving both high survivability and self-healing efficiency in concrete.

Highlights

The high brittleness and low ductility make concrete susceptible to cracking in the presence of mechanical loadings or environmental attacks
Different self-healing approaches have been investigated in concrete materials, including; (i) autogenous healing based on filling of cracks by hydration of unhydrated cement particles [15,16] or carbonation of the hydration products in the presence of external moisture and carbon dioxide [15,17]; (ii) autonomous healing, which is primarily achieved by incorporating engineered healing agents such as supplementary cementitious materials [18], mineral admixtures [19], polymer agents or water glass [20]; and (iii) microbial healing achieved by direct incorporation of bacteria spores or encapsulation of bio-agents into concrete that can implement the conversion of hydrolysis of urea or calcium compound (Ca-lactate) [21,22,23,24,25]
The survivability of capsules during concrete mixing is characterized by determining the resistance of the capsules to breakage during regular concrete mixing

Summary

Introduction

The high brittleness and low ductility make concrete susceptible to cracking in the presence of mechanical loadings or environmental attacks. In a recent investigation by Xue et al [30], crystalline admixture coupled with magnesium oxide expansive agent was employed for crack-healing via carbonation precipitation by conditioning concrete samples in a chloride-rich environment. Another study conducted by Yoo et al showed the potential for self-healing in ultra-high performance concrete reinforced with steel microfibers via calcite precipitation in the cracks [31]. It is worth noting that, significant efforts have been made on concrete self-healing, capsule-based self-healing is still the most effective and economical way to achieve robust crack repair. This is especially the case for concrete structures subjected to extreme mechanical and environmental conditions

Methods

Results

Conclusion