Abstract
Recently, cost-efficient nitrate reducing biogranules were suggested as an alternative to axenic microbial cultures for development of microbial self-healing concrete. In a marine environment, biogranule containing microbial self-healing concrete showed simultaneous self-healing of cracks and immunisation against rebar corrosion. Yet, information about the production strategy of these biogranules and their compatibility with a mortar matrix is limited. This study presents the production of biogranules and their compatibility with mortar specimens when incorporated at dosages between 0.36% to 4.30% w/w cement (0.25% to 3% of bacteria w/w cement). In-house produced biogranules composed of 70% bacteria and 30% of minerals w/w of biogranule were used for the compatibility tests. In test mortars, calcium formate (CF) and calcium nitrate (CN) were used as regular nutrient admixtures, and nutrient content was set identical in every batch. Up to 2.9% incorporation, biogranules had no significant influence on the fresh properties of mortar. More than 2.9% incorporation caused poor workability and a 26% decrease in 3-Day compressive strength of biomortar specimens. Overall, the biogranules produced are compatible with a cementitious matrix up to 2.9% w/w cement, and even up to 3.6% if early age strength is not essential, which makes biogranules one of the most compatible microbial healing agents among the suggested agents in the literature.
Highlights
The formation of microcracks is a prevalent issue in reinforced concrete structures, which requires continuous and delicate monitoring for detection, and labour intensive maintenance
Biogranules with an activated compact denitrifying core (ACDC) can be produced from old dry ACDC granules and the properties of produced fresh granules are similar to the old ones
A CaCO3-Ca3(PO4)2 coating surrounding the ACDC biogranules minimizes the interaction between the mortar matrix and the core bacteria, and contributes to the biogranules’ compatibility with mortar
Summary
The formation of microcracks is a prevalent issue in reinforced concrete structures, which requires continuous and delicate monitoring for detection, and labour intensive maintenance. Significant effort was put on development of selfsensing and self-healing concrete in order to minimize external maintenance practices. Exploiting microbes and microbial induced calcium carbonate precipitation (MICP) can be mentioned among the popular self-healing concrete development strategies. Various microbes have already been tested for the proof of the principle and several useful strains were identified for the development of microbial self-healing concrete (Table 1). The field requires optimization and improvement of the developed microbial self-healing concrete to enable cost-efficient upscaling of the technology. Economic feasibility, practicality of the proposed self-healing strategy and the delicacy of the microbial healing agent should be evaluated carefully. The constraints for the dosages of typical components of microbial self-healing concrete (nutrients, protective carriers and microbial healing agents) should be determined
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