Investıgatıon of Performance Propertıes of Cement-Bınder Systems Wıth Mıcrobıal Self-Healıng Abılıty

Abstract

Microbials incorporated cement-binder system is a kind of self-healing cementitious material that contains micro-organisms which induce a precipitation of calcium carbonate in cracks. Ureolytic pure cultures have been used in the majority of research conducted for microbials incorporated cement-binder system development. Biogranules made up of nitrate-reducing bacteria have lately become more sustainable, cheaper, and feasible. Since in the self-healing studies of microbial introduced cement binding systems the bacteria content was selected randomly, it is still unknown the most acceptable content of bacteria for self-healing in these systems. In this thesis study, the biogranules , which had 0.45 to 2.00 mm of size and have an active nitrate-reducing core surrounded by a protective outside layer consisting of CaCO3 and Ca3(PO4)2, were produced in the laboratory and, acceptable biogranules content for self-healing cement-binder systems was investigated. During the assessment of the acceptable content of biogranules, cement-binder systems with various doses of biogranules were analyzed with regards to their workability, compressive strength, self-healing rate, and self-healing. Mortar specimens with 12 different doses of biogranules corresponding to the contents of bacteria ranging from 0.05% to 2.50% w/w cement were poured and cracks were obtained at the end of a 28-day curing period. The cracked specimens were held in tap water over 4 weeks and weekly percentages of crack closure have been monitored to investigate the acceptable and minimum levels of bacteria for microbial cement binding systems by using macroscope. The addition of bacteria into the mortar in the form of biogranules up to 2,50% w/w cement has no adverse effect on the properties of the mortar. The acceptable and lowest bacteria content in microbial self-healing concrete should be 0.25% and 0.05% w/w cement, respectively, based on microbial self-healing rates and capacities when added in the form of biogranules. Cracks as wide as 800 ± 30 µm could be healed in acceptable doses after 3 weeks, but this healing performance decreased with an increase or decrease in the bacteria content. Microbial healing performed consistently better than autogenous healing independent of bacteria content.