Cellulose fiber as bacteria-carrier in mortar: Self-healing quantification using UPV

Abstract

Crack formation due to shrinkage or tensile forces is a major weakness of cementitious materials. To overcome this problem, in this study a self-healing mortar is produced using mineral producing alkaliphilic bacteria. Authors have used bacilius subtilis strain 168 type of bacteria to improve the ability of cementitious mortar to heal any formed cracks without any external intervention. Bacteria-based self-healing concrete/mortar needs bacteria-carriers to protect bacteria in a dense matrix to maintain the mineral-forming capacity of bacteria. However, the currently used bacteria-carriers are not always suitable for concrete because of their complex procedures or high cost. To develop a more suitable bacteria-carrier, in this paper feasibility of alkali treated micro cellulose fiber as a novel bacteria-carrier for self-healing mortar is investigated. Two types of bacterial mortar by using cellulose fiber as a bacteria-carrier were prepared. For one type, nutrients were added inside the mortar mix, while for the other, nutrients were added into the curing water. The crack healing efficiency of bacterial mortars was investigated using image analysis and ultrasonic pulse velocity (UPV) test and compared with unreinforced and control cellulose fiber mortars. Research shows that self-healing mortar using cellulose fiber as a bacteria-carrier result in maximum self-healing as compared to other mixes, 8.23% more than control samples, pre-cracked at 28 days with damaged degree between 0.1 to 0.2. At the dosage investigated, addition of cellulose fiber resulted in a decrease in compressive strength. It was observed that cellulose fiber increase the availability of bacteria in cracked region by acting as a bridge across the crack. Furthermore, cellulose fibers have a low cost and simplest method of immobilizing bacteria when compared with other bacteria carriers.