Effect of self-healing on strength and durability of zeolite-immobilized bacterial cementitious mortar composites Sini Bhaskar a , Khandaker M. Anwar Hossain a, * , Mohamed Lachemi a , Gideon Wolfaardt b , Marthinus Otini Kroukamp b a Department of Civil Engineering, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada b Department of Chemistry & Biology, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada article info Article history: Received 22 October 2016 Received in revised form 16 April 2017 Accepted 23 May 2017 Available online 26 May 2017 Keywords: Bacteria Carrier Crack healing Compressive strength Permeability Self-healing Cementitious mortar composites abstract There is a compelling economic incentive to develop concrete materials that can repair its own damage, increase durability and prevent structural failure. This research investigated the potential of adding two different mineral producing bacteria into two types of cementitious mortar matrix to enhance self- healing ability for autonomous crack repair. In this study, zeolite was used as a carrier material to protect bacteria in high pH environment normally exists in concrete. The spore forming ability and ureolytic activity of zeolite-immobilized bacteria were investigated in order to examine potential for producing healing compounds. The self-healing ability of bacteria incorporated normal and fiber rein- forced mortars was judged based on the development of compressive strength and permeation prop- erties of cracked specimens with age as well as micro-structural characterization of crack healing compounds using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is the most commonly used construction material worldwide. However, concrete structures suffer from cracking that leads to deterioration and shorter service life. Cracks can occur at any stage of a structure's service life due to volume instabilities within concrete or external factors affected by extreme loading, harsh environmental exposure, poor construction procedures, design errors, etc. Micro-cracks permit the penetration of water and other impurities such as chloride and sulphate ions into the concrete matrix, leading to premature matrix degradation, corro- sion of embedded reinforcement and other deterioration, which hinder structural integrity. Huge expenses are incurred maintain- ing and repairing concrete structures; the estimated damage due to corrosion in the US alone is $276 billion [1], with annual repair costs at $18e21 billion [2]. Moreover, indirect costs due to traffic jams and loss of productivity due to repairs are 10 times higher than the direct costs of maintenance and repair [3]. It is therefore imperative that crack propagation in concrete be minimized to extend longevity and reduce maintenance; developing a concrete that can treat and repair the damage on its own is a worthwhile goal. Animals and plants have a natural capability to heal minor damage on their bodies in a relatively short time, without external influence. Similarly, the natural self-healing ability of concrete e also known as autogenous healing e has been observed for many years [4e6]. Micro-cracks in old structures self-heal through the recrystallization of calcite [7]; in the right environment, with augmentation of chemical and/or biological additives and in the presence of moisture, concrete is able to seal its own cracks. In general, carbon dioxide in the air is dissolved in water, reacting with calcium ions in the concrete to produce calcium carbonate crystals that attach and grow on the crack surface. This growth leads to reduced crack width and eventual repair of the whole crack [7,8]. However, with this natural process alone, only limited cracks with widths up to 100 mm can be repaired [4,5]. To repair larger cracks and ensure better healing consistency, chemical and bio- logical amendments may be needed. Previous studies by various researchers have concluded that self-healing behavior can be ach- ieved by introducing bacteria into the concrete matrix [9,10]. Once moisture enters through freshly formed cracks, dormant but viable bacterial spores become metabolically active. Cracks are then * Corresponding author. E-mail address: ahossain@ryerson.ca (K.M. Anwar Hossain). Contents lists available at ScienceDirect Cement and Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp http://dx.doi.org/10.1016/j.cemconcomp.2017.05.013 0958-9465/© 2017 Elsevier Ltd. All rights reserved. Cement and Concrete Composites 82 (2017) 23e33