Bacterium amended 100% fly ash geopolymer

Abstract

The production of cement results in the release of a significant amount of solid waste materials and gaseous emissions. Actually this industrial sector is thought to represent 5-7% of the total CO2 anthropogenic emissions. In addition to the generation of CO2, the cement manufacturing process produces millions of tons of the waste product cement kiln dust each year contributing to respiratory and pollution health risks. All significant environmental impacts in their life cycle can be addressed by evaluating the Life cycle assessment (LCA) of the processes or products on the environment. It have been estimated the green house gas emissions from Portland cement concrete pavement construction where they have shown that the main greenhouse gas is CO2, which accounts for more than 98% of the total emissions in the process. Fly ash is a coal combustion by-product that leads to many environmental problems like ground water contamination, spills, heavy metal contamination etc. The release of considerable amount CO2 by cement industries and large quantity of fly ash by thermal power plants are both undesirable for environment. A geopolymer material was developed by incorporating genetically-transformed Bacillus subtilis bacterium to an alkali-activator-treated 100% Fly ash to minimize environmental pollution. The use of bacteria in concrete is associated with mineral precipitation (Calcium carbonate and Gehlenite) that helps to fill micro pores and cracks thus reducing its permeability and increasing its strength and durability. The self-bioremediation in bacterial amended geopolymer material is one of the most interesting avenues relating to damage management and self-life of constructions, which needs to be cogitated. The self-bioremediation of bacterial amended thermostable geopolymer material has been explored in this work. The main challenge of this study is to development of ambient temperature curing geopolymer mortar with the addition of transformed Bacillus subtilis bacterial cells and spores followed by self-healing. Artificial cracks were generated within the mortar samples by applying partial breaking load (50 %) and the samples were cured for different days. Image analysis by Crackscope and microstructure analysis by field emission scanning electron microscope ascertained the formation of irregular crystalline healing material within the cracks of the test samples. Increase of ultrasonic pulse velocity and compressive strength, augmentation of sulphate resistance, decrease of chloride permeability and water absorption capacity revealed that there were overall improvement of mechanical properties and durability of the bacteria-incorporated mortar samples compared to the control (without bacteria incorporation) mortar samples. This cost effective and eco-friendly self-bioremediation phenomenon observed in geopolymer mortar is evolved due to the biosilicification activity of bioremediase protein which is being formed by the transformed bacteria. The exceptional potential of the microbial bioremediase protein for self -bioremediation attribute may add a new dimension in self-healing construction technology in near future.