Microbial Calcite Precipitation In Cementitious And Earth-based Building Materials:Ease,Economical And Fungal Aspects

Various infrastructures have been built in the development process of world during the last hundred years and there still remain tremendous infrastructure demands in emerging economies.As the most commonly used cementitious material,Portland cement occupies an important position in modern infrastructure and its consumption has grown at a very fast pace.However,more environment-friendly cementitious materials or technologies are increasingly desired due to the environmental concerns resulting from CO₂ emissions during cement production and the sustainability issues of cement.On the other hand,earth-based materials including rammed earth provide sustainable construction;however,suffer of strength and durability issues.Microbially induced calcite precipitation?MICP?has been proposed as a novel technique to address above concerns.MICP is a type of biomineralization process widespread in natural environment and it could be used for the improvement of building materials and structures.As MICP is mainly achieved with bioaugmentation,the ease to carry out this process in natural environment is of concern.Further,the cost of media used in the process makes MICP expensive,thus economization of the process is highly warranted.Also,most of MICP was achieved with ureolytic bacteria,while role of fungi is often ignored despite of several advantages associated with fungi.Considering these aspects including,ease?for application?,economization?to reduce the cost of process?,and fungal?as an alternative to bacterial-mediated calcite precipitation?,in this thesis,MICP process and its product?biocement?were expected to achieve a partial substitute of cement without compromising or even improving engineering properties of building materials.The main research results were as following four aspects:?1?Cement stabilized rammed earth?CSRE?has been enjoying a renaissance as sustainable construction material.At the same time,it is important to convert CSRE to be a stronger,durable and environment-friendly building material.MICP was associated with biostimulation to improve engineering properties of CSRE.Results showed that the compressive strength of CSRE was increased by 29.6%,while water absorption was reduced by 27.7%,compared to control,after biostimulation leading to carbonate precipitation in rammed earth.Further,Illumina MiSeq sequencing identified the change of soil bacterial community structure after biostimulation.The majority of ureolytic bacteria dominated by phylum Firmicutes and genera Sporosarcina played the major role in biocementation.?2?The foremost challenge in microbial carbonate precipitation is cost of the process in terms of nutrient to grow microbes that can be up to 60%of total operating costs.Thus,tofu wastewater?TW?,an industrial by product,was utilized to grow Bacillus cereus for nutrient cost reduction in biocementation process,and results were compared with those obtained with commercially available nutrient broth medium.There was no significant difference in bacterial growth between two media with TW as preferable media for growth and urease activity on which biocementation depends.Further,the compressive strength of sandstone and mortars were improved with TW medium and that showed important insights into the greater feasibility of TW as biocementation source for future studies.?3?Most research on microbial carbonate precipitation,to date,has concentrated on prokaryotic system despite of several limitations associated with bacteria.Thus,as last objective of this dissertation,an attempt was taken to study biocementation using fungi.The efficiency of urease-positive fungal strain Penicillium chrysogenum CS1 in biocementation of sand was exploited by producing sandstone with significant compressive strength.The research provided understanding of the involved mechanisms and advantages of fungal-mediated carbonate precipitation in cementing sand granules over same process using bacteria.