Biomineralization In Building Materials For Sustainable Construction

With the intensification of urbanization,the construction industry has developed rapidly that makes concrete as the most widely used and consumed building material in the world.However,its main component,cement,is not a sustainable building material.Each ton of cement production releases roughly a ton of carbon dioxide into the environment,which seriously affects the urban ecological construction.Promoting sustainable construction is even identified by the Chinese government as an important strategy for energy conservation.Eco-environmental material is the inherent need for the low-carbon development of construction.Ecological wisdom prevailing in nature provides solutions for the dichotomy of building materials while maintaining the environment.Many of the biological materials of nature,be it calcium-containing ceramics or polymeric substances of corals,bones,teeth or shells formed in the process of biomineralization,provides a new way for sustainable construction.Microorganisms,mainly bacteria producing urease enzyme,emulate the similar process occurring in nature by precipitating calcium carbonate.This product coming from biomineralization is termed as‘biocement'and the process is exclusively known as Microbially Induced Calcium carbonate Precipitation?MICP?.The thesis focuses on the central issue of the application potential of the MICP-based biomineralization process in developing sustainable building materials for eco-construction.Biocement as a chief product of MICP was researched and applied to repair damaged building materials to prolong service life span,and also in building materials to bring energy saving and emission reduction by combining with supplementary cementitious materials such as metakaolin and fly ash in order to reduce the content of cement and enhance the desirable properties of resulting projects.In addition,asparaginase induced MICP in building material was also explored to mitigate the secondary pollution caused by urea hydrolysis in the form of excessive ammonia production.The main research conclusions and innovations achieved include the following four aspects:1.Analyze complete bacterial diversity of karst cave and selection of efficient ureolytic bacteria for healing cracks in masonry cement mortarsAlthough many bacteria possess ureolytic activity,still few bacteria are reported in MICP-related research in environmental or construction engineering.As a typical calcium carbonate deposition environment,there may exist suitable bacteria in the karst caves for the repair of stone materials.The present study is to isolate efficiency calcifying bacteria for consolidate cracks in masonry cement mortar based on the understanding of the diversity of bacterial communities in cave.Thus,under this objective bacterial diversity of the limestone cave sample was analyzed using the Illumina MiSeq sequencing the 16S rRNA V3-V4 regions.A total of 5286 operational taxonomic units?OTUs?were obtained for species classification,covering 31 bacterial phyla.Predominant species included Masiilia?15.38%?,Pseudomona?10.91%?,and Acinetobacter?9.1%?.The highest urease-producing bacterium,Acinetobacter sp.SC4 was isolated by selection pressure method and further used to produce biocement for consolidation of cracks?depth of 25.4 mm and width of2 mm?created in masonry cement mortars.After bio-consolidation treatment,a large amount of white substances precipitated in the cracks,which significantly improved its durability?mechanical strength and anti-permeability?.X-ray diffraction?XRD?,Scanning electron microscopy and energy dispersive spectroscopy?SEM-EDS?,Thermogravimetry and differential scanning calorimetry?TGA-DSC?analyses were used to verify the biodeposition?mainly in form of calcite?by Acinetobacter sp.SC4to heal the crack.The results of this study indicated that Acinetobacter sp.SC4 isolated from the limestone cave can be used to heal cracks in masonry cement mortar and regain the mechanical strength.2.Utilize biomineralization process to improve the strength of metakaolin modified cement mortars containing lower amount of cementAs a mineral admixture,metakaolin?MK?could reduce the embodied energy of concrete by replacing a certain proportion of cement;however,when it is replaced by large amount,the mechanical properties of resulting structure decrease significantly.Thus the aim of study under this objective was to use biomineralization in improving mechanical properties of metakaolin-modified mortars substituting cement as large as50%with MK.The aim of this study was to increase the substitution rate of cement in metakaolin mortars by biomineralization process,thus further reduce the embodied energy of cement-based materials.The effect of biocement produced by one of ureolytic strain Bacillus cereus NS4was studied to improve the mechanical properties of MK modified mortars where cement was replaced from 0-50%.The results showed that the addition of biocement increased 27%of the compressive strength of the modified mortars despite of 50%cement replacement with metakaolin,which was still comparable to those mortars with100%cement.The crystal types and morphologies of the calcium carbonate formed in the modified mortars by biocement were further analyzed and compared.Fourier transform infrared spectroscopy?FTIR?was used to identify the characteristic peaks including the C-O bonds in calcium carbonate,the Si-O bonds in the silica sand and the-SH bond in the CSH gel.The results concluded that the biocement filled the pores in the modified mortars and yielded an additional cementitious C-S-H gel to improve the strength and durable properties of mortars as well as the substitution rate of cement.The study indicated that the biomineralization process can greatly support reducing the use of cement in construction without compromising mechanical and durable properties of building structure.3.Utilize biomineralization process to enhance the properties of fly-ash amended expansive soilThe poor properties of expansive soil caused great difficulties and losses to the construction.Fly ash can be used to improve the engineering properties of expansive soil to limited degree.On the other hand,fly ash is used as a carrier material to enhance the metabolic activity of ureolytic bacteria and the process of MICP.This study proposed the use of biocement to improve properties of fly-ash amended expansive soil.Biocement was incorporated with fly ash at different proportions?0%,10%,25%,50%?to improve the behavioral characteristics?liquid limit,plastic limit,plasticity index,and swelling potential?and mechanical properties of expansive soil.The most significant performance of expensive soil was achieved using the mixture containing biocement with 25%fly ash,where the unconfined compressive strength of expansive soils reached to 719.4 kPa with biocement that was only 294.6 kPa in its absence.SEM-EDS,FTIR and XRD were used to analyze the characteristics and mechanism of biocement incorporated with fly ash in promoting the agglomeration of expansive soil particles.The cations present in the fly ash can co-precipitate with the calcium carbonate induced by bacterial cells and resulting ions promote flocculation of clay particles leading to formation of cementing compound due to reduction in the surface area and water affinity,and thus swelling potential.The research results showed that the incorporation of biocement in fly ash is an effective way to increase the strength of expansive soil.4.Explore alternative enzymatic process to urease driven calcium carbonate precipitation in building material to reduce secondary pollution resulting fromurease mediated mineralizationThe urease enzyme is widely reported to carryout the process of microbially induced calcium carbonate precipitation?MICP?.However,there is environmental concern in terms of excessive ammonia production associated with it.To overcome excessive ammonia as secondary pollution generated during the urease-based MICP,asparaginase-driven MICP process was proposed in this study.Bio-grout as a building material was developed in this study for the cementation in sand using one standard bacterium,Bacillus megaterium,and results were compared between the process driven by urease and asparaginase.The results showed that the unconfined compressive strength?UCS?of asparaginase-based bio-grout was 980 kPa,the permeability was2.3?10^-7 m s^-1 and released only 40.6 U ml^-1 ammonia in cementation process.Comparatively,although the UCS of urease-based bio-grout was little higher?1002 kPa?with permeability 2.0?10-7 m s^-1,it released much higher amount of ammonia(592 U ml^-1)than asparaginase-driven carbonate precipitation.The microstructure of asparaginase-based bio-grout and mechanism of cementation were further characterized.X-ray computed tomography?XCT?and thermogravimetric analysis?TGA?were used to analyze the distribution of biocalcite inside the cemented sand column.The results indicated that the asparaginase-based MICP process can be used for sand solidification,and relief the secondary pollution generated during the urease-based MICP process for sustainable construction.Based on presented results,this PhD thesis evaluated biomineralization based on microbially induced calcium carbonate precipitation to bring sustainability in building materials and construction from several aspects.This PhD research concludes that adoption and application of biologically produced cement in construction is important,as it offers much potential in lowering environmental load of building materials and securing sustainability.In further research,it is necessary to consider technical challenges,cost-effectiveness and scale-up of MICP as technology in field.