ESEM micrograph of silica sand cemented by bacterial calcium carbonate after two weeks from the completion of the cementation reaction. The calcium carbonate was precipitated as nano-rhombohedral crystals in spherical aggregates forming point-to-point contacts between the sand particles (dash circles in A). A and B: overview of point-to-point contact of calcium carbonate; C: a close view of the nano-rhombohedral crystals in spherical aggregates; inset circle: magnification of calcium carbonate crystals showing solid crystals (not hollow) from inside; and D–F: closer images to the rhombohedral crystals in the point-to-point contacts (different field of focus). 

Contexts in source publication

Context 1

... are considered as two phenomena occurring during the precipitation of calcium carbonate. What enhances the strength of the cemented particles is the point- to-point contact between the particles and not the filled spaces. [18] According to Ismail; [19] the strength of the consolidated sand increases with strength of the individual particles, sand density, and decreases with particle size, particles pre- coating with calcium carbonate, and roundness of particles. In this study the strength production by concentrating a ureolytic bacterium in situ was examined. Furthermore, the shape and type of calcium carbonate crystals that were precipitated between the sand particles was examined by environmental scanning electron microscope (ESEM), Energy Dispersive X-ray (EDS), and X-ray diffraction (XRD). SiO 2 sand (90–400 m) was dry packed in a 60 mL plastic syringe (10 cm long, diameter of 3 cm). The packed sand-columns were tapped for about 3 min with a rubber hammer to give an even bulk density. They were then up-flushed with 3-void volumes of deionized water for 2 h and the stoppers were inserted to maintain a confining pressure. Microbial calcite precipitate Bacillus sp . MCP11 (DSM 23526), which was isolated from a previous study, [20] was grown in 50 mL of a growth medium (250-mL shaking flasks, at 28 ◦ C, pH 9.2, for 24 h). The growth medium consisted of 20 g.L − 1 yeast extract (YE), 1 M urea, 152 mM ammonium sulfate, and 100 mM sodium acetate. The conductivity (mS) of Bacillus sp . MCP11 (DSM 23526) in the presence of urea was used to determine the enzymatic rate of reaction. It was converted to urease activity by multiplying the conductivity with the dilution factor (11.11). [15] Then, specific urease activity was calculated by dividing urease activity over optical density at 600 nm. Three packed sand-columns were up-flushed with Bacillus sp . MCP11 (DSM 23526) (urease activity of 3.9 mM urea hydrolysed.min − 1 and a specific urease activity of 1.7 mM urea hydrolysed.min − 1 .OD − 1 ). Four-void volumes of the bacterial culture were up-flushed at a flow rate of 833 mL.h − 1 . Cementation solution (equiva- lent concentration of 1 M calcium/urea solution) was up-flushed into the columns (1.2-void vol- ume) directly after up-flushing bacterial cells. Four sand-columns were prepared for testing different applications of cementation mix (bacterial cells and cementation solution, from one to four flushes). Then, the columns were kept for 24 h at room temperature for the reaction to complete (Figure 1). UCS of the cemented column was examined by the Centre for Offshore Foundation Systems, UWA, Australia. A thin sliced section of the cemented column (4 flushes) was prepared and examined by Environmental Scanning Electron Microscope (ESEM, examined by the Centre for Offshore Foundation Systems, UWA, Australia). Energy Dispersive X-ray Microanalysis of calcium carbonate crystals was carried out using Oxford ISIS-5175 micro-analyzer. The samples were analyzed with powder X- ray diffraction (XRD) using a Philips diffractometer equipped with Cu α -radiation ( λ = 1.5418 Å) from 2 θ = 20 ◦ up 70 ◦ , with step size of 0.04 ◦ and counting time of 2.5 s. To determine the possibility of obtaining strength from concentrating the bacterial cells in situ and the type of CaCO 3 crystal formations; four packed sand-columns were up-flushed with bacterial cells first, followed by up-flushing of the cementation solution. After one d from the initiation of CaCO 3 precipitation, three further applications of cementation mix (cells and cementation solution) were applied. Then, the de- veloped strength was measured by unconfined strength (UCS) and the crystals were examined by ESEM, EDS, and XRD. Continuous up-flow of the ureolytic bacteria through the packed sand-column concentrates the cells in situ. Due to this concentration of cells, a soft rock (1200 kpa, tested by Centre for Offshore Foundation Systems, UWA, Australia) was obtained through three applications of bacterial cells and cementation solution (Figure 2). The cemented sand-column was permeable and uniform with a smooth surface. With one or two applications of cells and cementation solution, the consolidation of sand was very weak (Figure 3).Thus, by concentrating the cells in situ, consolidation of sand was achieved without clogging the injection point as the direct contact between the cementation solution and cells was in situ. To examine the arrangement of calcium carbonate crystals between the sand particles, thin slices of the cemented sands with four applications of cementation mix (bacterial cells and cementation solution) were examined under ESEM. It was shown that point-to-point contacts binding the sand particles together (Figure 4 and Figure 5). These contacts were com- posed of nano rhombohedral crystals in spherical aggregates, which were found in the pore spaces between the sand particles. The rhombohedral crystals in spherical arrangement were solid (Figure 4) and some were coating the surface of the sand particles (Figure 4 C and D; Figure 5). The presence of voids between the sand particles (Figure 4 C–F) indicated that improved packing of the sand was advisable in future experiments. The nano crystals were calcium carbonate crystals as shown by EDS (Figure 6). From XRD analysis (Figure 7), it is clear that the prepared sample contains calcite (indexed as C), Vaterite (indexed as V), and some additional peaks attributed to impurities formed during the preparation (indexed as I) accompanied by a sharp peak that correspond to sand particles (Si). The conversion of vaterite into calcite in bacterial biocementation was evident in a previous study. [20] The calculated full with at half maxi- mum (known as FWHM) of the major phase’s calcite and vaterite are 0.157 ◦ and 0.104 ◦ , respectively. This indicates that the two phases have different particle size distributions; for in- stance, the calcite particles are much smaller than that of vaterite. The Microstructure parameter, i.e., the crystallites size and the microstrains, which have important effects on the properties of materials, were estimated using peak profile analysis with software provided with the diffractometer, where the FWHM is determined, then used for the calculation by introducing a standard value for the instrument contribution to the peak broad- ening. The estimated crystallites size was 145 nm for calcite and more than in the micrometric size for vaterite. This is clear evidence that the formed calcite was an aggregate of nano-sized particles. A soft rock was produced by concentrating the cells in situ through 3–4 applications of se- quential up-loading of cells followed by cementation solution (calcium/urea). Interestingly, the obtained strength was attributed to the point-to- point contact of nanoparticles of calcite crystals in the form of aggregates, which formed bridges between the adjacent particles. The production of strength due to this type of contact has been confirmed by research. [20] More- over, Ismail and his colleagues [19] have stated that the strength of the cemented matrix—by using CIPS which is a non-microbial cementation process—will increase as the contact points increases, enhancing the potential cementation sites for calcite precipitation. The void spaces in ESEM images (Figure 4) indicate that the sand particles in the biocemented column should be compressed more to increase the number of the effective point-to-point contacts, which is a critical factor for improving strength. [19,21] The success in the strength production by concentrating the cells in-situ has provoked the following question: Is it possible to attach the bacterial cells in-situ and by how much? This question should be addressed in future studies. Concentrating ureolytic bacterial cells in situ could lead to a successful cementation without clogging the injection end or reducing the per- meability when suitable concentrations of urea and calcium ions are ...

Context 2

... of calcium carbonate. What enhances the strength of the cemented particles is the point- to-point contact between the particles and not the filled spaces. [18] According to Ismail; [19] the strength of the consolidated sand increases with strength of the individual particles, sand density, and decreases with particle size, particles pre- coating with calcium carbonate, and roundness of particles. In this study the strength production by concentrating a ureolytic bacterium in situ was examined. Furthermore, the shape and type of calcium carbonate crystals that were precipitated between the sand particles was examined by environmental scanning electron microscope (ESEM), Energy Dispersive X-ray (EDS), and X-ray diffraction (XRD). SiO 2 sand (90–400 m) was dry packed in a 60 mL plastic syringe (10 cm long, diameter of 3 cm). The packed sand-columns were tapped for about 3 min with a rubber hammer to give an even bulk density. They were then up-flushed with 3-void volumes of deionized water for 2 h and the stoppers were inserted to maintain a confining pressure. Microbial calcite precipitate Bacillus sp . MCP11 (DSM 23526), which was isolated from a previous study, [20] was grown in 50 mL of a growth medium (250-mL shaking flasks, at 28 ◦ C, pH 9.2, for 24 h). The growth medium consisted of 20 g.L − 1 yeast extract (YE), 1 M urea, 152 mM ammonium sulfate, and 100 mM sodium acetate. The conductivity (mS) of Bacillus sp . MCP11 (DSM 23526) in the presence of urea was used to determine the enzymatic rate of reaction. It was converted to urease activity by multiplying the conductivity with the dilution factor (11.11). [15] Then, specific urease activity was calculated by dividing urease activity over optical density at 600 nm. Three packed sand-columns were up-flushed with Bacillus sp . MCP11 (DSM 23526) (urease activity of 3.9 mM urea hydrolysed.min − 1 and a specific urease activity of 1.7 mM urea hydrolysed.min − 1 .OD − 1 ). Four-void volumes of the bacterial culture were up-flushed at a flow rate of 833 mL.h − 1 . Cementation solution (equiva- lent concentration of 1 M calcium/urea solution) was up-flushed into the columns (1.2-void vol- ume) directly after up-flushing bacterial cells. Four sand-columns were prepared for testing different applications of cementation mix (bacterial cells and cementation solution, from one to four flushes). Then, the columns were kept for 24 h at room temperature for the reaction to complete (Figure 1). UCS of the cemented column was examined by the Centre for Offshore Foundation Systems, UWA, Australia. A thin sliced section of the cemented column (4 flushes) was prepared and examined by Environmental Scanning Electron Microscope (ESEM, examined by the Centre for Offshore Foundation Systems, UWA, Australia). Energy Dispersive X-ray Microanalysis of calcium carbonate crystals was carried out using Oxford ISIS-5175 micro-analyzer. The samples were analyzed with powder X- ray diffraction (XRD) using a Philips diffractometer equipped with Cu α -radiation ( λ = 1.5418 Å) from 2 θ = 20 ◦ up 70 ◦ , with step size of 0.04 ◦ and counting time of 2.5 s. To determine the possibility of obtaining strength from concentrating the bacterial cells in situ and the type of CaCO 3 crystal formations; four packed sand-columns were up-flushed with bacterial cells first, followed by up-flushing of the cementation solution. After one d from the initiation of CaCO 3 precipitation, three further applications of cementation mix (cells and cementation solution) were applied. Then, the de- veloped strength was measured by unconfined strength (UCS) and the crystals were examined by ESEM, EDS, and XRD. Continuous up-flow of the ureolytic bacteria through the packed sand-column concentrates the cells in situ. Due to this concentration of cells, a soft rock (1200 kpa, tested by Centre for Offshore Foundation Systems, UWA, Australia) was obtained through three applications of bacterial cells and cementation solution (Figure 2). The cemented sand-column was permeable and uniform with a smooth surface. With one or two applications of cells and cementation solution, the consolidation of sand was very weak (Figure 3).Thus, by concentrating the cells in situ, consolidation of sand was achieved without clogging the injection point as the direct contact between the cementation solution and cells was in situ. To examine the arrangement of calcium carbonate crystals between the sand particles, thin slices of the cemented sands with four applications of cementation mix (bacterial cells and cementation solution) were examined under ESEM. It was shown that point-to-point contacts binding the sand particles together (Figure 4 and Figure 5). These contacts were com- posed of nano rhombohedral crystals in spherical aggregates, which were found in the pore spaces between the sand particles. The rhombohedral crystals in spherical arrangement were solid (Figure 4) and some were coating the surface of the sand particles (Figure 4 C and D; Figure 5). The presence of voids between the sand particles (Figure 4 C–F) indicated that improved packing of the sand was advisable in future experiments. The nano crystals were calcium carbonate crystals as shown by EDS (Figure 6). From XRD analysis (Figure 7), it is clear that the prepared sample contains calcite (indexed as C), Vaterite (indexed as V), and some additional peaks attributed to impurities formed during the preparation (indexed as I) accompanied by a sharp peak that correspond to sand particles (Si). The conversion of vaterite into calcite in bacterial biocementation was evident in a previous study. [20] The calculated full with at half maxi- mum (known as FWHM) of the major phase’s calcite and vaterite are 0.157 ◦ and 0.104 ◦ , respectively. This indicates that the two phases have different particle size distributions; for in- stance, the calcite particles are much smaller than that of vaterite. The Microstructure parameter, i.e., the crystallites size and the microstrains, which have important effects on the properties of materials, were estimated using peak profile analysis with software provided with the diffractometer, where the FWHM is determined, then used for the calculation by introducing a standard value for the instrument contribution to the peak broad- ening. The estimated crystallites size was 145 nm for calcite and more than in the micrometric size for vaterite. This is clear evidence that the formed calcite was an aggregate of nano-sized particles. A soft rock was produced by concentrating the cells in situ through 3–4 applications of se- quential up-loading of cells followed by cementation solution (calcium/urea). Interestingly, the obtained strength was attributed to the point-to- point contact of nanoparticles of calcite crystals in the form of aggregates, which formed bridges between the adjacent particles. The production of strength due to this type of contact has been confirmed by research. [20] More- over, Ismail and his colleagues [19] have stated that the strength of the cemented matrix—by using CIPS which is a non-microbial cementation process—will increase as the contact points increases, enhancing the potential cementation sites for calcite precipitation. The void spaces in ESEM images (Figure 4) indicate that the sand particles in the biocemented column should be compressed more to increase the number of the effective point-to-point contacts, which is a critical factor for improving strength. [19,21] The success in the strength production by concentrating the cells in-situ has provoked the following question: Is it possible to attach the bacterial cells in-situ and by how much? This question should be addressed in future studies. Concentrating ureolytic bacterial cells in situ could lead to a successful cementation without clogging the injection end or reducing the per- meability when suitable concentrations of urea and calcium ions are ...

Context 3

... is the point- to-point contact between the particles and not the filled spaces. [18] According to Ismail; [19] the strength of the consolidated sand increases with strength of the individual particles, sand density, and decreases with particle size, particles pre- coating with calcium carbonate, and roundness of particles. In this study the strength production by concentrating a ureolytic bacterium in situ was examined. Furthermore, the shape and type of calcium carbonate crystals that were precipitated between the sand particles was examined by environmental scanning electron microscope (ESEM), Energy Dispersive X-ray (EDS), and X-ray diffraction (XRD). SiO 2 sand (90–400 m) was dry packed in a 60 mL plastic syringe (10 cm long, diameter of 3 cm). The packed sand-columns were tapped for about 3 min with a rubber hammer to give an even bulk density. They were then up-flushed with 3-void volumes of deionized water for 2 h and the stoppers were inserted to maintain a confining pressure. Microbial calcite precipitate Bacillus sp . MCP11 (DSM 23526), which was isolated from a previous study, [20] was grown in 50 mL of a growth medium (250-mL shaking flasks, at 28 ◦ C, pH 9.2, for 24 h). The growth medium consisted of 20 g.L − 1 yeast extract (YE), 1 M urea, 152 mM ammonium sulfate, and 100 mM sodium acetate. The conductivity (mS) of Bacillus sp . MCP11 (DSM 23526) in the presence of urea was used to determine the enzymatic rate of reaction. It was converted to urease activity by multiplying the conductivity with the dilution factor (11.11). [15] Then, specific urease activity was calculated by dividing urease activity over optical density at 600 nm. Three packed sand-columns were up-flushed with Bacillus sp . MCP11 (DSM 23526) (urease activity of 3.9 mM urea hydrolysed.min − 1 and a specific urease activity of 1.7 mM urea hydrolysed.min − 1 .OD − 1 ). Four-void volumes of the bacterial culture were up-flushed at a flow rate of 833 mL.h − 1 . Cementation solution (equiva- lent concentration of 1 M calcium/urea solution) was up-flushed into the columns (1.2-void vol- ume) directly after up-flushing bacterial cells. Four sand-columns were prepared for testing different applications of cementation mix (bacterial cells and cementation solution, from one to four flushes). Then, the columns were kept for 24 h at room temperature for the reaction to complete (Figure 1). UCS of the cemented column was examined by the Centre for Offshore Foundation Systems, UWA, Australia. A thin sliced section of the cemented column (4 flushes) was prepared and examined by Environmental Scanning Electron Microscope (ESEM, examined by the Centre for Offshore Foundation Systems, UWA, Australia). Energy Dispersive X-ray Microanalysis of calcium carbonate crystals was carried out using Oxford ISIS-5175 micro-analyzer. The samples were analyzed with powder X- ray diffraction (XRD) using a Philips diffractometer equipped with Cu α -radiation ( λ = 1.5418 Å) from 2 θ = 20 ◦ up 70 ◦ , with step size of 0.04 ◦ and counting time of 2.5 s. To determine the possibility of obtaining strength from concentrating the bacterial cells in situ and the type of CaCO 3 crystal formations; four packed sand-columns were up-flushed with bacterial cells first, followed by up-flushing of the cementation solution. After one d from the initiation of CaCO 3 precipitation, three further applications of cementation mix (cells and cementation solution) were applied. Then, the de- veloped strength was measured by unconfined strength (UCS) and the crystals were examined by ESEM, EDS, and XRD. Continuous up-flow of the ureolytic bacteria through the packed sand-column concentrates the cells in situ. Due to this concentration of cells, a soft rock (1200 kpa, tested by Centre for Offshore Foundation Systems, UWA, Australia) was obtained through three applications of bacterial cells and cementation solution (Figure 2). The cemented sand-column was permeable and uniform with a smooth surface. With one or two applications of cells and cementation solution, the consolidation of sand was very weak (Figure 3).Thus, by concentrating the cells in situ, consolidation of sand was achieved without clogging the injection point as the direct contact between the cementation solution and cells was in situ. To examine the arrangement of calcium carbonate crystals between the sand particles, thin slices of the cemented sands with four applications of cementation mix (bacterial cells and cementation solution) were examined under ESEM. It was shown that point-to-point contacts binding the sand particles together (Figure 4 and Figure 5). These contacts were com- posed of nano rhombohedral crystals in spherical aggregates, which were found in the pore spaces between the sand particles. The rhombohedral crystals in spherical arrangement were solid (Figure 4) and some were coating the surface of the sand particles (Figure 4 C and D; Figure 5). The presence of voids between the sand particles (Figure 4 C–F) indicated that improved packing of the sand was advisable in future experiments. The nano crystals were calcium carbonate crystals as shown by EDS (Figure 6). From XRD analysis (Figure 7), it is clear that the prepared sample contains calcite (indexed as C), Vaterite (indexed as V), and some additional peaks attributed to impurities formed during the preparation (indexed as I) accompanied by a sharp peak that correspond to sand particles (Si). The conversion of vaterite into calcite in bacterial biocementation was evident in a previous study. [20] The calculated full with at half maxi- mum (known as FWHM) of the major phase’s calcite and vaterite are 0.157 ◦ and 0.104 ◦ , respectively. This indicates that the two phases have different particle size distributions; for in- stance, the calcite particles are much smaller than that of vaterite. The Microstructure parameter, i.e., the crystallites size and the microstrains, which have important effects on the properties of materials, were estimated using peak profile analysis with software provided with the diffractometer, where the FWHM is determined, then used for the calculation by introducing a standard value for the instrument contribution to the peak broad- ening. The estimated crystallites size was 145 nm for calcite and more than in the micrometric size for vaterite. This is clear evidence that the formed calcite was an aggregate of nano-sized particles. A soft rock was produced by concentrating the cells in situ through 3–4 applications of se- quential up-loading of cells followed by cementation solution (calcium/urea). Interestingly, the obtained strength was attributed to the point-to- point contact of nanoparticles of calcite crystals in the form of aggregates, which formed bridges between the adjacent particles. The production of strength due to this type of contact has been confirmed by research. [20] More- over, Ismail and his colleagues [19] have stated that the strength of the cemented matrix—by using CIPS which is a non-microbial cementation process—will increase as the contact points increases, enhancing the potential cementation sites for calcite precipitation. The void spaces in ESEM images (Figure 4) indicate that the sand particles in the biocemented column should be compressed more to increase the number of the effective point-to-point contacts, which is a critical factor for improving strength. [19,21] The success in the strength production by concentrating the cells in-situ has provoked the following question: Is it possible to attach the bacterial cells in-situ and by how much? This question should be addressed in future studies. Concentrating ureolytic bacterial cells in situ could lead to a successful cementation without clogging the injection end or reducing the per- meability when suitable concentrations of urea and calcium ions are ...

Context 4

... of cementation mix (bacterial cells and cementation solution, from one to four flushes). Then, the columns were kept for 24 h at room temperature for the reaction to complete (Figure 1). UCS of the cemented column was examined by the Centre for Offshore Foundation Systems, UWA, Australia. A thin sliced section of the cemented column (4 flushes) was prepared and examined by Environmental Scanning Electron Microscope (ESEM, examined by the Centre for Offshore Foundation Systems, UWA, Australia). Energy Dispersive X-ray Microanalysis of calcium carbonate crystals was carried out using Oxford ISIS-5175 micro-analyzer. The samples were analyzed with powder X- ray diffraction (XRD) using a Philips diffractometer equipped with Cu α -radiation ( λ = 1.5418 Å) from 2 θ = 20 ◦ up 70 ◦ , with step size of 0.04 ◦ and counting time of 2.5 s. To determine the possibility of obtaining strength from concentrating the bacterial cells in situ and the type of CaCO 3 crystal formations; four packed sand-columns were up-flushed with bacterial cells first, followed by up-flushing of the cementation solution. After one d from the initiation of CaCO 3 precipitation, three further applications of cementation mix (cells and cementation solution) were applied. Then, the de- veloped strength was measured by unconfined strength (UCS) and the crystals were examined by ESEM, EDS, and XRD. Continuous up-flow of the ureolytic bacteria through the packed sand-column concentrates the cells in situ. Due to this concentration of cells, a soft rock (1200 kpa, tested by Centre for Offshore Foundation Systems, UWA, Australia) was obtained through three applications of bacterial cells and cementation solution (Figure 2). The cemented sand-column was permeable and uniform with a smooth surface. With one or two applications of cells and cementation solution, the consolidation of sand was very weak (Figure 3).Thus, by concentrating the cells in situ, consolidation of sand was achieved without clogging the injection point as the direct contact between the cementation solution and cells was in situ. To examine the arrangement of calcium carbonate crystals between the sand particles, thin slices of the cemented sands with four applications of cementation mix (bacterial cells and cementation solution) were examined under ESEM. It was shown that point-to-point contacts binding the sand particles together (Figure 4 and Figure 5). These contacts were com- posed of nano rhombohedral crystals in spherical aggregates, which were found in the pore spaces between the sand particles. The rhombohedral crystals in spherical arrangement were solid (Figure 4) and some were coating the surface of the sand particles (Figure 4 C and D; Figure 5). The presence of voids between the sand particles (Figure 4 C–F) indicated that improved packing of the sand was advisable in future experiments. The nano crystals were calcium carbonate crystals as shown by EDS (Figure 6). From XRD analysis (Figure 7), it is clear that the prepared sample contains calcite (indexed as C), Vaterite (indexed as V), and some additional peaks attributed to impurities formed during the preparation (indexed as I) accompanied by a sharp peak that correspond to sand particles (Si). The conversion of vaterite into calcite in bacterial biocementation was evident in a previous study. [20] The calculated full with at half maxi- mum (known as FWHM) of the major phase’s calcite and vaterite are 0.157 ◦ and 0.104 ◦ , respectively. This indicates that the two phases have different particle size distributions; for in- stance, the calcite particles are much smaller than that of vaterite. The Microstructure parameter, i.e., the crystallites size and the microstrains, which have important effects on the properties of materials, were estimated using peak profile analysis with software provided with the diffractometer, where the FWHM is determined, then used for the calculation by introducing a standard value for the instrument contribution to the peak broad- ening. The estimated crystallites size was 145 nm for calcite and more than in the micrometric size for vaterite. This is clear evidence that the formed calcite was an aggregate of nano-sized particles. A soft rock was produced by concentrating the cells in situ through 3–4 applications of se- quential up-loading of cells followed by cementation solution (calcium/urea). Interestingly, the obtained strength was attributed to the point-to- point contact of nanoparticles of calcite crystals in the form of aggregates, which formed bridges between the adjacent particles. The production of strength due to this type of contact has been confirmed by research. [20] More- over, Ismail and his colleagues [19] have stated that the strength of the cemented matrix—by using CIPS which is a non-microbial cementation process—will increase as the contact points increases, enhancing the potential cementation sites for calcite precipitation. The void spaces in ESEM images (Figure 4) indicate that the sand particles in the biocemented column should be compressed more to increase the number of the effective point-to-point contacts, which is a critical factor for improving strength. [19,21] The success in the strength production by concentrating the cells in-situ has provoked the following question: Is it possible to attach the bacterial cells in-situ and by how much? This question should be addressed in future studies. Concentrating ureolytic bacterial cells in situ could lead to a successful cementation without clogging the injection end or reducing the per- meability when suitable concentrations of urea and calcium ions are ...