Relative Compressive Strength Research Articles

Effect of moisture content on mechanical behavior of ultra-high toughness cementitious composites

This study presented an investigation into the basic mechanical properties of Ultra-high toughness cementitious composites (UHTCC) under varying moisture levels (0%, 56.5%, and 100%). UHTCC have been recognized for their excellent deformation and crack control abilities, making them ideal for repairing and reinforcing hydraulic structures. In this study, static compressive test and direct tensile test were conducted to determine the influence of free water on compressive strength, tensile stress and strain relationship, elastic modulus and energy absorption ability of UHTCC. Meanwhile, the notched beam fracture test and single fiber pull-out test were also performed to investigate the mechanism behind such phenomenon. The results of the study revealed that as the relative moisture content of UHTCC increased, the compressive and tensile strengths decreased to varying degrees. The softening effect of water on compressive strength of UHTCC was found to be more significant than that on its tensile strength. Furthermore, the direct tensile deformation capacity of UHTCC increased from 2.4% to 4.0% as the relative moisture content increased. Water infiltration into UHTCC was found to have a minimal effect on the number of tensile cracks but significantly increased their width. The results of notched beam fracture and fiber pull-out tests demonstrated that water infiltration led to a 30.4% decrease in matrix fracture toughness, a 37.3% decrease in chemical bonding strength, and a 23.4% decrease in frictional bonding strength between fibers and the matrix. The increased deformation ability of UHTCC in water environments was attributed to the increase in strain hardening energy index (Jb’/Jtip).

Research on fire resistance of silica fume insulation mortar

Due to the increasingly tight energy supply situation, thermal insulation mortar is more and more widely used in the exterior wall insulation layer of buildings in various countries. However, the existing academic papers have less research on the key properties of thermal insulation mortar such as fire resistance and economic feasibility. Based on the previous research results, this study selected silica fume as an admixture to improve the comprehensive performance of insulation mortar. The goal is to develop a high-performance fireproof insulation mortar. This paper focuses on the fire resistance of the improved insulation mortar. The results show that silica fume mixed into the mortar will play a fine particle filling and hydration gelation cooperation, and the amount of silica fume mixed from 0 to 10% can significantly improve the bond strength and compressive strength of the mortar. For the thermal conductivity and dry density of mortar, there is a certain increase in the range of silica fume dosing from 0 to 4%, while the range of silica fume dosing from 4% to 10% decreases again. Silica fume has a favorable effect on improving the fire resistance of insulating mortar, and the mortar with 10% admixture of silica fume has about 28.30% lower mass loss rate after high temperature and about 14.73% higher relative compressive strength after high temperature after 28 days of maintenance. The final selected optimum admixture of silica fume is 10%, and the best ratio of raw materials is cement: aggregate: water: dispersible emulsion powder: fly ash: diabase rock powder: AOS foaming agent: gelatin: silica fume = 1: 1.67: 2: 0.045: 0.15: 0.225: 0.035: 0.02: 0.138.

Dynamic behaviors of water-saturated and frozen sandstone subjected to freeze-thaw cycles

In high-altitude cold areas, freeze-thaw (F-T) cycles induced by day-night and seasonal temperature changes cause numerous rock mass slope engineering disasters. To investigate the dynamic properties of rock in the natural environment of a high-altitude cold area, standard specimens were drilled from the slope of the Jiama copper mine in Tibet, and dynamic compression tests were performed on water-saturated and frozen sandstone with different numbers of F-T cycles (0, 10, 20, 30, and 40) by the split Hopkinson pressure bar (SHPB) system with a cryogenic control system. The influence of water-saturated and frozen conditions on the dynamic performance of sandstone was investigated. The following conclusions are drawn: (1) With increasing strain rate, the attenuation factor (λa) of water-saturated sandstone and the intensifying factor (λi) of frozen sandstone linearly increase. As the number of F-T cycles increases, the dependence factor (λd) of water-saturated sandstone linearly decreases, whereas the λd of frozen sandstone linearly increases. (2) The prediction equation of the dynamic compressive strength of water-saturated and frozen sandstone is obtained, which can be used to predict the dynamic compressive strength of sandstone after various F-T cycles based on the strain rate. (3) The mesoscopic mechanism of water-saturated and frozen sandstone's dynamic compressive strength evolution is investigated. The water softening effect causes the dynamic compressive strength of water-saturated sandstone to decrease, whereas the strengthening effect of pore ice causes it to increase. (4) The decrease in the relative dynamic compressive strength of water-saturated sandstone and the increase in the relative dynamic compressive strength of frozen sandstone can be attributed to the increased porosity.

Pengaruh Serbuk Besi Dari Limbah Bubut Sebagai Subtitusi Agregat Halus Dan Variasi Tawas Sebagai Subtitusi Agregat Kasar Terhadap Kuat Tekan Beton

This study aims to analyze the relationship of compressive strength of concrete with iron powder mixture from lathe waste by 10% and alum variation by 0%, 5%, 10%, 15%, 20% and 25%. The method of this study is to compare the compressive strength of normal concrete with the compressive strength of concrete variations of iron powder and alum. The percentage of iron powder of 10% and the percentage of alum of 0% experienced a decrease in the compressive strength value against normal concrete by 8.7%, which used an iron lathe of 10% and alum of 5% experienced a drastic decrease against the compressive strength of normal concrete by 30.4%. It can be concluded that 10% iron lathe impersonation as a substitution of fine aggregates and variations of alum of 0%, 5%, 10%, 15%, 20% and 25% as substitutions of coarse aggregates lead to a decrease in the compressive strength value of concrete

The Study of the Effects of Supplementary Cementitious Materials (SCMs) on Concrete Compressive Strength at High Temperatures Using Artificial Neural Network Model

In this study, an artificial neural network (ANN) model was developed to predict the compressive strength of concrete containing supplementary cementitious materials (SCMs) at high temperatures. For this purpose, 500 experimental results were collected from the available literature. The effective parameters in the model are the volumes of coarse and fine aggregates, water, cement, coarse-aggregate type, percentage SCMs as the cement replacement, temperature levels, and test methods. The proposed ANN model was developed at a correlation coefficient of 0.966. A parametric study was conducted to evaluate the impact of the combined effects of input parameters (aggregate types and SCM content) on the relative compressive strength of concrete at high temperatures. It was shown that siliceous aggregate has a better performance by producing stronger bonds with cement paste than calcareous aggregates. The optimum SCM contents depend on the aggregate types. The optimum silica fume (SF) content for concrete with a water-to-binder ratio of 0.6 subjected to high temperatures is 8% and 3% for siliceous and calcareous concrete, respectively. The analysis of the ANN model has provided a conclusive understanding of the concrete behaviour at high temperatures.

The effect of milling time, and sintering temperature and time on the microstructure-property relationship of aluminium-matrix hybrid composites

The present study investigates the effect of milling time, and sintering temperature and time on the microstructure and properties of aluminium matrix hybrid composites (AMHCs). The AMHCs containing aluminium nitride (AlN) and yttrium tungstate (Y2W3O12) have been fabricated by powder metallurgy route. The powder mixtures were subjected to milling for different times, i.e., 0.5, 2, 4, 6, 8, 10, 12 & 14 h followed by compaction and sintering in a temperature range of 550–650 °C for different times, e.g., 1, 1.5 and 2 h. The smallest crystallite size along with the homogeneous distribution of reinforcements is observed at 10 h of milling time. The microstructure and corresponding properties, i.e., relative density, hardness and compressive strength are influenced by milling time, sintering temperature and sintering time. The optimised processing parameters for getting the maximum values of relative density, hardness, and compressive strength of the AMHCs are found to be 10 h of milling time, 600 °C of sintering temperature, and 1 h of sintering time.

Numerical model of cumulative damage evolution of offshore wind turbine grouted connection under cyclic axial load

GCs in OWTs are exposed to fatigue loads that can lead to damage of the grout before ultimate limit state is reached. A uniaxial and fatigue compression test of high strength grout material were carried out to obtain the compressive strength, failure mode, fatigue life and load-displacement relationship of test cubes. A uniaxial and fatigue tests were carried out on GCs specimens to study the damage evolution of the GCs. The fatigue test on GC was done by applying six incremental amplitude cyclic load ranges of 30%–80% of ultimate load on the GC. The scalar damage degradation parameter (SDEG) from the result of the numerical simulation was used to estimate a damage index which measured the cumulative damage evolution. The cumulative damage evolutions were influenced by the cyclic load amplitude. The larger the load amplitude, the higher the damage index accumulated. The numerical simulation results compared with the DNV code method showed that the DNV code predicted lower damage values for fatigue loads ratio of up to 0.725 and predicted higher damage values beyond the 0.725 loads ratio for the GC. The proposed numerical model predicted the laboratory test results of the grout cube and the grouted connections.

A New Type of Mineral Admixture and Its Impact on the Carbonation Resistance of EPS Concrete

In this study, the effect of microbead dosages (0%, 5%, 10%, 15%, and 20%) on the carbonation resistance of expanded polystyrene (EPS) concrete was investigated. Five groups of EPS concrete specimens were produced and underwent rapid carbonation testing. The carbonation depth and strength after carbonation of the specimens were measured at different carbonation ages (7 days, 14 days, and 28 days) and analyzed to determine the effect of microbead dosages and compressive strength on carbonation resistance. Results indicated that the carbonation depth increased with the progression of carbonation time. The introduction of microbeads was found to significantly improve the carbonation resistance of EPS concrete, leading to a reduction in carbonation depth of over 50% after 28 days and an increase in strength after carbonation by 18–56%. A relative compressive strength model for EPS concrete after carbonation was developed, which could accurately characterize the growth of compressive strength. Based on the analysis of EPS concrete carbonation depth data, a prediction model for the carbonation depth of EPS concrete with microbead dosage was established through fitting, providing improved accuracy in predicting carbonation resistance. The microstructure of EPS concrete was also examined using scanning electron microscopy to uncover the underlying mechanisms of microbead enhancement on carbonation resistance. These findings have potential implications for future research and engineering applications in the carbonation resistance of EPS concrete.

Effect of the stearic acid modified metakaolin on sulfate resistance of mortar based on the experimental study and capillary theory analysis

In this study, a stearic acid modified metakaolin (MMK) was developed to improve the sulfate resistance of cement-based materials, which could effectively avoid the adverse effects of traditional hydrophobic modifier on the mechanical properties of cement mortar itself. Firstly, the effects of the stearic acid content and grinding time on the water contact angle of the MMK were studied, and the results showed that the MMK had the maximum water contact angle when the stearic acid content was 5% and the grinding time was 20 min. On this basis, abundant systematic tests were conducted to study the effects of the MMK mass fraction on water contact angle and water absorption of the mortar. Subsequently, the sulfate resistance of the mortar with MMK was examined under partial immersion, including the apparent morphology, linear expansion rate, relative dynamic elastic modulus, compressive strength and microstructure. Finally, a mathematic model considering water absorption and evaporation was developed, and the effects of the MMK on the corrosion height, capillary absorption and water evaporation of the specimen under partial immersion in sulfate solution were analyzed. The model analysis showed that the MMK could reduce the capillary water absorption height of the specimen under partial immersion in sulfate solution, and the mechanism of sulfate resistance for the mortar with the MMK was to reduce the amount of corrosive ions by reducing the capillary coefficient.

Capability of R3 test to evaluate pozzolanicity of ground raw and calcined sugarcane bagasse ashes

Sugarcane bagasse ash (SCBA) is a by-product of sugar and ethanol production and is largely disposed in landfills. Although the SCBA feasibility as pozzolanic material has been widely explored, traditional screening reactivity tests have shown inappropriate to evaluate alternative supplementary cementitious materials (SCM). The R3 test is a novel method to assess the reactivity of SCMs in a simplified system without Portland cement. This work aims to investigate the capability of the R3 test methods to measure the reactivity of ground raw (SCBA) and calcined (SCBA600) sugarcane bagasse ashes benchmarked against 2,7, 28, and 90-days compressive strength of mortars using SCM as cement replacement. Besides SCBA specimens, two traditional SCMs, silica fume (SF) and metakaolin (MK), were also evaluated. As expected, the R3 test obtained the same order regarding the reactivity of the studied SCMs for the three methods, from the highest to the lowest MK > SF > SCBA600 > SCBA. Regarding the R3 heat release evolution, raw and calcined sugarcane bagasse ashes had a very analogous trend and slow reaction of hydration. In R3 bound water results, a more prominent distinction was verified between SCBA and SCBA600. Moderate to poor correlations are observed between the R3 CH consumption and the portlandite content of cementitious pastes. The benchmark test confirmed the slow reaction of the studied ashes, presenting a significant increase in compressive strength only after 28 days. R3 test results correlate well (R2 ≥ 0.85) with the relative compressive strength of mortars at 7 days. Only a moderate relationship exists between the R3 tests and the relative strength at 28 days, decreasing at 90 days. This contribution indicates that the R3 test methods are sensible to evaluate the early age pozzolanic reactivity of SCBA and SCBA600.

Bond durability between BFRP bars and recycled aggregate seawater sea-sand concrete in freezing-thawing environment

Fibre reinforced polymer (FRP) bar reinforced recycled aggregate seawater sea-sand concrete (RASSC) structures can reasonably solve the two key problems of reinforcement corrosion and resource shortage. In this paper, the bond durability between basalt fibre reinforced polymer (BFRP) bars and RASSC in freezing-thawing environment was studied by eccentric pull-out tests. The research parameters were freezing-thawing cyclic numbers and concrete cover thicknesses. The results revealed that the bond strength between BFRP bars and RASSC decreased significantly with the increase in freezing-thawing cyclic numbers. Additionally, the bond strength increased with concrete cover thicknesses. The variation laws of slip at bond strength and bond stiffness were similar to those of bond strength. Considering the effect of freezing-thawing cyclic numbers, the equations for relative compressive strength and relative dynamic elastic modulus of RASSC were established. Considering the effects of freezing-thawing cyclic numbers and concrete cover thicknesses, the equations for bond strength, slip at bond strength, and bond stiffness between BFRP bars and RASSC were given. Furthermore, mBPE model and CMR model were calibrated.

Influences of Carbonated Recycled Concrete Fines on Cement Hydration

The preparation of recycled concrete aggregate generates a lot of fines, which are obstacles for implementing the recycled concrete aggregate. In this work, carbonation treatment is applied to improve the properties of recycled concrete fine, and the influences of carbonated recycled concrete fine (CRCF) on cement hydration process are evaluated. Both fresh and hardened properties of the cement paste samples replacing 0 to 30% of the CRCF are measured. The results reveal that the addition of CRCF obviously accelerates the hydration process of cement, especially during the early stage, and the initial and final setting times of the cement paste containing 30% CRCF are both reduced by approximately 25% compared to the control. The CRCF improves the strength gain of cement, and that influence becomes obvious with longer curing; the relative compressive strength of cement paste containing 30% CRCF is increased by 18% relative to the control after being cured for 28 days. At the same time, the early hydration of cement paste is accelerated with the addition of CRCF and the total hydration heat after 48 h of cement paste is significantly decreased with the addition of CRCF. Specifically, the total hydration heat after 48 h of cement paste with 30% CRCF is less than 50% of that with 0% CRCF. Besides that, CRCF consumes CH in cement paste and improves the pore structure of hardened cement paste. The morphology of hydrated samples shows that the shape of ettringite formed within the control sample with 0% CRCF is longer than those of the other ones formed in cement paste with CRCF, and the length decreases as the CRCF contents increase. In addition, the sample containing 30% CRCF does not show the particles, which means that CRCF reduces the ettringite forming in hardened paste samples. Thus, the findings from this work provide a better understanding of the field of waste concrete reuse.

3D printing concrete with recycled sand: The influence mechanism of extruded pore defects on constitutive relationship

Recycled sand (RS) as an environmental-friendly building material, has shown great prospects for the digital construction of buildings. In this study, 3D printed recycled sand concrete (3DPRSC) mixed with RS was prepared, and the related compressive strength and constitutive relationships were investigated on different RS replacement ratios and construction methods. The geometric characteristics and spatial distribution of pore defects were analyzed by the combined X-CT and MIP, and the microscopic morphology of RS and natural sand was analyzed by SEM. The results showed that the compressive strength and constitutive curves have apparent anisotropic characteristics. With the increase in the RS replacement rate, the compressive strength tended to decrease. The ellipsoidal pore geometry's arrangement of 3DPRSC extruded pore defects differs in different printing directions, and the pore defect distribution characteristics vary with the accumulated height of the filaments and the printing direction. The mechanism of the formation and distribution of extruded pore defects on the compressive strength and constitutive relationship was analyzed, and a model of the constitutive curve based on extruded pore defects and anisotropy was established, which provided a theoretical basis for the nonlinear analysis of the engineering structure of 3DPRSC.

The effect of size and shape of pores on the prediction model of compressive strength of foamed concrete

The Balshin’s model is the most well-known of the models used to predict the compressive strength of aerated concrete. Among the pore characteristics such as the amount of porosity, the size of the pores, and their shape, Only the amount of porosity is placed as a specific parameter in the Balshin’s model. The impact of the other two characteristics, on the other hand, is included in the power value of the Balshin’s equation. Compressive strength tests and identifying the characteristics of air voids using microscopic imaging were performed on the mixtures produced in this study, which had weight ratios of sand to the cement of 1, 1.5, and 2, and the percentage of foam volumes of 0, 15, 25 and 35. In this study, a review of some of the factors influencing the change in the pore characteristics was performed, including the porosity of the foamed mixture and the size of sand used, in addition to the effect of the pore characteristics such as size and shape on the compressive strength of the foamed mixture. This study aims to conduct a comparative analysis of the models introduced in previous research to determine the effect of the pore characteristics of semi-structural and structural foamed mixtures (with sand) caused by mixture porosity and the sand size on the Balshin’s model. Among the types of relationships presented for the Balshin’s model, the relationship based on the paste fraction porosity was used. According to the findings of this study, foam porosity is the most important factor influencing pore size change, followed by sand size. The increase in the size of the pores and their non-sphericality decreased the relative compressive strength and, as a consequence, increased the power of the Balshin’s model because the maximum level of stress concentration was created adjacent to the middle diameter of the pores at the period of concrete rupture.

Effect of unconventional supplementary cementitious materials on the hardened cement pastes exposed to high temperature

An investigation was conducted to determine how Ordinary Portland Cement and several unconventional cementitious additives, such as magnetite, chamotte, perlite, boron carbide, and more common powdered quartz, affected the behaviour of hardened cement paste when subjected to high temperatures. The test was conducted using a constant water–fines ratio of 0.3. The water–cement ratios were nevertheless 0.25 and 0.222 as a result of the two fine replacement ratios (20% and 35%, respectively). Seven heat steps were used to heat the specimens of hardened cement paste to 900 °C. On the cooled specimens, comparisons between relative residual compressive strength and residual compressive strength were made. Additionally, a new approach known as "temperature endurance" is used to express the total area under each strength curve. Furthermore, the specimens were analysed using a scanning electron microscope. Our research has shown that perlite, when employed as additional cementitious material, performs remarkably well and has favourable effects, even at high temperatures. Up to 600 °C, it has the longest-lasting, practically constant residual strength values. In this area, the relative strength reductions are less than 15%. Furthermore, it is shown that boron carbide increases compressive strength at 900 °C in comparison to values at 600 °C. Due to the material's low melting point and the formation of secondary bindings at the highest heat step, this effect results. The other materials under investigation, such as powdered quartz, magnetite, and powdered chamotte, perform only slightly better than the reference homogeneous Ordinary Portland Cement, particularly in the mid and high heat ranges. In low heat ranges and by lower addition of fines, particularly in the well-known local strength maximum of 200–300 °C, homogeneous matrixes perform better.

Analysis of the Relationship between Mechanical Properties and Pore Structure of MSW Incineration Bottom Ash Fine Aggregate Concrete after Freeze-Thaw Cycles Based on the Gray Theory

The destruction of concrete building materials in severely cold regions of the north is more severely affected by freeze-thaw cycles, and the relationship between the mechanical properties and pore structure of concrete with fine aggregate from municipal solid waste (MSW) incineration bottom ash after freeze-thaw cycles is analyzed under the degree of freeze-thaw hazard variation. In this paper, the gray correlation method is used to calculate the correlation between the relative dynamic elastic modulus, compressive strength, and microscopic porosity parameters to speculate on the most important factors affecting their changes. The GM (1,1) model was established based on the compressive strength of the waste incineration ash aggregate concrete, the relative error between the simulated and actual values in the model was less than 5%, and the accuracy of the model was level 1, indicating that the GM (1,1) model can well reflect the change in the compressive strength of the MSW incineration bottom ash aggregate concrete during freeze-thaw cycles. Using the gray correlation method, the correlation between the relative dynamic elastic modulus, compressive strength, air content, specific surface area, pore spacing coefficient, and pore average chord length was calculated, and the pore spacing coefficient and pore average chord length were determined to be highly correlated with each other. This determination can help analyze and infer the deterioration mechanism of concrete subject to freeze-thaw cycles. These results can provide a theoretical basis for guiding the engineering practice of concrete with fine aggregates of household bottom ash in the northern cold region.

Fracture behavior of dredged sand concrete under freeze–thaw cycles

In order to investigate the frost resistance and fracture behaviors of dredged sand concrete, three kinds of concrete with different dredged sand contents (0%, 25%, and 50%) by weight were designed and subjected to different freeze–thaw cycles (0, 25, 50, 75 and 100). Three-point bending fracture tests were performed on the frozen concrete specimens combined with acoustic emission (AE) technique. The results show that the mass loss of dredged sand concrete increases, the relative dynamic elastic modulus and compressive strength decreases with the increase of the freeze–thaw cycles. With the increase of dredged sand content, the pore structure is improved, so the fracture behavior and frost resistance of concrete are improved. With the increase of the dredged sand content of concrete, the fractal dimension of the fracture surface decreases. With the increase of the freeze–thaw cycles, the fractal dimension of the fracture surface increases, and the fracture surface is rougher. The higher the freeze–thaw cycles, the lower the peak load, fracture toughness and fracture energy of dredged sand concrete. The higher the content of dredged sand, the greater the fracture energy of dredged sand concrete. The accumulate AE counts, AE energy and AE b-value can reflect three-stage failure process of dredged sand concrete. The damage model of dredged sand concrete established based on the AE events obeys Weibull distribution, which can reflect the effect of freeze–thaw cycles on damage.

Effect of cooling methods on the residual properties of concrete exposed to elevated temperature

One of the most damaging effects a building may suffer is a fire. Structures may be exposed to temperatures of more than 1000 °C while the fire is burning. In the course of and after the fire, structural concrete loses its rigidity and strength. The concrete's residual strength qualities may also be significantly influenced by the cooling phase's speed and cooling medium. In an attempt to compare the impact of various cooling regimes on concrete, an investigation has been made. The effects of adding polypropylene fibres and air entrainment admixtures were examined in addition to studies on traditional concrete. The water-cement ratio, cement mass and type, and aggregate type were all the same throughout the test. After cooling down from five distinct heat stages ranging from 150 to 900 °C, samples were compared to their unheated counterparts' results. Five distinct approaches, including slow cooling, forced air cooling, cooling with water mist, quenching, and the “normal” cooling under laboratory conditions, were used to study the cooling effects. The study aimed to examine integrated temperature endurance numbers, relative residual compressive strength values, and residual compressive strength values in addition to visual observation. Regulations were matched with the outcomes. The findings demonstrated that, up to 600 °C, there were no appreciable changes in the residual properties between the various cooling methods or between the different mediums with virtually the same cooling pace. The apparent disintegration of water-cooled samples was evident after cooling from 900 °C.

The Effect of Elevated Temperature on Ordinary Portland Cements

A study was directed to analyze the influence of the different types of Ordinary Portland Cements (OPC) on the hardened cement paste exposed to high temperatures. Hardened cement paste specimens with three types of cement and nine water-cement ratios were investigated and heated to 11 heat steps at 28 days of age. Residual compressive strength and relative residual compressive strength were compared to the unheated results. It was shown that the expected range for the relative residual strength of the different types of OPC up to 400 °C is between 90 and 100%. From the local minimum at 150 °C to the maximum at 300 °C. The CEM I 52.5 type of cement shows the least favorable behavior to the increased (over 400 °C) temperature, according to the results of the residual compressive strengths curves and the newly introduced Integrated Temperature Endurance values after the first water-cement ratio (0.3). Nine water-cement ratios were tested with the favorable types of OPC (CEM I 42.5 and CEM I 32.5). At all water-cement ratios, the residual strength tendencies for the two types of cement were parallel. It has been observed that changes in the water-cement ratio have little to no impact on the relative strength curve's shape or the relationship between strength and the water cement ratio. As a result of our experiments applying simply Ordinary Portland Cement, it is obvious that the CEM I 32.5 type of OPC cement significantly outperformed the CEM I 42.5 type in regards of post-heating strength tendencies.

Biocementation of coral sand under seawater environment and an improved three-stage biogrouting approach

The Sporosarcina pasteurii (S. pasteurii)-DSM 33 was acclimated to grow and secrete urease under different salinity level conditions via direct evolution method, and ultimately the new acclimated species, S. pasteurii-DSM 33-ASW100, was of higher cell growth rate and ureolysis activity under seawater environment. Meanwhile, this study further revealed a fact that high concentration of calcium chloride (>0.25 mol/L) would inhibit the existing urease activity but hardly affect the urease secretion function of S. pasteurii-DSM 33-ASW100. The rising of urea concentration would not mitigate the inhibitory effect of calcium chloride on urease activity; by contrast, it could stimulate S. pasteurii-DSM 33-ASW100 to secrete more urease, ultimately conducting the microbially induced carbonate precipitation (MICP) reaction under a higher pH level (∼8.0). In the seawater environment, the optimal coral sand particle size for MICP reaction was about 0.5–1.0 mm. Moreover, the new designed three-stage biogrouting method significantly mitigate the issue of non-uniform distribution of cells and crystals in the column, thereby greatly increasing the unconfined compressive strength of MICP-treated coral sand column (>9.0 MPa) with a relatively high CaCO3 content (∼32 % by weight) as well as calcium ion utilization rate (∼85 %). Results also indicated that excessive input of CaCl2 (>0.5 mol/L) may result in less uniformity of crystallization and thus lead to a relative lower unconfined compressive strength (∼4.0 MPa). Excessive addition of urea (>1.0 mol/L) may lead to partial clogging issues due to too fast reaction of MICP, consequently column strength dropping down to around 2.0 MPa.