Cementation Solution Research Articles

Prospects for using amorphous ferromagnetic alloy microwire for reinforcement of cement mortar

Traditionally, fibers for fiber-reinforced concrete are made of metal, polypropylene, basalt or glass. На сегодняшний день для строительства актуально использование волокон с уникальными электрофизическими свойствами. The possibilities of using a microwire made of an amorphous ferromagnetic alloy based on cobalt with a shell of borosilicate glass in concrete technologies are studied in this paper. The influence of the content of fibers of different sizes (length 7 and 15 mm) on the rheological and physico-mechanical properties of the solution was established. The deterioration of the workability of mixtures and the average density of the composite with the introduction of the studied fiber is shown. It has been established that the spread diameter of the mortar mixture with a fiber content of 0.5...3.0 % by weight of Portland cement is reduced by 9.8...26.1% compared to the control composition. It is shown that the short fiber (7 mm) at the maximum content (3 %) leads to a more significant decrease in the average density (up to 9.6 %) compared to the long fiber (15 mm) of the same concentration (reduction is no more than 4 %). A positive effect on the flexural strength and crack resistance of the solution was established. The increment of flexural and compressive strength ranges from 1.11 to 1.54 and from 0.99 to 0.78 respectively with increasing fiber concentration. The presence of fiber in the composition of the solution allows you to increase the crack resistance from 0.098 to 0.164. The increase in the crack resistance coefficient for compositions with a fiber 7 mm long is 51...68 % and compositions with a fiber 15 mm long is 22...37 %. The possibility of using such microwire based on a ferromagnetic alloy for dispersed reinforcement of cement solutions opens up prospects for the creation of “smart” materials.

ЗАСТОСУВАННЯ ДРІБНОДИСПЕРСНИХ ВІДХОДІВ КАМЕНЕОБРОБНИХ ПІДПРИЄМСТВ В ЯКОСТІ НАПОВНЮВАЧІВ БУДІВЕЛЬНИХ РОЗЧИНІВ

Purpose. Based on the study of the chemical and mineralogical composition of rocks, which are raw materials of stone processing enterprises, it is necessary to consider the feasibility of using finely dispersed waste of stone processing enterprises in the composition of concrete materials and products as a fine filler. Methodology. A conclusion, based on of a generalized analysis of the chemical and mineralogical composition of the rocks processed at the enterprises for the production of stone facing products, has been made about the expected composition of the pulp and its suitability for use in cement mortars. The limit of compressive strength of samples with different percentages of replacement of construction sand with waste from stone-working enterprises has been determined experimentally. Results. The analysis of the chemical and mineral composition of natural facing stone confirms the chemical inertness of finely dispersed waste from stone processing enterprises and the possibility of their use as a filler for cement solutions and concrete. On the basis of the results obtained in the course of experimental studies, a conclusion has been made about the increase in the strength limit of concrete samples with partial replacement of construction sand in the concrete recipe. An increase in the density of the obtained samples has also been observed Scientific novelty. The dependence of the content of fine-dispersed waste from stone-working enterprises processing natural stone from gabbro, granite, and labradorite deposits on the compressive strength limit of concrete samples, with their partial replacement of building sand in the concrete recipe, has been investigated. Practical significance. The ability to add fine-dispersed waste from stone-working enterprises to the composition of concrete when they replace construction sand has been proven. It makes it possible to develop a practical algorithm for using these wastes as secondary raw materials and save extractable natural resources.

Experimental Investigation on the Effect of Using Different Calcium Sources with Biogrouting on the Improvement of Poorly Graded Fine Sand

In light of the cities' growth, it has now become necessary to establish infrastructure in areas that were previously deemed inappropriate.To improve the engineering characteristics of these problematic lands, many methods have been applied. Recently, an innovative and sustainable technique called Microbial Induced Calcite Precipitation has emerged for soil improvement. Many factors that affect the efficiency of this technique include the concentrations of bacteria solution, the concentrations, and the type of the chemical solutions, in addition to methods to introduce the bacteria and these chemical solutions to the soil, pH, etc.The objective of this study is to evaluate the performance of the Microbial Induced Calcite Precipitation as a technique to improve and enhance the very fine poorly graded sandy soils and expand knowledge about improving a loos sand by using the MICP technique. Furthermore, this study was carried out using six types of calcium sources in the cementation solution, two concentrations of cementation solution as well as two types of soils. This study shows that the use of low concentrations provides a greater improvement in the engineering properties of the treated soil. The pH values were not greatly affected by soil type or the type of cementation chemical solutions and their concentration. The samples with axial splitting had a lower unconfined compressive strength than that shown by the samples with shear fracture.

Laboratory Experiment on Formation of MICP Horizontal Seepage-Reducing Body in Confined Aquifer for Deep Excavation

Using a soil improvement biotechnology based on microbial-induced carbonate precipitation (MICP) to form a horizontal water barrier in foundation pit dewatering can not only achieve a good dewatering control effect, but also control the cost and obtain good economic and environmental benefits. In this study, taking the Shanghai layer ⑨ sand as the research object, the solution injected into the layer ⑨ sand by MICP grouting technology includes bacterial solution (Sporosarcina pasteurii) and cementation solution (urea and CaCl2 solution). The migration mechanism of the bacterial solution and cementation solution in groundwater was analyzed through batch experiment and column test, and the mathematical model of migration was established. The dynamic adsorption characteristics of the S. pasteurii, Ca2+, and urea were obtained by dynamic adsorption test. Through isothermal adsorption test, the Freundlich isotherm was used to describe the isothermal adsorption of S. pasteurii onto fine sand, and the partition coefficient of the S. pasteurii was found to be 1.5 × 10−7 L/mg. The Langmuir isotherm can be used truly reflect the isothermal adsorption of Ca2+ onto fine sand. The distribution coefficient of the Ca2+ was 7 × 10−8 L/mg. The maximum adsorption capacity of the solute was 2404.8 mg/kg. The adsorption capacity of the urea was very small. According to the sand column test, the vertical dispersion was 11.5 cm. Due to the obvious size effect of dispersion, the sensitivity of dispersion in actual working conditions should be analyzed in a subsequent numerical simulation. The determined solute transport parameters provide support for the further study of the numerical simulation of the solute transport process of the HSRB formed by MICP grouting technology and provide a basis for further field application.

Reinforcement of reclaimed sand by stimulating native microorganisms for biomineralization.

The method of biological stimulation to reinforce soil has good environmental benefits. The optimization of stimulation solutions can not only improve soil reinforcement but also effectively reduce treatment costs. Response surface methodology was used to optimize a biostimulation solution to reinforce reclaimed sand by native microorganism-induced mineralization. First, response surface methodology was used to obtain the optimal stimulation solution. Then, the effect of the optimal stimulation solution in inducing mineralization to reinforce reclaimed sand was evaluated. Finally, the reinforcement mechanism was revealed by SEM, XRD, and microbial diversity analysis. The results showed that the urease activity of the sample optimized by response surface methodology was 1.17 times higher than that of the sample treated with the initial stimulation solution. The uniaxial compressive strength of samples treated with the optimal biostimulation solution and 1.0 M cementation solution over 15 cycles reached 3.94 MPa. The product of microbial mineralization was calcite, which was the main substance responsible for the improvement in the mechanical properties of the reclaimed sand. The concentration of the cementation solution not only affected the production of calcium carbonate but also affected the morphology of calcium carbonate crystals. After sample treatment with the stimulation solution, ureolytic microorganisms became the dominant bacteria in the sample. A comprehensive assessment of the reinforcement effect and cost revealed that using the optimal stimulation solution and 1.0 M cementation solution over 10 cycles was ideal for reinforcing reclaimed sand. Biostimulation is an effective method to reinforce reclaimed sand; however, the actual application effect requires further examination.

Experimental study on the calcium carbonate production rates and crystal size of EICP under multi-factor coupling

The production and microstructure of calcium carbonate are the fundamental indicators to evaluate the effectiveness of Enzyme-induced Carbonate Precipitation (EICP). Soybean urease is extracted, and the urease activity is controlled by the soybean powder concentration in this study. The urease reacts with the cementation solution with different concentrations of urea and calcium ions at different temperatures to determine the calcium carbonate production rates (RCC). The crystal sizes of calcium carbonate (SCC) are investigated by scanning electron microscopy (SEM) and image processing method. The RCC increase and subsequently decrease with increasing calcium ion concentration and peak at 0.75 M. A lower urea concentration is more favourable to the formation of CaCO3. Increased urease activity and temperature will lead to an increased RCC and SCC. Some crystals appear as capsules when the temperature goes up. The SCC decreases slightly with increasing calcium ion concentration under low urease activity and increases under high urease activity. The SCC increases first and subsequently decreases with increasing urea concentration under high urease activity, while the effect of urea concentration under low urease activity is not significant. XRD test results show that the calcium carbonate produced in this study is dominated by calcite crystals. The study provides additional data, a useful base to move forward toward a better understanding of the method of stabilization and its applications, for example, the treatment of different soils.

Influence of injection methods on calcareous sand cementation by EICP technique

Calcareous sands are widely distributed on continental shelves, coastal zones, islands and reefs in the tropical oceans. For being used as construction materials, calcareous sands should be artificially treated to improve their engineering properties. Enzymatically induced carbonate precipitation (EICP) is an innovative soil treatment technique. In this paper, urease was extracted from soybean powder using artificial seawater for calcareous sands cementing by the EICP technique. Cementation tests were conducted with three injection methods (the pre-mixed, staged and proposed parallel injections) and two injection rates (2 and 5 mL/min). The hydraulic conductivity, shear wave velocity (SWV) and unconfined compressive strength tests were conducted and the cementation effects were evaluated. The hydrodynamic diameter of the particles generated in the mixed solutions was measured with reaction time by a laser particle size analyzer and the influence of injection rate on the CaCO3 distribution in the specimen was discussed. The coefficient of variation of the SWV values along the cemented specimen height was calculated for evaluation of the cementation uniformity. Results show that a high injection rate was conducive to reducing clogging and improving the cementation uniformity by completing injection within the urea hydrolysis phase. The promising parallel injection method proposed in this study provided a lag time for reaction by simultaneous injection of crude urease and cementation solutions using two separate tubes. Specimens treated at a high parallel injection rate were uniformly cemented with high mechanical strengths and high overall hydraulic conductivities because of a high proportion of CaCO3 in contact-cementing distribution.

Microfluidic study in a meter-long reactive path reveals how the medium’s structural heterogeneity shapes MICP-induced biocementation

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is one of the major sustainable alternatives to the artificial cementation of granular media. MICP consists of injecting the soil with bacterial- and calcium-rich solutions sequentially to form calcite bonds among the soil particles that improve the strength and stiffness of soils. The performance of MICP is governed by the underlying microscale processes of bacterial growth, reactive transport of solutes, reaction rates, crystal nucleation and growth. However, the impact of pore-scale heterogeneity on these processes during MICP is not well understood. This paper sheds light on the effect of pore-scale heterogeneity on the spatiotemporal evolution of MICP, overall chemical reaction efficiency and permeability evolution by combining two meter-long microfluidic devices of identical dimensions and porosity with homogeneous and heterogeneous porous networks and real-time monitoring. The two chips received, in triplicate, MICP treatment with an imposed flow and the same initial conditions, while the inlet and outlet pressures were periodically monitored. This paper proposes a comprehensive workflow destined to detect bacteria and crystals from time-lapse microscopy data at multiple positions along a microfluidic replica of porous media treated with MICP. CaCO3 crystals were formed 1 h after the introduction of the cementation solution (CS), and crystal growth was completed 12 h later. The average crystal growth rate was overall higher in the heterogeneous porous medium, while it became slower after the first 3 h of cementation injection. It was found that the average chemical reaction efficiency presented a peak of 34% at the middle of the chip and remained above 20% before the last 90 mm of the reactive path for the heterogeneous porous network. The homogeneous porous medium presented an overall lower average reaction efficiency, which peaked at 27% 420 mm downstream of the inlet and remained lower than 12% for the rest of the microfluidic channel. These different trends of chemical efficiency in the two networks are due to a higher number of crystals of higher average diameter in the heterogeneous medium than in the homogeneous porous medium. In the interval between 480 and 900 mm, the number of crystals in the heterogeneous porous medium is more than double the number of crystals in the homogeneous porous medium. The average diameters of the crystals were 23–46 μm in the heterogeneous porous medium, compared to 17–40 μm in the homogeneous porous medium across the whole chip. The permeability of the heterogeneous porous medium was more affected than that of the homogeneous system, while the pressure sensors effectively captured a higher decrease in the permeability during the first two hours when crystals were formed and a less prominent decrease during the subsequent seeded growth of the existing crystals, as well as the nucleation and growth of new crystals.

Effect of Fines Content in Silt-Sand Mixtures with Different Saturations on Microbial-Induced Calcium Carbonate Precipitation

In general, soil in its natural state is not geotechnically suitable to achieve the intended engineering objectives. Therefore, refining them to improve their mechanical properties is essential. In recent years, soil improvement based on microbial-induced calcium carbonate precipitation has been proposed as a new branch in geotechnical engineering, also referred to as the green method. In this method, via nonpathogenic microorganisms capable of producing urease enzyme, a calcium carbonate precipitate bond is formed by the carbonate ion and its bond with the calcium ion. This causes the soil particles to adhere. In this study, using Sporosarcina pasteurii with high urea enzyme activity and a suitable cementation solution, the formation of calcium carbonate precipitate in three types of sand with different percentages of silt and with different degrees of saturation was investigated, and a uniaxial compressive strength test was conducted. The results indicated that the highest compressive strength was obtained with a 10% increase in the fines content with a degree of saturation of 20%. Moreover, as the fine content and degree of saturation increased, the compressive strength decreased despite forming a high percentage of calcium carbonate precipitate. The results also presented here indicate that the effect of MICP on silty sands depends on degree saturation, fine content and the fabric governing the soil structure. The findings also demonstrated that in low fines content, calcium carbonate bio-deposition could be utilized to improve soil parameters owing to their economical nature.

Study on the Solidification Effect of Dredger Fill by Microbial-Induced Calcium Precipitation (MICP).

This paper puts forward a new soft soil reinforcement technology-microbial-induced calcite precipitation (MICP) technology-which considers the problem of dredger fill soft-soil reinforcement in Dalian Taiping Bay. In this paper, the calcium carbonate content (CCC) and unconfined compressive strength (UCS) of microbial solidified dredger fill (MSDF) samples were determined using laboratory experiments. The microstructure and chemical composition of MSDF samples were studied by SEM-EDS and XRD. The failure and reinforcement mechanism of MSDF under different experimental conditions (ambient temperature, cementation solution concentration, and clay content) were investigated. The results showed that there was a certain residual strength after the peak strength of MSDF. With the increase of ambient temperature, the number of microorganisms increased, but the activities of urease, CCC, and UCS decreased. The UCS and CCC increased with the increase of cementation solution concentration, while they first increased and then decreased with the increase of clay content. The clay content enhanced the compactness of MSDF samples but reduced the soil permeability and weakened the mineralization. There were significant differences in the morphology of microbial-induced precipitation caused by different concentrations of cementation solution.

Soil stabilization for dunes fixation using microbially induced calcium carbonate precipitation

Climate change and desertification caused increases in sandstorms and sand movements due to the erosive force of the wind. Wind erosion is a phenomenon depending on the climatic components and surface roughness in arid and semi-arid regions responsible for health and economic loss. The phenomenon is controlled by increasing the resistance of soils using chemical, physical and biological methods. Due to the high cost and environmental issues of conventional techniques, the use of alternative green stabilization methods is inevitable. Therefore, in the present study, the effect of microbially induced calcium carbonate precipitation (MICP) on the fixation of in situ dunes in north-east of Iran was assessed. The cementation solution of 0.1–0.5 M was sprayed and evaluated after 7, 15, and 30 days. The MICP treated samples were exposed to wind tunnel for the variation of wind threshold detachment velocity (TDV) as well as other macro/micro evaluation such as unconfined compressive strength, seed germination, scanning electron microscope (SEM), and energy-dispersive X-ray spectroscope (EDX). The results suggested the critical impact of both geotechnical and geoenvironmental parameters for the selection of soil stabilizers on the fixation of dunes. It can be stated that the bio-crust formation with 0.3 M showed 123 kPa and no wind erosion potential after 30 days under the wind speed of 30 m/s. The results of the germination of H. persicum demonstrated that the contemporaneous of MICP treatment with native plants positively affect the TDV.

An experimental investigation of wind erosion resistance of desert sand cemented by soybean-urease induced carbonate precipitation

This study experimentally investigated the efficiency of soybean urease-induced carbonate precipitation (SICP) cemented desert sand in resisting wind-blown sand erosion. A suite of wind-blown sand tests was conducted on desert sand at various controlling factors, including the soybean-urease solution (SUS) concentration, cementation solution (CS) concentration, the volume of SICP solution, and the treatment cycles. The wind-blown sand was simulated by introducing a certain amount of impacting particles to the wind flow at a velocity varying from 5 m/s to 15 m/s. The erosion rate, along with penetration resistance and CaCO3 content, were evaluated and correlated with the threshold detachment velocity (TDV). Results indicated that the SICP treatment could effectively reduce the wind-induced erosion potential of desert sand, as the erosion rate of the SICP-treated soil was significantly decreased under the coupled effects of wind shear force and the impacting particles. An optimum SICP recipe is obtained to treat the sand by spraying two cycles of SICP solution at 4 L/m2 containing 40 g/L soybean urease solution and 1 mol/L cementation solution (urea - calcium chloride).

Experimental Study on the Influence of Different Factors on the Mechanical Properties of a Soil-Rock Mixture Solidified by Micro-Organisms.

In this paper, we focus on the application of mechanical properties in a soil–rock mixture modified by microbial mineralization under the influence of different factors, including pH value, cementing solution concentration, and cementing time. Cementing fluids and samples with different pH values, calcium ion concentrations, and mineralization cementation were prepared. The process of urea hydrolysis MICP under different factors was studied. A solidified soil–rock mixture sample under triaxial compression was measured. Then, combined with scanning test methods, such as SEM and XRD, the influence of different factors on the mechanical strength and failure mode of the soil–rock mixture structure was analyzed from a microscopic point of view. The results show that a low concentration of cementing solution with a high concentration of bacteria liquid generated the highest calcium carbonate content and the strongest cementing ability. When the pH value of the cementation solution is six, the cementation effect between the pores is the best, and the deviatoric stress is stronger. When wet-curing samples, short or long curing time will adversely affect the strength of soil–rock mixture samples, the strongest curing and cementing ability is 5 days. The microscopic results show that the microbial mineralization technology fills the pores between the particles, and the interaction force between particles is enhanced to enhance the strength of the soil–rock mixture.

Experimental study on mitigating wind erosion of calcareous desert sand using spray method for microbially induced calcium carbonate precipitation

Wind erosion is one of the significant natural calamities worldwide, which degrades around one-third of global land. The eroded and suspended soil particles in the environment may cause health hazards, i.e. allergies and respiratory diseases, due to the presence of harmful contaminants, bacteria, and pollens. The present study evaluates the feasibility of microbially induced calcium carbonate precipitation (MICP) technique to mitigate wind-induced erosion of calcareous desert sand (Thar desert of Rajasthan province in India). The temperature during biotreatment was kept at 36 °C to stimulate the average temperature of the Thar desert. The spray method was used for bioaugmentation of Sporosarcina ( S. ) pasteurii and further treatment using chemical solutions. The chemical solution of 0.25 pore volume was sprayed continuously up to 5 d, 10 d, 15 d, and 20 d, using two different concentration ratios of urea and calcium chloride dihydrate viz 2:1 and 1:1. The biotreated samples were subjected to erosion testing (in the wind tunnel) at different wind speeds of 10 m/s, 20 m/s, and 30 m/s. The unconfined compressive strength of the biocemented crust was measured using a pocket penetrometer. The variation in calcite precipitation and microstructure (including the presence of crystalline minerals) of untreated as well as biotreated sand samples were determined through calcimeter, scanning electron microscope (SEM), and energy-dispersive X-ray spectroscope (EDX). The results demonstrated that the erosion of untreated sand increases with an increase in wind speeds. When compared to untreated sand, a lower erosion was observed in all biocemented sand samples, irrespective of treatment condition and wind speed. It was observed that the sample treated with 1:1 cementation solution for up to 5 d, was found to effectively resist erosion at a wind speed of 10 m/s. Moreover, a significant erosion resistance was ascertained in 15 d and 20 d treated samples at higher wind speeds. The calcite content percentage, thickness of crust, bulk density, and surface strength of biocemented sand were enhanced with the increase in treatment duration. The 1:1 concentration ratio of cementation solution was found effective in improving crust thickness and surface strength as compared to 2:1 concentration ratio of cementation solution. The calcite crystals formation was observed in SEM analysis and calcium peaks were observed in EDX analysis for biotreated sand.

Recycling of dredged river silt reinforced by an eco-friendly technology as microbial induced calcium carbonate precipitation (MICP)

A large amount of river silt is continuously dredged and usually dumped in landfills or oceans, resulting in land occupation and environmental pollution. Traditionally, cement-based materials are used to cement dredged river silt as building materials, which not only increases carbon dioxide emissions but also uses very little dredged silt. In order to realize the resource utilization of dredged river silt, microbial induced calcium carbonate precipitation (MICP) technology, which has the advantages of lower energy consumption, less environmental pollution and lower carbon emissions, is adopted to solidify the dredged river silt as roadbed materials in this paper. The unconfined compressive strength (UCS) test, calcium carbonate (CaCO3) content test and microstructure test are carried out to analyze the mechanical properties of the solidified dredged river silt. The test results show that the MICP mixing method can be employed to solidify loose dredged river silt into high-strength construction materials. The concentration of the cementation solution has a significant effect on the solidification effect, and the most reasonable concentration of the cementation solution is 1.5 mol/L. With the increase of treatment times, the pores in the soil are filled with CaCO3, and the UCS of the specimens after 10 times of treatment can reach 6.75 MPa with a relatively uniform CaCO3 content of 27.8 %. The main crystal form of CaCO3 is calcite, which can fill the pores and make the river silt particles cement as a whole, which is the main reason for the improvement of mechanical properties of dredged river silt.

COMPARATIVE ANALYSIS OF THE USE OF EXPANSION AGENTS IN REPAIR SOLUTIONS OF DRY BUILDING MIXTURES FOR IMPROVING HARDENING CONDITIONS

The article examines the possibility of increasing the compatibility of repair solutions based on dry mixes with damaged concrete and reinforced concrete structures by improving the curing conditions of such materials through comparative analysis of adhesive strength and linear shrinkage of cement samples using different types of superabsorbents, namely SAP Newsorb based on sodium polyacrylates from the Japanese manufacturer Newstone, Chinese MNC-SAP based on potassium polyacrylates from MUHU Construction Materials and AquaGel based on cross-linked copolymer of acrylamide and potassium acrylate from the Australian Baroid. The data obtained during experimental studies show that the use of investigated SAP superabsorbents additives due to the improvement of hydration conditions in the cement matrix of the repair material can partially compensate the growth of shrinkage deformations, which, in turn, slightly improves the indicators of the adhesive strength of the bond with the surface of the damaged structure. A positive effect of the use of the specified polymer admixtures on the investigated cement solutions was established. Compared to the base sample, on average, for each of the studied days of hardening, the shrinkage rate of all samples containing SAP was reduced by 35%, which justifies their use in order to facilitate the creation and further high-quality functioning of the repair system. The addition of the studied SAPs allows to improve the adhesion index by 1.5-2.3 times compared to the basic one, which should ensure the maximum ability of the repaired system to perceive the workload. The optimal contents of SAP additives in the composition of the studied cement mortars to reduce shrinkage and increase the adhesive strength were determined. The compositions of non-structural repair cement mortars of class RM3 and R1-R2 in terms of adhesive strength and classes RM1-RM2 in terms of shrinkage deformation in accordance with Ukrainian and European standards were obtained.

Incorporation of Mixing Microbial Induced Calcite Precipitation (MICP) with Pretreatment Procedure for Road Soil Subgrade Stabilization.

Microbial induced carbonate precipitation (MICP) provides an alternative method to stabilize the soil. To further improve the reinforcement effect, this study aims to propose a strategy by incorporating the mixing MICP method with pretreatment procedure. A series of laboratory tests were performed to investigate the preparation parameters (including the moisture content and dry density of the soil, the concentration of urea and CaCl2 in cementation solution), the engineering properties, the CaCO3 distribution as well as the mineralogical and micro structural characteristics of pretreatment-mixing MICP reinforced soil (PMMRS). Based on the orthogonal experiment results, the optimum preparation parameters for PMMRS were determined. The UCS of PMMRS was more strongly dependent on the moisture content and concentration of CaCl2 than the concentration ratio of CaCl2 to urea. Moreover, it was testified that incorporation of pretreatment procedure improved the stabilization effect of traditional mixing MICP method on the clayed sand (CLS). The UCS of PMMRS specimen was increased by 198% and 78% for the pure CLS and the simple mixing MICP reinforced soil, respectively. Furthermore, the CaCO3 products generated consisted of the aragonite, calcite and vaterite, which distributed unevenly inside the specimen no matter the lateral or vertical direction. The reason for the uneven distribution might be that oxygen content varied with the regions in different directions, and hence affected the mineralization reaction. In addition, the mineralization reaction would affect the pore structure of the soil, which was highly related to the stabilization effect of MICP reinforced soil.

Valorization of tannery solid wastes for sustainable enzyme induced carbonate precipitation process

Biocementation via enzyme induced carbonate precipitation (EICP) is an emerging ground improvement technique that utilizes urease for calcium carbonate precipitation. Usage of expensive laboratory grade chemicals in EICP hinders its implementation at field level applications. In this study, the feasibility of utilizing solid wastes generated from leather industry was investigated for EICP process. Initially, the proteinaceous fleshing waste was used as nitrogen source for production of an extracellular urease from Arthrobacter creatinolyticus MTCC 5604 followed by its subsequent use in EICP with suspended solids of tannery lime liquor, as alternative calcium source. The calcium ion solution was prepared by treating suspended solids of lime liquor with 1 N HCl. The EICP was optimum with 1000 U of urease, 1.0 M urea and 1.0 M CaCl2.2H2O for test tube experiments. Sand solidification experiments under optimal conditions with five times addition of cementation solution yielded a maximum unconfined compressive strength (UCS) of 810 kPa with laboratory grade CaCl2.2H2O and 780 kPa with calcium from lime liquor. The crystalline phases and morphology of the CaCO3 precipitate were analyzed by XRD, FTIR and SEM-EDX. The results showed the formation of more stable calcite in EICP with calcium obtained from lime liquor, while calcite and vaterite polymorphs were obtained with CaCl2.2H2O. Utilization of fleshing waste and lime liquor in EICP could reduce the pollution load and sludge formation that are generated during the pre-tanning operations of leather manufacturing. The results indicated the viability of process to achieve cost effective and sustainable biocementation for large scale applications.

Pilot-scale feasibility study for the stabilization of coal tailings via microbially induced calcite precipitation

Sustainable long-term solutions to managing tailings storage facilities (TSFs) are integral for mines to operate in a safe and environmentally responsible manner. The long-term storage of subaqueous tailings can pose significant safety, environmental, and economic risks; therefore, alternative containment strategies for maintaining geochemical stability of reactive materials must be explored. In this study, the physical and geochemical stabilization of coal tailings using microbially induced calcite precipitation (MICP) was evaluated at a laboratory pilot scale. Three application techniques simulated commonly used agricultural approaches and equipment that could be deployed for field-scale treatment: spraying on treatment solutions with irrigation sprinklers, mixing tailings and treatment solutions with a rototiller, and distributing treatment solutions via shallow trenches using an excavator ripper. Test cells containing 1.0 × 1.0 × 0.5 m of tailings were treated with ureolytic bacteria (Sporosarcina pasteurii) and cementation solutions composed of urea and calcium chloride for 28 days. Penetrometer tests were performed following incubation to evaluate the extent of cementation. The spray-on application method showed the greatest strength improvement, with in an increase in surface strength of more than 50% for the 28-day testing period. The distribution of treatment solution using trenches was found to be less effective and resulted in greater variability in particle size distribution of treated tailings and would not be recommended for use in the field. The use of rototilling equipment provided a homogenous distribution of treatment solution; however, the disruption to the tailings material was less effective for facilitating effective cementation. Bacterial plate counts of soil samples indicated that S. pasteurii cultures remained viable in a tailings environment for 28 days at 18 °C and near-neutral pH. The treatment was also found to stabilize the pH of tailings porewater sampled over the 28-day incubation period, suggesting the potential for the treatment to provide short-term geochemical stability under unsaturated conditions.

Research on the Hydration and Mechanical Properties of NAC-Hardened Cement under Various Activation Methods

Adding mineral admixture is one of the leading technical ways to improve the durability of cement-based materials. Nano attapulgite clay (NAC) is a unique fiber rod crystal structure that can change the physical and mechanical properties of cement-based materials, and opens up a new idea for exploring the durability of high-performance cement-based materials. This paper studied the effects of NAC on the hydration process, pore structure, and mechanical properties of a cement substrate under different activation methods. The results show that the pH value of the pore solution of cement mixed with 5% NAC high-viscosity ore (calcined) was 8.8% higher than that of the cement without NAC. The chemically bound water contents in the 1% and 3% NAC raw (calcined) cement were 14.11% and 14.04%; when the content of calcined NAC raw ore was 1%, the improvement effect on the cement hydration process is the best. The content of calcined NAC was 1%, 3%, and 5%, and the porosity of hardened cement paste was 19%, 19.04%, and 22.27% lower than that of the cement without NAC. Calcining NAC raw ore can improve cement’s hydration process, promote cement’s hydration reaction, and increase the compactness of hardened cement paste. The fluidity of the cement mortar mixed with calcined high-viscosity ore (D and E) at a mixing amount of 5% was reduced by 32.66% and 26.13%, respectively, compared to the ordinary specimens. The flexural strength of the cement paste mixed with calcined raw ore and high-viscosity ore at a mixing amount of 1% was generally improved by 28.40% and 17.28% compared to the cement without NAC paste. After calcination, the NAC raw ore is better than the high-clay ore in improving the mechanical properties of cement.