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Seawater based bio-cementation through microbially-induced carbonate precipitation was proposed for the calcareous sand improvement in marine environment. The method used seawater instead of traditional fresh water to culture urease producing-bacteria (UPB) and prepare cementation solution (CS) for the bio-cement. A series of comparative bio-treatment tests using seawater based bio-cementation and traditional bio-cementation methods on three types of soil were conducted. Experimental results indicate that seawater based bio-cementation method has the ability to improve soil physico-mechanical properties, and performed better than traditional bio-cementation method. The dominant reason can be explained as that the mixture of the productions of calcite, monohydrocalcite and calcite magnesium produced during seawater based bio-cementation process have better cementation ability than the mixture of the productions of calcite and vaterite produced during bio-cementation process. UCS of coarse Ottawa sand blocks are smaller than that of medium Ottawa sand blocks is because the specific surface area of fine sand is higher and larger number of effective bondings can be formed. UCS of calcareous sand blocks are smaller than those of coarse Ottawa sand blocks can be attributed to the fact that calcareous sand has higher porosity and rougher surface, resulting in more carbonate crystals being precipitated on un-connected locations. [ABSTRACT FROM AUTHOR]

Earthen sites (i.e., ancient earthen buildings) with important historical, cultural, artistic, social, and scientific value have been seriously damaged. Soil treatment with chemical additives can decrease the degradation rate of earthen sites. In the past, polyvinyl alcohol (PVA) and quicklime as chemical additives were studied separately for the protection of earthen sites. In arid and semi-arid northwest China, the early strength of the lime-treated soil may be insufficient due to an inappropriate reaction environment, and the PVA as the additive can quickly increase the soil strength. However, calcium carbonate has been proven to not be decomposed for hundreds of years, while there is still a lack of experimental evidence to show that the PVA cannot be decomposed in decades. The PVA and lime as the additives show the potential to make up for the defects each other. Therefore, the physical and mechanical properties of the PVA and lime composite soil are analysed, and the microscopic properties of the composite soil are discussed in this study. The results show that the addition of the PVA decreases water vapour permeability and pore size, which causes a delay in the carbonization reaction of lime, but it acts as a cementing agent to improve soil strength before the lime appropriately reacts. The addition of quicklime can decrease the hydrophobicity of the PVA-treated soil. The mixing of these two materials is conducive to the colour control of the sample. For the composite soil applied to earthen sites in northwest China, the optimal ratio is 10% lime and 1.0% PVA. [ABSTRACT FROM AUTHOR]

• The biocementation waste solution containing ammonium ions that can be converted into struvite for cementing sand columns. • Chemical components and microstructure of the resulting cementation are analyzed through XRD patterns and SEM images. • The cementation properties of the sand columns are determined for both bio-struvite and composite biocementation. • A comprehensive analysis of the biomineralization and biocementation mechanisms is provided. Microbial-induced carbonate precipitation (MICP) cementation of sand results in the generation of waste liquid containing ammonium ions, posing environmental pollution concerns that necessitate appropriate treatment prior to discharge. To address this issue, the addition of hydrogen phosphate (HPO 4 2−) and magnesium (Mg2+) ions to the biocementation waste solution (BWS) enables the efficient conversion of ammonium (NH 4 +) ions into environmentally friendly bio-struvite (Cell-MgNH 4 PO 4 (H 2 O) 6 , MgNH 4 PO 4 ·6H 2 O or NH 4 MgPO 4 ·6H 2 O) through microbial-induced struvite precipitation (MISP), thereby mitigating environmental pollution risks. X-ray diffraction (XRD) patterns confirm the presence of struvite minerals, while field emission scanning electron microscopy (FESEM) images reveal the blocky or irregular blocky structure of bio-struvite, with sizes ranging from 10 to 25 μm. The bio-struvite effectively fills the pores between sand particles, resulting in reduced permeability. Following 4 cementation levels, the permeability coefficient of the bio-struvite cemented sand column measures 5.04 × 10−3 cm/s, with a bio-struvite content of 5.12 % within the sand column. The principal chemical components of the cementitious materials in MICP and MISP composite cementation sand consist of struvite (MgNH 4 PO 4 (H 2 O) 6 , MgNH 4 PO 4 ·6H 2 O or NH 4 MgPO 4 ·6H 2 O) and calcium carbonate (CaCO 3), forming spherical or massive aggregates smaller than 10 μm. The most effective composite cementation sands exhibit an average permeability coefficient of 4.85 × 10−4 cm/s and an unconfined compressive strength (UCS) of 197.96 kPa. Consequently, MICP and MISP composite cementation sand significantly diminishes permeability and offers a viable solution for desert dust control. [ABSTRACT FROM AUTHOR]

Nickel ions in electroplating wastewater can be removed by the bio-mineralization method. Bacillus subtilis can produce alkaline phosphatase, which hydrolyzes organophosphate monoesters and produces phosphate ions. Fourier-transform infrared spectroscopy (FTIR) showed that the precipitated material contains phosphate ions. X-ray diffraction (XRD) showed that nickel ions in electroplating wastewater react with Bacillus subtilis and organophosphate monoesters to obtain nickel phosphate octahydrate (Ni 3 (PO 4) 2 ·8H 2 O). The removal efficiency of nickel ions could reach 76.41% with the optimum content of the organophosphate monoester (0.02 mol), Bacillus subtilis powder (2 g), pH (6), standing time (36 h), and reaction temperature (25 °C) in the medium solution (100 mL). The average particle size of Ni 3 (PO 4) 2 ·8H 2 O was 80.51 nm, which was calculated by the Scherrer formula. The Lorentz–Transmission Electron Microscope (L-TEM) further showed that Ni 3 (PO 4) 2 ·8H 2 O was composed of clusters of irregular nanoparticles, and the individual particle size was in the range of 40–90 nm. The TGA curve shows that the mass loss of crystal water was 25.45%, which was close to the theoretical total mass loss of 28.24% in bio-Ni 3 (PO 4) 2 ·8H 2 O. Image 1063 • Nickel ions in electroplating wastewater can be removed by the Bacillus subtilis mineralization method. • The optimum removal conditions of the nickel ions were determined by the bio-mineralization experiment. • Chemical composition and microstructure of the bio-nickel phosphate were analyzed. [ABSTRACT FROM AUTHOR]

Highlights • Ammonia gas can be converted into bio-magnesium ammonium phosphate in cementation process. • Loose desert sand particles can be cemented by the bio-magnesium ammonium phosphate cement. • Micro-structure of the bio-sandstones has been studied. Abstract Loose desert sand grains can be cemented through the microbially-induced magnesium ammonium phosphate sediment into sandstone. Ammonia and ammonium were produced by Sporosarcina-Pasteurii hydrolyzing urea and effectively became environmentally friendly magnesium ammonium phosphate in the presence of HPO 4 2− ions (hydrogen phosphate). This a new kind of the bio-cement based on Sporosarcina-Pasteurii , and the bio-phosphate mineral has cementation. The chemical components of the bio-sandstone were mainly MgNH 4 PO 4 (H 2 O) 6 (struvite) and quartz, as discovered through X-ray diffraction (XRD) analysis. The internal micro-structure of the desert sand was observed by scanning electron microscopy (SEM), and its morphology was of irregular spheres with a size in the range of 100–300 µm. SEM images of the bio-sandstones showed the morphology of the cementation products as irregular flakes. The average hardness of two bio-sandstones cemented by spraying 1 and 3 times with cementation solution was 4.4 and 12.3, respectively. The evolution law of the micro-structure for the bio-sandstone cemented by spraying 3 times with cementation solution was revealed by the X-ray computed tomography (XRCT) technique. Maximum defect volume and average porosity of the bio-sandstone was 134 mm3 and 18.39%, respectively. Interface binding forces between the bio-cement and smooth sheet glass (SiO 2) were determined with WS-2005 coating adhesion scratch tester, which was 3.69 ± 1.02 N. [ABSTRACT FROM AUTHOR]

Highlights • The bio-barium phosphate slurry could be applied to bind loose sandy soil grains. • Chemical composition and shape of bio-barium phosphate slurry were analyzed. • Dust grains could be consolidated by spraying bio-phosphate cement. Abstract Loose quartz sand grains can well be cemented by microbially-induced barium phosphate precipitation into a sand column. The bio-barium phosphate slurry was composed mainly of BaHPO 4 , and this was assessed through X-ray diffraction (XRD) analysis. The average compressive strength of sand columns increases with curing time, and increases when the content of bio-phosphate slurry is 20% and 30%wt. The results suggest the best curing time is 7 days, and the optimum content of bio-barium phosphate is 30%wt. Scanning electron microscopy (SEM) images of the sand columns showed the morphology of the cementation products is block, dumbbell-shaped, and spherical, and the products' particles can continue to grow in wet-dry circulation conditions. The sand columns (ϕ5 cm × 5 cm) could be cemented by bio-BaHPO 4 , and its average strength was 0.6 Mpa. The consolidation layer of dust grains was formed after spraying 1 time and 3 times of bio-BaHPO 4 cement, and wind erosion rate of dust was 5 g/m2/h and 0 g/m2/h, respectively. The mixture of NaBaPO 4 and Ba 5 (PO 4) 3 OH under different time was selected and applied to bind loose sand particles, results indicating it could not glue loose sand grains. [ABSTRACT FROM AUTHOR]

This paper intends to evaluate the influence of content of rice husk fiber and cementitious materials on mechanical properties and thermal conductivity of thermal insulation wallboards. Thermal insulation wallboard contained different mass of rice husk fiber was prepared when the weight of cement, fly ash, cellulose ether, naphthalene superplasticizer, and recycled concrete aggregates was equal. Scanning electron microscopy (SEM) shows the internal structure of the insulation wallboards is very dense. Compared to thermal conductivity of blank group (0.9600 W/m·°C), B2 (0.1997 W/m·°C) and C2 (0.1810 W/m·°C) measured by the DRCD-3030 intelligent thermal conductivity tester can meet certain engineering requirements. Average compressive strength, flexural strength, and thermal conductivity of wallboards decreases with content of rice husk fiber increasing when other materials mass are the same. Under the same conditions of curing time and rice husk content, average compressive and flexural strength increase with the increase of the amount of cementitious material. [ABSTRACT FROM AUTHOR]

Bio-cement, based on microbial-induced mineralization, can consolidate the loose particles and be applied to foundation reinforcement, dust control, desert settlement, repair cementitious materials crack, and other fields. In the paper, two kinds of bio-cement, such as bio-carbonate cement and bio-phosphate cement, were discussed as novel binders. The calcium carbonate (calcite), induced precipitation via Sporosarcina pasteurii, could cement between loose sandy soil particles. A series of sand-cemented experiments were conducted to confirm the cemented properties, and a numerical model based on the distribution of the concentration of Sporosarcina pasteurii was established to further analyze bio-grouting process. The evolution law of microstructure was revealed by X-ray computed tomography (X-CT) technique. The atomic binding energy of C-O bond in calcium carbonate, Si-O bond and Si in sand analysis showed that microbial-induced calcium carbonate interacted with surface of loose sand particles formed the intermolecular hydrogen bond. The other kind of bacteria (Bacillus subtilis) could hydrolyze organic phosphate monoester and released PO43-, which could react with different metal cations formed bio-phosphate minerals. The bio-phosphate cement can be used as treatment of sandy soil foundation, functional materials, remediation of heavy metals in contaminated soil, and so on. [ABSTRACT FROM AUTHOR]

• The biocement is prepared using steel slag acidification. • Calcium ions can be extracted from steel slag in the form of calcium acetate using plain vinegar. • Calcium acetate is a better agent to use than calcium chloride as it is efficient and chloride free. This paper presents a method to make biocement using steel slag and apply it for soil improvement. Steel slag contains calcium which can be converted into calcium chloride or calcium acetate using ammonium chloride or plain vinegar. Calcium chloride or calcium acetate so produced can be used for biocementation via microbially induced carbonate precipitation (MICP). The concentration of calcium ions extracted using plain vinegar is higher than that using ammonium chloride. The cementation effect for sand using calcium acetate is better than or as good as that using calcium chloride in both one-phase and two-phase treatment methods. The crystal types of calcium carbonate in the biocemented sand using calcium acetate are mainly calcite and vaterite. The study in this paper shows that the biocement produced using steel slag has two main advantages: 1) it is more cost-effective and sustainable as steel slag as a waste material is used; 2) it is chloride free and thus can be used in many cases where the conventional cementation method is not applicable such as in the present of reinforced concrete. [ABSTRACT FROM AUTHOR]

Using bio-composite cement, loose sand particles can be aggregated into bio-sandstone with good mechanical strength. The average compressive strength, hydraulic conductivity, and porosity of bio-sandstone made with 6 injections of bio-composite cement were 1.33 MPa, 2.03 × 10 −2  cm/s, and 25.15%, respectively. The ingredients of the bio-sandstone, as determined through X-ray diffraction (XRD) analysis, were mainly quartz sand, MgNH 4 PO 4 (H 2 O) 6 , and Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O. Scanning electron microscopy (SEM) images of the bio-sandstone showed that the cementation products have an irregular flake morphology. The maximum defect volume of the bio-sandstone creating using 2, 4, and 6 injections of bio-composite cement was 1401 mm 3 , 930 mm 3 , and 738 mm 3 , respectively. The internal microstructure of quartz sand, as observed by SEM, was found to be irregular spheres of 100–300 µm. The wind erosion rate of bio-sandstone created by spraying bio-composite cement on quartz sand 1 or 3 times was 0 g/m 2 /h, after 1 h of wind erosion. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD) analysis was carried out on a new kind of bio-cement based on phosphate-mineralized microbes to confirm the composition of phosphate products, i.e. Ca 10 (PO 4 ) 6 (OH) 2 and BaHPO 4 . Meanwhile, the bio-cement was researched in terms of the cementation interface. The results show that the interfacial bonding strength of bio-phosphate cement is lower than bio-calcite cement in the scratch experiment. The microstructure between calcite and loose sand particles was analyzed by X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR). The results of XPS and NMR analysis confirm that the microbially-induced precipitation of minerals in loose sand particles means they interact with other particles to generate bonding effects, which plays a role in the binding function between loose sand particles and bio-cement. [ABSTRACT FROM AUTHOR]

This paper reports a mixture based on the calcium carbide sludge (CCS) activation of fly ash. The formed calcium silicate hydrate (C–S–H) gel binds sands and gravel particles to synthesize pozzolanic-lime mortars and concretes. In both seawater and tap water, Ca(CO 3), Ca(OH) 2 , and C–S–H were the main phases of hydration, as determined by powder X-ray diffraction. The optimal mixture was obtained using a CCS to FA ratio of 0.8 and curing time of 14 d. The surface morphology of spherical FA in the tap water mixed pozzolanic-lime materials had relatively loose rod-like, flower-like, and block structures, which were different from the irregular and dense block structure in the seawater mixed pozzolanic-lime mixture. For the fiber-reinforced mortar, the optimal content of polypropylene fiber was 0.1%. The surfaces of the fiber reinforced pozzolanic-lime mortars prepared using seawater were more compact than those prepared using tap and distilled water. The strengths of the fiber-reinforced specimens soaked in both seawater and tap water were maintained after 14, 28, 60, 90, and 120 d. The water permeability of pozzolanic-lime mixture with cracks was effectively reduced by spraying a seawater-mixed bioslurry cement. This work demonstrates the potential of a seawater-mixed pozzolanic-lime mortar as an offshore road base material and a bioslurry cement as its crack repairing material. • The optimal ratio of pozzolanic-lime mortars modified by PP fibers has been determined. • Softening coefficients of mortars are determined by soaking test. • Cracks of fly ash-lime mixture can be repaired by spraying seawater-based bioslurry cements. • The seawater-based pozzolanic-lime mortars and bioslurry cements are low-carbon emission in the production process. • The chemical component of bioslurry cements is mainly the mixture of calcium carbonate and calcite magnesian. [ABSTRACT FROM AUTHOR]

Microbial-induced struvite precipitation (MISP) is a new biocementation method for soil improvement and hydraulic permeability reduction. Compared with traditional microbial-induced carbonate precipitation (MICP), MISP can significantly reduce the production of harmful ammonium ions during biochemical reactions and convert ammonium ions into struvite with promising mechanical strength. In this study, a series of experiments were conducted to compare the performance of the MICP and the MISP processes on sandy soils. Results showed that the average content of calcium carbonate in MISP cemented sand columns after 3 times of injection is similar to that in MICP cemented sand columns after 9 times of injection. The hydraulic permeability of MISP cemented sand columns after 3 times of injection is an order of magnitude lower than that of MICP cemented sand columns after 9 times of injection. To further investigate the physicochemical interactions during MISP and MICP processes, a one-dimensional finite element code considering the chemical reactions and the solute transportation was proposed. Results show that most of the MISP were formed in the early 3 h of the 6 h injection cycle, whereas most of the MICP were formed in the last 5 h of the injection cycle. The simulated total mass of the MISP precipitation, 11.3 g, was close to the experimental result of 9.6 g. The spatial distribution of MISP is more uneven as compared to MICP, as a result of the much faster reaction rate of struvite than calcium carbonate. The findings suggested that MISP could partially replace MICP in the applications of leakage mitigation and reinforcement of sandy soils. • MISP and MICP biocementation methods are experimentally and numerically compared. • MISP method convert harmful ammonium ions into struvite with mechanical strength. • MISP method can replace MICP method in leakage mitigation and reinforcement of sandy soils. • Most of the MISP were formed in the early 3 h of the injection cycle. • Spatial distribution of precipitations of MISP is more uneven than MICP. [ABSTRACT FROM AUTHOR]

Loose sand particles could be cemented by the microbial induced phosphate and carbonate precipitation into a bio-sandstone with a certain mechanical strength when the Sporosarcina pasteurii contained K 2 HPO 4 ·3H 2 O and the mixture solution of urea and MgCl 2 in the 1:1 of volume ratio were injected by a peristaltic pump into quartz sand mold. The result shows that loose quartz sand particles are well cemented into a bio-sandstone, and the compressive strength of bio-sandstones is greater than 1.0 MPa. Ammonia/ammonium was produced during the hydrolysis of the urea and could be effectively become into environment-friendly struvite in the cementation process. In addition, the ingredients of the bio-sandstones were mainly quartz sand, struvite and hydromagnesite through XRD analysis. The internal microstructure of bio-sandstone was observed by SEM and the bio-phosphate and carbonate composite cement between sand particles indicated the shape was mainly irregular particles. The solidified layer of the surface of dust and sand particles was formed after spray bio-phosphate and carbonate composite cement, and wind erosion rate of dust and sand is 0 g/m 2 /h and 0 g/m 2 /h, respectively. [ABSTRACT FROM AUTHOR]

Nano-sized CePO 4 @NaCe(SO 4 ) 2 (H 2 O) and CePO 4 with hexagonal phase have been prepared by simply varying the reactant P/Ce molar ratio in bacterial liquid. The phase composition of two samples was checked via Fourier transform infrared spectroscopy (FTIR), energy dispersive analysis of X-rays (EDS) and X-ray diffraction (XRD) analyses, displaying the presence of CePO 4 @NaCe(SO 4 ) 2 (H 2 O) and CePO 4 with average crystallite size are 32.34 and 15.61 nm, respectively. The scanning electron microscopy (SEM) images show that nano-clusters and sphere-like in shape with a narrow diameter distribution were observed in two samples. The transmission electron microscopy (TEM) photographs further indicate obtained CePO 4 @NaCe(SO 4 ) 2 (H 2 O) and CePO 4 nanoparticles correspond to nanosheets and nanorods, respectively. The emission spectra of CePO 4 @NaCe(SO 4 ) 2 (H 2 O) and CePO 4 display a broad band of 300–380 nm range with the strongest emission at 342 nm in the violet region. [ABSTRACT FROM AUTHOR]

Loose sand particles can be cemented by the microbial inducing the slurry of barium hydrogen phosphate precipitation into a bio-sandstone with certain mechanical strength, which is a new technique to bound loose sand particles with biological phosphates. This paper confirms the feasibility of biological phosphates binding loose sand particles and presents results from laboratory researches on the influence of standing time and content of the slurry on the mechanical properties of sandstone biological phosphates bound. The results show that standing time and content of the slurry have a strong influence on the mechanical properties of bio-sandstone. The best standing time, which is 24 h, of the slurry mixing with quartz sand and obtained higher compressive strength of sand column (bio-sandstone) than three other standing times. The maximum compressive strength of bio-sandstone is 2.1 MPa when the content of the slurry reaches 50% with 24 h standing time. In addition, the ingredients of the slurry and bio-sandstone are mainly hydrogen phosphate barium through XRD analysis. The corresponding variation of porous characteristics of sand column is observed by scanning electron microscope (SEM) and indicated that the cementitious materials between quartz sand are mainly irregular sphere clusters in shape. The technique can be used in other fields: including dust-fixing, foundation reinforcement, slope and so on. [ABSTRACT FROM AUTHOR]

• Sand blocks can be cemented by seawater based MICP. • The urease activity in the seawater based UPB was measured. • Building materials can be prepared by the seawater based MICP. • One/two-phase seawater based MICP was compared. • Biocementation sand blocks of mechanism was analyzed and discussed. The Sporosarcina pasteurii strains can grow and multiply in seawater medium and have certain urease activity. The two-phase and one-phase cementation methods can be used for the construction of ocean islands and reefs far away from the mainland in seawater seawater based MICP (Microbial-Induced Carbonate Precipitation). The compressive strength, carbonates content and porosity of sand blocks cemented by seawater based MICP with two-phase and one-phase methods are measured and compared. The results show that the strength and carbonates content of sand blocks with two-phase biocementation are greater than that of one-phase. The SEM images show that the principle of seawater based MICP cementing loose sand blocks is that carbonates particles grow between the sand particles, and them act as a bridge to bind the loose sand particles into a whole. The seawater based UPB of different pH can induce calcium carbonate deposition at different time. The seawater based UPB of different pH can be selected according to the actual project to reinforce the island reef sand foundation and prepare building materials under one-phase biocementation. [ABSTRACT FROM AUTHOR]

Using mineral powder, fly ash and cement as the basic three-component composite system, machine-made sand and gravel powder and expansion agent are introduced to prepare five-component composite grouting materials. The water-binder ratio, stone powder content, the water glass modulus, the alkali content, the water-cement ratio, and machine-made sand and gravel powder content were studied for the physical and mechanical properties of alkali-activated multi-component composite grouting materials. The law of influencing factors and the optimal parameters of each factor were determined according to fluidity, setting time, compressive strength, and drying shrinkage. The optimal values of water glass modulus and alkali content are 1.0 and 6%, respectively. Increasing the water-binder ratio significantly improves fluidity, but results in a substantial delay in setting time and a decrease in strength. Therefore, it is not advisable to exceed a water-binder ratio of 0.6. Furthermore, the stone powder content should not surpass 10%. The hydration process of alkali-activated materials mainly includes crystallization nucleation and growth, phase boundary reaction and diffusion. Three types of expansion agents, CaO, MgO and SC (the mixture of calcium sulfoaluminate and calcium oxide), were selected, and four levels of 0%, 4%, 8%, and 12% were set, including a total of 9 mix ratios besides the benchmark group. The effects of expansion agents on the fluidity setting time, compressive strength and volume stability of composite grouting materials were discussed. The addition of an expansion agent proves effective in reducing drying shrinkage, with the sequence of effectiveness as follows: CaO expansion agent > MgO expansion agent > SC expansion agent. The optimal content of CaO expansion agent is found to be 8%, leading to a remarkable reduction in 28 d shrinkage. • A five-component composite grouting material was developed. • The fluidity, setting time, strength, and volume stability were studied. • The mechanism of action for stone powder was discussed and analyzed. • The composite grouting material was modified by the addition of expansion agents. • The factors affecting expansion agents for the composite grouting material have been discussed. [ABSTRACT FROM AUTHOR]

• Bio-phosphate minerals can be prepared by the MIPP, have cementation effect. • The bio-phosphate cement can consolidate the loose particles and heavy metals. • The bio-phosphate cement has important application prospect. The main mineralization process is hydrolysis of the organic phosphomonoester with the alkaline phosphatase produced by the Bacillus subtilis. The structural characterization of phosphate nanomaterials showed that the nanostructures of phosphate could be prepared by the microbial mineralization method. The nano-sized bio-BaHPO 4 and bio-BaNaPO 4, with an average size 100 nm, could be well synthesized in the supernatant liquid of the bacteria at the pH = 8 and 11, but the nano-sized bio-BaHPO 4 and bio-BaNaPO 4 were not prepared by the chemical method in the same conditions. The bio-Mg 3 (PO 4) 2 ·5H 2 O had a honeycomb-like structure, but the chem-Mg 3 (PO 4) 2 ·5H 2 O was irregular. The average particles size of the bio-Mg 3 (PO 4) 2 ·5H 2 O was less than the chem-Mg 3 (PO 4) 2 ·5H 2 O. The bio-Fe 3 (PO 4) 2 ·8H 2 O, bio-Ca 5 (PO 4) 3 (OH) and bio-CePO 4 could also be prepared by the microbial mineralization method, but the chem-Fe 3 (PO 4) 2 ·8H 2 O, chem-Ca 5 (PO 4) 3 (OH) and chem-CePO 4 could not be synthesized by a simple chemical reaction. Compared with the Sporosarcina pasteurii induced carbonate precipitation, the Bacillus subtilis induced the formation of phosphates that were more stable than carbonates in the weak acid environments. The Sporosarcina pasteurii induced carbonate precipitation produced a large amount of harmful ammonia, whereas the Bacillus subtilis induced the formation of phosphates that did not produce any harmful gases. According to the literature reported, the microbially-induced phosphate precipitation (MIPP) had the cementitious properties. The cementation mechanism was the bio-phosphates interact with pure quartz sand to form van der Waals bond in the sand columns. Therefore, the use of MIPP can not only apply to the preparation of functional materials, but also has potential applications in the removal of heavy metals, treatment of solid waste, consolidation of sandy soil, and so on. [ABSTRACT FROM AUTHOR]

Biocementation using a microbially-induced carbonate precipitation (MICP) process has become a new method for soil improvement. However, this method produces ammonia gas which is not desirable. A new biocementation method using a microbially-induced struvite precipitation (MISP) process is proposed in this paper. The main cementation components produced by this method are struvite and basic magnesium phosphate as identified using X-ray diffraction (XRD). This new method can reduce the amount of ammonia discharge by more than 8 times. Sand treated using this method can reach an unconfined compressive strength of more than 1.47 MPa after three rounds of treatments. • Ammonia can be much reduced using the proposed MISP method. • The optimum formulae for the MISP method has been established. • Using optimum formulae, the UC strength could reach 1.47 MPa. • The ammonia gas could be reduced to be below the tolerable limit. [ABSTRACT FROM AUTHOR]

As a new type of green cementitious materials, inorganic minerals synthesized by microbial-induced mineralization could cement loose sand particles. Their advantages included efficient preparation process, easy control and environmental friendliness, and accordingly they could be used in desert treatment, fugitive dust control, foundation reinforcement, and slope stability. This study identified microbial growth under different conditions and obtained effective methods for the promotion of microbial growth were obtained. The enzyme protein expression was identified using an electrophoretic and gel imaging system, and the results indicated that the main enzyme protein in the bacterial solution was carbonic anhydrase. By means of X ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis, it was concluded that mineralization products were near-spherical calcite with particle sizes of approximately 5 μm. The microstructure between the mineralization products and loose sand particles was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the difference of cementing effect between different methods was determined. The feasibility of cementing sand by microbial-induced mineralization was demonstrated. Based on the analysis of interaction between the mineralization products and loose sand particles by fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR), it was found that the essential reason for cementing loose sand particles was the formation of intermolecular hydrogen bonds. Therefore, this study identified the mechanism of microbial-induced mineralization as the basis for the optimization and regulation of the whole process of mineralization and cementation. In this study, characteristics of the mineralization product and hydrogen bonding mechanism were investigated systematically. Carbon dioxide was used as a carbon source to synthesize mineralization products, and greenhouse gas was effectively utilized without toxic and harmful by-products. The research provided new ecological materials and technologies for environmental governance, which was expected to attract considerable attention. [ABSTRACT FROM AUTHOR]

• Evaluation of spore germination was investigated by the absorbance difference. • The effect of heat shock, germination agent and nutriment on spore germination was optimized. • Effect of spore dosage on microstructure and mechanical properties was determined. Microbial cementitious material, as a new type of green environmental protection cementitious material, was getting more and more attention. In this paper, improving the consolidation properties of microbial cementitious material by promoting spore germination ratio was studied systematically. Evaluation of spore germination was investigated by the absorbance difference between spores and vegetative bodies, and the relationship between absorbance of microbial solution and spore germination ratio was determined. The effect of heat shock, germination agent and nutriment on spore germination was optimized. The results displayed that the suitable heat shock temperature was 70 °C for 10 min, and the optimum germination agent was alanine with 6 mmol/l of concentration, while nutrient could not effectively improve the spore germination ratio. Effect of spore dosage on microstructure and mechanical properties of consolidation sand were also determined. Compared with the control group, consolidation properties of microbial cementitious material with 2.5 g of spores was better, and that with 2.0 g of spores was basically consistent. The results demonstrated that the spore dosage could be reduced after improving the spore germination, and the cost of microbial cementitious material was greatly declined. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) has been regarded as a promising cementitious material to consolidate loose sand and soils for ground improvement. The main adverse effect of the urease driven MICP is the ammonia emission during bio-cementation process, which poses negative impact on environment when large dose of ammonia has been released. In order to create environment-friendly bio-cement materials, this paper presents series of experiments to select the optimal formulation of a new bio-cement that can convert ammonia into cementitious materials. Based on previous research, carbonate-mineralization microbe (also named as Sporosarcina pasteurii) has been adopted as the carbonate-mineral microbe. The bio-magnesium phosphate cement is obtained by selecting an optimal formulation (molar ratio), which is bio-carbonate cement: MgCl 2 : K 2 HPO 4 ·3H 2 O = 1 : 2: 2. The ammonia fixation ratio achieved in solution test is up to 62.75%. This value increases to 75.12% when the formulation is applied to bind loose sand columns (sand column tests). For the purpose of increasing the ammonia fixation ratio, the effects of pH, temperature, dosage of additive ingredients, etc. have been investigated. In order to evaluate the performance of this formulation, the properties of sand column cemented by this formulation are studied by uniaxial compressive testing, micro-scale image analysis, chemical component analysis (X-ray diffraction, XRD), etc. Experimental results demonstrate that, the average permeability of the sand columns (3.97 × 10−2 cm/s, initially) is reduced to 2.37 × 10−2 cm/s and the achieved average uniaxial compressive strength of bio-sandstones is 1.43 MPa. SEM (Scanning electron microscope) images of sand column indicates that loose sand grains can well be filled through bio-magnesium phosphate cement. • Series of tests are presented to select the optimal formulation for a new bio-cement. • The optimal ammonia fixation ratio can be obtained through this optimal formulation. • The mechanical properties of bio-sandstone cemented by the formulation are studied. • Influence factors on fixation ration and mechanism of ammonia conversion are investigated. [ABSTRACT FROM AUTHOR]

Streptomyces-induced calcite precipitation (SICP) was used to bind loose dredger fill into soil columns. The composition, microstructure, strength, and permeability of the soil columns were studied. The X-ray diffraction (XRD) results show that the cementitious material of calcium carbonate was found in the soil columns. The morphology of the soil columns with and without streptomyces was the sheet and the block structure, respectively. The compressive strength of the soil columns was highest (2.29 MPa) when the content of streptomyces was 30%. The compressive strength of the soil columns with streptomyces was higher than other groups when the medium solution pH was 9, although the hydraulic conductivity of the soil columns containing streptomyces (15% of calcium oxide) was similar to those without. Under the optimal bacterial powder content of 30%, the average resulting content of calcium carbonate was 12.73% in the soil columns. Compared with microbially-induced carbonate precipitation (MICP), the SICP process did not release ammonia gas during biomineralization. Therefore, the SICP technique is environmentally friendly for the cementation process. [ABSTRACT FROM AUTHOR]

The removal efficiency of Cu(II) in aqueous solution by bentonite, graphene oxide (GO), and nanoscale iron decorated on bentonite (B-nZVI) and nanoscale iron decorated on bentonite/graphene oxide (GO-B-nZVI) was investigated. The results indicated that GO-B-nZVI had the best removal efficiency in different experimental environments (with time, pH, concentration of copper ions, and temperature). For 16 hours, the removal efficiency of copper ions was 82% in GO-B-nZVI, however, it was 71% in B-nZVI, 26% in bentonite, and 18% in GO. Bentonite, GO, B-nZVI, and GO-B-nZVI showed an increased removal efficiency of copper ions with the increase of pH under a certain pH range. The removal efficiency of copper ions by GO-B-nZVI first increased and then fluctuated slightly with the increase of temperature, while B-nZVI and bentonite increased and GO decreased slightly with the increase of temperature. Lorentz-Transmission Electron Microscope (TEM) images showed the nZVI particles of GO-B-nZVI dispersed evenly with diameters ranging from 10 to 86.93 nm. Scanning electron microscope (SEM) images indicated that the nanoscale iron particles were dispersed evenly on bentonite and GO with no obvious agglomeration. The qe,cal (73.37 mg·g−1 and 83.89 mg·g−1) was closer to the experimental value qe,exp according to the pseudo-second-order kinetic model. The qm of B-nZVI and GO-B-nZVI were 130.7 mg·g−1 and 184.5 mg·g−1 according to the Langmuir model. [ABSTRACT FROM AUTHOR]

• The hydration heat of cement paste mixed with MgAl-LDHs/TiO 2 composites was recorded. • The effect of MgAl-LDHs/TiO 2 on the interface transition zone of recycled aggregates was studied. • The photocatalytic activity of recycled aggregates loaded MgAl-LDHs/TiO 2 was evaluated. • The addition of MgAl-LDHs/TiO 2 can shorten the initial setting time and final setting time of cement pastes. • The total degradation efficiency of methylene blue could reach 82.2% in recycled aggregates loaded MgAl-LDHs/TiO 2. To study the effects of MgAl-LDHs/TiO 2 on the properties of cement paste and recycled aggregates, MgAl-LDO (MgAl-LDHs calcined products) and TiO 2 were mixed during the reconstruction of MgAl-LDHs laminates based on the memory effects of layered double hydroxides (LDHs), and then MgAl-LDHs/TiO 2 was synthesized. The performance changes were characterized with hydration heat tests, the microscopic morphologies of the hydration products, and the physical and mechanical properties of the cement paste. The effect of the MgAl-LDHs/TiO 2 on the multi-interfacial transition zone (ITZ, the interface between the old paste and new paste) of the recycled aggregates was characterised with the micromorphology, meso -mechanical properties, and element diffusion behaviour. The photocatalytic activity of MgAl-LDHs/TiO 2 loaded on recycled aggregate was evaluated with the degradation of methylene blue under sunlight. The results showed that the addition of MgAl-LDHs/TiO 2 promoted the initial hydration of ordinary Portland cement (OPC) and induced and promoted the growth and formation of crystalline cement hydration products. The initial setting time and final setting time were shortened, and the compressive strength of the hardened paste was improved when MgAl-LDHs/TiO 2 was added to the cement paste. The MgAl-LDHs/TiO 2 compacted the recycled aggregates and improved the structural properties of the ITZ. The MgAl-LDHs/TiO 2 altered diffusion within the ITZ. The total efficiency for the degradation of methylene blue by the 5–10 mm MgAl-LDHs/TiO 2 loaded on recycled aggregate reached 82.2% after 80 min under simulated sunlight. [ABSTRACT FROM AUTHOR]

In order to study the effects of exposure conditions (atmospheric, tidal and splash zones) on chloride ingress into concrete and time-dependent chloride diffusivity of concrete, the chloride concentration of existing concrete in the Beibu Gulf was tested by field investigation. In addition, a reasonable calculation model was chosen by comparative analysis to achieve an accurate corrosion initiation time of the tested concrete. The results indicate that splash zone affects the durability of concrete structures more harshly than tidal and atmospheric zones. The age factor, which represents the time-dependent properties of chloride diffusion coefficient, is a normally distributed random parameter. In atmospheric, tidal and splash zones, the mean value of the age factor equated to 0.19, 0.35 and 0.43, respectively. Compared with the Life 365 model and the LNEC E465 model, the DuraCrete 2000 model can better characterize the chloride transport in the tested concrete. Based on this model, given the target reliability index β d = 1.3–1.5, the corresponding corrosion initiation time is 42–47.5a. [ABSTRACT FROM AUTHOR]

As a renewable energy source, biomass has the potential to replace non-renewable, fossil fuels. However, the disposal of the waste biomass ash (generated during energy generation) needs to be studied. While prior studies attempted to utilise composite additives containing biomass ash for soil, the introduction of other additives, such as cement, was an environmental burden. By employing biomass ash composition as the sole additive for strengthening purple soil under various curing conditions using high-temperature treatment, this study maximised its utilisation. The results showed that the unconfined compressive strength (UCS) varied across different curing conditions as the biomass ash content increased. After high temperature treatment at 800 ℃, the biomass ash consistently reinforced purple soil under all the curing conditions. However, the biomass ash stabilisation mechanism differed between dry and humid curing conditions. Under dry curing conditions, the UCS increase depended on the cementing effect of soluble salt and/or insoluble calcite; under humid curing conditions, the UCS change was attributed to the damage to clay minerals, contact mode, and cementing effects of multiple components. Therefore, the 800 ℃ temperature-treated biomass ash can be used alone to reinforce purple soil, inhibiting the soil-water loss. This study presents a novel avenue for utilising waste, biomass ash, with considerable implications for environmental protection and soil stabilisation. • Purple soil can be reinforced by biomass ash treated at 800 ℃. • Curing condition has a significant impact on stabilising effect. • Stabilisation mechanisms differ between dry and humid curing conditions. • A novel avenue to utilize waste biomass ash is provided. [ABSTRACT FROM AUTHOR]

In recent years, the preparation of new microbial dust suppressants based on microbial induced carbonate precipitation (MICP) technology through enriched urease-producing microbial communities has become a new topic in the field of coal dust control. The deposition of CaCO 3 was the key to suppress coal dust. However, deposition characteristics in the field is not sufficient and the relationship between deposition characteristics and erosion resistance is not clear, which hinders the development of engineering application of new microbial dust suppressant. Therefore, based on X-CT technology, this paper observed and quantified micro-deposition of bio-consolidated coal dust with different calcium sources. Furthermore, a conceptual framework for deposition was proposed and its correlation with erosion resistance was revealed. The results showed that CaCO 3 induced by calcium chloride and calcium lactate was aggregate deposited. Aggregate deposited CaCO 3 was small in volume, showed the distribution of aggregation in the central area and loose outside, and mosaiced pores. CaCO 3 induced by calcium nitrate was surface deposition due to attached biomass. Surface deposition was mostly large volume CaCO 3 expanding from the inside out, which could cover coal dust to a high degree and completely cemented pores. In addition, the threshold detachment velocity of coal dust cemented by surface deposition was increased by 17.6–19.1% compared to aggregate deposition. This depended on the abundance and strength of CaCO 3 bonding between coal dust particles under different deposition. The two-factor model based on porosity and CaCO 3 coverage can well express relationship between erosion resistance and depositional characteristics. Those results will help the engineering application of MICP technology in coal dust suppression. • Different depositional property for different calcification condition. • Aggregate deposition formed "bridges" between particles. • Surface deposition formed calcite layer with a thickness of 6–7 μm. • Differences in deposition caused to 17.6–19.1% variation in TDV. [ABSTRACT FROM AUTHOR]

Abstract Bentonite, an important geotechnical material in the fields of environmental geotechnical engineering, can effectively adsorb harmful substances from the environment and fuel oil. This study investigated the formulation of sodium polyacrylate-modified bentonite that improves the permeant performance in the context of chemical resistance. The optimum material mix ratio and synthesis process were determined through multiple experiments. To better understand the sodium polyacrylate/bentonite interaction, the swelling index, filtrate loss, cation exchange capacity (CEC) and hydraulic conductivity performance in solutions of Pb(NO 3) 2 and acid were compared. The microstructures of raw bentonite and sodium polyacrylate bentonite were analyzed using scanning electron microscopy and infrared spectroscopy. The results showed that the microstructure of modified bentonite was characterized by isolated cavities, whereas the original configuration comprised a stacked layer, and the free swell index (FSI) increased from 25 to 50 mL/2 g. The modified bentonite showed a significant improvement in terms of chemical resistance through FSI testing and filtrate loss experiments, particularly in hydraulic conductivity tested in acidic and saline solutions. The permeability decreased by an order of magnitude through the modification process under the deionized water condition, and the chemical resistance increased to more than 40 mM in the Pb(NO 3) 2 solution. In addition, the CEC increased from 62.06 to 96.1 meq./100 g as a result of sodium polyacrylate modification. [ABSTRACT FROM AUTHOR]

Highlights • HAM has been applied to solve 1-D reactive transport equation. • General boundary conditions and smooth initial conditions are considered. • A convenient way is adopted to control and adjust the convergence of series solutions. • Approximate solutions produced by HAM agree well with exact solutions. Abstract The one-dimensional advective-dispersive-reactive transport equation has been widely applied to describe the transportation process of landfill leachate through liners or anti-seepage curtains. However, most existing methods solving this problem are limited to simple initial conditions. In order to eliminate these limitations, homotopy analysis method (HAM) is implemented to solve the contaminant transport model in this paper. Applying auxiliary linear and nonlinear operator, zero order deformation equation is developed to solve contaminant transport problems numerically, with smooth initial conditions and variable source concentration being considered. HAM has been applied to simulate different contamination transport problems in one-dimensional space reported in literature. Good agreement between HAM solutions and analytical solutions has been achieved for all cases considered, demonstrating the feasibility of HAM to solve the contaminant transport model with more general, smooth initial conditions. [ABSTRACT FROM AUTHOR]

A new chitosan-based fluorimetric "off-on" type adsorbent with excellent selectivity and sensitivity towards Hg (II) is prepared for mercury removal from aqueous solution due to photo-induced electron transfer. • The synthesized adsorbent RMC shows selective fluorimetric "off-on" response for Hg (II) in water. • The adsorption of Hg (II) with RMC could be easily detected by naked eyes with obvious colour variation. • RMC displays good sensitivity with detection limit of RMC towards Hg (II) as low as 8.24 × 10−7 M. • The adsorbent RMC shows highly selectivity with Hg (II) with barely interference with more than ten kinds of competitive metal ions. Rhodamine chromophore was introduced into a chitosan based adsorbent developing for Hg (II) detection and removal in aqueous solution. The adsorbent displayed highly sensitive and selective fluorimetric and colorimetric response to Hg (II) with barely interference with more than ten kinds of competitive metal ions. The adsorbent exhibited strong orange fluorescence emission while encountering Hg (II) with the colour turning to red immediately and could be easily detected by naked eyes. In addition, the detection limit of the adsorbent was calculated to be 8.24 × 10−7 M, and the adsorption capacity was as high as 139.08 mg/g according to the batch adsorption experiments. Furthermore, the interaction between adsorbent and Hg (II) was verified to fit well with Langmuir isotherm model and the pseudo-second-order kinetic model. Thermodynamic studies demonstrated that lower temperature was benefit for the adsorption. [ABSTRACT FROM AUTHOR]

For the purpose of investigating lining concrete durability, this study derives a modified chloride diffusion model for concrete based on the odd continuation of boundary conditions and Fourier transform. In order to achieve this, the linear stress distribution on a sectional structure is considered, detailed procedures and methods are presented for model verification and parametric analysis. Simulation results show that the chloride diffusion model can reflect the effects of linear stress distribution of the sectional structure on the chloride diffusivity with reliable accuracy. Along with the natural environmental characteristics of practical engineering structures, reference value ranges of model parameters are provided. Furthermore, a chloride diffusion model is extended for the consideration of multi-factor coupling of linear stress distribution, chloride concentration and diffusion time. Comparison between model simulation and typical current research results shows that the presented model can produce better considerations with a greater universality. [ABSTRACT FROM AUTHOR]