•Examination of different Mg2+ concentrations in 0.5M Ca(CH3COO)2/urea cementation solution.•Aragonite crystals were precipitated under the involvement of carboxyl groups.•0.01 M Mg2+ can bring about ...40-percentage promotion in UCS of a bio-cemented sample.•Mg2+ can promote aragonite precipitation while inhibit calcite crystallization.
This study examines the magnesium ions effect on carbonate crystal polymorph when Ca(CH3COO)2/urea acts as cementation solution in microbially induced carbonate precipitation (MICP) process. The results of unconfined compressive strength (UCS) indicates that the involvement of Mg ions in Ca(CH3COO)2/urea cementation solution can greatly improve the physical and engineering properties of bio-cemented samples. Compared with the bio-cemented sample without any Mg ions, additional 0.01 M Mg ions in 0.5 M Ca(CH3COO)2/urea solution will contribute to 40% higher UCS, and additional 0.5 M Mg ions in 0.5 M Ca(CH3COO)2/urea solution will make the average UCS twofold higher. While, UCS of the samples treated with MgCl2/urea with poor crystallinity magnesium carbonate is one-tenth of that treated with 0.5 M Ca(CH3COO)2/urea. Furthermore, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) images show that acicular aragonite and rhombohedral calcite are two main types of calcium carbonate crystal precipitated when Ca(CH3COO)2/urea acts as the cementation solution, and the incorporation of Mg ions modifies the crystal polymorph, promoting more aragonite precipitation but inhibiting calcite growth. The mechanism of magnesium ions effect on crystal polymorph is also summarized in the end. The efficiency of Ca(CH3COO)2/urea with a small amount of Mg ions is particularly noteworthy in MICP process.
•Full-scale TRT and TPT of CFG pile exchangers are performed.•Heat exchange capacity of CFG energy piles is estimated from different power TRT.•Effects of inlet water temperature and flow velocity on ...TPT are studied.•Heat exchange of CFG energy piles varies with different operation modes.•Temperature influence radius of a single CFG pile exchanger is over 4m.
Pile geothermal exchangers are a popular new type of geothermal exchanger for use in ground source heat pump systems due to their technical and cost improvements over traditional borehole geothermal exchangers. An in-situ full-scale study using the thermal response and thermal performance tests (TRT and TPT) is performed to investigate the heat exchange capacity of the cement-fly ash-gravel (CFG) piles usually used in foundations for low to medium high-rise buildings in Beijing. This paper analyzes the influences of the hydration heat of cement, heating power, inlet water temperature, circulating water flow velocity, operation mode, and group-pile effects on the heat exchange capacity of CFG pile geothermal exchangers. The test results can be used for the thermal design of CFG energy piles.
Granite residual soil is widely distributed in the southern coastal areas of China, and the slopes of granite residual soil are prone to instability and failure under the alternating action of ...rainfall and drying, which will cause great disasters to human society. In order to study the response mechanism of granite residual soil slopes under the alternating action of rainfall–drying–static–rainfall (RDSR), this study conducted indoor scaling model tests to analyze the response during dry and wet cycles. This study presented the response process of the slope under the influence of dry and wet cycles and discussed the change laws of slope deformation, water content, and matric suction. The results show that, under the alternating action of rainfall–drying–static–rainfall, 1) the network cracks on the slope form a dominant channel for rainwater seepage, which is the main reason for the rapid decline in soil anti-sliding ability within a short time; 2) at a rainfall intensity of 1.7–2.4 mm/min, the erosion effect of rain on the slope is obviously stronger than that of osmotic erosion, and the surface erosion failure of the granite residual soil slope tends to occur without an obvious sliding surface; 3) after the loss of matric suction over a certain period, the phenomenon of channeling and loss failure on the slope serve as a sufficient condition for slope instability failure but is not a necessary condition. The above research results are expected to provide the basis and reference for preventing and controlling landslide hazards in granite residual soil slopes under similar conditions.
Microorganisms can mediate the formation of minerals by a biomineralization process. This offers an efficient way to sequester inorganic pollutants, including heavy metals within relatively stable ...solid phases, and the main mechanisms involved in mineral precipitation by microorganisms were investigated in this study. Biomineralization of nickel, copper, lead, cobalt, zinc and cadmium, by six metal-resistant bacterial strains, were investigated using microcosm experiments. These bacteria were isolated from nursery garden soil and characterized for their potential application in bioremediation. These bacteria produced the enzyme urease which can hydrolyze urea. Due to this enzymatic reaction, soil pH increased and carbonate was produced, which results in mineralization of the soluble heavy metal ions present in soil water and their ultimate conversion to carbonates. The selected bacteria showed high removal rates, ranging from 88% to 99% of heavy metals following incubation for 48 h. Scanning electron microscopy and X-ray diffraction analyses revealed that bioaccumulated heavy metals ions were deposited around the cell envelope as rhombohedral, sphere and needle shaped crystalline carbonate minerals when the pH was 8–9. This study demonstrated that indigenous bacteria can survive heavy metal toxicity from soil and wastewater and sequester soluble heavy metals into biominerals and these bacteria can play important role in heavy metal bioremediation.
The analytical solution for temperature distribution in an aquifer was derived from Lauwerier’s plane-symmetric model (J. Appl. Sc. Res., A5(2–3):145–150,
1955
). A deficiency of this solution is ...that it does not consider the effect of heat conduction in the aquifer. Six years later, an analytical solution that considered the effect of heat conduction under adiabatic conditions was presented by Ogata and Banks (US Geol. Survey,
1961
). Closed form solutions for the plane-symmetric model of heat transport during steady-state flow that considered both heat conduction and heat convection were provided by Barends (SPE Annual Technical Conference and Exhibition, Florence,
2010
). The distinctions between these solutions are discussed in this paper. Barends’ solution is more complete than those offered in previous studies. But it could be readily used for engineering applications as long as users can evaluate numerically or analytically the integrals involved in this solution. This paper introduces a plane-symmetric model under Cauchy’s boundary condition that considers heat conduction and convection. The Laplace transform technique is applied to obtain the solution for this model, and two important parameters (the Peclet number and the convective heat transfer coefficient) are discussed in detail. The result of this simplified solution agrees well with that of the numerical solutions (Ansys and Comsol).
Bio-stimulated sealing technology is an interesting and promising technology for leakage repair in geotechnical engineering. Advancing studies of this technology have shown that some nutrients can be ...used to activate the metabolic process of
in-situ
soil microorganisms that induce bio-mediated sealing in a relatively short time. In this paper, we injected nutrient solution into sand columns with leakage and investigated the sealing mechanism. Two sand columns, each with a 2-cm diameter hole, were set up. One was treated with nutrient solution and the other received no nutrients as a control. The results showed that 900 mL of nutrient solution per day, with a concentration of 4.4 g L
−1
potato extract solution, could notably decrease the volume of groundwater seepage. Finally, the volume of the seepage in the treated column was 0.85% of the control column. Evidence of micro morphological changes to the sand samples after the bio-stimulated sealing tests is given using the ESEM observations. Chemical element composition, organic and iron compound analyses were performed for an enhanced understanding of the underlying bio-stimulated sealing mechanism. The preliminary results obtained indicate that iron compound deposits, and organics (biomass and biofilm) produced during the sealing process near the leakage enhanced the sealing effect.
•Full-scale field tests are used to study thermo-mechanical behavior of CFG energy piles.•Heat extraction or sink induces thermal tensile or compressive stress in pile shaft, respectively.•Energy ...pile head settles or heaves slightly during one cycle of heating and cooling process.•Heated energy piles possess unchanged bearing capacity.•Cooled energy piles possess slightly decreased bearing capacity.
Energy piles have gradually emerged as a new application of ground source heat pump systems due to the heat exchange efficiency per unit length, excellent heat conductivity and low construction cost. Full-scale field tests are carried out to study the thermo-mechanical behavior of “Cement Fly-ash Gravel (CFG) piles”, a popular ground improvement technology in China. These piles are actually constructed by continuous flight auger (CFA) with the cement, fly ash, gravel, etc., being the constituents of the concrete used to form the pile shaft. The displacement of the pile head is measured, thermal stress due to temperature change of the pile is calculated and the changing laws of the stress/strain and temperature profiles along the depth of the pile under thermal loads and constant mechanical loads applied on pile head are analyzed. An ultimate bearing capacity test of a single CFG pile/soil composite foundation is carried out to investigate the effects of the heating–cooling exchange process on the bearing capacity of CFG energy piles. Systematic tests are implemented to study the mechanical responses of CFG energy piles and the effects of thermal stress on the mechanical behavior of the piles, which will benefit the design and application of CFG energy piles.
Due to environmental and sustainable concerns, the green bio-cementation technique has received growing attentions from both the academic world and engineering field. One of its essential ...applications is ground improvement, since the precipitated CaCO3 crystals in bio-cementation process could act as the solid bridges to cement separated particles together and enhance the mechanical behaviors of soils. Although researchers have realized the significance of the precipitated CaCO3 bondings and microstructures of bio-cemented materials, only few studies focus on improving the bio-cementation efficiency from a microscopic perspective. Consequently, in this paper, an integrative review is adopted to collect, review, and analyze the published studies and literature, indicating that the CaCO3 cementation pattern and crystal polymorph are the two principal aspects that reflect the bio-cementation efficiency to a certain extent. Subsequently, the major factors affecting the CaCO3 cementation pattern and crystal polymorph are comprehensively discussed. In a nutshell, the conducted discussions in this paper attempt to provide noteworthy insights into bio-cementation improvement, which may potentially inspire future studies.
In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground ...and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.
Background. To evaluate ibuprofen and acetaminophen in the treatment of infectious fever in children. Methods. We searched randomized controlled trials and retrospective cohort studies comparing ...ibuprofen and acetaminophen in the treatment of infectious fever among children. Data were extracted from eligible studies. We sought to evaluate temperature after taking drugs in 1, 2, and 4 hours, respectively, and analyzed the adverse events. Results were expressed as mean difference(MD) and risk ratio (RR) with 95% confidence intervals. Results. Ten studies were included in this study with a total of 1773 patients. The results showed that acetaminophen had higher temperature than ibuprofen after 1 hour (The overall mean difference was −0.29 with 95% CI (−0.49, −0.09). The P value of the overall effect was = 0.004, I2 = 91%), 2 hours (MD = −0.46, 95% CI (−0.67, −0.25), P < 0.00001, I2 = 95%), and 4 hours (MD = -0.57, 95% CI (−0.82, −0.33), P < 0.00001, I2 = 97%). There is no difference between two drugs in the adverse events (RR = 0.8, 95% CI (0.52, 1.24), P = 0.32, I2 = 0%). The sensitivity analysis and funnel plot showed that our study was robust and had low publication bias. Conclusion. Our study suggested that ibuprofen is more effective than acetaminophen in children with infectious fever.
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