Water-saturated Conditions Research Articles

Interactions between C-steel and blended cement in concrete under radwaste repository conditions at 80 °C

Deep geological repository is widely considered as the preferred solution for the final disposal of high-level radioactive waste. Investigation representative of the Hungarian disposal concept was conducted using mock-up diffusion cells to study the chemical changes of S235JR carbon steel canister and CEM II/B concrete of the Public Limited Company for Radioactive Waste Management under anerobic and water saturated conditions at 80 °C. Micro-Raman, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy, fluid and potentiometric analysis were performed over a period of 12 months. The analysis was supported by thermodynamic and reactive transport modeling using the HYTEC code. The findings revealed that a uniform corrosion process occurred, leading to rapid passivation of the C-steel with magnetite as the primary corrosion product. Modeling demonstrated that the increase in temperature to 80 °C and the chemical evolution of the concrete did not significantly affect the corrosion passivation process. Although the formation of Fe-siliceous hydrogarnets is thermodynamically possible at 80 °C, it did not jeopardize magnetite passivation. The results show that the passivation of the containers occurred under the test conditions and this is a promising result for further investigations.

Retention and transport of PFOA and its fluorinated substitute, GenX, through water-saturated soil columns

Perfluoro-2-propoxypropanoic acid (GenX) has emerged as a substitute for perfluorooctanoic acid (PFOA) especially since PFOA was listed among the persistent organic pollutants (POPs) by the Stockholm Convention in 2019. However, limited knowledge exists regarding the behavior and mobility of GenX in natural soils hindering the prediction of its environmental fate. This study investigated the mobility and retention of GenX and PFOA in soils under batch and water-saturated flow-through conditions. Batch experiments revealed that GenX has a lower binding affinity to soil than longer-chained PFOA, potentially threatening groundwater resources. Unlike metal-oxides/minerals (ferrihydrite, gibbsite and manganese dioxide), biochar (BC) and activated carbon (AC) amendments significantly enhanced the sorption of both GenX and PFOA in soil. Sorption data on minerals and carbonaceous materials implied that for shorter-chained GenX, the predominant mode of sorption was through electrostatic (ionic) interactions, while for longer-chained PFOA, hydrophobic interactions became progressively more important with increasing chain length. The dynamic flow experiments demonstrated that these soil amendments enhanced the retention of both compounds, thereby decreasing their mobility. Simultaneous injection of both compounds into columns pre-loaded with either PFOA or GenX increased their retardation. GenX sorption was more affected by pre-sorbed PFOA compared to the minimal impact of pre-loaded GenX on PFOA sorption. A newly developed reactive transport model, which incorporates a two-site sorption model and accounts for kinetic-limited processes, accurately predicted the sorption and transport of both compounds in single and binary contamination systems. These findings have important implications for predicting and assessing the fate and mobility of per- and polyfluoroalkyl substances (PFAS) in soils and groundwaters.

Experimental characterization of dynamic strength and failure behavior of saturated reef limestone concrete under biaxial stress constraint

On the basis of not destroying the island's ecological environment, concrete mixed with reef limestone aggregates in situ is beneficial to solve the problem of shortage of terrestrial rock resources in the island area. Considering the influence of water-saturated state, lateral stress constraint and strain rate, the dynamic mechanical properties and failure characteristics of reef limestone concrete under biaxial stress constraint are studied by using true triaxial Hopkinson bar test technology. The dynamic failure behavior of reef limestone concrete is analyzed from macro-meso level by means of SEM test method, and the stress intensity factor theory of crack tip is cited to reveal the enhancement effect of dynamic strength of water-saturated reef limestone concrete under the coupling effect of biaxial stress constraint and impact load. The results show that the dynamic compressive strength of reef limestone concrete increases with the strain rate in a power function, and the growth rate decreases gradually. Under the same impact load, the compressive strength of reef limestone concrete in water-saturated state increases more significantly than that in dry state. The lateral stress constraint has a significant enhancement effect on the dynamic strength of reef limestone concrete samples, and changes the Poisson's ratio of reef limestone concrete samples. In addition, based on the equivalent crack model theory, it is verified that under the combined action of biaxial stress constraint and high strain rate, the dynamic stress intensity factor of the crack tip of the reef limestone concrete sample in water-saturated state is larger than that in dry state.

Quantifying hydrolytic degradation of poly(ethylene terephthalate glycol) under storage conditions and for fused filament fabrication mechanical properties

Poly(ethylene terephthalate glycol) (PETG) is a promising polyester for additive manufacturing (AM) applications. However, an important question is its thermal and hydrolytic stability under storage conditions. The current work investigates which measuring technique is most suited to qualitatively answer this question, completing the field for polyester stability analysis by focusing on more amorphous structures. In combination with regression analysis under lab accelerated conditions to practically estimate characteristic degradation time scales and currently lacking (overall) Arrhenius parameters, a distinction is made between techniques dealing with molecular and larger scale properties, distinguishing between Fourier Transfer Infrared (FTIR) spectroscopy, size exclusion chromatography (SEC), rheological measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It is shown that hydrolytic scission is dominant over thermal scission, and mainly affects the lower mass region of the molar mass distribution. However, the degradation sensitivity can only be assessed using the SEC number average molar mass, and a more pronounced qualitative sensitivity is only obtained applying rheological analysis, with an extrapolated very low half-life time under water-saturated conditions of ca. 3 days in the Newtonian region and of 2 days in the shear thinning region. It is further highlighted that hydrolytic degradation influences the tensile properties of parts fabricated with fused filament fabrication, which is an important AM technique.

Analyzing the Energy and Damage Constitutive of Cemented Backfill with Different Water Content under Dynamic Load.

The dynamic characteristics of the filling body are the key parameters for designing the filling ratio and evaluating the stability of an underground stope. The different environment (water-bearing state) of the filling body in the underground stope exerts a complex impact on the mechanical behavior of the filling body. Therefore, six groups of cemented filling body specimens with different states were formed and subjected to dynamic uniaxial impact tests. The effects of water content on the mechanical properties, fractal dimension, and deformation damage characteristics of the cemented backfill under dynamic load were analyzed in depth, and a dynamic damage constitutive model that considers water damage and the compaction stage was established. The results indicate the following: (1) Due to the change of the specimen from the dry state to the water saturation state, the dynamic compressive strength of the cemented filling body decreases from 5.03 Mpa to 1.79 Mpa; however, the ductility of the specimen generally increases, and the filling body specimens with different water contents mainly exhibit tensile failure. (2) There is a significant nonlinear relationship between the water content and the fractal dimension Db of the cemented backfill specimen, and the growth rate of the fractal dimension Db tends to slow down with the increase in the water content. (3) From the energy evolution perspective, the water content of the specimen exerts a significant effect on the elastic deformation and failure stage of the stress-strain curve, and the slope of the dissipated energy-strain curve decreases with the increase in water content. (4) Based on the Weibull distribution and damage theory, a statistical damage constitutive model of cemented backfill was established, and it was compared with the experimental curve to verify the rationality of the model. Therefore, the relationship between stress and damage and the strain curves is discussed, and it is inferred that the damage evolution curve of cemented backfill is a typical S-shaped curve that exhibits a stable development-rapid increase-tending to be gentle. This study can provide a theoretical reference for further understanding the dynamic behavior and stability of backfill under different water conditions.

Assessment of the theoretical models of effective thermal conductivity based on digital rock physics for clean sandstones

Knowledge of the effective thermal conductivity (ETC) of porous media provides valuable insights into the heat flow and profoundly affects the feasibility analysis of thermal enhanced oil recovery methods and geothermal field development. Theoretical assessment of ETC based on structural properties of the porous medium and various simplification assumptions by prediction models have shown acceptable results towards ETC quantification; however, their applicability must be investigated further due to the availability of various types of such models. In this study, we first employed a digital rock approach to simulate the heat conductivity of micro-CT images of 10 clean sandstone samples using Avizo software in different directions for evacuated, air-saturated, and water-saturated conditions. The filtered and segmented images were applied to perform voxel-based ETC simulations under steady state condition. Then, the simulation results were compared to the computed ETCs for each sample by 11 theoretical models. Two well-known thermal conductivity bounds, i.e., Hashin and Shtrikman bounds and Wiener bounds were used to confirm the validity of models and simulation outputs. It was shown that the Haung model generates the best outputs for vacuum (MAPE = 0.08 and RMSE = 0.37) and air-saturated (MAPE = 0.07 and RMSE = 0.32) states. While the water-saturated condition was competently predicted by the Ribaud model (MAPE = 0.05 and RMSE = 0.31). The overall analysis indicated that the Haung model is the best model for the prediction of ETC in all three pore-filling states for clean sandstones.

Autogenous self-healing of polypropylene fiber reinforced ettringite-based composite

This study intends to advance the poor knowledge on the ability of an ettringite-based binder to obtain autogenous self-healing and its relevant mechanism. We developed a high-performance polypropylene fiber-reinforced cementitious composite using a slag-based ettringite binder and investigated its autogenous healing property under water-saturated conditions. Cracks were created via four-point bending loads on prismatic specimens at different crack opening displacements (i.e., 0.5, 1, and 2 mm in total crack opening). After curing times, the mechanical retention and recovery of the damaged composite were compared with the sound sample. We found that the material effectively heals micro cracks (i.e., under 100 μm) after 1 month of aging, while larger cracks could not completely close during the total curing times (up to 3 months). The healing products were mainly CaCO3 and ettringite observed through both experiments and thermodynamic modelling. These crystals mainly formed from the carbonation of ettringite and other AFm phases in aqueous conditions. The strength retention slightly reduced (about 10%) after healing, however, the composite still exhibited deflection-hardening behavior. Findings show the high potential of ettringite-based binder to be a matrix for self-healing cementitious composites. Further improvements, nevertheless, are needed to increase the healing rate and strength recovery of the composite.

Water-Weakening and Time-Dependent Deformation of Organic-Rich Chalks

The Ghareb Formation is a shallowly buried porous chalk in southern Israel that is being considered as a host rock for a geologic nuclear waste repository. Setup and operation of a repository will induce significant mechanical, hydrological and chemical perturbations in the Ghareb. Developing a secure repository requires careful characterization of the rock behavior to different loads. To characterize hydromechanical behavior of the Ghareb, several short- and long-term deformation experiments were conducted. Hydrostatic loading tests were conducted both dry and water-saturated, using different setups to measure elastic properties, time-dependent behavior, and permeability. A set of triaxial tests were conducted to measure the elastic properties and rock strength under differential loading at dry and water-saturated conditions. The hydrostatic tests showed the Ghareb began to deform inelastically around 12–15 MPa, a relatively low effective pressure. Long-term permeability measurements demonstrated that permeability declined with increasing effective pressure and was permanently reduced by ~ 1 order of magnitude after unloading pressure. Triaxial tests showed that water saturation significantly degrades the rock properties of the Ghareb, indicating water-weakening is a significant risk during repository operation. Time-dependent deformation is observed during hold periods of both the hydrostatic and triaxial tests, with deformation being primarily visco-plastic. The rate of deformation and permeability loss is strongly controlled by the effective pressure as well. Additionally, during holds of both hydrostatic and triaxial tests, it is observed that when water-saturated, radial strain surpassed axial strain when above effective pressures of 13–20 MPa. Thus, deformation anisotropy may occur in situ during operations even if the stress conditions are hydrostatic when above this pressure range.

Comparative study on the electric resistance of mortars made of low carbon binders

Against the background of the high CO2 emissions generated in the production of Portland cement (OPC), research is being carried out worldwide into alternative binders that can be produced with lower energy consumption. These have a lower clinker-cement factor or contain no Portland cement at all. To enable these binders to be used on a large scale, also in reinforced concrete structures, their performance in terms of durability must be ensured. The specific electric resistance is a parameter for characterizing different binders. At a young age, the hydration progress and the formation of the pore structure can be observed based on the specific electric resistance. In connection with the electrical conductivity of the pore solution, statements about the pore structure and the resistance to the penetration of corrosion-promoting substances are possible. Finally, the electric resistance is an influencing factor for estimating possible corrosion rates after depassivation of the steel reinforcement. In this study, a wide range of mortars produced with different alternative binders were characterized in terms of their resistivity as a function of age and water content. From the group of clinker substitutes (SCMs), calcined clays and modified steel slag were investigated. The other binders included in the investigation program are produced entirely without Portland cement: In addition to a calcium sulfoaluminate (CS̅A) cement and the C-S-H binder Celitement®, alkali-activated materials (AAMs) in the form of geopolymers and alkali-activated slags were also investigated. The results show a wide range of specific electric resistances in a naturally water-saturated state of the mortar specimens between 5.5Ωm for an alkali-activated metakaolin and 971Ωm for the Celitement®. Clinker replacements with calcined clays metakaolin, or metaillite result in increased specific electric resistances. In addition, the different binders show a very different influence on the dependence of the resistivity on the water content.

Numerical Simulation of Electrical Properties of Carbonate Reservoirs Using Digital Rocks

Rock electrical experiments are essential means of researching the conductive properties of rocks and are fundamental to interpreting resistivity logging. Carbonate rocks have more complex pore structures than sandstone, which results in more complex conductive properties. However, conducting experiments on representative rock samples from carbonate reservoirs is difficult, making it challenging to study the micro factors affecting electrical properties. Therefore, researching the conductive properties of carbonate rocks is difficult. To address this, in this paper, three-dimensional (3D) digital rock models with different porosities are generated, and conductive simulations are carried out on these models using the finite element method (FEM). Firstly, a micro-computed tomography (μ-CT) 3D image of a carbonate rock is obtained. Secondly, mathematical morphology-based methods are used on the μ-CT image to generate cores with varying porosities and fluid distributions. Then, the electrical properties are simulated using the FEM method, and the results are analyzed. The results reveal that the formation factor of the reservoir is mainly influenced by the shape and structure of the pores. The Archie equation is more suitable for carbonate reservoirs with water saturation levels greater than 60%. The wettability of the rock can alter the distribution of fluid in the reservoir space under different water saturation conditions. In pure water-wet rocks, the water phase mainly occupies small pores, while the oil phase occupies larger pores. As a result, compared to pure oil-wet rocks, water-wet rocks have more conductive channels and better conductivity. Therefore, it is important to determine the wettability of the rock when calculating water saturation using the Archie equation. The saturation index value of water-wet carbonate rock is about 2, while that of oil-wet rock is around 3–4. This research lays a foundation for studying the electrical conductivity of carbonate reservoirs using digital rocks.

Modelling biogeochemical reactions triggered by graphene's addition in a fertilized calcareous sandy soil

Graphene production has dramatically increased in the last years and new ways to recycle this engineered material need to be investigated. To this purpose, a reactive model network was developed using PHREEQC-3 code to quantify the relevant biogeochemical reactions induced by graphene scraps' incorporation in a calcareous sandy soil. The numerical model was calibrated versus a complete dataset of column experiments in water saturated conditions using two different fertilizers, a synthetic NPK fertilizer and fertigation water produced in a wastewater treatment plant. Column experiments consisted of 50 cm columns filled with a mixture of graphene scraps (0.015 % dry weight) and soil in the first 10 cm, while the remaining 40 cm had only soil. The model performance was tested using classical statistical indices (R2, Modelling Efficiency, and Index of Agreement), resulting to be satisfactory. Besides, a simple sensitivity analysis via the perturbation of relevant parameters showed a low degree of uncertainty. The main outcome of this study was the quantification of the increased denitrification rate triggered by graphene incorporation into the soil. Moreover, graphene incorporation substantially increased soil CEC and DOC sorption capacity, demonstrating a good adsorption capacity for ammonium and organic compounds, thus decreasing nutrients leaching that represents a major concern related to agricultural practice. Indeed, Graphene incorporation increased by 40 % the CEC in the first 10 cm of the CSG_NPK column (2.50e−02 mol/L) respect to the CS_NPK column (1.75e−02 mol/L) and increased it by 150 % in the first 10 cm of the CSG_FW column (2.50e−02 mol/L) in comparison with the CS_FW column 1.00e−02 (mol/L). pH fluctuations were most likely due to the precipitation of Ca5(PO4)3OH, indeed the consumption of H+ ions could have triggered the pH lowering during the experiment. These results could be relevant for future graphene applications as a soil improver or as suitable material to enhance soil bioremediation in order to include graphene in a circular economy loop.

Dynamic properties and fragmentation fractal characteristics of water-saturated reef limestone concrete under impact loading

Reef limestone was used as a coarse–fine aggregate to prepare concrete with a strength class of C30. The mechanism of influences of water-saturated state on dynamic compressive strength, energy dissipation, and macroscopic and microscopic failure modes of reef limestone concrete was studied, and the relationships between fractal dimension and loading rate, fragmentation characteristics, and energy dissipation were discussed. The results indicated that the dynamic compressive strength of reef limestone concrete presents power function growth with increasing loading rate, the free water reduces the degree of cementation among particles and weakens the quasi-static state and dynamic mechanical properties of reef limestone concrete. Meanwhile, under the same loading rate, water-saturated reef limestone concrete demonstrates a stronger energy absorption effect and a greater energy dissipation density, and the energy dissipation density is linearly correlated with the dynamic compressive strength. In addition, the irregular shape and porous structure of reef limestone aggregate particles effectively enhances the friction strengths between the aggregates and cement slurry, causing most of the dynamic cracks in reef limestone concrete to occur in the cement-sand slurry and aggregates themselves. Finally, the results also show that the fractal dimension of the fragments of reef limestone concrete increases linearly with increases in the loading rate and fragmentation energy dissipation density. At approximately the same loading rate, the fractal dimension of dry specimens was larger, and when the fractal dimensions in the two states were similar, the energy consumed per unit mass water-saturated specimen exceeds that of dry specimens.

Experimental Validation and Calibration of the Galvin Model with Artificial Tight Sandstones with Controlled Fractures

The study of fractures in the subsurface is very important in unconventional reservoirs since they are the main conduits for hydrocarbon flow. For this reason, a variety of equivalent medium theories have been proposed for the estimation of fracture and fluid properties within reservoir rocks. Recently, the Galvin model has been put forward to model the frequency-dependent elastic moduli in fractured porous rocks and has been widely used to research seismic wave propagation in fractured rocks. We experimentally investigated the feasibility of applying the Galvin model in fractured tight stones. For this proposal, three artificial fractured tight sandstone samples with the same background porosity (11.7% ± 1.2%) but different fracture densities of 0.00, 0.0312, and 0.0624 were manufactured. The fracture thickness was 0.06 mm and the fracture diameter was 3 mm in all the fractured samples. Ultrasonic P- and S-wave velocities were measured at 0.5 MHz in a laboratory setting in dry and water-saturated conditions in directions at 0°, 45°, and 90° to the fracture normal. The results were compared with theoretical predictions of the Galvin model. The comparison showed that model predictions significantly underestimated P- and S- wave velocities as well as P-wave anisotropy in water-saturated conditions, but overestimated P-wave anisotropy in dry conditions. By analyzing the differences between the measured results and theoretical predictions, we modified the Galvin model by adding the squirt flow mechanism to it and used the Thomsen model to obtain the elastic moduli in high- and low-frequency limits. The modified model predictions showed good fits with the measured results. To the best of our knowledge, this is the first study to validate and calibrate the frequency-dependent equivalent medium theories in tight fractured rocks experimentally.

Determination of Ce3+, Co2+, Mn2+ and Fe2+ diffusion coefficients in Nafion® membrane

Concentration gradient diffusion coefficients for Ce3+, Co2+, Mn2+ and Fe2+ cations are determined in Nafion®211 membranes over a wide range of environmental conditions. Measurements are made using finite-width cation-rich bands introduced to NR211 via a hot-pressing procedure. A robust method of accurate diffusion coefficient determination of the finite-width deposits is developed using a Fick's second law of diffusion solution for one-dimensional systems. The transition metal dications are found to have nearly identical NR211 diffusion coefficients under water saturated conditions over the 22–80 °C range. The powerful chemical mitigant, Ce3+, is about one-half as diffusive as the dications under identical conditions. Derived diffusion coefficients for Ce3+ and Co2+ are found to be independent of initial cation concentration over the range of 12.5–70 mol% exchange level. The diffusion behavior of Ce3+ in 80 °C liquid water and saturated water vapor is identical. The diffusion coefficients of Ce3+ are shown to have a strong dependence on membrane hydration level varying by a factor of more than 30 over the range of 95 to 40% RH. The implications of these new diffusion findings are applied to a discussion of potential guidelines for the development of highly durable fuel cell systems, which employ mobile metal cations as lifetime-extending redox stabilizers.

Composite Dielectric Model for Cement Concrete Considering Water Saturation

Water has a significant impact on the dielectric constant of materials. As a multiphase composite material, the effect of water content must be taken into account when modeling the composite dielectric of cement concrete. Cement concrete traditionally has been thought of as a three-phase mixed material consisting of mortar, aggregate (limestone), and pores (air). Water was used as a constituent material of cement concrete in this paper, and its content was described in terms of water saturation. By abstracting the components of cement concrete into independent medium units and arranging them according to certain rules, the four-phase mixing model of cement concrete can be established. To investigate the effect of water, the dielectric constant of cement concrete was measured using a network analyzer at various water saturation levels. The experimental results show that water significantly can enhance the dielectric constant of cement concrete, and this effect is related to porosity: the higher the water saturation, the faster the dielectric constant increases. According to the established concrete four-phase mixed model, combined with the parallel plate capacitor theory, a composite dielectric model considering water saturation was developed which can improve the prediction accuracy under different water saturation conditions and provide a foundation for the application of ground-penetrating radar (GPR) in the quality inspection of cement concrete pavement.

Simulation of nuclear magnetic resonance response based on 3D CT images of sandstone core

In recent years, nuclear magnetic resonance (NMR) logging has become increasingly prevalent in the characterization of rock properties such as porosity, permeability, saturation, and pore size distribution. However, interpreting such properties accurately from NMR logging data is challenging for some reservoirs. In particular, the impact of salinity, viscosity, and saturation on NMR measurements is not always clear, which can lead to inaccuracies in the resulting data interpretation. Properly accounting for these factors is essential in order to obtain accurate and reliable measurements for effective characterization of subsurface formations. This study utilized a random walk technique to simulate the NMR response of homogeneous sandstones using 3D CT images and conducted a sensitivity analysis under various salinity, crude oil viscosity, and water saturation conditions. The results indicate that the T2 relaxation time slightly shifts toward the short relaxation direction as the salinity of the formation water increases. In addition, longer echo intervals result in a more significant forward shift in the T2 value than shorter intervals. Whereas, for crude oil, the T2 relaxation time becomes shorter as its viscosity increases. Furthermore, the effect of echo interval on the forward T2 shift is less pronounced for crude oil than it is for formation water. Under water wet conditions, the T2 spectrum of crude oil exhibits a peak at the volume relaxation position. As the water saturation decreases, the left two peaks in the T2 spectrum shift toward shorter relaxation times. Under oil wet conditions, the T2 spectrum exhibits a complex three-peak structure. The method provides a physical basis for interpreting NMR macroscopic responses, and the simulated NMR responses can help identify fluids in reservoirs.

Research on effective pit fencing solutions for the construction of a two-level parking lot of a multi-story building

A study on the effective placement of the piles in the retaining wall of the pit was carried out. A comparison of internal forces and horizontal displacements of the retaining wall piles was drawn among three variants of their placements in the wall. The influence on the calculation results of the detailing of the soil excavation process during modeling using the Plaxis 2D was examined. Based on the research on the stress-strain state (STS) of the retaining wall piles using the spatial setting of the problem, a comparison to the problem with the flat setting was drawn. Additionally, an analysis of the bending moments and horizontal displacements in the retaining wall piles with a spatial setting of the problem was made.
 Based on the obtained results, information on the effectiveness of different variants of the pile placement in the retaining wall of the pit, as well as the convergence of the calculation results with different detailing of the excavation process modeling is presented. Also, a comparison of the values of internal forces, horizontal displacements, and the elevation of the pit bottom between flat and spatial problem settings was made. The distribution of forces between piles of the retaining wall using a spatial problem setting is presented.
 The finite element model consists of the soil base and retaining wall structure. Modeling of the base was executed using the Hardening soil model, in which the following soil characteristics are used during the calculation: γ – the specific weight of the soil in its natural state; γsat – the specific weight of the soil in the water-saturated state; c – cohesion; φ – the effective stress friction angle; ψ – dilatancy angle; E50 – stiffness for primary loading; Eoed – oedometer loading stiffness; Eur – stiffness for un-/reloading. The calculation was made using the Plaxis program complex.
 Today, the effective and the most rational way of retaining wall design during the construction of buildings and structures with underground parts is significant. A successful choice of the construction of the excavation fencing not only ensures the reliability of the construction but also allows using building materials in the most efficient way. In addition, the choice of the method of the problem definition and its detailing are important factors when approaching the modeling process of similar problems, as they affect the accuracy of the obtained results, the degree of labor-intensiveness, and the time spent on the calculation.

Effect of Hydrothermal Curing on the Hydration and Strength Development of Belite Cement Mortar Containing Industrial Wastes

This paper describes the impact of hydrothermal conditions on the strength properties and hydration processes of belite cement mortar samples. The belite-rich binder was synthesized by sintering the initial mixture of raw materials (granite cutting waste, the silica-gel waste from AlF3 production, and natural materials) in a high-temperature furnace at a temperature of 1150 °C for 2 h. The prepared clinker consists of larnite, mayenite, srebrodolskite, ye’elimite, and gehlenite. To control hydration kinetics and optimize the hardening of belite cement mortar, the produced clinker was blended with 7.5% of gypsum. The mechanical properties were assessed by curing the standard prisms (following the EN 196-1 standard, cement/sand = 1:3, W/C= 0.67) under water-saturated conditions in a stainless steel autoclave. The curing process was performed in a temperature range of 90 °C to 200 °C at various hydrothermal curing durations (6–48 h). The results indicated that the curing conditions highly influence the compressive strength evolution of belite cement mortar and the formed mineralogy of hydrates. The highest compressive strength value (exceeded 20 MPa) was obtained at 200 °C, i.e., when the main belite cement mineral was entirely hydrated and recrystallized into 1.13 nm tobermorite. The microstructural evolution and the phase assemblage during the hydrothermal curing were determined by X-ray diffraction analysis and differential scanning calorimetry.

Accelerated mineral bio-carbonation of coarse residue kimberlite material by inoculation with photosynthetic microbial mats

Microbiological weathering of coarse residue deposit (CRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa enhanced mineral carbonation relative to untreated material. Cultures of photosynthetically enriched biofilm produced maximal carbonation conditions when mixed with kimberlite and incubated under near surface conditions. Interestingly, mineral carbonation also occurred in the dark, under water-saturated conditions. The examination of mineralized biofilms in ca. 150 µm-thick-sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron—scanning electron microscopy-energy dispersive x-ray spectrometry demonstrated that microbiological weathering aided in producing secondary calcium/magnesium carbonates on silicate grain boundaries. Calcium/magnesium sulphate(s) precipitated under vadose conditions demonstrating that evaporites formed upon drying. In this system, mineral carbonation was only observed in regions possessing bacteria, preserved within carbonate as cemented microcolonies. 16S rDNA molecular diversity of bacteria in kimberlite and in natural biofilms growing on kimberlite were dominated by Proteobacteria that are active in nitrogen, phosphorus and sulphur cycling. Cyanobacteria based enrichment cultures provided with nitrogen & phosphorus (nutrients) to enhance growth, possessed increased diversity of bacteria, with Proteobacteria re-establishing themselves as the dominant bacterial lineage when incubated under dark, vadose conditions consistent with natural kimberlite. Overall, 16S rDNA analyses revealed that weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation. Enhanced weathering and carbonate-cemented microcolonies demonstrate that microorganisms are key to mineral carbonation of kimberlite.

Efficiency of Solar Power Generation System Application on Agricultural Automatic Drip Irrigation in Indonesia

Irrigation is one of the important components of farming producers in cultivation. Lack of irrigation water causes crop failure risk, while excess water also causes agricultural crop failure. It is necessary to regulate irrigation water to achieve technical and economic farming efficiency. This study aims to determine the efficiency of solar power generation in agricultural automatic drip irrigation. This study uses experimental research with the design of materials and research tools. Efficiency estimation uses a simple ratio by looking at the cost components of each treatment so that the value that appears becomes the final efficiency value. This study showed that automatic drip irrigation for solar power generation was more economically efficient than ordinary electricity. The use of automatic drip irrigation can save costs of Rp. 4,346,200. In addition, unlimited renewable energy support is a major advantage besides being environmentally friendly and an agricultural climate change adaptation strategy. The system’s performance on the automatic pump is running well, as seen from P1, P2, P3, P4, and P5; the pump turns on at a percentage of water ranging from 10-90% and turns off after reaching 100% water or water-saturated soil conditions. The main obstacle faced during the research was the climate problem because this research model used the solar system. This means that as long as sunlight shows its existence, the energy obtained is also perfect, but vice versa. In addition, it is still difficult for traditional farmers to carry out the operational control system, so further research is needed.