Effects of Acidic Environment on Dynamic Mechanical Properties and Porosity Evolution Characteristics of Coal

Coal pillars left in coal mines are often subjected to long-term submersion by groundwater and chemical solutions and are susceptible to deterioration and even destabilization damage under dynamic load disturbance. In order to investigate the effects of acidic environment on dynamic mechanical properties and porosity evolution characteristics of coal, a split Hopkinson bar (SHPB) was used to test the dynamic compressive strength and tensile strength of coal samples under different acid environment. The results showed that the sample density gradually decreased with the increase of the number of wet and dry cycles, but the decrease was significantly related to the pH value. Longitudinal wave velocity of coal sample decreases gradually with the increase of drying and wetting cycles, and the decreasing speed is first fast and then slow. The stronger the acidity of the solution, the more times the dry-wet cycle, and the higher the water absorption of the sample. In the early stage of dry-wet cycle, the coal is significantly affected, and the average deterioration degree is large. After that, the influence of cyclic action is reduced, and the average degradation degree is small. Porosity of coal increases continuously under the action of dry-wet cycle. The stronger the acidity, the greater the change in initial porosity. In the 20th cycle, the porosity of the acidic environment increases significantly at once and then decreases continuously.

Physical Protection in Aggregates and Organo-Mineral Associations Contribute to Carbon Stabilization at the Transition Zone of Seasonally Saturated Wetlands

Wetlands store significant soil organic carbon (SOC) globally due to anoxic conditions that suppress SOC loss, yet this SOC is sensitive to climate and land use change. Seasonally saturated wetlands experience fluctuating hydrologic conditions that may also promote mechanisms known to control SOC stabilization in upland soils; these wetlands are therefore likely to be important for SOC storage at the landscape-scale. We investigated the role of physicochemical mechanisms of SOC stabilization in five seasonally saturated wetlands to test the hypothesis that these mechanisms are present, particularly in the transition between wetland and upland where soil saturation is most variable. At each wetland, we monitored water level and collected soil samples at five points along a transect from frequently saturated basin edge to rarely saturated upland. We quantified physical protection of SOC in aggregates and organo-mineral associations in mineral horizons to 0.5 m depth. As expected, SOC decreased from basin edge to upland. In the basin edge and transition zone, the majority of SOC was physically protected in macroaggregates. By contrast, overall organo-mineral associations were low, with the highest Fe concentrations (5 mg Fe g -1 soil) in the transition zone. While both stabilization mechanisms were present in the transition zone, physical protection is more likely to influence SOC stabilization during dry periods in seasonally saturated wetlands. As future climate scenarios predict changes in wetland wet and dry cycles, understanding the mechanisms by which SOC is stabilized in wetland soils is critical for predicting the vulnerability of SOC to future change.

Experimental Study on the Damage and Degradation Characteristics of Red Sandstone after Dry and Wet Cycling by Low Magnetic Field Nuclear Magnetic Resonance (NMR) Technique

To study the damage evolution of rocks under the action of wet and dry cycles, nuclear magnetic resonance (NMR) technology was used to test red sandstone under different times of wet and dry cycles. The T 2 spectral distribution curve, porosity, spectral peak area, and damage distribution curve of the rock were obtained, and the quantitative relationship between porosity, damage degree, and number of cycles was established. The results show that with the increase of the number of wet and dry cycles, the T 2 spectral curve of rock gradually moves to the right, but the moving amplitude gradually decreases. The porosity and spectral area increase with the increase of the number of wet and dry cycles, coupled with a declining growth rate, and the maximum increase in porosity is 18.789%. The damage degree of rock increase with the increase of the number of cycles, but with the continuous increase of the number of cycles, the damage rate decreases, and finally the damage degree of rock tends to be a constant value.

Multiscale Analysis of the Strength Deterioration of Loess under the Action of Drying and Wetting Cycles

To study the strength degradation mechanism of compacted loess during dry-wet cycles, 0–5 dry-wet cycles tests and many triaxial compression tests were carried out on loess with an optimal moisture content. During the dry-wet cycles, the loess samples were analyzed by nuclear magnetic resonance and scanning electron microscopy. Studies have shown that at the macro level, with increasing numbers of wet and dry cycles and increasing cycle amplitude, the cohesive force and internal friction angle of the loess decrease, and the shear strength of the loess deteriorates significantly. At the micro level, with the number of wet and dry cycles increasing, the connection between particles changes from surface-to-surface contacts to point-to-point or point-to-surface contacts. The edges and corners of the particles decrease, the roundness increases, the large pores gradually decrease, the small pores gradually increase, and the fractal dimension gradually increases. In terms of microscopic view, the NMR test shows that with increasing numbers of dry-wet cycles, the T2 peak curve increases, the curve width increases slightly, the peak area gradually increases, and the porosity increases. From the macroscopic, mesoscopic, and microscopic multiscale analysis, the structure of loess is degraded under the action of dry and wet cycles; the strength of the loess is degraded significantly after 0 to 3 cycles and then gradually stabilizes. These research results can provide a certain reference value for the management of loess collapse geological disasters in semiarid climates.

Physical protection in aggregates and organo-mineral associations contribute to carbon stabilization at the transition zone of seasonally saturated wetlands

Wetlands store significant soil organic carbon (SOC) globally, yet this SOC is sensitive to climate and land use change. Seasonally saturated wetlands experience fluctuating hydrologic conditions that may promote the physicochemical mechanisms known to control SOC stabilization in upland soils; these wetlands are therefore likely to be important for SOC storage at the landscape-scale. We investigated the role of physicochemical mechanisms of SOC stabilization in five seasonally saturated wetlands to test the hypothesis that these mechanisms are present, particularly at the transition zone between wetland and upland where saturation in the upper soil profile is most variable. At each wetland, we monitored water level and collected soil samples at five points along a transect from frequently saturated basin edge to rarely saturated upland. We quantified physical protection of SOC in aggregates and organo-mineral associations in mineral horizons to 0.5 m depth. As expected, SOC decreased from basin edge to upland. In the basin edge and transition zone, the majority of SOC was physically protected in macroaggregates. By contrast, overall organo-mineral associations were low, with the highest Fe concentrations (5 mg Fe g− 1 soil) in the transition zone. While both stabilization mechanisms were present in the transition zone, physical protection is more likely to be a dominant mechanism of SOC stabilization in seasonally saturated wetlands. As future climate scenarios predict changes in wetland wet and dry cycles, understanding the mechanisms by which SOC is stabilized in wetland soils is critical for predicting the vulnerability of SOC to future change.

Controlled drainage in future climate scenarios

<p>Climate change is projected to result in higher temperatures, higher annual precipitation and more uneven distribution of precipitation in the northern regions. This requires adaptation in agriculture where both excessively wet and dry cycles pose challenges to cropping. Until now, water management in northern agricultural fields has been resting primarily on efficient drainage, but interest towards more flexible measures has increased.</p><p>This study focuses on the hydrological effects of climate change and controlled drainage operated with subsurface drains and an open collector ditch in an agricultural field. The objective was to computationally estimate how groundwater levels and water balance respond to controlled drainage and open ditch scenarios in climate conditions projected to take place in Finland during this century. A hydrological model FLUSH was used to simulate the hydrology of an experimental field in Sievi, Northern Ostrobothnia, Finland during years 1970–2100. Down-scaled climate projections from EURO-CORDEX (RCP 8.5 and RCP 2.6) were used as meteorological input. The temporal development of the field hydrology and the effects of controlled drainage were examined by dividing the time series into four subsequent time intervals (historical period and three future periods).</p><p>Two different control scenarios were studied. Drainage intensity was reduced during growing seasons in summers (Jun.–Aug.) and either in autumn (Oct.–Nov.) or from autumn to spring (Oct.–Mar.). During these periods, groundwater table was on average 17–29 cm, 28–30 cm and 36–40 cm higher, respectively, in the control scenarios when compared to conventional subsurface drainage in different study intervals and emission scenarios. The implementation of controlled drainage reduced annual drain discharge by 21–46 mm. The projected temporal evolution of the effects of controlled drainage on groundwater levels and annual drain discharges were not monotonous, but the projected effects were larger during the future periods when compared to the historical period. Controlled drainage effect on groundwater levels was seen during both dry and wet years. Controlled drainage was assessed to be an effective method to control field water processes currently and in the future decades. The open collector ditch lowered groundwater levels within a distance of 115 m from the ditch.</p>

Effect of experimental wet and dry cycles on bamboo fibre reinforced acrylic polymer modified cement composites

This study experimentally evaluated the effect of accelerated wet/dry cycles on the dimensional stability and some selected mechanical properties of polymer modified vegetable fibre cement composites. The bamboo fibres were pre-treated with 10% conc. of sodium hydroxide and varied from 0 – 2.0% while acrylic polymer admixture of 10% w/w of cement was added to improve the properties. The modified fibre-cement composites were subjected to 50 cycles of wet/dry processes to simulate natural weathering process of the environment. The samples were subjected to water absorption, thickness swelling, modulus of rupture (MOR) and modulus of elasticity (MOE) after 28 days of curing and aging cycles respectively using 5 replicates. One way ANOVA at p<0.05 was used to analyse the results. Scanning electron microscope (SEM) and Fourier Transformer Infrared Spectroscopy (FTIR) analyses were conducted on the samples. The results showed improvement of 33.3, 64, 71 and 57% in MOR and 135, 85, 101 and 188% in MOE for samples with 0.5, 1, 1.5 and 2% fibre inclusion after ageing tests. Significantly improved dimensional stability values were observed in this study in comparison with data from similar ageing tests conducted on unmodified vegetable fibre-cement matrix. SEM micrographs showed marginal increase in the size of the pores before and after ageing tests. FTIR analysis indicated increase in intensities during the ageing tests especially for spectra bands located at 3384 – 3520cm−1 which are denoted for OH vibration stretching as well as 1676, 1726 and 1794 cm−1 which depict the presence of carbonyl groups because of absorption of polymers to the fibre surface during the ageing cycles. The study has shown thatwet/dry ageing cycles showed less harmful effect on vegetable fibre cement composites provided the cement matrix is modified with polymer admixtures.

Mesocosm study of microalgae in different weather conditions

Microalgae have valuable contributions in carbon dioxide sequestration. There are no much investigations about motivation of mix microalgae productivity in outdoor cultures. This study aims to evaluate microalgae biomass production in outdoor mesocosms under different weather conditions. The experiment was done in Tilapia pond in the hatchery of fisheries of Universiti Putra Malaysia. Weather parameters were recorded daily. Microalgae seeds were obtained from Tilapia pond effluent and added to eight floating aerated mesocosms. Mesocosms were divided into four treatments. Two g triple supper phosphate: 20g Urea were used as fertilizers. Physical and chemical conditions, microalgae primary productivity and biomass, and species composition were measured every two days. Three cycles were categorized as mix, wet and dry cycles based on weather recording scores. Water quality parameters in Treatments and controls cultures showed significant variations. Primary production variables were higher in the fertilized non-sheltered mesocosms (treatment 1). Productivity variables were lower in the dry cycle and higher in the mix cycle. The highest value of fixed CO2 was (3.2) mg/L/d in treatment 1 in the mix cycle, while the lowest value was (0.11) mg/L/d in treatment 3 and control 1 in dry cycle. Changes in weather patterns are seen in the light and temperature values. Microalgae biomass was lower in dry weather conditions because of effect of high air temperature. Weather conditions and different treatments significantly influenced microalgae species composition, due to the sensitivity in some of them to different light intensities. Chlorophytes were the most abundant due to their ability to adapt with different culture conditions.