scholarly journals Experimental Investigation of Cement/Soda Residue for Solidification/Stabilization of Cr-Contaminated Soils

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Fusheng Zha ◽  
Fanghua Zhu ◽  
Bo Kang ◽  
Long Xu ◽  
Yongfeng Deng ◽  
...  
Keyword(s):  
Contaminated Soils ◽  
Soil Structure ◽  
Pore Space ◽  
Curing Time ◽  
Reaction Products ◽  
Microstructural Characteristics ◽  
Strong Adsorption ◽  
Soil Pore Space ◽  
Binder Ratio

Adopting more efficient and sustainable remediation materials is of great importance for the development of solidification and stabilization (S/S) technology. Among them, soda residue could be considered as a desirable binder due to its strong adsorption for heavy metals. For understanding of the performance of Cr-contaminated soils treated by cement/soda residue, the strength, leaching and microstructural characteristics, and the long-term effectiveness under wetting-drying cycles were comprehensively investigated in this study. The results showed that the unconfined compressive strength (UCS) increased and the leached Cr3+ concentration decreased with curing time, binder content, and binder ratio. Increasing the soda residue from C6S14 to C6S24 could improve soil strength and reduce leachability of Cr3+, while a reverse trend was presented with increasing initial Cr3+ concentration. With subsequent wetting-drying cycles, the UCS further increased and then decreased; inversely, the leached Cr3+ decreased, followed by an increase of Cr-contaminated soils. For the specimens of C6S14 and C6S24, the maximum UCS of 6.04 MPa and 6.48 MPa was reached; correspondingly, the minimum leached Cr3+ concentration of 2.78 mg/L and 1.93 mg/L was reached after 3 wetting-drying cycles, respectively. Microstructure analysis results found that reaction products like calcium silicate hydrate (C-S-H) and ettringite (AFt) increasingly occupied the soil pore space and caused a denser soil structure after 3 wetting-drying cycles, which indicated the long-term effectiveness of contaminated soils treated by cement/soda residue.

Soil pore space arrangement as a geometric indicator of soil structure

2008 ◽  
Vol 41 (11) ◽  
pp. 1198-1204 ◽  
Author(s):  
E. B. Skvortsova ◽  
V. F. Utkaeva
Keyword(s):  
Soil Structure ◽  
Pore Space ◽  
Soil Pore Space

scholarly journals Influence of cropping and fertilization on soil pore characteristics in a long-term field study

2020 ◽  
Author(s):  
David Nimblad Svensson ◽  
Jumpei Fukumasu ◽  
Gunnar Börjesson ◽  
John Koestel
Keyword(s):  
Organic Carbon ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Soil Structure ◽  
Management Practices ◽  
Pore Space ◽  
Pore Characteristics ◽  
Bare Fallow ◽  
Term Field

<p>Soil porosity, pore size distribution and pore characteristics such as connectivity are important for a range of soil processes including ease of root growth and air and water transport. The pore structure is therefore an important part of soil fertility. The pore space is sensitive to management practices such as tillage, fertilization and cropping. Understanding how these practices influence the pore space is important for maintaining a good soil structure that is well aerated and has sufficient drainage. X-ray computed tomography has become a widely used method for studying the pore space as it offers the advantage of enabling soil to be studied in its undisturbed form. In this study it was used to compare the effects of crop growth, tillage and N-fertilizing with Ca(NO3)<sub>2</sub> or farm yard manure (FYM). Soil samples were taken just below the surface from the long-term experiment in Ultuna, Sweden which was started in 1956. The bare fallow, FYM and Ca(NO3)<sub>2</sub>-treatment were sampled with minimum disturbance in two column sizes with inner diameters of 22.2 and 65.5 mm. Differences in pore space morphology were quantified and compared through pore size distribution and a range of connectivity measures, including the Euler number, the critical pore diameter and Gamma connectivity. Biopores were separated from non-biopores and their volume was quantified. Soil organic carbon was determined by dry combustion. Visible porosity and pores in the 150-500 µm class were significantly larger in the FYM and Ca(NO3)<sub>2</sub>-treatment compared to the bare fallow. The porosity occupied by biopores was not found to significantly differ between treatments but the biopores were found to have the largest diameters in the FYM-treatment. Despite that the organic carbon content was 1.7 times higher in the FYM compared to the Ca(NO3)<sub>2</sub>-treatment the visible porosity was similar. This may be due to the positive effects calcium has on the soil structure. The connectivity measures indicated that the FYM-treatment had the best connected pore networks. This may be partly due to the larger biopores. Ca(NO3)<sub>2</sub> showed to be a promising alternative to increase porosity. However, as all the management practices in the long-term field study are done by hand, future studies will have to investigate if the effect is equally similar to FYM under field conditions which are subject to heavy machineries.  </p>

scholarly journals Bodenveränderungen und Typisierung von Fahrspuren nach physikalischer Belastung | Changes in the soil and the classification of ruts according to physical loading

2010 ◽  
Vol 161 (12) ◽  
pp. 504-509 ◽  
Author(s):  
Peter Lüscher
Keyword(s):  
Soil Structure ◽  
Pore Space ◽  
Soil Protection ◽  
Soil Physics ◽  
Physical Loading ◽  
Saturated Water ◽  
Soil Functionality ◽  
Term Maintenance

In Swiss environment legislation, protection of the soil is defined by reference to the long-term maintenance of soil fertility. To fulfil this commitment, long-lasting damage to the soil must be prevented, respectively reduced to a minimum. When the forest floor is driven over with heavy logging machinery, this can lead to profound and long-lasting changes in the soil structure in the ruts thus formed. Based on driving trials under controlled conditions in the Heiteren region of the forest near Bern, investigations were made to find out whether the classification of ruts into three distinct types showing morphologically determined changes in the soil could be substantiated with the help of known values in soil physics. It was shown that the non-compacted reference soils could be clearly distinguished from all three types of rut by comparison of the stratification density, the total pore space and the saturated water permeability. In addition, the three types significantly differed from each other. Damage to the soil can be reduced to a minimum through consequent planning of skidding tracks and by paying due attention to the prevailing humidity of the soil at the time when vehicles are used. Thanks to the connection established between the character of the ruts and soil functionality, the classification of rut types provides a practically relevant and objective instrument for effective physical soil protection.

Drainage and soil structure - a review

Soil Research ◽  
1991 ◽  
Vol 29 (6) ◽  
pp. 923 ◽  
Author(s):  
N Collis-George
Keyword(s):  
Soil Structure ◽  
Numerical Solutions ◽  
Pore Space ◽  
Structural Description ◽  
Complex Structures ◽  
Wetting And Drying ◽  
Naturally Occurring ◽  
The Matrix ◽  
Soil Pore Space ◽  
Areas Of Interest

Definitions of soil structure and drainage are proposed that would allow a more useful interaction between the two areas of interest that appear to have developed independently. Drainage phenomena in three structural systems are quantitatively described. Firstly a simple uniform profile is described; then wormholes and stones are added to the upper layer of this soil; finally the upper layer is given a 23% stable macropore space and its depth is proportionately increased by biotic activity. Numerical solutions of these geometries (supported by experimental work) show that if the structure enhancements are confined to the upper horizons, the drainage behaviour of the matrix is unaffected and only the early stages of the drainage hydrograph are affected. More complex structures are considered qualitatively. The influence of entrapped and encapsulated air within the soil pore space is outlined. It is concluded that a major problem in correlating drainage phenomena with soil structure is that the structural description of wet soils is rarely attempted. In particular, the descriptions of structures, naturally occurring and those enhanced by cultivation, which change with time and with wetting and drying, are presently only described by soil surveyors in qualitative terms.

Effects of liming on soil structure and GHG fluxes at three spruce sites in SW Germany

2021 ◽  
Author(s):  
Martin Maier ◽  
Valentin Gartiser ◽  
Verena Lang ◽  
Raphael Habel ◽  
Lelde Jansone ◽  
...  
Keyword(s):  
Soil Ph ◽  
Forest Soils ◽  
Soil Structure ◽  
Pore Space ◽  
Mineral Soil ◽  
Soil Gas ◽  
Long Term Effects ◽  
Gas Diffusivity ◽  
Humus Layer

<p>Forest soils in Central Europe received massive atmospheric deposition of SO<sub>2</sub> and NO<sub>x</sub> during the second half of the 20<sup>th</sup> century. The resulting fast acidification of the soils was accompanied by massive forest dieback and problematic nutrient imbalances at some sites. After the emissions of SO<sub>2</sub> have been reduced in the 80´s and 90´s, the situation of acidic deposition has been gradually improving. Yet, the deposition of N compounds remains high and still has an impact on forest ecosystems. Natural soil development and “regeneration” is a slow process, which is why other options were investigated to recover heavily affected forest soils. A well-known means to mitigate the observed effects of the anthropogenic acidification surges is liming, i.e. the application of minerals such as CaCO<sub>3</sub> and CaMg(CO<sub>3</sub>)<sub>2</sub> that are able to buffer strong acids. Liming directly affects soil pH which is a “master variable” of the soil. Soil pH, and thus, liming, affects and interacts with many soil processes from mineralization of organic matter and humification, to (de-) stabilization soil structure, nutrient availability and mobility, plant growth and more.</p><p>Several study sites were established in the 1980 in Baden-Wuerttemberg to study long term effects of liming on soil structure and forest growth. At all sites a “control” plot and a “limed” plot were established next to each other. The limed plots were treated with approx. 3 t ha<sup>-1</sup> of CaCO<sub>3</sub> in the 1980´s and 6 t ha<sup>-1</sup> of Ca/MgCO<sub>3 </sub>in 2003. Here we report on results from three sites (Bad Waldsee, Hospital, Herzogenweiler) with Spruce stands (70-110 years), where long term effects of liming on the physical soil structure and soil gas profiles (2017-2019) were studied (Jansone et al., 2020). Liming resulted in a reduction of the thickness of the humus layer and a blurring of the previously clearly separated boundary between the mineral soil and the humus layer. Even though total pore space in the top soil was slightly reduced at the limed plots, soil gas diffusivity was higher at a given air-filled pore-space. This indicates a better connectivity in the air-filled pores, that means more larger pores connecting the atmosphere at the soil surface and the mineral soil. Soil CO<sub>2</sub> concentrations showed clear seasonal patterns and a typical increase with depth. Higher CO<sub>2</sub> concentrations tend to be found in the un-limed control plots. Soil CH<sub>4</sub> concentrations at the soil–humus interface were closer to atmospheric concentrations in the limed plots compared to the control plots. This can be interpreted as an effect of the decrease in the thickness of the humus layer and the increase in the soil gas diffusivity (better aeration) or in a reduced activity of the methanotrophic community.</p><p> </p><p>Acknowledgement</p><p>This research was financially supported by Bundesministerium für Ernährung und Landwirtschaft (BMEL), grant number 28W-B-4-075-02 (2018–2021).</p><p><em>Literature</em></p><p><em>Jansone, L., von Wilpert, K. and Hartmann, P., 2020. Natural Recovery and Liming Effects in Acidified Forest Soils in SW-Germany. Soil Systems, 4(38): 1-35.</em></p>

Properties and Microstructure of the New Phosphate Bonded Magnesia Cement

2006 ◽  
Vol 302-303 ◽  
pp. 543-549
Author(s):  
Zhu Ding ◽  
Zong Jin Li ◽  
Feng Xing
Keyword(s):  
Fly Ash ◽  
Physical And Mechanical Properties ◽  
High Strength ◽  
Hardened Cement ◽  
Reaction Products ◽  
Dense Microstructure ◽  
Binder Ratio ◽  
Water Sorptivity ◽  
Water To Binder Ratio

A novel phosphate bonded magnesia cement was developed recently, which sets quickly and develops high strength in the early ages. In the present research, the physical and mechanical properties, hydration products, and microstructure of the new cement were investigated. The new cement was mainly consists of dead burned magnesia, phosphate and fly ash. The results showed that it not only has high early strength, but also has high long-term strength. Interestingly, the strength of the cement increase with the content of fly ash, from 10 % - 40 % by weight. The hardened cement paste has a dense microstructure, low open porosity and water sorptivity due to the low water to binder ratio. The reaction products after hydration of the cement includes struvite mineral and amorphous species.

scholarly journals Effects of Long-Term Repeated Freeze-Thaw Cycles on the Engineering Properties of Compound Solidified/Stabilized Pb-Contaminated Soil: Deterioration Characteristics and Mechanisms

2020 ◽  
Vol 17 (5) ◽  
pp. 1798 ◽  
Author(s):  
Zhongping Yang ◽  
Xuyong Li ◽  
Denghua Li ◽  
Yao Wang ◽  
Xinrong Liu
Keyword(s):  
Contaminated Soils ◽  
Permeability Coefficient ◽  
Unconfined Compressive Strength ◽  
Soil Structure ◽  
Ct Scanning ◽  
Engineering Properties ◽  
Freeze Thaw ◽  
Pollution Levels ◽  
Deterioration Characteristics

The effects of long-term repeated freeze-thaw cycles and pollution levels on the engineering properties (qu, E50, φ, c, and k) of Pb-contaminated soils were investigated in various laboratory tests. These soils were solidified/stabilized (S/S) with three types of cement-based combined binders (C2.5S5F5, C5S2.5F2.5, and C5S5, cement, lime, and fly ash, mixed in different proportions; these materials are widely used in S/S technology). The strength and permeability coefficient of compound solidified/stabilized Pb-contaminated soils (Pb-CSCSs) were determined based on measurements of unconfined compressive strength (UCS), direct shear, and permeability. CT scanning, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) tests were employed to analyse the deterioration mechanisms under various repetitions of freeze-thaw cycles. The results showed that, under repeated freeze-thaw cycles, the engineering properties of Pb-CSCSs all degraded to varying degrees, though degradation tended to stabilise after 30 days of freeze-thaw cycles. The study also found that the pollutants obstruct hydration and other favourable reactions within the soil structure (such as ion exchanges and agglomerations and pozzolanic reactions). The activation of hydration reactions and the rearrangement of soil particles by freeze-thaw cycles thus caused the engineering properties to fluctuate, and soils exhibited different deterioration characteristics with changes in Pb2+ content.

scholarly journals Effect of Long-Term Soil Management Practices on Tree Growth, Yield and Soil Biodiversity in a High-Density Olive Agro-Ecosystem

Agronomy ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1036
Author(s):  
Sauro Simoni ◽  
Giovanni Caruso ◽  
Nadia Vignozzi ◽  
Riccardo Gucci ◽  
Giuseppe Valboa ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Structure ◽  
Soil Management ◽  
Carbon Pools ◽  
Grass Cover ◽  
Soil Biodiversity ◽  
Canopy Effect ◽  
Soil Organic Carbon Pools

Edaphic arthropod communities provide valuable information about the prevailing status of soil quality to improve the functionality and long-term sustainability of soil management. The study aimed at evaluating the effect of plant and grass cover on the functional biodiversity and soil characteristics in a mature olive orchard (Olea europaea L.) managed for ten years by two conservation soil managements: natural grass cover (NC) and conservation tillage (CT). The trees under CT grew and yielded more than those under NC during the period of increasing yields (years 4–7) but not when they reached full production. Soil management did not affect the tree root density. Collecting samples underneath the canopy (UC) and in the inter-row space (IR), the edaphic environment was characterized by soil structure, hydrological properties, the concentration and storage of soil organic carbon pools and the distribution of microarthropod communities. The soil organic carbon pools (total and humified) were negatively affected by minimum tillage in IR, but not UC, without a loss in fruit and oil yield. The assemblages of microarthropods benefited, firstly, from the grass cover, secondly, from the canopy effect, and thirdly, from a soil structure ensuring a high air capacity and water storage. Feeding functional groups—hemiedaphic macrosaprophages, polyphages and predators—resulted in selecting the ecotonal microenvironment between the surface and edaphic habitat.

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