Gypsum Content Research Articles

Counterions, smectite, and palygorskite increase microstructural stability of saline-sodic soils

Saline-sodic soils are susceptible to wind and water erosion when the dispersive effect of sodium overcomes inter-particle bonds. Rheological parameters of viscoelasticity can help to quantify inter-particle attractive forces and account for the effect of salinity in these soils. The main objective of the present study was to investigate the viscoelasticity behavior of saline-sodic soils of the Sirjan playa in south-central Iran. Three representative pedons were excavated and described by horizon. Soil physicochemical properties and rheological properties were determined, namely the micromechanical parameters flow point (γf), loss factor tan δ, and integral z, with samples analyzed at three matric potentials (0, −6, and −15 kPa). Results showed that soil microstructural stiffness was mainly influenced by soil texture, clay minerals, gypsum, calcium carbonate equivalent (CCE), and matric potential. The dispersive effect of sodium, as indicated by low integral z and γf values, decreased with increasing gypsum content in − 6 and − 15 kPa matric potentials (0.6 < r < 0.8) and CCE percentage in the quasi-saturated (0 kPa) condition (r > 0.8). However, greater microstructural stability (i.e., higher integral z and γf) was observed for fine-textured soils with relatively high amounts of smectite and palygorskite and low pH. Furthermore, integral z and γf increased with lower matric potentials due to the stabilizing effect of menisci forces. Therefore, the viscoelastic behavior of the saline-sodic soils was negatively associated with water content and high sodium concentration, while the presence of smectite, palygorskite, gypsum, and CCE improved the soil physical conditions and thus the rigidity of the porous system. These results demonstrate that rheological measurements can identify saline-sodic soils that have strongly degraded microstructural stability and would most benefit from active management and amelioration.

Experimental Study on Early Age Characteristics of Lime-GGBS-Treated Gypseous Clays under Wet–Dry Cycles

Gypseous soils are capable of presenting ground construction challenges to civil and geotechnical engineers due to their unpredictable deformation characteristics. These undesirable responses are sometimes caused by environmental changes in moisture content due to temperature variations, fluctuation of underground water table, surface water, and gypsum content. Hence, the adoption of effective and economical means of stabilising gypseous soils is imperative. This study’s focus is on the early age strength and microstructural characteristics of gypseous soils treated with lime and GGBS. Treated and untreated gypseous soils with 5%, 15%, and 25% gypsum content were subjected to wet–dry cycles while investigating unconfined compressive strength (UCS), water absorption, pH, microstructural changes, and swell. The analysis of the results shows that at zero cycle, the UCS of the untreated gypseous soils increases from 0.62 to 0.79 MPa and swell decreases from 69 to 23%, respectively, as gypsum content increases. However, upon subjection to wet–dry cycles, the UCS reduced from 0.16 to 0.08 MPa at the end of the sixth cycle due to dissolution of gypsum within the soil pores which reduced the strength. The result also shows that gypsum content increases water absorption and reduces the pH of the untreated gypseous soils because of the neutral pH of gypsum. Furthermore, lime-GGBS-treated gypseous soils maintained a higher pH after six wet–dry cycles compared to untreated gypseous soils due to the high pH of lime and the increase in calcium content which improved bonding. In addition, microstructural analysis using SEM indicated early age precipitation of cementitious compounds (CSH) for increasing strength of lime-GGBS-treated gypseous soils compared to untreated gypseous soils.

Evaluation of Suitability of Red Clay from Selected Areas of Gercus Formation, Sulaimaniyah, North Iraq, for the Construction of Embankment Dams

In this research, a geotechnical assessment was conducted for clay of the Gercus Formation to determine its suitability for embankment dams. The selected area is located in the north of Iraq. Six samples were collected from two sites in Dokan (Sulaimaniyah) and Haibat Sultan mountain (Koysinjaq), three samples each. Various geotechnical (physical, mechanical and chemical) tests were conducted based on standard specifications.&#x0D; The results of the grain size test of clay samples showed their conformity with Zone C curves and their suitability for the construction of embankment dams, according to the Iraqi standard for roads and bridges. The results of the plasticity limits test showed that the soil is made of fine, low plasticity silt (ML), and low plasticity clay (CL), according to the unified standard soil classification. The water content and plasticity limit tests (liquid limit, plastic limit, and plasticity index) demonstrated that these clays are conformable with the limits of the Iraqi standards. The results of the modified compaction test found a maximum dry density value of 1.962 g/cm3 with an optimum moisture content of 11.5%. The results of the permeability index (K) revealed low permeability according to the Das classification and, therefore, showed the suitability of the samples as raw filling materials in the construction of dams. Chemical tests (sulfate content, organic materials content, total dissolved salts, gypsum content, and pH value) showed compatibility with the requirements for the use in dams construction under the Iraqi standard (SoRB/ R5).

Established soil science methods can benefit the construction industry when determining gypsum content

We reviewed the treatment of gypsum and related calcium sulfates in a variety of scientific articles, most of which are about construction materials and their recycling. We checked if the substances involved in the reviewed articles had their gypsum content determined, and we depicted how these determinations were recently addressed in soil science. The corollary is that the easy and reliable analytical methods developed in soil science for gypsum content are overlooked in industrial studies. We suggest that the methods from soil science would work for many construction materials namely those with earthy or loose consistence and with heterogeneous composition, such as is the case for debris or rubble needing an assessment of gypsum content for their re-use, recycling, or disposal. The simple, robust proposed methods developed in soil science will reduce the isolation of the disciplines, an effect of the atomization of science in increasingly narrower sub-disciplines. • Gypsum is an abundant, cheap, and recyclable material used worldwide for construction. • The gypsum content determination in building materials is often overlooked in research articles. • Many gypsum detection methods are unsuited for content appraisal in earthen materials. • We propose methods from soil science for mixed materials common in building industry.

Do soil features condition seed germination of gypsophiles and gypsovags? An analysis of the effect of natural soils along an alkalinity gradient

Gypseous soils are widespread across drylands worldwide. They present remarkable challenges to plants and host a unique flora. We aimed to assess if the specificity and distribution of species on gypsum might be driven by species-specific germination responses to soil gypsum availability. We analyzed the germination of six gypsum specialists (gypsophiles) and four closely related generalist plant species (gypsovags) from the Iberian Peninsula and the Chihuahuan Desert in different field soils with contrasting concentrations of gypsum, pH and soil texture. Plant restriction to gypsum was unrelated to the germinating ability of seeds on different substrates. Irrespective of their affinity for gypsum, most species germinated better on mixed gypsum-calcareous soil and worse in the acidic soil treatment. Our data suggest soil pH and Ca availability were the main soil features driving seed germination, while the effect of gypsum content was generally not significant. The main exception was the Iberian gypsophile Helianthemum squamatum (L.) Dum. Cours., which showed increased germination on gypseous soils and higher germination in response to increased soil gypsum content. Except for this species, our findings indicate alkaline soils with high Ca availability favor the germination of most of the species analyzed, irrespectively of their gypsum content.

Experimental Study on the Thermal Performance of Rice Straw-Mortar Composite Materials

Thermal properties of mortar block can be improved through adding straw, which is related to the type, size, amount of the straw, and so on. In order to test the thermal insulation performance of rice straw-mortar composite materials, this paper adopted response surface methodology (RSM), which employed a four-factor, three-level Box-Behnken design regarding gypsum content (% mass fraction of gypsum), straw size (mm), straw content (% mass fraction of straw) and water content (g) of rice straw-mortar composite materials as independent variables. Thermal conductivity, thermal diffusivity and thermal resistance of composite materials were response variables. The straw content and water content extremely significantly affected all the responses; the straw size had extremely significant effect on the thermal resistance as well as significant effect on the thermal conductivity. According to the optimum solution of regression equations, the optimum values of thermal conductivity, thermal diffusivity and thermal resistance were 0.048 W (m K)−1, 0.163 mm2 s−1, and 12.743 K W−1, respectively. The optimization options of gypsum content, straw size, straw content and water content were 5.01%, 20 mm, 22.7% and 0.06 g, respectively. Due to the state change of pore water, thermal conductivity of rice straw-mortar composite materials containing free water decreased seriously after complete freezing and increased slightly after 15 times freeze-thaw. During first freezing process, the thermal conductivity increased obviously with the increasing of freezing time, then increased slowly. A theoretical basis was provided by the experimental results, which was essential for the study on the thermal performance of rice straw-mortar composite materials as well as the application of similar materials.

Detailed Processes and Potential Mechanisms of Pliocene Salty Lake Evolution in the Western Qaidam Basin

Hyperarid climate and salty lakes prevail in the current Qaidam Basin, but this basin was once a large paleolake until the early Quaternary. However, its evolution history and relationship with climate and tectonics are still elusive. Here we present detailed stratigraphic descriptions combined with total organic carbon content and weight ratio of organic carbon to total nitrogen records from fluvio-lacustrine sediments in the western Qaidam Basin to infer how the lake evolved during the late Pliocene-early Pleistocene. These data reveal a drying trend since 3.3 Ma, which we attribute to low latitude forcing and/or local tectonic activities. However, this trend was interrupted during 2.84–2.48 Ma, in which climate wetting was observed. We attribute the climate wetting during 2.84–2.48 Ma to intensified East Asian summer monsoon as is documented by the Chinese Loess Plateau records. Halite and gypsum content increased dramatically after 2.5 Ma, indicating the formation of salty lake in the western Qaidam Basin. These data improve our understanding of the detailed processes of Qaidam aridification and its potential forcing mechanisms.

Livestock grazing effect on the hydraulic properties of gypseous soils in a Mediterranean region

Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (Sc) and hydraulic conductivity (Kc) of the soil surface layer and the soil bulk density (ρb), saturated hydraulic conductivity (Ks), saturated volumetric water content, θs, and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρb, a significant influence of grazing on ρb was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content.

Water Volume Change Due to Wetting of Unsaturated Gypseous Sand Using Modified Oedometer

This paper investigates the water volume changes in gypseous sand soils within the change in matric suction and under different stress levels. The present research aims to examine water entry into the soil with different matric suction under different levels of constant net normal stress (221, 442, and 885 kPa). The soil sample is collected from Al-Najaf city, Iraq. The main soil of the city is sand with different percentages of gypsum at different locations and depths. These experiments revealed a clear relationship between decreasing the matric suction (wetting) and changing the gypseous soil structure, i.e., increasing the void ratio, and this behavior also depends on the net stress level. With the demolition of the voids under high-stress levels, there is a decrease in water volume change at zero matric suction (saturation). A comparison is made between the predicted soil water characteristics curve (SWCC) for the soil with the investigated values. The results show a shifting, which may be due to the accuracy of the curve fitting or/and the effect of the loading and gypsum content. This new understanding should help improve predictions of the impact of the load, gypsum content, and time.

Experimental Investigation of Square Footing Resting on Gypseous Soils Contaminated by Kerosene

This study investigated the behavior of square footing (Length = 100 mm) constructed over a gypseous soil contaminated with four percentages of kerosene (5, 10, 15, and 20%) and several thicknesses of the contaminated soil (0.5B, B, and 1.5B) was taken from Tikrit University in Salah Al-Deen governorate from the depth of (1.5-2) m under natural ground level. The tests revealed that the soil is high gypsum content (62%). The main loading tests of the gypseous soil were carried out [field density (dry) and field density (with soaking)] which are a reference for comparison with the contaminated gypseous soil loading tests. The results that are represented by the relationship between pressure and settlement show that the gypseous soil has a good resistance reached to (385 kN/m2) when compacted to field density before soaking. For the contaminated gypseous soil tests, the bearing capacity does not improve as the bearing capacity is reduced by 50% or more compared to the non-contaminated gypseous soil, as for the settlement there is a slight improvement. As for the soaked gypseous soils, it was showing an improvement in bearing capacity and an improvement in the settlement of footing.

Examine Some of Geotechnical Properties of Quaternary Deposits in Sharqat City/Salah El-Din Governorate and Suitability for Concrete

The present study aims to assess quaternary deposits’ engineering properties and usability in the study area (Al-Shirqat/Salah Al-Din). Four selected stations were investigated using the modeling method and grain size analysis; deposits were classified as coarse (GS-GW) according to the Unified Soil Classification System (USCS) standard. It’s found that the specific gravity of soil ranged between (2.57-2.71), and the absorption is about (1.12-1.83) %. The gypsum content of tested soil samples ranged between (1.35-5.08) %, and the total dissolved salts ranged between (3.61-9.52) %. The results of tested samples showed that the content of organic materials (0.56-0.89) % and the pH value between (7.96-8.11) %. The Los Angeles test showed that the percentage of weight loss ranged between (14.9-19.7) %, and the stability test results ranged between (0.623-0.867), while uniaxial compressive strength values ranged between (154-189) MPa. The study resulted that the study area models are suitable for use in structural concrete works.

Online measurements of material flow compositions using acoustic emission: Case of gypsum and anhydrite

In this study, acoustic emission technology (AE), an established technology in various applications, has been investigated for its suitability for material flow characterization of bulk material. High-frequency waves generated during impact processes are recorded as acoustic emission signals to be used as a suitable measurement technology. By analysing the acoustic emission signals of known material flow compositions, suitable parameters and algorithms can be developed. Based on AE technology, the study focused on determining the gypsum and anhydrite content of an unknown material flow with the aim of building an online measuring system that could be integrated into the process of gypsum mining and processing. If successful, this approach could partly replace current offline analysis methods and enable real-time process control in the gypsum industry. The AE application was tested in laboratory experiments on a custom-built circulation test bench as well as in gypsum processing plants. Online measurements of the gypsum content were successfully achieved with an accuracy of 2.5% and an update rate of every five seconds.

Mixing Ratios and Cementing Mechanism of Similar Silty Mudstone Materials for Model Tests

The similarity model test is one of the important means to study the engineering properties of soft rock. This study aims to develop similar materials for silty mudstone, which has characteristics of low strength and water expansion, based on traditional materials including gypsum, barite powder, clay minerals, and distilled water. The orthogonal design method was used to determine the mixing ratios of the similar materials. The density, uniaxial compressive strength, tensile strength, elastic modulus, and Poisson’s ratio were selected as control indicators of the similar materials. The results show that the water content is the dominant factor for the density, tensile strength, elastic modulus, and Poisson’s ratio of the similar materials of silty mudstone, while the gypsum content is the dominant factor for the uniaxial compressive strength. The physical and mechanical properties of the similar material samples with water content of 19%, barite powder ratio of 32%, and gypsum mass of 250 g show good similarity to those of the raw silty mudstone. The water absorption and expansibility of similar materials with clay mineral ratio of 12% are consistent with those of the raw silty mudstone. The scanning electron microscopy (SEM) observation indicates that the similar material with optimal mixing ratios exhibits a similar microstructure to that of silty mudstone.

Influence of Some Additives on the Properties of OPC Solidified Sandy Silt

The ordinary Portland cement (OPC)-based solidification process is used extensively to reinforce soils due to its available and good bonding properties. Alternative products are used in cementitious materials to enhance the strength and to reduce OPC consumption. In this study, the effect of additive type and mass fraction on the microstructure and mechanical properties of solidified sandy silt are investigated. There are four types of additives (gypsum, lime, clay particles, and fly ash) at mass fractions of 2, 3, and 4% that are considered in order to study their mechanical properties (unconfined compression, indirect tensile, flexural strength, and compressive resilient modulus) at 7, 14, 28, 60, and 90 days. The optimal contents of additive gypsum, clay particles, and fly ash are determined to be 2%, 4%, and 4%, respectively. Such improvement of additive-modified OPC solidified sandy silt is due to the formation of the crystalline compound or the gradation composition improvement via field emission scanning electron and X-ray diffraction analysis.

Effect of Heat Treatment Temperature on Properties of Phosphogypsum Based Wall Materials

The waste of land resources and the destruction of ecological environment caused by the massive storage of phosphogypsum are becoming increasingly prominent. In order to solve this problem, industrial solid waste phosphogypsum was used to the main raw material in this paper and aimed at the building materials utilization of phosphogypsum, and prepared a phosphogypsum‐based wall material. Through the pretreatment of phosphogypsum at different temperatures, the influence of heat treatment temperature on the performance of phosphogypsum based wall materials was explored. The experimental results show that with the increase of heat treatment temperature, the setting time, volume density and mechanical properties of phosphogypsum‐based wall materials gradually increase, and the hygroscopicity first increases and then decreases. Based on the performance and energy consumption, the best performance after 160°C heat treatment, when the content of hemihydrate gypsum in phosphogypsum is 53.62%, sample bulk density is 1.304 g/cm^3, moisture absorption is 30.7%, compressive strength is 3.74 MPa.

Investigation settlement for unsaturated soil AL-NAJAF upon matric suction and different loading using Oedometer

This research aims to conduct investigations on the settlement using an Oedometer matric suction device for unsaturated soil. The type of soil taken from the city of Najaf is as one model, a sandy gypsum soil, the percentage of gypsum content is 29% and the moisture content of the soil is 3%. The research includes experimenting by choosing three relative densities 95%, 85% and 75% with an amount of 150 KPA constant pore air pressure and three pore water pressure. 100 KPA, 130 KPA and 150 KPA where the matric suction values are 50 KPA, 20 KPA and 0 KPA respectively. Also, the soil is tested in the partially saturated state and fully saturated state under the influence of placing multiple loads 1kg, 2kg, 4kg, 8kg and 16 kg at a different matric suction (50 KPA, 20 KPA and 0 KPA) and relative densities. The settlement is measured by the LVDT device to measure the vertical displacement, where the data is recorded through a program installed on the calculator to measure the settlement data every second, where the results are then analyzed by excel program. The analysis of the experimental results achieves that the highest settlement ratio of 5.5% was achieved when loading (1kg) when applying matric (20 KPA) within 500 sec. The settlement increases with increasing time and stabilizes at the lowest interval of 76 sec., in the case initial of matric suction (50 KPA) at the relative density of 95% and 25 sec., in the case matric suction (0 KPA) at the relative density of 85%.

The history of the forming and the features of the soil, lithological and geomorphological structure of the Jizzakh steppe as the basais for its natural zoning

The paper provides initial materials characterizing the complicated history of formation, natural soils and lithological-geomorphological conditions of the Jizzakh steppe before the beginning of reclamation development. It is shown that on the basis of soil-lithological and geomorphological zoning, the Jizzakh steppe is divided into a number of natural regions belonging to different levels (altitude levels) of the piedmont plain. In total, 22 districts have been identified within the Jizzakh steppe, including the foothill margins. On the piedmont plain itself, the regions are combined into two high-altitude levels: the upper step and the lower step or blanket zone. These two levels differ sharply in terms of drainage conditions and soil salinity. The upper level, covering the upper and middle parts of the alluvial fan, the high interconal Zaamin-Sanzar plain and the Lomakino plateau, is characterized by a weak manifestation of salinity due to relatively good drainage, except for the sloping depressions of the Lomakino plateau. In contrast to the upper level, the lower level, located in the blanket zone of the piedmont plain, is characterized by active natural salinization because of the poor drainage. The saline sediments of the Zaamin cone delta are characterized by the greatest thickness. To a lesser extent, the rocks of the Sanzar cone delta, which are drained by deep gullies, are salinized. The Khavast sloping plain is characterized by a strongly saline upper two-meter layer, with salt and gypsum content decreasing with depth. Thus, it is shown that high salinity and gypsum bearing rocks, as well as high groundwater salinity of the cone delta zone are the source of modern salt accumulation in soils of foothill Golodnostepskaya plain, as well as in soils of the cone delta zone of Djizak steppe.

Obtaining Calcium Sulfoaluminate Using Aluminate Waste

In this work, studies have been carried out to replace bauxite with aluminate slags. Compounds of raw mixtures without use of fossil aluminate materials with different gypsum content have been developed. Instability of assimilation of anhydrite into calcium sulphoaluminate has been established. X-ray phase analysis has shown a weak dependence of increase in the firing temperature and increase in the yield of the main mineral C3A3·CŜ. Results of the study allow us to conclude that it is possible to obtain high-quality calcium sulphoaluminate (SAC) based on technogenic aluminate raw material.

Investigation of distinctive physico-chemical soil correlations for Kirkuk city using spatial analysis technique incorporated with statistical modeling

In the sense of challenging economic situation, it is difficult to perform laboratory tests in a whole intended area to define the soil characteristics for whatever task or situation within an entire city. Hence, this study has used the spatial analysis through applying the inverse distance weighted (IDW) technique to integrate with the available data for 56 different soil samples collected from various depths of Kirkuk city. The studied characteristics were mainly classified to physical soil properties included gravel, sand, silt, and clay contents with chemical soil properties included organic and gypsum contents, pH content, sulfur trioxide, and total dissolved solids (TDS) content. Moreover, statistical investigations such as physico-chemical correlation, linear single and linear multi regression models have been applied. The results of this study have focused on constructing thematic digital maps for visualizing different physical and chemical characteristics of Kirkuk soil. In statistical analysis, negative linear correlations are obtained from the relation between the values of the pH, gypsum, organic, and SO3 contents with the increase of the gravel content, whereas a positive linear correlation is attained for the values of TDS content with the increase of the gravel content. Furthermore, the proposed linear multi regression model predicts the pH values reasonably where most of the values were close to the equality line. The obtained digital maps accompanied with the statistical models will provide comprehensive spatial, agricultural, chemical and mechanical visualizations of the nature and morphology of the soils in Kirkuk city.

SIMILAR MATERIALS FOR QUASI-STATIC SCALED TESTS OF FAULT-CROSSING TUNNELS

The design of similar materials is one of the key links to ensure the matching of the physic-mechanical properties between the prototype and the test specimens. Based on the prototype of the Xianglu mountain tunnel of the water diversion project in the central Yunnan province, China, the scaling relationship of the physical quantities in the quasi-static scaled test of a fault-crossing tunnel is derived in this study according to the similarity theory and dimensional analyses. The similar materials of concrete and rock mass used in the test are developed with barite powder and sand as the aggregates and with gypsum and lime as the cementing material. The effects of each component on the physic-mechanical properties of the similar materials are investigated through orthogonal tests. The test results indicate that the strength, elasticity modulus and density of the similar materials can be significantly changed by the overall content of the high-strength gypsum and water-gypsum ratio. Small variation of the strength of the similar material is found when the sand-gypsum ratio is between 0.8 and 1.2, but the strength significantly decreases when the sand-gypsum ratio is between 3 and 12. The elastoplastic performance and the brittle failure mode of Grade C30 concrete can be well simulated by the similar material made of high strength gypsum, low strength gypsum, barite powder and sand. The tensile splitting and the diagonal shear failure modes of rock mass of Grade IV and V can be well simulated by the proposed similar material made of high strength gypsum, lime and sand. The development process and ratios of similar materials can provide important reference for model test and numerical simulation.