Gypsum Content Research Articles

Understanding and mitigating settlement in gypseous soils: A comprehensive study on the role of saturation and soil stabilization techniques

This study examines the influence of saturation levels and soil additives on the load-settlement properties of gypseous soils, a significant geotechnical concern in regions like Iraq. The study analyzes the deficiencies of conventional oedometer testing, which often fail to adequately represent the true unsaturated conditions prevalent in these soils. The research investigates the impact of varying matric suction (Ψ) values on the compressibility of untreated, cement-treated, and CKD-treated gypseous soils. A modified oedometer apparatus, engineered to control and quantify matric suction, was used to replicate diverse moisture conditions. The experimental program investigated soils with varying gypsum contents (8.8%, 12.66%, and 30%), reflecting the diversity of gypseous soils seen in the field. The findings demonstrate that increased saturation levels significantly enhance settling in gypseous soils. As matric suction increases, settlement is markedly reduced due to elevated soil suction pressure and enhanced effective stress. The findings underscore the importance of unsaturated conditions in improving the load-bearing capacity of these soils. The study illustrates the advantageous impacts of cement and CKD treatments in reducing settling. The effectiveness of these methods is particularly apparent in partially saturated environments, emphasizing the need of including matric suction into design considerations. This research improves understanding of the complex behavior of unsaturated gypseous soils. The findings have practical importance for geotechnical engineering, including foundation design, ground improvement methods, and the development of effective solutions for settlement issues in areas with high gypsum concentrations.

Understanding the utilization potential of lepidolite slag in cementitious materials: Composition characteristics, hydration properties, and high value-added cementitious system design

Lepidolite slag (LES) is a kind of solid waste produced by extracting lithium from lepidolite, but researches focused on it are still limited. This paper works on understanding the utilization potential of LES in cementitious materials from its composition characteristics, hydration properties, and high value-added cementitious system design. Results show that the reactivity of LES is notably low in both water and alkaline solution. As a supplementary cementitious material (SCM), LES exhibits several drawbacks, including prolonging setting time, reducing compressive strength, and deteriorating pore structure. With addition of 30 % LES, the compressive strength at 28 d decreased by 63.3 %. Considering the high gypsum content within LES, an all-solid waste cementitious system was designed using high-volume LES combined with blast furnace slag (BS) and a small amount of lime. System with 40 % LES presents similar compressive strength with system composed entirely of BS at both 7 d and 28 d. The mechanism is that the excellent compound activation effect of gypsum in LES and lime on BS promoted the transformation of hydrotalcite to ettringite in the system. Even when LES content reached 70 %, compressive strength at 28 d surpassed 15 MPa. This study proposes a novel high value-added utilization way for LES in cementitious materials.

Study on Failure Characteristics and Acoustic Emission Laws of Rock-like Specimens under Uniaxial Compression

Complex underground conditions make it challenging to conduct extensive coring, and it is difficult for laboratories to carry out a large number of rock mechanics experiments due to the limited number of cores. Rock-like specimens are commonly used in the laboratory to replace coal-rock specimens. In this paper, rock-like specimens with different proportions are produced to study the mechanical properties, failure characteristics, and acoustic emission laws of rock-like specimens under uniaxial compression. The results show that when the rock-like specimen does not contain gypsum, the stress of the specimen decreases rapidly after reaching the peak stress, which is similar to the mechanical properties of hard brittle rock. When the rock-like specimen contains gypsum, the stress of the specimen decreases slowly after reaching the compressive limit, and the failure of the specimen is gentle, which is similar to the mechanical properties of soft rock. When the specimen lacks gypsum, the strength of the rock-like specimen is larger, and the strength of the specimen is positively correlated with the proportion of cement. When the specimen contains gypsum, the strength of the rock-like specimen decreases sharply, and the strength of the rock-like specimen is negatively correlated with the proportion of gypsum. The maximum acoustic emission ringing count increases with higher cement content but decreases with increased gypsum content. The cumulative count change of acoustic emissions approximately underwent four stages, aligning well with the four stages of uniaxial compression failure observed in typical rock. The research results have important reference value for the selection of rock-like materials to replace the original rock materials for laboratory research.

A genetic explanation for the anhydrite–halite cyclic layers in the Middle Jurassic Louann Salt, U.S. Gulf Coastal Region

ABSTRACT Successions of bipartite layers (couplets) form the bedding fabric of salt stocks of the U.S. Gulf Coastal Region, south-central U.S.A. The cyclic couplets typically have a thickness range of 3–20 cm and a mean of about 10 cm. Each couplet consists of a white band of halite interstratified with a thinner, gray band of halite mixed with anhydrite (generally 3–8 wt % of each couplet). Successions of couplets, which lack siliciclastic beds and significant hiatuses, make up the thick (∼ 1.5 km) Middle Jurassic Louann Salt. Deeply buried (by up to ∼ 18 km), the Louann couplets moved laterally by ductile flow into the base of salt stocks and rose (or appeared to). The Dead Sea is a unique, modern analog of the Louann Salt. The huge lake is a model of how surface evaporation, brine temperature, and double-diffusive salt fingering combined to form the Louann couplets. Halite varves (couplets) presently precipitate from the Dead Sea’s deep (∼ 300 m), marine-like brine. If these modern varves are to be a valid genetic model for the Louann couplets, they too must be annual layers. An explicit similarity of the Louann couplets with two modern and four ancient varve-established evaporitic couplets demonstrates that the Louann anhydrite–halite couplets are truly varves. The Louann varves accumulated at such a rapid rate (∼ 1 m every 10 years) that a deep-water depositional basin must have pre-existed. In the basin, an abrupt destabilized thermocline existed in summer between a surface zone (tens of meters thick) of warm, high-salinity brine and a deep zone (hundreds of meters thick) of cooler, lesser-salinity brine. This disposition resulted in a vertical flux from the thermocline of alternating rising and sinking salt fingers (millimeter wide, centimeter long, and millions per km2). When heat diffused from the warm surface zone into the cooler fingers, their density decreased, they rose, and blended with the ambient brine; and when heat diffused from the warm fingers into the cooler deep zone, their density increased, they sank, and blended with the ambient brine. Salinity also diffused into and from fingers but at a rate ∼ 100 × slower than heat. In summer, the Louann surface zone was NaCl undersaturated because: 1) solar heating caused enhanced NaCl solubility, 2) ascending fingers transferred low-salinity brine into the higher-salinity surface zone, and 3) descending fingers transferred high-salinity brine into the lower salinity deep zone. The Louann surface zone, however, was CaSO4·2H2O supersaturated because of: 1) gypsum’s retrograde solubility and 2) gypsum concentration by evaporation in the surface zone. Gypsum cumulates rained from the surface zone onto the seafloor. As fingers descended from the thermocline into the Louann deep zone, their NaCl salinity state changed from saturated to supersaturated. Cumulate and bottom-growth halite precipitated, and the halite and gypsum accumulated together on the seafloor. With subsequent dehydration of the gypsum, the precipitates formed the thin, gray, anhydrite(halite) summer band of the Louann varves. In the fall, brine above the thermocline began to cool. By mid-winter, energized by wind and convection, the brine column overturned, became significantly cooler, and intensely NaCl-supersaturated. Halite cumulates crystallized throughout and rained onto the seafloor to form the thicker, white, halite winter band of the Louann varves.

Eco-friendly corrosion inhibition and scale control in seawater using Foeniculum vulgare and Pimpinella anisum extracts with chemical compounds

This study investigated the corrosion inhibition and scale control properties of both natural extracts and chemical inhibitors for C25 galvanized steel sheets with an 85-μm thick zinc coating steel exposed to seawater. The inhibitors, including Foeniculum vulgare (AF-Sha), Pimpinella anisum (AF-Sim), M640, and Veo, underwent rigorous evaluation through techniques such as Tafel extrapolation, potentiodynamic polarization analysis, concentration factor scale, seawater analysis, X-ray diffraction (XRD), infrared spectroscopy (IR), and conductivity-temperature analysis. Notably, AF-Sha and AF-Sim exhibited outstanding corrosion prevention capabilities, achieving inhibitory efficiencies of 87% and 85%, respectively. Comparative analyses with chemical inhibitors, M640 and Veo, demonstrated promising performance, positioning natural inhibitors as environmentally friendly alternatives. Corrosion rates, inhibition efficiency, and concentration factor scale results provided insights into the inhibitory effectiveness of each compound, with Veo showing superior performance. The study also explored the antiscalant behavior of inhibitors, revealing their ability to prevent corrosion and scale formation. XRD analysis indicated the impact of inhibitors on the crystal structure of scales, while IR spectra provided insights into vibration properties. Conductivity and temperature analyses illustrated the inhibitors' role in reducing ion exchange and gypsum concentration in seawater. These findings suggest that the inhibitors offered robust protection for ferrous metal surfaces and hold significant potential for practical applications. Additionally, our weight loss investigation extends this understanding, demonstrating the practical applicability of corrosion inhibitors like AF-Sha and AF-Sim in real-world scenarios. The presented results contribute significantly to the understanding of galvanized steel corrosion behavior in seawater, offering valuable insights for corrosion engineering applications.

Desilication and purification of phosphogypsum waste by flotation using a photosensitive collector

Phosphogypsum (PG) is the main by-product of wet phosphoric acid production and has seriously polluted the environment. In this study, PG was purified by reverse flotation using a photosensitive azobenzene surfactant (PASF). After reverse flotation, the content of gypsum in PG increased from 89.16 % to 93.32 %, the whiteness of PG increased from 25.62 % to 60.9 %, and the content of quartz decreased from 4.87 % to 2.12 %. The Zeta potential of quartz and gypsum became positive after being treated with PASF, indicating that PASF enhanced the floatability of quartz and gypsum. The results of FTIR and XPS indicated that there were both electrostatic attraction and hydrogen bonding between PASF and quartz. Density functional theory (DFT) calculations indicated that the adsorption of PASF on the quartz surface was more stable than on the gypsum surface. Upon exposure to UV irradiation, the molecular structure of PASF was transformed from trans to cis. Meanwhile, the adsorption amount of PASF on the quartz surface was decreased and the rigidity of the corresponding adsorbed layer was increased. This work provides a method to purify PG waste, which is important for the comprehensive utilization of PG.

Effects of nano-clay on the geotechnical properties of gypseous soil

Abstract Gypseous soils suffer from sudden settlement when subjected to water flow due to dissolving of gypsum salts, so all structures constructed on gypseous soil undergo significant deformations due to the soil’s ability to collapse. Around the world, specifically in the arid and semi-arid regions gypseous soils are mostly found also, and can be found in the west desert of Iraq and even in the southern regions, amounting about between 30 and 35% of the country’s total area. There are several techniques to improve the geotechnical properties of collapsible soils, but one of the most recent techniques is using the nano technology. Five different proportions of nano-clay (NC) were incorporated into a gypseous soil containing 80% gypsum in order to enhance its chemical and geotechnical characteristics (1, 2, 3, 4, and 5%). The tests findings (chemical, physical, and mechanical tests) demonstrated that the addition of nano-clay to gypseous soil has a significant impact on the geotechnical properties of soil where it leads to decrease the gypsum content of soil, pH value, maximium dry density, specific gravity, and collapse index. On the other hand, the utilized of nano clay material causes to increase shear strength parameters (c and φ), optimum water content and liquid limit. Adding 4% of nano-clay results in a significant decrease of 53% in the collapse index and an increase of 311% in soil cohesion and 30% in the angle of internal friction.

Influence of adding gypsum on the properties of lime-stabilized expansive soil

Abstract Expansive soils present major structural and geotechnical engineering problems. Expansive soil undergoes considerable changes in volume because of variations in water content. These variations in volume can occur as either swelling or shrinking and are commonly referred to as swell-shrink soils. Considering key aspects, such as the characteristics of the soil, is essential when dealing with swelling soils. There are expansive soils in both humid areas, where they pose problems with a high plasticity index, and in semi-arid or arid areas, where even moderately swelling soils can cause considerable damage. In order to solve problems related to expansive soil, it is important to stabilize it using various additives like gypsum, lime, and so on. The effects of adding three percentages of gypsum (2%, 4%, and 8%) to 6% lime-stabilized expansive soil to improve its engineering properties are investigated through several tests. The results of tests displayed that adding gypsum has improved properties of prepared soil with 6% lime. The optimum mixture for (gypsum-lime) that gets the highest improvement in soil properties is (6% lime + 4% gypsum). This mixture shows reducing in the free swell, swelling pressure, and plasticity index (from 8.51% to 2.81%, from 715.68 Kpa to 89.18 Kpa, from 33% to 29% respectively). Also, this mixture shows increasing in CBR (from 13.69% to 16.17%) and unconfined compressive strength (UCS) for the curing time of 0, 7, and 14 days (from 264.318 Kpa to 492.131 Kpa, from 380.584 Kpa to 736.318 Kpa, and from 480.192 Kpa to 828.590 Kpa respectively). The maximum dry density (MDD) and optimum moisture content (OMC) increase with increasing gypsum content, While the specific gravity decreases.

Enhancing the hydration and micromechanical properties of C3A-gypsum systems with a plant-derived biomolecule

This study investigates the influence of tannic acid (TA), a natural plant-based biomolecule, on the hydration of tricalcium aluminate (C3A)-gypsum systems, aiming to elucidate its potential as a novel concrete strength enhancer. To this end, detailed investigations were conducted into the hydration and nano-mechanical properties of C3A-gypsum system regarding the content of sulfate. In the absence of gypsum, the addition of TA accelerates the hydration of C3A, leading to a 30.6 % increase in accumulated heat until 10 h. This acceleration is attributed to TA's intercalation with metastable hydration products, impeding their transformation into final hydrates (C3AH6). Characterization using XRD, TGA, and FTIR techniques confirms the presence of hexagonal hydrates as the main hydration products in C3A-TA pastes, while the main hydration products in C3A-DI pastes was cubic one. In scenarios involving gypsum, TA markedly retards the hydration of C3A-gypsum mixtures, with SEM analysis indicating the promotion of AFt formation at low sulfate content while inhibiting its transformation to AFm. Furthermore, comprehensive nanoindentation results demonstrate that TA consistently enhances the micromechanical properties of C3A-gypsum hydrates, irrespective of gypsum content. This study provides valuable insights into the mechanisms through which TA influences the hydration of C3A-gypsum systems, offering promising avenues for enhancing the performance of concrete materials.

Projection-Pursuit Regression-Based Optimization of Frost Resistance and Mechanical Performance in Alkali-Activated Slag Cement Pavements

In recent years, applying slag micro-powder as a substitute for cement in preparing alkali-activated slag cement stabilized sand (AASCSS) mixtures has become increasingly widespread. In the severe cold regions of Xinjiang, multi-objective optimization of the mechanical and frost resistance properties of AASCSS is particularly crucial. This paper adopts slag micro-powder to replace Portland cement, together with lime and desulfurization gypsum as activators, to explore the effects of activator type and dosage on the mechanical and frost-resistance properties of AASCSS. A prediction model for the mechanical and frost-resistance properties of AASCSS based on projection-pursuit regression (PPR) was proposed and established. Using the developed PPR model, contour plots of the comprehensive performance were calculated, simplifying the multi-objective problem into two single-objective problems focusing on mechanical and frost resistance properties for analysis. This method avoids subjective weighting and hypothesis-based modeling. By analyzing the contour plots of comprehensive performance, the optimal performance indices for mechanical and frost–thaw properties and the corresponding types and dosages of activators can be directly determined. When the required 7-day unconfined compressive strength in road engineering is 5.6 MPa, the optimal value of the freeze–thaw performance index (BDR) is 94.08%. At this point, the corresponding lime content is 2.1%, and the desulfurization gypsum content is 3.3%. The research results provide a reference for applying slag to road-based materials.

Ring Footing Bearing Capacity Erected on Dry Gypseous Soil

This study investigates the behavior of ring footing erected on gypseous soil and compares it with the circular footing, including conducting (24) experiments of loading ring footings, where the inner and external diameter ratio was (Din./Dout. = 0, 0.2, 0.3 and 0.4), resting on two types of Gypseous soil, for the circular footing the external diameter was (150mm) and thickness (15mm) made from solid steel. The results for study showed the ring footings were best than the circular footings. The ratio (Din./Dout. = 0.4) was beast for all ratios of (Df/D). Capacity of bearing increased when the ratio (Df/D) increase. Bearing capacity for high-gypsum content soil showed good results compared to the low-gypsum content soil. The first was high content of gypsum (63.42%) obtained from the Tikrit University, and the second was low content of gypsum (8.15%) from the Baiji area. The tests were doing inside box have dimensions (900×900×700 mm). The experiments were divided into twelve tests for dry gypsum soil condition with high gypsum content using density of (13.76 kN/m3), and twelve tests for dry soil with low gypsum content using density of (14.87 kN/m3). Experiments were conducted for different ratios (Df/D=0, 0.5, and 1).

Effect of Different Colorless Properties of Zinc on Solid Development in Soils with Different Gypsum Content

Effect of Different Colorless Properties of Zinc on Solid Development in Soils with Different Gypsum Content

Pedogenic and Spatial Distribution of Gypsum Content in Soil Series units in Al-Dur District in Salah Al-Din Governorate

Pedogenic and Spatial Distribution of Gypsum Content in Soil Series units in Al-Dur District in Salah Al-Din Governorate

Interaction of Curing and Soaking on Collapse Potential of Nanoclay-Treated Soil

This study examines the combined impact of pre-test curing and soaking periods on the soil's resistance to collapse those results from treating gypseous sand with varying amounts of nanoclay. The soil comes from the Iraqi city of Najaf. The soil sample is mainly sand. The nanoclay named "Montmorillonite K10" is used, and it is non-toxic. The tests are performed with a computerized Oedometer. The collapse potential is estimated according to a single Oedometer test (SOT), where the specimens are initially dry and then soaked under a stress level of 200 kPa. Four data sets related to the percentages of 0, 3, 6, and 12% nanoclay are used. Each data set comprises three groups of pre-tests for curing duration and different soaking durations. All experiments have a constant initial dry density of 1.64 g/cm3, water moisture of 3%, and gypsum content of 29%. The findings of this study show that the collapse potential (CP) of natural soil specimens decreases as the pre-test curing time increases. Generally, there is a decrease in CP due to adding the nanoclay and 6% of the nanoclay exhibited the highest reduction in CP. Also, there is an increase in the pre-test curing for the nanoclay-treated soil specimens, which leads to an increase in the CP related to the no-curing state.

Quantification of Gypsum in Soils via Portable X-ray Fluorescence Spectrometry

Abstract This study explores the potential of X-ray fluorescence (XRF) as a rapid, nondestructive, and cost-effective technique for in situ sulfate quantification. Gypsum, the main source of sulfate in soils, reacts with calcium-based stabilizers to form expansive minerals, which reduces the long-term strength of the treated soil. Therefore, accurate detection of sulfate content prior to employing calcium-based chemical stabilization is important to mitigate the possibility of expansive mineral formation and ensure acceptable engineering behavior of the stabilized soil. Portable handheld XRF (PXRF) has shown the ability to estimate gypsum content accurately, utilizing calcium as a proxy. However, detecting sulfur, in the form of sulfite or sulfate remains challenging due to device sensitivity limitations. This research aims to address this limitation and develop a method for direct sulfur detection, enhancing the utility of PXRF for in situ sulfate quantification. Laboratory standards were created with known amounts of gypsum and portions were sent to a commercial laboratory for whole rock analysis. The remainder of the reference standards were used to calibrate several soil library standards within the PXRF. The calibrated PXRF was able to accurately detect the anhydrous form of gypsum, anhydrite (CaSO4), in these reference standards for contents ranging from 0 to 8 %. The proposed XRF-based approach offers the potential to revolutionize sulfate detection in soils, providing a rapid and reliable tool for assessing soil stability and optimizing chemical stabilization efforts. By enabling real-time, on-site analysis, this method holds promise for improving construction practices and reducing the risk of structural damage associated with soils containing sulfate-bearing minerals.

Speciation of Zn in Arid Soils With Saline Accumulations. Case Study of the Biskra Region, Algeria

Zinc (Zn) deficiency in plants is closely related to its bioavailability in soil. However, the behaviour of Zn in soils, especially in saline areas, remains complex. This research aims to clarify the distribution and dominant forms of Zn in arid soils with salt accumulations from the Biskra region by studying soil samples from ten representative profiles. Soil samples were collected from dif ferent horizons of each profile to a depth of 120 cm and subjected to speciation analysis using sequential extraction. The results indicate a deficiency of Zn in all soil samples, resulting in reduced concentrations of dif ferent forms of Zn. The dominant forms were residual Zn (R-Zn) and oxide-bound Zn (O-Zn), which accounted for over 90% of total Zn. The study revealed a negative correlation between soil salinity and all Zn forms, except for R-Zn, which showed a positive correlation. Additionally, Zn concentrations showed a negative correlation with gypsum, except for exchangeable Zn (E-Zn). It is important to note that the presence of gypsum in soils was significantly and negatively correlated with O-Zn. Although the sequential extraction method used may have limitations in accurately quantifying all forms of Zn, this study fills a gap in the literature on Zn assessment and speciation in arid soils. The study emphasizes the significance of soil characteristics, particularly salinity and gypsum content, in shaping Zn distribution. Overall, these results contribute to a better understanding of Zn availability and mobility in arid and saline environments, providing valuable insights for improved soil management practices in such regions.

Ion transportation properties of cement-based material under standard curing and steam curing

In coastal and saline environments, the infiltration of chloride and sulfate ions into cementitious materials can result in erosion and deterioration. This research focuses on the impact of temperature-related curing methods on the ion transport properties and microstructure of these materials. The results show the curing method does not alter the hydration products of cementitious materials. High-temperature curing reduces the content of ettringite, resulting in decreased Friedel's salt and gypsum after chloride ion corrosion. Meanwhile, high-temperature curing reduces the content of Ca(OH)2 and SiO2, decreasing the content of gypsum after sulfate ion erosion. It indicates that high-temperature curing reduces the binding capacity of both chloride ions and sulfate ions. Besides, high-temperature steam curing deteriorates the pore structure compared to standard curing. As a result, the resistance of concrete to ion corrosion is reduced under high-temperature steam curing. Besides, the surface ion concentration and binding capacity of chloride ions and sulfate ions both increase with the duration of erosion. Under the same erosion age, the binding capacity of sulfate ions is significantly higher than that of chloride ions. This research provides new insights into the transport characteristics of eroding ions under high-temperature steam curing.

Mechanical properties, micro-mechanisms, and constitutive models of seawater sea-sand engineered cementitious composites

Three mixing proportions of engineered cementitious composites (ECCs) were prepared using seawater, sea-sand, and PVA fibers, corresponding to three strength grades of C30, C40, and C50, respectively. The mechanical properties of these three kinds of seawater sea-sand engineered cementitious composites (SS-ECCs), including compressive strength, tensile strength, flexural strength, elastic modulus, ultimate elongation, uniaxial compressive and tensile stress-strain relationship, and so on, were analyzed by compressive, tensile, and flexural tests. The tensile and flexural strength of SS-ECCs are influenced by their ductility. The SS-ECC with C40 strength grade exhibited the best ductility, with an average ultimate tensile strain reaching 3.42 %, and possessed the highest tensile and flexural strength. The C50 specimen had the worst ductility, but its tensile strength and flexural strength came in second place. As the strength grade increased, the elastic modulus gradually increased, while the Poisson's ratio decreased. Uniaxial compressive and tensile constitutive models for SS-ECCs were established. The uniaxial compressive constitutive model was divided into a nonlinear ascending stage and a bilinear descending stage. XRD and TGA results revealed that the improvement in the strength of SS-ECCs was mainly attributed to the increased content of Ca(OH)2 in the reaction products. Additionally, the gypsum content in the raw materials decreased with the increasing strength grade, resulting in a reduction in the generation of ettringite (AFt).

Clinker-Free Cement Manufactured with Metallurgical Slags

Steel slag is a significant environmental liability generated by pyrometallurgical processes. Residue generation, such as granulated blast furnace slag and basic oxygen slag (BOF), is intrinsic in steel production. Blast furnace slag, generated in the carbothermal reduction of iron ore, is almost entirely used as a supplementary cement material in Portland cement. BOF slag, produced in the conversion of pig iron into steel in a basic oxygen converter, is still not consolidated or valued for reuse. This research proposes the reuse and valorization of BOF slag combined with blast furnace slag in clinker-free cement production. Cement formulations were produced with different slag and gypsum contents, ranging from 80 to 90% blast furnace slag, 10 to 20% gypsum, and 10 to 15% BOF slag. All formulations were evaluated for compressive strength at ages of 3, 7, 14, 28, 91, and 180 days of curing. At the initial ages, the cement formulations exhibited high resistance. On the 3rd day, the cement formulations reached up to 10 MPa, and on the 7th day, 40 MPa. At late ages, the best-performing formulation, ECO2, showed, after 28 days of hydration, a compressive strength greater than 50 MPa, and at 180 days, a compressive strength greater than 80 MPa. It was possible to understand that BOF slag acts in cement alkaline activation with pH increase, more or less actively due to the presence of lime, portlandite, and calcite.

Geomechanical characterization and mineralogical correlation of compositionally diverse world-class Kazakhstani source rocks: Insights from nanoindentation testing

Extensive nanoindentation testing over a range of deflection depths of up to 4 μm yielded a large dataset, providing a viable framework for the statistical assessment of the mechanical properties, specifically elastic modulus (E) and hardness (H), of compositionally diverse organic-rich mudstone samples. The data from indentations as shallow as 300–400 nm were clustered using the k-means algorithm to identify three mechanical categories in the samples: a soft pseudophase (e.g., organic matter, gypsum, and clay minerals), a stiff pseudophase (e.g., quartz and feldspar), and a transitional composite-like pseudophase bridging the soft and hard minerals. The initially diverse values of E and H for the mechanical pseudophases were observed to converge to a constant value at indentations beyond 2–2.5 μm (varying between different samples), implying the existence of a minimal probing depth for assessing the bulk E and H of heterogeneous mudstone samples. The obtained bulk E and H values (8–21 GPa and 0.3–0.9 GPa, respectively) demonstrated a strong correlation with the mineralogical composition of the indented samples. Despite containing a notable proportion of mechanically stiff components (>45 vol%), the bulk mechanical parameters determined in this study were significantly lower than those reported for major shale formations such as the Barnett and Longmaxi Shale. This discrepancy is primarily due to the presence of organic matter with low thermal maturity (Ro < 0.6%), which constitutes <36 vol% of the samples, and a significant gypsum content, accounting for <15 vol%.The employed approach not only demonstrated the importance of choosing the proper indentation depths for investigating the mechanical properties of highly heterogeneous mudstone rocks and their constituent minerals, but it also illustrated the capability of examining various volumes of investigation using nanoindentation, approaching macroscopic values, and identifying a representative element volume (REV). The findings also provided crucial insights into the fracability and overall producibility of the investigated formations, thereby enhancing our understanding of their extraction potential.