Synergistic Influence of Cement–Lime Stabilization on the Mechanical Properties and Mineralogical Changes of Sabkha Soils from Aïn M’lila

Carbon dioxide (CO2) interacts with rock minerals due to a series of geochemical reactions affecting rock geomechanical properties. These changes in mineralogy, mechanical, and elastic properties weaken the reservoir rock and caprocks. These effects, as consequences, affect the deep saline formation’s mechanical integrity, storage capacity, storage efficiency, and permanence or safety of Carbon Capture and Sequestration (CCS). Generally, CO2 is injected into the rock continuously in supercritical conditions. Different injection schemes and strategies have been proposed to manage these effects; however, the dynamics of CO2 interaction when subjected to these strategies are unknown. This paper provides a comprehensive analysis of the geochemical and geomechanical impacts of supercritical CO2 (scCO2) on rock formations, employing three distinct injection strategies: Continuous scCO2 Injection (CCI), Water- Alternating Gas (scCO2) Injection (WAG), and Simultaneous Water and scCO2 Aquifer Injection (SAI). Through experimental approaches, the study utilizes core samples from Gray Berea sandstone and Indiana limestone to examine short-term and long-term effects on rock elasticity, strength, and mineralogy. This research assesses the alterations in elastic and mechanical properties by employing a suite of coupled experimental approaches, including core flooding, uniaxial compression testing, and X-Ray Diffraction (XRD). Results demonstrate that different scCO2 injection strategies significantly affect the rock mechanical integrity and mineral stability due to acidification, geochemical reaction, sequences of the dissolution and precipitation processes, cyclic effect, and mineral hardness. CCI and WAG demonstrate a more favorable impact on the geomechanical properties of both rock types. Conversely, the SAI strategy proves less beneficial, adversely affecting both elastic and mechanical properties despite occurring geochemical reactions. The study highlights the interplay between mineral dissolution and precipitation processes under varying injection conditions, providing insights into optimizing injection schemes to maximize CO2 storage while maintaining the structural integrity of the geological formations.

The effect of weathering on changes of physical and mechanical properties of rocks is a prime concern in the perspectives of geology and engineering. These properties have been studied mostly on weathered igneous and sedimentary rocks under humid climates. Studies on weathering of metamorphic rocks, especially under a tropical climate, are rare. This study evaluates change of physical, mechanical, chemical, and mineralogical properties of metamorphic rocks that weather under tropical climatic conditions. Samanalawewa hydropower project area was selected for this study, because rapid weathering of a metamorphic rock (sillimanite garnet gneiss) was observed in the project site. Fresh rocks that are subjected to weathering have reached to completely weathered condition in a time span of less than 25 years in this area. Visually assessed weathering grades were physically and mechanically evaluated using bulk density, equotip hardness, porosity, specific gravity, point load strength, and slake durability tests. Mechanical properties, especially point load strength, change rapidly at the onset of weathering, while chemical properties show significant changes at later stages of weathering. Mineralogical changes such as appearance of secondary minerals are at the latter part of weathering. Physical properties gradually change during weathering. The observed changes in physical, mechanical and chemical properties indicate that their variations during weathering are independent of lithology and climatic conditions.

Injection of carbon dioxide (CO2 ) underground, for long-term geological storage purposes, is considered as an economically viable option to reduce greenhouse gas emissions in the atmosphere. The chemical interactions between supercritical CO2 and the potential reservoir rock need to be thoroughly investigated under thermodynamic conditions relevant for geological storage. In the present study, 40 samples of Lavoux limestone and Adamswiller sandstone, both collected from reservoir rocks in the Paris basin, were experimentally exposed to CO2 in laboratory autoclaves specially built to simulate CO2 -storage-reservoir conditions. The two types of rock were exposed to wet supercritical CO2 and CO2 -saturated water for one month, at 28 MPa and 90°C, corresponding to conditions for a burial depth approximating 3 km. The changes in mineralogy and microtexture of the samples were measured using X-ray diffraction analyses, Raman spectroscopy, scanning-electron microscopy, and energy-dispersionspectroscopy microanalysis. The petrophysical properties were monitored by measuring the weight, density, mechanical properties, permeability, global porosity, and local porosity gradients through the samples. Both rocks maintained their mechanical and mineralogical properties after CO2 exposure despite an increase of porosity and permeability. Microscopic zones of calcite dissolution observed in the limestone are more likely to be responsible for such increase. In the sandstone, an alteration of the petrofabric is assumed to have occurred due to clay minerals reacting with CO2 . All samples of Lavoux limestone and Adamswiller sandstone showed a measurable alteration when immersed either in wet supercritical CO2 or in CO2 -saturated water. These batch experiments were performed using distilled water and thus simulate more severe conditions than using formation water (brine).

The changes in the composition and structure of the rock matrix caused by weathering lead to great alterations in its mechanical and physical properties. When considering this, geologists and engineers should pay special attention to materials from transition zones, namely, between the soil and rock over the weathering profiles. This research aimed to perform a wide characterization of the physical, mineralogical and geomechanical properties of a syenogranite rock in various degrees of weathering developed in a Brazilian tropical climate. Laboratory tests were performed to characterize the rock matrix properties at 5° of weathering. The mineralogical composition, the types and number of microstructures, the main physical and chemical changes, and the micropetrographic and microfracturing indexes of the matrix were obtained from analysing petrographic thin sections. The physical and geomechanical characterization included the determination of physical properties, index properties, strength and strain. The thin sections showed that the tropical climate had a great influence on the mineralogical changes, with the occurrence of mainly chemical processes from the medium to the highest degree of weathering. Among the properties evaluated, porosity was the most sensitive to the weathering, reaching 51 times higher in the highly weathered rock. The microfracturing index did not change much, showing a 42.0% increase from the low value of the fresh rock to the slightly weathered rock. Regarding the mechanical properties, the uniaxial compressive strength was the most sensitive to weathering, as observed by a loss of approximately 99.0% of its initial strength when in highly weathered rock conditions. In agreement with previous studies published on granites worldwide, the larger variations in the syenogranite rock properties were also presented from the medium degree of weathering. An experimental study on the use of Digital Image Correlation produced satisfactory results for determining the axial strain and elasticity modulus for more weathered syenogranite materials. New correlations and a quali-quantitative procedure for its classification have been proposed and tested based on the concepts of applicability, representativeness and significance. From 10 proposed correlations, 50% were considered with high or total applicability, and its use is highly recommended for estimating the parameters for syenogranite. Alternatively, from 31 correlations found in the literature, only 16% have shown high or total applicability for syenogranite.

Carbonate reservoirs dominate 70% of oil and 90% of gas reserves in Middle East region, and imbibition is the main mechanism for fracturing fluid up-take during hydraulic fracturing stimulation process. Due to highly heterogeneous nature of tight carbonate source rocks, it is crucial to understand effects of the imbibed fluid on the mechanical, morphological and flow properties of the carbonate rocks. While the influence of imbibed fluids on the wettability of carbonate reservoir has been studied intensively, the research on effects of imbibed fluids on the texture and mineralogy of the carbonate rocks is very limited. This paper aims to provide a conceptual approach and workflow to characterize and quantify microstructure and mineralogy changes resulting from the imbibed fluids. A thin-section of low permeability organic-rich carbonate rock sample with a dimension of 7mm × 7mm × 0.3mm (length × width × thickness) was used in the study. The sample was submerged into 2% KCl (pH = 7.1) fluid from one end to simulate the spontaneous imbibition process. Scanning Electron Microscope (SEM) was used to capture the sample’s morphological change before and after spontaneous imbibition. Energy Dispersive Spectroscopy (EDS) mapping was used to study mineralogy changes (dissolution and precipitation) before and after fluid treatment. Inductively coupled plasma (ICP) equipped with optical emission spectrometer (OES) detector has been used to quantify dissolved ion concentrations in the treatment fluid. Permeability and porosity were measured using core plugs (1" in diameter × 1.5" in length) before and after imbibition process with half-length of the sample submerged into the treatment fluid. The SEM images for the thin-section sample show three zones with distinct fluid up-take characters. In Zone I, which was submerged into the testing fluid, considerable mineral dissolution has been observed. In Zone III, which was above the testing fluid level, considerable mineral precipitation was detected. While in the transition zone (Zone II, which was between the above two zones around the water-air level), minor amount of mineral dissolution was observed. The mineralogy changes resulting from the dissolution and precipitation have been identified by EDS analysis in all three zones. Gypsum and calcite were found to be dissolved in the imbibed fluids, while gypsum was found to be deposited on the rock surface in zones above fluid level. The observed gypsum deposition might result from the dissolution of the gypsum and calcite and re-precipitaion later from the imbibition experiment due to water evaporation and/or from sample drying process. Absolute permeability and porosity measurements for core plug samples show that both increased after the imbibition process.

This study investigates the fire resistance of alkali-activated mortar incorporating crushed brick as both a precursor and aggregate. The optimal alkaline activator was identified as a combination of KOH and Na₂SiO₃, with a curing period of 3 days at 70 °C. Two mortar series were produced, each exhibiting different workability: on series comprised cement mortar, while the other included three alkali-activated mortars, with variations in the molarity of the KOH solution. The mortar samples were subsequently heated to 600°C, and their mechanical properties and mass were measured to determine residual values/losses. The best-performing alkali-activated and cement mortars underwent visual assessments of cross-sections to evaluate the impact of mortar consistency on fire resistance. Additionally, changes in mineralogy and microstructure were followed by instrumental techniques to clarify the results before and after heating. While cement mortars had superior mechanical properties at room temperature, alkali-activated mortars retained a higher percentage of their mechanical properties post-heating, demonstrating better fire resistance. Mortars with plastic consistency showed better fire resistance than those with fluid consistency. These findings suggest that brick-based alkali-activated mortars could be developed into fire protection boards for structural members. Doi: 10.28991/CEJ-2025-011-04-05 Full Text: PDF

This paper investigates mortars with fifty percent cement replacement of supplementary cementitious materials in binary and ternary blends, according to DS/EN 197-5: 2021. A new standard that allows for up to 50% of cement replacement levels than previously. Different aspects ranging from rheology, mechanical properties, and mineralogical changes were measured. The selected shale was ground in a laboratory disk mill, blended and tested in binary blends (only shale), and together with limestone filler as ternary blends. As expected, the mechanical properties of these mortars are lower than the mortar made only with Portland cement. The binary binder, with 50% cement replacement by calcined shale alone, developed larger compressive strengths and larger reductions in portlandite than the ternary binder, due to the additional pozzolanic reactions. The replacement of one-third of the shale by limestone filler, with a total cement replacement of 50%, had the lowest compressive strength values but less superplasticizer demand for the target workability. This allows, when judged by the rheology and mechanical properties alone, a mixture of both SCMs might be beneficial, for example where no risk of corrosion would be expected (X0, XC1). Furthermore, one might consider the optimization of the relation between the calcined shale and limestone where CO2 emissions are being reduced.

Performance of alkaline activation for the consolidation of earthen architecture

The effect of alteration in the petrographic characteristics of charnockite on its strength, its engineering properties and transformations of the specific gravity which took place during weathering has been examined in this study. This study characterized selected samples of un-weathered and weathered charnockite rocks of Ijare, Ondo State, Nigeria. The physical properties determined were specific gravity, density, porosity, water content and water absorption while the mechanical properties investigated include the point load strength index. Results from the analysis carried out reveal: the point load index of 5.74Mpa and 3.72Mpa for unweathered and weathered samples; average uniaxial compressive strength of 136.90Mpa and 65.50Mpa for unweathered and weathered samples; slake durability of 98.80% and 97.80% for unweathered and weathered sample; Schmidt rebound value of 49Mpa and 45Mpa for both the unweathered and weathered samples respectively. The rock samples were also subjected to petrographical analysis whose result shows that weathering increases some investigated physical properties like porosity, water content and water absorption of the rock while decreasing the specific gravity and density. The result of the tests shows the bulk and dry densities increase for both the weathered and unweathered samples; increased degree of weathering equally results in a major reduction in the strength of the charnockite rock which is directly associated with changes in mineralogy and associated porosity. The point load strength, uniaxial compressive strength test and rebound hardness result values decreases because of weathering. Weathering processes also affected the physical properties of rock, mineralogy, chemical composition as well as the mechanical properties of the rock thereby reducing the strength and mechanical behavior of the rock materials.

A view of microstructure with technological behavior of waste incorporated ceramic bricks

ABSTRACT: The Bakken Petroleum System in the Williston Basin consists of three main members: Upper Bakken Shale (UB), Middle Bakken (MB), and Lower Bakken Shale (LB). The Middle Bakken is a calcareous siltstone and fine-grained sandstone which is a proven reservoir within the Williston Basin. Injection of Supercritical CO2 (ScCO2) may cause changes in the elastic behavior of the rock and therefore may reactivate the fault in the Bakken Formation. This research aims at studying the changes in the MB mechanical properties when flooded with ScCO2 for 30 days, and to quantify the physical and chemical effects of ScCO2 saturation on the mineralogy composition and fluid properties of the formation. This will be achieved using different rock physics models before and after ScCO2 injection. Two different samples were taken from MB clastic and carbonate portions of well 24123 in McKenzie County. X-Ray Diffraction (XRD) analysis was applied on two samples pre-and post-CO2 saturation. The results of post-CO2 modeling resulted in a decrease of densities and elastic properties of both lithologies at different rates. Only change in mineralogy and fluid properties were considered for the post-CO2 injection modeling. 1. INTRODUCTION The Bakken formation consists of three main members: Upper Bakken Shale (UB), Middle Bakken (MB), and Lower Bakken Shale (LB). The UB and LB shales are proven source rocks with a similar lithology and are composed of an organic-rich, siliceous, pyritic black shale. The UB covers a larger areal extent than the LB within the Williston Basin. The MB member is a calcareous siltstone and fine-grained sandstone which is aproven reservoir within the Williston Basin (Lefever & Helms, 2006; Nordeng et al., 2010; Pitman et al., 2012). Despite the enormous hydrocarbon reserves within the Bakken formation, the Bakken is classified as unconventional oil-bearing reservoir due to its ultra-low porosity and permeability characteristic (Sorensen et al., 2008). The variation of MB lithology across the Williston Basin from mainly clastic to carbonate led to divide it intoseven distinct lithofacies (Lefever & Helms, 2006; LeFever & LeFever, 2005; Ozotta et al., 2021c).

The escalating greenhouse gas emissions have compelled global economies to implement climate change mitigation strategies. Geological hydrogen storage in depleted oil and gas reservoirs emerges as a groundbreaking solution, offering a dual benefit of repurposing existing geological structures while advancing sustainable energy storage, potentially facilitating the transition to a low-carbon economy. However, the potential for hydrogen leakage over extended storage periods is a significant concern. To assess the risk of leakage, it is essential to understand the interactions between hydrogen, brine, and the reservoir caprock integrity. In this study, we collected core samples from three depleted oil and gas reservoirs in the Bakken Formation (W17351, W21884, and W24881), from three distinct fields: Antelope, Alger, and Ranch Coulee. The Upper Bakken formation serves as a seal for potential underground hydrogen storage in the Middle Bakken reservoir. The core samples were subjected to hydrogen and brine exposure under high-pressure, high-temperature (HPHT) conditions in an autoclave reactor for 1 and 5 days to simulate reservoir conditions and assess the impact of hydrogen-brine-caprock interactions on the reservoir's integrity. We analyzed the samples' porosity, permeability, and mechanical properties before and after long-term exposure to hydrogen-brine using Nuclear Magnetic Resonance (NMR), permeability measurements, and ultrasonic measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM) to assess changes in their properties. The results showed a consistent increase in permeability across all samples, with the magnitude of increase varying based on exposure duration. NMR measurements indicated a substantial, time-dependent increase in porosity for all samples. Mechanical properties, such as Young's modulus and Poisson's ratio, decreased after exposure to hydrogen-brine, suggesting increased susceptibility to deformation and reduced ability to withstand stresses. SEM analysis revealed the development of fracture pores, interparticle pores, and dissolution-induced pores, as well as changes in elemental composition. XRD analysis showed changes in the relative abundances of minerals, with a decrease in clay and quartz content and an increase in K-feldspar content. These findings have significant implications for the integrity and sealing capacity of the Upper Bakken formation when considering its suitability for underground hydrogen storage. The observed changes in permeability, porosity, mechanical properties, microstructure, and mineralogy raise concerns about the potential for hydrogen leakage and the long-term stability of the reservoir seal.

Performance of the bentonite barrier at temperatures beyond 100 °C: A critical review

Precast concrete structures may be affected by delayed ettringite formation (DEF) if an improper curing method is used. DEF can lead to cracking and a reduction in the concrete's strength, which, in the event of a fire, may decrease the structure's fire resistance duration. Given that, in both DEF occurrence and fire scenarios, microstructural changes are the primary causes of alterations in mechanical properties, this study evaluated the mineralogical changes induced by exposure to high temperatures in mortars with potential DEF. To accomplish this, samples of reference mortars and mortars with a potential for DEF formation (molar ratio SO3/Al2O3 of 1.1) were prepared. The samples underwent a DEF induction period (curing in water at 80°C) and were subsequently exposed to high temperatures (200, 400, 600 and 900ºC). X-ray diffraction and scanning electron microscopy analyses revealed that mortars with a molar ratio SO3/Al2O3 equal to 1.1 exhibited a higher incidence of ettringite with type II morphology, which possesses an expansive behavior. Additionally, the curing process resulted in the decomposition of ettringite. For specimens subjected to 200°C, there was no significant increase in the intensity of portlandite peaks in the thermally cured samples. Regarding the change in the SO3/Al2O3 molar ratio, its influence became evident in samples heated to 600 and 900ºC. At these temperatures, anhydrite was observed, which might hinder material recovery in a post-fire scenario.

This study focuses on the valorization of glass waste in the field of geotechnics, particularly for the reinforcement of clay soils used in road construction. Glass waste, produced in large quantities, represents a potentially sustainable resource. The experimental work involves incorporating ground glass (particle size < 80 µm) into clay soils in order to evaluate its effects on their mechanical properties. The addition of 30% glass reduces the plasticity index from 28 to 15%, indicating a decrease in water sensitivity. The internal friction angle increases from 11° to 25°, highlighting a significant improvement in shear strength. CBR tests show an increase in bearing capacity, supporting the feasibility of its use in road embankments. XRD analyses reveal mineralogical changes due to the presence of glass, while infrared spectroscopy confirms the existence of amorphous phases. The optimum dry density increases, indicating better compaction. Moreover, oedometer tests show a reduction in swelling and settlement indices. In summary, the incorporation of glass improves the stability and durability of clay soils. This approach represents an ecological and economical solution while contributing to the sustainable management of glass waste.