Mechanical alterations in shale formations due to exposure to water-based fracturing fluids and supercritical carbon dioxide (ScCO2) significantly affect the performance of shale gas exploration and CO2 geo-sequestration. In this study, a hydrothermal (HT) reaction system was set up to treat Longmaxi shale samples of varying mineralogies (carbonate-, clay-, and quartz-rich) with different fluids, i.e. deionized (DI) water, 2% potassium chloride (KCl) solution, and ScCO2 under HT conditions expected in shale formation. Statistical micro-indentation was conducted to characterize the mechanical property alterations caused by the shale-fluid interactions. An in situ morphological and mineralogical identification technique that combines scanning electron microscopy (SEM) and backscattered electron (BSE) imaging with energy-dispersive X-ray spectroscopy (EDS) was used to analyze the microstructural and mineralogical changes of the treated shale samples. Results show no apparent changes in the Young's modulus, E, and hardness, H, after treatment with DI water under room temperature (20 degrees C) and atmospheric pressure for 7 d. In contrast, E and H were decreased by 31.2% and 37.5% at elevated temperature (80 degrees C) and pressure (8 MPa), respectively. The addition of 2% KCl into DI water mitigated degradation of the mechanical properties. Quartz-rich shale specimens are the least sensitive to the water-based fracturing fluids, followed by the clay-rich and carbonate-rich shale formations. Based on in situ morphological and mineralogical identification, the primary factors for the mechanical degradation induced by water-based fluids include carbonate dissolution, clay swelling, and pyrite oxidation. Slight increases in the measured E and H and compression of porous clay aggregates were observed after treatment with ScCO2. The major factor contributing to the mechanical changes resulting from the exposure to scCO2 appears to be the competition between swelling caused by adsorption and compression of shale matrix. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
One of the major negative environmental implications of economic growth and the advancement of information technology is the large quantity of electronic waste dumped in landfills. Cathode ray tubes (CRTs) from outdated televisions and computer monitors are a significant source of electrical waste. The CRT funnel primarily consists of silica, significant alkalis (Na2O-K2O), and heavy metals like barium-strontium, along with a substantial lead (Pb) content that may contaminate the soil. Owing to its heavy metal content, CRT is considered hazardous waste, and regulations require its glass to be recycled or repurposed instead of landfill disposal. The low pozzolanic activity of CRT silica suggests that its high content, when paired with an optimized particle size and specific curing conditions, can enhance the mechanical properties of cement-based products. Hydrothermal treatment has been found to speed up both the hydration of ordinary Portland cement (OPC) and the pozzolanic reactions. Since the main objective was to safely recycle large amounts of CRT, three mixes were proposed with 10%, 20%, and 30% OPC + 90%, 80%, and 70% CRT, respectively, and the effect of hydrothermal curing conditions on mechanical properties and durability of these blends was investigated. CRT-70, a blend containing 70% CRT glass waste, showed enhanced strength due to the formation of zeolitic phases and calcium silicate hydrate (CSH). These phases also provided CRT-70 with notable fire resistance, ensuring its structural stability under elevated temperatures. These results demonstrate the possibility of production of precast building products via high-volume recycling of hazardous CRT waste.