A universal hydro-mechanical coupled behavior model for clay-bearing strata-Molecular-level simulation approach.

Clay minerals in soils and rocks exhibit large volume change upon interaction with water and this behavior becomes even more complex when the strata are being stressed by the engineering and environmental loads. Therefore, a realistic prediction of the hydro-mechanical behavior of the clay-bearing strata is always a challenge due to their coupled swelling-mechanical response in the cases of geotechnical and geoenvironmental engineering problems, nuclear waste storage in clay-bearing rock repositories, shale gas extraction, and other uses of clay in the manufacturing industry. All the existing behavior models have restricted applications in the engineering and other fields of practice mainly due to the partial consideration of the structure and fabric of clay-bearing strata in the model formulation. In this study, a hydro-mechanical behavior model has been formulated using the parameters acquired from the molecular-level simulations and modeling of the volume change and stress-strain behavior of the clay-bearing structure. The Molecular Mechanics and Molecular Dynamic simulations were performed on the natural structure of the clay-bearing strata formulated using Monte Carlo technique. The mathematical model, developed from the simulation results, can predict the overall hydro-mechanical behavior of clay-bearing strata for all possible combinations of clay minerals, non-clay minerals, salts causing cementation of the soil/rock structure, confining pressures, and the induced strain levels. The developed model has successfully been validated through laboratory and field testing on the clay-bearing strata in both the elastic and elasto-plastic regions of the stress-strain behavior and also from the data of two (02) swelling clays (MX-80 and FEBEX Bentonite) from the existing literature, supporting the universal nature of the developed behavior model.

Investigating the Soil Unconfined Compressive Strength Based on Laser-Induced Breakdown Spectroscopy Emission Intensities and Machine Learning Techniques.

Laser-induced breakdown spectroscopy (LIBS) is a remarkable elemental identification and quantification technique used in multiple sectors, including science, engineering, and medicine. Machine learning techniques have recently sparked widespread interest in the development of calibration-free LIBS due to their ability to generate a defined pattern for complex systems. In geotechnical engineering, understanding soil mechanics in relation to the applications is of paramount importance. The knowledge of soil unconfined compressive strength (UCS) enables engineers to identify the behaviors of a particular soil and propose effective solutions to given geotechnical problems. However, the experimental techniques involved in the measurements of soil UCS are incredibly expensive and time-consuming. In this work, we develop a pioneering technique to estimate the soil unconfined compressive strength using artificial intelligent methods based on the spectra obtained from the LIBS system. Decision tree regression (DTR) and support vector regression learners were initially employed, and consequently, the adaptive boosting method was applied to improve the performance of the two single learners. The prediction power of the established models was determined using the standard performance evaluation metrics such as the root-mean-square error, CC between the predicted and actual soil UCS values, mean absolute error, and R2 score. Our results revealed that the boosted DTR exhibited the highest coefficient of correlation of 99.52% and an R2 value of 99.03% during the testing phase. To validate the models, the UCS values of soils stabilized with lime and cement were predicted with an optimum degree of accuracy, confirming the models' suitability and generalization strength for soil UCS investigations.

Analysis of Unconfined Compressive Strength of Rammed Earth Mixes Based on Artificial Neural Network and Statistical Analysis.

Earth materials have been used in construction as safe, healthy and environmentally sustainable. It is often challenging to develop an optimum soil mix because of the significant variations in soil properties from one soil to another. The current study analyzed the soil properties, including the grain size distribution, Atterberg limits, compaction characteristics, etc., using multilinear regression (MLR) and artificial neural networks (ANN). Data collected from previous studies (i.e., 488 cases) for stabilized (with either cement or lime) and unstabilized soils were considered and analyzed. Missing data were estimated by correlations reported in previous studies. Then, different ANNs were designed (trained and validated) using Levenberg-Marquardt (L-M) algorithms. Using the MLR, several models were developed to estimate the compressive strength of both unstabilized and stabilized soils with a Pearson Coefficient of Correlation (R2) equal to 0.2227 and 0.766, respectively. On the other hand, developed ANNs gave a higher value for R2 than MLR (with the highest value achieved at 0.9883). Thereafter, an experimental program was carried out to validate the results achieved in this study. Finally, a sensitivity analysis was carried out using the resulting networks to assess the effect of different soil properties on the unconfined compressive strength (UCS). Moreover, suitable recommendations for earth materials mixes were presented.

Role of casting and curing conditions on the strength and drying shrinkage of greener concrete.

The shrinkage of cement-based materials is a critical dimensional property that needs proper attention as it can influence the corresponding characteristics especially when the preparation of such cement-based material is done in hot weather. Studies have shown that the casting or curing conditions influence the performance of concrete. However, there is limited understanding of the combined role of casting temperature and curing conditions, especially for concrete made with unconventional binders. In this study, five supplementary cementitious materials (SCMs) were utilized as the substitute of the ordinary Portland cement (OPC) at different ratios to produce greener concrete and improve its characteristics and sustainability. The influence of four casting temperatures (i.e., 25 °C, 32 °C, 38 °C, and 45 °C) and two curing regimes (i.e., covering of samples using wet burlap and applying curing compound on the surface of samples) on the corresponding compressive strength and drying shrinkage at various ages was studied. The outcomes of this research revealed that the composition of the binders has a substantial impact on the characteristics of concrete. In addition, the casting temperature and curing regimes also have a huge role on the compressive strength of concrete produced with binary binders. For example, the compressive strength at 3 days of concrete made at 25 °C made with binary binders was reduced up to 31% compared to that made with only OPC as the binder when cured using wet burlap. Nonetheless, less than 38 ℃ was suitable to minimize the durability issues in the studied blended cement mixes.

The validity of laser diffraction system to reproduce hydrometer results for grain size analysis in geotechnical applications.

The grain size analysis plays a significant role in any geotechnical study. The grain size analysis, by means of sieving, is usually used for coarse material of particle size > 75 µm. For the fine material; the sedimentation methods are frequently adopted (e.g., hydrometers). Other methods also exist such as electron microscopy, digital image analysis and laser diffraction. The fine geomaterials commonly undergo agglomeration which makes the recognition of individual grain size using digital image analysis or electron microscopy challenging. To facilitate and enhance the grain-size analysis, this study was conducted using the Laser Diffraction System (LDS). Seven samples with different nature (composition and texture) and sources were analyzed by hydrometer and LDS. For LDS, various factors were studied such as air pressure, sonication, dilution, refractive index, and distribution method (volume or number). The results were compared qualitatively and quantitatively based on soil classification systems, fractal dimensions, and other parameters. Furthermore, this study provided a novel criterion to determine which LDS distribution method (volume or number) is to be used depending on the Liquid Limit. A combined sieve-LDS system is recommended to obtain the entire grain size distribution. It is concluded that the LDS is a viable technique that can replace the time-consuming hydrometer method to assess the grain-size distribution.

Utilization of Portland cement with limestone powder and cement kiln dust for stabilization/solidification of oil-contaminated marl soil.

Stabilization/solidification (S/S) is a technique that has been widely used to treat contaminated soils using several types of stabilizers, such as ordinary Portland cement (OPC). In this research, marl soil that was collected from eastern Saudi Arabia was contaminated by either diesel or crude oil at different dosages (i.e., 2.5, 5, and 10% by the dry weight of the soil) and tested to assess its geotechnical and environmental properties. Thereafter, the contaminated soil was stabilized using OPC, limestone powder (LSP), and cement kiln dust (CKD) at different proportions. The contaminated-stabilized soils were evaluated by measuring the changes in their geotechnical properties, and both metal and hydrocarbon contents. Results of this investigation indicated that the S/S treatment of the contaminated soils enhanced the compaction characteristics with a significant improvement in the unconfined compressive strength (UCS) results, and all of S/S-treated mixtures were found to pass the strength criterion of the U.S. Environmental Protection Agency (USEPA) (i.e., 340 kPa after 28 days of curing). Moreover, The UCS results of the stabilized soils were compared to the minimum strength requirements for both paved and unpaved road materials (i.e., 1380 and 690 kPa, respectively). Finally, scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses were used to elucidate the changes in the microstructure of the stabilized soils.

Efficiency of generic and proprietary inhibitors in mitigating Corrosion of Carbon Steel in Chloride-Sulfate Environments.

The efficiency of generic and proprietary corrosion inhibitors (based on nitrite, amine carboxylate or amino alcohol) in corrosion mitigation of carbon steel, which is exposed to concrete solutions with different amounts of chloride as well as sulfate, was studied. The corrosion protection provided by the selected corrosion inhibitors was investigated by performing a potentiodynamic polarization study. In addition, the surface morphological properties of carbon steel samples exposed to the electrolyte mixed with or without inhibitors was also evaluated by scanning electron microscopy. The potentiodynamic polarization measurements showed that the evaluated inhibitors decreased the corrosion current density by 1.6 to 6.7 times depending on the type of inhibitor and the level of sulfate concentration in the electrolyte. The performance of inhibitors based on nitrite was better than that of inhibitors based on amine carboxylate or amino alcohol. The possible mechanisms of the inhibition in the chloride plus sulfate environments are also elucidated.

Method and Mechanisms of Soil Stabilization Using Electric Arc Furnace Dust.

This paper reports the method and mechanism for improving the strength of marl and desert sand utilizing electric arc furnace dust (EAFD), an industrial by-product, in lieu of cement or lime. EAFD was used in conjunction with a small quantity (2%) of cement. The mechanical properties and durability characteristics of marl and sand mixed with 2% cement plus 5-, 10-, 20- or 30%-EAFD, by weight of the soil, were evaluated. The soil-cement-EAFD mixtures were used to determine their unconfined compressive strength (UCS), soaked California Bearing Ratio (CBR) and durability. The risk of leaching of toxic heavy metals, such as lead and cadmium, from the stabilized soils to the groundwater was also investigated. The mechanisms of stabilization of the selected soils due to the use of EAFD along with a small quantity of cement are also elucidated. The usage of 20 to 30% EAFD with 2% cement was noted to considerably improve the mechanical properties and durability of both marl and sand.

The Saudi Guidelines for the Diagnosis and Management of COPD.

The Saudi Thoracic Society (STS) launched the Saudi Initiative for Chronic Airway Diseases (SICAD) to develop a guideline for the diagnosis and management of chronic obstructive pulmonary disease (COPD). This guideline is primarily aimed for internists and general practitioners. Though there is scanty epidemiological data related to COPD, the SICAD panel believes that COPD prevalence is increasing in Saudi Arabia due to increasing prevalence of tobacco smoking among men and women. To overcome the issue of underutilization of spirometry for diagnosing COPD, handheld spirometry is recommended to screen individuals at risk for COPD. A unique feature about this guideline is the simplified practical approach to classify COPD into three classes based on the symptoms as per COPD Assessment Test (CAT) and the risk of exacerbations and hospitalization. Those patients with low risk of exacerbation (<2 in the past year) can be classified as either Class I when they have less symptoms (CAT < 10) or Class II when they have more symptoms (CAT ≥ 10). High-risk COPD patients, as manifested with ≥2 exacerbation or hospitalization in the past year irrespective of the baseline symptoms, are classified as Class III. Class I and II patients require bronchodilators for symptom relief, while Class III patients are recommended to use medications that reduce the risks of exacerbations. The guideline recommends screening for co-morbidities and suggests a comprehensive management approach including pulmonary rehabilitation for those with a CAT score ≥10. The article also discusses the diagnosis and management of acute exacerbations in COPD.

Detection of chloride in reinforced concrete using a dualpulsed laser-induced breakdown spectrometer system: comparative study of the atomic transition lines of Cl I at 594.85 and 837.59 nm.

The presence of chloride in reinforced concrete can cause severe damage to the strength and durability of buildings and bridges. The detection of chloride in concrete structures at early stages of the corrosion buildup process is, therefore, very important. However, detection of chlorine in trace amounts in concrete is not a simple matter. A dual-pulsed laser-induced breakdown spectrometer (LIBS) has been developed at our laboratory for the detection of chloride contents in reinforced concrete by using two atomic transition lines of neutral chlorine (Cl I) at 594.8 and 837.5 nm. A calibration curve was also established by using standard samples containing chloride in known concentration in the concrete. Our dual-pulsed LIBS system demonstrated a substantial improvement in the signal level at both wavelengths (594.8 and 837.5 nm). However, the new atomic transition line at 594.8 nm shows a significant improvement compared to the line at 837.5 nm in spite of the fact that the relative intensity of the former is 0.1% of the latter. This weak signal level of the 837.5 nm transition line of chlorine can be attributed to some kind of self-absorption process taking place in the case of the concrete sample.

Chemical composition and antioxidant activities of Jeddah corniche algae, Saudi Arabia.

The increased use of natural product in the pharmaceutical industry has led to an increase in demand for screening for bioactive compounds in marine algae. An important economic algae, through chemical composition analysis and their antioxidant activities were investigated in this study. Chemical composition analysis of three algal samples from the Chlorophyta Ulva lactuca (U), Phaeophyta Sargassum crassifolia (S) and Rhodophyta Digenea simplex (D) was tested. Main components were sugars (57.40-185.13 mg/g dry weight), uronic acids (29.3-45.26 mg/g dry weight), sulfate (94.7-181.2 mg/g dry weight), amino acids (7.6-16.7 mg/g dry weight) and small amounts of betaines (2.38-8.47 mg/g dry weight). Hydrolyzed chemical composition analysis fractions of algal extract was shown a great proportion of sugars plus sulfate (as polysaccharide composed) ranges between 332 and 538.2 mg/g dry weight with trace amounts of uronic acids (⩽9%). All three algal extract showed antioxidant activities on lipoxygenase, DPPH and on Ames test. Two of aqueous extracts (U and D) inhibited lipoxygenase activity by less than 50%, where as the methanolic extract (S) caused 76% inhibition of the control. In all cases, the methanolic extract were more inhibitory than the aqueous extract. The (S) showed the highest antioxidant activity with DPPH (69%) in aqueous extract and in methanol extract with Ames test (85%). Both U and D showed antioxidant activity with DPPH in hexane by less of 25% where as in both aqueous and methanolic extracts by less than 50% of the control. Aqueous and methanolic extracts of U and D showed high inhibition by Ames test which caused 70% and 75% respectively. IR spectra of algal extracts (U; D and S) range from 1450 to 750 cm(-1) were very similar absorption band at 1430, 1370, 1250, 1130, 1110, 1050 and 1020 cm(-1). Absorption bands were due to uronic acids, glucosides and sulfate. The presence of sulfated polysaccharide material in the fractions UF2, DF2 and SF2 were found as cell wall storage of marine algae, confirmed by (13)C NMR spectroscopy. It is concluded that the algal species probably have a different components and can be used in the activities of antioxidant enzymes as reduced the risks of enzymes. But the correlation between the chemical composition and antioxidant activities of algal extracts needs further investigation.