Effects of sodium chloride on the mechanical strength of alkali activated volcanic ash and slag pastes under room and elevated temperatures

This study investigated effects of the sodium chloride on the microstructural and mechanical properties of alkali activated volcanic ash (VA) and ground granulated blast furnace slag as well as Portland cement pastes. To this end, unconfined compressive strength (UCS), scanning electron microscopy (SEM)-EDS-Mapping, FTIR, and XRD tests were conducted. Furthermore, effects of curing temperature on the binding capacity of chloride in alkali activated cements were examined in both elevated (HT) and room (RT) temperature conditions. The VA was replaced by slag at 0, 50, and 100 wt%. Based on the results, samples containing 100 wt% slag showed the highest mechanical strength in both curing conditions. Besides, addition of sodium chloride from 0 to 10 wt% did not significantly affect the strength of samples containing 100 wt% volcanic ash in both curing conditions. On the other hand, in HT condition, mechanical strength of samples containing 50 and 100 wt% slag, as well as Portland cement pastes increased with increasing sodium chloride from 0 to 2.5 wt%, and further addition of sodium chloride by up to 10 wt% led to a reduction in their strength. However, compressive strength of samples containing 50 and 100 wt% slag, as well as Portland cement samples, decreased with the addition of sodium chloride from 0 to 10 wt% in RT condition. Microstructural investigations were conducted, aiming to find the mechanism controlling the reactions. It was found that (N,C)-A-S-H and C-S-H gels were the dominant factor in the solidification and encapsulation of chloride ions in slag-based samples

Mechanical strength of saline sandy soils stabilized with alkali-activated cements

Saline soils usually cannot satisfy the requirements of engineering projects because of their inappropriate geotechnical properties. For this reason, they have always been known as one of the problematic soils worldwide. Moreover, the lack of access to normal water has intensified the use of saline water resources such as seawater in many construction and mining projects. Although cement stabilization is frequently used to improve the engineering properties of saline soils, Portland cement’s usage as a binder is constrained by its negative consequences, particularly on the environment. In this line, the effects of NaCl on the microstructural and mechanical properties of alkali-activated volcanic ash/slag-stabilized sandy soil were investigated in this study. Moreover, the effects of binder type, slag replacement, curing time, curing condition, and NaCl content on the mechanical strength of stabilized soils were examined. In addition, microstructural analyses, including XRD, FTIR, and SEM–EDS mapping tests, were performed to understand the physical and chemical interaction of chloride ions and alkali-activated cements. The results show that alkali-activated slag can be a sustainable alternative to Portland cement for soil stabilization projects in saline environments. The increase in sodium chloride (NaCl) content up to 1 wt.% caused the strength development up to 244% in specimens with 50 and 100 wt.% slag, and adding more NaCl had no significant effect on the strength in all curing conditions. Microstructural investigations showed that the replacement of volcanic ash with slag resulted in the formation of C-S-H and C-A-S-H gels that reduced the porosity of the samples and increased mechanical strength. Furthermore, surface adsorption and chemical encapsulation mechanisms co-occurred in stabilized soil samples containing slag and volcanic ash

Investigating accelerated carbonation for alkali activated slag stabilized sandy soil

Portland cement as a commonly used material in soil stabilization projects, releases considerable amounts of CO2 into the atmosphere, highlighting the need to use green binders such as ground granulated blast furnace slag as a substitute for cement. On the other side, extensive research is being conducted on accelerated carbonation treatment to decrease the industry’s carbon footprint. Carbonation transforms CO2 into carbonate minerals. This study investigates the influence of accelerated carbonation on the unconfined compressive strength (UCS) of soil stabilized with alkali-activated slag under ambient and oven curing conditions. Effects of curing time, binder content, relative density, and carbonation pressure (100, 200, and 300 kPa) were also studied. Furthermore, a calcimeter test was conducted to determine the amount of carbonate generated, which reflects CO2 sequestration in soil. The results showed that the carbonated samples achieved higher strength than the non-carbonated samples. However, a slight decrease in UCS was observed with the increase in CO2 pressure. The generated carbonate content directly correlated with the UCS of the samples, which explained the higher strength of carbonated samples. Also, the ambient curing condition was more favorable for the samples stabilized with GGBS, which can be attributed to the supply of required moisture. Results from XRD, SEM, and FTIR indicated that the strength development was due mainly to the formation of carbonation products (CaCO3), which facilitated the densification of solidified materials

Effect of CO2 exposure on the mechanical strength of geopolymer-stabilized sandy soils

In recent years, there has been growing interest in developing methods for mitigating greenhouse effect, as greenhouse gas emissions continue to contribute to global temperature rise. On the other hand, investigating geopolymers as environmentally friendly binders to mitigate the greenhouse effect using soil stabilization has been widely conducted. However, the effect of CO2 exposure on the mechanical properties of geopolymer-stabilized soils is rarely reported. In this context, the effect of CO2 exposure on the mechanical and microstructural features of sandy soil stabilized with volcanic ash-based geopolymer was investigated. Several factors were concerned, for example the binder content, relative density, CO2 pressure, curing condition, curing time, and carbonate content. The results showed that the compressive strength of the stabilized sandy soil specimens with 20% volcanic ash increased from 3 MPa to 11 MPa. It was also observed that 100 kPa CO2 pressure was the optimal pressure for strength development among the other pressures. The mechanical strength showed a direct relationship with binder content and carbonate content. Additionally, in the ambient curing (AC) condition, the mechanical strength and carbonate content increased with the curing time. However, the required water for carbonation evaporated after 7 d of oven curing (OC) condition and as a result, the 14-d cured samples showed lower mechanical strength and carbonate content in comparison with 7-d cured samples. Moreover, the rate of strength development was higher in OC cured samples than AC cured samples until 7 d due to higher geopolymerization and carbonation rate

Standardised computed tomographic assessment of left atrial morphology and tissue thickness in humans

Aims: Left atrial (LA) remodelling is a common feature of many cardiovascular pathologies and is a sensitive marker of adverse cardiovascular outcomes. The aim of this study was to establish normal ranges for LA parameters derived from coronary computed tomographic angiography (CCTA) imaging using a standardised image processing pipeline to establish normal ranges in a previously described cohort. Methods: CCTA imaging from 193 subjects recruited to the Budapest GLOBAL twin study was analysed. Indexed LA cavity volume (LACVi), LA surface area (LASAi), wall thickness and LA tissue volume (LATVi) were calculated. Wall thickness maps were combined into an atlas. Indexed LA parameters were compared with clinical variables to identify early markers of pathological remodelling. Results: LACVi is similar between sexes (31 ml/m2 v 30 ml/m2 ) and increased in hypertension (33 ml/m2 v 29 ml/m2 , p = 0.009). LASAi is greater in females than males (47.8 ml/m2 v 45.8 ml/m2 male, p = 0.031). Median LAWT was 1.45 mm. LAWT was lowest at the inferior portion of the posterior LA wall (1.14 mm) and greatest in the septum (median = 2.0 mm) (p < 0.001). Conditions known to predispose to the development of AF were not associated with differences in tissue thickness. Conclusions: The reported LACVi, LASAi, LATVi and tissue thickness derived from CCTA may serve as reference values for this age group and clinical characteristics for future studies. Increased LASAi in females in the absence of differences in LACVi or LATVi may indicate differential LA shape changes between the sexes. AF predisposing conditions, other than sex, were not associated with detectable changes in LAWT. Clinical trial registration: http://www.ClinicalTrials.gov/NCT01738828

Combined effect of laser irradiation and fluoride application in dental caries prevention

Background and Aims: Despite significant decline in dental caries in recent decades, the disease remains a public health problem especially in developing countries. In recent years combined application of laser and fluoride has been introduced as a new caries-preventive measure. The purpose of the present study was to review the literature on the preventive effect of combined application of laser and fluoride on the dental caries. Materials and Methods: PubMed, Google Scholar and EMBASE databases were searched for articles published from 1990 to November 30, 2013. Various combinations of the following keywords were used: Dental caries, Laser, Fluoride, Fluoride therapy, Prevention and Enamel. The inclusion criteria included all levels of available evidence. Articles published only in english language were evaluated, and unpublished data were not sought. Results: Several studies evaluating the effect of laser alone or combined with topical fluoride to prevent dental enamel demineralization were found. Studies assessing the combined effect were more frequently done on permanent teeth and just a few studies were done on primary teeth. In total, most of the studies confirmed that combined application of laser and topical fluoride has a remarkable effect in prevention of enamel demineralization compared to application of each of them alone. Conclusion: Laser irradiation combined with topical fluoride application seems to provide the best prevention effect on the dental caries initiation and progression in enamel of permanent teeth. However, more experimental and clinical studies are necessary to be done on the primary teeth in this area

Comparison of Two Educational Methods to Improve Emergency Management Among Dentists

The efficacy of different educational methods needs to be evaluated in dental courses. The main objective of the present study was to compare the effectiveness of two educational methods in the improvement of medical emergencies management among dentists in terms of knowledge, diagnosis, practice, and availability of necessary drugs and equipment. The target population of this randomized controlled trial study was all the dentists working in public and private offices in the city of Tehran, Iran. Baseline data collection through a designed and piloted questionnaire was conducted among 210 randomly selected dentists. The dentists were then randomly assigned to one of the one-day workshop program (W), flipchart (F), and control (C) groups. One month after interventions the follow-up data collection using the same questionnaire was performed. Chi-square, non-parametric Kruskal Wallis, and Wilcoxon Signed Ranks were used to compare outcome variables among the three groups before and after the interventions. The total response rate was 61.5%. No statistical differences existed among the three groups regarding the background at baseline. Diagnosis, practice, and knowledge score before and after the intervention improved significantly among the participants in W group (P=0.02, P<0.001 and P<0.001, respectively). In both F and C group, improvement occurred in practice scores (P=0.03 and P<0.001, respectively). Continuing education in the form of attending workshop seemed to be superior to receiving educational flipchart in the enhancement of the self-reported knowledge and practice of practicing dentists. None of these educational methods seemed to have significant effect on the availability of necessary equipment and drugs to manage medical emergencies in dental offices

Effect of Hydrogen on the Tensile Behavior of Austenitic Stainless Steels 316L Produced by Laser-Powder Bed Fusion

Hydrogen was doped in austenitic stainless steel (ASS) 316L tensile samples produced by the laser-powder bed fusion (L-PBF) technique. For this aim, an electrochemical method was conducted under a high current density of 100 mA/cm2 for three days to examine its sustainability under extreme hydrogen environments at ambient temperatures. The chemical composition of the starting powders contained a high amount of Ni, approximately 12.9 wt.%, as a strong austenite stabilizer. The tensile tests disclosed that hydrogen charging caused a minor reduction in the elongation to failure (approximately 3.5% on average) and ultimate tensile strength (UTS; approximately 2.1% on average) of the samples, using a low strain rate of 1.2 × 10−4 s−1. It was also found that an increase in the strain rate from 1.2 × 10−4 s−1 to 4.8 × 10−4 s−1 led to a reduction of approximately 3.6% on average for the elongation to failure and 1.7% on average for UTS in the pre-charged samples. No trace of martensite was detected in the X-ray diffraction (XRD) analysis of the fractured samples thanks to the high Ni content, which caused a minor reduction in UTS × uniform elongation (UE) (GPa%) after the H charging. Considerable surface tearing was observed for the pre-charged sample after the tensile deformation. Additionally, some cracks were observed to be independent of the melt pool boundaries, indicating that such boundaries cannot necessarily act as a suitable area for the crack propagation