Strength performance of low-bearing-capacity clayey soils stabilized with ladle furnace slag.

In this paper, the performance of ladle furnace slag (LFS), a by-product of secondary steel refining, is evaluated as a binder to stabilize clayey soils of low bearing capacity. The aim is to define whether additions of this by-product to clayey soil can stabilize the soil in accordance with the technical specifications of Spanish standards. To do so, three different soils stabilized with 5% LFS were compared with the same soils stabilized with 2% lime and with no stabilization, in order to investigate their different behaviors. The chemical and mineralogical characterizations of all the soil mixes were conducted using X-ray fluorescence, X-ray diffraction, and scanning electron microscopy. The Atterberg limit test was used to study the plastic behavior of the soils, and the results of compaction, bearing capacity, unconfined compressive strength, and direct shear strength (cohesion and friction angle) tests defined their strength characteristics. The analysis was completed with the pH monitoring of the mixes along the curing time in order to relate the pH changes with the strength evolution. The addition of LFS to the soils has resulted in an increase in the liquid limit and plastic limit, causing therefore a slight decrease in the plasticity index. All the soils showed increases between 30% and 70% in their California Bearing Ratios immediately after mixing with 5% LFS, and after 90 days of curing, improvements of 30-188% in their unconfined compressive strength were noted in comparison with untreated soil, which were higher than the lime-stabilized soils. The cohesion of soils stabilized with LFS at 28 days of curing obtained improvements ranging from 40 to 300% depending on the type of soil. However, the friction angle showed a slight increase of 10% in two of the soils and zero in another. The high initial pH in LFS-stabilized soils was maintained during the curing time, which favored the development of pozzolanic reactions that improve the soil strength. These results confirmed that the substitution of lime with LFS is a feasible option for soil stabilization.

Teaching lessons learnt by civil-engineering teachers from the COVID-19 pandemic at the University of Burgos, Spain.

The COVID-19 lockdown in Spain caused abrupt changes for students following the Bachelor's Degree in Civil Engineering at the University of Burgos when face-to-face classes switched to online teaching. The recovery of face-to-face teaching after lockdown meant that classes were taught with obligatory social distancing and the use of masks. Teachers were therefore unable to interact with students closely, to perceive their facial expressions during class, or to conduct group work. The changes to civil-engineering teaching linked to the COVID-19 pandemic and the lessons that civil-engineering teachers learnt from the new teaching scenarios are studied in this paper. The reflections of teachers throughout all three stages of the pandemic (pre-pandemic and lockdown, during lockdown, and post-lockdown), and the qualitative and mixed analysis of their responses to a survey of open-ended questions contributed to the identification of six major lessons: (1) asking questions and using real-time quiz tools enliven classes and help to determine which concepts to emphasize for proper student understanding; (2) autonomous student learning can be promoted through the provision of supplementary documentation and the digitalization of solutions to classroom exercises; (3) virtual site visits and real visual examples interspersed with explanations bring concepts closer to their real applications; (4) the delivery of projects in the form of audio-recorded presentations enable their distribution, so that other students can also learn from them as well as the students who created them; (5) online videoconferences, adapted to the concepts that are addressed, facilitate fast and flexible communication with students; and (6) online continuous-assessment exams can promote better student learning patterns and final-exam preparation. Nevertheless, these six lessons were drawn from the experience of teachers at a small Spanish university where the period of solely online teaching during the COVID-19 pandemic lasted only four months. Thus, it would be interesting to analyze the experience of civil-engineering teachers at larger universities and universities that had longer periods of solely online teaching. A study of the level of implementation of the six aspects when the pandemic is declared over might also be worthwhile.

Reflections throughout the COVID-19 Lockdown: What Do I Need for Successful Learning of Engineering?

The intention of this study was to identify the elements that engineering students consider fundamental for successful learning on engineering courses. The aim was to provide generic guidelines suitable for any engineering course with which the teaching may be adapted in the light of comments from students, while student learning improves. The abrupt transition from face-to-face to asynchronous online teaching due to the COVID-19 pandemic prompted reflection among students on both teaching methods. Students were invited to evaluate each method through a survey of open-ended questions, identifying useful elements for their learning. The survey was repeated over nine weeks, to obtain the views of students after they had accepted the change and had critically analyzed how to improve online teaching. A cross-coded qualitative and mixed (word counting) analysis showed that the explanation of engineering concepts should be organized, hierarchical, repetitive, and exemplified. Furthermore, the teacher should link all the activities and projects to the concepts explained and quickly solve any doubts that they raised. As a consequence of the online teaching resulting from COVID-19, the need of independent student learning and peer support was also very evident. Teaching functions are essential on engineering courses, as teachers have to explain the overall concepts carefully, identify the key concepts, and demonstrate their industrial and professional applications. Furthermore, teaching methodologies that balance these aspects with autonomy and peer support for learning on engineering courses should be promoted.

The Outbreak of the COVID-19 Pandemic and its Social Impact on Education: Were Engineering Teachers Ready to Teach Online?

The major impacts of the COVID-19 pandemic are still affecting all social dimensions. Its specific impact on education is extensive and quite evident in the adaptation from Face-to-Face (F2F) teaching to online methodologies throughout the first wave of the pandemic and the strict rules on lockdown. As lesson formats changed radically, the relevance of evaluating student on-line learning processes in university degrees throughout this period became clear. For this purpose, the perceptions of engineering students towards five specific course units forming part of engineering degree courses at the University of Burgos, Spain, were evaluated to assess the quality of the online teaching they received. Comparisons were also drawn with their perceptions of the F2F teaching of the course units prior to the outbreak of the pandemic. According to the students' perceptions, the teachers possessed the technical knowledge, the social skills, and the personal capabilities (empathy and understanding of the at times troubled situation of each student) for a very abrupt adaptation of their courses to an online methodology. The shortcomings of the online teaching were related to its particularities and each teacher's personality traits. Overall, engineering teachers appeared well prepared for a situation of these characteristics and, if similar online teaching scenarios were ever repeated, the quality of engineering teaching appears to be guaranteed.

Performance and Durability of Porous Asphalt Mixtures Manufactured Exclusively with Electric Steel Slags.

Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are by-products of the electric steelmaking sector with suitable properties for use in bituminous mixtures as both coarse and fine aggregates, respectively. In this research, the production of a porous asphalt mixture with an aggregate skeleton consisting exclusively of electric steelmaking slags (using neither natural aggregates nor fillers) is explored. The test program examines the asphalt mixtures in terms of their mechanical performance (abrasion loss and indirect tensile strength), durability (cold abrasion loss, aging, and long-term behavior), water sensitivity, skid and rutting resistance, and permeability. The results of the slag-mixes are compared with a standard mix, manufactured with siliceous aggregates and cement as filler. The porous mixes manufactured with the slags provided similar results to the conventional standard mixtures. Some issues were noted in relation to compaction difficulties and the higher void contents of the slag mixtures, which reduced their resistance to raveling. Other features linked to permeability and skid resistance were largely improved, suggesting that these mixtures are especially suitable for permeable pavements in rainy regions. In conclusion, a porous asphalt mixture was produced with 100% slag aggregates that met current standards for long-lasting and environmentally friendly mixtures.

Heavy-metal extraction from sewage sludge using phosphorous-based salts: optimization process with Na2H2P2O7.

Land application is one of the important disposal alternatives for sewage sludge, but availability of potential toxic metals often restricts its uses. Three phosphorous-based salts (Na2H2P2O7, K4P2O7, KH2PO4) were studied as potential metal extractants. The conclusions of the research were that greater extractive efficiency is achieved through a 30-min process of vertical shaking with disodium diacid pyrophosphate - Na2H2P2O7 - at a concentration of 0.2 M at pH 2. Alternatively, the optimized process with oscillating shaking equipment would require 60 min. In both cases the average of set of extracted metals is around 50%. A second extraction process with potassium pyrophosphate - K4P2O7 at pH 6 achieved the reduction of further total amounts of metal, upper 65% with respect to the initial content. In this way the sludge could be used in land applications, with restrictions on each soil, according to the limit values specified in the future regulations.