A comparison between low-clinker cement and geopolymer mortars for their application in 3 D printing is discussed in this paper. The mortars are composed of materials with low environmental impact, such as cements with low clinker content, by-products of the industry and recycled aggregates. The developed mortars were both mechanically and rheologically characterized. The environmental impact was studied by LCA. To select the most suitable dosages, MCDM analysis was applied based on cost of materials, printability and LCA. Compressive strength was considered as a normalizing parameter for both the LCA and cost. The mortars showed good printability and suitable mechanical strength, being higher in the cement mortars. The LCA showed that the geopolymer mortars have a higher environmental impact due to the use of sodium hydroxide. Likewise, MCDM revealed that low-clinker cement mortars are at the top of the ranking, due to a lower environmental impact and lower cost of materials.

3D concrete printing (3DCP) has developed rapidly in recent years, with a relatively high amount of mortars emerging apt for 3D printing. Some of these mortars include fibers to improve their strength. Despite mechanical properties having been quite well studied, there still is missing information on cost, printability, and environmental impacts. The objective of this research is to select the best mortars with fibers considering four criteria: printability, mechanical strength, and economic and environmental impact applying a multi-criteria decision-making analysis (MCDMA). Seven types of fibers with different dosages were assessed in the reinforced mortars: zylon, aramid, carbon, glass, cellulose, textile, and polypropylene. AHP method and equal weights were used as ponderation techniques of the criteria while WASPAS and TOPSIS methods were used to calculate the rankings of the MCDMA. Printability was measured through rheological tests using a rotational rheometer, mechanical strength through flexural tests at 28 days based on EN 196–1, and cost just considering the materials and environmental impact through a life cycle assessment (LCA). The results showed that 13-mm-long glass fibers with a content of 0.1% were the best alternative, closely followed by the mortar with 6 mm cellulose fibers with a content of 0.05%. For the best option (G13;0.1), the increments in the printability index, flexural strength, cost, and LCA were − 14.37%, 16.70%, 5.88%, and 2.86%, respectively. It can also be concluded that high elastic modulus fibers (zylon and aramid), although able to increase significantly the flexural strength (up to 30% in the case of zylon), prevent them from being an optimal solution due to their high cost.

The huge increase in production of construction and demolition waste (CDW) worldwide is leading to the valorisation of as recycled aggregates. One of the most promising alternatives is its use as a recycled aggregate in the manufacture of structural concrete, which motivates the study of the dynamic behaviour of these materials in order to ensure their suitability for use in elements subjected to dynamic loads. This work evaluated the resonant compressive fatigue behaviour of structural concretes with 25% or 50% recycled mixed aggregates, either individually or in combination with 25% recycled cement of clay-based materials both from CDW. All mixes were subjected to compressive fatigue tests using the accelerated Locati method. Regarding the fatigue limit, the results showed that for all mixes, it was between 30% and 45% of the compressive strength. In addition, a correlation was also found between the resonance frequency of the test and the deformation suffered by the specimen. This correlation enabled the estimation of the fatigue limit through a more stable parameter than the strain measured by strain gauges, namely, the resonance frequency. In addition, it was found that the resonance frequency of the test changed as the specimen damage increased. This observation enabled the estimation of the fatigue limit through a more stable parameter than the strain measured by strain gauges, namely, the resonance frequency.

Concrete 3D printing in the field of construction is rapidly developing in recent years. Some key aspects of mortars used in 3D printing include good extrudability and sufficient load-bearing capacity to support their own weight during the printing process. Thus, the rheological properties of the fresh mortar should be determined since they have to be comprised between certain values to make mortars suitable for 3D printing. In this study, a low-cost rotational rheometer has been developed to obtain the rheological characteristics of different mortar mixtures apt for 3D printing. In order to validate it, numerical simulations have been undertaken, which have shown a good correlation between the experimental and analytical results. Furthermore, a comparison with another commercial rheometer has been conducted using a mortar without fibers and a common testing protocol, showing results with similar variability to other proficiency tests undertaken with cement pastes. In addition, the rheological behavior of various sustainable mixtures incorporating recycled materials and different types of fibers was studied. The article further examines how the types, lengths, and percentages of fibers influence rheological parameters, establishing ranges suitable for 3D printing.

The unique circumstances created by the COVID-19 pandemic pose serious challenges to mood stability and emotional regulation at all ages. Although many people tend to react resiliently to stress, others appear to display emotional anxiety and depression-related symptoms. In this study, we carried out a survey (N = 10,053) during the first week of the general lockdown (quarantine) in Argentina to measure early affective reactions in Argentine adults. Respondents showed substantial anxious and depressive symptoms, with 33 % and 23% of participants reporting possible depressive and anxious syndromes, respectively, with the youngest group (18 to 25 y.o.) showing the highest prevalence of symptoms. Even if prior mental health problems predisposed or aggravated the reaction, participants without prior complaints showed signs of psychological impact. Using linear regression, the most important independent variables related to depressive symptoms was the feeling of loneliness followed by daily stress. In the case of anxious states, the strongest variables were negative repetitive thinking and feeling of loneliness. Other psychological, economic, and social factors are discussed. This study is in line with previous literature that highlight the importance of the psychological impact of pandemics, but additionally demonstrates that these reactions are present at a large scale immediately after the start of quarantine with very low infectious rates as an early anticipatory adaptive reaction leading to potential negative outcomes from adjustment disorders to major disorders. In addition, the present results provide potentially relevant information about sudden environmental impacts on affective states and specific pathways for anxiety and depression to be expressed. We end by discussing implications for public policy based on considering the most vulnerable groups. Key Findings: More than a third of the studied sample (n = 10,053) showed substantial depressive and anxious symptoms between 5 and 7 days after the start of the national quarantine. 33.7% of the sample scored above the PHQ-9 cutoff for possible diagnosis of a depressive disorder and 23.2% for an anxiety disorder. 28.6% of the participants showed moderate and severe levels of depressive symptoms and 23.2% showed moderate and severe levels of anxiety. The youngest participants were affected the most by the situation. The most important factor related to depressive symptoms was the feeling of loneliness followed by daily stress. The most important factor related to anxious states was negative repetitive thinking followed by feeling of loneliness. The existence of previous mental health difficulties aggravated the reactions, but even people who had not sought out treatment previously showed signs of psychological impact.