Service life estimation of cracked and healed concrete in marine environment

In the aggressive seawater environment, the durability of concrete is strongly influenced by the presence of chlorides and sulfates. Marine structures mostly have an important social function with a high economic impact, which makes durability a key issue. In addition, early-age cracks are a common problem, specifically for massive structural components. Repair of cracks is expensive and often impossible due to inaccessibility. Self-healing concrete is a promising solution to make marine structures more durable. In this study, capsules containing Polyurethane (PU) prepolymers were embedded in the concrete to release their contents when cracks appear. In cracked mortar, the chloride diffusion coefficients in the zone immediately around the crack significantly increased compared to uncracked mortar. The crack width dependency could be introduced into the service life model using a crack effect function. For crack widths in the range of 100 mu m to 300 mu m a service life decrease of around 80% was calculated. Autonomous crack healing had a beneficial influence on the resistance against chloride diffusion. However, for about one third of the cracks the healing mechanism failed, probably due to shifting of the tubes, tubes not rupturing properly, too high capillary forces in the tubes, etc. Nevertheless, on average, the service life of autonomously healed structures by means of encapsulated polyurethane increased with around 100% compared to cracked, unhealed structures. Moreover, in the most beneficial situation of proper healing, a service life increase of 150-550% was obtained, reaching values similar as for sound structures

Influence of chlorides on magnesium sulphate attack for mortars with Portland cement and slag based binders

Sulphate containing environments are aggressive and cause damage to cementitious materials by means of cracking, spalling and strength loss. In realistic conditions, sulphates may be found in combination with e.g. chlorides. Therefore, to predict concrete's durability, it is important to understand the (combined) attack mechanisms and estimate their effect. This study aimed to elucidate especially the influence of chlorides on magnesium sulphate attack at two different relevant temperatures (5 degrees C and 20 degrees C) and for mortars with different binders, including ordinary Portland cement (OPC), high-sulphate resistant Portland cement (HSR) and a binder composed of 50% blast-furnace slag (BFS) and 50% ordinary Portland cement. Mass change measurements were performed to examine the influence of Cl- on MgSO4 attack, and XRD-analyses to identify phase changes. It can be concluded that the influence of Cl- on MgSO4 attack is temperature and binder type dependent. The presence of chlorides does not affect deterioration due to magnesium sulphate for OPC and HSR at an environmental temperature of 20 degrees C, however, it increases the degradation when BFS is used as partial binder and/or when temperature decreases to 5 degrees C. The presence of BFS decreases the formation of a protecting brucite layer and favours decomposition of calcium silicate hydrates to magnesium silicate hydrates. At 5 degrees C the degradation involves thaumasite formation, and is more equal for the different binders and quite severe. (C) 2017 Elsevier Ltd. All rights reserved

The village people?

The impact of COVID-19 on urban life and cities has been increasingly discussed over the last months. Academics, civil society organisations, policy makers and journalists have reflected on how this exceptional situation impacts cities, urban life, and people’s lives in general. A wide range of perspectives emerged in these contributions in the popular media. Almost all of these pieces point at the current shortcomings of our cities and discuss possibilities for improvement, and the role of policy makers in realising greener cities and adequate housing. When discussing the impact of COVID-19 on people’s housing preferences it is often assumed that a growing number of people will (prefer to) leave the dense urban cities and move to the country side or the more rural areas where the qualitative living environment rejoices their heart and where they can enjoy their own private gardens. At least two points of critique need to be raised in relation to these opinion pieces: First, the suggestions and findings are old wines in new barrels. Sufficient green and open spaces, qualitative housing options, the need for mixed area developments and proximity to amenities etc. are indeed important if we want to have cities that provide a good life for all. We have known this for years and the literature on this is substantial. Second – and central in this contribution – is the observation that these opinion pieces are exactly that: opinions... They reflect the ideas, beliefs and the gut feelings of the authors, but are not grounded in research on the effects of COVID-19. We aim for a more nuanced debate about the urban context, grounded in empirical insights and research findings

The influence of sodium and magnesium sulphate on the penetration of chlorides in mortar

Marine environments are very aggressive to concrete, mainly due to the presence of chlorides and sulphates. The influence of sulphates on chloride penetration in mortars was investigated by immersion in combined test solutions containing 165 g/l NaCl and 33.8 g/l SO42- (as MgSO4 or Na2SO4) at temperatures of 5, 20 and 35 degrees C. After immersion periods ranging from 7 weeks up to 37 weeks, chloride profiles were measured by means of potentiometric titrations, XRD analysis and electron probe micro analysis. In general, chloride ions penetrate much deeper into the mortar than sulphate ions. Nevertheless, chloride penetration is clearly influenced by the presence of sulphates in the environment. Sulphate ions compete with chloride ions to bind to aluminate phases. Therefore, the presence of sulphates initially increases chloride diffusion. When magnesium sulphate is present the formation of Mg-related reaction products such as brucite additionally influences the chloride penetration. Later, up to 37 weeks of immersion, a decreasing chloride diffusion is noticed compared to samples exposed to a single chloride solution, due to pore blocking products of the sulphate reaction. Contrarily, immersion periods longer than 37 weeks in combined solutions result in increasing chloride diffusion due to sulphate induced cracking at the outermost layers. Notwithstanding the reciprocal influence of chlorides and sulphates, the magnitude of the effect of sulphate on the chloride diffusion coefficient was limited. Chloride diffusion generally increases with increasing temperature. The presence of sulphates decreases chloride binding even more significantly at 5 and 35 degrees C than at 20 degrees C

Comparison of personality traits among patients with psoriasis, atopic dermatitis, and stress: a pilot study

Background: Psoriasis and atopic dermatitis are chronic skin diseases that greatly affect the quality of life. Both diseases can be triggered or exacerbated by stress. Objective: We aimed to differentiate personality traits between patients with chronic skin conditions and people treated for stress in a pilot study. Methods: Patients participating voluntarily in educational programs in Belgium and Switzerland were recruited to complete personality trait questionnaires, including the Temperament and Character Inventory (TCI) and the Tridimensional Personality Questionnaire (TPQ). A comparison was made with patients treated for work-related stress. Results: A total of 48 and 91 patients suffering from skin diseases and work-related stress, respectively, were included in the study. Based on the questionnaires, we found that dermatology patients were less persistent and impulsive than those with work-related stress. Dermatology patients also exhibited more rigidness and less focus on performance. Finally, patients with work-related stress seem more likely to change in response to health-promoting programs than patients with chronic dermatoses. Conclusion: Patients with chronic skin diseases may perceive and cope with stress differently in comparison to patients with work-related stress due to inherent personality traits. Therefore, stress coping mechanisms may differ among different diseases. More research is needed into the design of educational interventions and the impact of personality traits in disease-specific groups

Self-healing concrete in aggressive enironments

Although certain crack widths are allowed in reinforced concrete structures, without having immediate effects on the structural stability, they may impair the durability and service life of the structure in the long term. Cracks wider than 10 μm will result, for instance, in a faster penetration of chlorides into the crack and from there onwards into the concrete matrix. Fortunately, the autogenous healing ability of concrete may close cracks of up to 100 μm completely. The further hydration of binder particles, will be supplemented by the deposition of calcium carbonate crystals in case of wet/dry cycles. In case of marine infrastructures in tidal zones, the presence of magnesium sulfates may enhance the crack sealing by means of brucite precipitation. These processes will result in reduced chloride penetration rates. If the cracks are larger than 100 μm or the conditions are not favourable for autogenous healing, autonomous healing mechanisms can be incorporated. In this case, healing is obtained through encapsulated polymeric healing agents, superabsorbent polymers, microbial agents, expansive additives, etc. With encapsulated polyurethane based healing agents, a reduction of the chloride concentration by 75% or more was obtained in a zone with a 300 μm wide crack after chloride diffusion tests, relative to the case in which cracks were not healed. As a result, the service life of reinforced concrete elements in marine environments could be increased with a factor of about 10. Neutron radiography images obtained during a capillary sorption test indicated that release of encapsulated polyurethane in wet conditions was favourable for the polyurethane reaction. As an alternative to the autonomous healing with encapsulated polyurethane, also the incorporation of encapsulated water repellent agents and corrosion inhibitors, has proven to effectively delay reinforcement corrosion during electrochemical measurement campaigns. Accelerated corrosion tests on cracked, manually treated mortar samples, allowed to rapidly screen different agents for their efficiency

Evaluation of a brief intervention for promoting mental health among employees in social enterprises : a cluster randomized controlled trial

Evidence on the effectiveness of workplace mental health promotion for people with disabilities is limited. This study aimed to evaluate the effectiveness of a brief mental health promotion intervention in social enterprises. It had a non-blinded cluster randomized controlled trial design with follow-up one and four months after the intervention. In total 196 employees agreed to participate (86 intervention and 110 control). Empowerment was the main outcome; secondary outcomes were resilience, palliative behavior, determinants of four coping strategies of mental health, quality of life, and life satisfaction. A brief participant satisfaction survey was conducted after the intervention. No significant intervention effect on empowerment was found. However, at one month follow-up, significant favorable effects were found on perceived social support for coping strategies for mental health and on palliative behavior. At four months follow-up, favorable intervention effects were found on quality of life, but unfavorable effects were found on unjustified worrying. In addition, the intervention was well received by the employees. This brief intervention might be a promising first step to improve mental health in people with disabilities working in social enterprises. Nevertheless, additional monitoring by professionals and managers working in the organizations might be needed to maintain these effects

Effects of post-weaning altrenogest treatment in primiparous sows

Major losses of body weight and fat reserves during the first lactation are a cause of unsatisfying reproductive performances in primiparous sows. This study, conducted in three commercial sow herds, investigated whether weaning the sows three days earlier together with administering altrenogest was effective for improving reproductive performance (weaning-to-estrus interval, pregnancy rate after first insemination, total litter size and number of live born piglets in the second litter) and body condition. In the herds suffering from the second litter syndrome, a non-significant improvement of the second litter size was found with on average 1.9 extra piglets born. During the treatment period, the treated sows gained on average 1.4 mm back fat, while the control sows lost 0.4 rum back fat. In conclusion, the treatment is useful for putting the sows in better condition at the moment of insemination and it may possibly improve reproductive performance in farms with the second litter syndrome