The evolution of nanotechnology provides materials with new properties and over the last years a lot of effort has been put to introduce nano-particles into cement pastes in order to improve their ...properties and to produce materials of better performance. In the present research work, nano-SiO2 produced by pyrolysis and with specific area of 200m2/g has been added at different percentages (0%, 0.5%, 1%, 2% and 5%) to high-strength cement pastes. These pastes were tested for their mechanical and structural properties at different ages. Nanoparticles act as nuclei for crystallization and large, idiomorphic crystals of Ca–Si composition were formed assisting, up to a certain percentage, in producing materials with dense structure, reduced porosity and improved strength.
•HCFA, EAF Slag and CDW can be combined to produce environmentally friendly concrete.•EAF slag aggregate increases and fine CDW decreases concrete strength.•EAF slag and CDW aggregate combination ...shows some advantages.
An experimental program was carried out in order to investigate the possibility of producing concrete incorporating large volumes of industrial by-products and secondary materials. The alternative materials tested were fly ash as binder for cement replacement, recycled fine aggregate originating from mixed construction and demolition waste and steel slag as coarse aggregate. Several mortar and concrete mixtures were prepared using different aggregate and binder combinations in order to identify the feasibility of producing concrete with maximum use of alternative materials. The different mixtures were tested for mechanical strength at different ages, while durability measurements such as chloride ion penetration and freeze–thaw resistance were also carried out. The results showed that the use of fine construction and demolition waste aggregate increases porosity in concrete and also reduces strength and durability, while its combination with steel slag aggregate partly recovers strength and durability loss. Concrete with mixed construction and demolition waste as fine aggregate and steel slag as coarse aggregate reached 30MPa 28-day compressive strength and showed adequate durability for low grade applications. Also, 50% cement replacement with high calcium fly ash and use only of steel slag and recycled aggregates resulted in concrete of adequate strength and considerable environmental gains.
•The technology of an insulating render based on simple and cheap materials.•The combination of techniques to record specific properties of the render.•Contribute in order to find ways to reduce the ...cost of buildings’ insulation.
The functional role of renders as a mean to protect structures by increasing their resistance to weathering was known even from prehistoric times. Through centuries the demands in construction were increased as functional, aesthetic, economic and insulating criteria had to been fulfilled. Into this frame, renders had to play a malty-phase role. In the present work a series of renders were produced based on white cement and lime and three different aggregate types were tested in order to achieve a render with insulating properties. The insulating capacity was characterized by the thermal conductivity (λ) measurements. The aggregates were silica sand, glass particles (laboratory produced from recycled bottles) and glass-spheres. Mechanical, physical, micro-structure properties were recorder and thermal conductivity was measured. As a result, renders with λ of 0.3W/mK were produced and this could be considered as a material that can contribute to the thermal insulation of buildings.
•The different technologies for non-structural repair of concrete are presented.•Compatibility between repair product and concrete surface is a critical aspect.•Advanced multifunctional solutions ...with smart properties are being investigated.•Several characterization methods are applied for the effectiveness assessing.•The development of standardized studies with common testing criteria is important.
In the present paper different external surface treatments published in the literature as preventive solutions for improving the performance of existing concrete constructions are presented and discussed. They are categorized as repair materials for concrete conservation, protection surface methods against moisture and aggressive agent penetration, injection techniques for crack sealing and preventive repair solutions with smart functionalities. In a final section, the most extended testing methods for evaluating the effectiveness of the different repair solutions are summarized depending on the property to be enhanced: moisture control and resistance against penetration of aggressive agents. The review shows that although several possibilities exist for the repair of the existing constructions, there is a lack of comparative analysis between the different methodologies. SARCOS COST Action CA15202 stablishes as scientific objectives to carry out comparative studies including the most advanced solutions for the external repair of concrete, giving criteria for effectiveness assessment and defining robust and reliable methods for charactering the performance of the repaired structures.
•Manually produced bricks were fired at temperatures below 900°C and tested by the immersion technique.•Hydrophobicity achieved by linseed oil decreased porosity and capillary ...absorption.•Silane/siloxane solutions formed hydrophobic surface which did not remain after the ageing tests.•Alkosiloxanes offered the highest protection in bricks and presented high penetrability.•Nano-silica had a positive role in all the solutions tested as the surface roughness was increased.
For millenniums, bricks were the main building material for the load-bearing structural elements of constructions. They were produced manually and they were fired at low temperature. They also present low apparent specific density, high absorption, high surface roughness and relatively low compressive strength. Nowadays, bricks used for restoration works should be compatible to the old ones. As the existing line of modern brick manufacturing is far from the above mentioned criteria, the way to solve the problem is to manually produce these special building materials which render them expensive and laborious. Additionally, their high porosity and soft nature make them easily deteriorated by different environmental conditions. The protection of traditional bricks is an important step towards their durability and a challenge especially nowadays where nanotechnology has been proven efficient when it is incorporated in coatings for building materials.
In the present paper, hand-made brick samples were treated with different coatings by the technique of total immersion. The solutions tested were both traditional such as linseed oil but also silanes and alkosiloxanes both neat and nano-modified. In order to compare the physical properties of the treated bricks, parameters like capillarity, porosity, absorption and durability have been tested. It was concluded that silica nano-particles and micro-clay enrichment of alkosiloxane was the most sufficient way to protect those special building materials.
•Develop alkali activated earthen materials with enhanced physical and mechanical properties.•The role of pH has been proven critical for the influence of the alkali activators on the properties of ...clay mortars.•Water-glass addition (WGS) is as unadvisable activator for clay materials.•Sodium carbonate(SC) is a promising alkali activator even at lower pH values.•Water-glass with the NaOH solution (WGN), is a promising activator in terms of mechanical characteristics and structural cohesiveness of the mortar.•Clay mortars activated with potassium metasilicate (PO) and water-glass with the NaOH solution (WGN), with pH = 12–14, presented the highest compressive strength.
The purpose of this study was to develop alkali activated earthen materials with enhanced physical and mechanical properties. Specifically, clay mortars were produced, by using various alkaline activators of different pH (values 11–14). The specimens were cured in certain conditions. The physical and mechanical properties of the mortars manufactured were measured at the age of 28 days. Specifically, capillary absorption, shrinkage, Karsten tube penetration, porosity, as well as compressive and flexural strength tests were performed. Additionally, microscopic analysis was also conducted. The results of the experiments indicated the positive effect of potassium metasilicate and the combination of sodium metasilicate with sodium hydroxide solution on mechanical characteristics. The influence of sodium carbonate as an alkali activator was also proven beneficial on the physical properties of the specimens. In conclusion, the alkaline activators with pH > 12, lacked in enhancing physical properties, yet allowed the development of mechanical strength, while the alkaline activators with lower pH values showed reversed results.
Zinc : a multipurpose trace element STEFANIDOU, M; MARAVELIAS, C; DONA, A ...
Archives of toxicology,
2006, 2006-Jan, 2006-1-00, 20060101, Letnik:
80, Številka:
1
Journal Article
Recenzirano
Zinc (Zn) is one of the most important trace elements in the body and it is essential as a catalytic, structural and regulatory ion. It is involved in homeostasis, in immune responses, in oxidative ...stress, in apoptosis and in ageing. Zinc-binding proteins (metallothioneins, MTs), are protective in situations of stress and in situations of exposure to toxic metals, infections and low Zn nutrition. Metallothioneins play a key role in Zn-related cell homeostasis due to their high affinity for Zn, which is in turn relevant against oxidative stress and immune responses, including natural killer (NK) cell activity and ageing, since NK activity and Zn ion bioavailability decrease in ageing. Physiological supplementation of Zn in ageing and in age-related degenerative diseases corrects immune defects, reduces infection relapse and prevents ageing. Zinc is not stored in the body and excess intakes result in reduced absorption and increased excretion. Nevertheless, there are cases of acute and chronic Zn poisoning.
Lime mortars have been used for centuries in civil engineering construction. Considering ancient monuments and historical buildings it seems that these mortars have proved to be durable and reliable ...materials although they are of low strength in comparison with cement mortars. Nowadays, they are used for the repair of monuments and for the manufacture of renderings and plasters.
In the present paper the role of aggregates on the structure and behaviour of lime mortars is examined by studying the influence of the aggregate content and the grain size on strength, porosity and volume stability of the mortars. Capillary porosity by suction was also measured as an indicator of resistance to weathering. It is shown that coarse aggregates contribute to the volume stability of lime mortars independent of strength enhancement when adequate compaction reduces the capillary pores. The highest strength values, and consequently, the low porosity, were attained by lime mortars of low binder/aggregate ratio which contained aggregates of maximum size 0–4
mm.
Anabolic-androgenic steroids (AAS) are used as ergogenic aids by athletes and non-athletes to enhance performance by augmenting muscular development and strength. AAS administration is often ...associated with various adverse effects that are generally dose related. High and multi-doses of AAS used for athletic enhancement can lead to serious and irreversible organ damage. Among the most common adverse effects of AAS are some degree of reduced fertility and gynecomastia in males and masculinization in women and children. Other adverse effects include hypertension and atherosclerosis, blood clotting, jaundice, hepatic neoplasms and carcinoma, tendon damage, psychiatric and behavioral disorders. More specifically, this article reviews the reproductive, hepatic, cardiovascular, hematological, cerebrovascular, musculoskeletal, endocrine, renal, immunologic and psychologic effects. Drug-prevention counseling to athletes is highlighted and the use of anabolic steroids is must be avoided, emphasizing that sports goals may be met within the framework of honest competition, free of doping substances.
Microneedle devices have been proposed as a minimally invasive delivery system for the intradermal administration of nucleic acids, both plasmid DNA (pDNA) and siRNA, to treat localised disease or ...provide vaccination. Different microneedle types and application methods have been investigated in the laboratory, but limited and irreproducible levels of gene expression have proven to be significant challenges to pre-clinical to clinical progression. This study is the first to explore the potential of a hollow microneedle device for the delivery and subsequent expression of pDNA in human skin. The regulatory approved MicronJet600® (MicronJet hereafter) device was used to deliver reporter plasmids (pCMVβ and pEGFP-N1) into viable excised human skin. Exogenous gene expression was subsequently detected at multiple locations that were distant from the injection site but within the confines of the bleb created by the intradermal bolus. The observed levels of gene expression in the tissue are at least comparable to that achieved by the most invasive microneedle application methods e.g. lateral application of a microneedle. Gene expression was predominantly located in the epidermis, although also evident in the papillary dermis. Optical coherence tomography permitted real time visualisation of the sub-surface skin architecture and, unlike a conventional intradermal injection, MicronJet administration of a 50μL bolus appears to create multiple superficial microdisruptions in the papillary dermis and epidermis. These were co-localised with expression of the pCMVβ reporter plasmid. We have therefore shown, for the first time, that a hollow microneedle device can facilitate efficient and reproducible gene expression of exogenous naked pDNA in human skin using volumes that are considered to be standard for intradermal administration, and postulate a hydrodynamic effect as the mechanism of gene delivery.
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