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[en] This paper presents the results of an experimental study aiming to assess the influence of the cement degradation on Cs-137 sorption. Sorption experiments have been carried out on fresh mortar and also on two types of degraded mortars resulted from a sulphate attack test and from a carbonation test. CEM II ordinary Portland cement that is commonly used in the waste immobilization process and quartz sand were used to prepare the fresh mortar paste with a water/cement ratio of 1/3. The sorption isotherms obtained from the batch sorption experiments were linear both for fresh mortar and degraded ones with increased cesium distribution coefficient on degraded samples compared with the fresh one. On fresh mortar cesium ions are mainly sorbed on the quartz sand and to a less extend on the hardened cement paste (HCP). The competition between Cs+ and Na+/K+ strongly reduce cesium uptake by fresh HCP. But this effect is decreased in the mortar samples obtained from the sulphate attack test due to the rapid alkali release and consequently the Kd for this degraded sample is higher than for the fresh one. For the mortar sample exposed in air for carbonation the higher value for the cesium Kd could be explained either by a precipitation process or by the physical and chemical changes in the mortar sample due to the carbonation process. (authors)
[en] Cracks in reinforced concrete elements can cause major durability issues due do the accelerated ingress of aggressive substances. In this study, repair of cracks was addressed by incorporating encapsulated polyurethane based healing agents in the cementitious material as an autonomous healing mechanism. Capillary sorption tests showed that a high viscosity healing agent could reduce the water ingress in cracked mortar, but a large scatter in the results was found, resulting in a large range of healing efficiencies (18 – 108%). The low viscosity polyurethane showed a more complete and consistent crack healing. Healing efficiencies ranging from 95 to 124% were observed (crack width up to 295 µm). The proposed healing mechanism is very effective in blocking the ingress of water. This will enhance the durability of cementitious materials and consequently extend their lifetime.
[es]Las fisuras en hormigón armado pueden causar graves problemas de durabilidad debido al ingreso acelerado de sustancias agresivas. En este estudio, la reparación de fisuras fue llevada a cabo mediante la incorporación de agentes de curado encapsulados, a base de poliuretano, en el material cementíceo como mecanismo de curado autónomo. Los ensayos de absorción capilar mostraron que un agente de curado con alta viscosidad redujo el ingreso de agua en morteros fisurados, pero se Encontró una gran dispersión en los resultados, lo que da lugar a un amplio rango de eficiencias de curado (18 – 108%). El poliuretano de baja viscosidad mostró un curado de las fisuras más completo y consistente. Se observaron eficiencias de curado del 95 al 124% (ancho de fisura de hasta 295 µm). El mecanismo de curado propuesto es muy efectivo para bloquear el ingreso de agua. Esto mejorará la durabilidad de los materiales cementíceos y consecuentemente extenderá su vida útil.
[en] Recently, there are many fields have been required for the precision measurements, as an advanced example of which, a precise change of inner structure during the hydration process of mortar was observed by ultrasonic and dielectric measurements. The results show that it is possible to determine the safety of mortar and mixing ratio, and strength growth and shrinkage rate by heat evolution
[en] In this study, the results of experimental tests performed on unreinforced masonry infill walls are presented. The out-of-plane response of infills different for the thickness and for the boundary conditions but equal for the construction procedure and the materials used is investigated. Infills with two different height-to-thickness slenderness ratios are tested. In addition, three different boundary conditions at edges are considered. The experimental results are used to assess, for different values of the slenderness ratio, the effectiveness of the out-of-plane strength formulations for unreinforced masonry enclosures in which the mono-directional or bi-directional arching mechanism can occur. A discussion on the different post-peak response of specimens with different boundary condition (brittle, for vertical spanning infills, non-brittle for infills mortared along three or four edges to the confining elements) is also presented. In the case of one-way arching, literature and code models underestimate the out-of-plane strength of thinner specimens and overestimate it for thicker specimens. In the case of two-way arching, all the existing strength formulations are significantly conservative and potentially adequate for a code-based safety check of unreinforced masonry infill walls under out-of-plane seismic demand.
[en] A shield is described which is placed on the skin of a patient to protect it from radiation injuries. In a very flat container (of polyamide, elastomer or tissue) which has an opening in the centre to allow the penetration of the radiation, there is a thermosetting resin (epoxy, polyester or phenol resin) which is mixed with radiation-absorbing materials (BaSO4, Sb2O3, SiO2, PbO2) as well as, if necessary, a wetting agent, which can be released before use. The form of the container is described in detail. (UWI)
[de]Es wird eine Abschirmung beschrieben, die auf die Haut eines Patienten aufgelegt wird, um diesen gegen Schaeden bei Bestrahlungen zu schuetzen. In einem sehr flachen Behaelter (aus Polyamid, Elastomer oder Gewebe), der in der Mitte eine Oeffnung zum Durchgang der Strahlung besitzt, befindet sich ein waermehaertbares Harz (Epoxy, Polyester- oder Phenolharz), dem strahlenabsorbierende Stoffe (BaSO4, Sb2O3, SiO2, PbO2) beigemischt sind, sowie gegebenenfalls ein Vernetzungsmittel, das vor Gebrauch freigesetzt werden kann. Die Ausgestaltung des Behaelters wird im Einzelnen beschrieben. (UWI)
[en] The paper addresses the consolidation of plasters and renders showing loss of cohesion, with the use of a treatment with a liquid consolidating product aiming to reach a depth of several mm up to several cm. The main aim of the paper is offering a guideline on how to choose a consolidant, suitable and compatible for the mortar type and its condition, and how to assess the performance of a consolidation treatment.
[en] Self-compacting concrete was created as an effective solution to problems associated to low quality consolidation. Successful self-compacting concrete (SCC) mixes are designed to flow freely and cohesively without the intervention of mechanical compaction. The research presented in this paper has as objective to findthe effect of different types of superplasticizers on the performance of concrete mixes. The understanding of this technology was acquired through a comparative study of mixes made with second generation sulphonated naphthalene formaldehyde based superplasticizerand third generation polycarboxylate-based superplasticizer. To meet the pre-defined objectives, the research program was subdivided into two interdependent phases. Phase I studies the effect of second and third generation superplasticizeron the fresh and hardened properties of mortar mixes. Phase II studies the effect of second and third generation superplasticizer on the fresh and hardened properties of concrete mixes.The experimental outcomes revealed that third generation superplasticizers induce more efficient dispersion defined by superior consistency levels and increased hardened strengths. (author)
[en] Since a long time ago, some products have been used in order to preserve and protect natural stone monuments as well as bricks and mortars and thus achieve greater resistance to deterioration processes. At first, natural resins of animal and vegetable origin were used but, in the last decades, synthetic polymers have been commercialized to cover the capillary pores of the material, lowering its water suction capacity, coating the material and isolating it from the aggressive environment [1-4]. Regarding to its effect, two main types of products are distinguished: consolidants and water repellents. First ones are substances that --penetrating inside the stone or ceramic material porous network-- improve their internal cohesion and therefore their mechanical behavior. They work attempting to achieve the adhesion between the surface --generally more weathered-- and the unaltered inner base. A water repellent is a product with a behavior that prevents the penetration of water in its liquid state but allows moisture vapor transmission. It can be applied on the surface of the already altered material or under weathering process. These products act in a double way, both narrowing pore radius and thus avoiding liquid water penetration into the pore network on one side, and repelling water due to a chemical hydrophobic behavior on the other side . In recent years, numerous commercial products have emerged in the market for restoration and conservation of architectural and monumental heritage stone materials. It has generated a great confusion among professionals of the sector because of a lack of knowledge of its long-term performance. Therefore, the evaluation of these products is necessary before their use on the materials surfaces.
[en] The compressive strength, flexural strength, porosity and electrical resistivity properties of cement mortars with nano-Fe2O3 and nano-SiO2 are studied. Amorphous silica is the main component of pozzolanic materials due to its reaction with calcium hydroxide formed from calcium silicate (C3S and C2S) hydration. The pozzolanic reaction rate is not only proportional to the amount of amorphous silica but also to the surface area available for reaction. Subsequently, fine nano-Fe2O3 and nano-SiO2 particles in mortars are expected to improve mortar performance. The experimental results showed that the compressive strength of mortars with nano-Fe2O3 and nano-SiO2 particles were lower than those obtained with the reference mortar at seven and 28 days. It was shown that the nano-particles were not able to enhance mechanical strength on every occasion. The continuous microstructural progress monitored by mercury intrusion porosimetry (MIP) measurements, pore-size distribution (PSD), total porosity and critical pore diameter also confirmed such results.
[es]Se estudia la resistencia a compresión y flexión, porosidad y resistividad eléctrica de morteros de cemento con nano-Fe2O3 y nano-SiO2. La sílice amorfa reacciona con el hidróxido de calcio formado en la hidratación del C3S y C2S. La tasa de reacción puzolánica es proporcional a la cantidad de sílice amorfa y la superficie disponible para la reacción, esperando que las partículas finas de nano-Fe2O3 y nano-SiO2 mejoren las propiedades de los morteros. Los resultados experimentales han mostrado que la resistencia a compresión a siete y 28 días de morteros con partículas de nano-Fe2O3 y nano-SiO2 era, en ocasiones, inferior a la obtenida con el mortero de referencia. Se muestra que las nano-partículas no siempre son capaces de mejorar la resistencia de los morteros. Las medidas mediante porosimetría de intrusión de mercurio (PIM) de la distribución de tamaño de poro (DTP), porosidad total y diámetro de poro crítico confirmaron estos resultados.