Effect of supplementary cementitious materials on capillary sorption : relation with drying rate and testing time

The water sorption phenomenon in a cementitious matrix is responsible for the ingress of several deleterious agents, and it is directly related to pore connectivity and pore volume. One of the most common tests used to describe this mechanism is the capillary sorption test. Furthermore, the drying rate (DR) is a process that strongly depends on the transport properties and also provides valuable information related to porosity and durability. Supplementary cementitious materials (SCMs) are known to enhance durability-related properties, especially pore refinement with time due to the pozzolanic action. Therefore, changes in the pore structure could be assessed by means of the capillary sorption and drying rate. For this study, mortars with ground granulated blast-furnace slag, natural pozzolan and limestone powder at three different levels of replacement were made and the capillary sorption test was performed at 28 and 90 days. Weight loss was also assessed at 28 days and the DR was calculated. Calculation of the weight gain, weight loss, DR and capillary sorption rate (CSR) is made considering the stoppage of the test at different stages. A comparison between different approaches in the calculations is made. Also, the relation of DR and CSR is assessed. Results show the effect of SCMs with time, and also the influence of the calculations on the CSR and DR values

Recycled powder as filler admixture in cementitious systems : production and characterization

In concrete production, aggregate represents almost 75% of the materials used. The exploitation of natural sources for this purpose also causes an environmental impact, while deposition of wastes from construction industry pollutes soil and water. The feasibility of recycled coarse aggregate used as component of concrete has been amply proved. Fine recycled aggregate is a by-product derived from the processing of recycled coarse aggregate, but there are some technological difficulties for its use in concrete, because of the high water absorption and powder content. The aim of this study is to propose and analyse the alternative use of milled recycled fine aggregate as mineral admixture. For this purpose, dry recycled fine aggregate was processed in a laboratory ball mill for cement, with the aid of cylpebs. Grinding was carried out for 2:00, 2:45 and 3:30 hours, and the sampling of ground recycled fine aggregate (GRFA) was done after each period. For the three grindings periods, the characterization of GFRA was performed for assessing its suitability as mineral filler. Tests included determinations of contents of material < 45 μm and < 75 μm by wet sieving, density, particle size distribution by laser diffraction, chemical composition and Blaine specific surface. Additionally, water demand for standard consistency paste with ordinary Portland cement (OPC) was prepared as reference, and also determined for pastes with replacement of 15% and 30% of cement by GRFA for each grinding period. Also, setting times and strength were measured. Results showed limited filler effect from GRFA when incorporated in cementitious materials, with the consideration of the grinding period as an important factor. Thus, further feasibility studies are necessary in order to investigate different potential applications of this ground material

Servicio Provincial de Aguas Rurales

En esta ponencia presentamos un diagnóstico acerca de la dinámica de funcionamiento organizacional del S.P.A.R. (Servicio Provincial de Aguas Rurales), que pertenece al Ministerio de Infraestructura y Obras Publicas. Este organismo tiene como objetivo es proveer de agua potable y saneamiento básico a pequeñas comunidades urbanas y rurales de Buenos Aires. El trabajo se realizó en el marco de la materia Sociología de las Organizaciones de la carrera Licenciatura en Sociología. El objetivo fue observar las formas de organización del trabajo, la cultura organizacional, los objetivos organizacionales en relación con el de los trabajadores, las formas de liderazgo, el tipo de motivación del personal y la comunicación.Jornadas realizadas junto con el I Encuentro Latinoamericano de Metodología de las Ciencias Sociales.Facultad de Humanidades y Ciencias de la Educació

Neutron radiography based visualization and profiling of water uptake in (un)cracked and autonomously healed cementitious materials

Given their low tensile strength, cement-based materials are very susceptible to cracking. These cracks serve as preferential pathways for corrosion inducing substances. For large concrete infrastructure works, currently available time-consuming manual repair techniques are not always an option. Often, one simply cannot reach the damaged areas and when making those areas accessible anyway (e.g., by redirecting traffic), the economic impacts involved would be enormous. Under those circumstances, it might be useful to have concrete with an embedded autonomous healing mechanism. In this paper, the effectiveness of incorporating encapsulated high and low viscosity polyurethane-based healing agents to ensure (multiple) crack healing has been investigated by means of capillary absorption tests on mortar while monitoring the time-dependent water ingress with neutron radiography. Overall visual interpretation and water front/sample cross-section area ratios as well as water profiles representing the area around the crack and their integrals do not show a preference for the high or low viscosity healing agent. Another observation is that in presence of two cracks, only one is properly healed, especially when using the latter healing agent. Exposure to water immediately after release of the healing agent stimulates the foaming reaction of the polyurethane and ensures a better crack closure

Intervenciones en torno a las infancias. Hacia una perspectiva de derechos en la educación inicial

El presente trabajo surge como resultado de un dispositivo-taller, realizado con un grupo de estudiantes de Residencia Pedagógica en Educación Inicial. El norte del mismo y que devino en lo aquí compartido, fue plantear como objeto de debate, el grado de injerencia de las perspectivas de protección integral de derechos, en las intervenciones actuales en el trabajo de sala. Es decir, cotejar hasta qué punto es asumido como demanda, lo planteado dentro de esta nueva perspectiva, en la cotidianeidad de su tarea educativa, O de otro modo, qué tipo de significaciones son las que operan, orientando su accionar. A partir de ello, la estructura y dinámica del dispositivo giró en torno a recuperar sus voces como elemento de análisis y habilitar un espacio de interrogantes y reflexiones en las que se reflejara el grado de consistencia entre su pensar, decir y actuar. Como resultado se advierte, la coexistencia de dos perspectivas bien marcadas; a nivel discursivo, posee mayor predominio la perspectiva de derechos, pero en su decir y su práctica, imperan concepciones de una figura de infancia moderna. Trazos mixtos, que ponen en relieve los cambios significativos que aún quedan por efectuar a nivel cultural, social y esencialmente subjetivo

Servicio Provincial de Aguas Rurales

En esta ponencia presentamos un diagnóstico acerca de la dinámica de funcionamiento organizacional del S.P.A.R. (Servicio Provincial de Aguas Rurales), que pertenece al Ministerio de Infraestructura y Obras Publicas. Este organismo tiene como objetivo es proveer de agua potable y saneamiento básico a pequeñas comunidades urbanas y rurales de Buenos Aires. El trabajo se realizó en el marco de la materia Sociología de las Organizaciones de la carrera Licenciatura en Sociología. El objetivo fue observar las formas de organización del trabajo, la cultura organizacional, los objetivos organizacionales en relación con el de los trabajadores, las formas de liderazgo, el tipo de motivación del personal y la comunicación.Jornadas realizadas junto con el I Encuentro Latinoamericano de Metodología de las Ciencias Sociales.Facultad de Humanidades y Ciencias de la Educació

Lucas-Washburn vs Richards equation for the modelling of water absorption in cementitious materials

The Lucas-Washburn equation is still being applied by a significant number of researchers for the modelling of water absorption in cementitious materials. A modern approach considers the extended Darcy's law leading to the Richards equation instead. Three main assumptions are implied by the application of the Lucas-Washburn equation: the flow occurs in one direction only, the material is separated into one fully wet and one fully dry region, and pores are modelled as an assembly of parallel tubes of a particular radius. Its application to analyse experimental results allows defining these three assumptions as mere simplifications. Therefore, all the parameters comprised in the Lucas-Washburn model are apparent. Consequently, a very limited description of the transport properties of the material can be achieved. For many engineering purposes this would not be an issue, but for an intrinsic description of the material a more realistic model is required. This paper discusses the limitations of the Lucas-Washburn equation, and the advantages of the Richards equation regarding the modelling of water absorption in cementitious materials. The comparative analysis reveals the versatility of the Richards equation, with an approach that considers the material as a continuum and describes it through measurable parameters

Trainable Weka Phase segmentation of SEM/BSE images of slag blended cement pastes

Scanning electron microscopy with backscattered electrons (SEM/BSE) is a powerful technique that allows the visualization of polished cross sections with good reproducibility and level of detail. It is widely used to study the microstructure of cement-based materials and identify different phases in the cement paste. However, in some cases it is difficult to distinguish between some phases due to a similar grey level, as in the case of slag and portlandite. Then, X-ray elements mapping is necessary to help in the differentiation according to composition, but it can be quite time consuming and tedious with standard detectors. A machine learning tool, trainable WEKA segmentation (TWS), can be used to train a classifier by means of pixel grey values and segment the different phases automatically without any assistance of compositional mapping, transforming the problem into a pixel classification issue. The trained models can be improved by adjusting each class. The application of the model to the images results in a segmented image that can be used for quantification. In this paper TWS is applied for segmenting SEM/BSE images without the need of elements mapping. Slag blended cement pastes at different ages are studied. Results are compared with image analysis through elements mapping and selective dissolution. From this comparison, some information regarding the image density of the portlandite is derived