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

On the quantitative thermogravimetric analysis of calcite content in hydrated cementitious systems

Calcite is a compound that is present in hydrated cementitious materials when carbonation of portlandite occurs or when limestone constituents are used. The quantification of its content in cementitious systems is then frequently necessary. Thermogravimetry (TG) measures the change in mass of a material (as a function of time) over a temperature range using a predetermined heating rate. It can be applied to estimate calcite content in the hydrated cement system, considering the temperature range at which it decomposes and releases carbon dioxide. However, the quantification is not easy because the onset of this decomposition is a function of many variables. The tangential method over the TG signal or the integration method over the derivative TG curve (DTG) are usually used to discount the background over the temperature range at which calcite decomposes. However, consistent underestimation of compounds is frequently described. The reasons for this are unclear and some hypothesis are discussed in this paper. Additionally, experimental quantitative TG of cement paste and aggregate containing calcite and diluted with low contents of analytical calcite are compared with the expected contents, as a calibration method regarding calcite content in the samples is given to improve the reliability of the results

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

Capacidad de fijación y adsorción de cloruros en morteros elaborados con distintos cementos

La retención de iones cloruro por parte de los hidratos del cemento se puede producir por dos mecanismos: por adsorción superficial, principalmente en la fase de silicato hidratado; y por fijación, mayormente en la fase de aluminato hidratado. Este trabajo tiene por objetivo determinar las capacidades de adsorción y de fijación de cloruros en morteros con una misma relación a/c, realizados con distintos cementos (normal, fillerizado, compuesto y de alto horno). El estudio comprende dos series de ensayos, en una los cloruros se incorporaron en forma previa a la hidratación del cemento (morteros contaminados) y en la otra en forma posterior a la misma (morteros sin contaminar). La adsorción de cloruros se determinó en los morteros sin contaminar mediante la disminución de la concentración de las soluciones de cloruro de sodio en las cuales se sumergieron partes pulverizadas de los morteros. La fijación-adsorción se determinó en los morteros contaminados mediante la diferencia entre la cantidad de cloruros incorporados durante el mezclado y los que permanecieron solubles en agua luego de la hidratación del cemento. Para representar los fenómenos de adsorción y fijación se utilizan los modelos matemáticos de isotermas de adsorción de Langmuir y de Freundlich. Se compara el comportamiento de distintos tipos de cementos y se analizan las diferencias entre los fenómenos de adsorción y de fijación, y su influencia en la cantidad de cloruros retenidos respecto al total de cloruros. Los resultados obtenidos presentan mejor correlación con el modelo de Freundlich. En todos los casos la adsorción de cloruros resulta inferior a la fijación de cloruros en los morteros analizados

Introducción a la durabilidad y patología de las estructuras de hormigón armado

El hormigón como material estructural brinda amplias posibilidades de diseño. Es un material con ventajas económicas, técnicas y durables por sobre otros materiales estructurales. Si bien la durabilidad del hormigón armado es prolongada, esta circunstancia muchas veces hace ignorar la necesidad de tareas de mantenimiento adecuadas y periódicas. Son varias las causantes posibles para el deterioro del hormigón armado. Existen mecanismos de degradación físicos, químicos, electroquímicos y biológicos. Estos dependerán del ambiente y las condiciones de exposición. En este trabajo se desarrollan brevemente los mecanismos de degradación del hormigón armado, y se hace hincapié en los parámetros que deben ser tenidos en cuenta para preservar la funcionalidad de las estructuras con interés patrimonial

Approximation by the Finite Element Method to the Preferential Chloride Diffusion through Interfacial Transition Zone in Concrete

Chloride diffusion in concrete is a main aspect of reinforced concrete durability. It defines the time required for reinforcement corrosion in marine structures. Concrete porosity is one of the main concerns involved in the process of chloride ingress from the environment into concrete. However, concrete can hardly be considered homogeneous in the meso-level. Natural coarse aggregates are usually less porous than the cementitious matrix, whereas interfacial zones between aggregates and the matrix are the most porous phase in concrete. This aspect is difficult to be experimentally studied, as very little samples need to be collected and analyzed. As an approach, the diffusion process can be simulated with the Finite Element Method (FEM). In this paper, chloride diffusion into concrete is simulated with a 2D FEM model, distinguishing three phases with different porosities in the material. Interfacial zone is identified as preferential path for chloride ingress.Fil: Villagrán Zaccardi, Yury Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Área Tecnología del Hormigón; ArgentinaFil: Taus, Valeria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Área Tecnología del Hormigón; Argentin

Comparison of reaction degrees of slag and fly ash obtained by thermogravimetry and selective dissolution

The evolution of the reaction degree of supplementary cementitious materials (SCM) with time is an important aspect regarding the design and use of blended cements. However, this quantification is complex due to the multiple actions of SCM in the cementitious system, such as the filler effect, the consumption of CH and the formation of secondary calcium silicate hydrates. In this sense, different methods for the estimation of the reaction degree may be recommended for each type of SCM. Some of them are indirect methods that quantify hydration products and compute a reaction degree on that basis, e.g. thermogravimetric analysis, and others are direct methods that measure the amount of unreacted SCM, e.g. selective dissolution. In this paper, thermogravimetric analysis and selective dissolution are applied to estimate the reaction degree of cement pastes admixed with 40% slag or 30% fly ash. Curing periods ranged from 1 till 90 days. Results from both methods are compared and some comments on practicalities for their application are made. Although not enough evidence could be collected for any of the applied methods to be considered as a reference method, the simultaneous application of these two techniques offers increased reliability than when only one method is applied

Arresto cardiaco prolongado por bloqueo en un PSC

Se trata de un bloqueo más en el PSC de tipo S-A con la característica bradicardia manifiesta (22') y prolongado arresto cardíaco que oscila entre los 3960 y 7560 mseg. Origen vagotónico como lo demuestra la prueba del sulfato de atropina.It is about another blockade in PBH of type S-A wíth evident characteristical bradycardia (22') and lengthening cardíacal arrest that oscillates between 3960 and 7560 msec. Its vagotonic source is demonstrated by the atropin sulphate test.Facultad de Ciencias Veterinaria

Electrical resistivity measurement of unsaturated concrete samples

Electrical conduction in concrete primarily occurs via the liquid in pores. Since concrete resistivity is sensitive to moisture content, resistivity can be used to infer other moisture-dependent concrete properties. However, quantitative assessment of the relationship between concrete resistivity and the pore liquid content can be a difficult task due to contact issues between electrodes and the surface of unsaturated concrete. Resistivity is usually measured using wet sponges to assess contact with a concrete surface. This is a very effective procedure for saturated concrete but implies minor alterations in the condition of unsaturated concrete. This paper deals with a contact method to measure the resistivity of unsaturated concrete samples. Resistivity measurements dispensing with wet contacts are performed on thin samples of conventional concrete. A dry contact is achieved by means of painted electrodes on the concrete surface. Dry and wet contact methods are compared when applied to saturated concrete, and resistivity values of unsaturated concrete are related to concrete moisture content and the relative humidity of the surrounding environment. As a result, resistivity is related to the volumetric fraction of conducting water in pores and its hygroscopic equilibrium with the surrounding environment.Fil: Villagrán Zaccardi, Yury Andrés. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Di Maio, Angel Antonio. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Laboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Arresto cardiaco prolongado por bloqueo en un PSC

Se trata de un bloqueo más en el PSC de tipo S-A con la característica bradicardia manifiesta (22') y prolongado arresto cardíaco que oscila entre los 3960 y 7560 mseg. Origen vagotónico como lo demuestra la prueba del sulfato de atropina.It is about another blockade in PBH of type S-A wíth evident characteristical bradycardia (22') and lengthening cardíacal arrest that oscillates between 3960 and 7560 msec. Its vagotonic source is demonstrated by the atropin sulphate test.Facultad de Ciencias Veterinaria