No abstract

In light of their excellent mechanical properties and other advantages over conventional systems for repairing and rehabilitating structures, fibre-reinforced polymers (FRPs) are commonly used to enhance the shear strength of RC members. Because of the relatively recent application of the technique in civil engineering, however, it is addressed in very few recommendations or guides. While the design guides in place contain a single, well defined and generally accepted procedure for calculating bending moments, they collectively propose a wide variety of numerical models for shear, none of which is universally acknowledged. The present article focuses on the calculation of ultimate shear strength and describes an experimental study in that context conducted on reinforced concrete beams retrofitted with unidirectional carbon fibre reinforced polymer (CFRP) fabric.Keywords: fibre-reinforced polymers (FRP); concrete; shear strengthening; experimental study. RESUMENLa técnica de refuerzo externo a cortante en elementos de HA con polímeros armados con fibra, conocida como EBR-FRP por sus siglas en inglés, se ha ganado un puesto importante en el área de reparación y rehabilitación de estructuras gracias a las excelentes propiedades mecáni-cas de estos materiales, y sus enormes ventajas respecto a otras técnicas. Sin embargo, debido a que su uso es relativamente reciente en la ingeniería civil, existen pocas recomendaciones o guías que consideren esta técnica. Las guías de cálculo existentes muestran un procedimiento bien definido y aceptado con respecto al cálculo a flexión, sin embargo, los modelos de cálculo a cortante resultan ser altamente variados y controvertidos. Este documento muestra el enfoque actual para el cálculo de esfuerzos cortantes y sus limitaciones, así como el proceso de una investigación experimental sobre vigas de hormigón armado reforzadas externamente con tejido unidireccional de CFRP.Palabras clave: polímeros armados con fibras (FRP); hormigón; refuerzo a cortante; estudio experimental.

ABSTRACT. Numerous studies have been carried out and various guidebooks published in the

In foamed concrete, porosity is essential because it is strongly related to other properties such as density, permeability, and strength. Porosity measurement (usually expressed as a percentage of total volume) is obtained in a laboratory using experimental water vacuum saturation and MIP methods. However, pore structure -including size, distribution, shape, and connection- is also needed to understand foamed concrete performance. Pore structure characterization is estimated through specialized digital image analysis. Micro CT, scanning electron microscopy or X-ray tomography images are frequently used to obtain pore structure on cellular concrete. However, these images are highly specialized and require equipment that is not easy to find and very expensive. Also, image processing is complex, and it includes some specialized software. This paper presents a pore structure characterization and porosity estimation using non-specialized digital images on foamed cement paste made with alternative agents. The procedure for acquiring images uses only a camera without any specialized equipment. The proposed methodology isolates the pores in the image and measures shape features such as pore diameter, eccentricity, and solidity. Acquiring and processing the images is simpler, faster, and cheaper than other specialized analyses. Results show that the volumetric porosity estimation was entirely accurate, with an estimation deviation of less than 10%. Also, the pore structure parameters such as pore size and distribution of foamed pastes can be quantified accurately.

ABSTRACT. Numerous studies have been carried out and various guidebooks published in the