No presente artigo, é descrito um método de concepção para betão auto-compactável reforçado com fibras de aço (BACRFA) de custo competitivo, a ser usado na indústria de pré-fabricação. Uma das questões mais importantes na indústria da pré-fabricação é a da descofragem dos elementos, que deve ser feita com a maior brevidade possível. Deste modo, foi levado a cabo um programa experimental para estimar a influência da idade na resistência e na ductilidade do BACRFA desenvolvido. A relação tensão-abertura de fenda foi determinada com base na relação força-flecha obtida em ensaios realizados segundo as recomendações da RILEM (TC 162-TDF). Foi analisada a influência da idade do BACRFA nos parâmetros de fractura deste material. Foi analisada a influência da idade do BACRFA nos parâmetros de fractura deste material.
Over the last few decades, the astonishing developments of super plasticizers technology allowed great achievements on the conception of concrete mixes exhibiting self-compacting ability. Since the eighties, some methodologies have been proposed to achieve self-compacting requirements in fresh concrete mixes, based on the evaluation of the flowing properties of these mixes. There still persist, however, some doubts about the most appropriate strategy to define the optimum composition of a self-compacting concrete (SCC) mix, based on a required performance. The behavior of SCC as a structural material can be improved if adequate steel fiber reinforcement is added to SCC mix composition. In fact, the fiber reinforcement mechanisms can convert the brittle behavior of this cement based material into a pseudo-ductile behavior up to a crack width that is acceptable under the structural design point-of-view. Fiber addition, however, increases the complexity of the mix design process, due to the strong perturbation effect that steel fibers cause on fresh concrete flow. In the present work, a mix design method is proposed to develop cost effective and high performance Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC). The material properties of the developed SFRSCC are assessed as well as its potentiality as a structural material, carrying out punching and flexural tests on panel prototypes. A material nonlinear analysis is carried out, aiming to address the possibility of calibrating the constitutive model parameters by obtaining, with an inverse analysis, the fracture parameters using forcedeflection relationships recorded in simpler laboratory tests, like the three point notched beam bending test. The contribution of steel fibers for punching resistance is also, by this means, discussed.
The process of designing Strain Hardening Cementitious Composites (SHCC) is driven by the need to achieve certain performance parameters in tension. These are typically the pseudo-strain hardening behavior and the ability to develop multiple cracks. The assessment of the tensile load-deformation of these materials is therefore of great importance and is frequently carried out by characterizing the material tensile stress-strain behavior. In this paper an alternative approach to evaluate the tensile performance of SHCC is investigated. The behavior of the material in tension is studied at the level of a single crack and the tensile performance is evaluated in terms of the tensile stress-crack opening behavior. The experimental procedure and test setup used are discussed. The derived tensile stress-crack opening behavior is utilized to analyze and compare the influence of various composite parameters on the resulting tensile behavior. The deformations occurring during tensile
processes are discussed based on the experimental results obtained, as well as the micro-mechanisms underlying the contribution of different fibers to bridge cracks resulting from tensile loading.
Over the last decades, researchers have been studying fibre reinforced polymer (FRP) materials and their advantages in retrofitting of existing structures. The externally bonded reinforcement (EBR) technique is the most common practice in improving existing reinforced concrete (RC) structures with carbon FRP (CFRP) materials. In this regard, several additional advantages have been reported to the use of prestressed CFRP materials, mainly strips. However, the experience with RC strengthening using prestressed EBR-CFRP materials is still limited. Some concerns regarding the efficiency of the technique still exist, especially the durability and the long-term behaviour. This work aims at contributing to the knowledge on durability of RC slabs strengthened with prestressed CFRP laminate strips according the EBR technique. The durability was studied by exposing strengthened RC specimens to the following environments for approximately 8 months: (i) reference environment-specimens kept in a climatic chamber at 20 ºC; (ii) water immersion in tank at 20 ºC of temperature; (iii) water immersion in tank with 3.5% of dissolved chlorides at 20 ºC of temperature; and (iv) wet/dry cycles in a tank with a water temperature of 20 ºC. Additionally, half of the specimens were subjected to sustained loading at a load level of 1/3 of the ultimate load, with the occurrence of cracking. After the exposure period the slabs were monotonically tested up to failure by using a four-point bending test configuration. The results showed that the environmental conditions and the sustained loading, separately or combined, led in general to slight losses of performance and ductility. Although these losses were subtle, considering that the tests were carried out for 8 months, clear indications are given towards the importance of conducting similar tests
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