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![Lascamento devido à combinação dos mecanismos de pressão nos poros e tensões térmicas [24]. [Figure 3: Spalling due to the combination of pore pressure and thermal stress mechanisms [24].]](profile/Victor-Pandolfelli/publication/262445302/figure/fig1/AS:392509973909515@1470593078913/Figura-3-Lascamento-devido-a-combinacao-dos-mecanismos-de-pressao-nos-poros-e-tensoes.png)
Lascamento devido à combinação dos mecanismos de pressão nos poros e tensões térmicas [24]. [Figure 3: Spalling due to the combination of pore pressure and thermal stress mechanisms [24].]
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The fire resistance of a structural concrete is evaluated by the time length that the element keeps performing its functions under high temperature conditions. It is usually believed that the concrete has an excellent durability before fire; however, in practice the stability of this material is reduced by high temperatures. Unfortunately, under su...
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... Tensile strength by diametral compression: similar to the results obtained in the axial compression strength, Fig. 6b indicates that for the tensile strength by diametral compression, compositions 1 and 3 suffered a reduction in the strength with the increase of the temperature, whereas for composition 2 there was an increase in the strength at 450 °C. With a temperature increase, microcracks were created, along with the decomposition of Ca(OH) 2 and other hydrates, making the concrete tensile strength more sensitive to high temperatures and crack formation than compressive strength, corroborating other results [29,30]. The analysis of (Table II) presented a significance level of 80% for the temperature. ...
... At 670 ºC, calcite (CaCO 3 ) decarbonation occurs, resulting in the release of carbon dioxide (CO 2 ) and the formation of calcium oxide (CaO). The mass loss above 700 ºC can be related to the decomposition of the cement paste and aggregates [29]. The ANOVA for mass loss (Table II) indicated that composition and temperature were significant, with 86% and 99% confidence intervals, respectively. ...
Concrete structures must be sized to ensure stability over their lifetime. Moreover, there are criteria that must be followed for fre
safety verifcation. Given this context, this study aimed to evaluate the influence of the partial and integral replacement of CPII-Z32
cement by a refractory cement in concrete compositions related to the residual properties after exposure to different temperature
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... The fire performance of concrete structures can be assessed by measuring the spalling on the section and the mechanical strength loss (Gil et al., 2017;Ollivier & Vichot, 2014). When concrete is exposed to fire, it becomes susceptible to explosive spalling, mainly between temperatures of 100°C and 400°C (Castro, Tiba, & Pandolfelli, 2017). However, studies that have been conducted to analyze this phenomenon have focused on small specimens, like Hager (2013), Ali, Dinkha, & Haido (2017), and Ozawa & Morimoto (2014). ...
... A permeable mesh begins to form at this temperature, which allows the percolation of water and vapor in the structure. This new mesh of pores helps to reduce internal pressure and can therefore eliminate explosive spalling (Castro et al., 2017). ...
... None of the three systems that were tested presented spalling, result that was influenced by the long curing age of the concrete boards. Another plausible explanation for the absence of this phenomenon may be related to the pressure relief provided by the significant difference between porosities of concrete with and without the addition of polypropylene microfibers, due to the exposure to high temperature and the consequent total degradation of the fibers (Castro et al., 2017). ...
Reinforced concrete elements with long curing ages tend not to present spalling when subjected to high temperatures since heat transfer in concrete is influenced mostly by the materials constituting its composition. Polypropylene microfiber-reinforced concrete presents more porosity and higher thermal insulation as the fibers melt when exposed to high temperatures. Therefore, this study aimed to assess the influence of the addition of polypropylene microfibers on the resistance to fire of reinforced concrete boards. The mechanical tests required crafting 18 boards and 3 walls in real scale, which measured 3.15x3.00 m. The analysis comprised 3 types of systems, being the reference reinforced concrete and the concretes with polypropylene microfiber ratios of 0.97 kg/m³ and 1.94 kg/m³. Were extract 18 specimens for the axial compression test. The fire test was performed in a vertical furnace under the ISO 834 curve. None of the 3 walls displayed spalling and the boards with higher microfiber ratios presented better fire performance, with smaller maximum displacements. The wall with 1.94 kg/m³ microfiber ratio obtained a gain of 23.5 min in thermal insulation compared to the reference reinforced concrete wall. It was also perceived that the incorporation of polypropylene microfibers in the concrete reduces its compressive strength.
This paper presents results from experimental studies on residual mechanical properties of high-performance concrete reinforced with polypropylene microfibers after exposure to elevated temperatures. A conventional concrete (compressive strength of 25 MPa) and high-performance concretes (compressive strength above 78 MPa) with 1 kg/m³, 2 kg/m³ and 3 kg/m³ additions of polypropylene microfibers were developed. The mixtures were subjected to temperatures of 100°C, 200°C, and 300°C, for 60 minutes. In the second part of this study, a high-performance concrete with 2 kg/m³ of microfibers was analyzed. Compressive strength, splitting tensile strength and elastic modulus tests were also performed at 200°C, 400°C, and 600°C. Results from the experiments show that polypropylene microfibers were extremely important in minimizing the reduction of compressive strength, where the contents of 2 and 3 kg/m³ were the most effective. Through numerical simulation, it was possible to find the longitudinal elastic modulus, and the Poisson's coefficient at each temperature tested.
Concrete is a ubiquitous construction used extensively in structural engineering due to its high compressive strength and low cost. Concrete is an inherently brittle material, this lowers its strength and strain capacity. However, concrete has a number of shortcomings such as shrinkage and cracking, very low tensile and flexural strength, high brittleness and low shock resistance. The use of synthetic polymeric fibers within concrete helps to alleviate some of these shortcomings in concrete slabs. Furthermore, synthetic polymeric fibbers are lightweight and help prevent the development and growth of cracks in concrete slabs. Synthetic polymers such as polypropylene, polyethylene, polyamides and olefins have been used in concrete slabs with some success. The workability and strength of fiber reinforced concrete slabs is dependent on the fiber loading and fiber aspect ratio. The purpose of this study is to review synthetic polymer fiber reinforced slabs and their effects on the mechanical properties.
