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Abstract
Abstract The present paper evaluated the potential application of the functionally graded material (FGM) concept to develop more durable concrete to carbonation, one of the main degradation mechanisms of reinforced concrete structures. Accelerated carbonation tests with controlled temperature (27 ( 2°C), CO2 concentration (3 ( 0.5%) and humidity (65 ( 5%) were carried out in homogeneous concretes and with functional gradation in which the porosity of the material was varied across the slices. For the manufacture of graded concrete specimens, concretes with water/cement ratios equal to 0.35, 0.45, and 0.55 were produced, with lower porosity (w/c = 0.35) close to the surface of the specimen. The advance of the carbonation front was evaluated after 8, 9, 10, 14, and 24 weeks of accelerated exposure, using the chemical indicator phenolphthalein. The results show that the functionally graded concrete had a carbonation coefficient (K) slightly higher than that of the concrete with a w/c ratio equal to 0.35 (1.71 and 1.54 mm.week-0.5, respectively) and much lower than concrete with water-cement ratio equal to 0.45 (2.31 mm.week-0.5) and 0.55 (3.78 mm.week-0.5). This demonstrates that functional grading can be an efficient method to increase the durability of concrete elements subject to carbonation.
Highlights
The graded concrete is expected to present porosity and density associated with its volumetric fractions and the properties of the layers that constitute it
The results showed that the practical porosity was around 8% higher than the theoretical one suggested through numerical simulation due to interface problems
The specimen with radial porosity gradation showed an accelerated carbonation coefficient (Ka) which was slightly higher than that of concrete with a w/c ratio equal to 0.35 (1.71 and 1.54 mm.week-0.5, respectively) and much lower than concretes with water/cement ratio equal to 0.45 (2.31 mm.week-0.5) and 0.55 (3.78 mm.week-0.5). This shows that functional gradation can be an efficient method to increase the durability of concrete elements subject to carbonation (Figure 12)
Summary
About 50 years ago, Bever and Duwez (1972) recognized that synthetic composites could be designed and produced by locally varying the characteristics (or volumetric fraction) of the dispersed phases, the composition, and the microstructure of the matrix to obtain more efficiency in various applications and properties of materials. Graded materials (FGM) are different from conventional materials in that the presence of a composition and/or structure variation, progressively throughout their volume, results in corresponding alterations to their material properties (Nogata, 1999; Kieback; Neubrand; Riedel, 2003; Ramu; Mohanty, 2014). In a material with functional gradation, properties can vary in a uni, bi or tridirectional way, as shown, resulting in a desired performance (Dias; Savastano Junior; John, 2010).
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