Porous Structure of Ultra-High-Performance Fibre-Reinforced Concretes

Abstract

The aim of this experimental work was to study the porous structure of Ultra-High-Performance Fibre-Reinforced Concretes (UH) made with different fibre volume contents (0%, 1%, 2%) under several curing conditions (laboratory environment, 20 °C, 60 °C, 90 °C), comparing the results with those recorded for ordinary, high strength and very high strength concretes. Scanning electron microscopy, mercury intrusion porosimetry, thermogravimetry, water absorption and oxygen permeability tests were carried out. The results showed a low portlandite content in UH (in the order of 75% lower than in concrete C50) and a low degree of hydration, but they rise with curing temperature. These concretes have a very fine porous structure, with a high concentration of pores on the nanoscale level, below 0.05 µm. Their porosity accessible to water is consequently around 7-fold lower than in conventional (C30), 6-fold lower than in high-strength (C50) and 4-fold lower than in very high-strength (C90) concretes. Their oxygen permeability is at least one order of magnitude lower than in C90, two orders of magnitude lower than in C50 and three orders of magnitude lower than in C30. The percentage of added steel fibre does not affect the UH porous structure.

Theoretical and Experimental Substantiation of the Efficiency of Combined-Reinforced Glass Fiber Polymer Composite Concrete Elements in Bending

“…In particular, we have proved that fiber reinforcement increases the characteristics of concrete by 10-20% percent and improves its microstructure in accordance with [51,52], while the microstructure receives a denser packing of particles and, due to a more rational distribution of fiber fibers, microcrack formation near concentration of fibers in the body of the concrete matrix. In this regard, in comparison with the works of the authors [9,[17][18][19][20][21][22][23][24][25][26][27], we obtained higher results in terms of strength and also achieved an improved microstructure of the material. All this is proposed for use not only in compressed elements, as in [18,19,[28][29][30][31][32][33], but, of course, in tensioned bending elements, which emphasizes the more rational operation of fiber-reinforced elements, since fiber reinforcement is primarily directed for bending and tensile loads.…”

“…Using various types of fibers in concrete, the parameters of the distribution of fibers in the body of concrete and the recipe factors for obtaining fiber-reinforced concretes with improved characteristics have been studied in many works [9,[17][18][19][20][21][22][23][24][25][26][27]. The effect of fiber on the structure and characteristics of concrete products and structures was studied under the influence of high temperatures [17,21].…”

“…The effect of fiber on the structure and characteristics of concrete products and structures was studied under the influence of high temperatures [17,21]. In addition, the influence on performing fiber-reinforced concrete of various dosages of fiber [20,25], types of fiber (glass, basalt, polypropylene, steel) [21,22,26], and fiber diameter [24] was also studied in detail. An important technological parameter is the orientation of the fibers and its control in the composite matrix [18].…”

Effect of macrocell currents on rebar corrosion in reinforced concrete structures exposed to a marine environment

“…Figure 6 shows the curve fitting with the experimental data obtained for each concrete type. (Valcuende et al, 2021a;2021b). The 𝐷 𝑎𝑝𝑝 value obtained with concrete C90 was one order of magnitude higher than that for UH-150.…”

Macrocell Corrosion Currents in Simulated Concrete Pore Solution and Reinforced Concrete

“…In ultra-high performance fibre-reinforced concretes, such as UH150, the steel fibres present in the mix increased the concrete's conductivity because steel possesses negligible resistance to electrons' movement (Valcuende et al, 2021a). Nevertheless, these concretes are characterised by having a very dense porous structure (Scheydt & Muller, 2012;Valcuende et al, 2021b) and, consequently, very high resistivity. In fact, although steel fibres reduce resistivity, UH150 electrical resistance was nearly threefold greater than concrete C90 (Lliso-Ferrando, 2022).…”