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Volumen 67 (2022): Edición 2 (December 2022)

Volumen 66 (2022): Edición 1 (July 2022)

Volumen 65 (2021): Edición 2 (December 2021)

Volumen 64 (2021): Edición 1 (June 2021)

Volumen 63 (2020): Edición 2 (December 2020)

Volumen 62 (2020): Edición 1 (June 2020)

Volumen 61 (2019): Edición 2 (December 2019)

Volumen 60 (2019): Edición 1 (June 2019)

Volumen 59 (2018): Edición 1 (December 2018)

Volumen 58 (2018): Edición 1 (June 2018)

Detalles de la revista
Formato
Revista
eISSN
2545-2819
Publicado por primera vez
30 Sep 2018
Periodo de publicación
2 veces al año
Idiomas
Inglés

Buscar

Volumen 67 (2022): Edición 2 (December 2022)

Detalles de la revista
Formato
Revista
eISSN
2545-2819
Publicado por primera vez
30 Sep 2018
Periodo de publicación
2 veces al año
Idiomas
Inglés

Buscar

7 Artículos
Acceso abierto

Empirical Modelling of Lithium Mitigation for Alkali-Silica Reactivity

Publicado en línea: 14 Jan 2023
Páginas: 1 - 14

Resumen

Abstract

The Alkali-Silica Reaction (ASR) is a deleterious concrete chemical reaction that has been studied a lot since its discovery in 1940. The reaction produces a highly hygroscopic silica gel that swells into the pores of concrete, resulting in the critical decrease of the mechanical performances of the affected structures. Some methods have been investigated to limit expansion under a certain limit, among them lithium mitigation. However, the mechanisms are not really understood yet and determining the right amount of lithium is still arduous. An attempt for a method in coherence with experience is presented in this study, using the chemo-mechanical model of Larive and curve-fitting. The results provide accuracy to experimental measurements from several protocols, and call for further research.

Palabras clave

  • Concrete
  • Alkali-Silica Reaction
  • Lithium mitigation
  • Modified chemo-mechanical model
Acceso abierto

Effect of Set Accelerator on Capillary Suction and Porosity of Concrete – Cast Samples with Constant Water/Binder Ratio

Publicado en línea: 14 Jan 2023
Páginas: 15 - 34

Resumen

Abstract

Alkali-free set accelerators are added at the nozzle to ensure rapid set of wet sprayed concrete. The accelerator affects the strength development, porosity and transport properties, and hence the durability, of the sprayed concrete. We developed a method to cast samples with varying set accelerator doses to measure the effect of the accelerator on porosity, but with a constant effective water/binder ratio of 0.45 for each accelerator dose. Six cylinders of concrete were cast with set accelerator doses of 0, 2, 4, 6, 8 and 10 % of effective binder mass. High workability was achieved to enable mixing before rapid stiffening occurred, though this high workability led to some aggregate settlement in the cylinders. Porosity was measured by capillary suction on dried specimens of hardened concrete and subsequent pressure saturation of macro pores (PF test). The samples cast with higher doses of set accelerator had higher suction porosities and higher rates of capillary suction. Using a modified Powers equation gave very low calculated degree of hydration values for concrete with set accelerator, indicating that the equation is not applicable for concrete with set accelerators, due to the higher suction porosity in accelerated matrices, caused by different hydration products.

Palabras clave

  • Sprayed concrete
  • shotcrete
  • accelerator
  • porosity
  • tunnel
  • durability
Acceso abierto

Effect of High-Pressure Washing on Chloride Ingress in Concrete – Development of an Accelerated Test Method

Publicado en línea: 14 Jan 2023
Páginas: 35 - 50

Resumen

Abstract

Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.

Palabras clave

  • Bridge maintenance
  • preventive maintenance
  • chloride ingress
  • test development
  • high-pressure washing
Acceso abierto

Evaluation of Crushed Fine Materials

Publicado en línea: 14 Jan 2023
Páginas: 65 - 77

Resumen

Abstract

As natural resources of sand and fine material used in the concrete industry are becoming more scarce, crushed materials are being used to a greater extent. Shape and texture of machine crushed materials differ from aggregates naturally ground, layered and sorted under the course of millions of years. It is assumed that crushed aggregates are more angular and of less smooth texture than natural aggregates, which will affect the flow behaviour of a suspension containing crushed material. In the mix design process of cementitous suspensions, an adequate rheology of the micro mortar (all constituents in the concrete being able to pass a 0.125 mm sieve, including the cement) is crucial. In this paper, the shape of fine particles is linked to the micro mortar plastic viscosity of the filler suspension including cement. The plastic viscosity here serves as an important quality assessment of the filler, since the micro mortar workability features are vital for the final mix design quality of the concrete workability.

Palabras clave

  • Instructions
  • layout
  • headings
  • figures and tables
  • references
Acceso abierto

Failure Mechanisms of Fibre Reinforced Shotcrete: Numerical Simulations Considering Local Variations in Thickness and Bond Strength

Publicado en línea: 14 Jan 2023
Páginas: 51 - 64

Resumen

Abstract

Fibre-reinforced shotcrete is the most common support method for hard rock tunnels in the Nordic countries. The design of shotcrete is often based on empirical methods or simplified analytical equations, which neglect variations in mechanical properties and shotcrete thickness. Data collected from the field shows that significant variations in shotcrete thickness and bond strength should be expected during tunnel construction. However, how this affects the structural behaviour and capacity of the shotcrete lining is unknown. Moreover, the design philosophy for shotcrete assumes that the primary failure modes of shotcrete, i.e. bond and flexural failure, can be treated separately. This was derived based on observations of experiments in a laboratory environment. Therefore, the focus of a finalized doctoral project was to develop a numerical framework to simulate the structural behaviour of fibre-reinforced shotcrete in interaction with hard rock and rock bolts. The effect of variations in shotcrete thickness and bond strength was studied through numerical simulations to increase the understanding of its effect on the failure load of the lining. The results indicate that the most important parameter is the mean value of the shotcrete thickness and bond strength around a narrow perimeter of the block.’

Palabras clave

  • fibre-reinforcement
  • shotcrete
  • rock support
  • failure modes and bond strength
Acceso abierto

Is Cement Paste Modified with Carbon Nanomaterials Capable of Self-Repair after a Fire?

Publicado en línea: 14 Jan 2023
Páginas: 79 - 97

Resumen

Abstract

This manuscript presents preliminary results on the cement paste potential, with and without carbon nanomaterials, to heal high-temperature cracks. Cement paste beams were subjected to thermal loading of 200°C and 400°C after 28 days of water curing. High temperature caused the formation of microcrack networks on the specimen’s surface. Self-healing was achieved by exposing the cracked samples to cyclic water immersion. The efficiency of the process was evaluated based on the crack closure and mechanical properties recovery after 24 days. The results indicated a distinct dependence of the healing on the loading temperature. Carbon nanotubes had a positive effect on self-repair efficiency.

Palabras clave

  • self-healing
  • cement paste
  • nanomaterials
  • Multi-Wall Carbon Nanotubes
  • high temperature
  • microcracking
  • image analysis
Acceso abierto

Preface

Publicado en línea: 14 Jan 2023
Páginas: I - I

Resumen

7 Artículos
Acceso abierto

Empirical Modelling of Lithium Mitigation for Alkali-Silica Reactivity

Publicado en línea: 14 Jan 2023
Páginas: 1 - 14

Resumen

Abstract

The Alkali-Silica Reaction (ASR) is a deleterious concrete chemical reaction that has been studied a lot since its discovery in 1940. The reaction produces a highly hygroscopic silica gel that swells into the pores of concrete, resulting in the critical decrease of the mechanical performances of the affected structures. Some methods have been investigated to limit expansion under a certain limit, among them lithium mitigation. However, the mechanisms are not really understood yet and determining the right amount of lithium is still arduous. An attempt for a method in coherence with experience is presented in this study, using the chemo-mechanical model of Larive and curve-fitting. The results provide accuracy to experimental measurements from several protocols, and call for further research.

Palabras clave

  • Concrete
  • Alkali-Silica Reaction
  • Lithium mitigation
  • Modified chemo-mechanical model
Acceso abierto

Effect of Set Accelerator on Capillary Suction and Porosity of Concrete – Cast Samples with Constant Water/Binder Ratio

Publicado en línea: 14 Jan 2023
Páginas: 15 - 34

Resumen

Abstract

Alkali-free set accelerators are added at the nozzle to ensure rapid set of wet sprayed concrete. The accelerator affects the strength development, porosity and transport properties, and hence the durability, of the sprayed concrete. We developed a method to cast samples with varying set accelerator doses to measure the effect of the accelerator on porosity, but with a constant effective water/binder ratio of 0.45 for each accelerator dose. Six cylinders of concrete were cast with set accelerator doses of 0, 2, 4, 6, 8 and 10 % of effective binder mass. High workability was achieved to enable mixing before rapid stiffening occurred, though this high workability led to some aggregate settlement in the cylinders. Porosity was measured by capillary suction on dried specimens of hardened concrete and subsequent pressure saturation of macro pores (PF test). The samples cast with higher doses of set accelerator had higher suction porosities and higher rates of capillary suction. Using a modified Powers equation gave very low calculated degree of hydration values for concrete with set accelerator, indicating that the equation is not applicable for concrete with set accelerators, due to the higher suction porosity in accelerated matrices, caused by different hydration products.

Palabras clave

  • Sprayed concrete
  • shotcrete
  • accelerator
  • porosity
  • tunnel
  • durability
Acceso abierto

Effect of High-Pressure Washing on Chloride Ingress in Concrete – Development of an Accelerated Test Method

Publicado en línea: 14 Jan 2023
Páginas: 35 - 50

Resumen

Abstract

Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.

Palabras clave

  • Bridge maintenance
  • preventive maintenance
  • chloride ingress
  • test development
  • high-pressure washing
Acceso abierto

Evaluation of Crushed Fine Materials

Publicado en línea: 14 Jan 2023
Páginas: 65 - 77

Resumen

Abstract

As natural resources of sand and fine material used in the concrete industry are becoming more scarce, crushed materials are being used to a greater extent. Shape and texture of machine crushed materials differ from aggregates naturally ground, layered and sorted under the course of millions of years. It is assumed that crushed aggregates are more angular and of less smooth texture than natural aggregates, which will affect the flow behaviour of a suspension containing crushed material. In the mix design process of cementitous suspensions, an adequate rheology of the micro mortar (all constituents in the concrete being able to pass a 0.125 mm sieve, including the cement) is crucial. In this paper, the shape of fine particles is linked to the micro mortar plastic viscosity of the filler suspension including cement. The plastic viscosity here serves as an important quality assessment of the filler, since the micro mortar workability features are vital for the final mix design quality of the concrete workability.

Palabras clave

  • Instructions
  • layout
  • headings
  • figures and tables
  • references
Acceso abierto

Failure Mechanisms of Fibre Reinforced Shotcrete: Numerical Simulations Considering Local Variations in Thickness and Bond Strength

Publicado en línea: 14 Jan 2023
Páginas: 51 - 64

Resumen

Abstract

Fibre-reinforced shotcrete is the most common support method for hard rock tunnels in the Nordic countries. The design of shotcrete is often based on empirical methods or simplified analytical equations, which neglect variations in mechanical properties and shotcrete thickness. Data collected from the field shows that significant variations in shotcrete thickness and bond strength should be expected during tunnel construction. However, how this affects the structural behaviour and capacity of the shotcrete lining is unknown. Moreover, the design philosophy for shotcrete assumes that the primary failure modes of shotcrete, i.e. bond and flexural failure, can be treated separately. This was derived based on observations of experiments in a laboratory environment. Therefore, the focus of a finalized doctoral project was to develop a numerical framework to simulate the structural behaviour of fibre-reinforced shotcrete in interaction with hard rock and rock bolts. The effect of variations in shotcrete thickness and bond strength was studied through numerical simulations to increase the understanding of its effect on the failure load of the lining. The results indicate that the most important parameter is the mean value of the shotcrete thickness and bond strength around a narrow perimeter of the block.’

Palabras clave

  • fibre-reinforcement
  • shotcrete
  • rock support
  • failure modes and bond strength
Acceso abierto

Is Cement Paste Modified with Carbon Nanomaterials Capable of Self-Repair after a Fire?

Publicado en línea: 14 Jan 2023
Páginas: 79 - 97

Resumen

Abstract

This manuscript presents preliminary results on the cement paste potential, with and without carbon nanomaterials, to heal high-temperature cracks. Cement paste beams were subjected to thermal loading of 200°C and 400°C after 28 days of water curing. High temperature caused the formation of microcrack networks on the specimen’s surface. Self-healing was achieved by exposing the cracked samples to cyclic water immersion. The efficiency of the process was evaluated based on the crack closure and mechanical properties recovery after 24 days. The results indicated a distinct dependence of the healing on the loading temperature. Carbon nanotubes had a positive effect on self-repair efficiency.

Palabras clave

  • self-healing
  • cement paste
  • nanomaterials
  • Multi-Wall Carbon Nanotubes
  • high temperature
  • microcracking
  • image analysis
Acceso abierto

Preface

Publicado en línea: 14 Jan 2023
Páginas: I - I

Resumen