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Volume 65 (2021): Edition 2 (December 2021)

Volume 64 (2021): Edition 1 (June 2021)

Volume 63 (2020): Edition 2 (December 2020)

Volume 62 (2020): Edition 1 (June 2020)

Volume 61 (2019): Edition 2 (December 2019)

Volume 60 (2019): Edition 1 (June 2019)

Volume 59 (2018): Edition 1 (December 2018)

Volume 58 (2018): Edition 1 (June 2018)

Détails du magazine
Format
Magazine
eISSN
2545-2819
Première publication
30 Sep 2018
Période de publication
2 fois par an
Langues
Anglais

Chercher

Volume 61 (2019): Edition 2 (December 2019)

Détails du magazine
Format
Magazine
eISSN
2545-2819
Première publication
30 Sep 2018
Période de publication
2 fois par an
Langues
Anglais

Chercher

8 Articles
Accès libre

Effect of AEA-SP Dosage Sequence on Air Entrainment in FA Concrete

Publié en ligne: 31 Dec 2019
Pages: 1 - 21

Résumé

Abstract

Laboratory measurements show that varying the dosage sequence of air-entraining agent and co-polymer in the mix (SP added before, after or together with AEA) greatly affects air entrainment in fresh and hardened fly ash concrete. Image analysis shows a somewhat lower specific surface when SP is added together with AEA. Foam Index measurements on the same binder materials, admixtures, and dosage sequences were therefore found less useful for studying the effect of admixture combinations. Obtaining a certain air content using the experience with AEA-SP dosage was found to be an untrivial task if there is a lack of parameter control. Finally, examples of successful mixing procedure for air entrainment in a series of high-volume fly ash concrete are shown.

Mots clés

  • Air entrainment
  • Dosage sequence
  • Fly ash
  • Admixtures
Accès libre

In-Situ and Laboratory Investigation on Leaching and Effects of Early Curing of Shotcrete

Publié en ligne: 31 Dec 2019
Pages: 23 - 37

Résumé

Abstract

During the construction of a rock tunnel in Stockholm, several sections with leaching shotcrete (sprayed concrete) were found one year after the spraying was completed. An investigation was therefore conducted, and its results are presented in this paper. The amount of leaching after such a short time indicated that a one-sided water pressure existed in combination with a permeable shotcrete. The reason for the water pressure was likely a partly unsuccessful grouting that created sections with leaking water. The permeable shotcrete could be a combined result of insufficient curing and the use of accelerators, and the effect of in-situ curing was therefore investigated. A total of six slabs were sprayed and cured under different conditions in the tunnel. Test results according to standards indicated that curing has no significant effect on the development of mechanical strength or water penetration through the shotcrete. However, this is believed to be a result of the test method rather than the non-existing effect of curing. Lastly, some modifications to the test standard were proposed for future studies of in-situ curing.

Mots clés

  • shotcrete
  • curing
  • experiments
  • investigation
  • testing
Accès libre

The Choice of Materials for the E39 Fjord Crossing Project

Publié en ligne: 31 Dec 2019
Pages: 39 - 51

Résumé

Abstract

In the studies for crossing the long and deep Norwegian fjords along the E39 road, on the west coast of Norway, some challenging structures have been evaluated. Some of them are known structures, like floating bridges, and some others are structures never built before, like suspension bridges on tension leg platforms and submerged floating tube bridges. In the development of the feasibility studies for these crossings, the choice of materials has played an important role. The materials influence not only the design and the cost, but also the behaviour of the structure towards the environmental loads and some particular loads as the ship collision. The article illustrates the different solutions proposed for the fjord crossings and discusses the influence in the choice of the material, with special regards to the type of concrete. The pros and cons of the application of the light weight concrete are discussed.

Mots clés

  • Materials
  • concrete
  • light weight concrete
  • bridges
Accès libre

Topological and Size Optimization of RC Beam Bridges: An Automated Design Approach for Cost Effective and Environmental Friendly Solutions

Publié en ligne: 31 Dec 2019
Pages: 53 - 78

Résumé

Abstract

This work presents a procedure for the automated design and optimization of reinforced concrete beam bridges. The aim is to find solutions that minimize the investment cost and the environmental impact of the bridge. The complete structure is optimized including: number of spans, pier locations, pier-deck connections and deck dimensions. A detailed design of the deck reinforcement is included as well. Furthermore, constructability is considered and quantified within the investment cost to avoid a merely theoretical optimization. Genetic Algorithm (GA) and Pattern Search (PS) optimization algorithms are used. To reduce the computational time and make the procedure more user-friendly, a memory system is integrated and a modified version of GA is developed. In this paper, the proposed procedure is applied to re-design an existing bridge originally designed according to Eurocodes by an experienced engineer in 2013. Savings of 10-15% for both investment cost and environmental impact have been obtained. Finally, the proposed procedure has been applied to several alternatives with different total bridge lengths to suggest the optimal number of spans for a given total bridge length.

Mots clés

  • Structural optimization
  • automated design
  • beam bridges
  • environmental impact
  • investment cost
Accès libre

Effect on Radon Exhalation Rate Due to Cracks in Concrete

Publié en ligne: 31 Dec 2019
Pages: 79 - 90

Résumé

Abstract

The second largest cause of lung cancer in the World is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced.

The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.

Mots clés

  • Radon
  • concrete
  • cracks
  • radon exhalation rate
  • building materials
Accès libre

Freeze-thaw Damage Dependence on Wind-driven Rain of Outdoor Exposed Concrete – A Case Study

Publié en ligne: 31 Dec 2019
Pages: 91 - 106

Résumé

Abstract

It has been shown in previous studies that the existing precast concrete element building stock in Finland has quality issues, especially with freeze-thaw durability and reinforcement corrosion. In addition, it has been presented that deterioration rate is the fastest in coastal area and decreases towards north which has been supposed to be a reason of lower amount of wind-driven rain (WDR). The aim of this study was to examine the connection between the amount of WDR on structures and the freeze-thaw damage more comprehensively. Condition investigation reports of 472 precast concrete element buildings were reanalysed to study the relation and the results were compared to climate data of the same time period to study the correlation between condition investigation observations and the amount of WDR. In addition, the observations made in a condition investigations and their relation to climate load at the same building were studied as a case study. The results show that there is a significant connection between the WDR related climate load and the freeze-thaw damage occurrence. The results can be used to plan protective methods and be a base for service life estimations.

Mots clés

  • Concrete
  • climatic stress
  • freeze-thaw attack
  • service life
  • durability properties
Accès libre

Bonded Concrete Overlays: A Brief Discussion on Restrained Shrinkage Deformations and Their Prediction Models

Publié en ligne: 31 Dec 2019
Pages: 107 - 129

Résumé

Abstract

Bonded concrete overlays (BCO) on bridge decks are beneficial solutions due to their superior properties as compared to the typical asphalt pavement. A significant number of overlays suffer however, from occurrence of cracks and delamination due to poor bond, and restrained shrinkage and thermal dilation. Over the past years different appraisals for estimation of the restrained deformations have been developed, from micro-scale models, based on poromechanics, to empirical equations as given in B3 or B4 models suggested by Bažant. This paper provides a short overview of calculation models along with a brief theoretical explanation of shrinkage mechanism.

Mots clés

  • bridge
  • overlay
  • concrete
  • shrinkage
  • creep
Accès libre

Width and Edge Beam Effects on the Ultimate Behaviour of RC Bridge Overhangs

Publié en ligne: 31 Dec 2019
Pages: 131 - 152

Résumé

Abstract

The bearing capacity of RC overhangs under concentrated loads can be dependent on the width of the slab. The goal of this paper is to investigate the effect of different widths using tests from the literature and non-linear FE-simulations as a reference. Shear force redistributions along the loading process and the shear concrete capacity are analysed. The shear effective width and the influence of an edge beam are also addressed. The results show that the bearing capacity of RC overhangs increase with the width until a transition area is reached and the increase flattens. An increased shear distribution sideways and posterior redistributions under the loading process are enabled. The shear capacity of concrete increases with the width and for loads close to the root an arch effect is observed. The edge beam contributes to a further increase of the ultimate capacity for wide enough overhangs. The effect of the width and the edge beam is not only quantitative but also qualitative since the failure mode and the critical section are influenced. Existing formulation for shear effective widths should be revisited. Experimental tests used for this purpose should consider wide enough specimens to capture the real behaviour of a bridge overhang slab.

Mots clés

  • Overhang slab
  • Bearing capacity
  • Width
  • Edge beam
  • Shear force
  • FE-modelling
8 Articles
Accès libre

Effect of AEA-SP Dosage Sequence on Air Entrainment in FA Concrete

Publié en ligne: 31 Dec 2019
Pages: 1 - 21

Résumé

Abstract

Laboratory measurements show that varying the dosage sequence of air-entraining agent and co-polymer in the mix (SP added before, after or together with AEA) greatly affects air entrainment in fresh and hardened fly ash concrete. Image analysis shows a somewhat lower specific surface when SP is added together with AEA. Foam Index measurements on the same binder materials, admixtures, and dosage sequences were therefore found less useful for studying the effect of admixture combinations. Obtaining a certain air content using the experience with AEA-SP dosage was found to be an untrivial task if there is a lack of parameter control. Finally, examples of successful mixing procedure for air entrainment in a series of high-volume fly ash concrete are shown.

Mots clés

  • Air entrainment
  • Dosage sequence
  • Fly ash
  • Admixtures
Accès libre

In-Situ and Laboratory Investigation on Leaching and Effects of Early Curing of Shotcrete

Publié en ligne: 31 Dec 2019
Pages: 23 - 37

Résumé

Abstract

During the construction of a rock tunnel in Stockholm, several sections with leaching shotcrete (sprayed concrete) were found one year after the spraying was completed. An investigation was therefore conducted, and its results are presented in this paper. The amount of leaching after such a short time indicated that a one-sided water pressure existed in combination with a permeable shotcrete. The reason for the water pressure was likely a partly unsuccessful grouting that created sections with leaking water. The permeable shotcrete could be a combined result of insufficient curing and the use of accelerators, and the effect of in-situ curing was therefore investigated. A total of six slabs were sprayed and cured under different conditions in the tunnel. Test results according to standards indicated that curing has no significant effect on the development of mechanical strength or water penetration through the shotcrete. However, this is believed to be a result of the test method rather than the non-existing effect of curing. Lastly, some modifications to the test standard were proposed for future studies of in-situ curing.

Mots clés

  • shotcrete
  • curing
  • experiments
  • investigation
  • testing
Accès libre

The Choice of Materials for the E39 Fjord Crossing Project

Publié en ligne: 31 Dec 2019
Pages: 39 - 51

Résumé

Abstract

In the studies for crossing the long and deep Norwegian fjords along the E39 road, on the west coast of Norway, some challenging structures have been evaluated. Some of them are known structures, like floating bridges, and some others are structures never built before, like suspension bridges on tension leg platforms and submerged floating tube bridges. In the development of the feasibility studies for these crossings, the choice of materials has played an important role. The materials influence not only the design and the cost, but also the behaviour of the structure towards the environmental loads and some particular loads as the ship collision. The article illustrates the different solutions proposed for the fjord crossings and discusses the influence in the choice of the material, with special regards to the type of concrete. The pros and cons of the application of the light weight concrete are discussed.

Mots clés

  • Materials
  • concrete
  • light weight concrete
  • bridges
Accès libre

Topological and Size Optimization of RC Beam Bridges: An Automated Design Approach for Cost Effective and Environmental Friendly Solutions

Publié en ligne: 31 Dec 2019
Pages: 53 - 78

Résumé

Abstract

This work presents a procedure for the automated design and optimization of reinforced concrete beam bridges. The aim is to find solutions that minimize the investment cost and the environmental impact of the bridge. The complete structure is optimized including: number of spans, pier locations, pier-deck connections and deck dimensions. A detailed design of the deck reinforcement is included as well. Furthermore, constructability is considered and quantified within the investment cost to avoid a merely theoretical optimization. Genetic Algorithm (GA) and Pattern Search (PS) optimization algorithms are used. To reduce the computational time and make the procedure more user-friendly, a memory system is integrated and a modified version of GA is developed. In this paper, the proposed procedure is applied to re-design an existing bridge originally designed according to Eurocodes by an experienced engineer in 2013. Savings of 10-15% for both investment cost and environmental impact have been obtained. Finally, the proposed procedure has been applied to several alternatives with different total bridge lengths to suggest the optimal number of spans for a given total bridge length.

Mots clés

  • Structural optimization
  • automated design
  • beam bridges
  • environmental impact
  • investment cost
Accès libre

Effect on Radon Exhalation Rate Due to Cracks in Concrete

Publié en ligne: 31 Dec 2019
Pages: 79 - 90

Résumé

Abstract

The second largest cause of lung cancer in the World is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced.

The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.

Mots clés

  • Radon
  • concrete
  • cracks
  • radon exhalation rate
  • building materials
Accès libre

Freeze-thaw Damage Dependence on Wind-driven Rain of Outdoor Exposed Concrete – A Case Study

Publié en ligne: 31 Dec 2019
Pages: 91 - 106

Résumé

Abstract

It has been shown in previous studies that the existing precast concrete element building stock in Finland has quality issues, especially with freeze-thaw durability and reinforcement corrosion. In addition, it has been presented that deterioration rate is the fastest in coastal area and decreases towards north which has been supposed to be a reason of lower amount of wind-driven rain (WDR). The aim of this study was to examine the connection between the amount of WDR on structures and the freeze-thaw damage more comprehensively. Condition investigation reports of 472 precast concrete element buildings were reanalysed to study the relation and the results were compared to climate data of the same time period to study the correlation between condition investigation observations and the amount of WDR. In addition, the observations made in a condition investigations and their relation to climate load at the same building were studied as a case study. The results show that there is a significant connection between the WDR related climate load and the freeze-thaw damage occurrence. The results can be used to plan protective methods and be a base for service life estimations.

Mots clés

  • Concrete
  • climatic stress
  • freeze-thaw attack
  • service life
  • durability properties
Accès libre

Bonded Concrete Overlays: A Brief Discussion on Restrained Shrinkage Deformations and Their Prediction Models

Publié en ligne: 31 Dec 2019
Pages: 107 - 129

Résumé

Abstract

Bonded concrete overlays (BCO) on bridge decks are beneficial solutions due to their superior properties as compared to the typical asphalt pavement. A significant number of overlays suffer however, from occurrence of cracks and delamination due to poor bond, and restrained shrinkage and thermal dilation. Over the past years different appraisals for estimation of the restrained deformations have been developed, from micro-scale models, based on poromechanics, to empirical equations as given in B3 or B4 models suggested by Bažant. This paper provides a short overview of calculation models along with a brief theoretical explanation of shrinkage mechanism.

Mots clés

  • bridge
  • overlay
  • concrete
  • shrinkage
  • creep
Accès libre

Width and Edge Beam Effects on the Ultimate Behaviour of RC Bridge Overhangs

Publié en ligne: 31 Dec 2019
Pages: 131 - 152

Résumé

Abstract

The bearing capacity of RC overhangs under concentrated loads can be dependent on the width of the slab. The goal of this paper is to investigate the effect of different widths using tests from the literature and non-linear FE-simulations as a reference. Shear force redistributions along the loading process and the shear concrete capacity are analysed. The shear effective width and the influence of an edge beam are also addressed. The results show that the bearing capacity of RC overhangs increase with the width until a transition area is reached and the increase flattens. An increased shear distribution sideways and posterior redistributions under the loading process are enabled. The shear capacity of concrete increases with the width and for loads close to the root an arch effect is observed. The edge beam contributes to a further increase of the ultimate capacity for wide enough overhangs. The effect of the width and the edge beam is not only quantitative but also qualitative since the failure mode and the critical section are influenced. Existing formulation for shear effective widths should be revisited. Experimental tests used for this purpose should consider wide enough specimens to capture the real behaviour of a bridge overhang slab.

Mots clés

  • Overhang slab
  • Bearing capacity
  • Width
  • Edge beam
  • Shear force
  • FE-modelling

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