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Eriksson, D., Gasch, T. & Ansell, A. (2019). A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete. Transport in Porous Media, 127(1), 113-141
Open this publication in new window or tab >>A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
2019 (English)In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 127, no 1, p. 113-141Article in journal (Refereed) Published
Abstract [en]

Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.

Place, publisher, year, edition, pages
Netherlands: Springer, 2019
Keywords
Air-entrained concrete, Multiphase model, Long-term absorption, Diffusion, Pore size distribution
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-240364 (URN)10.1007/s11242-018-1182-3 (DOI)000459472600005 ()2-s2.0-85055973654 (Scopus ID)
Note

QC 20190108

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-03-19Bibliographically approved
Ansell, A. (2019). Guidelines for practical use when shotcreting close to blasting and vibrations in hard rock. Stockholm
Open this publication in new window or tab >>Guidelines for practical use when shotcreting close to blasting and vibrations in hard rock
2019 (English)Report (Other academic)
Abstract [en]

Uncertainty about the vibration levels that can be tolerated near newly sprayed concrete (shotcrete) often leads to excessively conservative limit values being used in the construction of tunnels and structures in rock, with additional costs and planning uncertainties as a result. Previously, it has only been possible to give general recommendations for safe vibration levels. A project with the aim of producing a set of practical vibration limit levels for shotcrete work close to blasting in hard rock has therefore been carried out. These recommendations span situations that may arise during "normal" construction in hard rock, and contain guidelines for safe distances and waiting times for newly sprayed shotcrete exposed to vibrations. In the project, the focus is on wet-mixed shotcrete on hard rock, of the type found in Sweden and Scandinavia.

A large number of calculations have been carried out with a previously developed and relatively computationally effective numerical elastic stress wave propagation model. As input data, various combinations of the weight of explosives, distance, rock type, shotcrete type, shotcrete age and thickness are used. For each combination of input parameters, the stresses that arise at the bond interface between rock and shotcrete have been calculated. The results are saved in a database and can be illustrated graphically with a 3D surface, as a function of shotcrete age and distance to the explosive charge. This surface has then been compared with another, which represents the growth of bond strength between rock and shotcrete. The intersection curve between the two surfaces represents the limit for safe blasting, taking into account combinations of shortest distances and the youngest allowable shotcrete at time of blasting.

The report contains a larger number of graphs showing limit values for safe blasting, which will be of value as reference in design work, enable comparisons with data from the field, and thereby feedback of experience. Based on the recommended limit values, dimensioning in the design stage will be made so that the results will be undamaged and safer shotcrete with longer life. Reduced need for re-spraying and repair leads to a high economic sustainability for large infrastructure projects and environmental sustainability when material consumption is reduced. The safety of tunnels and underground constructions will also be increased.

Place, publisher, year, edition, pages
Stockholm: , 2019. p. 73
Series
BeFo Report ; 189
National Category
Geotechnical Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-265633 (URN)BEFO-R-189-SE (ISRN)
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2019-12-18Bibliographically approved
Sjölander, A. & Ansell, A. (2019). In-Situ and Laboratory Investigation on Leaching and Effects of Early Curing of Shotcrete. Nordic Concrete Research, 61(2), 23-37
Open this publication in new window or tab >>In-Situ and Laboratory Investigation on Leaching and Effects of Early Curing of Shotcrete
2019 (English)In: Nordic Concrete Research, ISSN 0800-6377, ISSN 0800-6377, Vol. 61, no 2, p. 23-37Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
shotcrete, curing, experiments, investigation, testing
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-266762 (URN)10.2478/ncr-2019-0014 (DOI)000508428100002 ()
Funder
Rock Engineering Research Foundation (BeFo), 379
Note

QC 20200123

Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-02-10Bibliographically approved
Magnusson, J., Hallgren, M., Malm, R. & Ansell, A. (2019). Numerical analyses of shear in concrete structures subjected to distributed blast loads. Engineering structures
Open this publication in new window or tab >>Numerical analyses of shear in concrete structures subjected to distributed blast loads
2019 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323Article in journal (Refereed) Submitted
Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Dynamic loading, shear failure, numerical modelling, FEM, shear span
National Category
Other Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-250797 (URN)
Note

QC 20190509

Available from: 2019-05-06 Created: 2019-05-06 Last updated: 2019-05-13Bibliographically approved
Gasch, T., Eriksson, D. & Ansell, A. (2019). On the behaviour of con-crete at early-ages: A multiphase description of hygro-thermo-chemo-mechanical properties. Cement and Concrete Research, 116, 202-216
Open this publication in new window or tab >>On the behaviour of con-crete at early-ages: A multiphase description of hygro-thermo-chemo-mechanical properties
2019 (English)In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 116, p. 202-216Article in journal (Refereed) Published
Abstract [en]

Understanding the early-age behaviour of concrete is of importance for designing durable concrete structures. To contribute to the improvement of this, a hygro-thermo-chemo-mechanical model is presented that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is based on a multiphase porous media framework, using the Thermodynamically Constrained Averaging Theory (TCAT) as starting point to derive the governing equations of the system. This allows for a systematic treatment of the multiscale properties of concrete and how these develop during hydration, e.g. chemical and physical fixation of water. The proposed mathematical model is implemented within the context of the Finite Element Method (FEM), where all physical fields are solved in a fully-coupled manner. Chosen properties of the model are demonstrated and validated using three experimental results from the literature. Generally, the simulated results are in good agreement with the measurements.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Hydration, Microstructure, Creep, Shrinkage, Modeling
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-240363 (URN)10.1016/j.cemconres.2018.09.009 (DOI)000457667500023 ()2-s2.0-85057608758 (Scopus ID)
Note

QC 20190109

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-03-15Bibliographically approved
Strömberg, L., Löfsjögård, M., Ansell, A. & Hintze, S. (2019). Optimization parameter sets for sustainable concrete in tunnels. In: ISEC 2019 - 10th International Structural Engineering and Construction Conference2019: . Paper presented at 10th International Structural Engineering and Construction Conference, ISEC 2019; Chicago; United States; 20 May 2019 through 25 May 2019. ISEC Press
Open this publication in new window or tab >>Optimization parameter sets for sustainable concrete in tunnels
2019 (English)In: ISEC 2019 - 10th International Structural Engineering and Construction Conference2019, ISEC Press , 2019Conference paper, Published paper (Refereed)
Abstract [en]

Public and private clients are beginning to set complex optimization requirements, taking into consideration environmental and cost-efficiency parameters over the built construction’s lifetime. The early design process is currently irreversible and this makes it difficult to change a concrete structure in the later detailed design stage, when more accurate information is available regarding environmental impact and life-cycle costs. There is a dilemma in complying with existing standards to achieve technical requirements while optimizing a concrete structure in order to reduce the climate impact. The long-term goal of the project is to develop a new theoretical concept for dynamic optimization strategies which can be applicable to the early design, the client-requirement preparation, the detailed design, the production and the follow-up stages. This paper presents the results of the up-start phase of the project. Our work has focused on the identification of current practice regarding clients’ requirements for technical, environmental and cost-efficiency parameters. An analysis of these requirements with sprayed concrete in a number of ongoing projects has led to the identification of optimization parameter sets. The project has also shown how the physical values of those parameters can be collected from existing statistics, experience recovery databases and previous project requirements, or calculated according to standardized methods and tools. The concept developed will be used in a demonstrative modeling in the next project step.

Place, publisher, year, edition, pages
ISEC Press, 2019
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-260967 (URN)2-s2.0-85070406057 (Scopus ID)9780996043762 (ISBN)
Conference
10th International Structural Engineering and Construction Conference, ISEC 2019; Chicago; United States; 20 May 2019 through 25 May 2019
Note

QC 20191002

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-10-02Bibliographically approved
Ansell, A. (2019). Practical guidelines for shotcrete work close to blasting and vibration in hard rock. In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress: . Paper presented at World Tunnel Congress, WTC 2019 and the 45th General Assembly of the International Tunnelling and Underground Space Association, ITA-AITES 2019; Naples; Italy; 3 May 2019 through 9 May 2019 (pp. 4659-4668).
Open this publication in new window or tab >>Practical guidelines for shotcrete work close to blasting and vibration in hard rock
2019 (English)In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress, 2019, p. 4659-4668Conference paper, Published paper (Refereed)
Abstract [en]

Limited knowledge on safe vibration levels near newly sprayed concrete (shotcrete) often leads to over-conservative limits in underground construction and tunnelling, with additional costs and planning uncertainties as a consequence. Work on compiling a database of practical vibration levels for shotcrete work close to blasting in hard rock have been initiated and will provide guidelines for safe distances and waiting times for newly sprayed wet-mix shotcrete. A large number of calculations are carried out with a previously developed and relatively computationally effective numerical elastic stress wave propagation model, which will result in a systematically compiled database. These guidelines, giving relationships between the amount of explosives, distance, rock type, shotcrete type, age and thickness, will be of great value as reference for design work and facilitate comparisons with in situ data. It will be possible to adopt the design to ensure undamaged and safer shotcrete constructions with longer service life.

National Category
Civil Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-260964 (URN)10.1201/9780429424441-494 (DOI)2-s2.0-85068415880 (Scopus ID)9781138388659 (ISBN)
Conference
World Tunnel Congress, WTC 2019 and the 45th General Assembly of the International Tunnelling and Underground Space Association, ITA-AITES 2019; Naples; Italy; 3 May 2019 through 9 May 2019
Note

QC 20191115

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-11-15Bibliographically approved
Sjölander, A. & Ansell, A. (2019). Probabilistic modelling of fibre reinforced shotcrete. In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress: . Paper presented at World Tunnel Congress, WTC 2019 and the 45th General Assembly of the International Tunnelling and Underground Space Association, ITA-AITES 2019; Naples; Italy; 3 May 2019 through 9 May 2019 (pp. 3105-3112). CRC Press
Open this publication in new window or tab >>Probabilistic modelling of fibre reinforced shotcrete
2019 (English)In: Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art- Proceedings of the WTC 2019 ITA-AITES World Tunnel Congress, CRC Press, 2019, p. 3105-3112Conference paper, Published paper (Refereed)
Abstract [en]

Shotcrete is widely used as rock support and can support the load from blocks either by bonding to the rock or by bending between rock bolts. By introducing fibres, the ductility of the shotcrete will increase and the crack widths decrease. Predictions of the structural behaviour for fibre reinforced shotcrete (FRS) are however complicated due to the large scatter normally seen in test results. The reason is mainly related to the non-uniform distribution and orientation of the fibres which could lead to uncertainties regarding the quality of in-situ shot-crete. The aim with this paper is therefore to investigate if a probabilistic material model for FRS can be used to capture the scatter in the results. An isotropic damage model that combines an exponential softening curve for unreinforced shotcrete and a bi-linear curve to account for the effect of fibres were used. Suitable distributions for each of the parameters in the model have been proposed based on fitting of experimental results. Thereafter, Monte Carlo simula-tions were used to produce results for a large number of lab tests. Results show that the model together with the proposed distributions was able to capture the scatter in test results.

Place, publisher, year, edition, pages
CRC Press, 2019
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
urn:nbn:se:kth:diva-260966 (URN)10.1201/9780429424441-329 (DOI)2-s2.0-85068357299 (Scopus ID)9781138388659 (ISBN)
Conference
World Tunnel Congress, WTC 2019 and the 45th General Assembly of the International Tunnelling and Underground Space Association, ITA-AITES 2019; Naples; Italy; 3 May 2019 through 9 May 2019
Note

QC 20191112

Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2019-11-12Bibliographically approved
Gasch, T., Malm, R. & Ansell, A. (2019). Three-dimensional simulations of ageing concrete structures using a multiphase model formulation. Materials and Structures, 52(4), Article ID 85.
Open this publication in new window or tab >>Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
2019 (English)In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 52, no 4, article id 85Article in journal (Refereed) Published
Abstract [en]

The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (Cem Concrete Res 116:202–216, 2019. https://doi.org/10.1016/j.cemconres.2018.09.009) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.

Place, publisher, year, edition, pages
Springer Netherlands, 2019
Keywords
Concrete, Early-age, Finite Element Method, Hygro-thermo-chemo-mechanical, Structural application
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-262551 (URN)10.1617/s11527-019-1383-4 (DOI)000478086000001 ()2-s2.0-85069913179 (Scopus ID)
Note

QC 20191021

Available from: 2019-10-21 Created: 2019-10-21 Last updated: 2019-10-21Bibliographically approved
Eriksson, D., Gasch, T., Malm, R. & Ansell, A. (2018). Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour. International Journal of Solids and Structures, 152-153, 294-304
Open this publication in new window or tab >>Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour
2018 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 152-153, p. 294-304Article in journal (Refereed) Published
Abstract [en]

Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.

Keywords
Freezing, Partially saturated, Air-entrained concrete, Structural scale, Finite element modelling
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-237303 (URN)10.1016/j.ijsolstr.2018.07.004 (DOI)000447576100023 ()2-s2.0-85051402406 (Scopus ID)
Note

QC 20181114

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2019-01-07Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-8336-1247

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