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Rajczakowska, Magdalena
Publications (7 of 7) Show all publications
Ghasemi, Y., Rajczakowska, M., Emborg, M. & Cwirzen, A. (2020). Shape-dependent calculation of specific surface area of aggregates versus X-ray microtomography. Magazine of Concrete Research, 72(2), 88-96
Open this publication in new window or tab >>Shape-dependent calculation of specific surface area of aggregates versus X-ray microtomography
2020 (English)In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 72, no 2, p. 88-96Article in journal (Refereed) Published
Abstract [en]

The specific surface area (SSA) of constituents in a concrete mixture has a significant effect on its workability in fresh state. Excess layer theories relate the SSA to the flow behaviour of mixtures and can be used as part of an approach to mix design. However, measurement of SSA is complex and includes several issues, and thus is commonly replaced by mathematical estimation of the parameter. The mathematical approximation of surface area is based on the assumption of a spherical shape for the particles, which leads to failure of taking into account the effect of shape and the square–cube law. The article explores the possibility of replacing the assumption of a spherical shape with that of Platonic solids as the representative shape to account for the angularity of aggregates. The calculation was conducted based on information on the particle size distribution (PSD) obtained from dry sieving method. A calculated surface area on the assumption of a dodecahedron shape for natural aggregates and a cubical shape for crushed aggregates showed good agreement with SSA measurements conducted by X-ray microtomography. Furthermore, the effect of changes in PSD on the accuracy of the approach was also studied. It was found that the estimated value of SSA was improved in comparison with the traditional way of calculation on the assumption of a spherical shape.

Place, publisher, year, edition, pages
ICE publishing, 2020
Keywords
Mix design, Water film thickness, Excess water layer theory, specific surface area, aggregates, testing, apparatus & methods, workability
National Category
Infrastructure Engineering Other Materials Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-71374 (URN)10.1680/jmacr.18.00121 (DOI)
Funder
Swedish Research Council Formas
Note

Validerad;2020;Nivå 2;2019-12-16 (johcin)

Available from: 2018-10-30 Created: 2018-10-30 Last updated: 2019-12-16Bibliographically approved
Rajczakowska, M., Habermehl-Cwirzen, K., Hedlund, H. & Cwirzen, A. (2019). Autogenous Self-Healing: A Better Solution for Concrete. Journal of materials in civil engineering, 31(9), Article ID 3119001.
Open this publication in new window or tab >>Autogenous Self-Healing: A Better Solution for Concrete
2019 (English)In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 31, no 9, article id 3119001Article in journal (Refereed) Published
Abstract [en]

Self-healing can be defined as the ability of a material to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on optimized mix composition, or autonomous, when using additionally incorporated capsules containing a healing agent and/or bacteria spores. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria released into the crack from a broken capsule or activated through access of water and oxygen. The critical reviewing of both methods indicates that the autogenous self-healing is more efficient, more cost effective, safer, and easier to implement in full-scale applications. Nevertheless, a better understanding of the mechanism and factors affecting the effectiveness of the process is needed. The main weaknesses of the autonomous method were identified as loss of workability, worsened mechanical properties, low efficiency and low probability of the healing to occur, low survivability of the capsules and bacteria in harsh concrete environment, very high price, and lack of full-scale evaluation.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2019
National Category
Other Materials Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-75206 (URN)10.1061/(ASCE)MT.1943-5533.0002764 (DOI)000475694700023 ()2-s2.0-85067520596 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-07-03 (svasva)

Available from: 2019-07-03 Created: 2019-07-03 Last updated: 2019-10-28Bibliographically approved
Rajczakowska, M., Nilsson, L., Habermehl-Cwirzen, K., Hedlund, H. & Cwirzen, A. (2019). Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?. Materials, 12(20), Article ID 3298.
Open this publication in new window or tab >>Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?
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2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 20, article id 3298Article in journal (Refereed) Published
Abstract [en]

It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and having a low water-to-cement ratio reach the hydration degree of only 70–50%. Consequently, the presence of a large amount of unhydrated cement should result in excellent autogenous self-healing. The main aim of this study was to examine whether this commonly accepted hypothesis was correct. The study included tests performed on UHPC and mortars with a low water-to-cement ratio and high cement content. Additionally, aging effects were verified on 12-month-old UHPC samples. Analysis was conducted on the crack surfaces and inside of the cracks. The results strongly indicated that the formation of a dense microstructure and rapidly hydrating, freshly exposed anhydrous cement particles could significantly limit or even hinder the self-healing process. The availability of anhydrous cement appeared not to guarantee development of a highly effective healing process.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
continued hydration, ultra-high performance concrete, cracking, microstructure, calcite
National Category
Other Materials Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-76510 (URN)10.3390/ma12203298 (DOI)000498402100021 ()
Note

Validerad;2019;Nivå 2;2019-10-28 (johcin)

Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-12-18Bibliographically approved
Rajczakowska, M. (2019). Self-Healing Concrete. (Licentiate dissertation). Luleå tekniska universitet
Open this publication in new window or tab >>Self-Healing Concrete
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
Självläkande Betong
Abstract [en]

Concrete is a brittle material prone to cracking due to its low tensile strength. Crack repairs are not only expensive and time-consuming but also increase the carbon footprint. Designing a novel concrete material possessing the ability to self-repair cracks would enhance its sustainability. Self-healing can be defined as a material’s ability to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on an optimized mix composition, or autonomous, when additional capsules containing some healing agent and/or bacteria spores are incorporated into the binder matrix. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria precipitating calcite which are released into the crack from a broken capsule or activated by access to water and oxygen. The main disadvantages of the autonomous method are the loss of the fresh concrete workability, worsened mechanical properties, low efficiency, low survivability of the capsules and bacteria during mixing and the very high price. On the other hand, the autogenous self-healing was found to be more efficient, more cost effective, safer, and easier to implement in full-scale applications. Knowledge related to mechanisms and key factors controlling the autogenous self-healing is rather limited. Therefore, the aim of this research work was to better understand the autogenous self-healing process of concrete and to optimize the mix design and exposure conditions to maximize its efficiency. This licentiate thesis summarizes the main findings of the first 2.5 years of the PhD project. Several factors affecting autogenous self-healing were studied, including the amount of unhydrated cement, mix composition, age of material, self-healing duration and exposure conditions. The process was investigated both externally, at the surface, and deeper inside of the crack, by evaluating the crack closure and chemical composition of formed self-healing products. In addition, the flexural strength recovery was also studied. It was observed that a large amount of cement in the concrete mix does not ensure an efficient autogenous self-healing of cracks. A very dense and impermeable binder microstructure limited the transport of calcium and silicone ions to the crack and diminished the precipitation of the healing products. Addition fly ash increased the crack closure ratio close to the crack mouth, but its presence did not support the recovery of the flexural strength, presumably due to a very limited formation of load bearing phases inside the crack. Calcium carbonate was detected mainly at the crack mouth, whereas calcium silicate hydrate (C-S-H) and ettringite were found deeper inside the crack. The formation of C-S-H and ettringite presumably resulted in a regain of the flexural strength. On the other hand, calcite crystals formed close to the surface of the specimen controlled conditions inside the crack through its external closure. Healing exposure based on pure water appeared to be inefficient even despite the application of different temperature cycles and water volumes. The application of a phosphate-based retarding admixture in the curing water resulted in the highest self-healing efficiency. The admixture presumably inhibited the formation of a dense hydration shell on the surface of the unhydrated cement grains and promoted the precipitation of calcium phosphate compounds inside the crack. In addition, water mixed with microsilica particles caused a regain of the flexural strength through formation of C-S-H in the crack.

Place, publisher, year, edition, pages
Luleå tekniska universitet, 2019
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
cementitious materials, self-healing, exposure, fly ash, calcite, C-S-H, cracking
National Category
Engineering and Technology Other Materials Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-76527 (URN)978-91-7790-490-8 (ISBN)978-91-7790-491-5 (ISBN)
Presentation
2019-12-12, C305, University of Technology, Luleå, 08:00 (English)
Opponent
Supervisors
Funder
Svenska Byggbranschens Utvecklingsfond (SBUF)Swedish Transport Administration
Available from: 2019-10-28 Created: 2019-10-28 Last updated: 2019-11-27Bibliographically approved
Rajczakowska, M., Habermehl-Cwirzen, K., Hedlund, H. & Cwirzen, A. (2019). The effect of exposure on the autogenous self-healing of Ordinary Portland cement mortars. Materials, 12(23), Article ID 3926.
Open this publication in new window or tab >>The effect of exposure on the autogenous self-healing of Ordinary Portland cement mortars
2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 23, article id 3926Article in journal (Refereed) Published
Abstract [en]

Exposure conditions are critical for the autogenous self-healing process of Portland cement based binder matrixes. However, there is still a significant lack of fundamental knowledge related to this factor. The aim of this paper was to investigate and understand the effects of various potentially applicable curing solutions on the efficiency of the crack closure occurring both superficially and internally. Four groups of exposures were tested, including exposure with different water immersion regimes, variable temperatures, application of chemical admixtures, and use of solutions containing micro particles. The self-healing process was evaluated externally, at the surface of the crack, and internally, at different crack depths with the use of optical and scanning electron microscopes (SEM). The phase identification was done with an energy dispersive spectrometer combined with the SEM. The results showed very limited self-healing in all pure water-based exposures, despite the application of different cycles, temperatures, and water volumes. The addition of a phosphate-based retarding admixture demonstrated the highest crack closure, both internally and externally. The highest strength recovery and a very good crack closure ratio was achieved in water exposure containing micro silica particles. The main phase observed on the surface was calcium carbonate, and internally, calcium silicate hydrate, calcium carbonate, and calcium phosphate compounds. Phosphate ions were found to contribute to the filling of the crack, most likely by preventing the formation of a dense shell composed of hydration phases on the exposed areas by crack unhydrated cement grains as well as by the additional precipitation of calcium and phosphate-based compounds. The micro sized silica particles presumably served as nucleation sites for the self-healing products growth. Changes in the chemical composition of the self-healing material were observed with a distance from the surface of the specimen.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
autogenous self-healing, cementitious materials, cracking, exposure, microstructure, calcium phosphate
National Category
Infrastructure Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-76526 (URN)10.3390/ma12233926 (DOI)31783574 (PubMedID)2-s2.0-85075858886 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-12-09 (johcin)

Available from: 2019-10-28 Created: 2019-10-28 Last updated: 2019-12-16Bibliographically approved
Tole, I., Habermehl-Cwirzen, K., Rajczakowska, M. & Cwirzen, A. (2018). Activation of a Raw Clay by Mechanochemical Process: Effects of Various Parameters on the Process Efficiency and Cementitious Properties. Materials, 11(10), Article ID 1860.
Open this publication in new window or tab >>Activation of a Raw Clay by Mechanochemical Process: Effects of Various Parameters on the Process Efficiency and Cementitious Properties
2018 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 10, article id 1860Article in journal (Refereed) Published
Abstract [en]

The efficiency of the mechanochemical activation (MCA) is influenced by various process parameters as well as by the properties of the treated material. The main objective of this research was to optimize the MCA process, gaining enhancement of the chemical reactivity of a Swedish raw clay, which is going to be used as an alkali-activated cementitious binder. The effects of the amount of water, the filling ratio, the rotation speed, and the grinding duration on the amorphization degree were evaluated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Generally, wet and dry processes showed an extensive amorphization of both kaolinite and muscovite minerals present in the studied clay. On the contrary, quartz was amorphized mainly by the wet grinding process. The efficiency of both dry and wet grinding processes was enhanced by the increased number of grinding media versus the amount of the activated material. However, longer processing times caused significant agglomeration while a higher rotational speed enhanced the amorphization. Preliminary tests have shown that alkali activation of the processed clays produced hardened samples. Furthermore, the increased amorphization corresponded to the increased compressive strength values.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
clay minerals, dry grinding, fine grinding, mechanochemical activation, mechanochemistry, wet grinding
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-71035 (URN)10.3390/ma11101860 (DOI)30274273 (PubMedID)2-s2.0-85054276282 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-03 (marisr)

Available from: 2018-09-30 Created: 2018-09-30 Last updated: 2019-04-02Bibliographically approved
Sobótka, M., Pachnicz, M. & Rajczakowska, M. (2018). Induced Crack Network Evolution in Geomaterials: µct Examination and Mathematical Morphology Based Analysis. In: Proceedings of China-Europe Conference on Geotechnical Engineering: . Paper presented at China-Europe Conference on Geotechnical Engineering, Vienna, Austria, August 13-16 2018 (pp. 216-219). Cham: Springer, 1
Open this publication in new window or tab >>Induced Crack Network Evolution in Geomaterials: µct Examination and Mathematical Morphology Based Analysis
2018 (English)In: Proceedings of China-Europe Conference on Geotechnical Engineering, Cham: Springer, 2018, Vol. 1, p. 216-219Conference paper, Published paper (Refereed)
Abstract [en]

Fracture parameters of the rock material are known to change due to applied loading, having effect on, e.g. the rock permeability coefficient which can be estimated based on the geometrical descriptors of the crack space. In this paper, a method of crack network evolution analysis is proposed for the rock samples subjected to uniaxial compression. Fracture development is investigated using ex-situ time-lapse micro-computed tomography (µCT). The sets of images are acquired for each specimen at three damage levels: before loading, at approximately 50% of compressive strength and, finally, after reaching micro-dilatancy threshold (or compressive strength). The reconstructed and segmented 3D crack network is examined at each loading stage. The analysis consists of image processing and determination of the selected morphological parameters, i.e. volume fraction of the crack, spatial distribution of the fracture aperture, tortuosity as well as the structure model index (SMI).

Place, publisher, year, edition, pages
Cham: Springer, 2018
Series
Springer Series in Geomechanics and Geoengineering, ISSN 1866-8755
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-70310 (URN)10.1007/978-3-319-97112-4_49 (DOI)978-3-319-97111-7 (ISBN)978-3-319-97112-4 (ISBN)
Conference
China-Europe Conference on Geotechnical Engineering, Vienna, Austria, August 13-16 2018
Available from: 2018-08-09 Created: 2018-08-09 Last updated: 2018-08-09Bibliographically approved
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