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  • 1
    In: Materials, MDPI AG, Vol. 16, No. 18 ( 2023-09-08), p. 6128-
    Abstract: This study investigates the cyclic load application impact on fly-ash-based geopolymer composites that are reinforced with a low amount of fibre reinforcement. For reinforcement purposes, polyvinyl alcohol and steel fibres are used. For testing purposes, four geopolymer composite mixes were made, three of which had fibre reinforcement. Simultaneously, specimens were tested for shrinkage, static-load-induced creep, and cyclic-load-induced creep. For static and cyclic creep testing, specimens were loaded with 20% of their strength. For cyclic creep testing, load application and release cycles were seven days long. When each cycle was introduced, the load was applied in steps. Necessary load application or unloading lasted for 5 min and consisted of four steps, each 25% of the necessary load. From the long-term static and cyclic creep tests, it was seen that only the plain specimens showed that static creep strains are within cyclic creep strains. For all the other specimens, the static load was higher than the cyclic-load-induced creep amplitude. Also, 1% polyvinyl alcohol fibre-reinforced specimens showed the most elastic characteristics under cyclic load, and 1% steel fibre-reinforced specimens appeared to be the most resistant to the cyclic load introduction.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2487261-1
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  • 2
    In: Materials, MDPI AG, Vol. 15, No. 17 ( 2022-09-03), p. 6132-
    Abstract: Three-dimensional concrete printing (3DCP) is an innovative technology that can lead to breakthrough modifications of production processes in the construction industry. The paper presents for the first time the possibility of 3D printing concrete–geopolymer hybrids reinforced with aramid roving. Reference concrete samples and concrete–geopolymer hybrids composed of 95% concrete and 5% geopolymer based on fly ash or metakaolin were produced. The properties of the samples without reinforcement and samples with 0.5% (wt.) aramid roving were compared. The frost resistance tests, UV radiation resistance, and thermal conductivity were evaluated for samples that were 3D-printed or produced by the conventional casting method. Compressive strength tests were carried out for each sample exposed to freeze–thaw cycles and UV radiation. It was observed that after the frost resistance test, the samples produced by the 3D printing technology had a minor decrease in strength properties compared to the samples made by casting. Moreover, the thermal conductivity coefficient was higher for concrete–geopolymer hybrids than concrete reinforced with aramid roving.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2487261-1
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  • 3
    Online Resource
    Online Resource
    IOP Publishing ; 2023
    In:  Journal of Physics: Conference Series Vol. 2423, No. 1 ( 2023-01-01), p. 012030-
    In: Journal of Physics: Conference Series, IOP Publishing, Vol. 2423, No. 1 ( 2023-01-01), p. 012030-
    Abstract: For the last 40 years, there has been increased interest in geopolymer composite development and its mechanical properties. In the last decades, there have been cases when geopolymer composites have been used for civil engineering purposes, such as buildings and infrastructure projects. The main benefit of geopolymer binder usage is that it has a smaller impact on the environment than the Portland cement binder. Emissions caused by geopolymer manufacturing are at least two times less than emissions caused by Portland cement manufacturing. As geopolymer polymerization requires elevated temperature, it also has a significant moisture evaporation effect that further increases shrinkage. It can lead to increased cracking and reduced service life of the structures. Due to this concern, for long-term strain reduction, such as plastic and drying shrinkage and creep, fibre reinforcement is added to constrain the development of stresses in the material. This research aims to determine how different fibre reinforcements would impact geopolymer composites creep and shrinkage strains. Specimens for long-term property testing purposes were prepared with 1% of steel fibres, 1% polypropylene fibres (PP), 0.5% steel and 0.5% polyvinyl alcohol fibres, 5% PP fibres, and without fibres (plain geopolymer). The lowest creep strains are 5% PP fibre specimens, followed by 1% PP fibre, plain, 0.5% steel fibre and 0.5% PVA fibre, and 1% steel fibre specimens. The lowest specific creep is to 5% PP fibre reinforced specimens closely followed by 1% PP fibre followed by 0.5% steel and 0.5% PVA fibre, plain and 1% steel fibre reinforced composites. Specimens with 0.5% steel and 0.5 PVA fibre showed the highest compressive strength, followed by 1% PP fibre specimens, plain specimens, 1% steel fibre, and 5% PP fibre reinforced specimens. Only specimens with 1% PP fibre and 0.5% steel, and a 0.5% PVA fibre inclusion showed improved mechanical properties. Geopolymer concrete mix with 1% PP fibre inclusion and 0.5% steel and 0.5% PVA fibre inclusion have a 4.7% and 11.3% higher compressive strength. All the other fibre inclusion into mixes showed significant decreases in mechanical properties.
    Type of Medium: Online Resource
    ISSN: 1742-6588 , 1742-6596
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 2166409-2
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  • 4
    In: Applied Sciences, MDPI AG, Vol. 11, No. 18 ( 2021-09-08), p. 8334-
    Abstract: Creep and shrinkage of Cement and Concrete Composites (CCC) are significant properties that need to be considered to use these materials in practice. Many previous scientific studies revealed CCC creep characteristics under sustained compression and shrinkage, using traditional test methods from design standards. Because of the complexity of experimental procedures, CCC creep in tension has not been studied as close. Furthermore, there is no unified standard that proposes applicable testing methods or specific testing apparatus. This study examines the suitability of 2D—Digital Image Correlation (DIC) to observe the creep deformations of specimens under tension. Ordinary Portland cement (OPC) mortar with 1% polyvinyl alcohol (PVA) fibres has been investigated in the research. Compact tension (CT) specimens 150 × 150 × 12 mm (with a notch) were used. Creep deformations under sustained uniaxial tension (applied loading corresponding to 60% of the ultimate strength) were measured. DIC images were captured using an entry/mid-level DSLR camera. Results show that DIC is suitable for studying uniaxial tensile creep of cement and concrete composites. Deformation of specimens in tension was similar to that measured using the conventional method (using surface-attached gauges).
    Type of Medium: Online Resource
    ISSN: 2076-3417
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2704225-X
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  • 5
    Online Resource
    Online Resource
    Trans Tech Publications, Ltd. ; 2013
    In:  Advanced Materials Research Vol. 705 ( 2013-6), p. 75-80
    In: Advanced Materials Research, Trans Tech Publications, Ltd., Vol. 705 ( 2013-6), p. 75-80
    Abstract: This research deals with experimentally studied time-dependent deformations of polyvinyl alcohol (PVA) fiber reinforced high performance concrete (HPFRC). The creep in compression and crack propagation of the new concrete compositions were determined. Several kind of concrete mixes adding microsilica and nanosilica have been made. For each composition cylinders with dimensions 190x47mm and Compact Tension (CT) specimens with dimensions 150x150x12mm were prepared. Concrete specimens were tested in a controlled constant temperature and with a constant level of moisture. Creep specimens were put into a creep lever test stand and subjected to a uniform, constant compressive load but CT specimens were subjected to a tension load. Deformations and crack mouth opening displacements were measured with extensometers. The compression strength and modulus of elasticity also were determined. The results have shown that nanosilica dont have significant influence on the high performance fiber reinforced concrete time-dependent behavior.
    Type of Medium: Online Resource
    ISSN: 1662-8985
    URL: Issue
    Language: Unknown
    Publisher: Trans Tech Publications, Ltd.
    Publication Date: 2013
    detail.hit.zdb_id: 2265002-7
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  • 6
    Online Resource
    Online Resource
    Rezekne Academy of Technologies ; 2015
    In:  Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference Vol. 1 ( 2015-06-16), p. 205-
    In: Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference, Rezekne Academy of Technologies, Vol. 1 ( 2015-06-16), p. 205-
    Abstract: 〈 p class="R-AbstractKeywords" 〉 〈 span lang="EN-US" 〉 The cracking properties in cement-based composites widely influences mechanical behavior of construction structures. The challenge of present investigation is to evaluate the crack propagation near the crack tip. During experiments the tension strength and crack mouth opening displacement of several types of concrete compositions was determined. For each composition the Compact Tension (CT) specimens were prepared with dimensions 150x150x12mm. Specimens were subjected to a tensile load. Deformations and crack mouth opening displacement were measured with extensometers. Cracks initiation and propagation were analyzed using a digital image analysis technique. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The obtained experimental curve shows the stages of crack development. 〈 /span 〉 〈 /p 〉
    Type of Medium: Online Resource
    ISSN: 1691-5402 , 1691-5402
    Language: Unknown
    Publisher: Rezekne Academy of Technologies
    Publication Date: 2015
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  • 7
    Online Resource
    Online Resource
    Rezekne Academy of Technologies ; 2015
    In:  Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference Vol. 2 ( 2015-08-05), p. 125-
    In: Environment. Technology. Resources. Proceedings of the International Scientific and Practical Conference, Rezekne Academy of Technologies, Vol. 2 ( 2015-08-05), p. 125-
    Abstract: Every year there are several hundred tons of waste glass produced in Latvia. Glass can be re-used as a fine raw material and it presents a possibility to save natural, non-renewable materials. The use of glass powder in concrete production can make the construction industry more environmentally friendly. This paper examines the possibility of using glass powder as cement replacement in a new type of concrete. In the experiment, cement was partially (20% and 40%) replaced with glass powder. The long-term deformation (creep) of this new concrete was monitored. Three different concrete mixtures were batched. Specimens of 20% and 40% cement replacement were compared with the specimens made of standard concrete. The samples were tested in two extreme conditions: in one case they were kept in 100% humidity ensured by preventing the desiccation of the concrete, and in the other case samples were air-dried by preventing them from becoming wet. Compression strength and modulus of elasticity of 7 and 28 days old cubic samples was determined.
    Type of Medium: Online Resource
    ISSN: 2256-070X , 1691-5402
    Language: Unknown
    Publisher: Rezekne Academy of Technologies
    Publication Date: 2015
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  • 8
    Online Resource
    Online Resource
    Rezekne Academy of Technologies ; 2021
    In:  ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference Vol. 3 ( 2021-06-16), p. 72-77
    In: ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference, Rezekne Academy of Technologies, Vol. 3 ( 2021-06-16), p. 72-77
    Abstract: For more than 40 years, low calcium alkali-activated cement composite, or in other words, geopolymer, has been around. In recent years there has been increased interest in this material and its properties. It is mainly due to the claim that geopolymer is the cement of the future. This claim is based on environmental factors. For instance, the CO2 emissions for geopolymer binder can be up to 6 less than for Portland cement binder. Most of the researches regarding geopolymer composite properties examine only mechanical and long-term properties in compression. There has been a lack of long-term tests in tension due to difficulties in performing them. As the tensile stresses are an essential part of structure assessment, it is necessary to evaluate new material properties as thoroughly as possible. Due to the nature of geopolymer specimen hardening (polymerisation), there is a difference in modulus of elasticity development and shrinkage caused by binding that could have factors that regular Portland cement specimens do not.This article aims to evaluate the surface composition of plain and 1% PVA reinforced geopolymer compact tension specimens that have been subjected to creep and shrinkage tests. Specimen cross-section images were acquired using the scanning electron microscope (SEM). Using the quantitative image analysis method, amounts of cross-section composition elements are determined. Furthermore, the amount of cracks is determined and compared between plain and PVA fiber-reinforced specimens.It has been determined that even though 1% of PVA fibre-reinforced specimens have lower tensile strength, their creep and shrinkage strains are lower, and the number of microcracks at the notch base of the specimen. Still, it has to be acknowledged that the amount of air voids in all analysed specimens is relatively high.  
    Type of Medium: Online Resource
    ISSN: 2256-070X , 1691-5402
    Language: Unknown
    Publisher: Rezekne Academy of Technologies
    Publication Date: 2021
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  • 9
    In: Crystals, MDPI AG, Vol. 11, No. 7 ( 2021-06-29), p. 760-
    Abstract: Geopolymer composites have been around only for 40 years. Nowadays, they are used in buildings and infrastructures of various kinds. A geopolymer’s main benefit is that it is a green material that is partially made by utilizing waste products. The carbon footprint from geopolymer matrix manufacturing is at least two times less than Portland cement manufacturing. Due to the nature of the geopolymer manufacturing process, there is a high risk of shrinkage that could develop unwanted micro-cracks that could reduce strength and create higher creep strains. Because of this concern, a common strategy to reduce long-term strains of the material, such as shrinkage and creep, is to add fiber reinforcement that would constrain crack development in the material. This article aims to determine how various kinds and amounts of different fiber reinforcement affect fly ash-based geopolymer composites’ creep strains in compression. Specimen mixes were produced with 1% steel fibers, 1% polypropylene fibers, 5% polypropylene fibers, and without fibers (plain geopolymer). For creep and shrinkage testing, cylindrical specimens Ø46 × 190 mm were used. The highest creep resistance was observed in 5% polypropylene fiber specimens, followed by 1% polypropylene fiber, plain, and 1% steel fiber specimens. The highest compressive strength was observed in 1% polypropylene fiber specimens, followed by plain specimens, 1% steel fiber specimens, and 5% polypropylene fiber-reinforced specimens. The only fiber-reinforced geopolymer mix with improved long-term properties was observed with 1% polypropylene fiber inclusion, whereas other fiber-introduced mixes showed significant decreases in long-term properties. The geopolymer composite mix with 1% polypropylene fiber reinforcement showed a reduction in creep strains of 31% compared to the plain geopolymer composite.
    Type of Medium: Online Resource
    ISSN: 2073-4352
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2661516-2
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  • 10
    Online Resource
    Online Resource
    Elsevier BV ; 2013
    In:  Procedia Engineering Vol. 57 ( 2013), p. 294-301
    In: Procedia Engineering, Elsevier BV, Vol. 57 ( 2013), p. 294-301
    Type of Medium: Online Resource
    ISSN: 1877-7058
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2013
    detail.hit.zdb_id: 2509658-8
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