| 1. |
- Nejad Ghafar, Ali, 1971-, et al.
(författare)
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Uncertainties in Grout Penetrability Measurements; Evaluation and Comparison of Filter pump, Penetrability meter and Short slot
- 2017
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Ingår i: Geotechnical and Geological Engineering. - : Springer. - 0960-3182 .- 1573-1529.
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Tidskriftsartikel (refereegranskat)abstract
- To measure grout penetrability in fractured hard rock, various measuring instruments have been developed over the years. Penetrability meter and Filter pump have been designed to use in both the lab and the field. Short slot has been applicable mainly in the lab due to its complexity. The fact, that these instruments have been built based on different assumptions, limitations, and test conditions, makes their results occasionally in contradict. Deficiency in design of the instruments as well as the methods of evaluating grout penetrability is additionally a basis for uncertainty in results. This study is an experimental effort to determine and thoroughly perceive the nature of the most governing uncertainties in grout penetrability measurements. The test apparatus, procedure, and method used to evaluate the grout penetrability in both Penetrability meter and Filter pump were thus modified. The aim was to control the corresponding uncertainties and make their limitations and test conditions as similar as possible with the ones in Short slot. The results suggested that to obtain a more realistic evaluation of the grout penetrability, measurement should be accomplished at both the high and the low pressures with sufficient grout volume using Short slot. Moreover, application of both Filter pump and Penetrability meter is no longer recommended due to the revealed uncertainties.
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| 2. |
- Ahmed, Lamis, et al.
(författare)
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Crack propagation under water pressure
- 2018
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Rapport (refereegranskat)abstract
- Cracks in concrete structures such as a concrete dam can be exposed to water pressure, for example, uplift pressure. The water pressure can be significant and may result in cracks propagating through the structures and thus it may result in reduced service life. However, the knowledge of water pressure within the cracks is relatively limited and is often neglected or just roughly estimated. The influence of crack opening rate on the uplift pressure distribution in the crack and the pressure variation during opening or sudden crack closure are questions needed to investigate. As an attempt to answer those questions, a pilot study presented here describes the possibilities and limitations of the proposed experimental setup; and technology (penetrability meter and tomography) as an examination method for water pressure in propagation concrete cracks. The test specimens examined here are exclusively cylinders cast of concrete with or without an initial crack.The penetrability meter can be used to apply water pressure and to visualize the crack opening, X-Ray computed tomography test, was performed. KTH Civil and Architectural Engineering department has organized the laboratory resources.The examples reported in this work show that the technology and equipment have great potential for future work on crack propagation, however, sample design and preparation, as well as testing need further development.
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| 3. |
- Badenes, Borja, et al.
(författare)
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Development of advanced materials guided by numerical simulations to improve performance and cost-efficiency of borehole heat exchangers (BHEs)
- 2020
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Ingår i: Energy. - : Elsevier Ltd. - 0360-5442 .- 1873-6785. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- One promising way to improve the efficiency of borehole heat exchangers (BHEs) in shallow geothermal applications is to enhance the thermal properties of the materials involved in its construction. Early attempts, such as using metal tubes in the 1980s or the utilization of thin–foil hoses, did not succeed in being adopted by the market for diverse reasons (cost, corrosion, fragility, etc…). In parallel, the optimization of pipe size, the use of double-U-tubes, thermally enhanced grout, etc. were able to bring the measure for the BHE efficiency, the borehole thermal resistance, from 0.20 to 0.15 K/(Wm) down to 0.08–0.06 K/(Wm) in the best solutions today. A further improvement cannot be expected without development of new, dedicated materials, combining the versatility of plastic like PE with an increased thermal conductivity that matches the respective properties of the rock and soil. This goal was included in the Strategic Research and Innovation Agenda of the European Technology Platform on Renewable Heating and Cooling in 2013. Within an EU supported project, both BHE pipes and grouting materials have been produced prototypically in small amounts, suitable for the first tests in the intended environment. The present work explains the research pathways envisaged and the resulting sensitivity analysis to highlight the influence of some of the most critical parameters that affect the overall performance of a GSHP system. The results have allowed guiding the real development of more efficient new advanced materials for different scenarios representative of different European regions. Finally the developed materials and their properties are discussed, including a comparative assessment about their compliance with reference material properties as currently seen in the BHE market. © 2020 The Author(s)
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| 4. |
- Berktas, Ilayda, et al.
(författare)
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Facile synthesis of graphene from waste tire/silica hybrid additives and optimization study for the fabrication of thermally enhanced cement grouts
- 2020
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Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 25:4
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Tidskriftsartikel (refereegranskat)abstract
- This work evaluates the effects of newly designed graphene/silica hybrid additives on the properties of cementitious grout. In the hybrid structure, graphene nanoplatelet (GNP) obtained from waste tire was used to improve the thermal conductivity and reduce the cost and environmental impacts by using recyclable sources. Additionally, functionalized silica nanoparticles were utilized to enhance the dispersion and solubility of carbon material and thus the hydrolyzable groups of silane coupling agent were attached to the silica surface. Then, the hybridization of GNP and functionalized silica was conducted to make proper bridges and develop hybrid structures by tailoring carbon/silica ratios. Afterwards, special grout formulations were studied by incorporating these hybrid additives at different loadings. As the amount of hybrid additive incorporated into grout suspension increased from 3 to 5 wt%, water uptake increased from 660 to 725 g resulting in the reduction of thermal conductivity by 20.6%. On the other hand, as the concentration of GNP in hybrid structure increased, water demand was reduced, and thus the enhancement in thermal conductivity was improved by approximately 29% at the same loading ratios of hybrids in the prepared grout mixes. Therefore, these developed hybrid additives showed noticeable potential as a thermal enhancement material in cement-based grouts. © 2020 by the authors.
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| 5. |
- Berktas, Ilayda, et al.
(författare)
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Synergistic effect of expanded graphite-silane functionalized silica as a hybrid additive in improving the thermal conductivity of cementitious grouts with controllablewater uptake
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 13:14
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a growing demand for geothermal applications has led to the exploitation of energy efficiently by developing grouting materials in the borehole between pipes and the ground. Therefore, the current study developed newly formulated cementitious grouts by the integration of expanded graphite (EG)-based hybrid additives synthesized by building chemical bridges between silica particles and EG in the presence of amino functional silane coupling agents. These produced hybrid additives with controlled EG and silica ratios were utilized in grout mixtures used in borehole heat exchangers to enhance the thermal conductivity. According to the optimization study on the formulation development of grout mixtures with bentonite, silica sands, cement, and superplasticizer by adding neat EG and EG-based hybrids, the relationship between the carbon amount and water demand was found to have a significant impact on thermal conductivity. The highest thermal conductivity value of 2.656 W/mK was achieved by the incorporation of 5 wt% hybrid additive with the ratio silica/EG of 1:5 compared to the reference grout, which showed a thermal conductivity of 2.373 W/mK. Therefore, the enhancement in thermal conductivity was dependent on the increase in the EG content and also the additive loading ratio, resulting in a slight increase in the water demand.
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| 6. |
- Draganović, Almir, 1964-, et al.
(författare)
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Issues in Measurements and Evaluation of Penetrability of Cement-Based Grout Measured with Filter Pump and Penetrability Meter in the Field
- 2017
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Ingår i: Grouting 2017. - Reston, VA : American Society of Civil Engineers (ASCE). - 9780784480793 ; , s. 404-414
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Konferensbidrag (refereegranskat)abstract
- Grouting of underground constructions is important to decrease water inflow into constructions. It is therefore important to use grout with good penetration ability to achieve this goal. The purpose of this paper is to show issues connected to measuring of the penetration ability of cement-based grouts in the field with a filter pump and penetrability meter and show the need for improvement or use of some other method. Three main reasons which contribute to a different estimated critical aperture with these two methods are: different maximum test volume in regression analysis of measured data, limited maximum test volume in the filter pump, and different test pressure. Test volume should be related to volume of designed grout spread in the critical aperture and test pressure should be related to grout spread velocity in the field.
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| 7. |
- Ghafar, Ali Nejad, et al.
(författare)
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Ett nytt sätt att förbättra inträngnigs egenskaperna hos cementbaserat injekteringsbruk med momentant varierande tryck
- 2016
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Ingår i: Bygg och Teknik. - Stockholm : Förlags AB Bygg & teknik. - 0281-658X .- 2002-8350. ; :1, s. 17-22
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Ett mycket viktig moment i samband med undermarksbyggande är tätning av konstruktioner för att hindra vatteninflöde eller ett eventuellt läckage av lagrade material i konstruktionen. Sedan mitten på 1980-talet har man på Kungliga tekniska högskolan (KTH) forskat kring injekteringen av sprickor i berg med varierande tryck för att förbättra inträngningsförmågan av cementbaserade bruk. I tidigare studier har man huvudsakligen undersökt effekten av högfrekventa oscillerande tryck på brukets inträngningsförmåga men den uppnådda förbättringen har visat sig vara relativt begränsad. I ett doktorandprojekt på KTH har vi genomfört en experimentell studie för att undersöka påverkan av istället ett lågfrekvent tryck med en momentan tryckförändering på brukets inträngningsförmåga. Resultaten har visat på en betydande förbättring av inträngningsförmågan hos bruket jämfört med injektering med konstant tryck. Projektet har finansierats av Stiftelsen Bergteknisk Forskning (BeFo), Svenska Byggbranschens Utvecklingsfond (SBUF) och Trafikverket.
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| 8. |
- Hesami, Ebrahim, 1982-, et al.
(författare)
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Multi-Scale Characterization of Asphalt Mastic Rheology
- 2013
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Ingår i: Multi-Scale Modeling and Charactrization of Infrastructure Materials. - Dordrecht : Springer. - 9789400768772 - 9789400768789 ; , s. 45-61
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Konferensbidrag (refereegranskat)abstract
- Understanding the influence of the fundamental parameters on asphalt mastic rheology is an important step towards improving the quality of asphalt mixtures. Due to the size of fillers and the sensitivity of the rheological behaviour of mastic, it is not always possible to study the effect of all parameters at one scale. Hence in this study, a theoretical framework is established for calculating the relative viscosity of asphalt mastics as a function of its filler concentration. Furthermore, a new test protocol is introduced for measuring the viscosity of asphalt mastic at higher temperatures and different filler concentrations. To characterize the fillers and their agglomeration and distribution inside solid mastics, X-ray tomography, laser scattering, scanning electron microscopy, BET and Helium Pycnometery were utilized. To characterize the energy dissipation potential of the mastics under cyclic loads, as a function of their fillers, the dynamic mechanical analyzer was utilized. The research shown in this paper further investigated the various dominant parameters related to fillers and bitumen in mastics and relate them to the workability and resulting mechanical properties and developed an overall framework to connect different scales. The developed characterization protocols have the potential to allow the asphalt engineers to design their hot and warm asphalt mixtures on a more fundamental and thus sustainable basis.
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| 9. |
- Javadi, Hossein, et al.
(författare)
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Laboratory and numerical study on innovative grouting materials applicable to borehole heat exchangers (BHE) and borehole thermal energy storage (BTES) systems
- 2022
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 194, s. 788-804
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a laboratory-scale prototype of a borehole field has been designed and built to assess various innovative grouting products in a fully controlled environment. Three novel grout formulations are developed and evaluated: enhanced grout, a mixture of enhanced grout and microencapsulated phase change material, and a mixture of enhanced grout and shape stabilized phase change material. The objective is to evaluate the enhancement in their thermal properties (i.e., thermal conductivity and thermal energy storage capacity) compared to those using a commercial reference grout. Besides, three-dimensional numerical modeling is performed to provide a better understanding of the heat transfer and phase transition inside and outside the grout columns and to study the capability of the developed grouts to be used in a borehole heat exchanger or as borehole thermal energy storage system. To the best of the authors' knowledge, there have been just a few numerical studies on using phase change materials inside borehole heat exchangers to assess thermal energy storage applications. The experimental and numerical results showed much higher efficiency of the grout developed with a high thermal conductivity than the reference grout in terms of heat transfer in both the grout column and the surrounding sand. Furthermore, the results indicated the noticeable influence of the microencapsulated phase change material's presence in the grout formulation in terms of heat absorption/storage during the phase transition (from solid to liquid). However, it is concluded that reengineering shape stabilized phase change material should be conducted to make it more appropriate for thermal energy storage applications.
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| 10. |
- Nejad Ghafar, Ali, et al.
(författare)
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A laboratory study on grouting in vibratory host rock
- 2019
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Ingår i: ISRM 9th Nordic Grouting Symposium, NGS 2019. - : International Society for Rock Mechanics and Rock Engineering. - 9789517586481 ; , s. 131-138
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Konferensbidrag (refereegranskat)abstract
- To sufficiently seal an underground facility in fractured rock, it is necessary to obtain adequate grout spread into the surrounding fractures. The grout spread itself depends on parameters, the most significant of which are the grout filtration tendency and rheological properties. These properties can be affected by the applied pressure. Use of high-frequency oscillating pressure is a method that has been shown to improve grout spread by virtue of reducing the grout apparent viscosity. However, this method has not yet been industrialized due to limited efficiency and rapid attenuation of the oscillation along a fracture. To address these issues, we present a pilot investigation to show the potential of high-frequency oscillation applied to the host rock to improve grout spread in fractures. The proposed method is examined using an artificial fracture, the so-called Varying Aperture Long Slot (VALS) that has been recently developed. The results are compared between the two cases with and without vibration. The study shows the potential of the method on improving the grout spread in rock fractures.
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