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Article

Synergistic Effect of Expanded Graphite-Silane Functionalized Silica as a Hybrid Additive in Improving the Thermal Conductivity of Cementitious Grouts with Controllable Water Uptake

1
Sabanci University Integrated Manufacturing Technologies Research and Application Center & Composite Technologies Center of Excellence, Teknopark Istanbul, Pendik, Istanbul 34906, Turkey
2
Department Infrastructure and Concrete Construction, RISE Research Institutes of Sweden, 11428 Stockholm, Sweden
3
Cimsa Cimento Sanayi A. S., Toroslar Mah. Tekke Cad., Yenitaskent, Mersin 33013, Turkey
4
Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli, Tuzla, Istanbul 34956, Turkey
*
Author to whom correspondence should be addressed.
Energies 2020, 13(14), 3561; https://doi.org/10.3390/en13143561
Received: 13 May 2020 / Revised: 5 June 2020 / Accepted: 11 June 2020 / Published: 10 July 2020
(This article belongs to the Special Issue Shallow Geothermal Energy 2021)
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. View Full-Text
Keywords: expanded graphite; silanization; hybridization; thermal conductivity; cementitious grout; cement-based composites; ground source heat exchangers expanded graphite; silanization; hybridization; thermal conductivity; cementitious grout; cement-based composites; ground source heat exchangers
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MDPI and ACS Style

Berktas, I.; Nejad Ghafar, A.; Fontana, P.; Caputcu, A.; Menceloglu, Y.; Saner Okan, B. Synergistic Effect of Expanded Graphite-Silane Functionalized Silica as a Hybrid Additive in Improving the Thermal Conductivity of Cementitious Grouts with Controllable Water Uptake. Energies 2020, 13, 3561. https://doi.org/10.3390/en13143561

AMA Style

Berktas I, Nejad Ghafar A, Fontana P, Caputcu A, Menceloglu Y, Saner Okan B. Synergistic Effect of Expanded Graphite-Silane Functionalized Silica as a Hybrid Additive in Improving the Thermal Conductivity of Cementitious Grouts with Controllable Water Uptake. Energies. 2020; 13(14):3561. https://doi.org/10.3390/en13143561

Chicago/Turabian Style

Berktas, Ilayda; Nejad Ghafar, Ali; Fontana, Patrick; Caputcu, Ayten; Menceloglu, Yusuf; Saner Okan, Burcu. 2020. "Synergistic Effect of Expanded Graphite-Silane Functionalized Silica as a Hybrid Additive in Improving the Thermal Conductivity of Cementitious Grouts with Controllable Water Uptake" Energies 13, no. 14: 3561. https://doi.org/10.3390/en13143561

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