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

Ilayda Berktas, Ali Nejad Ghafar, Patrick Fontana, Ayten Caputcu, Yusuf Menceloglu and Burcu Saner Okan
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Ilayda Berktas: Sabanci University Integrated Manufacturing Technologies Research and Application Center & Composite Technologies Center of Excellence, Teknopark Istanbul, Pendik, Istanbul 34906, Turkey
Ali Nejad Ghafar: Department Infrastructure and Concrete Construction, RISE Research Institutes of Sweden, 11428 Stockholm, Sweden
Patrick Fontana: Department Infrastructure and Concrete Construction, RISE Research Institutes of Sweden, 11428 Stockholm, Sweden
Ayten Caputcu: Cimsa Cimento Sanayi A. S., Toroslar Mah. Tekke Cad., Yenitaskent, Mersin 33013, Turkey
Yusuf Menceloglu: Sabanci University Integrated Manufacturing Technologies Research and Application Center & Composite Technologies Center of Excellence, Teknopark Istanbul, Pendik, Istanbul 34906, Turkey
Burcu Saner Okan: Sabanci University Integrated Manufacturing Technologies Research and Application Center & Composite Technologies Center of Excellence, Teknopark Istanbul, Pendik, Istanbul 34906, Turkey

Energies, 2020, vol. 13, issue 14, 1-15

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.

Keywords: expanded graphite; silanization; hybridization; thermal conductivity; cementitious grout; cement-based composites; ground source heat exchangers (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2020
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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