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.
Highlights
In geothermal energy systems, the thermal conductivity of the grout used for backfilling the heat exchange boreholes and the pipes used in the loops for circulating the heat carrier fluid has been considered as an important issue for the improvement of the efficiency of the system
NH2 groups of aminopropyl triethoxysilane (APTES) remained available in the tails for the hybridization with graphene nanoplatelet (GNP), whereas hydrolyzable groups were linked to the -OH groups on the surface of silica particles
GNP produced from the recycled carbon black obtained by the pyrolysis of waste tire was selected as a carbon source for the hybridization step
Summary
The thermal conductivity of the grout used for backfilling the heat exchange boreholes and the pipes used in the loops for circulating the heat carrier fluid has been considered as an important issue for the improvement of the efficiency of the system. Carbon-based materials obtained from waste sources such as gamma-irradiated recycled plastic [18], carbon powder waste obtained from the cutting process of laminate carbon composite [19] and rice husk ash [20] can be good alternatives to GO produced by harsh acidic and toxic conditions [21,22,23] to be used as an additive in grout mixtures Another important issue is to reduce manufacturing costs by using carbon-by products or waste carbon materials. The main objective is to develop hybrid silica-GNP additives to enhance the thermal conductivity of the grout and increase the efficiency of the heat transmission and prevent the aggregation of treated hybrid additives in grout mixture and decrease the manufacturing costs by using waste sources. The developed hybrid additives were added into the grout mixture by changing additive and water ratios, and the flow behaviors and the thermal conductivity property of the prepared grout mixtures were investigated in detail to monitor the effect of carbon content on the performance of the grouts
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