Abstract
A promising technology for renewable energy is energy piles used to heat and cool buildings. In this research, the effects of bio-cementation via microbially induced calcite precipitation (MICP) using mixed calcium and magnesium sources and the addition of fibres on the thermal conductivity of soil were investigated. Firstly, silica sand specimens were treated with cementation solutions containing different ratios of calcium chloride and magnesium chloride to achieve maximum thermal conductivity improvement. Three treatment cycles were provided, and the corresponding thermal conductivity was measured after each cycle. It was found that using 100% calcium chloride resulted in the highest thermal conductivity. This cementation solution was then used to treat bio-cemented soil samples containing fibres, including polyethylene, steel and glass fibres. The fibre contents used included 0.5%, 1.0% and 1.5% of the dry sand mass. The results show that the glass fibre samples yielded the highest thermal conductivity after three treatment cycles, and SEM imaging was used to support the findings. This research suggests that using MICP as a soil improvement technique can also improve the thermal conductivity of soil surrounding energy piles, which has high potential to effectively improve the efficiency of energy piles.
Highlights
Most energy production on a global scale comes from fossil fuels
The pores between the soil particles for each sample were filled with water to improve the thermal conductivity since water has a higher thermal conductivity value, k, of 0.595 W/mK compared to the k value of air (0.026 W/mK)
It was determined that using 100% calcium chloride resulted in the highest thermal conductivity of mined that using 100% calcium chloride resulted in the highest thermal conductivity of
Summary
Most energy production on a global scale comes from fossil fuels. This reliance on fossil fuels has led to some drastic environmental repercussions on a global scale through the effects of climate change. From the melting of polar ice caps, rising sea levels and bleaching of formerly vibrant coral reefs, to the diminished productivity of agriculture and the destabilisation of local ecosystems, the consequences of climate change are indisputable [1]. There is an ever-increasing need to prioritise energy production through renewable technology. One source of renewable energy is the earth-stored thermal energy, known as geothermal energy. One of the most common, direct uses of geothermal energy is energy piles, which can regulate the temperature within buildings by transferring thermal energy through a medium [2]. The main path of heat transfer occurs where the soil particles are in contact; larger contact surfaces play a significant role in improving the soil thermal conductivity
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