• Energy Research

Yes Utilizing seawater and sea-sand for producing ultra-high performance concrete (UHPC) can substantially reduce raw materials costs and alleviate the current freshwater and river sand resources shortage in coastal and marine areas. However, the corrosion risk to reinforcing fibers inside UHPC caused by chlorides in seawater and sea-sand cannot be ignored. In this study, a new type of sustainable UHPC composed of seawater and desalinated sea-sand (UHPSSC) reinforced with stainless profile, super-fine stainless wire (SSW) was developed. Its mechanical properties and chloride content were studied. The research results show that SSWs do not rust after immersion in seawater. The flexural and compressive strengths of UHPSSC incorporating 1.5% SSWs are 13.8MPa and 138.6MPa, respectively, and the flexural toughness of UHPSSC is increased by 428.9%, reaching the basic mechanical requirements of UHPC. The high specific surface area of SSW and enrichment of silica fume on its surface enhance the interfacial bond between fiber and matrix, further promoting the full play of the SSWs’ reinforcing mechanisms as proved by the decrease of the Ca/Si ratio at the SSW surface. The C-S-H gels with a high Ca/Si ratio within the ITZ as well as Friedel’s salt are conducive to immobilize chlorides, blocking the migration of chlorides through the matrix and further mitigating the risk of long-term chloride corrosion of SSWs. Overall, utilizing seawater and desalinated sea-sand in combination with SSWs can produce UHPC with improved strength and toughness, making it a suitable choice for applications where high durability and long-term mechanical performance is required.

Yes Utilizing seawater and sea-sand for producing ultra-high performance concrete (UHPC) can substantially reduce raw materials costs and alleviate the current freshwater and river sand resources shortage in coastal and marine areas. However, the corrosion risk to reinforcing fibers inside UHPC caused by chlorides in seawater and sea-sand cannot be ignored. In this study, a new type of sustainable UHPC composed of seawater and desalinated sea-sand (UHPSSC) reinforced with stainless profile, super-fine stainless wire (SSW) was developed. Its mechanical properties and chloride content were studied. The research results show that SSWs do not rust after immersion in seawater. The flexural and compressive strengths of UHPSSC incorporating 1.5% SSWs are 13.8MPa and 138.6MPa, respectively, and the flexural toughness of UHPSSC is increased by 428.9%, reaching the basic mechanical requirements of UHPC. The high specific surface area of SSW and enrichment of silica fume on its surface enhance the interfacial bond between fiber and matrix, further promoting the full play of the SSWs’ reinforcing mechanisms as proved by the decrease of the Ca/Si ratio at the SSW surface. The C-S-H gels with a high Ca/Si ratio within the ITZ as well as Friedel’s salt are conducive to immobilize chlorides, blocking the migration of chlorides through the matrix and further mitigating the risk of long-term chloride corrosion of SSWs. Overall, utilizing seawater and desalinated sea-sand in combination with SSWs can produce UHPC with improved strength and toughness, making it a suitable choice for applications where high durability and long-term mechanical performance is required.

Abstract The research of electric thermal storage (ETS) has attracted a lot of attention recently, which converts off-peak electrical energy into thermal energy and release it later at peak hours. In this study, new electric thermal storage composites are developed by employing paraffin wax as thermal storage media and carbon nanofiber (CNF) as conductive fillers. Electric heating and thermal energy release performances of the CNF/paraffin wax composites are experimentally investigated. Experimental results show that, when the composites are heated to about 70 °C, the developed electrically conductive CNF/paraffin wax composites present a thermal storage capacity of about 280 kJ/kg, which is five times of that of traditional thermal storage medium such as ceramic bricks (54 kJ/kg). The CNF/paraffin wax composites can also effectively store the thermal energy and release the thermal energy in later hours.

Abstract The research of electric thermal storage (ETS) has attracted a lot of attention recently, which converts off-peak electrical energy into thermal energy and release it later at peak hours. In this study, new electric thermal storage composites are developed by employing paraffin wax as thermal storage media and carbon nanofiber (CNF) as conductive fillers. Electric heating and thermal energy release performances of the CNF/paraffin wax composites are experimentally investigated. Experimental results show that, when the composites are heated to about 70 °C, the developed electrically conductive CNF/paraffin wax composites present a thermal storage capacity of about 280 kJ/kg, which is five times of that of traditional thermal storage medium such as ceramic bricks (54 kJ/kg). The CNF/paraffin wax composites can also effectively store the thermal energy and release the thermal energy in later hours.

Phase change materials (PCM) have been incorporated with cementitious construction materials to store thermal energy and control interior climate in buildings, which can reduce the energy consumption and improve thermal comfort. However, addition of PCM is found to decrease strength and thermal conductivity of the cement-based composite. Carbon nanotubes (CNT) are integrated into cementitious construction materials with microencapsulated PCM to improve their thermal-conductive and mechanical performances. Results of lab and outdoor tests show the modified cement mortar containing both PCM and CNT exhibits better heat insulation properties than plain cement mortar. A temperature difference up to 6.8 °C was observed between interiors of two same size scale-down building models (one made of plain cement mortar, the other one made of cement mortar with PCM and CNT). This indicates that the modified cement mortar can effectively enhance the thermal storage property of cement-based building materials.

Phase change materials (PCM) have been incorporated with cementitious construction materials to store thermal energy and control interior climate in buildings, which can reduce the energy consumption and improve thermal comfort. However, addition of PCM is found to decrease strength and thermal conductivity of the cement-based composite. Carbon nanotubes (CNT) are integrated into cementitious construction materials with microencapsulated PCM to improve their thermal-conductive and mechanical performances. Results of lab and outdoor tests show the modified cement mortar containing both PCM and CNT exhibits better heat insulation properties than plain cement mortar. A temperature difference up to 6.8 °C was observed between interiors of two same size scale-down building models (one made of plain cement mortar, the other one made of cement mortar with PCM and CNT). This indicates that the modified cement mortar can effectively enhance the thermal storage property of cement-based building materials.