The stable protection of the walls of high-temperature geothermal wells is a challenging issue for sustainably exploiting geothermal resources.However,the cement stone filling layer of the cemented portion of the well...The stable protection of the walls of high-temperature geothermal wells is a challenging issue for sustainably exploiting geothermal resources.However,the cement stone filling layer of the cemented portion of the well deteriorates gradually during geothermal mining due to the dry-wet cycles of the saline geothermal water,reducing the service life of the geothermal well.For this,this paper presented five groups of cement stone cylinders with salt contents of 0%,1%,6%,and 11%,which were subjected to heating to 300C and 1e5 dry-wet cycles.Nuclear magnetic resonance(NMR)and nonmetallic detection were used to test and analyze the porosity and wave velocity.Additionally,the damage evolution induced by dry-wet cycles was captured based on acoustic emission(AE)data.The experimental results indicated that the heating process primarily resulted in mineral and salt crystal expansion,which in turn caused damage.The damage threshold due to the salt content was found to be 6%.The sudden increase in the thermal stress caused by cooling and deterioration of the tensile strength of the cement column were the key factors in the damage during the cooling process.As the number of cycles increased,the accumulated AE energy moved forward and backward,with decreasing and increasing temperature,respectively.The threshold of signal mutation in the heating process is 200C,and the accumulated AE energy decreases by 11.7%.When the salt content was 0%,1%,6%and 11%,the wave velocity decreased by 19%,27.3%,35.5%and 35.9%,respectively.This study also proposed a damage model,which could provide theoretical support for long-term health monitoring and safety protection of geothermal wells.展开更多
Extensive growth in the developing countries due to infrastructure development is resulting into massive consumption of concrete thereby increasing the demand on concrete materials. Quite large amounts of fine aggrega...Extensive growth in the developing countries due to infrastructure development is resulting into massive consumption of concrete thereby increasing the demand on concrete materials. Quite large amounts of fine aggregates are required for concrete in developing countries thus shortages of quality river sand is putting pressure on availability of fine aggregates. To fulfill the high demand of fine aggregates, a search for alternative materials is in process. Stone crushing and processing industry is a large industry which generates large amounts of stone dust and slurry which is a waste produced from this process. Tons of such waste generated has no useful purpose except as landfill material. Some preliminary studies have been conducted into use of marble/ limestone waste for use in concrete [1] [2].?This study aims at using stone dust as partial replacement of sand in concrete to observe its effects on workability and other mechanical properties. This would result in useful consumption of this waste product thereby eliminating environmental issues related to its disposal. Partial replacement of 10% and 20% sand replacement with stone dust is carried out with the use of self-compacting concrete with blended cement. Blended cement used contains 50% rice husk ash and 50% Portland cement. Such high strength SCC with blended cement containing 50% rice husk ash and 50% Portland cement has already been tested to provide better quality concrete [3]. Wide ranging investigations covering most aspects of mechanical behavior and permeability were carried out for various mixes for compressive strengths of 60?MPa & 80?MPa. Compressive strengths of high strength SCC with blended cements and 10% and 20% replacement of sand with stone dust for 60?MPa and 80?MPa were observed to be higher by about 10% to 13% than the control specimen. Higher elastic moduli and reduced permeability were observed along with better sulphate and acid resistance. Better strengths and improved durability of such high strength SCC make it a more acceptable material for major construction projects thereby reducing the burden on environment and use of such waste product for a useful purpose promoting sustainable construction.展开更多
In this paper, the effect and mechanism of calcareous stone powder with size less than 0.074 mm are investigated in stone chippings concrete. The results show that the stone powder can participate in hydration reactio...In this paper, the effect and mechanism of calcareous stone powder with size less than 0.074 mm are investigated in stone chippings concrete. The results show that the stone powder can participate in hydration reaction and acts as crystal nucleus in hydration process, namely, it has hydration activity to an extent. The strength of stone chippings concrete is enhanced and the easy-mixing capacity of the concrete mortar is modified when stone chippings contain a proper amount of stone powder. The stone powder has little effect on the wearability of the concrete.展开更多
基金support from the National Natural Science Fundation of China(Grant Nos.52304097 and 42202308)the National Science Fund for Distinguished Young Scholars(Grant No.52225403).
文摘The stable protection of the walls of high-temperature geothermal wells is a challenging issue for sustainably exploiting geothermal resources.However,the cement stone filling layer of the cemented portion of the well deteriorates gradually during geothermal mining due to the dry-wet cycles of the saline geothermal water,reducing the service life of the geothermal well.For this,this paper presented five groups of cement stone cylinders with salt contents of 0%,1%,6%,and 11%,which were subjected to heating to 300C and 1e5 dry-wet cycles.Nuclear magnetic resonance(NMR)and nonmetallic detection were used to test and analyze the porosity and wave velocity.Additionally,the damage evolution induced by dry-wet cycles was captured based on acoustic emission(AE)data.The experimental results indicated that the heating process primarily resulted in mineral and salt crystal expansion,which in turn caused damage.The damage threshold due to the salt content was found to be 6%.The sudden increase in the thermal stress caused by cooling and deterioration of the tensile strength of the cement column were the key factors in the damage during the cooling process.As the number of cycles increased,the accumulated AE energy moved forward and backward,with decreasing and increasing temperature,respectively.The threshold of signal mutation in the heating process is 200C,and the accumulated AE energy decreases by 11.7%.When the salt content was 0%,1%,6%and 11%,the wave velocity decreased by 19%,27.3%,35.5%and 35.9%,respectively.This study also proposed a damage model,which could provide theoretical support for long-term health monitoring and safety protection of geothermal wells.
文摘Extensive growth in the developing countries due to infrastructure development is resulting into massive consumption of concrete thereby increasing the demand on concrete materials. Quite large amounts of fine aggregates are required for concrete in developing countries thus shortages of quality river sand is putting pressure on availability of fine aggregates. To fulfill the high demand of fine aggregates, a search for alternative materials is in process. Stone crushing and processing industry is a large industry which generates large amounts of stone dust and slurry which is a waste produced from this process. Tons of such waste generated has no useful purpose except as landfill material. Some preliminary studies have been conducted into use of marble/ limestone waste for use in concrete [1] [2].?This study aims at using stone dust as partial replacement of sand in concrete to observe its effects on workability and other mechanical properties. This would result in useful consumption of this waste product thereby eliminating environmental issues related to its disposal. Partial replacement of 10% and 20% sand replacement with stone dust is carried out with the use of self-compacting concrete with blended cement. Blended cement used contains 50% rice husk ash and 50% Portland cement. Such high strength SCC with blended cement containing 50% rice husk ash and 50% Portland cement has already been tested to provide better quality concrete [3]. Wide ranging investigations covering most aspects of mechanical behavior and permeability were carried out for various mixes for compressive strengths of 60?MPa & 80?MPa. Compressive strengths of high strength SCC with blended cements and 10% and 20% replacement of sand with stone dust for 60?MPa and 80?MPa were observed to be higher by about 10% to 13% than the control specimen. Higher elastic moduli and reduced permeability were observed along with better sulphate and acid resistance. Better strengths and improved durability of such high strength SCC make it a more acceptable material for major construction projects thereby reducing the burden on environment and use of such waste product for a useful purpose promoting sustainable construction.
文摘In this paper, the effect and mechanism of calcareous stone powder with size less than 0.074 mm are investigated in stone chippings concrete. The results show that the stone powder can participate in hydration reaction and acts as crystal nucleus in hydration process, namely, it has hydration activity to an extent. The strength of stone chippings concrete is enhanced and the easy-mixing capacity of the concrete mortar is modified when stone chippings contain a proper amount of stone powder. The stone powder has little effect on the wearability of the concrete.
