The resistivity of cement specimens mixed with carbon fibres under different pressures is studied. The results reveal that when pressure becomes larger and larger, the resistivity of speciments changes. The process ca...The resistivity of cement specimens mixed with carbon fibres under different pressures is studied. The results reveal that when pressure becomes larger and larger, the resistivity of speciments changes. The process can be di-vided into three stages; reversible sensing period, balance pe-riod, and sharp increasing period. These three periods re-spectively show the closure and opening of raw flaw in speci-mens , germination of fresh cracks and cracks extending to failure. The conducting mechanism is also analyzed. Ac-cording to the above characteristic of carbon fibre-cement specimen, it can be used as an intrinsic smart material to be ap-plied in the non-destructive detection of concrete dams,ect.展开更多
Quality of cement is evaluated via group of tests. The most important, and close to understanding, is the compressive strength test. Recently, Egyptian standards adopted the European standards EN-196 and EN-197 for sp...Quality of cement is evaluated via group of tests. The most important, and close to understanding, is the compressive strength test. Recently, Egyptian standards adopted the European standards EN-196 and EN-197 for specifying and evaluating quality of cements. This was motivated by the large European investments in the local production of cement. The current study represents a comparative investigation, experimental and numerical, of the effect of different parameters on evaluation of compressive strength. Main parameters are shape of specimens and type of sand used for producing tested mortars. Three sets of specimens were made for ten types of cements. First set were 70.6 mm cubes molded according to old standards using single sized sand. Second group were prisms molded from standard sand (CEN sand) according to the recent standards. Third group were prisms molded from local sand sieved and regenerated to simulate same grading of CEN sand. All specimens were cured according to relevant standards and tested at different ages (2,3,7,10 and 28 days). Results show that CEM-I Type of cement does not fulfill, in all of its grades, the strength requirements of Ordinary Portland cement OPC specified in old standards. Also, the use of simulated CEN sand from local source gives strengths lower than those obtained using standard certified CEN sand. A limited number of tests were made on concrete specimens from two most common CEM-I types to investigate effect on concrete strength and results were also reported. Numerical investigation of the effect of specimen shape and type of sand on evaluation of compressive strength of mortar specimens, presented in the current study, applies one of the artificial intelligence techniques to simulate and predict the strength behavior at different ages. The Artificial Neural Network (ANN) technique is introduced in the current study to simulate the strength behavior using the available experimental data and predict the strength value at any age in the range of the experiments or in the future. The results of the numerical study showed that the ANN method with less effort was very efficiently capable of simulating the effect of specimen shape and type of sand on the strength behavior of tested mortar with different cement types.展开更多
As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcrac...As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcracks and defects. In order to reduce the damage to cement ring and improve sealed cementing property at the interface, it is necessary to conduct research on the modification of the cement rock available. According to the principle of super mixed composite materials, various fillers are added to the ingredients of cement rock. Dynamic fracture toughness of cement rock will be changed under the influence of filler. In this paper, short rod specimens of cement rock are employed in the experiments to investigate the dynamic fracture toughness of cement rocks with different ingredients using split Hopkinson Pressure Bar, and partial experimental results are given. The results indicate that fiber reinforcement is an effective way to improve the impact resistance of cement rock.展开更多
基金Funded by National Natural Science Fundation of China key project No 59432061
文摘The resistivity of cement specimens mixed with carbon fibres under different pressures is studied. The results reveal that when pressure becomes larger and larger, the resistivity of speciments changes. The process can be di-vided into three stages; reversible sensing period, balance pe-riod, and sharp increasing period. These three periods re-spectively show the closure and opening of raw flaw in speci-mens , germination of fresh cracks and cracks extending to failure. The conducting mechanism is also analyzed. Ac-cording to the above characteristic of carbon fibre-cement specimen, it can be used as an intrinsic smart material to be ap-plied in the non-destructive detection of concrete dams,ect.
文摘Quality of cement is evaluated via group of tests. The most important, and close to understanding, is the compressive strength test. Recently, Egyptian standards adopted the European standards EN-196 and EN-197 for specifying and evaluating quality of cements. This was motivated by the large European investments in the local production of cement. The current study represents a comparative investigation, experimental and numerical, of the effect of different parameters on evaluation of compressive strength. Main parameters are shape of specimens and type of sand used for producing tested mortars. Three sets of specimens were made for ten types of cements. First set were 70.6 mm cubes molded according to old standards using single sized sand. Second group were prisms molded from standard sand (CEN sand) according to the recent standards. Third group were prisms molded from local sand sieved and regenerated to simulate same grading of CEN sand. All specimens were cured according to relevant standards and tested at different ages (2,3,7,10 and 28 days). Results show that CEM-I Type of cement does not fulfill, in all of its grades, the strength requirements of Ordinary Portland cement OPC specified in old standards. Also, the use of simulated CEN sand from local source gives strengths lower than those obtained using standard certified CEN sand. A limited number of tests were made on concrete specimens from two most common CEM-I types to investigate effect on concrete strength and results were also reported. Numerical investigation of the effect of specimen shape and type of sand on evaluation of compressive strength of mortar specimens, presented in the current study, applies one of the artificial intelligence techniques to simulate and predict the strength behavior at different ages. The Artificial Neural Network (ANN) technique is introduced in the current study to simulate the strength behavior using the available experimental data and predict the strength value at any age in the range of the experiments or in the future. The results of the numerical study showed that the ANN method with less effort was very efficiently capable of simulating the effect of specimen shape and type of sand on the strength behavior of tested mortar with different cement types.
文摘As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcracks and defects. In order to reduce the damage to cement ring and improve sealed cementing property at the interface, it is necessary to conduct research on the modification of the cement rock available. According to the principle of super mixed composite materials, various fillers are added to the ingredients of cement rock. Dynamic fracture toughness of cement rock will be changed under the influence of filler. In this paper, short rod specimens of cement rock are employed in the experiments to investigate the dynamic fracture toughness of cement rocks with different ingredients using split Hopkinson Pressure Bar, and partial experimental results are given. The results indicate that fiber reinforcement is an effective way to improve the impact resistance of cement rock.
