A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio ...A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.展开更多
The wetlands of the Brahmaputra valley include lake-like natural water bodies locally known as ＇beel＇, and degenerated lakes, which are often called as swamps. The role of such wetlands in socio-economic condition o...The wetlands of the Brahmaputra valley include lake-like natural water bodies locally known as ＇beel＇, and degenerated lakes, which are often called as swamps. The role of such wetlands in socio-economic condition of the people is significant from various angles. Apart from the wetlands act as the ideal habitats for feeding, nesting and breeding of a large variety of fishes, birds and other aquatic animals, these features maintain the environmental quality of the region. Present study has been conducted primarily in eight selected beels in the Dimoria region, which is located almost at the south-central part of the Brahmaputra valley. The water and soil samples from these wetlands had been collected using random sampling technique and analyzed to know about the nature of degradation of the wetlands. Once highly productive wetland waters now show very low DO, high BOD and COD, indicating dwindling productivity of fish and other aquatic resources. Higher value of pH in soils of most of the wetlands found probably due to the impact of industrial effluents and urban sewage and use of chemical fertilizers in the paddy field of the fringe areas, which again create toxic environment and ultimately reduces fish productivity.展开更多
基金Project(51408213)supported by the National Natural Science Foundation of China
文摘A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.
文摘The wetlands of the Brahmaputra valley include lake-like natural water bodies locally known as ＇beel＇, and degenerated lakes, which are often called as swamps. The role of such wetlands in socio-economic condition of the people is significant from various angles. Apart from the wetlands act as the ideal habitats for feeding, nesting and breeding of a large variety of fishes, birds and other aquatic animals, these features maintain the environmental quality of the region. Present study has been conducted primarily in eight selected beels in the Dimoria region, which is located almost at the south-central part of the Brahmaputra valley. The water and soil samples from these wetlands had been collected using random sampling technique and analyzed to know about the nature of degradation of the wetlands. Once highly productive wetland waters now show very low DO, high BOD and COD, indicating dwindling productivity of fish and other aquatic resources. Higher value of pH in soils of most of the wetlands found probably due to the impact of industrial effluents and urban sewage and use of chemical fertilizers in the paddy field of the fringe areas, which again create toxic environment and ultimately reduces fish productivity.
