利用现有的数据,分析蚯蚓密度与土壤物理肥力主要参数之间的关系,定量评价蚯蚓对土壤物理性状的影响。通过中国知网和Web of Science,输入关键词(蚯蚓、土壤容重、土壤含水量、土壤质地、土壤孔隙度、土壤水稳定性团聚体)搜索,提取其中...利用现有的数据,分析蚯蚓密度与土壤物理肥力主要参数之间的关系,定量评价蚯蚓对土壤物理性状的影响。通过中国知网和Web of Science,输入关键词(蚯蚓、土壤容重、土壤含水量、土壤质地、土壤孔隙度、土壤水稳定性团聚体)搜索,提取其中相关的数据,将文献提取的数据与调研获得的数据结合,进行Pearson相关性分析。研究发现,蚯蚓密度与砂粒相对含量呈极显著的负指数关系(P<0.001),与粉粒相对含量呈显著的正指数关系(P<0.05),而与黏粒相对含量呈极显著的幂函数关系(P<0.001);与土壤容重呈微弱的负相关关系(P<0.20),但与土壤孔隙度呈显著的正相关关系(P<0.05);与水稳定性团聚体含量呈微弱的正相关关系(P<0.5),但与水分含量呈极显著的正相关关系(P<0.001)。基于蚯蚓密度与砂粒、粉粒、黏粒相对含量,土壤容重、孔隙度,水稳定性团聚体、水分含量关系,可以将蚯蚓密度与土壤物理肥力主要参数之间的定量关系分为5个等级,以用于评价蚯蚓对土壤物理肥力指标的影响。展开更多
Failure of concrete structures leading to collapse of buildings has initiated various researches on the quality of construction materials. Collapse of buildings resulting to injuries, loss of lives and investments has...Failure of concrete structures leading to collapse of buildings has initiated various researches on the quality of construction materials. Collapse of buildings resulting to injuries, loss of lives and investments has been largely attributed to use of poor quality concrete ingredients. Information on the effect of silt and clay content and organic impurities present in building sand being supplied in Nairobi County and its environs as well as their effect to the compressive strength of concrete was lacking. The objective of this research was to establish level of silt, clay and organic impurities present in building sand and its effect on compressive strength of concrete. This paper presents the findings on the quality of building sand as sourced from eight supply points in Nairobi County and its environs and the effects of these sand impurities to the compressive strength of concrete. 27 sand samples were tested for silt and clay contents and organic impurities in accordance with BS 882 and ASTM C40 respectively after which 13 sand samples with varying level of impurities were selected for casting of concrete cubes. 150 mm × 150 mm × 150 mm concrete cubes were cast using concrete mix of 1:1.5:3:0.57 (cement:sand:coarse aggregates:water) and were tested for compressive strength at the age of 7, 14 and 28 days. The investigation used cement, coarse aggregates (crushed stones) and water of similar characteristics while sand used had varying levels of impurities and particle shapes and texture. The results of the investigations showed that 86.2% of the sand samples tested exceeded the allowable limit of silt and clay content while 77% exceeded the organic content limit. The level of silt and clay content ranged from 42% to 3.3% for while organic impurities ranged from 0.029 to 0.738 photometric ohms for the unwashed sand samples. With regard to compressive strength, 38% of the concrete cubes made from sand with varying sand impurities failed to meet the design strength of 25 Mpa at the age of 28 days. A combined regression equation of with R2 = 0.444 was generated predicting compressive strength varying levels of silt and clay impurities (SCI), and organic impurities (ORG) in sand. This implies that 44% of concrete’s compressive strength is contributed by combination of silt and clay content and organic impurities in sand. Other factors such as particle shapes, texture, workability and mode of sand formation also play a key role in determination of concrete strength. It is concluded that sand found in Nairobi County and its environs contain silt and clay content and organic impurities that exceed the allowable limits and these impurities result in significant reduction in concrete’s compressive strength. It is recommended that the concrete design mix should always consider the strength reduction due to presence of these impurities to ensure that target strength of the resultant concrete is achieved. Formulation of policies governing monitoring of quality of building sand in Kenya and other developed countries is recommended.展开更多
文摘利用现有的数据,分析蚯蚓密度与土壤物理肥力主要参数之间的关系,定量评价蚯蚓对土壤物理性状的影响。通过中国知网和Web of Science,输入关键词(蚯蚓、土壤容重、土壤含水量、土壤质地、土壤孔隙度、土壤水稳定性团聚体)搜索,提取其中相关的数据,将文献提取的数据与调研获得的数据结合,进行Pearson相关性分析。研究发现,蚯蚓密度与砂粒相对含量呈极显著的负指数关系(P<0.001),与粉粒相对含量呈显著的正指数关系(P<0.05),而与黏粒相对含量呈极显著的幂函数关系(P<0.001);与土壤容重呈微弱的负相关关系(P<0.20),但与土壤孔隙度呈显著的正相关关系(P<0.05);与水稳定性团聚体含量呈微弱的正相关关系(P<0.5),但与水分含量呈极显著的正相关关系(P<0.001)。基于蚯蚓密度与砂粒、粉粒、黏粒相对含量,土壤容重、孔隙度,水稳定性团聚体、水分含量关系,可以将蚯蚓密度与土壤物理肥力主要参数之间的定量关系分为5个等级,以用于评价蚯蚓对土壤物理肥力指标的影响。
文摘Failure of concrete structures leading to collapse of buildings has initiated various researches on the quality of construction materials. Collapse of buildings resulting to injuries, loss of lives and investments has been largely attributed to use of poor quality concrete ingredients. Information on the effect of silt and clay content and organic impurities present in building sand being supplied in Nairobi County and its environs as well as their effect to the compressive strength of concrete was lacking. The objective of this research was to establish level of silt, clay and organic impurities present in building sand and its effect on compressive strength of concrete. This paper presents the findings on the quality of building sand as sourced from eight supply points in Nairobi County and its environs and the effects of these sand impurities to the compressive strength of concrete. 27 sand samples were tested for silt and clay contents and organic impurities in accordance with BS 882 and ASTM C40 respectively after which 13 sand samples with varying level of impurities were selected for casting of concrete cubes. 150 mm × 150 mm × 150 mm concrete cubes were cast using concrete mix of 1:1.5:3:0.57 (cement:sand:coarse aggregates:water) and were tested for compressive strength at the age of 7, 14 and 28 days. The investigation used cement, coarse aggregates (crushed stones) and water of similar characteristics while sand used had varying levels of impurities and particle shapes and texture. The results of the investigations showed that 86.2% of the sand samples tested exceeded the allowable limit of silt and clay content while 77% exceeded the organic content limit. The level of silt and clay content ranged from 42% to 3.3% for while organic impurities ranged from 0.029 to 0.738 photometric ohms for the unwashed sand samples. With regard to compressive strength, 38% of the concrete cubes made from sand with varying sand impurities failed to meet the design strength of 25 Mpa at the age of 28 days. A combined regression equation of with R2 = 0.444 was generated predicting compressive strength varying levels of silt and clay impurities (SCI), and organic impurities (ORG) in sand. This implies that 44% of concrete’s compressive strength is contributed by combination of silt and clay content and organic impurities in sand. Other factors such as particle shapes, texture, workability and mode of sand formation also play a key role in determination of concrete strength. It is concluded that sand found in Nairobi County and its environs contain silt and clay content and organic impurities that exceed the allowable limits and these impurities result in significant reduction in concrete’s compressive strength. It is recommended that the concrete design mix should always consider the strength reduction due to presence of these impurities to ensure that target strength of the resultant concrete is achieved. Formulation of policies governing monitoring of quality of building sand in Kenya and other developed countries is recommended.
