The effects of four sand contents on the compressive, flexural and splitting-tensile strength of cement mortars were evaluated. Moreover, we experimentally investigated the pore structure of cement mortar brought abou...The effects of four sand contents on the compressive, flexural and splitting-tensile strength of cement mortars were evaluated. Moreover, we experimentally investigated the pore structure of cement mortar brought about by changing the sand content and water/cement ratio. The changes in the pore structure were quantified by measuring the porosity and pore size distribution obtained by using mercury intrusion porosimetry（MIP） technique. The test results show that the strengths of cement mortar increase with increasing sand content. It is also suggested that the traditional water/cement ratio law can be applied to cement mortar with different sand contents, provided that a slight modification is introduced. Sand content is an important parameter influencing the pore structure of cement mortar. Moreover, there is a good relationship between the pore structure and strength of cement mortar.展开更多
The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways. In order to verify the feasibility of blending coarse sand in modifying soft subsoil, undrai...The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways. In order to verify the feasibility of blending coarse sand in modifying soft subsoil, undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies. Laboratory testing results indicate that the fl ow characteristics of soft soil can be signifi cantly enhanced by high-frequency vibration;meanwhile the continuous increase in fl ow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil. The infl uence of sand content on fl ow characteristics is also studied in detail, and it is shown that the addition of coarse sand can weaken the fl ow characteristics of soft soil induced by sudden vibration at lower than 50 Hz. Under the condition of cyclic vibration, the growth of the fl ow characteristics of sand-clay mixtures is mainly caused by the fi rst-time vibration in the cycle, and the increase in sand content can make the fl ow characteristics present a faster convergent tendency.展开更多
It is generally accepted that the compositions and properties of soil organic matter(SOM) are in?uenced by many factors. In order to reveal the effects of soil texture on characteristics and dynamics of SOM and its su...It is generally accepted that the compositions and properties of soil organic matter(SOM) are in?uenced by many factors. In order to reveal the effects of soil texture on characteristics and dynamics of SOM and its sub-fraction,humic acid(HA), along two soil pro?les, a yellow soil pro?le and a purplish soil pro?le, under the same climate and vegetation conditions were determined. Results indicate that the decomposition and humi?cation degrees of SOM and HA of the purplish soils are higher than those of the corresponding yellow soils indicated by A/O–A ratios of HAs, TOCs and HA yields of bulk soil samples, nevertheless, the development degree of the purplish soil is lower than that of the yellow soil. The variations of E_4/E_6 ratios of HAs along the soil pro?les indicate the overall molecular sizes of HAs decreased downward along the soil pro?les.A/O–A ratios of HAs decreased downward along both the soil pro?les indicate that humi?cation processes decrease downward along both the soil pro?les. Leaching of SOM shows signi?cant effects on the distribution and characteristics of HAs in the yellow soil pro?le but the purplish soil pro?le, which is consistent with the higher hydrophobicity of HAs in purplish soils, shows that the distribution characteristics of SOM along the soil pro?les are a complex result of the combination of soil texture and characteristics of SOM itself. The remarkably different sand contents are concluded tentatively as one of reasons to the different distributions and dynamics of HAs along the soil pro?les,however, to profoundly understand the evolution and transport of SOM along soil pro?les needs more researches.展开更多
Muddy water irrigation,an effective water-saving irrigation method,has been widely used in the Yellow River Basin in China.To investigate the effect of sand content on water infiltration and dense layer formation unde...Muddy water irrigation,an effective water-saving irrigation method,has been widely used in the Yellow River Basin in China.To investigate the effect of sand content on water infiltration and dense layer formation under one-dimensional vertical infiltration of muddy water,muddy water infiltration experiments were performed in the laboratory,and five sand contents of muddy water(S=0%,3%,6%,9%,and 12%)were used.Models were established to describe the relationship between the cumulative infiltration amount[I(t)]and the infiltration duration(t);the relationship among the migration distance of the wetting front(Z),S,and t;the thickness of the sedimentary layer[H(t)];and the relationship between S and t.The results revealed that I(t)and Z decreased significantly with the increase of sand contents,while H(t)increased significantly with the increase of sand contents.I(t)and Z were in the range of 7 cm and 20 cm for each treatment,respectively.The variation in I(t)with t fitted Kostiakov and Philip models,and the coefficients of determination were all greater than 0.99.With the increase in S,the infiltration coefficient gradually decreased,the infiltration index gradually increased,and the sorptivity gradually decreased.The particle composition of the sedimentary layer was similar to that of the argillaceous sediment,and the content of particles with a size of less than 2 mm in the sedimentary layer was lower than that of the argillaceous sediment.Compared with the original soil,the content of particles with a size of less than 0.05 mm and physical clay particles(diameter less than 0.01 mm)in the soil with an infiltration depth of 0-2 cm increased.The retention layer was from the topsoil to the infiltration depth of approximately 2 cm.This study can provide a scientific basis for further research on soil infiltration mechanisms under muddy water.展开更多
Sand dabs, an important commercial flatfish in the Bohai Sea, has recently decreased gradually in biomass, resulting from overfishing and marine pollution. Artificial culture and multiplication of sand dabs are essent...Sand dabs, an important commercial flatfish in the Bohai Sea, has recently decreased gradually in biomass, resulting from overfishing and marine pollution. Artificial culture and multiplication of sand dabs are essential and practical in China. The present paper examines the food habitof this fish to provide detailed information for its culture and multiplication.展开更多
铁尾矿机制砂被广泛应用于混凝土中,然而部分铁尾矿机制砂中硫含量过高,可能会造成混凝土膨胀开裂。本文配制了不同硫含量的铁尾矿机制砂混凝土,研究硫含量对混凝土工作性能、力学性能和耐久性能的影响规律,并采用X R D、压汞、SEM等微...铁尾矿机制砂被广泛应用于混凝土中,然而部分铁尾矿机制砂中硫含量过高,可能会造成混凝土膨胀开裂。本文配制了不同硫含量的铁尾矿机制砂混凝土,研究硫含量对混凝土工作性能、力学性能和耐久性能的影响规律,并采用X R D、压汞、SEM等微观测试分析了铁尾矿机制砂中硫含量对混凝土性能的影响机理。结果表明:铁尾矿机制砂中硫含量的增加显著影响混凝土的工作性能;硫含量为2%的C30铁尾矿机制砂混凝土早期强度最高,养护龄期在3 d和7 d时,混凝土抗压强度比空白组分别提升了14.4%、11.7%,其抗碳化性能和抗氯离子扩散能力均优于其他硫含量的混凝土。少量的硫化物可以提供充足的SO42-,激发水泥混合材水化反应的进行;含硫量过高则会导致混凝土中的A Ft和石膏等膨胀性晶体增加,混凝土内部产生较大应力,造成混凝土开裂,对后期强度发展不利,对于铁尾矿机制砂混凝土,硫含量不宜超过4%。展开更多
基金Founded by the National Natural Science Foundation of China(Nos.51279054 and 51279052)
文摘The effects of four sand contents on the compressive, flexural and splitting-tensile strength of cement mortars were evaluated. Moreover, we experimentally investigated the pore structure of cement mortar brought about by changing the sand content and water/cement ratio. The changes in the pore structure were quantified by measuring the porosity and pore size distribution obtained by using mercury intrusion porosimetry（MIP） technique. The test results show that the strengths of cement mortar increase with increasing sand content. It is also suggested that the traditional water/cement ratio law can be applied to cement mortar with different sand contents, provided that a slight modification is introduced. Sand content is an important parameter influencing the pore structure of cement mortar. Moreover, there is a good relationship between the pore structure and strength of cement mortar.
基金Natural Science Foundation of Jiangsu Province of China under Grant No.BK2012810
文摘The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways. In order to verify the feasibility of blending coarse sand in modifying soft subsoil, undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies. Laboratory testing results indicate that the fl ow characteristics of soft soil can be signifi cantly enhanced by high-frequency vibration;meanwhile the continuous increase in fl ow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil. The infl uence of sand content on fl ow characteristics is also studied in detail, and it is shown that the addition of coarse sand can weaken the fl ow characteristics of soft soil induced by sudden vibration at lower than 50 Hz. Under the condition of cyclic vibration, the growth of the fl ow characteristics of sand-clay mixtures is mainly caused by the fi rst-time vibration in the cycle, and the increase in sand content can make the fl ow characteristics present a faster convergent tendency.
基金supported by National Major Research Program of China(2013CB956702)the National Science Foundation of China(41273149,41173129)+1 种基金the Science Foundation of Guizhou Province(20113109)the 100-Talent Program of CAS
文摘It is generally accepted that the compositions and properties of soil organic matter(SOM) are in?uenced by many factors. In order to reveal the effects of soil texture on characteristics and dynamics of SOM and its sub-fraction,humic acid(HA), along two soil pro?les, a yellow soil pro?le and a purplish soil pro?le, under the same climate and vegetation conditions were determined. Results indicate that the decomposition and humi?cation degrees of SOM and HA of the purplish soils are higher than those of the corresponding yellow soils indicated by A/O–A ratios of HAs, TOCs and HA yields of bulk soil samples, nevertheless, the development degree of the purplish soil is lower than that of the yellow soil. The variations of E_4/E_6 ratios of HAs along the soil pro?les indicate the overall molecular sizes of HAs decreased downward along the soil pro?les.A/O–A ratios of HAs decreased downward along both the soil pro?les indicate that humi?cation processes decrease downward along both the soil pro?les. Leaching of SOM shows signi?cant effects on the distribution and characteristics of HAs in the yellow soil pro?le but the purplish soil pro?le, which is consistent with the higher hydrophobicity of HAs in purplish soils, shows that the distribution characteristics of SOM along the soil pro?les are a complex result of the combination of soil texture and characteristics of SOM itself. The remarkably different sand contents are concluded tentatively as one of reasons to the different distributions and dynamics of HAs along the soil pro?les,however, to profoundly understand the evolution and transport of SOM along soil pro?les needs more researches.
基金the National Natural Science Foundation of China(Grant No.52079105 and 51779205)the Doctoral Dissertations Innovation Fund of Xi’an University of Technology(Grant No.310-252072107).
文摘Muddy water irrigation,an effective water-saving irrigation method,has been widely used in the Yellow River Basin in China.To investigate the effect of sand content on water infiltration and dense layer formation under one-dimensional vertical infiltration of muddy water,muddy water infiltration experiments were performed in the laboratory,and five sand contents of muddy water(S=0%,3%,6%,9%,and 12%)were used.Models were established to describe the relationship between the cumulative infiltration amount[I(t)]and the infiltration duration(t);the relationship among the migration distance of the wetting front(Z),S,and t;the thickness of the sedimentary layer[H(t)];and the relationship between S and t.The results revealed that I(t)and Z decreased significantly with the increase of sand contents,while H(t)increased significantly with the increase of sand contents.I(t)and Z were in the range of 7 cm and 20 cm for each treatment,respectively.The variation in I(t)with t fitted Kostiakov and Philip models,and the coefficients of determination were all greater than 0.99.With the increase in S,the infiltration coefficient gradually decreased,the infiltration index gradually increased,and the sorptivity gradually decreased.The particle composition of the sedimentary layer was similar to that of the argillaceous sediment,and the content of particles with a size of less than 2 mm in the sedimentary layer was lower than that of the argillaceous sediment.Compared with the original soil,the content of particles with a size of less than 0.05 mm and physical clay particles(diameter less than 0.01 mm)in the soil with an infiltration depth of 0-2 cm increased.The retention layer was from the topsoil to the infiltration depth of approximately 2 cm.This study can provide a scientific basis for further research on soil infiltration mechanisms under muddy water.
文摘Sand dabs, an important commercial flatfish in the Bohai Sea, has recently decreased gradually in biomass, resulting from overfishing and marine pollution. Artificial culture and multiplication of sand dabs are essential and practical in China. The present paper examines the food habitof this fish to provide detailed information for its culture and multiplication.
