冻融损伤对再生混凝土耐久性及与钢筋粘结性能分析

制作掺入引气剂和未掺入引气剂的100%粗骨料取代率的再生混凝土RC1和RC2两组试件以及掺入引气剂和未掺入引气剂的普通混凝土NC1和NC2两组试件,并分别对经过不同次数冻融循环试件的抗压强度、质量损失率、动弹性模量损失率进行研究。结果表明,冻融后各组试件的抗压强度、质量损失率及动弹性模量损失率均降低,对于添加引气剂的NC1和RC1两组试件损失较小,其中RC1组试件在200次冻融后抗压强度损失接近40%,质量损失率达0.5%,动弹性模量损失率38.5%。100%取代率并加入引气剂的ZRC组试件冻融后进行中心拨出实验,发生劈裂破坏和钢筋拔出破坏2种形式。再生粗骨料混凝土与钢筋的极限粘结应力均随冻融次数的增加而降低,200次冻融后极限粘结应力下降33.5,荷载滑移曲线既有上升段也有下降段。     

Stress Corrosion of Concrete Exposed to the Action of Freezing-thawing Cycles

Through the method of accelerated freezing-thawing and room-temperature corrosion, the stress corrosion of three kinds of concretes subjected to 5.0%MgSO4(in mass)solution was studied. The considered concretes include High Strength Concrete(HSC), High-Volume Mineral Admixture Concrete(HVMAC) and High Durable Concrete(HDC) added with high-volume mineral admixture, air-entraining agent, superplasticizer, fibers and expansion agent. The results showed that the relative dynamic elastic modulus of concrete went through strengthen and deterioration stages subjected to stress corrosion, whether the room temperature or freezing and thawing conditions. The length of time of these two stages are closely related with the experimental temperature. Freezing and thawing action significantly accelerated the process of sulphate stress corrosion damage. Under the action of freezing and thawing, stress corrosion strengthening the period length of HSC shorter 96%, deterioration section of the length of time shorter 88%, compared with the length of time at the corresponding room temperature. Deterioration section of the length of time of HVMAC is reduced by 98%, while the HDC reduced by 71%. The effect of freezing and thawing, HDC freezing-thawing cycles when the stress corrosion damage occurred were longer 1.5 times and 13 times than the HSC and HVMAC. Thus in the cold regions, HDC showed more resistance to sulfate stress corrosion.     

Experimental Research on Concrete Strength under Freeze-thaw Recycle Action with Ultra-low Temperature

The concrete structure has been used in low and ultra-low temperature environment. But few researches are experienced on its properties under freeze-thaw recycles with ultra-low temperature. Based on the standard for test methods of long-term performance and durability of ordinary concrete, considering the influence of the times and minimum temperature of recycles, water-cement ratio and the external environment humidity, compressive and tensile strength of cubic concrete and scanning electron microscopy on the residual sample are experimented to explore the impact of freezing and thawing cycles under ultra-low temperature on its strength and microstructure. The results show that the role of cryogenic temperature for freeze-thaw cycles has a greater effect on concrete performance. With the temperature decreasing and water-cement ratio increasing, the damage tends to grow up. Consistent with the results of the strength tests, electron microscopy tests show that the pore size of mortar increases and the material becomes looser.     

冻融作用对土壤氮转化影响的研究进展

氮素是限制植物生长的重要营养元素之一,其在土壤中转化程度受多种因素影响,作为中、高纬度或高海拔地区土壤氮转化的重要驱动力,冻融作用对于土壤氮转化过程也存在极大影响。本文基于国内外已有研究成果,概述了土壤冻融循环次数、结冻持续时间以及结冻强度对于土壤氮转化过程的影响。总结出冻融格局的改变对土壤氮转化关系的一般规律：随着冻融格局的改变,均有利于土壤氮的矿化;冻融强度的增加可显著提高土壤硝态氮的含量;冻融格局的改变也会提高N₂O的排放。     

冻融作用下特定污染物的清洗试验研究

抽出处理法是目前修复土壤污染常用的方法之一，为了解决抽出处理法中对渗透性差的土中污染物和低浓度污染物效率低的问题，利用土体冻结过程中在一定的温度梯度和水分条件下未冻土侧水分（溶质）向冻结锋面迁移和冻融作用导致渗透性增强的特性，开展了基础试验。试验将混有模拟污染物NaCl溶液的粘土作为研究对象，结合传统的抽出处理法，实施了单向冻融试验和污染物清洗模型试验，探索了利用冻融现象清洗污染土壤的可行性。结果表明，冻融作用有助于提高污染物的抽出效率。     

Experiments on heat loss characteristics in a fully opened cylindrical cavity receiver

The climate has a great impact on highway bridge rubber bearings than on building rubber bearings. In order to study the change of the mechanical properties during the life of the plain chloroprene rubber bearings of highway bridge under freeze-thaw cycle condition, the plain chloroprene rubber bearings were processed 25, 50, 75, 100 times by freeze-thaw cycle in the standard freeze-thaw chamber, then the axial compression tests were carried. The changes of the performance indicators in the bearing capacity , the ultimate compressive strength, vertical stiffness, elastic modulus under different freeze-thaw cycles were analyzed comparatively. The results show that the plain chloroprene rubber bearings are more prone to brittle failure after the freeze-thaw cycle, and the failure phenomena of steel plate exposing or cracks is more serious than the phenomena of the standard specimen. With the increase of the number of freeze-thaw cycle, the ultimate bearing capacity, ultimate compressive strength and compressive elastic modulus of the plain chloroprene rubber bearings decrease. The attenuation formula and decay curve in 50 years of ultimate compressive strength and elastic modulus of compression are analyzed by least square method, the trends of change are both in line with the exponential function. The mechanical properties of plain chloroprene rubber bearings of highway bridge significantly decreased under freeze-thaw cycle condition. therefore, the temperature ranges of plain chloroprene rubber bearings of highway bridge should be strictly controlled, and some suggestions, such as increasing its minimum applicable temperature, usng the natural rubber bearings as much as possible in cold regions, have been given.     

原状黄土冻融过程抗剪强度劣化机理试验分析

通过对西安Q₃原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验,研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化,大颗粒集粒数量明显减少,小粒径土颗粒所占比重增加,孔隙面积比增加。进一步基于损伤力学理论,得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势,反映出冻融作用一定程度上破坏黄土体的结构强度,但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏,且含水率越高,土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势,且含水率越高,粘聚力衰减幅值和速率越小;粘聚力随含水率增加表现出线性衰减特征,且冻融后粘聚力与含水率的变化规律近似重合;内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势,随含水率升高有增大趋势。基于试验数据规律性,进一步提出了原状黄土粘聚强度劣化模型,该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。     

新疆石河子冻土特征及冻土融化期地温、冻土深度预报研究

为了确保春季播种安全,有必要开展播种期地温的监测和冻土融化深度预报业务。利用新疆农八师冻土气象观测资料,运用相关系数和线性回归方法,分析冻土特征及融化过程中地温变化、深度变化规律,建立春季冻土融化预报模型。结果表明,新疆农八师垦区稳定冻土期在11月中旬至翌年3月下旬,冻土最大深度呈逐年变浅趋势,倾向率为-5.4 cm/10 a;冻土结冻日期推后,倾向率为2.0 d/10 a;冻土化通日期提前,倾向率为-1.5 d/10 a。冻土融化期在3月中旬至4月上旬,冻土融化速率在3.1~4.0 cm/d之间。春季地温与平均气温、冻土融化深度与正积温具有显著的正相关,以此建立了相应的预报模型。10 cm地温预报模型历史回代准确率在96%以上,冻土融化深度预报模型历史回代准确率在94%以上。通过模型可以开展春季地温和土壤融化预报业务。     

Simulation Analysis of Flexural Performance of Reinforced Concrete Beam in Salt-frost Environment

Considering the damage of concrete mechanical properties and bonding behavior between the steel bar and concrete after the freezing and thawing function in the numerical simulation, the nonlinear analysis on flexural performance of reinforced concrete beam which experiences different salt-frost cycles is conducted, and the evolution law of resistance performance of reinforced concrete beam is studied. It is shown that, in the salt-frost environment, the decrease of concrete mechanical properties is the main reason that causes the degeneration of RC beam on flexural performance, while the reduction of bonding property has an unobvious effect on the beam resistance performance. When the salt-frost cycles reach a certain level, the beam failure pattern would change from the under-reinforced failure to over-reinforced failure. The freeze-thaw damage of bonding property in the beam-ends anchorage zone has a certain effect on the beam resistance behavior, especially for the more serious freeze-thaw degree, the resistance performance of the beam reduces about 4% than the perfect anchor beam.     

Three-dimensional Random Damage Prediction Model of Concrete Caused by Freeze-thaw

In order to effectively assess the damage of concrete in freeze-thaw condition, prediction model for concrete frost damage is presented based on damage mechanical theory and the experimental test. The degeneration of tension strength of air-entraining concrete is tested after freezing and thawing. Provided with the fact that the degeneration of concrete is an interior damage evolving process, freezing and thawing damage accumulation of concrete is analyzed based on the discrete grid with probability of stochastic method. And Three-dimensional multi-parameters Weibull distribution model about concrete damage evolutions is presented. Parameters are estimated based on gradient method, and the mathematical model is verified according to the tested data. Corresponding algorithm is designed and programming is completed by C + + programming language to establish concrete durability prediction model under freeze-thaw conditions. It is indicated that the damage of concrete develops in nonlinear way as the freezing and thawing increases.     

Stability of Particle size Improved Roadbed in Permafrost

Roadbed stability, including thermal and strength stability, is the ability of roadbed to adapt to pavement settlement, slurry effusion, shear slide and haunching up of the roadbed resulting from moving vehicles and many natural influences. Thermal stability is the sensitivity of the thermal state of the roadbed to the external environmental condition. It is the key point of the roadbed stability in permafrost. Research concerning roadbed thermal stability in permafrost is analyzed, and the judgment principle of thermal stability is discussed. The regular change of the ground temperature and deformation of particle size improved roadbeds are analyzed by studying field observation data of the particle size improved roadbed after two freezing and thawing cycles. We conclude that the particle size improved roadbed can raise the upper limit of frozen soil. Based on the judgment principle, the particle size improved roadbed is regarded as a new type of stable structure.     

Mechanical Properties of Marble at High Temperature

为进一步优化超声波提取胡萝卜中β-胡萝卜紊的工艺条件,在超声功率、超声时间、提取温度、物料粒度、料液比及提取次数6个单因素试验结果的基础上,采用二水平部分因子析因设计（2—level fractional factorial design）法,筛选出了影响β-胡萝卜素提取的主要因素为提取时间（p=0．0145）、温度（p=0．0189）、料液比（p=0．0180）和提取次数（p=0．0114）。     

Effective Unloading Area between Cantilever Piles

The formation mechanism of the arching effect between cantilever piles is studied according to their stress characteristics. The soil arch is classified into three types based on its position in a space coordinate system, namely, a horizontal arch, a vertical arch and a free face arch. The master factor for distribution of unloading area between piles is the horizontal arch effect. The range of effective unloading area is defined. Based on the failure pattern of soil arches and the relationship between soil strength theory and the static equilibrium principle of soil arches, a calculation model is established by considering the presence of geostatic stress and sliding thrust force. The relation between soil strength and critical height is studied by variation of cohesion and friction angle. In addition, the impact of canonical distributions of the earth pressure to the vector height of unloading area is also discussed. Finally, the calculation model is verified by an example from real engineering work.     

Dynamic Properties of Yangla Copper Tailings Material

Tailing sands, coarse tailing sands and fine tailing sands all were prepared by artificial partitioning experimentation in accordance with the requirements of central line damming. DDS 70 electromagnet kinetic equipment was used to study the dynamic strength, stress strain relationship, dynamic modulus and damping ratio of three tailing sand types. The dynamic strength and parameters were determined, and some influential factors, such as particle composition, confining pressure, consolidated stress ratio and dynamic stress, were discussed. The test results provide basic data for the stability evaluation of the Yangla copper tailing dam under a magnitude 8 earthquake.     

松辽平原高产农田土壤孔性对冻结的响应及机理研究

为了进一步深入系统研究松辽平原玉米带黑土耕作区高产田（平面型）土壤质量的管理与评价提供理论支持和借鉴,并且对黑土资源的利用与保护、为粮食的丰产增收在土壤结构理论方面具有重要的现实意义,并且对黑土资源的利用与保护、为粮食的丰产增收在土壤结构理论方面的探索,以松辽平原玉米带耕作区高产田（波浪型）与低产田（平面型）0~20 cm耕层土壤为研究对象采用田间季节性冻融过程与室内模拟冻融试验相结合的方法,研究松辽平原玉米带高产田土壤的结构性对冻结的响应,包括影响范围较深和程度,进一步阐明高产田土壤对冻结的响应机理。采用高产田与低产田对比的方法,在不同的冻结条件下,设置含水量接近5%,10%,15%,20%,25%;设置冻结频率0、2、4、6次进行室内模拟冻结实验。通过对容重、孔隙度、孔隙面积、Feret直径等指标的测定与分析,研究了不同冻结频率不同含水量,对高产田和低产田0~20 cm耕层的土壤孔隙特征的影响。结果显示：冻融循环能够显著增加松辽平原玉米带高产田与低产田0~20 cm耕层土壤孔隙的数目,高产田增加百分比为32.58%;低产田增加百分比为17.95%。显著降低了低产田0~20 cm土层范围内Feret直径和土壤的平均孔隙面积以,Feret直径由冻结前的2.31降低到冻结后的1.92,降低百分比为16.88%,低产田土壤的平均孔隙面积由冻结前的8.91降低到冻结后的4.65,降低百分率为47.81%(P<0.05)。除了土壤孔隙的成圆率外,冻融循环对高产田与低产田不同径级团聚体的孔隙数目、平均孔隙面积、平均Feret直径均有不同影响程度的差异(P<0.05)。高产田>5 mm团聚体平均孔隙面积由冻结前的37.08降低到冻结后的23.84,降低百分比为38.40%,变化差异显著(P<0.05),这是高产田与低产田相比特有的变化规律。而高产田其他粒级团聚体和低产田所有粒级团聚体的平均孔隙面积对冻结的响应不明显。高产田与低产田都有>5 mm团聚体的孔隙成圆率变化显著,高产田由冻结前的0.36降低到0.27,变化百分比为25%;低产田由冻结前的0.25增加到冻结后的0.34,变化百分比为36%,差异显著(P<0.05),这两者的变化规律截然相反,也体现高产田大粒径团聚体孔隙成圆率对冻结的响应规律有别于低产田的特殊性,以上研究结论对系统研究松辽平原玉米带黑土耕作区高产田（平面型）土壤质量的管理与评价提供理论支持有一定的意义。     

On the Type of Stress-strain Relation Curves and the Critical State for Soils

In order to discuss the influence of stress history on the constitutive relations for soils,a series of drained conventional triaxial compression tests for normally consolidated and overconsolidated clays have been carried out.It is found through comparing the stress-strain relation curves under the different stress histories that the overconsolidated ratio is the determining factor for volumetric strain.The volumetric strain is less sensitive to consolidation pressure,however.For the shear capacity,the consolidation pressure is the determining factor,but the influence of the overconsolidated ratio can not be neglected since it determines whether there will be strain hardening or strain softening as well as the grade of strain softening.Despite that,the soil specimens will finally reach a unified critical state and approximately the same residual strength.According to the principle of interaction between plastic volumetric and shear strains,the mechanism of generating two types of stress-strain relation curves for clays is explained.It is shown that the critical state is a pure process of shearing deformation in which the interaction between plastic volumetric and shear strains completely disappears.The critical state is independent of the previous stress history.     

Effects of Vibration History on Modulus and Damping of Clay

Aiming at evaluating the effects of vibration history on dynamic characteristics of normally consolidated clay, a series of multi-cycled cyclic shear tests were conducted on 16 soil samples under consolidation pressure of 50 kPa, 100 kPa, 300 kPa and 500 kPa respectively. The experimental results reveal that, on the stage of drainage and consolidation, with the development of duration shear modulus curve ascends while damping curve descends; this trend became significant as consolidation pressure increased. The variation tends to be stable in 25 hours. When subjected to cyclic loading controlled by constant strain amplitude, both the modulus and damping of soil samples change significantly during the first 50 cycles, and then the differences become moderate afterwards, in which the damping curve acts in hyperbolical type. It is also found that there exists a clear sign of pre-straining that affects damping more significantly than modulus.     

Effect of Soil Content on Dynamic Modulus in Filling Sand Subgrade

To analyse the effect of the soil content on dynamic modulus in filling sand subgrade, the portable falling weight deflectometer (PFWD) test and degree of compaction test in field were carried out at first. The relationship of the soil content and the dynamic modulus was analysed as well. Based on the test data, the regression models among the dynamic modulus, degree of compaction, consistency and the soil content were established. Then combining with the out-and-indoor test results, the controlling standard of soil content in filling sand embankment was presented. The results turn out that the soil content in the embankment is 3.0%~5.5%. The dynamic modulus increases with the soil decreasing, and there is a good power function regression between them. There is also a good regression among dynamic modulus, degree of compaction, consistency and soil content. When the soil content is within 10%, the dynamic modulus increases then turn to decrease with the soil content increasing. When soil content is smaller than 3% or larger than 8%, the dynamic modulus are significantly smaller than others. So the controlling standard of soil content in filling sand embankment is recommended at 3%~8%.     

模拟雪被变化下三江平原湿地土壤理化性质的动态响应

为了研究不同雪被处理下土壤温度变化对土壤理化性质影响的动态贡献,采集三江平原小叶章湿地原状土样品,通过室内模拟实验对4个雪被处理W0 (31.05%)、W1200 (42.66%)、W3000 (51.21%)和W6000 (76.66%)下的土壤理化性质进行检测。结果表明：W6000处理显著的增加了土壤pH;3个雪被添加处理均显著增加了土壤可溶性有机碳含量;W3000和W6000处理均显著增加了土壤铵态氮含量;W6000处理显著降低了土壤硝态氮含量;不同雪被处理对土壤全磷和速效磷均未产生显著影响;W1200处理显著的增加了土壤微生物量碳,而W6000处理显著的降低了土壤微生物量碳;W1200处理显著的增加了土壤微生物量氮,W3000处理显著的降低了土壤微生物量氮。不同雪被处理下土壤温度是土壤理化性质变化的主要影响因子。不同雪被处理会改变冻融期土壤理化性质,进而对湿地生态系统碳氮循环产生重要影响。     

改良冷冻法测定梨果实的石细胞含量

为了提高梨石细胞的提取效率,以黄金梨和茌梨的果实为试材,在冷冻提取方法的基础上,通过设置不同的冷冻时间和冻融次数来研究其对梨石细胞提取效果的影响。结果表明：所有处理中以处理（1）(3 h+3 h+3 h)反复冻融处理的提取效果最好,石细胞提取的量随着冻融次数的增加而增加,说明增加冻融次数有利于梨果实石细胞的提取;在冻融次数相同时,每次冷冻时间满足3 h后,再增加冷冻时间对提取效果影响不大。冷冻法提取石细胞效果与冻融次数密切相关,在满足基本的冷冻时间后,增加冻融次数可以显著提高梨石细胞的提取率。