冻融循环下含水率对粉质黏土力学性质影响试验

为研究初始含水率对土体力学性质冻融循环效应的影响规律,以青藏高原粉质黏土为对象,进行不同含水率、围压及冻融次数条件下的三轴试验.结果表明:冻融循环使得不同初始含水率试样的应力-应变曲线趋于接近,低含水率试样的力学性质表现为劣化,在一定范围内,含水率越高,劣化效果越显著;当含水率增加至某一值后,一般为接近塑限时,冻融循环效应则表现为强化;封闭条件下土体冻融循环中的水分迁移会引起含水率的增减分区分布,且初始含水率越高,水分迁移量越大;土体破坏强度随含水率的增加以非线性规律减小,因此试样冻融循环后含水率增大区和减小区的强度变化幅度不同,会引起破坏强度增大、减小及不变等3种不同的变化趋势;冻融循环下土体力学性质会受到干密度、水分重分布及土体结构改变等多方面的影响,初始含水率和冻融次数不同,占主导地位的因素也不同,冻融循环效应就相应地呈现出多样化特征.     

冻融循环作用下不同含石量土石混合料剪切特性分析

为了探究冻融过程对土石混合料剪切特性的影响,采用室内冻融循环试验和大型直剪试验分析了含石量为10%、30%、50%、70%土石混合料试样(均处于最优含水率)和不同循环次数条件下抗剪强度变化规律。结果表明：冻融循环作用对土石混合料试样剪应力-剪切位移关系曲线变化有一定的影响,在高法向应力下随循环次数的增加剪应力峰值显著降低。     

冻融循环作用下砂质黄土强度劣化特性及影响因素研究

为揭示砂质黄土在冻融循环作用下的强度特性，以榆林子洲某地砂黄土为研究对象，对其进行不同初始条件的冻融循环试验，并测定土体冻融后的三轴剪切强度。结果表明：砂黄土冻融后表面出现明显的结构破坏现象；土体粘聚力随着冻融循环次数增加先减小然后有所回升，土体冻融后的粘聚力随初始含水率的增加而减小，冻结温度对不同含水率土体粘聚力的影响不同；土体内摩擦角在冻融循环作用下有所减小，总体下降量不大；土体强度下降主要受粘聚力劣化影响；高含水率极端低温冻结及低含水率较高温冻结均加速了冻融循环作用对土体强度的破坏。     

冻融对粉砂土力学特性及路堤边坡稳定性的影响

为研究粉砂土路堤在冻融循环作用下的力学特性以及采用粉砂土填筑的路堤边坡稳定性,基于静三轴试验,研究了不同含水量状态下,季冻区粉砂土在经历不同次数冻融循环后的粘聚力、内摩擦角等宏观力学特性的变化规律。以此为依据,采用有限元数值模型,针对不同坡度和不同填土高度对应的粉砂土填方路基,进行了冻融循环作用对边坡稳定系数的影响规律研究。研究结果表明:随含水量增大,冻融循环次数对粉砂土粘聚力的影响程度逐渐增强,当含水量较大时,粘聚力下降70%～80%;随冻融循环次数增加,粉砂土内摩擦角先降低,后略有增大;随含水量增大,冻融循环对粉砂土内摩擦角的影响有减弱趋势;冻融循环作用可使粉砂土路堤边坡稳定系数明显降低,冻融后的边坡稳定系数最大降幅可达到冻融前的49%;季冻区粉砂土路堤的最大填土高度不应超过4 m,小于3 m的填方路堤,极限坡度不应陡于1∶1.5,超过3 m的极限坡度不应超过1∶2.5。     

冻融循环作用对混凝土桥梁寿命的影响

在北方寒冷地区,冻融循环是影响混凝土桥梁结构使用寿命的重要因素之一.本文分析了冻融循环作用下混凝土的破坏机理,结合试验数据分别从材料性能和力学性能方面分析冻融循环使桥梁寿命衰减的变化趋势.     

纤维对纳米二氧化硅-石灰改良粉土力学性质的影响

山东黄泛区粉土分布广泛,在铁路路基填料紧缺的情况下,常用改良粉土作为路基填料。选用纳米二氧化硅和石灰作为改良剂,对黄泛区粉土进行改良,并通过击实试验以及无侧限抗压强度试验对其强度进行测定,发现纳米二氧化硅-石灰改良粉土虽然强度有显著提升,但也呈现出脆性较大的不良特性。为改善纳米二氧化硅-石灰改良粉土的脆性,在改良粉土中加入聚丙烯纤维,并通过试验研究了纤维掺量和长度对纳米二氧化硅-石灰改良粉土强度和脆性的影响,确定纤维的最优掺量和最优长度。结果表明：纤维的加入能改善纳米二氧化硅-石灰改良粉土的脆性,提高其抗压及抗剪强度;当纤维掺量为0.4%、纤维长度为2 cm时,改良效果最好。     

冻融循环条件下水泥稳定风化集料抗剪强度试验研究

选取质量分数分别为3%、5%、7%、9%的水泥,掺入到风化集料中,标准条件下养护7 d后,将冻融试验箱的温度调节在-15～15 ℃范围, 分别进行1、3、5、7、9次冻融循环,并在应变式直剪仪上进行直接剪切试验,得到了不同掺量的水泥稳定三峡库区风化集料内摩擦角和粘聚力经过不同次数的冻融循环作用后的变化规律。采用库仑理论计算出不同上覆荷载作用下,水泥稳定风化集料的抗剪强度变化规律,以期为三峡库区风化集料用作道路基层提供理论依据和试验指导。     

墙面纤维砂浆抹灰对砌体抗剪强度的影响

基于空心砖填充墙震害现象,对比分析了有砂浆抹面与无砂浆抹面填充墙的震害特征。试验测试了三种不同纤维类型、不同掺量下砂浆的抗压强度,分析了纤维类型和掺量对砂浆抗压强度的影响。完成了10组共计30个无抹面、普通砂浆抹面和纤维砂浆抹面的砌体通缝抗剪强度试验,研究纤维种类和掺量不同时,砌体沿通缝截面受剪的抗剪强度和破坏机理,并与无抹面、普通砂浆抹面的情况进行对比。研究表明,有无砂浆抹面对砌体通缝抗剪强度有影响;掺入合适数量纤维的砂浆抹面能显著提高砌体通缝抗剪强度,纤维掺入量过低时,反而会降低抗剪强度;砂浆中纤维的掺入可有效延缓砌体表面裂缝的形成并改善剪切破坏的延性,另外,对实现砌体裂后不倒也具有积极作用。     

动荷载下粉煤灰土冻融损伤特性试验

为研究粉煤灰土作为路基填料的动力特性,通过粉煤灰土冻融循环后的动三轴试验,得出了动强度与冻融循环次数的关系,动模量与冻融循环次数的关系及动模量损伤数学模型,与试验对比结果表明:冻融循环次数与初始动模量预测粉煤灰土路基的动力性能指标的变化,模型具有较高的精度.有助于评估冻融循环对粉煤灰土路基使用寿命的影响.     

Behavior of high water-cement ratio concrete under biaxial compression after freeze-thaw cycles

The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of a=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results, Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.     

Effect of freeze-thaw cycles on bond strength between steel bars and concrete

The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.     

冻融循环下粉质黏土的动力损失模型

通过冻融循环后的粉质黏土的动三轴试验,研究了粉质黏土作为路基填料的动力特性,得出了动强度和循环荷载次数及冻融循环次数的数量关系和动模量与冻融循环次数的关系曲线。建立了动模量损失模型,能够预测每一次冻融循环后的动强度和最大动模量。通过与试验对比可知,预测模型具有较高的精度,可以用来评估冻融循环对粉质黏土路基使用寿命的影响。     

Deterioration mechanism of sulfate attack on concrete under freeze-thaw cycles

The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.     

冻融循环对粉煤灰土动强度的影响

根据粉煤灰土和粉质黏土经过冻融循环后动强度的对比试验,对粉煤灰土和粉质黏土的动强度做出了定量分析。试验发现,冻融循环影响粉煤灰土的强度特性,经过1次冻融循环后,粉煤灰土的强度明显降低,但是粉煤灰土的动强度下降率低于粉质黏土的下降率。随着冻融循环次数的增加,粉煤灰土的动强度逐渐衰减,经历4~5次冻融循环的粉煤灰土的动剪强度趋于稳定,且高于粉质黏土,在季节性冻土地区可以减轻公路的冻害。     

初始损伤–载荷–冻融作用下红砂岩的孔隙结构及力学特性

中国寒区的岩体支护、边坡开挖等工程需要深刻认知、准确评估载荷和冻融诱发岩体的损伤情况,尤其是裂隙岩体的损伤。研究采用核磁共振技术测试含单裂隙红砂岩试样在初始、力学循环加载后、冻融循环后三个阶段的孔隙度、T2谱分布等微观孔隙参数,随后测试损伤后试样的力学参数,以量化、评估力学循环加载、冻融循环对试样孔隙参数及力学性质的影响。试验结果表明,荷载和冻融先后作用下不同试样的孔隙结构和力学性质有相似的变化规律。试样随着力学循环加载其孔隙度不断增大,随着冻融循环作用其孔隙度继续增大。循环载荷作用促使试样孔隙度的增大以原有孔隙扩展为主,冻融循环作用促使试样孔隙度的增大以新增小孔隙和原有孔隙扩展为主。载荷、冻融都将导致试样强度、弹性模量的损伤,单一冻融作用下红砂岩试样强度损伤在5%-10%,但载荷、冻融先后作用下试样强度损伤达到20%-30%,试样的初始强度越小其强度损伤越大。分析试样的微观孔隙和宏观力学之间的相关性,发现损伤试样的孔隙度增幅与试样的强度降幅呈正相关。     

Concrete damage and neutralization under coupling effect of carbonation and freeze-thaw cycles

Simulating the coupling effect brought by freeze-thaw and carbonation environment,we experimentally investigated concrete durability,the variation characteristics of both concrete dynamic elastic modulus,and its neutralization depth.The influences imposed by carbonation on the freeze-thaw damage of concrete was studied as well and vise versa so as to shed light on the influencing mechanism together with the mutual interaction between them.The experimental results show that the damage caused by the coupling effect of freeze-thaw and carbonation on concrete is severer than any single effect of them two could bring.This provides certain theoretical references and paves down foundations for the further study in concrete durability related by the coupling environmental effect.     

冻融环境下混凝土的断裂损伤试验研究

为研究冻融作用后混凝土的断裂性能及断裂特征,依据GBJ82-85混凝土快速冻融循环试验方法,对24组共72块混凝土试件进行冻融试验.采用四点弯曲试验法分析了300次快速冻融循环条件下水灰比、引气剂对混凝土断裂韧度,断裂能及相对动弹模损失率的影响,并进行了混凝土形貌分析.结果表明,随冻融循环次数的增加,混凝土的断裂韧度、断裂能及相对动弹模损失率呈明显下降趋势,水灰比越大、混凝土随冻融循环次数增加损伤程度越大.引气剂能够大幅度降低由于冻融循环造成的混凝土结构的损伤,断裂能损失率与相对动弹模损失率之间具有良好的线性关系.