Effect of rubber particles on cement stabilized gravel system

The primary objective of this paper was to study the mechanical properties and durability of the cement stabilized gravel by different compact method. The influence of rubber particle content on mechanical properties of samples was studied by compaction tests and freezing thawing recycle tests. Pore structure and fractal characteristic of mixture were analyzed quantitatively using mercury intrusion porosimetry （MIP）. X-ray diffraction （XRD） was adopted to identify the composition phases. The morphology analysis in micro scale and elemental analysis of samples were carried out by scanning electron microscope （SEM）. The optimum compressive strengths of rubber cement stabilized gravel （RCSG） with static compaction method and with vibratory compaction method were obtained by controlling compaction degree and vibration time, respectively. From the compaction tests, the vibratory compaction method is preferred compared with the static compaction method as better compressive strength can be improved by about 340%-360%. Besides, test results also reveal that compressive strength of samples with vibratory compaction method or static compaction method will decrease with the rubber particle bulk content increasing. The freezing thawing recycle tests indicate that freezing thawing resistance has been improved （frozen stability coefficient K has been increased from 0.89 to 0.97） by the addition of rubber particles. MIP tests show that the mean pore diameter and porosity of mixture have been increased from 70 to 250 nm and 9% to 24% respectively, with the rubber particles content increasing. Component analysis shows that the calcium silicate hydrate （CSH） is the predominant hydrate product with or without the addition of rubber particles.     

Residual Capacity of Friction-Type High-Strength Bolted T-stub Connection with Nut Corrosion Damage

Corrosion is a primary cause of the slippage of friction-type high-strength bolted(FHSB) T-stub connections. This paper attempts to quantify the residual capacity of FHSB T-stub connections with corroded nuts. Firstly, corrosion simulation tests were conducted on 48 manually cut nuts to find out the relationship between the damage degree of nut section and the residual clamping force(RCF) of bolt. Then, static load tests were carried out on 24 FHSB T-stub connections with nuts of different degre...     

Shear behaviour of a rock bridge sandwiched between incipient joints under the influence of hydraulic pressures

The rock bridges sandwiched in incipiently jointed rock mass were considered as barriers that block the fluid seepage, and provide certain shear strength reservation. For better revealing the influence of hydraulic pressure on the failure behaviour of rock bridges, direct shear tests were carried out through a newly proposed method on rock samples that contain two parallel incipient joints. By developing the gypsum-silicone pad coupling samples, a conventional triaxial test system was qualified ...     

Application of retardation time spectra of asphalt

To improve the performance of asphalt pavement, the dynamic and static tests of asphalt were used to measure its viscoelastic properties under different time. Based on the obtained data of static creep compliances and dynamic compliances according to the static creep test and dynamic test of asphalt using the dynamic shear rheometer, the discrete retardation time spectra were attained using the non-linear regression method. All viscoelastic functions are mathematically equivalent and belong to the same retardation time spectra, so the dynamic compliances of asphalt were converted to the static creep compliance using the retardation time spectra. Good correlations were found between calculation results and measurement results. In accordance to these findings, the retardation time spectra can accurately transform static and dynamic viscoelastic functions. Therefore, we can obtain viscoelastic properties over much larger time or frequency region than measurement results.     

Experimental investigation on strength and deformation of plain high-strength concrete under multiaxial stress state

To investigate the strength and deformation behavior of plain high-strength concrete (HSC) under multiaxial stress states,a large static-dynamic true triaxial machine was employed,and multiaxial tests were performed on 100 mm×100 mm×100 mm cubes concrete specimens.Friction-reducing pads were three-layer plastic membranes with glycerine in-between for the compressive loading plane.The tensile loading plane of concrete samples was processed by attrition machine,and then the samples were glued up with the loading plate with structural glue.Failure modes of specimens were described.The principal static compressive strengths,strains at the peak stress and stress-strain curves were measured,and the influence of stress ratios on them was analyzed as well.Experimental results show that the ratio of the compressive strength σ3f over the uniaxial compressive strength fc depends on brittleness-stiffness of concrete besides stress state and stress ratios.The formula of Kupfer-Gerstle’s and Ottosen’s failure criterion for plain HSC under biaxial compression and multiaxial stress state is proposed respectively.     

Spontaneous combustion liability between coal seams: A thermogravimetric study

The spontaneous combustion liability of coal can be determined by using different experimental techniques. These techniques are well-known in their application, but no certain test method has become a standard to prove the reliability of all of them. A general characterisation which included proximate and ultimate analyses, petrographic properties and spontaneous combustion tests(thermogravimetric analysis(TGA) and the Wits-Ehac tests) were conducted on fourteen coal and four coal-shale samples.The spontaneous combustion liability of these samples collected between coal seams(above and below)were predicted using the TGA and the Wits-Ehac tests. Six different heating rates(3, 6, 9, 15, 20 and 25 °C/min) were selected based on the deviation coefficient to obtain different derivative slopes and a liability index termed the TG_(spc) index. This study found that coal and coal-shale undergo spontaneous combustion between coal seams when exposed to oxygen in the air. Their intrinsic properties and proneness towards spontaneous combustion differ considerably from one seam to the other. The Wits-Ehac test results agreed with the TG_(spc) results to a certain extent and revealed the incidents of spontaneous combustion in the coal mines.     

Rheological properties of asphalt modified by supramolecular UV resistant material-LDHs

Dynamic rheological properties of asphalt modified by Supramolecular UV resistant material-layered double hydroxides(LDHs) was studied by means of the dynamic shear rheometer(DSR) test.Two typical base asphalts were chosen and modified by 2 different LDHs contents.DSR tests were performed on the original samples,samples after exposed to outdoor and samples after the artificial accelerated UV aging tests respectively to analyze the rheological properties.It is found that when the LDHs content is between 3wt% and 5wt% of asphalt weight,the high temperature performance and fatigue resistant property of the modified asphalt become better,the UV aging resistance properties are improved.     

Mechanical Performances and Morphology of LDPE/UHMWPE Single-Polymer Composites Produced by Extrusion-Calendering Method

Extrusion-calendering method was developed to prepare single-polymer composites(SPCs) of ultrahigh molecular weight polyethylene( UHMWPE) fabric reinforcing low density polyethylene(LDPE).Differential scanning calorimeter(DSC) experiments were executed to determine the setup of extrusion temperature.Effects of the die temperature on the tensile and interfacial performances of SPCs were studied through the tensile and T-peel tests,respectively. The results showed that both tensile strength and modulus increased initially and decreased afterwards as the temperature increased. The peak values of tensile strength and modulus of PE SPCs,which are 10. 8 and 3. 5 times as high as those of the unreinforced LDPE respectively,were obtained at 150 ℃. Higher temperatures also give a positive effect on peel strength. Scanning electron microscopy( SEM) and camera were also used to observe the morphology of the SPCs samples.     

Mechanical Performances and Morphology of LDPE/UHMWPE Single-Polymer Composites Produced by Extrusion-Calendering Method

Extrusion-calendering method was developed to prepare single-polymer composites (SPCs) of ultra-high molecular weight polyethylene (UHMWPE) fabric reinforcing low density polyethylene (LDPE).Differential scanning calorimeter (DSC) experiments were executed to determine the setup of extrusion temperature.Effects of the die temperature on the tensile and interfacial performances of SPCs were studied through the tensile and T-peel tests,respectively.The results showed that both tensile strength and modulus increased initially and decreased afterwards as the temperature increased.The peak values of tensile strength and modulus of PE SPCs,which are 10.8 and 3.5 times as high as those of the unreinforced LDPE respectively,were obtained at 150 ℃.Higher temperatures also give a positive effect on peel strength.Scanning electron microscopy (SEM) and camera were also used to observe the morphology of the SPCs samples.     

Fracturing behavior of brittle solids containing 3D internal crack of different depths under ultrasonic fracturingOA

Ultrasonic fracturing(UF) can be used to form crack networks for oil or gas in the mining industry and hard rock excavation. In this paper, the three-dimensional internal laser-engraved crack method(3D-ILC) is introduced to make penny-shaped internal crack within the samples without any damage to the surfaces. Physical experiments were performed on the transparent samples with internal cracks at different depths. The macro-and micro-fracture fractography characteristics were focused on and analy...     

Dynamic tensile behaviour and crack propagation of coal under coupled static-dynamic loading

The fracture behaviour and crack propagation features of coal under coupled static-dynamic loading conditions are important when evaluating the dynamic failure of coal. In this study, coupled static-dynamic loading tests are conducted on Brazilian disc(BD) coal specimens using a modified split Hopkinson pressure bar(SHPB). The effects of the static axial pre-stress and loading rate on the dynamic tensile strength and crack propagation characteristics of BD coal specimens are studied. The average dynamic indirect tensile strength of coal specimens increases first and then decreases with the static axial pre-stress increasing. When no static axial pre-stress is applied, or the static axial pre-stress is 30% of the static tensile strength, the dynamic indirect tensile strength of coal specimens shows an increase trend as the loading rate increases. When the static axial pre-stress is 60% of the static tensile strength, the dynamic indirect tensile strength shows a fluctuant trend as the loading rate increases. According to the crack propagation process of coal specimens recorded by high-speed camera, the impact velocity influences the mode of crack propagation, while the static axial pre-stress influences the direction of crack propagation. The failure of coal specimens is a coupled tensile-shear failure under high impact velocity.When there is no static axial pre-stress, tensile cracks occur in the vertical loading direction. When the static axial pre-stress is applied, the number of cracks perpendicular to the loading direction decreases,and more cracks occur in the parallel loading direction.     

两种不同大理岩SHPB动态劈裂实验

利用SHPB试验系统,结合高速摄影技术,研究了冬瓜山铜矿深部采集的两种不同大理岩在动态劈裂下的应变率和强度、破坏应变之间的关系。实验数据表明,应变率对试样抗拉强度的影响较为显著,两种大理岩的动态抗拉强度随着应变率的增加而增大;灰色大理岩当应变率小于50s-1时,随着应变率的增加,动态拉伸强度敏感系数变化较大,当应变率大于50s-1时,动态拉伸强度敏感系数则变化不大,而白色大理岩则是在应变率大于120s-1后;随着应变率的增加,试样的破坏应变也随之增加。     

CFRC抗弯试件的灵敏度

对CFRC抗弯试件进行了试验分析,探讨了不同载荷工况下CFRC抗弯试件的电阻变化规律。结果表明:CFRC抗弯试件上层电阻随载荷的增加先减小后增大,下层电阻随载荷的增加而增大;在重复载荷作用下,CFRC抗弯试件受拉区电阻不断增大,受压区电阻先减小后增大,残余电阻的存在反映了试件内部存在损伤和损伤积累;在交变载荷作用下,碳纤维混凝土试件的电阻随着载荷周期次数的增加而增大,直至破坏;试件电极形式不同,电阻变化规律也不同。     

单轴循环冲击下花岗岩力学特性与损伤演化机理

为研究循环冲击荷载下黑云母花岗岩的动态力学特性,利用改进的分离式霍普金森压杆,选取4种不同的入射波应力幅值对花岗岩试样进行等幅循环冲击,并对相关机理和试验现象进行探析.结果表明:入射波应力幅值为110.57和90.48 MPa时,随着冲击次数的增加,岩样的峰值应力逐渐降低,最大应变、平均应变率和损伤值均呈现增大趋势;入射波应力幅值为70.82 MPa时,花岗岩的峰值应力随着冲击次数的增加表现出先增强后降低的特性,而最大应变、平均应变率与损伤值则表现出相反规律;入射波应力幅值降为50.69 MPa时,岩样的力学性质基本不变,岩样未见明显的损伤.此外,研究还发现基于岩样静态压缩应力-应变曲线推求的静态裂纹起裂应力,经强度增长比例系数放大后可得到动态裂纹起裂应力,籍此能较好地解释上述循环冲击试验中所观测到的现象.     

Mechanical properties of deep-buried marble material under loading and unloading tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show: in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hoek-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.     

局部静载约束条件下动力扰动对煤岩损伤的影响

为得到局部静载约束条件下循环冲击荷载对煤岩损伤的影响特征,基于自行研制的约束式摆锤冲击动力加载装置研究局部静载约束条件下原煤试样分别受到恒定冲量循环冲击和递增冲量循环冲击过程中损伤因子和表面裂纹的演化规律。结果表明：当约束区处于弹性状态时,约束面积越大的分区抗冲击能力越强,当约束区处于塑性状态时,约束面积越大的分区抗冲击能力越差;递增冲量循环冲击对煤岩的致损效率高于恒定冲量循环冲击,两种冲击方式破岩效率的差异主要体现在静载约束区,并且静载值越大,损伤因子对冲击方式的敏感度越高;煤岩表面的裂纹扩展与损伤因子的分区特征较为一致,当约束区处于弹性状态时,静载约束对裂纹的扩展起到抑制作用,裂纹主要沿着约束面积较小的区域扩展、衍生;当约束区处于塑性状态时,裂纹主要在约束面积较大的区域扩展,并且约束区内主要以竖直方向的拉伸裂纹为主,而非约束区内的裂纹主要沿倾斜方向扩展;随着静载值增加,试样表面裂纹的分形维数先减小后增加。局部静载约束可以提高煤岩抗冲击能力,并且煤岩损伤演化呈明显的分区特征。     

大理岩抗拉强度的离散性及与厚度的关系

大理岩劈裂抗拉强度具有较大的离散性,并受非均质性、劈裂形式及尺寸效应等多种因素影响.采用钢丝垫条形式的大理岩劈裂抗拉强度离散度小于采用钢平板形式的离散度;大理岩劈裂抗拉强度值越高,其离散度越小;采用钢丝垫条形式的劈裂抗拉强度在总趋势上随厚度的增加先增加后减小;而采用平板形式的劈裂抗拉强度随厚度的增加而减小.     

冲击载荷下脆性岩板损伤断裂演化的实验模拟研究

在矿山运输系统中,井壁围岩冲击损伤破坏对经济和安全效益的影响是至关重要的,因为动态冲击载荷对井壁围岩和支护结构会产生严重的削弱破坏作用,室内研究表明,岩石样品如岩板在动态载荷的冲击作用下会失效。为研究在低速冲击载荷作用下,脆性岩石损伤断裂的演化过程,利用分离式霍普金森压杆(SHPB)装置中压缩气体发射球体子弹对脆性岩板进行变角度冲击损伤实验,岩板受到冲击后,边缘出现凹坑,表面裂纹从撞击凹坑直达岩板边缘,实验中样品的表面裂纹能有效代表试样内部的开裂状况,能有效反映冲击能量的耗散、破裂区面积与裂纹表面积随入射能量呈非线性增长趋势,同时与入射角度相关,但当破裂区面积急剧下降时,裂纹表面积反而急剧上升,表明裂纹的发生发展有明显的孕育期,在入射能量达到临界值前,主要表现为裂纹孕育增长,在达到临界值后,发生宏观断裂破坏,裂纹面积呈负增长,破裂区面积增大。实验结果分析表明在实际工程中,围岩和支护结构的抗冲击的最优化设计角度范围在15°～30°。     

冲击荷载下的新浇混凝土损伤特性及强度试验研究

以新浇混凝土养护过程会受到各类工程振动的作用与影响为工程背景,结合静载试验与冲击动载试验,得出冲击荷载影响下新浇混凝土的强度随龄期的变化规律。通过基于Weibull分布的统计损伤模型得出混凝土关于龄期的动态损伤本构模型。采用SHPB压杆装置进行混凝土试件破坏试验,得出在混凝土不同龄期的冲击动载下,混凝土抗压强度与静载下抗压强度的比值均为2:1左右;随着龄期的增长,混凝土试件受冲击破坏的破碎程度越来越小。采用SHPB压杆装置对不同龄期的混凝土做加载损伤试验,得出了冲击荷载下混凝土最薄弱龄期区段及其强度降低率达到峰值的龄期。     

动态时效对Al-Cu-Mg-Ag合金组织与力学性能的影响

对Al-Cu-Mg-Ag新型耐热铝合金进行预时效+中温轧制变形+终时效的动态时效工艺处理,采用硬度测试、拉伸性能测试,结合金相显微组织分析和透射电子显微分析,探究动态时效对其力学性能与微观组织的影响。结果表明：动态时效能够提高合金的时效硬化速率,随着变形量的增大,合金的峰时效时间逐渐减小,峰值硬度逐渐增大。动态时效能够改变晶粒形貌,随着变形量的增大,晶粒的纵横比增大,位错数量增多,强化相数量增多尺寸减小,使得合金强度随着变形量的增大而逐渐增大,但伸长率逐渐减小。变形量为50%合金的强度最高,抗拉强度和屈服强度最大,分别为527.4 MPa和467.0 MPa,伸长率保持在较高值9.1%。