混杂纤维混凝土力学性能研究

混杂纤维混凝土是以普通混凝土为基体掺入两种或多种不同性质的纤维以获得某些优异性能的一种复合材料。混杂纤维混凝土相比普通混凝土具有极高的抗拉、抗弯强度,良好的耐久性、耐磨性、抗冻融性等,因而引起了广大工程界人士的极大关注,成为土木工程界新兴的研究热点。本文通过一系列试验研究了钢纤维和聚丙烯纤维的不同组合及不同掺量与各种强度性能的关系,综合考察混杂纤维混凝土强度性能的各种影响因素,从而总结出混杂纤维混凝土的增强效应规律。     

混凝土轨枕企业发展与转型研究

针对混凝土轨枕企业发展存在的经济结构单一、原材料枯竭、设备老化、技术力量薄弱等制约因素进行了研究,结合当前我国铁路路网建设向西部地区倾斜的形势,指出转变混凝土轨枕生产模式,加强技术创新与全程质量监控,依托地理位置优势发展物流产业,实现企业转型升级,是混凝土轨枕企业缓解发展压力,适应今后生存发展与市场挑战的必然要求和明智举措。     

Impact fatigue responses of pre-stressed concrete sleepers in railway track systems

Pre-stressed concrete sleepers are the main components of railway track systems. To carry and transfer the dynamic wheel loads from the rails to the ground, their current design and construction are limited by allowable flexural stress constraints under service conditions. In current design practice for such a component, the dynamic load effects due to wheel/rail interactions are treated as a quasi-static load using a dynamic impact factor. Then, the allowable stresses eliminate a crack initiation. In reality, the impact events are frequently recorded because of the uncertainties of wheel or rail irregularities such as flat wheels and dipped rails. These effects cause cracking in the concrete sleepers, resulting in excessive maintenance. Limit states design philosophy for the pre-stressed concrete sleepers, containing ultimate and fatigue limit states, has been recently proposed based on structural reliability concept to rationalise the design method and minimise the maintenance. On the basis of probabilistic approach, the high-magnitude low-cycle fatigue limit states, which are more significant in terms of damage evolution, have been addressed in this article. Series of repeated impact tests for the in-situ pre-stressed concrete sleepers were carried out using the Australian largest high-capacity drop weight impact testing machine at the University of Wollongong. The impact forces have been simulated in relation to the probabilistic track force distribution obtained from a heavy haul rail network. This article focuses on the impact responses of the cumulatively damaged sleepers. The effects on such responses of the track environments including soft and hard track supports are also highlighted in this article. It is found that a concrete sleeper damaged by the impact fatigue cycles could possess significant reserve capacity for resisting the axle load in a similar manner as the undamaged sleeper.     

Experimental and parametrical investigation of pre-stressed ultrahigh-performance fiber-reinforced concrete railway sleepers

In this study, ultrahigh-performance fiber-reinforced concrete (UHPFRC) used in a type B70 concrete sleeper is investigated experimentally and parametrically. The main parameters investigated are the steel fiber volume fractions (0%, 0.5%, 1%, and 1.5%). Under European standards, 35 UHPFRC sleepers are subjected to static bending tests at the center and rail seat sections, and the screw on the fastening system is pulled out. The first cracking load, failure load, failure mode, crack propagation, load–deflection curve, load–crack width, and failure load from these tests are measured and compared with those of a control sleeper manufactured using normal concrete C50. The accuracy of the parametric study is verified experimentally. Subsequently, the results of the study are applied to UHPFRC sleepers with different concrete volumes to investigate the effects of the properties of UHPFRC on their performance. Experimental and parametric study results show that the behavior of UHPFRC sleepers improves significantly when the amount of steel fiber in the mix is increased. Sleepers manufactured using UHPFRC with a steel fiber volume fraction of 1% and a concrete volume less than 25% that of standard sleeper B70 can be used under the same loads and requirements, which contributes positively to the cost and surrounding environment.     

高速铁路双块式轨枕制造关键技术研究

系统介绍了基于德国双块式无碴轨道制造技术基础上的CRTSⅡ双块式轨枕制造技术的工艺流程,各施工工序的关键技术参数和操作注意事项,结合具体工程实践阐述了JCRTSⅡ双块式轨枕制造技术的优点,以期促进该技术的应用和推广。     

玄武岩纤维混凝土基本力学性能试验研究

采用短切浸胶玄武岩纤维,按0、1、2、3、4、5 kg/m3等不同纤维掺量制作玄武岩纤维混凝土试件,进行了抗压强度、劈裂强度和抗折强度试验,研究了不同掺量与强度之间的关系。当纤维掺量为4 kg/m3,抗压强度提高率为46.3%;当纤维掺量为3 kg/m3,劈裂强度提高率为27.3%,抗折强度提高率为25.0%。试验结果表明,掺加玄武岩纤维后混凝土抗压强度、劈裂强度和抗折强度提高较明显。     

钢纤维轻骨料混凝土力学性能的试验研究

将钢纤维掺入轻骨料(人造膨胀珍珠岩)混凝土成为钢纤维轻骨料混凝土,它集中了钢纤维混凝土和轻骨料混凝土的优点,弥补了普通混凝土存在的抗拉强度低和自重大等不足。本文对这种新型混凝土材料的力学性能开展初步研究,针对试验中得到的钢纤维轻骨料混凝土的立方体抗压强度、劈拉强度、抗折强度、轴心抗压强度和弹性模量等进行讨论,分析钢纤维体积率的变化对钢纤维轻骨料混凝土力学性能的影响,给出相应的计算表达式,以利于其在工程实践中的推广和应用。试验结果表明,采用轻骨料和加入钢纤维后,混凝土的强度和变形等力学性能的改善效果十分明显。     

钢纤维增强聚合物改性混凝土力学性能的研究

在对钢纤维增强聚合物改性混凝土力学试验的基础上,对不同聚合物掺量对钢纤维混凝土的改善作用进行了比较,并对其机理进行了分析,以提高混凝土的抗拉、抗折强度及承载力。     

钢结构装配式住宅用陶粒混凝土轻质板材力学性能研究

针对钢结构装配式住宅使用的陶粒混凝土轻质板材存在开裂,抗折强度偏低的问题,采用正交试验设计方法研究了水胶比、陶粒、粉煤灰和聚炳烯纤维四个不同的因素对陶粒混凝土板材力学性能的影响。试验结果表明,纤维的掺量是影响陶粒混凝土板材力学性能的最主要因素,纤维掺入后有效的提高了陶粒混凝土板材的抗折强度和抗压强度,陶粒混凝土板材的最优试验方案为水胶比为0.35,粉煤灰掺量为30%,陶粒和聚丙烯纤维掺量分别为530 kgm3和0.5 kgm3,满足了工程要求。     

钢纤维粉煤灰混凝土力学性能试验与分析(Ⅰ)

分别进行了掺入钢纤维、粉煤灰及两种混杂对混凝土抗压性能、抗拉性能增强效果的试验研究.讨论了钢纤维掺量、粉煤灰掺量对混凝土抗压、抗拉性能的影响.试验结果表明:在保证其强度、耐久性、节约材料、降低造价的同时,确定了钢纤维粉煤灰混凝土中合理的钢纤维和粉煤灰掺量;同时表明,钢纤维的掺入对混凝土的强度和变形有明显的改善效果.     

Finite element modelling and field validation of prestressed concrete sleepers and fastening systems

Prestressed concrete sleepers and elastic fastening systems have been widely applied in North America to accommodate increased freight axle loading and the development of high-speed passenger rail systems. However, the design standard of the American Railway Engineering and Maintenance-of-Way Association remains unclear about the relationship between some critical design parameters and the vertical and lateral load paths through the track structure. In this study, field experimentation is conducted at the Transportation Technology Center in Pueblo, CO, and the test data are compared with finite element (FE) models of the track structure for model validation. Strain gauges and potentiometers are installed in the field to measure the response of concrete sleepers and fastening systems. The FE models consist of two parts: a detailed single-sleeper model to capture the local response of the loaded rail seat, and a global multi-sleeper model to provide realistic boundary conditions for the detailed model. The bond–slip behaviour between concrete and prestressing wires, and inelastic material properties are incorporated in the FE models. Good agreement is observed between the test measurement and the model output. The validated FE model is used for parametric studies on the some critical design parameters, and conclusions about the load path through the sleepers and fastening systems are summarised.     

Probabilistic models for mechanical properties of concrete,reinforcing steel and pre-stressing steel

This paper presents probabilistic models for mechanical properties of pre-cast and cast-on-site concrete as well as of reinforcing and pre-stressing steel. An extended review of models available in the literature is made and new probabilistic models are developed based on a significant amount of data collected by the authors. New probabilistic models are proposed for concrete ultimate strength (separately for precast and cast-in-place concretes), for yield and ultimate strength of reinforcing steel and for proportionality limit and ultimate strength of pre-stressing steel. The new models account for a recent improvement of production and are more appropriate for the probabilistic assessment of modern concrete structures then the models available in the literature.     

中低强度混凝土动态弯拉特性的试验研究

本文采用MTS试验机对C35和C40两种强度的混凝土进行了动态弯拉试验,应变速率分别为10—6／s、10—5／s和10—4／s。试验中以10—6／s速率下得到的数据作为拟静态状态,并以此作为其它速率下得到实验数据的对比依据。实验结果表明：随着应变速率的增加两种强度混凝土的弯拉强度有明显增加的趋势;两种强度混凝土的弯拉峰值应变随着应变速率的增加而提高。     

钢纤维混凝土的弯拉强度模型

利用已有试验数据,得到钢纤维混凝土弯拉强度与抗拉强度的相互关系,再参考单向短纤维复合材料强度模型,得到钢纤维混凝土弯拉强度的理论公式,经验证,理论结果与试验数据吻合较好.     

Incremental collapse threshold for pushout resistance of circular concrete filled steel tubular columns

This paper presents the results of a series of pushout tests using static loading (SL) and variable repeated loading (VRL) on concrete filled steel tubular (CFT) circular stub columns. The main parameters examined in this paper were the strength and age of concrete and the loading protocol. Under SL tests, the interface bond strength in CFT columns filled with normal strength concrete was found to be higher than that with high strength concrete. The SL test results showed that the interface bond strength varied from 0.41 to 0.85 MPa but from 0.33 to 0.66 MPa under VRL tests. A lower bound for the incremental collapse threshold of the pushout resistance of 70% of the static collapse load was empirically derived. Also an expression of the average growth of slip per loading cycle was empirically derived and recommended for design purposes. A comparison between the bond strength of the columns obtained from the present and previous test results, and available design codes is presented. Two newly derived bond strength limits were experimentally obtained and proposed for the design of structures subjected to either predominantly static or predominantly cyclic loading.     

再生混凝土基本力学性能试验研究

设计并完成了再生粗骨料已使用年限分别为0、10、40年和取代率分别为0、30%、50%、70%、100%的C30级再生混凝土的立方体抗压强度、劈裂抗拉强度和抗折强度相关试验,并以天然骨料混凝土作为基准进行对比分析.试验结果表明:再生混凝土立方体抗压强度、劈裂抗拉强度和抗折强度破坏过程和破坏形态与普通混凝土基本一致,在水灰比相同的情况下,再生混凝土立方体抗压强度高于普通混凝土,劈裂抗拉强度低于普通混凝土,抗折强度基本接近普通混凝土;另外,还表明再生粗骨料的寿命对再生混凝土强度有一定影响.     

RPC混凝土力学性能的试验研究

以抗折强度和抗压强度为指标,研究活性混合材、钢纤维掺量、粗细集料类别及养护方式对RPC混凝土抗折强度和抗压强度的变化情况。结果表明,当硅灰和粉煤灰掺量相等时,RPC混凝土拌合物流动性好,抗压强度和抗折强度最高,分别达到124.2MPa和19.2MPa。钢纤维掺量的增加可有效提高RPC的抗折强度和抗压强度,但RPC混凝土抗压强度提高的幅度小于抗折强度。钢纤维体积掺量在1.0%-2.0%之间较合适。通过三种不同的养护制度发现,采用标准养护方式时,抗压强度值最小,采用高温养护方式时,抗压强度值最大,热水养护的抗压强度值介于二者之间。     

外掺钢纤维混凝土早期力学性能的试验研究

为研究外掺钢纤维对混凝土早期力学性能的影响,以不同钢纤维掺量和时间龄期为变化参数,设计了168个外掺钢纤维混凝土棱柱体试块进行早龄期轴心抗压强度及弹性模量试验。试验观察了试件的破坏过程及形态,获取了不同时间龄期外掺钢纤维混凝土的强度及弹性模量等关键特征参数,揭示了不同外掺钢纤维掺量对混凝土早龄期强度及弹性模量的影响规律,并推导出不同时间龄期外掺钢纤维混凝土强度和弹性模量的计算式,研究结果表明:外掺钢纤维对混凝土早期弹性模量的有所提高,对混凝土早期轴心抗压强度的提高不显著。当外掺钢纤维≥40 kg/m3时,可有效提高3、28 d龄期混凝土的弹性模量,因此,建议外掺钢纤维量应大于40 kg/m3。     

预应力钢纤维混凝土板弯曲试验研究

通过设计制作加载装置和位移传感器对三种不同钢纤维掺量(0、1%、2%)的预应力钢纤维混凝土板进行了弯曲试验研究,得到了弯曲过程中预应力钢纤维混凝土板跨中的荷载-挠度曲线,揭示了预应力钢纤维混凝土板的跨中挠度在弯曲加载过程中呈现三阶段变化,并且钢纤维的加入有助于提高板的弯曲韧性,通过等效截面法计算得出了不同钢纤维掺量板的抗弯强度.     

珍珠岩掺合料混凝土轨枕制备研究

通过试验测试研究珍珠岩矿物掺合料及其对混凝土主要性能的影响，在混凝土中珍珠岩掺合料替代水泥10％～20％可不同程度地改善工作性能，提高后期强度。该掺合料替代水泥20％制备C60混凝土铁道Ⅲ型轨枕的试验及其检测结果显示其主要性能指标均有所提高。