浅析钢纤维喷射混凝土在防护工程中的应用

本文通过对普通喷射混凝土与钢纤维喷射混凝土的对比分析，介绍了一种新型复合材料的优越性，由此阐述了钢纤维喷射混凝土在防护工程中的应用价值及适用范围，并对钢纤维喷射混凝土在施工中应注意的几个具体问题作了剖析，以供工程技术人员在实际施工中作参考。     

浅谈砼冻融性破坏机理和抗冻措施

混凝土在饱水状态下冻融循环产生的破坏作用称为冻融破坏。水在混凝土毛细}L中结冰造成冻胀开裂使混凝土弹性模量、抗压强度、抗拉强度等力学性能严重下降,危害结构物的安全。一般混凝土的冻融破坏,在其表面都可以看到裂缝和剥落。本文从混凝土的相关变化以及冻融破坏产生的原因出发,分析了影响混凝土抗冻性能的种种因素,以及改善混凝土抗冻性的措施。     

纤维混凝土抗冻性能研究

为研究冻融循环条件下纤维混凝土抗冻性能,采取快速冻融试验对不同掺加方式下钢纤维、聚丙烯纤维混凝土性能进行研究。并通过SEM分析了其微观结构。试验结果表明,在纤维掺量固定时,不同纤维掺加方式的混凝土性能有显著不同。随冻融循环次数的增加,其质量损失、动弹性模量、抗压、抗折强度都有显著不同变化,混杂纤维混凝土性能较单一纤维混凝土好,层布式纤维混凝土性能较整体式纤维混凝土好。     

合成纤维混凝土抗冻性与抗渗性的试验研究

文章通过对粗、细合成纤维,不同纤维体积率掺量的合成纤维混凝土试件,进行抗冻性能与抗渗性能的试验研究,获得了合成纤维混凝土抗冻性与抗渗性的有关数据,有助于加强对合成纤维混凝土耐久性的认识,为能找到一种相对性能较好的混凝土材料应用于桥梁加固,提供参考。     

水工抗冻混凝土施工问题探讨

本文分析了混凝土冻融破坏的机理和影响混凝土抗冻性能的因素,并对冻融破坏防治措施进行分析,供大家参考。     

钢纤维橡胶再生混凝土的抗冻性试验

为使废弃混凝土和再生橡胶在北方地区混凝土工程中得以应用,采用正交试验法研究再生粗骨料掺量、再生粗骨料强化方式、钢纤维掺量与橡胶掺量对钢纤维橡胶再生混凝土(C45)立方体抗压强度和抗冻性的影响规律。利用扫描电镜和螺旋CT扫描技术研究了钢纤维橡胶再生混凝土的宏观和细观结构及其对抗冻性能的影响机理。结果表明:橡胶颗粒掺量是影响再生混凝土含气量、抗压强度和相对动弹模量的重要因素,再生粗骨料掺量是影响相对动弹模量和强度损失率的次要因素,钢纤维掺量对混凝土抗压强度增强作用较小,粗骨料强化方式对混凝土性能影响不大;橡胶颗粒与砂浆界面的裂缝宽度在5~55μm之间,二者之间的相容性较差;当橡胶颗粒掺量(与砂的体积比)大于20%后,随橡胶颗粒掺量增大,混凝土内部孔洞数目增多,钢纤维橡胶再生混凝土抗压强度降低、抗冻性减弱。     

隧道工程中喷射混凝土运用探讨

本文分析了喷射混凝土在隧道工程中的作用,分析了喷射混凝土原材料要求.并对其施工过程中存在问题进行了探讨,供大家参考.     

浅谈码头方块抗冻性混凝土的试验技术

本文结合望海珍珠湾综合开发建设项目码头工程的方块施工,通过加入引气剂来提高混凝土的抗冻性,通过混凝土冻融破坏的分析和实际施工情况,提出了抗冻性混凝土原材料的选择和配合比的设计以及在施工管理方面控制的要点。     

隧道工程喷射混凝土施工质量控制分析

随着科学技术的发展,隧道施工技术也在超长、大跨度、防水、穿过不良地层等方面取得了长足的进步,涌现出了大量的科技成果,特别是作为新奥法施工工艺标志的锚喷构筑法更是如此,锚喷构筑法在技术上有速度较快、支护及时、施工安全;支护质量较好、强度高、密实度好、防水性能较好;省工,操作较简单,支护工作量减少;施工灵活性很大,可以根据需要分次喷射混凝土增加厚度,满足工程设计要求等优点,但在实际施工中有很多方面质量要点容易被忽视,从而影响了喷射混凝土施工质量。本文分析了喷射混凝土在隧道工程中的作用,对其施工过程中存在问题进行了探讨,供大家参考。     

粉煤灰对混凝土抗冻性能影响研究

本文通过对掺人粉煤灰在盐碱寒冷地区混凝土耐久性的研究,提高了混凝土的抗冻性,对以后粉煤灰在混凝土中的应用起到重要意义。     

多因素对再生混凝土力学性能及抗冻性的影响

为研究不同因素、不同水平对再生混凝土力学性能的作用。该文通过正交试验研究钢纤维掺量、再生粗骨料掺量和粉煤灰掺量对再生混凝土力学性能(抗压强度、劈裂抗拉强度和抗折强度)的影响,确定各因素对再生混凝土力学性能的影响程度,并加以量化表征,并提出多因素共同作用下再生混凝土力学性能的多元非线性回归模型且进行验证。在此基础上,该文进一步研究再生混凝土的抗冻性。结果表明:再生混凝土的力学性能随钢纤维掺量的增加而提高;随粉煤灰掺量增加而降低;再生粗骨料掺量对再生混凝土的力学性能影响较小。钢纤维的掺入可提高再生粗骨料的掺量。再生混凝土力学性能的实测值与通过建立的回归模型得到的计算值的最大误差在6.5%以内。此外,钢纤维的掺入和减少再生粗骨料的掺量均可以提高再生混凝土的抗冻性。     

Application of strain gradient plasticity theory to model Charpy impact energy of functionally graded steels using modified stress-strain curve data

Functionally graded ferritic and austenitic steels were produced through electroslag refining by setting the austenitic and carbon steels with appropriate thickness as electrode. Charpy impact energy of the specimen has been studied and modeled regarding the mechanism-based strain gradient plasticity theory. The hardness of each layer was related to the density of the dislocations of that layer and then by using a linear relation, the predicted hardness was related to its corresponding yield stress. Afterwards; by assuming Holloman relation for the corresponding stress-strain curves, tensile strengths and tensile strains of the constituent layer were determined via numerical method. By using load-displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress-strain curves from uniaxial tensile tests were modified. Charpy impact energy each layer was related to the corresponding area under modified stress-strain curve of that layer and finally by applying the rule of mixtures, Charpy impact energy of functionally graded steels was determined. The obtained results of the proposed model are in good agreement with the experimental ones.     

Cyclic stress-strain response during isothermal and thermomechanical fatigue

Isothermal high-temperature low-cycle fatigue and in-phase and out-of-phase thermomechanical fatigue tests were carried out on 316L austenitic stainless steel specimens controlled by computer. A non-linear kinematic hardening model with internal variables was used to simulate the cyclic stress-strain behaviour of isothermal fatigue. This model was modified by considering thermal cyclic effects in order to describe the cyclic stress-strain behaviour of thermomechanical fatigue (TMF) using only isothermal fatigue data and the material performance data. A very good approximation of the hysteresis loops was obtained by comparing with experiments of both in-phase and out-of-phase cases. The thermomechanical fatigue behaviour described by isothermal fatigue data gives the possibility of developing the TMF lifetime prediction technique.     

Simulation Charpy impact energy of functionally graded steels by modified stress-strain curve through mechanism-based strain gradient plasticity theory

In the present work, Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferritic or austenitic layers in both crack divider and crack arrester configurations has been modeled by finite element method. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and assuming by Holloman relation for the corresponding stress-strain curves, tensile strengths of the constituent layers were determined via numerical method. By using load-displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress-strain curves from uniaxial tensile tests were modified. The data used for each layer in finite element modeling were predicted modified stress-strain curves obtained from strain gradient plasticity theory. A relatively good agreement between experimental results and those obtained from simulation was observed.     

Investigation of stress-strain models for confined high strength concrete

The effects of confinement reinforcement on the behaviour of high strength concrete columns are investigated for which prismatic experimental specimens were prepared. In the experiment specimens, four longitude reinforcement and confinement reinforcement were used. For each experiment, stress-strain relationship of concrete was obtained and compared with models proposed earlier. The results show that confinement reinforcement improved the ductility of high strength concrete. The ascending branch of stress-strain curves depended on the ratio of confinement reinforcement was similar to the modified Kent-Park model and the descending branch similar to the Nagashima model.     

消泡剂和增稠剂复掺对模袋混凝土抗冻性的影响

为使模袋混凝土在大流动性下达到高抗冻性,应用正交试验法研究了含气量、消泡剂和增稠剂对混凝土工作性和抗冻性的影响.结果 表明,含气量和消泡剂掺量是影响模袋混凝土相对动弹性模量的显著因素,且含气量影响效果显著大于消泡剂掺量,增稠剂掺量对相对动弹性模量的提高幅度较小.消泡剂和增稠剂复掺能够达到协同改善模袋混凝土工作性、孔结构...     

Effect of low temperature thermocyling on the structure and stress-strain curve parameters of a TiAl alloy at 4.2 K

Transmission electron microscopy was used to study the features of the defect structure of the Ti-(3.5-5)%Al alloy induced by repeated thermocycling between 300 and 77 K and by low temperature plastic deformation at 4.2 K. The low temperature thermocycling combined with an applied stress brings about significant changes in the structural state of the alloy (dislocation density increase, redistribution of internal stresses, twinning difficulty), resulting in increasing strength and plasticity of the alloy at the liquid helium temperature.     

碳纤维单丝强伸实验的影响因素

碳纤维的脆性与高强使其强伸实验有别于柔性纺织纤维,为了得到更精确的试验结果,对试验中易于导致误差或错误的影响因素:纤维的倾斜、弯曲和紧绷等;粘结点的位置与粘结有效性;同轴夹持以及曲线校正等作了探讨.同时,为便于对碳纤维断裂端结构的原位对应分析,必须真实地保留纤维断面,相关试验及对断面保留影响的分析给出了较为理想的方法.     

圆高强钢管UHPC梁抗弯性能研究

为了研究三轴受压下UHPC的受力性能,以围压大小和钢纤维掺量为试验参数,进行20组UHPC试件常规三轴试验,分析UHPC的破坏形态、应力-应变曲线、峰值应力和应变等力学性能。结果表明：围压和钢纤维掺量均为零的试件破坏时呈劈裂破坏,其他试件则呈剪切破坏;围压和钢纤维掺量对应力-应变曲线弹性模量和弹性段曲线形状影响较小;随着围压增大,峰值应力和应变呈不断增大趋势;随着钢纤维掺量增大,峰值应力和轴向峰值应变呈先增大后不变和先增大后减小趋势,环向峰值应变则呈增大趋势。通过对UHPC八面体正应力-体积应变和剪应力-剪应变关系进行分析,基于Drucker-Prager二参数准则,建立了UHPC八面体破坏准则计算方法。`