共查询到20条相似文献，搜索用时 171 毫秒
1.
《东南大学学报》2021,(1)
通过对不同强度等级的全珊瑚海水混凝土(CASC)进行海水干湿循环试验和海水干湿-碳化耦合循环试验,以表面状态、质量损失率、动弹性模量、超声波波速、立方体抗压强度为评价指标,研究干湿循环、碳化和干湿-碳化耦合作用对CASC耐久性的影响.结果表明:干湿循环、干湿-碳化耦合作用下,CASC的质量损失率均随着侵蚀时间的延长而逐渐增加,先期比较平缓,增长幅度不大,经过10次循环后,其质量损失率的增长幅度明显增大;而CASC的动弹性模量和超声波波速均随着循环次数的增加逐渐降低,经过6次循环后,其速率趋于平缓,表面有微损伤;与初始28 d立方体抗压强度相比,CASC的立方体抗压强度下降幅度为8.8%～11.0%.干湿循环和碳化作用对CASC的海水侵蚀均有加速作用,干湿循环促进盐析现象的产生,加快混凝土的破坏.因此,干湿-碳化耦合作用加速CASC的破坏. 相似文献
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研究了在干湿循环和弯曲荷载作用下再生混凝土硫酸盐侵蚀劣化进程.试验中使用了3种不同的荷载率(0,0. 3和0. 5),通过对再生混凝土的相对动弹性模量和水溶性SO_4~(2-)含量的变化来研究其劣化进程.并利用XRD,ESEM和X-CT等测试手段来研究再生混凝土劣化过程中内部产物与微结构的变化.结果表明,弯曲荷载能够加速再生混凝土在硫酸盐侵蚀和干湿循环下的劣化,并且加快SO_4~(2-)向混凝土内部的传输速度.这是因为随着荷载率的增加,再生混凝土的微裂纹会加速扩展,为SO_4~(2-)的传输提供更多的通道.而SO_4~(2-)将会与水化产物反应生成膨胀性产物(石膏和钙矾石),进一步加速了再生混凝土的劣化过程. 相似文献
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冻融是混凝土结构随季节变化所必须经历的阶段,随着冻融次数的增加,混凝土的表观特征和强度将发生退变.采用冻融次数为0、30、50、70、100次,对补偿收缩混凝土进行冻融循环试验,分析补偿收缩混凝土的表面特征和强度劣化趋势,发现随着冻融次数的增加,普通混凝土与补偿收缩混凝土相比,表面破坏更严重,混凝土抗压和抗折强度呈现下降趋势.冻融100次后,普通混凝土抗压、抗折强度分别下降35.2%和44.1%,而补偿收缩混凝土抗压、抗折强度分别下降30.3%和35.3%,说明适当掺入膨胀剂对提高混凝土的抗冻性有一定的作用,有利于控制和降低混凝土冻融环境下强度的退化. 相似文献
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水闸在运行多年后,经过冻融破坏、水流冲刷、侵蚀等原因,造成混凝土表面裂缝、剩蚀现象,对水闸这种侵蚀破坏的处理是灌区管理当中一项重要的工作,我们在新安灌区水闸工程的裂缝和表面剥蚀、水质侵蚀、冲磨、空蚀、钢筋锈蚀等修补加固中采用了水泥基和树脂基修补材料进行维修,取得较好的效果. 相似文献
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采用浸-烘循环的试验方法研究了不同水灰比混凝土抵抗海水侵蚀的性能。结果表明:各组混凝土试件的相对动弹性模量变化包括4个阶段:快速下降段、上升段、水平段、逐渐下降段;质量损失率的总体变化趋势均为先上升后下降。混凝土的损伤度随着水灰比的增大而增大。 相似文献
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张建军 《泰州职业技术学院学报》2014,(6):51-53
通过对干湿循环后的掺石灰和砂混合料的改良膨胀土进行直接剪切试验,研究了干湿循环对于改良膨胀土抗剪强度影响。结果表明,龄期对于掺石灰和砂混合料的改良膨胀土抗剪强度影响较大,并且发现干湿循环五次后,随着干湿循环次数的增大,改良膨胀土的抗剪强度降低。 相似文献
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《西安文理学院学报》2015,(4)
近年来,我国城市化进程日益加快,高楼建筑如雨后春笋般相继涌现.作为一种最为常见的结构工程材料,混凝土被广泛应用于民用建筑、工业建筑、国防等建筑物中.对冻融及高温后混凝土多轴力学特性进行研究,以进一步研究混凝土的力学性能. 相似文献
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为了研究循环荷载历史对饱和混凝土的力学性能的影响,采用φ150×300mm的圆柱体试件,对饱和混凝土试件在不同荷载循环次数(0次、25次、50次、100次)与不同应变速率(10-5/s、10-4/s、10-3/s、10-2/s)作用下进行单轴压缩试验,分析了荷载循环次数以及应变速率对饱和混凝土的峰值应力、峰值应变和弹性模量的影响。研究表明:经历循环荷载历史后的饱和混凝土峰值应力随应变速率的增大而增大,随荷载循环次数的增加表现出先增大后减小的规律;随荷载循环次数的增加,饱和混凝土的峰值应变先增大后减小,随应变速率的增大总体呈增大的趋势;随应变速率的增加,饱和混凝土的弹性模量整体上呈现出增大的趋势。 相似文献
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为了研究补偿收缩混凝土的抗冻性能,采用慢冻法对普通混凝土和补偿收缩混凝土进行冻融对比试验。通过对比研究普通混凝土和补偿收缩混凝土冻融后质量损失、强度损失和相对动弹性模量变化趋势,从而得出补偿收缩混凝土的抗冻性能。试验结果表明,普通混凝土冻融100次后,质量损失率为2.09%,抗压强度下降35.2%,相对动弹性模量下降到60.8%;补偿收缩混凝土质量损失率为1.62%,抗压强度下降30.3%,相对动弹性模量下降到64.8%;试验三个参数指标表明添加膨胀剂有助于提高混凝土抵抗冻融破坏的能力,改善混凝土结构的损伤程度,体现了膨胀剂对混凝土的增强机理。 相似文献
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为了深入探究岩石物理力学性质,选取红砂岩作为试验材料,以冻融循环次数、围压作为研究指标,通过设计影响因素测试试验,探究这两项指标对岩石性能的影响。试验测试结果表明,围压、冻融循环次数两项影响因素对岩石的三轴抗压强度、弹性模量均有较大影响,力学性能变化显著。 相似文献
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再生混凝土力学性能的研究 总被引：1，自引：0，他引：1
对再生混凝土力学性能的研究进行了综述，主要包括再生混凝土力学性能的抗压强度、弹性模量、干缩与徐变。研究表明，和普通混凝土相比，再生混凝土力学性能的抗压强度低，弹性模量小，干缩与徐变较大。最后提出了再生混凝土力学性能需要进一步研究的问题。 相似文献
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We report an experimental investigation on the impact of the freezing rate on the cryo-deformation and cryo-damage of cementitious materials. Saturated, dried and air-entrained mortar specimens are subjected to laboratory freeze-thaw cycles under three freezing rates without moisture exchange with the environment. In addition to basic mechanical properties and pore distribution, the measurement is also effectuated for freezing expansion, residual deformation of the specimens in each cycle. From the results it is observed that a high freezing rate does augment the freezing expansion of material while the cryo-damage is more important for a low freezing rate. Accordingly, both the freezing rate and freezing duration should be taken into account for the cyro-damage extent of cementitious materials. 相似文献
14.
Selective laser melting (SLM) is one type of additive manufacturing which produces metal parts by powder bed fusion. Since the materials undergo repeated and sharp heating/cooling cycles, the SLMed parts have unique microstructures. The relations among SLM processing parameters, resultant microstructures, and mechanical properties have been investigated by many researchers. However, the wear performance of SLMed materials under various contact conditions has not been carried out until recently. This paper is a presentation of previous and recent research related to wear performance. This is a crucial aspect if SLM is to be expanded to produce friction pairs. Wear rates and mechanisms of the SLMed materials under dry, boundary lubrication, cavitation erosion, and corrosion conditions are discussed and compared with conventionally processed (CP) materials. SLMed materials benefit from fine grains and high hardness, which have higher wear resistance than CP materials. Moreover, a unique tribo-layer on the surface of the SLMed part is found to protect the bulk material under boundary lubrication conditions. An optimized combination of processing parameters increases part density, which further improves the wear resistance. Future work includes studying the influence of pores on the deforming and lubricating behaviors from dry conditions to different lubrication regimes. The final target is to actively control the processing parameters to obtain desirable material properties for improving wear performance. 相似文献
15.
We report an experimental investigation on the impact of the freezing rate on the cryo-deformation and cryo-damage of cementitious materials. Saturated, dried and air-entrained mortar specimens are subjected to laboratory freeze-thaw cycles under three freezing rates without moisture exchange with the environment. In addition to basic mechanical properties and pore distribution, the measurement is also effectuated for freezing expansion, residual deformation of the specimens in each cycle. From the results it is observed that a high freezing rate does augment the freezing expansion of material while the cryo-damage is more important for a low freezing rate. Accordingly, both the freezing rate and freezing duration should be taken into account for the cyro-damage extent of cementitious materials. 相似文献
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混凝土的级配及骨料含量对其宏观力学特性有直接影响，选择合适的骨料模型是进行混凝土细观力学数值模拟的前提，在已提出的三维随机凸多面体骨料模型的基础上选择合适的试件模型并进行有限元剖分，利用并行计算技术分别对湿筛混凝土试件三维球形骨料和凸多面体骨料细观模型进行了静载弯拉破坏数值模拟对比计算。计算结果表明，三维凸多面体骨料生成算法是可行的，能够满足混凝土三维细观力学模拟的需要。 相似文献
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混凝土冻融耐久性的试验研究 总被引：2，自引：0，他引：2
以混凝土冻融耐久性为研究内容，用不同种类混凝土的抗压强度、动弹性模量、超声波声速等指标的损失率来表征冻融过程中混凝土的性能劣化状况，并系统比较了不同种类混凝土的抗冻性优劣．通过研究得出：无论是普通混凝土，还是高强混凝土或高性能混凝土，其动弹模损失率、抗压强度损失率、超声波声速损失率均随冻融次数的增加而增大；提高混凝土强度在一定程度上可以提高混凝土抗冻融性能；掺入高效减水剂、优质引气剂和优质掺合料等，高性能混凝土抗冻融性能比对应的基准混凝土性能显著改善，而且通过这样的技术措施，较低强度等级的混凝土也可以获得高抗冻性．鉴于超声波测试方法方便、快捷、准确。而且可以直接用于实际工程的混凝土性能检测，所以，与动弹模测试方法相比，采用超声波测试技术来评价实际工程中混凝土的耐久性劣化程度具有明显的优势． 相似文献
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To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex. 相似文献
19.
To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the con-crete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex. 相似文献
20.
The properties of two types of fly ash geopolymers made from class F fly ashes produced in wet bottom and dry bottom boilers were investigated in the present study. The source material used in the geopolymer concrete was activated with sodium hydroxide and sodium silicate solution. The results revealed that the geopolymer produced with wet bottom boiler fly ash(CZ-FA)hardened quickly, and had higher early-age strength and lower shrinkage than the geopolymer produced with dry bottom boiler fly ash(SX-FA). The compressive strength of the two geopolymers made from CZ-FA and SX-FA was 45 MPa and 15 MPa respectively when cured at 60 ℃ and delayed for 14 d. However, after 90 days' delay, the compressive strength of both the samples is almost the same, up to 80 MPa. Nearly 20% volume shrinkage of the samples made from SX-FA was much higher than that made from CZ-FA, which was almost zero. XRD, SEM/EDS and FT-IR were used to analyze the main reason of the differences. 相似文献