共查询到20条相似文献,搜索用时 111 毫秒
1.
2.
压缩荷载作用下混凝土中氯离子扩散行为细观模拟 总被引:1,自引:0,他引:1
将外荷载作用的影响等效为外荷载引起的混凝土孔隙率的改变,来研究其对混凝土中氯离子扩散特性的影响,提出了压缩荷载作用下非均质混凝土氯离子扩散行为的细观模型.首先对混凝土在压缩荷载作用下的力学行为进行模拟分析;然后,将荷载作用后的"结果输出"作为氯离子扩散模拟的"初始输入"条件,以单轴压缩荷载为例,将混凝土看作由骨料、水泥浆体基质及界面过渡区组成的三相复合材料,建立了混凝土在力学与物理耦合作用下的细观模型,研究了压缩荷载对混凝土中氯离子扩散特性的影响,得到了氯离子有效扩散系数与压缩应力水平之间的关系式,揭示了压缩应力水平的影响规律. 相似文献
3.
分析了氯离子侵入混凝土的特性,采用FEMLAB有限元数值分析软件对结构混凝土内氯离子扩散规律进行了数值模拟,通过与试验结果的比较,验证了数值模拟的可行性与合理性;随后,在考虑表面氯离子浓度以及扩散速度随时间变化特性的情况下,研究了结构混凝土中氯离子的扩散行为,并与不考虑两者时变因素情况下的结果进行了比较.结果表明,差异十分明显. 相似文献
4.
在现有二维混凝土随机骨料模型基础上,通过引入正态分布随机数来模拟混凝土界面过渡区厚度的非均匀性,并耦合氯离子扩散、钢筋锈蚀和混凝土损伤,建立了海工结构服役寿命预测细观数值模型.研究表明:由氯离子扩散引起的单根钢筋非均匀锈蚀导致混凝土保护层形成3条主裂缝,3条主裂缝之间夹角约为120°,出现这种现象的主要原因是界面过渡区加速了氯离子扩散,次要原因是界面过渡区的力学性能劣化;在相同钢筋锈蚀量条件下,非均匀锈蚀钢筋混凝土比均匀锈蚀钢筋混凝土的服役年限短,混凝土保护层开裂形态也不一样;数值模拟的氯离子含量分布、裂缝形态与试验数据较为吻合,验证了所建立的数值模型的可靠性. 相似文献
5.
《Planning》2016,(17)
为了更好地理解氯离子在混凝土中的扩散机制,运用有限差分法,对混凝土圆柱在氯盐环境下服役时的氯离子扩散过程进行数值模拟,模型同时考虑了混凝土圆柱表面氯离子浓度和柱内氯离子扩散系数的时间依赖效应,得到了氯离子在混凝土圆柱截面内随时间变化的浓度分布云图。结果表明:为延长服役寿命,工程实践中可以考虑适时更换钢筋外侧的混凝土保护层,混凝土保护层的更换会产生结构内氯离子浓度的重新分布,可通过减小钢筋附近的氯离子浓度来有效延长结构服役寿命,数值模拟的结果对混凝土结构中钢筋的布筋位置具有指导意义。 相似文献
6.
为深入研究水泥浆体中氯离子的扩散性能,更好地考虑水泥颗粒形状特征带来的影响,建立了基于非球形颗粒水化堆积的水泥浆水化模型,通过第三方试验充分验证其可靠性后,明确了长细比对水化度和孔结构特征的影响;将First-passage理论应用于所建立的水泥浆水化模型,提出了综合考虑内、外水化层和未水化层扩散特性的布朗运动算法,并通过对比氯离子扩散试验数据对其可靠性进行了验证;利用建立的布朗运动算法分析了长细比对水泥浆氯离子扩散系数的影响.结果表明,本文建立的分析水泥颗粒形状对氯离子扩散系数影响的新方法,可为混凝土耐久性设计提供参考. 相似文献
7.
《混凝土》2017,(8)
就玻璃粉对粉煤灰复合硬化水泥浆氯离子结合能力影响进行了研究。首先对0~70%粉煤灰取代量的复合硬化水泥浆在90 d内的氯离子结合性能进行了研究。其次,采用玻璃粉与粉煤灰1∶4的比例以二者混合粉体替代水泥,玻璃粉替代量为0~8%,对玻璃粉-粉煤灰-水泥体系硬化浆体氯离子固定能力进行了研究。并通过XRD物相分析对氯离子结合机理进行了分析。结果表明,在粉煤灰复合水泥硬化浆体中,随粉煤灰对水泥取代量的增大,在不同龄期时,氯离子结合量出现极大值,且该极大值随龄期增长向小取代量方向移动。玻璃粉在粉煤灰复合水泥浆中的加入,有使硬化水泥浆氯离子结合能力降低的趋势。但根据XRD的结果,无论是粉煤灰复合水泥浆还是玻璃粉和粉煤灰复掺的硬化水泥浆,其Friedel盐含量和组成及龄期的关系均和氯离子结合量和同类因素的关系不一致。推测物理吸附对上述两种体系氯离子结合量随组成与龄期变化的规律有更大的影响。 相似文献
8.
9.
将混凝土视为由骨料、界面区和砂浆所组成的三相复合材料,利用MATLAB软件建立混凝土粗骨料随机模型.把模型导入COMSOL软件,通过设定不同骨料含量和界面区体积,来探究这2种因素对氯离子在混凝土中扩散的影响.首先借助试验设计方法验证了所建立的随机模型的重复性和再现性,进而确定了其模拟精度,并通过与试验数据的对比分析,验证了上述方法的有效性;随后展开了骨料含量和界面区体积对混凝土氯离子扩散性能影响的模拟试验.模拟结果表明:氯离子在混凝土中的扩散受骨料含量和界面区体积的影响;骨料含量的增加抑制了氯离子的扩散性能,表现为骨料的曲折效应;界面区体积的增加加速了氯离子的扩散性能,表现为界面效应;随着骨料含量的增加,界面效应越来越明显. 相似文献
10.
11.
硬化水泥浆体孔隙溶液的制取与研究 总被引:1,自引:0,他引:1
介绍了硬化水泥浆体孔隙溶液的制取,实验测定了孔隙溶液的成分。讨论了内掺Cl^-离子对孔隙溶液OH^-离子溶液或pH值的影响,以及氯化物种类、养护方法和水泥品种对孔隙溶液成分的影响,探讨了这些因素对化水泥浆体孔隙溶液成分的影响机制。 相似文献
12.
《Construction and Building Materials》2007,21(7):1534-1541
This research demonstrates the effect of fly ash fineness on pore size and microstructure of hardened blended cement pastes. Two sizes of fly ash, original fly ash and classified fly ash were used to replace Portland cement type I paste. Test results indicated that the pore sizes of hardened blended cement paste were significantly affected by the rate of replacement and the fineness of fly ash. The replacement of cement by original fly ash decreased the pore sizes of blended cement paste and the incorporation of classified fly ash resulted in a further decrease in the pore sizes of blended cement paste. The X-ray diffraction (XRD) results showed that the blended cement paste with classified fly ash was more effective at reducing the intensity of Ca(OH)2 than that with the original fly ash. The scanning electron microscope (SEM) results revealed that the hardened blended cement paste containing finer fly ash produced a denser structure than the one containing coarser fly ash. 相似文献
13.
为了研究水泥基复合材料传输与孔结构的定量关系,采用二次进汞的方法,系统研究了水灰比为0.23,0.35,0.53的硬化浆体在28 d的孔结构参数。研究表明:二次进汞的方法能很好表征有效孔结构参数,其中有效孔隙率是总孔隙率的25%~50%;由孔径分布曲线可知,水灰比为0.53时出现双峰,第一个峰值对应的是毛细孔的临界孔径,第二个峰值对应于凝胶孔的临界孔径,随水灰比的降低,第一峰值逐渐消失;0.23,0.35,0.53浆体对应的第一峰值分别是0.053,0.062,0.077μm。 相似文献
14.
Mingzhong Zhang Guang Ye Klaas van Breugel 《Construction and Building Materials》2011,25(4):2046-2052
In view of the crucial influence of water diffusion in cement paste on durability, it is necessary to predict the water diffusivity of cement-based materials. The main purpose of this paper is to present a computational approach to predict the water diffusivity in cement paste. A computer-based cement hydration model HYMOSTRUC3D is used to generate the 3D microstructure of cement paste. The simulated pore structure is compared with the experiments. Based on the generated microstructure, finite element method (FEM) is applied to simulate the diffusion process of tritiated water through the saturated cement paste. In the FE simulation, cement paste is modeled as a three-phase composite material, consisting of capillary pores, un-hydrated cement and hydration products. Un-hydrated cement is considered non-diffusible. The contribution of capillary pore phase and hydrating products phase to the diffusivity of tritiated water in cement paste are taken into account. Finally, the diffusivity modeling is applied for series of hardened cement paste with variations on water-to-cement (w/c) ratio and curing age. The simulations are validated with experimental data obtained from literature. The comparison between simulation and experiments indicate that the simulated and experimental data are of the same order of magnitude. Furthermore, the tendency of simulated relationship (diffusivity vs. w/c ratio, diffusivity vs. curing age) shows a good fit to the experiments. 相似文献
15.
研究了组成和龄期对粉煤灰/水泥浆体系硬化水泥浆Cl~-结合能力的影响。首先研究了组成和龄期对粉煤灰和水泥二组分体系硬化水泥浆Cl~-结合性能的影响,并且确定了Cl~-结合量最大的组成比。在该硬化水泥浆Cl~-结合量的组成比例下继续以钠钙硅玻璃粉和Ca(OH)_2混合组成取代水泥,并采用正交试验设计,探讨了玻璃粉掺量、细度和Ca(OH)_2掺量对Cl~-结合性能的影响。结果表明,14d和28d龄期时,粉煤灰对水泥取代量为50wt%的硬化水泥浆Cl~-结合能力达到极大值。正交试验结果表明,在10wt%、20wt%、30wt%的三个水平中,玻璃粉的掺量对硬化水泥浆的Cl~-结合量的影响最大,有使硬化水泥浆Cl~-结合能力降低的作用,而Ca(OH)_2具有使Cl~-结合能力增大的作用。但掺加了玻璃粉和Ca(OH)_2的粉煤灰-水泥浆体系硬化水泥浆Cl~-结合量随龄期的延长而下降。从正交试验的结果来看,少量玻璃粉的掺入并配合使用Ca(OH)_2,有望对掺粉煤灰硬化水泥浆的氯离子结合起到促进作用。 相似文献
16.
17.
Siavash Ghabezloo Jean Sulem Jérémie Saint-Marc 《International Journal of Rock Mechanics and Mining Sciences》2009,46(4):761-768
A method is presented for the evaluation of the permeability–porosity relationship in a low-permeability porous material using the results of a single transient test. This method accounts for both elastic and non-elastic deformations of the sample during the test, and is applied to a hardened class G oil well cement paste. An initial hydrostatic undrained loading is applied to the sample. The generated excess pore pressure is then released at one end of the sample while monitoring the pore pressure at the other end and the radial strain in the middle of the sample during the dissipation of the pore pressure. These measurements are back-analysed to evaluate the permeability and its evolution with porosity change. The effect of creep of the sample during the test on the measured pore pressure and volume change is taken into account in the analysis. This approach permits to calibrate a power law permeability–porosity relationship for the tested hardened cement paste. The porosity sensitivity exponent of the power–law is evaluated equal to 11, and is shown to be mostly independent of the stress level and of the creep strains. 相似文献
18.
19.
This paper describes a study of the effects of several factors on the strength of lightweight aggregate concrete composites: aggregate strength, w/c ratio and the porosities of the interfacial zone and within the hardened cement paste. Concrete samples with three different water cement ratios (i.e. 0.4, 0.44, 0.48) were compared. The crushing strengths of three grades of expanded clay lightweight aggregates (i.e. 25, 15, 5 mm) and the pore distributions of the hardened cement pastes were measured. Increasing the water/cement ratio was found to decrease the strength of lightweight aggregate concrete. The numbers of pores within the cement paste and in the aggregate/cement paste interfacial zone were found to increase. 相似文献