养护龄期对等粒径多孔水泥混凝土内部结构的影响

以不同养护龄期的等粒径多孔水泥混凝土为研究对象,与传统混凝土做对比,采用气孔分析法测试了不同养护龄期混凝土的孔结构。结果表明:等粒径与传统多气孔混凝土的相对孔含量均随着养护龄期延长在初期有小幅增长,而后逐渐降低最后趋于平稳,且在孔径相同时,龄期较短的混凝土相对孔含量要低。与相同条件下的传统径多气孔混凝土相对孔含量比较,养护3 d的等粒径多气孔混凝土最大孔含量要比养护75 d的低53.6%,比传统的混凝土孔含量要高出32.3%。与传统的多气孔混凝土相比,随着养护龄期延长,等粒径多气孔混凝土的比表面积、平均半径、气孔间距系数、气孔总弦长要比传统混凝土的要小,在龄期为75 d时,分别要小43.14%、28.76%、28.30%、37.33%;龄期为75 d的等粒径多气孔混凝土在比表面积、平均半径、气孔间距系数、气孔总弦长要比龄期为3 d的要大得多,分别要大65.36%、33.71%、60.75%、61.70%,表明等粒径混凝土比传统混凝土组织结构更加密实。

等粒径多孔水泥混凝土内部结构与破坏机理

为了更好地分析等粒径多孔水泥混凝土内部结构与破坏机理的关系,利用BT500工业CT对等粒径混凝土试件进行了内部结构扫描,并利用图像处理技术进行了初步分析,再通过数值模拟技术分析了等粒径多孔水泥混凝土与传统多孔水泥混凝土组成和内部结构的区别,从微观角度对比、探讨了等粒径多孔水泥混凝土的破坏机理。分析表明:等粒径多孔水泥混凝土忽略了集料级配的嵌挤作用,通过提高水泥膜的厚度来完成集料之间的堆积,从而在确保空隙率的基础上提高强度;等粒径多孔水泥混凝土独特的内部结构使得其可以在获得大空隙率的前提下,具有较大的抗压强度的能力。同时考虑到空隙率大既有利于排水,又有利于抵抗拉应变,因此,等粒径多孔水泥混凝土的开发为解决高速公路重载条件下路面基层开裂奠定了基础。

砂泥岩颗粒料压缩-回弹特性试验研究

为研究砂泥岩颗粒料中泥岩颗粒粒径对其压缩及回弹特性的影响,通过向砂岩颗粒中掺入相同颗粒级配曲线泥岩颗粒方法及同粒径组按比例替换方式配制了2类8种砂泥岩混合料,选用侧限压缩固结试验得到了8种混合料e-P曲线及ε-P曲线;并计算出其压缩指标和回弹指标。试验结果表明,按不同比例掺入同一级配曲线泥岩颗粒的砂泥岩混合料,回弹指标与压缩指标随泥岩颗粒百分比增加而呈相反的变化趋势。在同一粒径组中泥岩颗粒含量为20%的砂泥岩颗粒混合料中,其回弹指标与压缩指标随泥岩颗粒替换粒径的增大而呈相反的变化趋势;而泥岩粒径在0.5~1.0 mm时混合料轴向应变比其他粒径范围内小,压缩模量随掺入泥岩颗粒的中值粒径增大而减小,回弹模量则与之相反。在控制填料压缩指标及回弹指标条件下,岸坡填筑区填料可按有效粒径值部分掺入挖方泥岩颗粒。

Microstructure and mechanical properties of Mg-Gd-Y-Zr alloy processed by equal channel angular pressing

Microstructure evolution and texture development and their effects on mechanical properties of a Mg-Gd-Y-Zr alloy during equal channel angular pressing（ECAP） were investigated.It is found that the microstructure is still inhomogeneous after four passes,and two zones,namely the fine grain zone（FGZ） and the coarse grain zone（CGZ） are formed.The grain refinement occurs mainly by particle-stimulated nucleation（PSN） mechanism,which led to a more random texture after four passes of ECAP.In the ECAP-processed alloy,the strength did not increase while the ductility was enhanced dramatically compared with the as-received condition.The change of ductility of this alloy was discussed in terms of texture and second phase particles.

Effects of magnetic field and hot rolling on microstructures and properties of cryo ECAPed 1050 aluminum alloy during annealing

The evolution of hardness and microstructures of 1050 aluminum alloy prepared by hot rolling and subsequent equal- channel angular pressing at cryogenic temperature (cryoECAP) after annealing at 150?400 °C for 1 h without and with magnetic field of 12 T was investigated. The electron back scattering diffraction pattern (EBSD) and transmission electron microscopy (TEM) were utilized to characterize the grain microstructures and dislocations. It is demonstrated that the hot rolling before cryoECAP produces more equiaxed grains with a smaller average size and a higher fraction of high angle boundaries (HABs) in the subsequent cryoECAPed 1050 aluminum alloy, thus accelerating the recovery and recrystallization of cryoECAPed alloy and produces more homogeneous microstructure during annealing. The magnetic field promotes the recovery and recrystallization and leads to much lower hardness at 150?250 °C, while it can suppress the abnormal grain growth and form more homogeneous grain size distributions annealed at 300?400 °C.

Effect of soft Bi particles on grain refinement during severe plastic deformation

Two aluminum alloys,Al-8Zn and Al-6Bi-8Zn were subjected to equal channel angular pressing(ECAP)up to5passes at room temperature.The microstructural evolution and the grain refinement behavior of these alloys were systematically studied by electron backscatter diffraction(EBSD).After5passes of ECAP,ultrafine grained microstructures formed in both alloys.However,the grain structure in the Al-6Bi-8Zn alloy is much finer than that of Al-8Zn alloy,showing that the soft Bi particles have a strong influence on enhancing the grain refinement during ECAP.The strengths of the ECAP-processed materials were measured by hardness test and it showed that after5passes of ECAP,the hardness of the Al-6Bi-8Zn alloy was higher than that of the Al-8Zn alloy.The effects of soft Bi particles on the deformation behavior during ECAP and the final strength of the Al-6Bi-8Zn alloy were discussed.