微珠对隧道工程混凝土性能的影响及机理研究

针对广州新白云国际机场隧道工程建设中大体积混凝土的温度裂缝问题,通过复掺微珠和粉煤灰,研究了微珠掺量对混凝土的力学性能、干燥收缩、水化热以及早期抗裂性能的影响,并采用SEM分析了微珠对水泥水化反应的作用机理。结果表明:当矿物掺合料总量一定时,随着微珠掺量的增加,混凝土的力学性能早期变化较小,后期呈现出先增加后下降的趋势,且微珠掺量为10%时,混凝土养护60 d的抗压强度、劈裂抗拉强度以及弹性模量最高;混凝土干缩率随着微珠掺量的增加而减小,且这种趋势随龄期的增加而增大,当微珠掺量15%时,60 d混凝土的干缩率最小;当微珠掺量为10%时,混凝土早期抗裂性能最佳,平板试件表面24 h内无裂缝;微珠掺量对胶凝材料水化热总量影响较小,但对水化放热峰值及峰值产生时间影响较大;微珠可以加速浆体早期的水化进程,减少硬化浆体的孔隙,使其结构更密实。     

Use of recycled gypsum in the cement-based stabilization of very soft clays and its micro-mechanism

This paper presents an experimental study and micro-mechanism discussion on gypsum role in the mechanical improvements of cement-based stabilized clay (CBSC). A soft marine clay at two initial water contents (i.e. 50% and 70%) was treated by reconstituted cementitious binders with varying gypsum to clinker (G/C) ratios and added metakaolin to facilitate the formation of ettringite, followed by the measurements of final water contents, dry densities and strengths in accordance with ASTM standards as well as microstructure by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of the CBSC, and there exists a threshold of the G/C ratio, which is 10% and 15% for clays with 50% and 70% initial water contents, respectively. Beyond which adding excessive gypsum cannot improve the strength further, eliminating the beneficial role. At these thresholds of the G/C ratio, the unconfined compressive strength (UCS) values for clays with 50% and 70% initial water contents are 1.74 MPa and 1.53 MPa at 60 d of curing, respectively. Microstructure characterization shows that, besides the common cementation-induced strengthening, newly formed ettringite also acts as significant pore infills, and the associated remarkable volumetric expansion is responsible, and may be the primary factor, for the beneficial strength gain due to the added gypsum. Moreover, pore-filling ettringite also leads to the conversion of relatively large inter-aggregate to smaller intra-aggregate pores, thereby causing a more homogeneous matrix or solid skeleton with higher strength. Overall, added gypsum plays a vital beneficial role in the strength development of the CBSC, especially for very soft clays.     

The relationship between the micro-mechanism and macroscopic dielectric properties in Ba1−xBixTi1−x−yZn0.75xW0.25x+yO3+y systems

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO₃ ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε_r, dielectric stability and dielectric loss) in Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10¹² Ω cm. These features suggested that the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment.     

微平面机构的结构设计与制造

本文通过微平面机构的设计制造和测试研究,提出了一整套行之有效的工艺方法,所制造的微机构运动自如,文章还进一步探讨了有关运动、动力、摩擦等方面的问题。     

硅片直接键合的微观动力学研究

基于直接键合硅片表面能与退火温度的关系曲线,定量讨论了键合时键合界面上的微观动力学变化过程。首次提出五阶段键合模型计算值与实测表面能曲线相一致,初步确定了键合过程中界面发生的微观反应机理。     

微机械自跟踪双坐标光电自准直仪的研究

设计一种电磁驱动的微机械结构,实现自准直仪双坐标光电信号的自动跟踪,采用跟踪与读数分离的方法,提高仪器的测量精度。经实际测试和使用表明,设计方案合理,稳定可靠,双坐标工作范围为－100″－＋100″,仪器具有绝对零点,分辨力0．1″,非线性误差小于0．5″。     

空位掺杂La（1—x）2／3Zn1／3MnO3化合物的结构及微观机制

利用X射线衍射(XRD)和扫描电镜(SEM)对La(1-x)2/3Zn1/3MnO3结构及表面形貌进行了研究。X射线衍射测量分析表明空位掺杂后,样品的主相仍然是钙钛矿结构(Pnma),其晶体对称性不会随空位浓度的增加而改变。随着空位掺杂浓度的增加,样品的晶格常数增大,体积膨胀。当空位掺杂浓度x≤0.04时,该材料致密度较大;随着空位掺杂浓度继续增加,该材料致密度又逐渐变小。     

Post-liquefaction shearing behaviour of saturated gravelly soils: Experimental study and discrete element simulation

To investigate the post-liquefaction shearing behaviour of saturated gravelly soil, laboratory tests were conducted using a static–dynamic multi-purpose triaxial apparatus. In addition, numerical simulations using the discrete element method (DEM) were performed to preliminarily understand the micro-mechanism of gravelly soil in monotonic loading after liquefaction. The influences of dry density, initial confining stress and degree of liquefaction on the post-liquefaction shearing behaviour of gravelly soil were discussed, and the evolution of the micro-parameters of the granular system was also analysed. The results show that the stress–strain responses of gravelly soil after liquefaction can be divided into three stages: (1) low strength stage, (2) super-linear strength recovery stage, and (3) sublinear strength recovery stage, which are distinctly different from those of the general saturated gravelly soil without previous cyclic loading. The initial state and prior dynamic stress history have significant influences on the post-liquefaction shearing behaviour of gravelly soil. The DEM simulation revealed that the average coordination number sharply increases, the contact normal shows an obvious orientation distribution, and the destroyed force chain backbones are reconstructed in the monotonic reloading process after liquefaction. The evolution of the micro-parameters of the granular system clearly reflects the interior interaction process and micro-mechanisms in the particles during the three different stages of the macro-mechanical behaviour of gravelly soil.     

井壁强化机理与致密承压封堵钻井液技术新进展

井壁强化钻井液技术已成为提高地层承压能力的重要手段之一,目前中国在井壁强化微观机理、模拟实验评价方法和新材料研发等方面,均有待深入研究。基于微观颗粒物质力学的力链网络结构分析基本原理,探讨了裂缝地层致密承压封堵方法。提出了井壁强化材料特性的精细化表征参数,通过颗粒类型、粒度级配及浓度优化,利用刚性颗粒、弹性颗粒和纤维材料等协同封堵裂缝,可有效形成具有“强力链网络结构”的致密承压封堵层。利用自行研制的井壁强化钻井液封堵模拟实验装置,开展了井壁强化钻井液封堵模拟实验优化研究。模拟实验证明,新研制的井壁强化材料不仅能够有效封堵裂缝,形成致密承压裂缝封堵层,且当支撑裂缝至设计开度,可提升地层承压能力。