Properties and interfacial microstructure of cement-based materials with composite micro-grains

Silica fume, fly ash and nano-fiber mineral materials （NR powder） are employed to incorporate into cement-based materials. According to the grain grading mathematical model of cement-based materials, two packing systems, namely, spherical grading system and nano-fiber reinforced system were designed. Properties and interfacial microstructure of the two systems were studied according to secondary interface theory. It was shown that nano-fiber mineral materials can improve the grain grading of the admixture, increase the density of the system, improve the microstructure of the interface and the hardened paste, and enhance the uniformity of cement-based materials mixed with composite micro-grains and greatly increase their wearable rigidity and flexure strength. In this paper, two kinds of interface models, including spherical grain model and nano-fiber reinforced interface model of the cement-based materials mixed with composite micro-grains, were brought forward.     

Model of Coherent Interface Formation in Cement-Based Composites Containing Polyblend of Polyvinyl Alcohol and Methylcellulose

The texture of interfacial zone between cement paste and quartz in the cement-based composites containing polyvinyl alcohol (PVA) ,methylceUulose (MC) and their polyblend in an amount of 10 wt % with respect to cement, as well as the texture of dehydrated bodies of PVA , MC , and the polyblend solutions, were inves-tigated with SEM. The network texture of the dehydrated polyblend is confirmed by comparing the texture of dehy-drated bodies of PVA and MC. The network texture has restrained the movement of polyblend molecules in the ce-ment mortar but is helpful to forming a coherent interface between cement paste and quartz. The key factor of form-ing the coherent inteoCace is not the neutralization reaction between H ^ from hydrolysis of quartz and OH ^- from hydration of cement, but the electrostatic attraction and the chemical reaction between polar groups on the polyblend molecule and cations and anions from hydrolysis of quartz and hydration of cement, respectively. The model of the coherent interface formation is that excessive [ HSiO3 ]^ - and [ SiO3 ]^2- an/ons are bonded tgzh the hydrated cations such as Ca^2 and Al^3 , which is confumed by the gel containing Ca and Si on the quartz surface.     

Influence of fly ash fineness and shape on the porosity and permeability of blended cement pastes

The effects of the fineness and shape of fly ash on the porosity and air permeability of cement pastes were investigated. Pulverized coal combustion (PCC) fly ash and fluidized bed coal combustion (FBC) fly ash classified into three different finenesses were used. River sand with particle size distribution similar to that of fly ash was also used for comparison. Portland cement was replaced with fly ash and ground sand at the dosages of 0, 20wt%, and 40wt%. A water-to-binder ratio (w/b) of 0.35 was used thr...     

Effect of coal gangue with different kaolin contents on compressive strength and pore size of blended cement paste

The effects of activated coal gangue on compressive strength, porosity and pore size distribution of hardened cement pastes were investigated. Activated coal gangue with two different kaolin contents, one higher and one lower, were used to partially replace Portland cement at 0%, 10%, and 30% by weight. The water to binder ratio（w/b） of 0.5 was used for all the blended cement paste mixes. Experimental results indicate that the blended cement of activated coal gangue mortar with higher kaolin mineral content has a higher compressive strength than that with lower kaolin mineral content. The porosity and pore size of blended cement mortar were significantly affected by the replacement of activated coal gangue.     

石膏与硬石膏对蒸养水泥石结构和性能的影响

运用液相分离技术、化学分析、离子发射光谱、ＳＥＭ、ＤＳＣ和压汞测孔等手段,着重研究了石膏与硬石膏对蒸养水泥石结构和性能的影响。结果表明：加有硬石膏的水泥浆体或水泥石孔溶液中的ＳＯ２－４浓度任何时候都明显高于加入二水石膏的浆体;而ＯＨ－浓度在蒸养前硬石膏浆体较高,蒸养后则低于石膏浆体。在蒸养水泥中,以硬石膏代替二水石膏,可使钙矾石数量增加,结晶粗大,分布均匀,且大多远离固相表面;同时使Ｃ－Ｓ－Ｈ（ｇｅｌ）尺寸变小,水泥石的结构致密,总孔隙率和最可几孔径减小,强度大幅度提高。作者认为：控制水泥石结构形成的主要因素是水泥石液相中的ＳＯ２－４和ＯＨ－浓度,增加水泥石液相中ＳＯ２－４浓度,同时适当降低ＯＨ－浓度,可改善钙矾石形成条件和水泥石的结构,从而提高水泥石强度。     

传统无机材料的现状及新材料的发展趋势

介绍了我国传统无机非金属材料 (水泥、陶瓷、玻璃 )的现状和存在的问题 .指出了今后发展传统无机材料应走的道路 .阐述了高技术陶瓷———一种新型无机非金属材料的特点、作用及其应用领域 .论述了纳米材料的研究现状及其所取得的最新成果并对未来新材料的发展趋势作了展望 .     

非线性随机模型估计及应用

讨论了非线性随机模型估计的求解问题,分为方差σ^2已知和方差未知2种情况。方差σ^2已知的非线性随机模型估计适用于测量平差以及一切有规范规定的实验科学的数据处理;方差σ^2未知的非线性随机模型估计适用于没有规范的约束的社会统计学的统计推断。文中附有算例阐述具有同值子样由于σ2已知和未知的2种情况的数据处理结果。σ     

气动系统长气管建模与分析

由于气体的可压缩性,气压信号在长气管中的传递特性表现为非线性,这种非线性给系统设计和应用带来困难。从工程应用的角度出发,难过实验对气动系统中长气管的主要特征－气压信号的延迟进行了研究,根据长气管的物理特点建立了动力模型及数学模型,并对模型参数进行了辨识和分析,还根据流体力学的理论探讨了管内流体的状态,最后通过对数学模型的仿真和实验研究进行了比较,两者具有较好的一致性。     

基于Matlab平台实现二维复杂地质模型多边形网格建模及重力异常正演计算

对已知地质模型进行重力异常正演计算是利用重力场数据对地下介质的密度异常信息进行解释的重要手段。针对三维复杂地质体的建模困难且不便,而且多数三维线性地质体可以近似看作二维地质体以实现快速方便处理的情况,对二维地质体进行多边形网格建模,并利用Matlab平台编写了适用于复杂二维地质模型的重力异常计算的软件系统。该软件系统对模型设定简单、运算速度快。选择华北地区的剖面使用目前业内广为使用的IGMAS正演软件和文中的软件系统进行了对比试验,结果显示两种方法计算的重力异常结果相当。     

道路交通动态OD矩阵预测方法的研究

对现有的动态OD预测方法进行了研究比较,在此基础上提出了一种统计学方法采估算动态交通需求的参数.该方法是基于Bayesian定理的推论得到的,并运用了综合数据和经验数据.与诸如Kalman滤波法和最小二乘法等方法相比,该技术会使得OD分配比例的预测更加精确.如何将这些预测精确地转化为路段流量的预报则需要更进一步的研究.     

高密度聚乙烯过程动态建模与仿真的策略

介绍了高密度聚乙烯ＨＤＰＥ生产过程和用于过程动态模拟与仿真的数学模型的特点。针对ＨＤＰＥ过程,提出了机理＋经验＋神经网络技术的建模策略和方法。给出了数学模型的求解方法。实践证明,研究建立的模型可靠、精确和快速,能满足ＨＤＰＥ过程动态模拟与仿真的需要。     

集成双极晶体管基区表面电流的准二维模型及其参数的提取

考虑到少子准费米能级沿基区表面的非均匀分布,建立了集成双极晶体管基区表面电流的准二维模型。利用栅控晶体管作为测试结构,提取出了主要的基区表面参数。