Characterization of Cementitious Materials Exposed to Freezing and Thawing in Combination with Deicing Salts Using 3D Scans

Surface deterioration of concrete subjected to freezing and thawing in combination with deicing salts is one of the most important factors determining the durability of concrete infrastructure in cold climates. The freeze–thaw deicing salt (FTDS) resistance of cementitious materials can be determined by the capillary suction of de-icing chemicals and freeze–thaw (CDF) test. Specimens are subjected to repeated freeze–thaw cycles with simultaneous addition of deicing salt and the amount of material scaled off near the surface is determined. For concretes with adequate FTDS resistance, this test method works very well. However, specimens with unknown performance often experience increased edge scaling. This leads to a falsification of results and consequently to an underestimation of the actual freeze–thaw resistance. In materials research, however, concretes with high levels of surface deterioration are studied in order to investigate various factors of influence on the freeze–thaw resistance of concretes in a targeted manner. This article presents a novel methodology that delivers new information regarding surface deterioration of CDF samples using high-resolution 3D scan data. Change of volume is used to support deterioration results of the standard CDF methodology. Increase of surface area is used to estimate change in roughness of samples.     

特细砂自流密实砂浆

探讨了特细砂砂浆流动度和含砂率对特细砂砂浆自流密实能力的影响,提出用强度比表示特细砂砂浆的自流密实能力,目的在于充分发挥特细砂砂浆的自流密实能力,节约水泥．     

Assessment of the impacts of surface topography, off-nadir pointing and vegetation structure on vegetation lidar waveforms using an extended geometric optical and radiative transfer model

In order to prioritize the measurement requirements and accuracies of the two new lidar missions, a physical model is required for a fundamental understanding of the impact of surface topography, footprint size and off-nadir pointing on vegetation lidar waveforms and vegetation height retrieval. In this study, we extended a well developed Geometric Optical and Radiative Transfer (GORT) vegetation lidar model to take into account for the impacts of surface topography and off-nadir pointing on vegetation lidar waveforms and vegetation height retrieval and applied this extended model to assess the aforementioned impacts on vegetation lidar waveforms and height retrieval.Model simulation shows that surface topography and off-nadir pointing angle stretch waveforms and the stretching effect magnifies with footprint size, slope and off-nadir pointing angle. For an off-nadir pointing laser penetrating vegetation over a slope terrain, the waveform is either stretched or compressed based on the relative angle. The stretching effect also results in a disappearing ground peak return when slope or off-nadir pointing angle is larger than the “critical slope angle”, which is closely related to various vegetation structures and footprint size. Model simulation indicates that waveform shapes are affected by surface topography, off-nadir pointing angle and vegetation structure and it is difficult to remove topography effects from waveform extent based only on the shapes of waveform without knowing any surface topography information.Height error without correction of surface topography and off-nadir pointing angle is the smallest when the laser beams at the toward-slope direction and the largest from the opposite direction. Further simulation reveals within 20° of slope and off-nadir pointing angle, given the canopy height as roughly 25 m and the footprint size as 25 m, the error for vegetation height (RH100) ranges from − 2 m to greater than 12 m, and the error for the height at the medium energy return (RH50) from − 1 m to 4 m. The RH100 error caused by unknown surface topography and without correction of off-nadir pointing effect can be explained by an analytical formula as a function of vegetation height, surface topography, off-nadir pointing angle and footprint size as a first order approximation. RH50 is not much affected by topography, off-nadir pointing and footprint size. This forward model simulation can provide scientific guidance on prioritizing future lidar mission measurement requirements and accuracies.     

混凝土损伤的声发射特征分形分析

针对目前只有少量成熟的方法可用于评估混凝土的损伤破坏,并对结构的状态不能及时做出判断,本文提出用声发射技术来监测它的损伤演化．根据所得的声发射特征参数时间序列分形理论研究了它的损伤演化过程和破坏程度,得出了水泥砂浆破坏全过程各个应力水平声发射分形特征以及分形维值随实验时间的变化规律．其结果表明：在加载初中期,分形维数忽大忽小,在临近破坏时,分形维数出现“最小-最大”变化模式,利用此模式可为水泥砂浆临界损伤破坏提供一个新的判据．     

EPS保温砂浆的性能与施工

本文比较了不同容重的EPS保温砂浆和膨胀珍珠岩砂浆的基本性能 ,提出了不同容重EPS保温砂浆的配方及其施工方法。工程应用表明 ,EPS保温砂浆完全可用于外墙外保温     

纤维及砂对聚合物改性砂浆早期失水影响

采用滤纸称重法研究了聚丙烯纤维几何形态、纤维种类(聚丙烯纤维/玄武岩纤维)、砂浆搅拌方式(先掺/后掺法)、砂的粒径对聚合物改性砂浆早期失水的影响。结果表明:在0.2%(质量分数)掺量下,掺圆形截面PP纤维砂浆试样的失水率大于Y形截面试样,而在0.6%及1%掺量下,掺Y形PP纤维砂浆试样的失水率大于圆形试样;掺聚丙烯纤维试样的失水率小于掺玄武岩纤维的;不论是聚丙烯纤维还是玄武岩纤维,先掺法聚合物砂浆失水率都小于后掺法;在挤压状态而非自由状态下,随着砂的粒径减小,聚合物砂浆的失水率增大。     

高粘沥青胶浆抗剪性能评价与分析

针对不同沥青与矿粉组成的3种高粘沥青胶浆抗剪性能进行研究,分析锥重、材料组成、温度、粉胶比等对高粘沥青胶浆抗剪性能的影响。结果表明,锥重对沥青胶浆抗剪强度影响很小。随着温度升高,沥青胶浆抗剪强度下降,在25～35℃之间,且当粉胶比大于1.2时,抗剪强度变化趋势显著加快。同种沥青胶浆,随着粉胶比增大其抗剪强度增大,但抗剪强度随温度敏感性先减小后增大,粉胶比为1.2时沥青胶浆抗剪性能温度稳定性最好。与矿粉类型相比,沥青性质对胶浆抗剪强度及其温度敏感性影响更为显著。     

粘土对聚羧酸减水剂性能的影响及机理研究

粘土作为杂质存在于混凝土的组分如砂石中,粘土对聚羧酸减水剂有较强的吸附性,从而影响混凝土的工作性。研究了不同粘土对掺聚羧酸减水剂的水泥浆体及砂浆流动性的影响规律,探讨了聚羧酸减水剂与粘土的相互作用机理。研究结果表明,不同粘土对水泥浆体的流动性有不同程度的影响,蒙脱土和膨润土相对于高岭土及筛分土对砂浆的流动性影响更为显著;同时,相对于不掺聚羧酸的砂浆,粘土对掺聚羧酸减水剂砂浆的流动性影响更为显著。粘土自身的吸附性与疏水基的定向吸附共同作用及粘土中的金属离子与聚羧酸的螯合作用可能是粘土吸附聚羧酸减水剂的机理。     

邯郸地区再生骨料在混凝土和砂浆中应用研究

摘要：全面研究了邯郸地区用砖混结构建筑垃圾生成的再生骨料的粒径、堆积密度、吸水率、筒压强度等基本性能。通过试验,分别测试了以建筑垃圾为骨料的再生混凝土的干表观密度、抗压强度、抗渗性、抗冻性等相关的物理力学性能、以混凝土废渣为粗骨料的再生混凝土的抗压强度和以建筑垃圾作为细骨料等体积替代砂浆中的砂的再生砂浆的抗压强度,并分别与普通混凝土和砂浆对比分析。试验结果表明：以建筑垃圾为骨料的再生混凝土具有良好的基本力学性能,强度最高可达C30;用混凝土废渣作为粗骨料配制的再生混凝土的强度等级可达C50;再生砂浆的强度不降低。研究结果可供工程应用和科学研究参考,为再生混凝土和砂浆的进一步研究提供了一定的理论依据。     

高压喷射选用灌浆材料的探讨

高喷灌浆在使用水泥砂浆作为主材进行灌注后,板墙的稳定性和连续性得到了很大的提高,防渗效果明显,并节省了大量的水泥,有效降低了工程成本.