高等级公路沥青路面剪应力分布研究

基于线弹性层状体系理论,采用路面结构有限元法,主要探讨高等级公路沥青路面剪应力的分布规律及其影响因素。数据分析结果表明:在各结构层材料性能和厚度允许选择范围内,最大剪应力均分布在距路表3 cm深度范围内;影响剪应力大小的最主要的因素是沥青层模量、泊松比和基层模量。通过计算数据与试验测试抗剪强度对比分析可知:对于普通三层沥青层面层结构,上面层和中面层应进行剪应力验算,且验算时需找到准确的计算点位才能得到各层内最大剪应力值。     

碎石桩处理软土地基的设计

碎石桩处理软土地基主要是与原有软土形成复合地基,可提高地基承载力、减少沉降量,提高土体抗剪强度,加大土体的抗滑稳定性.这里介绍碎石桩处理软土地基的设计,包括承载力计算,沉降量计算,抗剪强度计算和施工工艺、施工中需要注意的问题.     

改性SiC粉悬浮浆料流变特性研究

采用亲水、亲油硅烷偶联剂WD-50、WD-20对SiC微粉进行包覆改性。研究表明,有机包覆改性SiC粉的表面结构中亲水与亲油基团的比例对料浆在低剪切速率下的流变特性有极大影响。改性粉表面全是亲水基团时,料浆触变性大,当固相体积含量由57.4%上升到58.5%时,料浆粘度突然增大1 236.0 mPa.s;随着亲油基团的引入,料浆触变性降低,高固相含量时粘度增大平缓。     

Evaluation of ageing in asphalt cores using low-field nuclear magnetic resonance

This paper introduces an innovative methodology for estimating the ageing of asphalt concrete cores without extracting the binder. Asphalt concrete samples at different ageing stages (unaged, 3-month and 6-month aged) and with different percent air voids (4%, 7% and 10%) were analysed with low-field nuclear magnetic resonance (NMR). The transverse relaxation time T₂ and relative hydrogen index (RHI) obtained from NMR measurements were related to the viscosity of the asphalt binder. The samples were analysed during cooling from 70°C to room temperature, showing increase in viscosity with decreasing temperature. There was a clear trend indicating higher viscosities in samples that were aged for a longer period and samples with higher percent air voids. The RHI and T₂ values obtained from low-field NMR measurements and the viscosity data calculated from measurements using a dynamic shear rheometer were correlated to develop a model that relates viscosity with RHI.     

Towards an optimised lab procedure for long-term oxidative ageing of asphalt mix specimen

Ageing of bitumen leads to increased stiffness and brittleness. Thus, bituminous bound pavements become more prone to failure by low-temperature and fatigue cracking. Therefore, the ageing behaviour of bitumen has a crucial impact on durability, as well as recyclability of pavements. To assess ageing of bitumen, the rolling thin film oven test and pressure ageing vessel are standardised methods for short-term and long-term ageing in the lab. For lab-ageing of hot mix asphalt (HMA), various methods have been developed in the last decades. This paper presents a study on the potential of employing a highly oxidant gas for simulating the long-term oxidative ageing of asphalt mix specimens in the lab. Based on the results, an optimised lab-ageing procedure (Viennese Ageing Procedure – VAPro) for compacted HMA specimens to assess mix performance of long-term lab-aged specimens is developed. Thus, it is possible to optimise mix design not only for short-term performance but to take into account effects of oxidative ageing during its in-service life. VAPro is based on a triaxial cell with forced flow of a gaseous oxidant agent through the specimen. The oxidant agent is enriched in ozone and nitric oxides to increase the rate of oxidation. It is shown by stiffness tests of unaged and lab-aged specimens, as well as by Dynamic Shear Rheometer tests of recovered binder from aged specimens that asphalt mixes can be long-term aged at moderate temperatures (+60°C) and within 4 days and a flow rate of 1 l/min by applying VAPro. Thus, an ageing procedure is at hand that can simulate long-term ageing at conditions that are representative of conditions that occur in the field within an efficient amount of time.     

Variation of optical properties,rheology, and microstructure in fullerene/poly(vinyl pyrrolidone) nanofluids with fullerene content in n-butanol

In this study, we report non-linear variation of optical and rheology properties in fullerene (C₆₀)/poly(vinyl pyrrolidone) (PVP) nanofluids (NFs) with C₆₀-content (C) in an alcoholic medium. From the absorption spectra, we found that the absorbance maximum (α_max) follows a non-linear path with C-value due to a donor–acceptor PVP → C₆₀ charge transfer in a C₆₀/PVP complex. The α_max value reaches maximum at a specific C₆₀-content of 13.9 μM due to percolation effect and then starts decreasing with a further increase in C-value over the subsequent region covered in this experiment. Models were proposed to show donor–acceptor interaction between C₆₀ and PVP. The molar extinction coefficient also drops through a peak maximum at 13.9-µM C₆₀. Regardless of the C-values, shear-thinning behavior was found in all NFs. The shear viscosity (η) value, which decreases with shear rate value over 5 to 100 s^?1, is shown to be increasing non-linearly against the C-value. The η-value varies non-linearly with C₆₀-content and shows a dip at a point near 13.9-µM C₆₀. High-resolution transmission electron microscope images reveal that the size of C₆₀/PVP nano-assemblies increases with C-value as PVP is anchoring C₆₀ molecules in specific structures.     

Reinforced masonry beams under shear load – Proposals for future designs / Bewehrte schubbeanspruchte Mauerwerksbalken – Vorschläge für zukünftige Bemessungen

This article is written against the backdrop of the work of the European standardisation committees on the amendment of EN 1996‐1‐1 [N 4] which will also exert an influence on the design of reinforced masonry in Germany. This paper focusses on the design approaches of DIN EN 1996‐1‐1 for untensioned reinforced masonry beams under shear load in the ultimate limit state (ULS). Proposals are made to discuss their revision. The contents of E DIN 1053‐3 [N 3] and of the final draft of the guideline ”Flat Lintels” [7] are taken into account.     

双向等轴拉伸载荷下二维编织陶瓷基复合材料的应力-应变行为预测

将二维编织结构简化为(0°/90°)s正交铺层结构。采用含损伤变量的剪滞分析理论,解得双向等轴拉伸载荷下,0°层和90°层开裂后各层的应力分布;基于随机基体裂纹演化理论,随机纤维损伤和最终失效理论,确定了0°层和90°层沿纤维方向的应力-应变关系,以及切线拉伸模量与施加载荷之间的关系;然后,将切线拉伸模量代入正交铺层结构的剪滞分析中,进而预测出二维编织陶瓷基复合材料在双向等轴拉伸载荷下的应力-应变关系。预测结果表明:在双向等轴拉伸载荷下,二维编织陶瓷基复合材料的横向和纵向应力-应变曲线基本相同,与单向加载时的应力-应变曲线相近。     

高粘沥青胶浆动态剪切流变特性

针对探索不同类型的高粘沥青胶浆动态剪切流变特性,有利于完善多孔沥青混合料配合比设计。分析材料组成、粉胶比、温度等对高粘沥青胶浆动态剪切流变特性的影响,结果表明,沥青粘度高、矿粉比表面积大,形成的高粘沥青胶浆相位角相对较小,抗车辙因子较大;与矿粉类型相比,沥青性质对胶浆抗车辙因子影响显著,对改善胶浆抗高温变形能力起主导作用;粉胶比增大,抗车辙因子随之增大,并随温度变化呈幂函数关系变化趋势。提高改性沥青粘度或增大矿粉比表面积,均可有效降低高粘沥青胶浆抗车辙因子的温度敏感性,改善高粘沥青胶浆高温抗变形性能。     

冻融循环作用下强氯盐渍土强度变化规律研究

为了研究冻融循环作用对强氯盐渍土不固结不排水抗剪强度的影响,选取罗布泊地区强氯天然盐渍土,分别配制2种不同干密度的试样,在不同冻融循环次数下进行三轴不固结不排水剪切试验,考察罗布泊强氯盐渍土不固结不排水抗剪强度随冻融循环次数的变化关系。结果表明:不同干密度的强氯盐渍土试样在0~7次冻融循环内粘聚力cu均随着冻融次数的增加而降低,并且最大干密度的试样粘聚力降低的幅度较大,内摩擦角φu略有增加但变化不大;相同的冻融循环次数下,干密度较大的试样较干密度小的试样抗剪强度参数cu、φu大。含盐类别及含盐量的不同是盐渍土在不同冻融循环次数下抗剪强度呈现不同变化的根本原因。