雨水对粉煤灰路基施工的影响研究

随着高等级公路的大量修建,粉煤灰等工业废渣用作路基填料不但取得了可观的经济效益,同时为节省土地、保护环境发挥了显著地社会效益。但在工程施工中,如何保证粉煤灰路基的施工质量,弄清影响粉煤灰路基的施工质量的主要因素,达到道路的使用要求显得尤为重要。经过大量工程实践,我们发现雨水是影响粉煤灰路基施工质量的主要因素,对粉煤灰路基的损害也最明显。因此研究雨水对已压实路堤的压实质量及影响深度,我们成立了专项课题组,结合徐济高速公路项目铜山一标段粉煤灰路基施工进行了专项研究。     

高液限红黏土的压实特性与路基填筑方案

红黏土由于水敏性一般不宜直接作为路基填料,工程中可通过加入碎石等粗骨料对其路用性能进行改良,但在实际工程应用中存在土石拌和不均的问题。基于此,为研究红黏土的压实特性,进行了标准击实和CBR强度试验。结果表明:红黏土的湿法击实结果更适用于指导工程实际,其击实曲线呈现双峰特性,分析认为第二个峰值是真正的最大干密度,其对应的含水率为最优含水率;探究了红黏土含水率与压实度、CBR强度之间的关系,压实度与强度并不呈正相关,最大CBR强度值对应的含水率比最优含水率高约5%,在适宜含水率和适当的击实功作用下,红黏土的CBR强度值和压实度都可以满足公路路基规范所需标准,这为红黏土用于路基填料提供了可能。因此,提出了"互层式"红黏土土石分层填筑方案,并运用Flac3D软件对几种不同工况下的路基填筑方式进行了数值模拟,其竖向沉降、数值模拟及工后沉降监测分析结果都表明,"互层式"红黏土土石分层填筑方式能满足高速公路路基沉降所要求的标准。     

浅谈桥梁、涵洞等构造物台背填筑

桥涵构筑物台背回填是路基工程中的关键部分,为保证桥头路堤稳定,在施工中应克服认为结构物回填工程量小、操作空间小而往往被忽视,致使回填材料不符合要求,压实度达不到设计标准的现象。本文结合实际施工简要的介绍台背回填的施工工序、填料的填筑范围,压实度等内容。     

公路填石路堤施工质量控制研究

填石路堤是指在路基施工中，利用石料（包括大卵石）填筑的路堤。只有当填料压实时才能使路堤具有足够的强度、耐久性和稳定性，同时施工又必然受经济指标的制约，故应在此原则下选择相应的施工机具、确定合理的施工工艺和质检手段，以获得既满足技术要求又经济的旅工方案。     

关于土石混合料填筑路基压实检测方法的探讨

在山区和丘陵地区的公路工程建设中,常用土石混合料作为路堤填方材料。该材料填筑的路基沉陷小,稳定性好,且易被压实,是一种较为理想的路基填筑材料。但是这种混合材料含石量、粒度、级配变化较大,与常用的细粒土路基填筑材料有较大差异。因此对土石混合料填筑路基压实进行检测是十分必要的,本文即详细阐述了土石混合料填筑路基压实检测方法的相关问题。     

脱硫粉煤灰进行路堤填筑研究

粉煤灰是热电厂燃烧排放的废料,具有颗粒轻、强度高、压缩性小特性和水硬性、易板结等优点,是一种典型的轻质材料。通过对粉煤灰脱硫后的化学、物理及力学等特点进行分析研究,提出利用脱硫粉煤灰进行路堤填筑的型式,以减少路堤填料取土场用地,节约土地资源,合理进行废料资源利用。     

循环振动作用下残积土动力变形特性试验研究

为研究压实残积土在循环荷载作用下的变形特性,对不同含水率压实残积土进行改变围压及轴向动应力幅值条件的动三轴试验,得到了不同物理力学条件下土的动应力-应变关系滞回曲线、累积塑性应变发展规律曲线及骨干曲线,分析了动弹性模量随应变的衰变规律,探究了含水率、围压及动应力幅值等因素对试验结果的影响。结果表明:当累积塑性应变达到一定值时,压实残积土变形随动应力幅值σ_d的增大增幅明显,但最终表现为弹性安定行为,该特性随含水率的增加逐渐减弱;含水率增加不利于土样变形稳定,而提高围压可抑制该趋势。另外,增湿会加快模量的衰减,并降低残余模量,围压对衰变规律的影响随应变的增大逐渐减小。研究可为花岗岩残积土作为路基填料的施工过程及土体改良提供技术参考。     

浅析高速公路高塑性粘土路基施工工艺

按公路规范要求,高塑性粘土不能满足高速公路对填料强度的要求。文章介绍对这类土不掺改良剂,通过控制其压实功、改进施工工艺增大其稳定强度,使所填路基质量满足设计要求的试验研究。     

路基压实粉质黏土动态回弹模量的四参数预估模型及有限元实现

利用动三轴试验,研究路基压实粉质黏土动态回弹模量的影响因素,分析动态回弹模量对偏应力、体应力等因素的依赖关系,通过双因素回归分析,在AASHTO-N37A动态回弹模量预估模型的基础上引入k4项,提出了含四参数的改进模型。为了使该改进模型能有效运用于有限元计算中,基于广义Hooke定律推导了其精确一致切线刚度矩阵,通过编写用户自定义材料子程序(UMAT)将改进模型移植入有限元软件ABAQUS中,分别在单个土体单元和路基路面结构条件下对改进模型进行了计算验证。研究结果表明:四参数改进模型能更好预估粉质黏土在不同压实度下的动态回弹模量,利用二次开发的改进模型在有限元软件中计算得出的土体单元的应力—应变关系与解析解较为吻合,而将改进模型运用于路基路面结构分析可以体现因应力不同造成的回弹模量在路基各个位置的差异,同时能反映车辆荷载作用下回弹模量的演变,实现了模量与应力状态的动态耦合,从而路基路面结构设计提供了更为真实的数值模拟方法。     

公路路基填土沉降特性分析

本文运用了土质学、土力学的基本原则,对5种较为典型压实填土沉降特点进行相应的研究,对其中每一种土样分别进行不同密度、分级荷载应力作用之下进行压缩方面的实验,并且掌握好沉降特点。通过研究分析,公路的路基压实性主要是受到填土颗粒组配、形状、最大密度等方面的影响,并且压实不足是造成路堤沉降的一个最重要的原因。经过工程的实际观察分析,实验数据分析结果和实践是相统一的。同时对压实填土在工程应用时的控制标准提出了相关的意见。     

Leaching of different elements from subbase layers of alternative aggregates in pavement constructions

The objective of this study was to analyze the accumulated effects of leaching in two test roads were municipal solid waste incineration (MSWI) bottom ash and aggregate from a railway embankment, respectively, were used as subbase aggregates. Solid samples from the subbase and the subgrade were collected in trenches, which were excavated perpendicular to the road extension. The samples were analyzed with respect to pH, water content, electrical conductivity and extractable fractions of macro and trace constituents. To conclude, spatial distribution patterns of different constituents in subbase and subgrade layers confirms the existence of two major transport processes in a road with permeable shoulders: diffusion underneath surface asphalt layers driven by a concentration gradient directed horizontally towards the shoulder of the road where the dissolved elements are carried away by advection.     

A new structure to control frost boiling and frost heave of embankments in cold regions

Frost boiling and frost heave are the main factors that cause road damage in cold regions. A new kind of embankment structure, which consists of geotextile, crushed-rock layer and geomembrane, was designed and investigated both in the laboratory and at the field of Budongquan located at Qinghai–Tibet Plateau. Comparison tests were conducted at the same time. The key of the new structure is the porous crushed-rock layer which has smaller thermal conductivity with function of drainage and blocking of moisture migration induced by freezing. Both the laboratory and field research results show that the frost penetration and thawing depths of the new structural embankment are much smaller than those of the coarse-grained soil embankment. Also, the new embankment structure has lower water content in the upper layer and smaller frost heave and thawing settlement than the latter does. In addition, it has good drainage effect. Water coming from the road surface can be drained away from the embankment through the porous crushed-rock layer. All these states that the new structure consisting of the porous crushed-rock layer is superior in frost damage mitigation to the normal structure used in cold regions.     

矿物掺合料对地聚合物抗冻性能的影响

以碱激发偏高岭土制备地聚合物混凝土,分别研究了掺入15%的钢渣、矿渣或粉煤灰的地聚合物混凝土的力学抗压强度和抗冻性能,测试了地聚合物混凝土的真空饱水体积吸液率,运用XRD、SEM和DSC-TG等测试方法分析了矿物掺合料对地聚合物微观结构和水化产物的影响。结果表明:钢渣或矿渣能有效提高地聚合物混凝土的抗压强度,而粉煤灰的掺入使其强度稍有降低;地聚合物表观形貌中存在较多的孔洞和微裂缝导致其抗冻性能较差,掺入钢渣或者矿渣后地聚合物形成了新的产物C-S-H凝胶、C-A-S-H凝胶等并填充在结构中形成更加密实的板状结构,降低了地聚合物混凝土冻融破坏速率,五次冻融循环后地聚合物的相对强度均在90%以上,抗冻性能得到提高;粉煤灰降低了制备地聚合物混凝土的用水量且未水化的粉煤灰颗粒镶嵌在结构中增加了其密实性和抗冻性能,五次冻融循环后相对强度为86.9%,基准组的相对强度仅为79.7%。     

粉煤灰涂层材料的控释水特性

提出了一种新型涂层导水纤维的制备方法.用粉煤灰和有机溶剂溶解的EVA混合做涂层材料,选用与膜材成分相同的聚乙烯纤维作为预涂层纤维基体.用比表面积分析仪表征粉煤灰的孔径分布,在环境扫描电子显微镜下观察纤维表面微观真实形貌,用快速水分测定仪测试纤维在不同温度下的连续失水情况.改变土壤的相对含水量,测定了优选配比涂层纤维的失水.结果表明:EVA含量最少的纤维涂层渗水效果最好,涂层纤维的保水功能是由于粉煤灰的多孔产生了毛细孔凝聚现象,该涂层导水纤维对温度以及土壤湿度都具有自调节功能.     

Cr(VI) concentration from batch contact/tank leaching and column percolation test using fly ash with additives

Batch contact, tank leaching and column percolation tests were conducted to investigate the Cr(VI) concentration in the solution/leachate from two fly ashes (fly ash A and B) with additives. The additives used were cement, low alkalinity additive and Ariake clay. There are several factors influencing Cr(VI) concentration in solution/leachate, namely (1) properties of solid/liquid mixture (chemical composition, pH value, etc.), (2) cementation effect, (3) amount of water in contact with the solid mass (solid/liquid ratio in case of batch contact test), and (4) adsorption characteristics of the solid particles to Cr ions. The test results indicate that fly ash A has less cementation component (CaO of 1.92%) and the amount of water in contact with the fly ash played an important role. As a result, Cr(VI) concentration from the column percolation test was much higher than that of the batch contact test. Adding Ariake clay had more effect on reducing Cr(VI) concentration for fly ash A than B because the pH value of the solution from fly ash A was lower, which provided a favorable condition for Cr(VI) ions to be reduced to Cr(III) and possibly to be adsorbed by clay particles. Fly ash B has more cementation component (7.15%) and for column percolation test, curing the sample for 1 week reduced Cr(VI) concentration significantly. The test results indicate that in engineering practice, a method which closely simulates the field condition should be selected to assess possible environmental effects and corresponding countermeasure methods.     

Mechanical characteristics of clay structural ceramics containing coal fly ash

In this work, the mechanical characterization of ceramic products processed from red clay with different amounts of added coal fly ash was investigated. Coal fly ash produced by power plants is a waste material that constitutes an alternative source of minerals for the production of traditional building ceramics, as it is a complex mixture of several oxides such as SiO₂, Al₂O₃, CaO, Fe₂O₃, Na₂O, TiO₂, which are usually present in the composition of such ceramics. A powder technology and firing route was followed for the processing of the clay and coal fly ash based ceramics. Different proportions of waste (10, 25 and 50%, by weight) were added to red clay, and then the mixed powders were pressed to form compacts that were fired at a selected temperature in the range 850–1,150°C. The effects of waste content and of heating conditions on the microstructure and mechanical characteristics of the obtained materials were investigated. The density, porosity, water absorption, flexural strength, hardness and fracture toughness of the produced materials were evaluated. A comparison was made between the properties of the produced ceramics with those of traditional ceramic materials used in construction, e.g. floor or wall tiles, and it was observed that the clay based products with coal fly ash additions may be used in similar applications.     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in the landfill site for solidified monoliths of fly ash

One landfill site, which co-treated solidified monoliths of fly ash and bottom ash, was investigated comprehensively to characterize its PCDD/F distribution. The solidified monoliths, soil, banyan leaves, groundwater in the monitoring wells and the treated landfill leachates in this landfill site for solidified monoliths of fly ash were all sampled to clarify their PCDD/F characteristics. Although the PCDD/F leaching concentrations were extremely lower than the Taiwan PCDD/F TCLP regulation of solidified monoliths, the PCDD/F contents in the surface soils of the landfill site are 460 times higher than that of urban soils and the highest value is 2.8 times higher than the Taiwan soil regulation (1000 ngI-TEQkg(-1)). The elevated PCDD/F contents in the soil reveal their potential for causing adverse health risk for humans, including the pathway of resuspension of soil particles and volatilization of PCDD/Fs from soil. The PCDD/F concentrations in the groundwater and the treated landfill leachates of the landfill site for solidified monoliths were both higher than that in the control samples, suggesting its potential to be a PCDD/F source of nearby water environment. Without proper control and management, landfill sites for solidified monoliths of fly ash can seriously hazard the surrounding environment, therefore, are important to consider.     

Strength of lime–fly ash compacts using different curing techniques and gypsum additive

Lime–fly ash mixtures are exploited for the manufacture of fly ash bricks finding applications in load bearing masonry. Lime–pozzolana reactions take place at a slow pace under ambient temperature conditions and hence very long curing durations are required to achieve meaningful strength values. The present investigation examines the improvements in strength development in lime–fly ash compacts through low temperature steam curing and use of additives like gypsum. Results of density–strength–moulding water content relationships, influence of lime–fly ash ratio, steam curing and role of gypsum on strength development, and characteristics of compacted lime–fly ash–gypsum bricks have been discussed. The test results reveal that (a) strength increases with increase in density irrespective of lime content, type of curing and moulding water content, (b) optimum lime–fly ash ratio yielding maximum strength is about 0.75 in the normal curing conditions, (c) 24 h of steam curing (at 80°C) is sufficient to achieve nearly possible maximum strength, (d) optimum gypsum content yielding maximum compressive strength is at 2%, (e) with gypsum additive it is possible to obtain lime–fly ash bricks or blocks having sufficient strength (>10 MPa) at 28 days of normal wet burlap curing.     

磁选粉煤灰砂浆的导电性研究

Fe3O4具有很强的磁性,利用简单的磁选工艺将普通粉煤灰中的铁氧化物(Fe1-δO)吸取出来,可得Fe3O4含量较高的磁选粉煤灰。Fe3O4在常温下的电导率为2.5×104Ω-1.m-1,和沥青基碳纤维的电导率为同一数量级。利用磁选粉煤灰作为导电材料可以制备出具有良好导电性能和力学性能且成本低廉的导电砂浆。随着磁选粉煤灰掺量的增加,粉煤灰颗粒互相接触并逐渐形成局部导电网络,使电子和空穴可通过隧道效应跃过水泥基体阻隔所形成的势垒进行传导;当磁选粉煤灰掺量超过"渗滤阈值"后,砂浆的导电性明显增强,与掺加细集料的碳纤维导电砂浆的导电性接近。