Forensic Evaluation of Premature Failures of Texas Specific Pavement Study–1 Sections

The Specific Pavement Study–1 pavement test section on US281 in south Texas comprise the largest Strategic Highway Research Program experimental site in the United States. The project was opened to traffic in 1997, and performance has been poor. Three of these test sections developed deep rutting within 1 year. Their surfaces were milled to restore ride quality. Three years after construction, 14 of the sections had 10 mm or more rutting. A forensic study was initiated by the Texas Department of Transportation to identify the cause of the problem. Nondestructive testing was conducted with both the falling weight deflector and ground penetrating radar. No structural problems were detected with either device, both indicating that the base and subbase layers were strong. A field investigation was initiated; the original plan was to cut nine trenches, however, after four trenches were cut, the problematic layer was identified and the trenching operation was terminated. Dynamic cone penetrometer, stiffness gauge, seismic pavement analyzer, and nuclear density gauge tests were then conducted on top of the base and subgrade layers. The trench profiles indicated that the rutting was coming primarily from the top 50-mm (2-inch) asphalt-concrete layer. Asphalt cores were taken from both rutted and nonrutted sections and bag samples of the base were tested in laboratory. The binder was recovered, and the asphalt content and penetration, aggregate gradation, and type were determined. The cause of the problem was traced to a change in aggregate screening, and also an excess of asphalt in the top layer.     

Line‐of‐Balance Scheduling in Pavement Construction

Linear Scheduling Methods are best suited to projects that display repetitive characteristics, but their use in the construction industry is limited. Line‐of‐Balance (LOB) is a Linear Scheduling Method that also makes use of network technology. Its benefits and shortcomings are investigated in a high‐way surface treatment project where LOB has been used experimentally. It was determined that LOB is extremely sensitive to errors in man hour, crew size, and activity duration estimates. There are also problems of a visual nature with the presentation of the diagram. On the other hand, LOB allows a better grasp of the project than any other scheduling technique because it is possible to adjust activities' rates of production. It provides a smooth and efficient flow of resources and requires less time and effort to produce than network schedules. Research to make Linear Scheduling Methods more attractive is recommended.     

Risk-Based Model for Valuation of Performance-Specified Pavement Maintenance Contracts

Many transportation agencies have started outsourcing maintenance activities to contractors by means of performance-based contracts. These outsourcing contracts are intended to transfer performance-based risk from transportation agencies to private contractors for a premium cost. Even though such contracts provide numerous benefits to both contractual parties, there are equally many concerns with their implementation. Certainly, one of the most important concerns is how to quantify performance-based risk. This paper presents a general and flexible framework for quantifying the performance-based risk in terms of premium cost for different contract specifications and preventive maintenance and rehabilitation strategies. The framework developed consists of three modular components: (1) the reliability-based pavement performance model; (2) the preventive maintenance and rehabilitation models; and (3) the pricing model. The developed framework is illustrated using the current design and rehabilitation methods for flexible pavements.     

Performance of Dowel Bar Retrofit Projects in Texas

In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required 50–75?mm thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade support. This is significant in that there are no effective and practical methods to improve subbase conditions in existing concrete pavement, whereas DBR can restore pavement conditions at a reasonable cost. However, not all DBR projects were successful. In one DBR project, faulting in the range of 6.4–9.5?mm occurred after less than 2 years of treatment. Forensic investigation revealed voids under the dowel bars, which indicates poor consolidation of the grout material. Efforts are currently underway in TxDOT to improve specifications for grout materials and DBR construction.     

Forensic Investigation of a Sulfate-Heaved Project in Texas

This paper focuses on the cause, possible solutions, and future prevention of pavement heave at a new construction project. We speculated that heaving on the east side of the project was caused by a reaction between the lime stabilizer and minerals in the soil. Because of a difference in soil chemistry, the west side of the project (which was still under construction) did not show evidence of heaving. A forensic investigation was initiated to test our hypothesis. The findings of the investigation concluded that the cause of the heaving on the east side of the road was related to the formation of the expansive mineral, ettringite. Ettringite formed due to the reaction of the lime stabilizer with seams of high sulfate soil on the east side. Laboratory testing did not find any effective stabilizer for the high-sulfate soils on the east side. Therefore, reconstruction would involve removing and replacing the treated layer with a select material that has less than 2,000?ppm sulfates. Test results indicate that there was no threat of sulfate heave on the west side. District personnel had performed the field conductivity tests to evaluate and monitor the concentration of the sulfate content on the remaining project. The treatment of 3%/72-h mellowing period/3% lime treatment was employed on the west side. The whole project has been completed for 1?year and no heave has been observed.     

Prediction of Permanent Deformations in Pavements Using a High-Cycle Accumulation Model

The present paper discusses the application of a high-cycle accumulation (HCA) model originally developed for sand for the prediction of permanent deformations in an unbound granular material (UGM) used for base and subbase layers in pavements. Cyclic triaxial tests on precompacted samples of an UGM have been performed in order to validate and calibrate the model. The stress amplitude, the initial density, and the average stress were varied. The test results are compared to those of air-pluviated samples of sand (subgrade material). Some significant differences in the behavior of both materials under cyclic loading are outlined. It is demonstrated that the functions describing the intensity of accumulation can be maintained for an UGM with different material constants, but that the flow rule must be generalized in order to describe the anisotropy. Recalculations of the laboratory tests show a good prediction of the modified HCA model.     

车辆二级维护中润滑作业的重要性

对在车辆二级维护润滑作业中曾经存在的错误做法以及给车辆造成的危害进行了分析 ,提出并组织实施了改进措施     

在线传感器网络智能预知维修诊断技术在空压机组上的运用

为解决企业传统设备管理中离线点巡检存在的问题,结合在线传感器网络的优点,以空压机组为实例,提出了一种在线智能预知维修诊断控制策略,进一步做好企业设备的运行管理工作。     

综合护炉技术在太钢3号高炉的开发与应用

太钢3号高炉在炉役后期采取了一系列有效措施：精心操作,稳定煤气流,在冷板损坏部位安装铜柱冷却器并定期进行硬质压入,自创了偏心冷却器的安装、灌浆技术和大面积开裂炉皮的修补技术等等。这些措施使护炉效果良好,实现了高炉长寿的目标     

10万m3POC型干式高炉煤气柜中修实践

通过对10万m3POC型干式高炉煤气柜存在问题的分析和中修内容的介绍,指出了中修重点及处理方法,为国内同类型煤气柜的生产检修提供了一些实践经验。     

莱钢1880m^3高炉计划检修后炉况快速恢复实践

莱钢1880m3高炉在长期稳定顺行时,通过精心操作,可以在休风后快速恢复炉况,主要方法是：做好前期准备工作;休风时出净渣铁,做好炉缸保温工作,适当控制水压、水量及顶温;复风时处理风量、赶料线、调整好火焰温度,抓好首次出铁工作。高炉曾经计划检修73h后,在5h之内恢复了全风作业,炉况稳定顺行。     

大型铝冶炼企业实施检修集中管理的创新实践

详细介绍中国铝业广西分公司实施检修集中管理的背景与思路,提出检修集中管理实践的持续改进措施,并介绍取得的成效与体会。     

Performance of a Combined Natural Wastewater Treatment System in West Texas

A study of performance of a combined natural wastewater treatment system was conducted in an arid and semiarid area of West Texas from October 2005 to September 2007. This study investigated the organic matter and nitrogen removal capability in a municipal wastewater land application system following a pond system. Municipal wastewater from the city of Littlefield, Tex. was pretreated by a pond system, and the secondary wastewater effluent from the pond system was surface applied to sprayfield at the wastewater treatment plant and the city farm. The 16 lysimeters were installed in situ to collect the leached water passing the grass root zone. The water samples were taken from the storage pond and the lysimeters for analysis of chemical oxygen demand (COD), total nitrogen, nitrate nitrogen, and ammonia nitrogen. The data show that the pond system played an important role in the treatment. The pond system pretreated COD in the municipal wastewater to the range of 10 to 127 mg/L, total nitrogen to the range of 5 to 19 mg/L, nitrate nitrogen to the range of 2.4 to 8.2 mg/L, and ammonia nitrogen to the range of 0.01 to 6.4 mg/L. The average mass removals and cumulative mass removals were 94 and 96% for total nitrogen, 92 and 93% for nitrate nitrogen, and 96 and 100% for ammonia nitrogen, respectively. There was no potential nitrogen contamination to groundwater found during the research period. The study illustrated that this type of combined natural wastewater treatment system can be used to effectively treat and safely dispose municipal wastewater, and save freshwater used for agricultural irrigation in arid and semiarid area.     

Dynamic Modeling of Storm Surge and Inland Flooding in a Texas Coastal Floodplain

The purpose of this study is to analyze the combined effects of storm surge and inland rainfall on the floodplain of a coastal bayou in the Houston area by using dynamic hydraulic modeling. Most existing floodplains in the Houston area are defined using only rainfall as an input into steady-state hydraulic models and do not consider the impact of hurricane-induced storm surge on the floodplain. HEC-RAS, a one-dimensional flow model, was run for both steady- and unsteady-states to analyze the additional effect storm surge has on the coastal floodplain. Storm surge and rainfall data from Hurricane Ike were utilized to run an unsteady hydraulic model on Horsepen Bayou near Galveston Bay. The dynamic model generated a good match between the modeled hydrograph and measured data in the watershed. Additionally, a timing sensitivity analysis was completed by shifting the timing of the storm surge both earlier and later in time. The dynamic model revealed that the timing of both rainfall and storm surge play a significant role in the magnitude of inland flooding.     

冬季15万m~3焦炉煤气柜并网运行日常维护要求

研究和分析了冬季15万m3焦炉煤气柜的全天候并网运行特点,剖析了在冬季运行时,气柜常出现的问题,落实了改造方案,优化了冬季运行方式,提出了日常维护要求。     

胶粘剂在设备维修中的应用

应用粘接技术进行设备维修时，应选择能够满足具体需要的最佳胶粘剂。粘接时应设计好粘接形式。注意清洁度、粗糙度、表面化学结构对表面处理的影响等。采用660型圆柱形零件固持胶粘接修复30t电弧炉倾炉大轴和倾炉齿轮，既方便又经济实用，修复后已正常使用4年，效果良好。     

焦化厂脱苯塔检修的实践经验

介绍了莱钢焦化厂创新脱苯塔清扫方式、对塔盘密封垫科学选型、科学优化塔盘拆卸、安装等检修的实践经验及其取得的较好效果.     

工艺创新在设备检修中的应用

结合设备检修实际情况，介绍了工艺创新在设备检修中的应用及给检修企业发展所带来的积极影响。     

酒钢450m~3高炉冷却壁破损原因分析及维护实践

酒钢450 m3号高炉2008年-2009年大修已运行6年,生产运行过程中炉身4-7段冷却水管破损呈加剧趋势,针对酒钢450 m3高炉炉身冷却壁破损状况,分析研究冷却水管破损原因,采取过内养和穿管、安装微型冷却器等外护措施,冷却壁破损加剧趋势得到遏制,为后期炉体维护提供依据。     

Attitudes of white and Negro high school students in a west Texas town toward school integration.

"1. Authoritarian attitudes… were not indicative of negative attitudes toward integration. 2. Negro students… show highly authoritarian attitudes as well as strong positive attitudes toward all areas of school integration. 3. White students in the segregated school systems studied show high authoritarianism though less than Negro students. 4. White students show a number of positive attitude responses toward many aspects of school integration, thus easing the expressed fear of widespread interracial conflicts in integrated schools in this area, though problems may arise in situations necessitating close personal-social contact." (PsycINFO Database Record (c) 2010 APA, all rights reserved)