Case Study of Urban Concrete Pavement Reconstruction on Interstate 10

Many urban concrete pavements in California need to be reconstructed, as they have exceeded their design lives and require frequent maintenance and repair. Information is needed to determine which methodologies for pavement design, materials selection, traffic management, and reconstruction strategies are most suitable to achieve the objectives of California Department of Transportation’s (Caltrans) long-life pavement rehabilitation strategies (LLPRS) program. To develop construction productivity information for several construction windows, a case study was performed on a Caltrans concrete rehabilitation demonstration project near Los Angeles on Interstate-10, where 20 lane-km was successfully rebuilt using fast setting hydraulic cement concrete (FSHCC) with one weekend closure for 2.8 lane-km and repeated 7- and 10-h nighttime closures for the remaining distance. The concrete delivery and discharge controlled the overall progress. In terms of the number of slabs replaced per hour, the 55-h weekend closure was 54% faster than the average nighttime closure. An excellent traffic management strategy helped to reduce the volume of traffic during the weekend closure and minimize the traffic delay through the construction zone.     

Investigation of a Pavement Premature Failure on a Weak and Moisture Susceptible Base

An investigation was conducted to determine the root cause of the premature pavement failure. The premature pavement failure occurred in the form of rutting and alligator cracking. Although the affected portion was repaired by removing and replacing the top 75-mm asphalt concrete (AC), the repaired AC experienced recurring rutting and alligator cracking in a few weeks. Through extensive field and lab testing, it was found that the weak base is the root cause of the premature failure and the brittleness of the AC is secondary. However, both the base and AC were built according to plan and met the current material and field density requirements. It was concluded that density alone for construction quality control is not sufficient, as it was not able to protect against premature failures from occurring. Although there are many different ways to minimize premature failures, an immediate action is to include proof rolling in construction quality control. Proof rolling has been used with success to ensure proper compaction and to locate unstable areas, as the stability is greatly influenced by the degree of densification achieved during compaction.     

Co/Ni比对93W-Co-Ni钨合金烧结温度及力学性能的影响

以Co、Ni作黏结剂,选择不同Co/Ni比,用粉末冶金法制备出HRC硬度在30⁴3之间的93W-Co-Ni钨合金。采用光学金相、扫描电镜对合金组织形貌进行表征,采用准静态拉伸试验对合金的抗拉强度及延伸率进行测试,采用洛氏硬度计对合金硬度进行测定。结果表明:随着Co/Ni比增加,合金的烧结温度逐渐增加,其抗拉强度与延伸率急剧降低,而硬度先增加之后趋于稳定;当Co/Ni≥1.0时,合金抗拉强度很低,延伸率≤1%;当Co/Ni≥4时,其HRC硬度值稳定在4143之间的93W-Co-Ni钨合金。采用光学金相、扫描电镜对合金组织形貌进行表征,采用准静态拉伸试验对合金的抗拉强度及延伸率进行测试,采用洛氏硬度计对合金硬度进行测定。结果表明:随着Co/Ni比增加,合金的烧结温度逐渐增加,其抗拉强度与延伸率急剧降低,而硬度先增加之后趋于稳定;当Co/Ni≥1.0时,合金抗拉强度很低,延伸率≤1%;当Co/Ni≥4时,其HRC硬度值稳定在41⁴3之间,明显高于一般的W-Ni-Fe合金,这主要与Co对W基体的润湿性较差及两者之间易形成脆性化合物Co7W6有关。