Structural Evaluation of Cement Concrete Roads in Mumbai City

Plain jointed concrete pavements laid in Mumbai City (India) during the early 1990s were structurally evaluated using a falling weight deflectometer (FWD) and testing of concrete cores extracted from the pavement slabs. The ultrasonic pulse velocity (UPV) of the concrete in the cores was determined first and then the cores were crushed under compression. The pavement deflections were found to be within the limits as suggested in the Indian codes and the international literature. The joint conditions were also found to be satisfactory. The design strength of the concrete was back-calculated from the compressive strength of the cores and was found to conform to the design specifications. However, the construction quality was found wanting as the thickness of pavement slabs at a few locations was lower than that specified and it has resulted in cracking of the slabs. The dynamic modulus of elasticity of concrete as determined by the FWD was found to correspond well with that computed from the UPV of cores and from the compressive strength of concrete. A method is suggested to estimate the structural parameters of uncracked pavement slabs from the dynamic modulus of elasticity obtained through the indirect method of UPV testing which is less expensive compared to evaluation by the FWD.     

Using Scanning Lasers to Determine the Thickness of Concrete Pavement

Due to limited budgets and reduced inspection staff, state departments of transportation are in need of innovative approaches for providing more efficient quality assurance on concrete paving projects. In Iowa, the current technique is to take core samples of the pavement, which is a labor intensive, destructive process. Due to these limitations, a limited number of cores are used to estimate the pavement thickness. Any method that can reduce or eliminate cores and increase the statistical accuracy of the thickness estimate will be beneficial. One method, which uses a laser to scan the surface of the base prior to paving and then to scan the surface after paving can determine the thickness at any point. Also, scanning lasers provide thorough data coverage that can be used to calculate thickness variance accurately and identify any areas where the thickness is below tolerance. The laser scanning methodology for this study involved the following: (1) investigating characteristics of the paving process; (2) using a laser scanner on three different sites; (3) processing the data to create clean surface models; (4) performing statistical analyses to determine thickness variability; and (5) summarizing the results.     

Evaluation of Full-Depth Asphalt Pavement Construction Using X-Ray Computed Tomography and Ground Penetrating Radar

In the past few years, a number of full-depth or perpetual pavements have been designed and constructed in the State of Texas. A study was conducted to examine the quality of the compaction of the thick asphalt layers within these pavements using advanced forensic tools such as X-ray computed tomography (X-ray CT) and ground penetrating radar (GPR). The GPR is a nondestructive tool for evaluating the uniformity of density in pavements at highway speed. X-ray CT is a laboratory tool that is used to conduct detailed analysis of air void distribution and uniformity in asphalt pavement cores. This paper presents the results of analyzing one of the perpetual pavements constructed in State Highway 114 (SH-114). In this project, two different structural asphalt pavement sections were placed, one included a 1?in. (25.4 mm) stone filled (SF) Superpave mix and the other included a traditional dense graded Type B material. The dense graded Type B material was found to be uniformly compacted. However, major compaction problems were identified with the coarse SF Superpave mix. The poor compaction and associated high percent air vsoids were found to permit moisture infiltration, which could potentially lead to rapid pavement deterioration. The analysis showed very good agreement between the GPR and X-ray CT results and demonstrated the efficiency of using GPR and X-ray CT in the evaluation of asphalt pavement compaction.     

Forensic Investigation of Ultrathin Whitetopping Pavements in Florida

Developed in the early 1990s, ultrathin whitetopping (UTW) is a relatively new technique for asphalt pavement rehabilitation. To evaluate the applicability of UTW pavement in Florida, in 1997, the Florida Department of Transportation (FDOT) constructed an experimental UTW pavement in a weigh station along I-10, located in north Florida. The performance of these test sections, however, was less than ideal, with the observation of some early cracking on the concrete surface, which developed into severe cracking with time. Therefore, a forensic investigation was conducted to determine the causes of the problems in these UTW sections, so that lessons could be learned from this experimental project, the use of UTW under Florida’s conditions could be adequately assessed, and UTW technology could be properly applied in the future. The scope of work consisted of field evaluation, laboratory testing, and pavement design evaluation. Field evaluation included a pavement condition survey, pavement temperature measurement, nondestructive load testing using a falling weight deflectometer, and slab thickness determination. Laboratory tests were performed to determine concrete and asphalt material properties. Other design and traffic data were also acquired from FDOT. Data collected from the field evaluation and laboratory testing were used in conjunction with a mechanistic UTW pavement design/evaluation procedure to determine the possible causes for premature failure. From this comprehensive evaluation, the primary cause for the failure was found to be inadequate UTW pavement design. The inadequacy of the combination of thickness and slab dimensions contributed to the early cracking of the UTW pavement.     

X射线测厚仪测量压延铜箔厚度精度的影响因素及故障处理

东芝X射线测厚仪是X型铜箔轧机的关键检测设备及厚控系统(AGC)的重要组成部分,其精确的厚度测量功能是保证轧机厚度控制有效的基本条件。基于测厚仪的构成和测量原理,对满量程校准和精度验证的机理进行分析研究,对标样箱内部标准样板脱落、x射线发生器劣化等故障,采取切实有效的措施,提高了测厚仪运行稳定性和测量精度。     

Fatigue Behavior of a Pavement Foundation with Recycled Aggregate and Waste HDPE Strips

A laboratory investigation was conducted to evaluate the fatigue behavior of an alternative pavement foundation material containing cement stabilized reclaimed crushed aggregate. Class C fly ash, and waste-plastic strip [high density polyethylene (HDPE)] reinforcement. The primary motivation for this research was to evaluate a composite that contained more than 90% recycled materials for use as an alternative foundation layer underneath conventional flexible or rigid pavement. The specific objectives of this study were (1) to evaluate the flexural fatigue behavior of the new composite, and (2) to evaluate the accumulation of fatigue damage in the material. The results indicate that the fatigue resistance of this material is similar to other traditional stabilized pavement materials. It was found that the dynamic elastic modulus remained approximately constant (degraded slowly) for most specimens up to the end of fatigue life. Fatigue damage computed using a dissipated energy approach showed that the damage accumulation in this material approximately follows Miner's rule for cumulative damage, which is often used in pavement engineering.     

Factors Affecting Initial Roughness of Concrete Pavement

Past studies have shown that initial pavement roughness greatly affects future pavement roughness and roughness progression rate. Initial pavement roughness is also an important input to the roughness prediction model in mechanistic-empirical design guide. This study analyzed the design and construction factors affecting initial pavement roughness. Initial international roughness index of 90 concrete pavements constructed in Wisconsin from 2000 to 2004 were analyzed using multiple regression method. The factors considered in this study included concrete pavement slab thickness, project location, dowel bar placement, joint spacing, base type, and pavement length. The factors affecting initial pavement roughness were identified.     

橡胶沥青应力吸收层在旧路面改造中的应用

分析了水泥混凝土路面沥青加铺层反射裂缝的产生机理,介绍橡胶沥青应力吸收层良好的抗反射裂缝效果及其路用性能.结合金溪县秀谷中大道改造工程的设计、施工情况,阐述了橡胶沥青应力吸收层在旧路面改造中的应用.     

Random Vibration of Laminated FRP Plates with Material Nonlinearity Using High-Order Shear Theory

The nonlinear response of laminated fiber reinforced plastic (FRP) plates modeled with finite elements and excited by stochastic loading is studied. FRPs are being used widely for structural applications in recent years due to their outstanding mechanical properties. Most FRP materials have strong anisotropic properties and exhibit significant nonlinearity in the shear stress-strain law. A high-order shear theory is used to account for the variation of strains through the thickness, since Kirchhoff and Mindlin plate theories are usually inadequate for modeling laminated FRP plates of reasonable thickness. Nonlinear random vibration analysis is performed using the method of equivalent linearization to account for material nonlinearity. A formulation for deterministic dynamic analysis is also developed and performed to verify the accuracy of the approximate nonlinear random vibration method. The random vibration analysis is found to be sufficiently accurate and is considerably more cost-effective than the use of deterministic simulations.     

Successful Application of CLSM on a Weak Pavement Base/Subgrade for Heavy Truck Traffic

Lack of proper pavement base and subgrade compaction leads to premature failures that account for millions of dollars in damages. Controlled low-strength material (CLSM) concrete was introduced in this study as pavement base material near a manhole where proper compaction is unachievable. Rut-resistant stone matrix asphalt was placed on top of the CLSM as a wearing surface layer. Dynamic cone penetrometer (DCP) testing was used to monitor CLSM construction. One day after placing, the CLSM gained sufficient strength to support construction traffic. Further, DCP results indicated that the CLSM possessed uniform characteristics of concrete that could improve the load-bearing capacity and serviceability of the pavement near the manhole. After 18 months of heavy truck traffic, maximum rutting was 5?mm, well below the failure criteria of 12.5?mm. Based on cost and performance, CLSM concrete has the potential to improve problematic areas in pavement.     

Performance of Geosynthetic-Reinforced Asphalt Pavements

This paper describes the performance of geosynthetic-reinforced asphalt pavement under monotonic, cyclic, and dynamic loading conditions. The study differed from current practice where geosynthetics are typically used as separators or to improve the bearing capacity of the subgrade. A geogrid layer was installed at the bottom of the asphalt concrete layer, along the asphalt-subgrade interface, to function as tensile reinforcement. The load was applied to the surface of the asphalt concrete layer using a rigid rectangular footing under plane strain conditions. The strains that developed along the geogrid over time and at different load levels were monitored. Two different types of geogrid reinforcements were used, and their restraining effects on the layered system were compared. The study showed that geosynthetic reinforcement increased the stiffness and bearing capacity of the asphalt concrete pavement. Under dynamic loading, the life of the asphalt concrete layer was prolonged in the presence of geosynthetic reinforcement. The stiffness of the geogrid and its interlocking with the asphalt concrete contributed to the restraining effect.     

Time Domain Backcalculation of Pavement Structure Material Properties Using 3D FEM with Ritz Vectors

The three‐dimensional finite element (3D FE) methods have been used increasingly to evaluate the bearing capacity of pavement structures. In this evaluation, layer moduli are backcalculated from measured surface deflections of the pavement structure. However, backcalculation requires repetitive computation to improve the parameter values in an iterative manner, and thus it is time consuming when 3D finite elements are used for the analysis. In this article, an effective method is developed to estimate layer moduli and damping coefficients in the time domain. The pavement is modeled using 3D finite elements. Gauss‐Newton and singular value decomposition methods are employed to backcalculate the unknown parameters. Ritz vectors are used to reduce the size of the matrices required for the analysis. Numerical simulations verify the effectiveness and accuracy of the Ritz vector method.     

Analytical Approach to Predicting Temperature Fields in Multilayered Pavement Systems

An accurate and rapid estimation of the pavement temperature field is desired to better predict pavement responses and for pavement system design. In this paper, an innovative method to derive the theoretical solution of an axisymmetric temperature field in a multilayered pavement system is presented. The multilayered pavement system was modeled as a two-dimensional heat transfer problem. The temperature at any location (r,z) and any time t in an N-layer pavement system can be calculated by using the derived analytical solution. The Hankel integral transform with respect to the radial coordinate is utilized in the derivation of the solution. The interpolatory trigonometric polynomials based on discrete Fourier transform are used to fit the measured air temperatures and solar radiation intensities during a day, which are essential components in the boundary condition for the underlying heat transfer problem. A FORTRAN program was coded to implement this analytical solution. Measured field temperature results from a rigid pavement system demonstrate that the derived analytical solution generates reasonable temperature profiles in the concrete slab.     

PCC Airfield Pavement Response during Thaw-Weakening Periods

A field study was performed at two regional airports in Wisconsin during spring thaw to determine its effects on portland cement concrete (PCC) airport pavements. This study was part of a research program to model the performance of airfield pavements for the Federal Aviation Administration. Subsurface temperature and falling weight deflection measurements of the pavement structures were taken at both airports and used to calculate the frost penetration depths, the changes in bearing capacity, and the joint and load transfer efficiencies. This paper summarizes the findings of this study and includes several relationships between various engineering properties of the subsurface layers below the PCC layer, along with a procedure for evaluating pavement performance using falling weight deflection data for PCC pavements during spring thaw.     

The evaluation of sizing accuracy of particle counters for parenteral drugs

Our evaluation of electronic liquid-borne particle counter systems has shown that, for accurate measurement of particulate matter in injections, the half count values of voltage thresholds from the particle counter itself should be used in the calibration for the particle sizes being evaluated. The manual method which uses the half count values in the USP XXIII<788> was improved, and the validity of our calibration method was supported by the results based on the ratio test, at 10 microns to those obtained at 15 microns is between 1.5 and 3.5, as per the Seventh Supplement of USP XXII <788>. Additionally, computer-based systems with automated calibration routines which solve the approximate Gaussian distribution of calibration particles have advantages. For the proper determination of the sizing accuracy of a particle counter, criteria of the ratio test at 10 microns and 15 microns as per the Seventh Supplement of USP XXII <788> should be applied at all critical particle sizes.     

基于雷达信号特征点提取的结构物埋深估算方法

为了克服经验法推算结构物埋深的缺陷,基于检测对象的雷达反射波形特征,通过提取反射波形上的少量特征点,提出一种估算结构物埋深的新方法,并考虑实际检测中结构物反射波形的畸变,对估算精度进行分析评价.结果表明:对于理想的无畸变检测数据,该方法对结构物埋深、水平位置及电磁波速的估算结果较为精确;当反射波形存在畸变时,该方法对埋深的直接估算结果误差较大,平均误差达到55.202%,但对于电磁波速的估算结果较为精确;对于实测的有畸变检测数据,可通过电磁波速估算结果及测得的目标体双程旅时对埋深进行间接估算,估算精度满足雷达法检测对埋深估算的要求.相比经验法,该方法在估算精度、误差控制方面具有显著优势.      

A filtration method for improving film dosimetry in photon radiation therapy

Successful radiotherapy requires accurate dosimetry for treatment verification. Existing dosimeters such as ion chambers, TLD, and diodes have drawbacks such as relatively long measurement time and poor spatial resolution. These disadvantages become serious problems for dynamic-wedged beams. Thus the clinical use of dynamic wedges requires an improved dosimetry method. X-ray film may serve this purpose. However, x-ray film is not clinically accepted as a dosimeter for photon beams, because it overresponds to photons with energies below about 400 keV. This paper presents and develops a method which was initially proposed by Burch to improve the dose response of x-ray film in a phantom. The method is based on placing high-atomic number foils next to the film. The foils are used as filters to preferentially remove low-energy photons. The optimal film and filter configuration in a phantom was determined using a mathematical scheme derived in this study and a Monte Carlo technique (ITS code). The optimal configuration thus determined is as follows: the filter-to-film distance of 6 mm and the filter thickness of 0.15 mm for percent depth-dose measurement; the distance of 1 cm and the thickness of 0.25 mm for off-axis (dose) ratio measurement. The configuration was then tested with photon beams from a 4 MV linac. The test result indicates that the in-phantom dose distribution based on the optimal configuration agrees well with those measured by ion chambers.     

Modeling Measured 3D Tire Contact Stresses in a Viscoelastic FE Pavement Model

Three‐dimensional (3D) contact stresses occurring between the road surface and the tire that were measured with the South African Vehicle Road Surface Pressure Transducer Array (VRSPTA) device under a moving wheel are transformed to a corresponding force/stress pattern representing the actual contact stress state under the tire by means of a software program. In combination with a dynamic load function such force patterns derived from these Stress‐in‐Motion (SIM) measurements with the VRSPTA device are used to introduce a more advanced load representation of the tire‐pavement interface into a three‐dimensional (3D) finite element (FE) model. Further, a method is presented to derive viscoelastic material properties of asphalt concrete (AC) mixes from dynamic frequency sweep shear (FS‐S) tests of lab specimens or field cores that can be used to define material behavior of the AC layers in the 3D FE pavement model. Linear elastic layered theory is utilized to validate the results of the FE computations in order to demonstrate that the FE method can successfully be used to include SIM measurements for more advanced analysis and design of pavements. First results of the 3D FE simulation of a load circle of the Heavy Vehicle Simulator (HVS) during accelerated pavement testing of a pavement test section are presented. These results encourage employment of the FE pavement model for further simulation work to assess the rutting potential of AC mixes in combination with different tire types and loading situations.     

Finite Element Analysis of Concrete Pavements Over Culverts

Accelerated distress of Portland cement concrete pavements (PCCP) over structures such as culverts, pipes, and tunnels beneath roadways is a common occurrence. In this article, finite element analysis is employed to analyze the response of concrete pavements over such structures. The factors that influence the overlying pavement slabs include: (1) cover depth, (2) pavement slab thickness and length, (3) cement concrete elastic modulus, (4) foundation modulus, and (5) backfill soil modulus. The tensile stresses at the bottom and top of the slab induced by wheel loads are predicted. In the traditional pavement design only the tensile stress at the bottom of the slab is considered to be significant. However, this study shows that the tensile stress at the top surface of pavement slabs over culverts may also cause the concrete pavements to fail. A laboratory model was employed to study the mechanical characteristics of Portland cement concrete pavement slabs over culverts and to verify the theoretical analysis.     

蒙特卡洛法在多点校准线性测量系统不确定度评定中的应用

多点校准线性测量系统相比单点或两点校准具有更宽的测定范围和更高的准确度、可靠性,在化学分析、物理测试等多个领域都有着广泛的应用。实验提出了蒙特卡洛法(MCM)评定多点校准线性测量系统不确定度的数学模型和仿真模拟方法,并以电感耦合等离子体原子发射光谱法(ICP-AES)测量低合金钢中锰含量为例,介绍了MCM评定测量不确定度的详细步骤和应用方法。首先采用MCM法,根据输入量的概率分布类型,通过模拟抽样分析进行测量不确定度评定,再采用GUM法进行评定。实验结果显示,试样中锰含量的平均测量结果为(0.919±0.012)%,k=1.96,与GUM法计算得到的扩展不确定度一致。给出的方法实现了MCM法在多点校准线性测量系统不确定度评估中的应用,一定程度上解决了标准样品参考值与线性校准波动性引入不确定度量值的导入问题,有助于进一步推动不确定度评估与应用的创新与发展。