A section of I-25 north of Denver was rehabilitated by cold milling the existing surface to a depth of three in. and replacing with new hot mix asphalt. The contractor received bonuses for quality and smoothness and the mixture passed both Hamburg and French LCPC rut tests. Within 1 year longitudinal cracks appeared in the pavement surface. The cracking appeared in the driving lanes of both the north and southbound directions. The severity of the cracking ranged from low to high. An investigation concluded that cracking on the project was surface initiated and caused by a number of factors. One factor was segregation observed at the bottom of the upper pavement lift that was not visible on the surface. After this so-called “top-down cracking” was discovered on this first project, other pavements began manifesting similar traits. Therefore, a statewide evaluation was conducted to determine the extent of this distress in other pavements. As a result of this study 28 sites were evaluated and of these 18 contained top-down cracking. Based on this finding a change in the mixture design process was implemented to allow for increased asphalt content in hope that the richer mixtures would not be as prone to segregate. In addition, a segregation task force was created with industry to develop a specification for segregation. This task force is in the process of developing a specification to identify subsurface segregation with the elimination of top-down cracking as the goal. Paving equipment manufacturers have also identified areas within the laydown equipment that can promote segregation. As a result manufacturers have taken the initiative to develop an antisegregation retrofit for some laydown machines. As a result of these efforts top-down cracking has been generally eliminated or, at least, greatly reduced.

Grouted macadam, a material that consists of a porous asphalt skeleton with 25–35% voids, filled with a cementitious grout, has traditionally been used as a specialist surfacing with excellent resistance to both deformation and fuel spillage. However, the actual engineering properties of the material have rarely been investigated in depth and design of pavements incorporating grouted macadam has relied heavily on past experience. The purpose of this study was to assess the consequences of applying analytical pavement design methods to pavements incorporating grouted macadam layers. Two different design methodologies were tested: (1) a conventional approach based on the traditional fatigue criterion used for bituminous materials; and (2) an iterative approach, which took realistic account of the actual damage accumulation within the material. For both methodologies, a comparison was made between a grouted macadam and a conventional bituminous mixture. The main conclusion drawn from this study is that extended fatigue life can be obtained from pavements incorporating grouted macadam although this advantage will be overlooked if design is carried out using the traditional fatigue failure criterion.

The present study investigates the benefits of reinforcing the subgrade soils in flexible pavements. Three types of Soils A, B, and C, and one type of polypropylene fiber having aspect ratios of 50, 84, and 100 were selected. The California bearing ratio (CBR) and unconfined compressive strength tests were conducted on unreinforced and reinforced soils. The optimum quantity of fibers was decided based on CBR, modulus of elasticity $\left(E_i\right)$ and failure stress. The static triaxial tests were conducted on unreinforced and reinforced soils as well as on other pavement layers at a confining pressure of $40\mathrm{kPa}$ . These stress-strain data were used as input parameters for evaluating the vertical compressive strain at the top of subgrade soils using elastoplastic finite-element analysis. This vertical compressive strain at the top of unreinforced and reinforced subgrade soils was used for estimating the improvement in service life of the pavement or reduction in thicknesses of different layers for the same service life due to reinforcing the subgrade soils.

Since reflective cracking is related to both the existing pavement condition and the overlay material, appropriate tools are needed to characterize both properties. The rolling dynamic deflectometer (RDD) was employed to measure the continuous deflection profiles that relate to vertical movements of the underlying joints and cracks. An overlay tester (OT) was utilized to characterize the asphalt mix’s ability to resist reflective cracking. The reported threshold values were employed in the study that include: (1) $W1–W3=6.5\mathrm{mils}$ for composite pavement with old asphalt concrete (AC) overlay; (2) $W1–W3=5.5\mathrm{mils}$ for exposed concrete pavement; and (3) 700 cycles of the OT were employed to evaluate six field rehabilitation projects (SH12, IH20, US96, SH73, SH225, and IH44). It was found that although there were severe transverse cracks and spalling on US96, all $W1–W3$ deflections were less than $5.5\mathrm{mils}$ , indicating low risk for reflective cracking. A stone-mastic asphalt (SMA) layer was placed 3 years ago and the performance is excellent. There are no visible cracks or distresses. The SMA was tested with the OT and exceeded 700 cycles (excellent property on resisting reflective cracking). For comparison, there were severe reflective cracks within 4 years on SH225 even with good underlying support and low vertical movements (all $W1–W3$ deflections less than $6.5\mathrm{mils}$ ) on the jointed concrete pavement (JCP). The reflective cracks were due to a stiff/brittle mix (with OT life of 2 cycles) used on top of the JCP. Dowel bar retrofit (DBR) and full depth repair did improve load transfer and lowered $W1–W3$ deflections on the SH73 project. After 10 years of service, those locations had minor cracks, as opposed to severe reflective cracks in sections without DBR or full depth repair. Based on the results obtained, the RDD, OT, and the three threshold values provide an objective evaluation that correlates to field performance data. It is strongly recommended that both tools be used for the rehabilitation of concrete pavement with an AC overlay to evaluate the potential for reflective cracking.

The resilient modulus of the materials used in various pavement layers has been used extensively as an important material property in structural design of pavement. The state of stress and moisture content of cohesive soils have been observed to exert significant effects on the measured resilient modulus. Since the moisture content in the cohesive subgrade soils underneath the pavement undergoes seasonal changes due to infiltration of precipitations and since characterization of moisture and stress dependent resilient modulus of cohesive soils is a demanding and tedious task, there is a practical need for a predictive equation for the resilient modulus as a function of stress states and moisture content. This paper presents a new predictive equation for the resilient modulus of cohesive soils using the concept of soil suction. The accuracy of the proposed model is validated against experimental data of A-4 and A-6 soils conducted by the writers as well as by other data available in the literature. The proposed model provides advantages over the existing predictive equations by reducing the number of tests and soil specimens needed for determining the regression coefficients in the equation. The proposed predictive equation compares well with the empirical equation in the new mechanistic empirical pavement design guide (MEPDG) in predicting the effect of moisture content variation on the resilient modulus. The proposed model provides an advantage over the MEPDG empirical equation in taking into account the effects of both the stress state and moisture content on the resilient modulus of cohesive soils.

This paper addresses the optimal contraflow lane configuration problem arising in the contraflow lane control strategy that has been implemented successfully in practice. The problem is formulated as a bilevel programming model in which the upper level problem is a binary integer programming formulation that aims to minimize the total travel time of a study area, while the lower level problem is a microscopic traffic simulation model that can simulate the dynamic reaction of the drivers resulting from a contraflow lane configuration scheme. A microscopic traffic simulation model is adopted in this study because it is easily handled by traffic engineers. Such an adoption results in inexistence of analytical expression of the objective function in the upper level problem. Accordingly, some conventional analytical solution methods for solving integer programming problems are no longer available for the proposed model. Therefore, this paper develops a variation of genetic algorithm that embeds with the microscopic traffic simulation model as well as a chromosome repairing procedure to find an optimal contraflow lane configuration solution. A case study in Singapore is carried out to evaluate the proposed methodology, in which PARAMICS as the microscopic traffic simulation model is applied.

There is growing concern over the problems associated with excessive use of trucks to transport freight. Such problems include air and noise pollution, damage to road surfaces, excessive fuel consumption, traffic congestion, and accidents. Underground capsule freight pipelines promise to alleviate and solve these problems. This paper examines the steady-state performance of a pneumatic capsule pipeline (PCP) freight transport system based on the use of a nonintrusive linear electric motor (LEM) to propel the capsules. A PCP system consisting of a single LEM and a section of pipeline is described, and the equations that relate the various system variables are used in a MATLAB program to conduct a parametric performance study. The results suggest ways to optimize system performance without excessively increasing costs. For example, system mechanical efficiency greater than 90.0% can be obtained with a normalized motor length of the order of 2.0% if the pipe line fill rate is at least 20.0%, the pipe capsule speed is at least $15.0\mathrm{m}∕\mathrm{s}$ , the capsule length-to-diameter ratio is at most $2.0\mathrm{m}∕\mathrm{m}$ , the capsule mass per unit length is at most $250.0\mathrm{kg}∕\mathrm{m}$ , and the end disk to motor-diameter ratio is at least 0.99. When these conditions are satisfied, the thrust per capsule required of the motor and the capsule speed in the motor are relatively insensitive to slight changes in motor length, pipe line fill rate, pipe capsule speed, capsule length or mass, or the drag coefficient in the pipe, results that should simplify the design of the motor.