Ilan Ishai

EFFECTS OF SOME AGGREGATE AND FILLER CHARACTERISTICS ON BEHAVIOR AND DURABILITY OF ASPHALT PAVING MIXTURES

A summary of some of the findings obtained during a series of research projects aimed to select, define, and evaluate the significant aggregate and filler properties and relate them to the behavior of bituminous concrete is presented. A concept and test method suggested for an objective quantitative evaluation of the geometric irregularity of aggregate particles (shape, angularity, and surface texture combined) in a wide range of particle sizes are discussed. The aggregate parameters were found to be significantly correlated to the physical properties and mechanical behavior of the bituminous mixtures composed of the aggregates tested. Research work and findings related to a special evaluation of important physicochemical properties of the filler and their significant effect on the immediate properties and the long-term durability behavior of bituminous paving mixtures are summarized.

THE ISRAELI EXPERIENCE WITH THE REGULAR AND EXTENDED DYNAMIC CONE PENETROMETER FOR PAVEMENT AND SUBSOIL-STRENGTH EVALUATION

One of the Israeli modifications in the dynamic cone penetrometer (DCP) apparatus is the extension of the length of the standard penetrating rod to a total of about 2.0 meters by screwing on an additional 1.0 meter rod after the original rod has completely penetrated the pavement or subgrade. Such a procedure is required when the strength profile is significant at depths exceeding 1.0 meter or when the total thickness of the pavement layers, including the relevant subgrade layers, exceeds the length of the standard penetrating rod. Through comparative in situ testing, it was found that a 20% deduction should be applied for this testing procedure to the CBR values calculated from the in situ DCP results, both for clayey and for granular subsoils, when the standard CBR-DCP equation is used. Similarly, a 10% reduction should be applied to the 1.5-meter penetration rod results.

Simplified Generalized California Bearing Ratio Pavement Design Equation

The probabilistic approach to pavement design and evaluation requires estimation of the diversity associated with each design parameter. Results and conclusions should be based on statistical analysis with wide application of mathematical statistics and theory of reliability methods. Consequently, statistical analysis of the California bearing ratio design equation was performed, and a new generalized design equation suggested. This equation provides a simplified and rapid pavement design prediction using the common basic design parameters. The suggested model and equation provide at least the same and, possibly, greater accuracy than the current deterministic pavement design method provides. At the same time, they eliminate the need to determine the equivalent singlewheel load curve for each loading and wheel configuration, depending instead on the number of wheels in the assembly only. It is believed that the suggested model and equation also provide an appropriate step toward the application of stochas...

Reacted and Activated Rubber: Elastomeric Asphalt Extender

Traditionally, asphalt rubber (AR) mixtures have been difficult to produce. Their production requires specialized plants and equipment, which has resulted in their high cost to manufacture. In part this difficulty is due to the need to produce AR binder by blending it at high temperatures for a significant period of time (typically at about 190°C for 45 min to 1 h). The complexities in the process have caused AR mixes to be significantly more expensive to produce than conventional paving mixtures. A new technology that produces a reacted and activated rubber (RAR), which is an elastomeric asphalt extender, has been developed by hot blending and activation of a rubber granulate with a selected asphalt binder and activated mineral binder stabilizer. RAR achieves results comparable to those of other types of polymer modified binders (PMBs). However, a principal advantage of RAR is that it can be added easily to any hot-mix asphalt manufacturing facility with systems designed to feed particulate material into a batch plant (pugmill) or drum mix plant. This paper describes how RAR is produced from raw constituent materials. Various binder tests contrast performance with typical paving grades and PMBs used in the United States. The implementation of RAR in various types of asphalt mixtures is discussed, and demonstrative examples of test results are provided. Tests on mixtures in wheel tracking and fatigue demonstrate how the binder performance tests translate into mixture performance. In all cases evaluated, the RAR mixtures outperformed nonmodified and even conventional rubber modified equivalent materials.

Comparative Economic-Engineering Evaluation of Concrete Block Pavements

ABSTRACT This paper presents a comparative engineering-economical evaluation and analysis of flexible, rigid, and Concrete Block Pavements (CBP) at different structure alternatives. Several key factors were involved in the analysis. They are: three types of traffic categories—Occasional, Medium, and Very Heavy; one subgrade strength (CBR=4%); local pavement design practice (current design curves for flexible, rigid and CBP pavements); consideration of both initial construction and maintenance costs; total pavement life—20 years with major maintenance implementation at 10 and 20 years; local construction and maintenance costs. The results of the analysis shows that: 1) The construction cost of the CBP is higher than that of the flexible pavement at the medium and low traffic categories; however, it is lower for the heavy traffic; 2) The absolute values of construction plus the maintenance cost of CBP are always equal or less than that of flexible pavements; 3) The total CBP cost capitalized to the first day of service is higher than that of the flexible for the low and medium traffic, but became lower for high pavement thickness; and 4) The cost of CBP is substantially lower than the rigid pavement for all traffic categories and all cost alternatives. The economic-engineering evaluation presented here may also provide a general methodology for a comparative evaluation of different types and combinations of pavement structures under any condition. Although the specific pavement design methods, maintenance techniques, and unit prices are local by nature, the basic scheme presented here may serve as a universal basis for evaluating specific conditions for any given transportation engineering project, in which the selection of a pavement type is a key issue.

Resistance of Steep Concrete Block Pavements to High-Velocity Water Flow

In some locations, the use of concrete block pavement (CBP) involves the combination of a very steep and storm-sensitive region with the consequent risk of high-velocity water flow on pavements. Under these conditions, and because of the special characteristics of CBP and its unknown response to high-velocity water flow, two problems must be addressed: (a) the danger of sand erosion from the bedding layer and the joints between the blocks, because of surface drainage and water flow, and (b) the danger of development of uplift forces from the downward water seepage. The cumulative effect of these two dangers may cause a gradual loss of support of the CBP, leading to total failure. CBP was tested under high-velocity water flow on a one-to-one scale, with definition of flow and failure mechanisms in the CBP and with the adoption of proper solutions. Five tests were performed in an experimental water flume, differing in type of bedding. Use of conventional sand bedding under continuous water-flow conditions was found to be inappropriate. Such bedding cannot provide the necessary stability for the CBP. However, the use of fine aggregate as bedding material ensured the stability of the CBP under continuous supercritical flow velocities and steep channel slopes. Excellent performance of the CBP was observed with the underlying fine aggregate bedding. The use of sufficiently coarse aggregate as bedding material is the proper engineering solution for preventing erosion and ensuring the absolute stability of a CBP under high water-flow velocities under supercritical conditions.