Segregation In Hot Mix Asphalt Pavements

This document discusses segregation in Hot Mix Asphalt. Considerable effort has been exerted over the last decade to improve the performance of Hot Mix Asphalt. At each point during the manufacturing process the mix has an opportunity to segregate, creating non-uniform mixes. A segregated spot may be "the birth of a pothole". When segregation is present in a mixture, there is a concentration of coarse materials in some areas of the paved mat, while other areas contain a concentration of finer materials. Segregation creates non-uniform mixes that do not conform to the original job mix formula in gradation or asphalt content. The resulting pavement exhibits poor structural and textural characteristics, provides poor performance and durability, and has a shorter life expectancy and higher maintenance costs. Problems associated with segregation are serious. There are basically five types of mix segregation that occur on the road. They are truck end segregation, centerline segregation, joint/edge segregation, truck end segregation/one side, and random segregation.

Segregation of hot mix asphalt is a recurring problem in the paving industry. There is little documented research that quantifies the effects of segregation on mix properties and performance. The Asphalt Pavement Analyzer (APA) is a new class of pavement tester available to evaluate pavement performance. The APA can evaluate the rutting potential, moisture susceptibility and fatigue life of bituminous mixtures. Materials were available from a previous study (K-TRAN: KU-96-6) on segregation for use in evaluating the use of the APA with Kansas mixtures and materials. Two surface mixes, a BM-1B and BM-2, were fabricated to different levels of segregation as determined in the K-TRAN: KU-96-6 study. The mixtures were tested in the APA for rutting, moisture damage and fatigue life.

Segregation of hot mix asphalt is a recurring problem in the paving industry. There is little documented research that quantifies the effect of segregation on mix properties and pavement performance. Many state highway agencies are embracing performance based quality control/quality assurance (QC/QA) programs but only a few states have performed studies to quantify the effect of segregation on pavement performance. This study was conducted on four newly constructed pavements which had noticeable spots of segregation. Cores were obtained from both segregated and non-segregated sections of the four pavements. The unit weights of the pavements were determined using a thin-lift nuclear gauge. The change in gradation on the 4.75 mm sieve was compared with asphalt content, nuclear gauge unit weight, core unit weight, and macro texture to determine if an indicator test could quantify segregation. The cores were tested for moisture sensitivity, fatigue life, and indirect tensile strength to determine the effect of segregation on performance.

Introductory technical guidance for civil engineers and construction managers interested in construction of hot mix asphalt pavement for streets, highways and other applications. Here is what is discussed: 1. INTRODUCTION 2. MILLING AND GRINDING 3. CRACK SEALING 4. REPAIR OF LOCAL DAMAGED AREAS 5. APPLICATION OF TACK COAT 6. APPLICATION OF PRIME COAT 7. SURFACE PREPARATION CHECKLIST 8. PLACEMENT.