Presentation on theme: "HMA Design (Surface) CEE 320 Steve Muench 4/28/2015 1 The surface course is the layer in contact with traffic loads and normally contains the highest quality."— Presentation transcript:
HMA Design (Surface) CEE 320 Steve Muench 4/28/ The surface course is the layer in contact with traffic loads and normally contains the highest quality materials. It provides characteristics such as friction, smoothness, noise control, rut and shoving resistance and drainage.
Surface HMA This top structural layer of material is sometimes subdivided into two layers: Wearing Course. This is the layer in direct contact with traffic loads. It is meant to take the brunt of traffic wear and can be removed and replaced as it becomes worn. A properly designed (and funded) preservation program should be able to identify pavement surface distress while it is still confined to the wearing course. This way, the wearing course can be rehabilitated before distress propagates into the underlying intermediate/binder course. Intermediate/Binder Course. This layer provides the bulk of the HMA structure. Its chief purpose is to distribute load.
HMA Types The three most common types of HMA pavement are: Dense-graded HMADense-graded HMA. Flexible pavement information in this Guide is generally concerned with dense-graded HMA. Dense-graded HMA is a versatile, all-around mix making it the most common and well-understood mix type in the U.S. Stone matrix asphalt (SMA)Stone matrix asphalt (SMA). SMA, although relatively new in the U.S., has been used in Europe as a material for years to support heavy traffic loads and resist studded tire wear. Also known as Gap Graded Open-graded HMAOpen-graded HMA. This includes both open-graded friction course (OGFC) and asphalt treated permeable materials. Open-graded mixes are typically used as wearing courses (OGFC) or underlying drainage layers because of the special advantages offered by their porosity.asphaltmaterials
Stone Matrix Asphalt (SMA)
0.45 Power Gradation
0.45 Power Gradation Curve Using 19.0-mm (0.75- inch) Maximum Aggregate Size Calculations for a 0.45 Power Gradation Curve Using 19.0-mm (0.75- inch) Maximum Aggregate Size Aggregate
0.45 Power Gradation Curve for Different Maximum Aggregate Sizes
Typical Aggregate Gradations and Permeabilities
FHWA gradation graph showing representative gradations 19 mm mm 4.75 mm No.200 No.4 ¾-in 0.45 power curve Gap Graded Open Graded Dense Graded Uniform Graded Restricted Zone Sieve Size % Passing
Hot Mix Asphalt (Dense-Graded)
Hot Mix Asphalt (Open-Graded)
Hot Mix Asphalt (Gap-Graded)
HMA MIX DESIGN Texas Gyratory Compactor (TGC). For dense-graded hot mix asphalt Superpave Gyratory Compactor (SGC). Marshalls Method
HMA MIX DESIGN, Performance Concerns Resistance to Permanent Deformation Resistance to Fatigue and Reflective Cracking Resistance to Low Temperature (Thermal) Cracking Durability Resistance to Moisture Damage (Stripping) Workability Skid Resistance
Marshall Mix Design Procedure The Marshall mix design method consists of 6 basic steps:mix design Aggregate selection. Asphalt binder selection. Sample preparation (including compaction). Stability determination using the Density and voids calculations. Optimum asphalt binder content selection.
Marshall Mix Design Procedure The Marshall Stability and Flow Test
Marshall Mix Design Procedure. Mix Criteria Light Traffic (< 10 4 ESALs) ESALs Medium Traffic (10 4 – 10 6 ESALs)ESALs Heavy Traffic (> 10 6 ESALs) ESALs Min. Max. Min.Max. Min. Max. Compaction Compaction (number of blows on each end of the sample) Stability (minimum) 2224 N (500 lbs.) 3336 N (750 lbs.) 6672 N (1500 lbs.) Flow (0.25 mm (0.01 inch)) Percent Air Voids Typical Marshall Design Criteria
Bad Mix blue smoke - blue smoke indicate that the mix is too hot. stiff appearance mix slumped in truck. lean, dull appearance - this indicates that the mix has insufficient asphalt. rising steam - too much moisture. segregation. contamination.