Presentation on theme: "HMA Design (Surface) The surface course is the layer in contact with traffic loads and normally contains the highest quality materials. It provides characteristics."— Presentation transcript:
1 HMA Design (Surface)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.4/13/2017CEE 320 Steve Muench
2 Surface HMAThis 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.
3 HMA Types The three most common types of HMA pavement are: Dense-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). 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 GradedOpen-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.
8 45 Power Gradation Curve Using 19. 0-mm (0 0.45 Power Gradation Curve Using 19.0-mm (0.75-inch) Maximum Aggregate SizeCalculations for a 0.45 Power Gradation Curve Using 19.0-mm (0.75-inch) Maximum Aggregate Size
9 0.45 Power Gradation Curve for Different Maximum Aggregate Sizes
10 Typical Aggregate Gradations and Permeabilities
15 HMA MIX DESIGNTexas Gyratory Compactor (TGC). For dense-graded hot mix asphaltSuperpave Gyratory Compactor (SGC).Marshalls Method
16 HMA MIX DESIGN, Performance Concerns Resistance to Permanent DeformationResistance to Fatigue and Reflective CrackingResistance to Low Temperature (Thermal) CrackingDurabilityResistance to Moisture Damage (Stripping)WorkabilitySkid Resistance
17 Marshall Mix Design Procedure The Marshall mix design method consists of 6 basic steps:Aggregate selection.Asphalt binder selection.Sample preparation (including compaction).Stability determination using theDensity and voids calculations.Optimum asphalt binder content selection.
18 Marshall Mix Design Procedure The Marshall Stability and Flow Test
19 Marshall Mix Design Procedure Typical Marshall Design CriteriaMix CriteriaLight Traffic (< 104 ESALs)Medium Traffic (104 – 106 ESALs)Heavy Traffic (> 106 ESALs)Min.Max.Compaction (number of blows on each end of the sample)355075Stability (minimum)2224 N (500 lbs.)3336 N (750 lbs.)6672 N (1500 lbs.)Flow (0.25 mm (0.01 inch))8201816Percent Air Voids35.
20 Bad Mix blue smoke - blue smoke indicate that the mix is too hot. stiff appearancemix slumped in truck.lean, dull appearance - this indicates that the mix has insufficient asphalt.rising steam - too much moisture.segregation.contamination.