Presentation on theme: "MODULE 4 ASPHALT MIX DESIGN*"— Presentation transcript:
1 MODULE 4 ASPHALT MIX DESIGN* What’s it all about?(*) Information taken from Asphalt Institute’s MS-2 manual, 6th Ed.
2 SCOPE What is a mix design? Would you recognize one if it walked up to you and asked for spare change?Basically, its just a recipe for making hot mix.What are the ingredients?
3 Well first you need a binder: That would be the asphalt cement. SCOPEWell first you need a binder:That would be the asphalt cement.What’s being bound together?That would be the aggregate.The objective of the design process is to “determine the proportions of asphalt cement and aggregate that will give long lasting performance as part of the pavement structure” (Asphalt Institute, MS-2)
4 SCOPEthe percent asphalt cement is in terms of the total mix mass in this coursein order to get the right balance between aggregate and binder we need to know some properties of these materialsthe basic property of the aggregate is its grain size distribution or gradationthis, more than any other property will affect the performance of the mix
5 OBJECTIVESObjective 3.01“to determine a cost-effective blend and gradation of aggregates and asphalt (cement) that yields a mix having:sufficient asphalt (cement) to ensure a durable pavementsufficient mix stability to carry traffic without distortion or displacementsufficient voids in the total compacted mix to allow for a slight amount of asphalt expansion due to temperature increases without flushing, bleeding and loss of stability
6 OBJECTIVESObjective 3.01a maximum void content to limit the permeability of harmful air and moisture into the mixsufficient workability to permit efficient placement of the mix without segregation and without sacrificing stability and performancefor surface mixes, proper aggregate texture and hardness to provide sufficient skid resistance in unfavourable weather conditions”(Asphalt Institute, MS-2)
7 MIX TYPESObjective 3.02The Asphalt Institute (MS-2) identifies 4 different types of asphalt paving mixtures based on their functions within the pavement:Surface Course Mixtures (fine MPS*)Binder Course Mixtures (medium MPS)Base Course Mixtures (coarsest MPS)Sand-Asphalt Mixes (finest MPS)(*) MPS = Maximum Particle Size
8 Surface Course Mixtures for wearing surfaces, so fine aggregate needed to give a smoother texturemust still have sufficient stability and durability for traffic loadsMaximum Particle Sizes range between mm and 19 mm (⅜” to ¾”)open-graded friction course (OGFC), a.k.a. porous friction course or popcorn mix used to reduce hydroplaning and increase skid resistanceObjective 3.02
9 Binder Course Mixtures intermediate layer between surface and baselarger Maximum Particle Sizes 19 mm - 38 mm (¾” – 1 ½”)can be used as a base course or as a surface course where heavy wheel loads and tight radius power steering turns are involved such as is port facilities, logging yards and industrial loading docksObjective 3.02
10 Base Course Mixturescan be placed directly on compacted subgrade or over a granular baseMaximum Particle Sizes range up to 75 mm (3”)larger particle sizes result in higher stability in dense-graded mixes and facilitate drainage in open-graded mixesObjective 3.02
11 Sand-Asphalt MixesObjective 3.02produce tightest surface texture and with proper aggregate type (hardness and shape) can be highly skid resistantminimum lift thickness is 15 mm (0.6”) which is useful as overlay padding (scratch course, leveling course)Maximum Particle Sizes range between mm and 1.18 mm (No. 4 to No. 16)a.k.a. plant mix seal or sheet asphalt
12 MIX TYPESObjective 3.02The percent asphalt cement required for mixes with the required properties varies among these mix types according to the maximum particle size:Sand-Asphalt Mixes (highest %AC)Surface Course Mixtures (lower % AC)Binder Course Mixtures (lower % AC)Base Course Mixtures (lowest % AC)
13 MIX DESIGN PROCESSThe Marshall mix design method involves preparing and testing mix specimen at trial % AC contents.The steps that we will be covering are:Sieve analyses of stock aggregates (stone, sand, mineral filler)Proportion stock aggregates to produce a blend that meets specsMeasure specific gravities of stock aggregates and asphalt cementLaboratory compaction of trial mix specimens (6 trial % AC’s)Stability (or strength) and volumetric testing of each specimenAnalysis of results (determination of mix properties and optimum %AC)Objective 3.02
15 Tests on Mineral Aggregates Objective 3.02Test/PropertyASTM DesignationAASHTO DesignationLos Angeles AbrasionC 131 or C 535T 96Unit WeightC 29T 19Sieve Analysis (Aggregates)C 136T 27Sieve Analysis (Filler)D 546T 37Specific Gravity (Coarse)C 127T 85Specific Gravity (Fine)C 128T 84Specific Gravity (Filler)D 854 or C188T 100 or T 133Sulphate SoundnessC 88T 104Sand EquivalentD 2419T 176Particle ShapeD 4791-
16 Tests on Paving Mixture Objective 3.02Test/PropertyASTM DesignationAASHTO DesignationAsphalt Content (Extraction)D 2172T 164Asphalt Content (Nuclear)D 4125T 287Recovery of AsphaltD 1856T 170Density and Voids AnalysisSee next slideMaximum Specific GravityD 2041T 209Bulk Specific GravityD 1188 or D 2726T 166
17 Steps for Voids Analysis (T is AASHTO Test and D or C is ASTM Test)Measure bulk specific gravities of coarse aggregate (T 85 or C 127) and fine aggregate (T 84 or C 128).Measure specific gravity of asphalt cement (T 228 or D 70) and of mineral filler (T 100 or D 854).Calculate the bulk specific gravity of the aggregate combination in the paving mixture.Measure maximum specific gravity of loose paving mixture (D 2041).Measure bulk specific gravity of compacted paving mixture (D 1188 or D 2726).Calculate the effective specific gravity of the aggregate.Calculate the asphalt absorption of the aggregate.