INNOVATIVE MAINTENANCE MATERIALS, EQUIPMENT AND OPERATIONS FOAMED ASPHALT Tomas Trevino, P.E. Maintenance Engineer Corpus Christi District
Today s Presentation will cover these topics: Traditional stabilization techniques. What is Foamed Asphalt. Pavement Design Testing Needs. Foamed Asphalt Case Study FM 99 Cost Comparison between traditional methods and foamed asphalt. 2
Pros / Cons of Traditional Cementitious Stabilizers Traditional Cement Stabilized Base Materials are very rigid because they are continuously bound. Because they are continuously bound they are prone to shrinkage that manifests itself as block cracking. This cracking is aggravated by repeated loading(normally in the millions of cycles) which causes fatigue failure or bottom up cracking. 3
Most importantly hard to get and maintain a good finish when roadway is opened up to traffic at the end of the work day. 4
Pros/Cons of Asphalt Stabilized Base Tend to be less rigid that cement stabilized base, but have improved shear properties. Two primary types of asphalt stabilization agents: asphalt emulsion and foamed asphalt. Both of these processes use a relatively soft road-grade asphalt. Primary failure mechanism is permanent deformation under loading rutting. ASB s with less than 3% cementitious binder do not experience fatigue cracking because they are not continuously bound. 5
So What is Foamed Asphalt? 6
FOAMED ASPHALT STABILIZATION Foamed Asphalt aims to combine the best of both methods by using a minimal amount of cement to act as an active filler therefore retaining strength without affecting the flexibility of an asphalt stabilized base. 7
BEFORE WE START FOAMING WE NEED TO CHECK IF OUR ROADWAY MATERIALS ARE SUITABLE FOR FOAMING. The two criteria that play the biggest role in candidacy are: Material Grading Curve Material Plasticity Index(PI) 8
Material Grading Curve 9
OPTIMUM MATERIAL GRADATION TABLE FOR FOAMED ASPHALT AND ASPHALT EMULSION STABILIZATION 10
TYPICAL ROADWAY BASE GRADATION CURVE 11
MATERIAL PLASTICITY INDEX The plasticity index of your roadway base material needs to be below 10. Should try to keep from incorporating subgrade material into the pavement section. Clay subgrades can be especially detrimental to performance. Since it is highly cohesive it will tend to lump together and remain in the new base section as a localized weak spot. 12
WHEN YOUR ROADWAY MATERIALS HAVE BEEN PROVEN TO BE GOOD CANDIDATES YOU CAN DEVELOP THE PAVEMENT DESIGN USING THE CRITERIA IDENTIFIED IN SPECIAL SPECIFICATION 3279 Property Test Procedure Criteria Min Indirect Tensile strength 1 Tex 226-F 45 psi Strain at Break in IDT Tex 226-F Report Min (wet) IDT 2 Tex 226-F 30 psi Tensile Strength Ratio 70% Min Unconfined Compressive Strength 3 Tex 117-E, Part II Report Table 1 Laboratory Mixture Design Properties Average of three specimens air dried overnight then oven dried at 104F for 3 days Average of three specimens 24 hours under water Average of three specimens subjected to 10 days capillary moisture absorption before conducting UCS Table 2 Foamed Asphalt Properties Test Method Min Asphalt Binder Expansion ratio * 8 times Asphalt Binder half life * 6 seconds 13
FOAM EXPANSION RATIO(ER) AND HALF LIFE FORM THE BASIS OF ASPHALT STABILITY 1. The expansion ratio is a measure of the viscosity of the foam and determines how well the asphalt will disperse in the mix. 2. The half-life is a measure of the stability of the foam and provides and indication of the rate of collapse of the foam. 14
THE FACTOR THAT INFLUENCES THE FOAM CHARACTERISTICS THE MOST IS THE AMOUNT OF WATER INJECTED INTO THE EXPANSION CHAMBER. By Increasing the application rate of water: Increases the expansion rate (ER) of foam. Decreases the half-life of the foam Therefore selection of the percent water to add is critical. 15
DETERMINING OPTIMUM % WATER TO ADD IS CRITICAL TO YOUR PAVEMENT DESIGN 16
ACTIVE FILLER ALSO PLAYS A CRITICAL ROLE Active fillers improve adhesion of the asphalt to the aggregate Improve dispersion of the asphalt in the mix Modify the plasticity index of the materials Increase the stiffness of the mix and the rate of strength gain Accelerate curing of the compacted mix 17
SPECIALIZED LABORATORY EQUIPMENT NEEDED TO DEVELOP A PAVEMENT DESIGN FOAMED ASPHALT LAB AND PUGMILL MIXER 18
OR DO WHAT WE DID AND GET A HOLD OF TOM SCULLION OUR PAVEMENT DESIGN RESULTED IN AN 11 INCH STABILIZED LAYER WITH 2.4% FOAMED ASPHALT AND 1.5% CEMENT 19
CASE STUDY FM 99 PROJECT LIMITS LIMITS OF FOAMED ASPHALT 20
FM 99 IS EXPERIENCING HEAVY OILFIELD ACTIVITY 21
WITH DRILLING ACTIVITY COMES A LOT OF HEAVY TRUCK TRAFFIC 22
THE COMBINATION OF HEAVY TRUCK TRAFFIC AND NARROW FM ROADS HAS UGLY RESULTS. 23
FOAMED ASPHALT LIMITS EXTENDED FROM: STA 8+40 TO 31+30 15 WIDE NB STA 8+40 TO 41+30 15 WIDE SB 24
Foamed Asphalt Mechanics The Asphalt Binder(in our case PG64-22) is heated to temperatures over 300 F. It is then injected with water which transforms the water into a vapor which is trapped in Asphalt bubbles. The foam bubbles collapse in less than a minute distributing the asphalt into the aggregate adhering to the finer particles to form a mastic. Upon compaction the asphalt particles in the mastic are pressed against and adhere to the larger aggregate resulting in localized non-continuous bonds. 25
BEGIN BY PRE-SPREADING THE 1.5% CEMENT 26
Secondly need to test the foaming characteristics of each asphalt transport truck. The mixer had a built-in test nozzle which made it easy to use. Minimum Requirements per our 3279 specification: Expansion: 8 times Half Life: 6 seconds Once we do this we can finally start foaming 27
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PAD-FOOT ROLLER COMPACT STEEL DRUM ROLLER SHAPE AS NEEDED 30
FINISHED ROADWAY FOG SEAL 31
Murphy s Law Came Calling received 4 of rain on the weekend after completion section held up very well compared to traditional cement treated base. FOAMED UNFOAMED 32
BASE DESIGN STRENGTH VALUES *PROJECT AND MATERIAL SPECIFIC VALUES FROM FM 99 *FPS VALUES BETWEEN 100-400 KSI ARE DEPENDANT ON MATERIALS AND MIX DESIGN 33
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WHAT ABOUT THE COSTS? Change Order Cost $233,887 to Treat 11,000 sy Approx. $21 /sy vs. $3.50 traditional cement trt. base costs Number of issues can reduce these costs on future projects: Possibly consider using an AC rather than a PG asphalt. Now that we have some idea of moduli values can design using these values resulting in thinner sections. Costs in renting the mixing and larger rollers used for compaction incorporated in the treatment costs. 35
FINALLY, HOW DOES YOUR MAINTENANCE SUPERVISOR FEEL ABOUT THE END PRODUCT 36