How to Use Recycled Foundry Sand in Hot Mix Asphalt (HMA) Hussain U. Bahia University of Wisconsin-Madison Foundry Sand Recycling Forum “Foundry Sand in Infrastructure Applications” October 31st, 2007 Chicago. IL Overview of Talk • Introduction: Why use these sands? • What are the Important properties of Sands ? • Foundry sands can vary by metals and molding binder systems • Gradations, Angularity, Clay and Organic Contents • Range in Properties measured • Can sands result in acceptable Asphalt Mixtures? • Studies completed • Effects on durability , constructibility, traffic resistance • Moisture effects • Guidelines for use • Questions Introduction Why use these sands? • For Asphalt contractors: • Natural aggregates are becoming more scarce. • More energy/money needed to extract natural aggregates. • In some areas fine aggregates are not available. Sands can be Variable based on Source (Metal + Binder) • Properties of sands can vary by • Metal type • Binder system used • DOE project- Most comprehensive study: • Metal Poured (8 Metals) • Binder System (10 Systems) • Data base can be used as a guide What are the Important Properties of Sands for Hot Mix Asphalt Application • Important properties are: • Gradation • Densities: Maximum, Effective and Bulk • Angularity • Organic Content • Clay Content Gradation- Size Distribution Gradation of 17 Sands 100.0 90.0 Percent Passin 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 #200 #100 #50 Sieve Size #30 It can be seen that the gradation varies widely, so it can’t be assumed that foundry sands have the same gradation. Angularity ASTM C1252 “Un-compacted Void Content of Fine Aggregates” Used to determine the surface characteristics. The more angular, the higher resistance to rutting. Variation in Angularity of Sands As measured by voids 46 Angularity, % Voids 45 44 43 42 41 40 39 38 l ro t n Co 1 2 3 4 5 6 7 8 9 10 11 12 Source of Sand 13 14 15 16 17 Organic Content Determined by AASHTO T267-86 “Determination Of Organic Content (OC) in Soils by Loss on Ignition” Expressed as percent loss. Less OC is better. Variation in Organic Content of Sands Organic Content, % mass 6 5 4 3 2 1 0 l tro n Co 1 2 3 4 5 6 7 8 9 10 11 12 Source of Sand 13 14 15 16 17 Clay Content • Traditionally used Sand Equivalent Test • Due to carbon content, this could not be used • Modified AFS 2210-00-S “Methylene Blue Clay Test, Ultrasonic Method” graduated cylinder clay reading flocculating solution suspended clay sand reading sedimented sand Sand Equivalent Test Clay Content Modified Method • Used a spectrophotometer instead of filter paper to determine “how blue is blue”. • Methylene blue index (milligrams of methylene per gram of sand- mg/g) tested at a wavelength of 670 nm. A typical bentonite has a MBV of about 387 mg/g, so a foundry sand with a MBV of 20 contains about 5% active clay. Methylene Blue Value mg/g Variation in Clay Content As measured by Methylene Blue 40 35 30 High Range 25 20 7 sands Better than control 15 10 5 0 l ro t n Co 1 2 3 4 5 6 7 8 9 10 11 12 Source of Sand 13 14 15 16 17 Can Sands be used for production of Acceptable Asphalt Mixtures ? • Studies at UW-Madison • First study (2000) by E. Miller • Second Study (2001) by K. Delage • Third Study (2002) by A. Braham • Fourth study (2004) by T. Snyder • With Penn State and First • 17 sands from 11 different states. • Developed Guidelines Asphalt Mixture Performance Indicators • Durability: • Asphalt Content • Voids Filled with Asphalt (VFA) • Mixture Stability / Volumterics: • % Maximum Density @ Nini, Ndes, Nmax • Constructability • Paver Energy Index: PEI • Rolling Energy Index: REI • Resistance to traffic action • Traffic Densification Index: TDI • Resistance to fatigue and moisture damage • Indirect Tension Strength Mix Designs – Superpave Technology Superpave Gyratory Compactor compacts the sample Loose mix is placed into compaction mold Ram used to compact sample. Aluminum arm gyrates around sample Durability and Economics Optimum A.C. 6.5 5.5 5 4.5 4 3.5 Asphalt Content is not affected significantly 12 14 2 4 3 5 16 6 1 Co 7 nt ro l 13 15 10 8 7 11 1 3 9 Opt. A.C. (%) 6 Constructability Roller Energy Index 30 25 15 10 5 16 7 3 12 4 2 14 13 5 1 Co 0 nt ro l 6 1 17 11 9 8 0 15 REI 20 Constructability is not affected significantly Resistance to Traffic Action 1 16 9 11 14 13 6 15 17 2 5 Co 7 nt ro l 3 8 10 4 900 800 700 600 500 400 300 200 100 0 12 TDI Traffic Densification Index Traffic Resistance is not affected significantly Resistance to Moisture Damage 7 5 2 4 16 15 3 6 10 12 13 8 on t ro l 11 C 17 9 100 90 80 70 60 50 40 30 20 10 0 1 Tensile Strength Ratio (%) Tensile Strength Ratio Sand For Some Sands, there is important Reduction Current Knowledge • Change in economics of HMA is minimal: • Some sands showed an increase in asphalt content, while others did not. • Asphalt contents ranged from 5.1 to 6.1% with the control at 5.5% • Effect of sand on moisture sensitivity varies: • 9 of the 17 foundry sands either caused an increase or no change in Tensile Strength Ratio values. • Based on this, over half the sands can be used safely in HMA. • Sodium Silicate binder system is detrimental to HMA. Case Studies • Departments of Transportation allows it: • Pennsylvania: DOT allows 8-10% in all mixes • Michigan: HMA producer use 10-20% • Tennessee: HMA producer uses 10 % • Ontario, Canada: HMA producer has used it for more than 10 years • Concerns of UMA suppliers • Consistency required • Environmental classification • Clay content • Total amount Where are Sands Used for HMA? Sands are accepted by DOT Sands used on experimental basis Guidelines for Using Sands in Asphalt Mixtures • Foundry Quality Check • Required: Report Binder system used • Required: Report if sand contains any Sodium Silicate • Required: Measure Methylene Blue value • Optional: Size Distribution • Optional: Anuglarity Guidelines for Using Sands in Asphalt Mixtures • Asphalt Contractors: • Try first at a minimum of 10 % • In general, do not cause an increase in asphalt content. Depends on specific foundry sand. • Test for moisture damage is necessary. • If MB < 10, no additive is needed. • If MB > 10, moisture damage needs treatment • If moisture damage is evident: • Anti-stripping additives may not solve problem. • Washing should be tried. Step by Step Procedure • Similar to other fine sands • Measure gradation • Measure angularity • Measure clay content • If passes all HMA limits by DOT, use as much as needed. • If not ( too much fines, low angularity or high clay content) • Add as much as possible to meet limits • Always test moisture damage of HMA after compaction Questions Contact: Hussain Bahia [email protected]