2/4/2019 W ‐ 26 A Practical Approach to Managing Density Todd Mansell, CAT Paving Caterpillar: Confidential Green What is Compaction? • Mechanical Process • Removes specified amount of air voids • Develops stone on stone contact • Builds strength 2 Caterpillar: Confidential Green What is Compaction? • Screed develops initial density • Vibratory screed produces compaction energy • Tamping and vibratory screed produces high compaction energy 3 Caterpillar: Confidential Green 1
2/4/2019 What is Compaction? • Compaction starts immediately behind paver • Asphalt layer at highest temperature • Limited time to develop density • Planning, preparation and operator training required 4 Caterpillar: Confidential Green Best Practices for Compaction • Type of rollers • Number of rollers • Roller settings • Number of passes (coverage) • Mix temperature • Rolling mainline • Rolling transverse & longitudinal joints • Pre ‐ compaction w/ screed • Stopping ‐ Starting the roller • Smoothness – where do we stop to get water, change direction, supported ‐ unsupported edges, tie ‐ ins 5 5 Caterpillar: Confidential Green Lines of Communication Foreman Superintendent Truck Boss Project Manager 6 Caterpillar: Confidential Green 2
2/4/2019 How do we achieve density? 1. Understand the factors affecting compaction Mix temperature & time available for compaction Four forces of compaction 2. Understand different types of rollers and how they work Steel drum, pneumatic, combination, oscillation, offset drums 3. How to establish a rolling pattern that achieves density & smoothness How to determine roller settings Determining the number of passes Dealing with harsh & tender mixes Good communication!! 7 Caterpillar: Confidential Green What does it take to get density? Temperature Temperature Temperature 8 Caterpillar: Confidential Green Time Available for Compaction Density must be achieved while the mix is still HOT 9 Caterpillar: Confidential Green 3
2/4/2019 Asphalt Binder • Visco ‐ elastic material • Hot asphalt binder acts as a lubricant for aggregate to aid in compaction • Cold asphalt binder becomes the glue that bonds the aggregate together 10 Caterpillar: Confidential Green Temperature is Critical 300 ‐ 260 Breakdown rolling 260 ‐ 220 Intermediate rolling 240 ‐ 190 possible tender zone 220 ‐ 160 Finish rolling 160 – Stop rolling Keep steel drums off the mix!!! 11 Caterpillar: Confidential Green MultiCool Website and Android App • Google Play App store • http://www.eng.auburn.edu/users/timmdav/MultiCool/FinalRelease/Main.html 12 12 Caterpillar: Confidential Green 4
2/4/2019 PaveCool website and App 13 Caterpillar: Confidential Green Mix Temperature • Creating density easiest at high temperature • Upper limit about 160 o C (320 o F) • Watch for layer movement in fine mixes • Stay back if layer is tender due to high temperature 14 Caterpillar: Confidential Green Mix Temperature • Reach target density before mat cools • Lower limit about 90 o C (190 o F) • Work close to paver • Increase compaction energy • Add breakdown rollers 15 Caterpillar: Confidential Green 5
2/4/2019 Mix Temperature Tender Zone • Some mixes get tender between upper and lower limits • Surface moves under drums or tires and cracks appear • Work ahead of tender zone and after 16 Caterpillar: Confidential Green Climate Conditions • High ambient temperature – asphalt retains heat – longer compaction time • Low base temperature – heat transfers quickly to base – shorter compaction time • Low ambient temperature – asphalt cools faster – shorter compaction time • Adjust rolling pattern as ambient conditions change 17 Caterpillar: Confidential Green Four Forces of Compaction 18 Caterpillar: Confidential Green 6
2/4/2019 Types of rollers • Static steel drum • Vibratory steel drum • Oscillation • Pneumatic • Vibratory pneumatic • Combination 19 Caterpillar: Confidential Green Static Steel Drum Pressure • Static pressure exerted by steel drum roller non ‐ vibratory • Weight at the drum divided by width of the drum 20 Caterpillar: Confidential Green Static Force Comparison • Heaviest model not always CB64 CB54 highest static force 6490 kg 5402 kg Weight @ drum 14,300 lb 11,900 lb • Narrower drum increases static force 213 cm 170 cm Drum width 84 in 67 in 31 kg/cm 32 kg/cm Static linear load 170 lb/in 178 lb/in 21 Caterpillar: Confidential Green 7
2/4/2019 Vibratory Steel Drum • Breakdown, intermediate and finish rolling • Settings for amplitude and frequency • Static mode for finish rolling Build density from the top down 22 Caterpillar: Confidential Green Impact Force • Impact is a dynamic force • Drum moves into the asphalt layer to produce high energy • Increased production benefit • Over ‐ compaction, broken aggregate risk 23 Caterpillar: Confidential Green Vibration • Spinning eccentric weight causes drum vibration • Vibratory force sets aggregates in motion • Aggregates orient better for stone on stone contact 24 Caterpillar: Confidential Green 8
2/4/2019 Amplitude • Impact equals amplitude • Defined as distance drum moves into the asphalt layer • Rollers have various amplitude settings • Operator must know which amplitude to choose 25 Caterpillar: Confidential Green Amplitude = compactive effort High Amplitude Low Amplitude 26 Caterpillar: Confidential Green Amplitude Checklist Lower Force Higher Force Factor 0.25 ‐ 0.6 mm >0.6 mm Layer Thickness <50 mm (2.0in) >50 mm (2.0in) Base Support Rigid Flexible Binder Viscosity Low (unmodified) High (modified) Aggregate Shape Rounded Angular Ambient Temperature High Low 27 Caterpillar: Confidential Green 9
2/4/2019 Frequency • Frequency affects working speed • Working speed set to generate 32 ‐ 46 impacts per meter (10 ‐ 14 impacts/foot) • Higher frequency allows for higher working speed 28 Caterpillar: Confidential Green Impacts per foot, Frequency & Roller Speed 10 to 14 29 Caterpillar: Confidential Green Verify Roller Settings • Is the equipment in good working condition? • Settings per test strip? Amplitude Frequency Speed (10 ‐ 12 ipf) 30 Caterpillar: Confidential Green 10
2/4/2019 Higher Amplitudes associated with Lower Frequencies High Amplitude (<0.80 mm) = Low Frequency (>2800 vpm) Medium Amplitude (0.5 mm – 0.8 mm) = Medium Frequency (2800 ‐ 3400 vpm) Low Amplitude (0.2 mm – 0.5 mm) = High Frequency (3400 vpm) 31 Caterpillar: Confidential Green Calculate roller ground speed Frequency (vpm) Roller speed (fpm) = Impacts per foot 3,000 vpm Speed = = 300 feet per minute 10 ipf 32 Caterpillar: Confidential Green Balanced Roller Vibration Optimum compaction occurs • when all forces are accepted by the asphalt layer Balance between forces of • compaction and the asphalt layer 33 Caterpillar: Confidential Green 11
2/4/2019 Balanced Roller Vibration • Forces out of balance create drum bounce • Inefficient operation • Solve bouncing: ‐ change speed ‐ lower amplitude ‐ higher frequency ‐ one drum static ‐ both drums static 34 Caterpillar: Confidential Green Oscillation • Back and forth drum movement • Maintains contact with surface • Less aggressive compaction 35 Caterpillar: Confidential Green 36 Caterpillar: Confidential Green 12
2/4/2019 Offset drums Advantages • Offset drums cover width of layer in fewer passes • May be a good option on thin mats that cool quickly • Following curbs, radius Disadvantages • Effectively a single drum roller More passes may be required • Less uniform compaction (PWL) 37 Caterpillar: Confidential Green Pneumatic Rollers • Most commonly used for intermediate rolling • Knead the mix • Close up surface voids and tension cracks • Efficient building density Build density from the bottom up 38 Caterpillar: Confidential Green Manipulation or kneading action • Manipulation occurs due to overlapping tires • Some forces move sideways • Tightens surface texture 39 Caterpillar: Confidential Green 13
2/4/2019 Pneumatic tire rollers • Adjust tire pressures based on mat thickness • Ballast weight is usually sand, water or steel plates 40 Caterpillar: Confidential Green Tire Pressures • Change static force by changing ballast • Change static force by changing tire pressure • Increase inflation pressure to increase force • Decrease inflation pressure to decrease force Higher Pressure Lower Pressure Keep Tire Pressures Equal • Keep tires hot • Within 30 ° ‐ 40 ° F of pavement • Tire pressures equal • Warm up before paving 42 Caterpillar: Confidential Green 14
2/4/2019 Vibratory pneumatic tire roller 43 Adjustable amplitude settings instead of ballast 43 Caterpillar: Confidential Green Combination Vibratory steel drum & pneumatic tires 44 Caterpillar: Confidential Green Establish an effective rolling pattern 1. Based production and density 2. Equipment Selection Decision Point 3. Balance paver & roller speed Decision Point 4. Test Strip 5. Verify during production 15
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