9Mixture Items that Affect Compaction Aggregate texture, hardness and shapeAsphalt Binder GradeMixture PropertiesVoidsAsphalt Binder ContentMixture Temperature and Cooling Rate
10Field Operations that Affect the Compaction of the Bituminous Mixture Number of Roller PassesTypes of Rollers and Order they are usedMode of the Steel RollersVibratory mode on or offHigh/Low AmplitudeHigh/Low Frequencyin most cases the roller should be set to high frequency and low amplitudeSpeed of Rollers
11Number of Roller Passes 1357924Number Passes to Cover Paver WidthMinimum Passes on Critical Longitudinal Section
12Roller Speed Example Given: Plant & Paver Specifics - 12 feet wide - 500 tons per hour- 1.5 inch liftRoller Specifics- minimum 3 passes coverage- roller width is 54 inchRequiredWhat is the minimum roller speed you need to compact the mat?
13Roller Speed Answer The speed of the paver is: 500 tons per hour = 500*2000/145 = 6900 cuft per hourPavement Cross section = 12 feet * 1.5 inch/12 = 1.5 sqftPaver speed = (6900 cuft/hr) / 1.5 sqft = 4600 ft/hourThe required roller speed is:Roller Speed = 4600 ft/hour * 9 passes /5280 ft/mi = 7.8 mph
14What are the Recommended Roller Speeds ? Range of Roller Speeds (mph)Operating PositionType of Roller Breakdown Intermediate FinishStatic Steel Wheel2 – 3.53 - 5Pneumatic4 - 7Vibratory2 - 32.5 – 3.5--From Chapter 18 of Hot Mix Paving Handbook
16Roller Settings and Roller Patterns Typical Rolling Pattern:Vibratory Steel Roller as break downPneumatic Roller as intermediateStatic Steel Roller as finish rollerVibratory Steel Roller generally works best in the high frequency and low amplitude modeOnly Pneumatic rollers should be used when the temperature of the mat is within the bituminous mixtures “tender zone”
19Amplitude (A) Time (T) For Full Cycle UpAmplitude(A)MovementTimeDownTime (T) ForFull CycleThe elements of comparison for the dynamic component of a vibratory roller are the magnitude of the centrifugal force, its vibrating frequency, the nominal amplitude, and the ratio of the vibrating and non-vibrating masses acting on the drum.Amplitude: How high does the drum jump?Frequency, f = the number of hertz (cycles/s)--a single cycleis one full rotation of the eccentric weight. Frequency = 1/TAmplitude, A = the maximum deviation from position atrest -- one-half the total movement.
20AmplitudeNormal values of nominal amplitude range from 0.25 to 1 mm (1/100 to 1/32 in).Some rollers can operate at only one fixed amplitude, while others have “high” and “low” amplitude positions.Typically as the layer thickness increases, it is often advantageous to increase the nominal amplitude applied to the asphalt mix.Unless ‘high’ amplitude is needed to achieve a particular density level, the vibratory roller should be operated in ‘low’ amplitude.Ask: Does changing frequency change the compaction effort? (Yes vibrations/ft. Never less than 10.)
21Frequency Low Frequency High Frequency Impact Spacing The frequency of vibration is the number of complete cycles that the eccentrics rotate per minute.The faster the rotation of the eccentrics, the greater the frequency of vibration.Some vibratory rollers can operate at only one frequency or have a very limited selection of frequencies.Other vibratory rollers can alter the frequency of the applied load between 1600 and 4000 vibrations per minute.Frequencies below 2000 vibrations per minute are not normally acceptable to compact asphalt mixtures.DIRECTION OF TRAVEL
22Joint CompactionCompaction of the Longitudinal Joint is the Weak Link in the Paving ProcessCompaction of the Both the Confined and Unconfined Edges is a ChallengeThe Unconfined Edge Needs to be Compacted with the Edge of the Steel Roller Over-hanging the Mat by 6 InchesIf a Pneumatic Roller is used in the Break Down Position, it Should not be Closer than 6 Inches to the Joint
23Joint CompactionCompaction of the Confined Joint is Best Achieved by Rolling on the Hot Mat and Overlapping the Cold Mat by 6 InchesRolling from the Cold Side is No Longer RecommendedSteel Rollers may Tend to Bridge from the Cold Mat and this May Impede Compaction Right at the Joint. A Pneumatic Roller will be More Effective in Reducing this Bridging.Raking of the Joint is Not Recommended
24Factors Affecting Rolling Time allows MORE timeallows LESS timeFACTORSMat ThicknessTHICKTHINLayer thickness is the thickness of an asphalt pavement layer, and it is the most important variable in the rate of cooling of asphalt mixtures.It is very difficult to obtain the desired density on thin lifts of mix in cool weather because of the rapid loss in temperature in the mix.A portion of the heat in the asphalt layer is lost to the air as well as the base as it is placed.Depending on the air and base temperature as well as moisture content, the loss of temperature could be large or small.Mix TemperatureHIGHLOWBase TemperatureHIGHLOW
27Paver OperationsThe primary objective of the paver is to place a bituminous mixture on the roadway, in a manner that results in mat that has an even distribution of temperature, thickness and pre-compaction, in both the longitudinal and transverse directions.
28Mix Placement Concerns Even and steady flow of mixture to the paverEven and steady flow of mixture into the paver hopperEven and steady flow of mixture through the paver and in front of the paver screedThe appropriate angle of attack of the screed needs to be set and frequent adjustments minimized
34What Affects the Thickness of the Bituminous Being Paved If the paver speed, the height of material behind the screed, and tow point height are held constant, there is only one screed angle of attack that will give you the desired mat thickness.
43Automatics Screed Controls Primary purpose of automatic screed control is to produce a smooth asphalt pavement layer.Smoother than a screed operator can accomplish by continually changing the setting of the thickness control cranks.
44Automatics Screed Controls Automatic Screed Functions by:maintaining the elevation of the screed tow points in relation to a reference other than that of the wheelbase of the paver itself.Elevation of the tow point is kept at a constant elevation in relation to a given grade reference.The automatics don’t allow the relative position of the tow point to change even though the tractor unit is moving up and down.
65Common Errors When Using Spread Sheets Most common error happens when the macros are disabled due to the security setting being set to highSet the security level to “low”Move cursor to the menu on top and under the “Tools” menu, pick Tools: Macro: SecurityIn the security dialog box, set the security level to “low” and press “OK”
68Common Errors When Using Spread Sheets Problems with creating random numbersThe two versions of the core locations spread sheets use random number functions to pick the core locations. The program must make a decision whether or not be make new random numbers. Read the instructions for the spread sheet to be sure that the random numbers are being treated properly.