Bituminous Road Deterioration Christopher R. Bennett Director - Data Collection Ltd.

Base Types and Surface Types and Materials Asphalt Concrete Hot Rolled Modified Asphalt Rubberized Asphalt Polymer Asphalt Concrete Soft Bitumen Mix (Cold Mix) Porous Asphalt Stone Mastic Cape Seal Double Bituminous Surface Dressing Single Bituminous Surface Dressing Slurry Seal Penetration Macadam Asphalt Mix Granular Base Asphalt Base Asphalt Pavement Base Stabilized Base Surface Treatment

Pavement Classification System (Bituminous Pavements)

Base and Surface Types Over Time

Distress Modes Surfacing Distress Cracking Ravelling Potholing Edge-Break Deformation Distress Rutting Roughness Pavement Surface Texture Distress Texture Depth Skid Resistance Drainage Distress Drainage New New New New

Surfacing Distress Cracking Area: Sum of rectangular areas circumscribing manifest distress (line cracks are assigned a width of 0.5 m), expressed as a percentage of carriageway area. Structural Cracking Narrow Cracking (1-3 mm crack width) Wide Cracking (> 3 mm crack width) Thermal Transverse Cracking Ravelling Area: Area of loss of material from wearing surface, expressed as a percentage of carriageway area.

Surfacing Distress Number of Potholes: Number of potholes per kilometer expressed in terms of the number of ‘standard’ sized potholes of area 0.1 m2. A pothole being defined as an open cavity in road surface with at least 150 mm diameter and at least 25 mm depth. Edge Break Area: Loss of bituminous surface material (and possibly base materials) from the edge of the pavement, expressed in square meters per km. HDM-4 assigns a depth of 100 mm to potholes and edge break area

Deformation Distress Rutting: Permanent traffic-associated deformation within pavement layers which, if channelised into wheelpaths, accumulates over time and becomes manifested as a rut, expressed as the maximum depth under 2 m straightedge placed transversely across a wheelpath. Roughness: Deviations of surface from true planar surface with characteristic dimensions that affect vehicle dynamics, ride quality, dynamic loads and drainage, expressed in the International Roughness Index, IRI (m/km).

Pavement Surface Texture Distress Texture Depth: Average depth of the surface of a road expressed as the quotient of a given volume of standardized material (sand) and the area of that material spread in a circular patch on the surface being tested. Skid Resistance: Resistance to skidding expressed by the sideways force coefficient (SDF) at 50 km/h measured using the Sideways Force Coefficient Routine Investigation Machine (SCRIM).

Drainage Distress Drainage: Drainage condition (excellent, good, fair, poor or very poor), which defines the drainage factor.

Interaction Mechanisms 1 Water ingress Further cracking Patches Shear Uneven surface Spalling Faster deformation ROUGHNESS Potholes Time Surface Lower strength Area of Cracking Rut depth

Roughness Scales BI = 360 IRI^1.12 QI = 13 IRI SI = 5 e^(-0.18 IRI) International Roughness Bump Integrator Quarter-car Index Present Serviceability Index Trailer TRRL Index Index IRI m/km BI mm/km QI counts/km PSI 5.0 1 700 13 4.2 Good Paved 2 1400 26 3.5 3 2200 40 3.0 4 3000 50 2.4 5 3800 65 2.0 6 4700 80 1.7 Good Unpaved 8 6500 100 1.2 10 8300 130 0.6 Poor Paved 12 10000 156 16 14000 210 Poor Unpaved 20 18000 260 24 22000 310 BI = 360 IRI^1.12 QI = 13 IRI SI = 5 e^(-0.18 IRI) IRI = 0.0032 BI^0.89 IRI = QI / 13 IRI = 5.5 ln (5.0/SI)

Paved Road Deterioration Sequence Input pavement strength, condition, age for initial analysis year Year Loop Compute traffic loading Compute surface distress increment Compute roughness increment Scheduled maintenance? Y N Compute maintenance effects Condition responsive? Y N Patching? Y N Compute post-maintenance condition, strength, age

Annual Change in Roughness Roughness at the End of the Year Roughness Increment during the analysis year RIe RI Roughness at the Beginning of the Year Analysis Year RIa RIe = RIa + IRI

Maintenance Effects IRIb1 = IRIb0 + dIRI + dIRIoper Roughness at the Beginning of the Year Roughness at the End of the Year Roughness Increment during the analysis year IRIb dIRI IRIe Analysis Year IRIb dIRI IRIe Analysis Year dIRIoper Maintenance Operation Effect IRIb1 = IRIb0 + dIRI + dIRIoper

Annual Change in Roughness

Roughness Environmental Coefficient ‘m’ by HDM-4 Climate Zones

Pavement Strength The strength of bituminous pavements is characterised by the adjusted structural number - SNP The SNP applies a weighting factor, which reduces with increasing depth, to the sub-base and sub-grade contributions so that the pavement strength for deep pavements is not over-predicted. SNPS = SNBASUS + SNSUBAS + SNSUBG SNBASU = contribution from surface and base layers SNSUBA = contribution from sub-base layers SNSUBG = contribution from subgrade S = season

Pavement Strength Structural Number (AASHTO) Contribution of subgrade function of CBR (HDM-III) Weighting factor, which reduces with increasing depth (HDM-4)

SNP Seasonal and Drainage Effects The average annual SNP used in the models is derived from the dry season SNP, SNPd, and the lengths of the dry SNP = fs* SNPd fs = function of SNPw / SNPd and length of dry season Drainage effect on pavement strength is modelled through the changes in the drainage factor DF [1 excellent - 5 very poor] SNPw / SNPd = f = function of DF, rainfall, surface distress

SNP Seasonal and Drainage Effects

“Final” Structural Number SNd = 0.0394 *  a * h SNPd = SNd + sub-base and sub-grade contributions SNP = fs * SNPd SNPk = SNP - dSNPK SNPK = “Final” Structural Number SNP = Adjusted Structural Number dSNPK = Reduction in adjusted structural number due to cracking

SNP Layer Strength Coefficients

Final Structural Number and Benkelman Deflection if base is not cemented SNPk = 3.2 DEF^-0.63 if base is cemented SNPk = 2.2 DEF^-0.63 if base is not cemented DEF = 6.5 SNPk^-1.6 if base is cemented DEF = 3.5 SNPk^-1.6 “Final” Structural Number

Crack Modelling Structural Cracking: This is effectively load and age/environment associated cracking. Transverse Thermal Cracking: This is generally caused by large diurnal temperature changes or in freeze/thaw conditions, and therefore usually occurs in certain climates. For each type of cracking, separate relationships are given for predicting the time to initiation and the rate of progression.

Cracking, Ravelling and Potholes Initiation and Progression

Crack Initiation ICA=Kcia{CDS2*a0exp[a1SNP+a2(YE4/SN2)] + CRT} ICA time to cracking initiation, in years CDS construction defects indicator for bituminous surfacings SNP structural number of pavement YE4 annual number of ESALs, in millions/lane Kcia calibration factor for cracking initiation CRT cracking retardation time due to maintenance

Crack Initiation

Crack Progression CRP retardation of cracking progression due to preventive treatment Progression of All cracking commences when tA > 0 or ACAa > 0

Crack Progression

Transverse Thermal Cracking Initiation ICT = Kcit max[a0, CDS3 (CCT +a1 + a2 HSNEW)] ICT time to cracking initiation, in years CCT coefficient of thermal cracking HSNEW thickness of the most recent surfacing, in mm Kcit calibration factor

Thermal Crack Progression dNCT incremental change in number of transverse thermal cracks, in no/km NCTa number of (reflected) transverse thermal cracks at the start of the analysis, in no./km NCTeq maximum number of thermal cracks, in no./km Kcpt calibration factor for cracking initiation

Ravelling Initiation IRV = Kvi CDS2 a0 RRF exp(a1 YAX) IRV time to ravelling initiation, in years YAX annual number of axles, in millions/lane Kvi calibration factor for ravelling initiation RRF ravelling retardation factor due to maintenance

Ravelling Progression Progression of ravelling commences when tv > 0 or ARVa > 0 dARV change in area of ravelling during analysis year, % of total carriageway area SRVa area of ravelling at the start of the analysis year, in per cent Kvp calibration factor

Pothole Initiation IPT time between the initiation of ACW or ravelling and the initiation of potholes, in years HS total thickness of bituminous surfacing, in mm CDB construction defects indicator for the base YAX annual number of axles , in millions/lane MMP mean monthly precipitation, in mm/month Kpi calibration factor for pothole initiation

Pothole Progression dNPTi additional number of potholes per km deriving from distress type i (wide cracking, ravelling, enlargement) ADISi per cent area of distress i at start of the analysis year TLF time lapse factor Kpp calibration factor

Edge break dVEB annual loss of edge material, in m3/km PSH proportion of time using shoulder AADT annual average daily traffic ESTEP elevation difference from pavement to shoulder, in mm MMP mean monthly precipitation, in mm/month S average traffic speed, in km/h CW carriageway width, in m Keb calibration factor

Damaged and Undamaged Area The total road surface will consist of the following: edge break potholes cracking ravelling undamaged

Rut Depth Modeling Rutting is defined as the permanent or unrecoverable traffic-associated deformation within pavement layers. The rut depth model is based on four components of rutting: Initial densification Structural deformation Plastic deformation Wear from studded tires

Rut Depth Progression Bituminous Roads Deterioration

Initial Densification RDO rutting due to initial densification, mm YE4 Number of equivalent standard axles DEF Benkelman beam deflection, in mm SNP structural number of the pavement COMP relative compaction, (%) Krid calibration factor

Structural Deformation Structural deformation without cracking Structural deformation after cracking

Plastic Deformation RDPD incremental increase in plastic deformation in analysis year, in mm CDS construction defects indicator for bituminous surfacings Sh speed of heavy vehicles, in km/h HS total thickness of bituminous surfacing, mm Krpd calibration factor

Wear by Studded Tires RDW incremental increase in rut depth due to studded tyres in analysis year, in mm PASS annual number of vehicle passes with studded tyres in one direction, in thousands SALT variable for salted or unsalted roads (2 = salted; 1 = unsalted) Krsw calibration factor

Rut Depth Standard Deviation RDS = a0 RDM RDS incremental increase in rut depth standard deviation in analysis year, in mm RDM incremental increase in total rut depth in analysis year, in mm a0 model coefficient (default =0.5)

Texture Depth TD incremental change in sand patch derived texture depth during analysis year, in mm TDa texture depth at the beginning of the analysis year NELV number of equivalent light vehicle passes during analysis year Ktd calibration factor for texture depth

Skid Resistance SFC50 = Ksfc a0 QCV SFC50 incremental change in side force coefficient during analysis year, measured at 50 km/h QCV annual incremental increase in the flow of commercial vehicles, in veh/lane/day Ksfc calibration factor

The End