Methods for measurements and analyses of cracks in flexible pavements

Abstract: When cracking has propagated through the entire asphaltbound layers, water may ingress into the unbound layers andaccelerate the deterioration of the road structure. Knowledgeon where cracks initiate and how they propagate vertically istherefore of great practical importance. The objective of thisdoctoral thesis is to develop and evaluate methods forcollection and analysis of crack data in flexible pavements.This thesis describes four methods for crack data collection onthe surface and in depth. One manual method was used to analysecracks at different depths on samples from an acceleratedpavement testing facility at University of California atBerkeley. Computerised Tomography was used to analyse cracksinside samples from a Swedish in-service road. Simultaneously,surface crack data collection methods were studied. One methodfor research on object level was developed and evaluatedthrough studies of surface crack propagation in 1998-2002 usingdigital photos and image analysis. Another method for use onroad network level as well as object level was evaluated,improved and re-evaluated. The last-mentioned method is anautomatic system using video images to collect crack data inhigh speed. New crack measures adjusted to high-speed crackdata collection were proposed and discussed. The methods areevaluated and their application and results are discussed. Thethesis also includes a literature review on cracking offlexible pavements focusing on crack data collection.The doctoral thesis is based on the following papers, whichwill be referred to by their Roman numbers:I.Offrell, P., Harvey, J., Scheffy, C., "Crack geometryanalysis in asphalt samples obtained from a Heavy VehicleSimulator test site." 9th International Conference on AsphaltPavements ISAP Copenhagen August 2002.II.Offrell, P., Magnusson, R., "Computerised Tomographyas a tool for crack analysis in asphalt layers." InternationalJournal of Road Materials and Pavement Design - Volume 3 -Issue 1/2002, pp49-72.III.Offrell, P., Magnusson, R., "In situ photographicsurvey of crack propagation in flexible pavements." Submittedfor publication in The International Journal of PavementEngineering.IV.Offrell, P., Sjögren, L., "Validation of anAutomatic Crack Data Collection System." Submitted forpublication in ASCE J of Transportation Engineering.V.Offrell, P., Sjögren, L., "Repeatability inCrack Data Collection on Flexible Pavements?A Comparisonbetween Surveys using Video Cameras, Laser Cameras and aSimplified Manual Survey. " Submitted for publication in ASCE Jof Transportation Engineering.