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Welcome to Chris Bennett's and Lis Pedersen's web site. If you are looking for information Chris' current work on affordable housing, please visit www.mygbhousing.info. The video below tells the background to Chris' project.


Cracking and Surface Distress

Cracking and surface distress.

This report identifies and evaluates technology solutions that meet asset management needs relating to road pavement performance. The increasing pace of change of technology brings considerable promise of more data, of a higher quality, captured for a lower cost. The report summarises current and emerging data collection technologies, and proposes and tests a technology evaluation framework. The evaluation of emerging technologies found existing equipment, such as mobile phones, was often repurposed to develop new methods of data collection. While this occasionally results in lower accuracy, this is consistently offset by high affordability and other strengths such as higher frequencies of data collection, data redundancy and secondary benefits. Accordingly, even emerging data collection technologies with relatively low accuracies have a role to play in addressing the data needs of road controlling authorities, and may be used to augment, rather than replace, existing data collection programs

An interesting study which develops a set of relationships between subjective pavement Surface Inspection Rating (SIR) and automated pavement distresses, with an investigation of interactions between pavement distresses. The pavement condition parameters/distresses include cracking, rutting, texture loss and roughness. In addition, the influences of pavement operating conditions (such as age and heavy vehicle traffic volume) on the measured strength of relationships between subjective rating and objective pavement distresses, are studied.

NZTA Research Report 617.

The manual road condition survey method used in New Zealand (road asset maintenance management ((RAMM)) surveys) was developed during the early 1980s with the primary purpose of feeding into the treatment selection algorithm. For more than 20 years the rating system was adequate for this purpose but as more sophisticated asset management evolved into deterioration modelling and advanced trend monitoring, the data quality from the manual surveys came under scrutiny. Attempts to improve the robustness of the rating system included increasing the recommended sampling size from 10% to 20% of the treatment length plus increasing the requirements for accreditation during the training of raters. Yet, these steps still fall short in increasing the overall usability and repeatability of rated data for the new demands of asset management processes. Automated defect data collection has been undertaken since the mid-1990s with early technology relying on photographic imaging and processing of road surface data. The technology was particularly popular for application on busy asphalt and concrete motorways in the northern hemisphere but failed to deliver acceptable robustness on chipseal surfaces. This situation changed with the arrival of laser scanning technology, which has overcome the limitations of photo-imaging technology. The measurements now solely depend on laser scanning at a high resolution, which gives a comprehensive 3D image of the road profile. Any defects such as cracks, potholes or surface defects can be identified on the image. The benefits this technology offers to the sector include: • surveys of 100% of the road are possible • all aspects of the condition of the surface are captured simultaneously • the measurements take place at high speed (60 to 80km/h), providing significant safety and traffic management benefits • ‘removing’ the human element from the measuring allows for more repeat measurements. Despite the accuracy of the measurement, the constraining factor for the technology is the algorithms that interpret the digital image to identify and quantify specific defects. This has resulted in the main question posed for this project – is the measurement sufficiently robust and is the sector ready to adopt this technology on a wide scale?

Specifications developed by Austroad for automatic crack detection and high speed deflectometer data collection.

The research presented in this thesis investigated the occurrence of flushing of chip seal pavements. The research aimed to determine the effects of volumetric properties of chip seal surfaces on flushing, focusing on the relationship between air voids and flushing initiation. Additionally, the research aimed to develop a pavement deterioration model to predict the initiation and progression of flushing on chip seal pavements. Mechanical testing was conducted on cores obtained from in-service, flushed chip seal pavements from Auckland, Waikato, Christchurch and Dunedin regions of New Zealand. The tests that were performed on the cores included wheel tracking, air voids measurement, bitumen extractions and sieve analyses to determine aggregate grading profiles. Measurements were made of the depth and pattern of deformation that had developed on the cores during wheel tracking. Samples extracted from tested cores were scanned using a computed tomography scanner and the scan images were analysed using image analysis techniques to calculate the volume of air voids within the samples. The reduction in air void volume during wheel tracking was compared to the flushing that had occurred on the samples to establish the relationship between flushing and air voids. Furthermore, data analysis was performed on pavement condition data gathered from New Zealand’s long-term pavement performance database to identify the combination of factors that provided the best prediction of flushing, and regression analysis was performed to develop a model to predict the initiation and progression of flushing. The laboratory testing described above revealed that the thickness of a chip seal surface has a direct correlation to flushing, where thicker surfaces tend to have more severe flushing. Moreover, the reduction in air void volume that occurred in a chip seal structure due to loading was directly related to the amount of flushing likely to occur on that surface. The pattern of deformation of a chip seal structure provided an indication of its state of stability, which in turn indicated the best method of treatment for flushing. From the data analysis it was identified that the combination of factors that provided the best indication of flushing were surface thickness, surface age, rutdepth and grade of aggregates. The flushing initiation model had an accuracy of 76% and the flushing progression model was also statistically strong at predicting the quantity of flushing. Using these research outcomes, a pavement condition assessment guideline was developed to aid with managing flushed pavements. Overall, this research has significantly increased the understanding of the mechanisms that lead to flushing and established ways to better identify and manage flushing.

The objective of this technical report is to help road administrations choose and select automated systems in regard to their needs, therefore increasing the quality of the crack data used in pavement management systems. The concepts presented in this document are not international standards, only a summary of the experiences exchanged between world experts. set as its principal objectives the development:


First, the paper presents a series of more objective and more detailed rules to measure and classify cracks. Some have the objective of increasing the reproducibility of measurements and allowing more reliable comparison of the cracking data gathered by different equipment. A monitored zone has been delimited as well as a better definition of a crack and a methodology to measure the crack severity and extent.


Similarly, three methods of evaluation of the reliability of automated crack measuring equipment are also proposed. The research level validation test is used to rate the sensor’s resolution and sensitivity regarding the capability to capture raw pavement data (images or 3D data). The project level validation test allows road administrations to rate the equipment’s bias and repeatability to precisely measure cracks on some small controlled reference track which presents specific and various conditions. While the last validation test, entitled network level validation test, differs from the preceding one by the scope of the measurement campaign and by the precision level sought. Performed on 50-100 km of road, the equipment can be tested on varied surfaces that are more representative of the network reality.

 Prepared by Working Group D of Committee TC 4.2 “Road/Vehicle Interaction” 

The objective of this technical report is to help road administrations to choose and select automated systems in regard of their needs and to increase the quality of the crack data used in pavement management systems. The concepts presented in this document are not international standards but only a summary of the experience exchanges between world experts.

2006 - USA - Evaluation of Crack Detection
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Paper describing an evaluation of automated crack detection.
Report evaluating whether a practical method of road surface texture measurement using information theory and fast Fourier transformation analysis could be developed.

2005 - UK - SCANNER Surveys: Specification for Services
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Guides to conducing the UK SCANNER (Surface Condition Assessment of the National Network of Roads) surveys. Specification for Services with details on survey procedures, data processing, route fitting and calculations of derived parameters.

2005 - UK - SCANNER Surveys: Quality Assurance and Audit
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Guides to conducing the UK SCANNER (Surface Condition Assessment of the National Network of Roads) surveys. Quality Assurance and Audit with procedures to ensure Services are consistent and reliable. Includes audit processes, monitoring, calibration, and requirements for repeat surveys.

2005 - UK - SCANNER Surveys: Further Technical Guidance
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Guides to conducing the UK SCANNER (Surface Condition Assessment of the National Network of Roads) surveys. Technical Guidance on interpretation of processed SCANNER data.

2005 - UK - SCANNER Surveys: Advice to Local Authorities
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Guides to conducing the UK SCANNER (Surface Condition Assessment of the National Network of Roads) surveys. Gives background infromation on the development of SCANNER surveys, advice on contract procurement and mobilization, glossary of technical tems and a model contract document as annexes.
Guides to conducing the UK SCANNER (Surface Condition Assessment of the National Network of Roads) surveys. Acceptance Testing and Accreditation describes the requirements for testing survey vehicles to become accredited by site and network tests. It also describes the requirements for the reporting and delivey of survey data.

2004 - Automated Pavement Distress Collection Techniques
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NHCRP Synthesis 334 describing various techniques for automated collection of surface distress data

1999 - New Zealand - Converting RAMM Data for Use with dTIMS.
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Report describing how the data from a pavement management system were converted for use with HDM pavement deterioration model

1994 - Universal Cracking Index
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Paper by Bill Paterson describing the Universal Cracking Index, a way of measuring cracking. The UCI has been implemented by some automated crack analysis software systems.
Internal paper by W.D.O. Paterson of the World Bank introducing the concept of the SII and how it is used in the field


Chris in the NCT Race 

Chris has an adventurous spirit which generally involves cycling, running, or just being out there having a good time. Read his 'Race Reports' below. This is a link to his SPOT GPS tracker. If you are interested in his 'geeky' sport technical blog it is at www.tri-duffer.com. He also has stories of his life as 'An Overtravelled Engineer Working for the World Bank' at World Bank Traveller.


Race Reports


Document Library


  • Chris' published papers and reports are here.
  • His Technical Library  has a range of reports 
  • Golden Bay community projects are here.
  • The history of the ROMDAS company is here.
  • The 'Road to Good Health' HIV/AIDs Toolkit is here.


Technical Library

Chris and Lis

Chris and Lis

We are Lis Pedersen and Chris Bennett. We’ve been married over 30 years and each found our way to New Zealand in the early 1980s from Denmark and Canada respectively. Golden Bay has been our happy place for almost 20 years and we are now based in Pohara just above the beach, with our two cats Coco and Max. 




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