Cracking and Surface Distress

Cracking and surface distress.

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 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