Keywords: expert system, concrete distress, database management system, knowledge management.

This paper outlines a proposed computer integrated knowledge-based expert system, called DEMAREC-EXPERT, to address the needs of diagnostic-related issues, identification and systems knowledge users involved in repair and maintenance activities, such as condition assessment, material failure analysis, material selection and rehabilitation recommendations. This program is created to disseminate knowledge of the concrete distresses and recent advancements in concrete repair problems. It is considered as a decision-making tool and to be a comprehensive computerized expert system that gives recommendations on concrete structures.

The DEMAREC-EXPERT system is designed to assist engineers in diagnosing distresses and in the assessment of current conditions in concrete structures. It has facility for sophisticated data management so it is coupled to an independent database management system, called REPCON, for obtaining recommendations on materials and procedures for repair and rehabilitation methods and taking recommendations in durability. Recognizing the importance of transferring information to practising concrete engineers, every effort is made to incorporate new concrete technology in the DEMAREC-EXPERT system.

DEMAREC-EXPERT is a knowledge-based expert system which contains all the parts of a typical expert system program. The structure of the DEMAREC-EXPERT system comprises M.4 as an expert system development shell, knowledge bases, the Visual Basic user-friendly interface and report generation modules. The user can read the parameters and answer the questions through the Visual Basic user interface. In some of the questions, the user can seek visual assistance in selecting pictures from the database. The M.4 expert system accesses the knowledge bases and based on the input variables makes a decision. The results are stored as codes in a separate text file and then decoded and fed into the user interface in where the user can review the result.

The initial step of the development strategy for the knowledge base is to organise the knowledge and then modified it by the author's experience using the approach an expert would take to address the problem or activity. Secondly, a narrative description of the knowledge is developed in a question-and-answer format and conclusions and recommendations are also included at this stage. Then the diagnostic (hierarchical) trees are generated to provide a logical sequence to the knowledge and to represent how the knowledge is linked together. The integrity of the knowledge base lies in the development of the diagnostic trees. The pieces of knowledge in the diagnostic trees are arranged in a manner allowing for an uninterrupted flow of knowledge upon completion of the tress.

The knowledge contained in DEMAREC-EXPERT includes information and rules on the three categories of distress in concrete structures such as cracking in concrete (CRACON), surface distresses in concrete (SURCON), and miscellaneous distresses (MISCON). The rules and the parameters in the DEMAREC-EXPERT knowledge bases contain confidence level (CL) values to indicate the degree of reliability about the acquired knowledge. The confidence levels can be combined with each other to obtain an overall confidence level for the final recommendation or conclusion. The confidence levels (CL) included in the DEMAREC-EXPERT are words and descriptive functions with pre-determined CL value which are used to describe the knowledge.

The system usability and results are validated by three case studies taken from actual cases of concrete diagnosis and repair. In these case studies, it is shown that the results of this research could have been used to enhance the process of determining the cause of the failure and in selecting the repair material and method. This system is a valuable tool in automating the acquisition of field information, in presenting a hypothesis on how known distresses relate to site specific problems, in preserving the knowledge of experts and in providing a record of the condition of structures at different ages. It also provides much needed guidance for practitioners while serving as a decision support system for other experts and specialists in the field.

This integrated knowledge system is designed to provide the user with recommendations related to the best course required for maintenance and in the selection of materials and methods for the repair, and give the recommendations to enhance durability of concrete structures. Therefore, it is a valuable tool for engineers and other professionals dealing with the maintenance and repair of concrete structures. DEMAREC-EXPERT's conclusions and recommendations are meant to be used as a decision-making tool. Misperception of the structure's conditions and requirements, misstatement of the inspectors or the absence of information may cause the conclusions and recommendations to be invalid. This is why users are encouraged to conduct tests and procedures recommended by the REPCON database.

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