Carrying out patch repairs to historic concrete buildings and structures needs to be done carefully if their cultural value and significance is to be maintained. This often means repairs using custom designed materials and mixes for compatibility with the original concrete, and with great care paid to good workmanship. But with most repairs, commercial mixes are used which are not compatible with the host concrete but are justified because they adhere well, cure quickly and require limited skills to implement. A research collaboration has been established to test the performance of both approaches. The Performance Evaluation of Patch Repairs on Historic Concrete Structures (PEPS) began in 2018 and is a collaboration between the Getty Conservation Institute, Historic England and the Laboratoire de Recherche des Monuments Historiques. Its purpose is also to better understand key design and specification parameters and application methods. The research is based on assessing case studies in USA, England and France within a variety of climatic and environmental conditions, typologies and repair materials. This paper will present the methodology adopted to evaluate the repairs in the first phase. This will also include historical research on the specification and application of the repairs, preliminary field assessment and some testing.
Monitoring the water content and detecting the presence of soluble salts in concrete is a key issue for its maintenance. Evanescent field dielectrometry, originally developed for the diagnostics of frescoes and mural paintings, is proposed as a tool for monitoring the decay of cement-based materials. A measuring system, based on a scalar network analyzer and a resonant probe, has been realized and tested on concrete samples taken from historical buildings in France or purposely developed in the laboratory. Measurements on water-saturated and oven-dry samples provide the basis for calibrating the instrument for on site monitoring of concrete historical buildings, sculptures and cement-based artifacts.
Corrosion in reinforced concrete is generally attributed to either carbonation or chloride presence in the vicinity of the bars. But in the field of cultural heritage, especially for the most ancient monuments, it is not rare to encounter both carbonated and chloride polluted concrete, inducing heavy corrosion, as was the case in the Villa E-1027 in Roquebrune-Cap-Martin, on the French Mediterranean seashore. The villa was designed by Eileen Gray and Jean Badovici between 1926 and 1929. Due to aggressive environmental conditions and a period of dereliction, the concrete of the villa was quite heavily decayed and a deep restoration was led between 2000 and 2006. But after a little more than 10 years, and despite active maintenance, the villa is again facing corrosion induced decay. Prior to the definition of a new restoration protocol, to better evaluate the corrosion activity, in 2017 a permanent monitoring of moisture and temperature both in the air and in the concrete was installed. In the meantime, a series of instant electrochemical measurements was performed from 2017 to 2018. A first analysis of the results of the monitoring and the non-destructive tests clearly evidences that probably due to the conjunction of the carbonation of the concrete and external active chloride pollution, corrosion can happen at quite low moisture content.
While there have been many studies on the performance criteria of concrete patch repairs, there are few specific studies on the long-term performance of patch repairs designed to preserve the aesthetic significance of the original fabric of culturally significant concrete structures. In order to address this issue, the Getty Conservation Institute (GCI), Historic England (HE) and the Laboratoire de Recherche des Monuments Historiques (LRMH) commenced work on an international collaborative research project, ‘Performance Evaluation of Patch Repairs on Historic Concrete Structures’ (PEPS). Begun in 2018, the PEPS project aims to produce practical guidance that will help those repairing historic concrete through the assessment of case studies in the USA, England and France within a variety of climatic and environmental conditions, typologies and repair materials. The operational phases of the research project consist of in situ tests and laboratory analysis performed on both the original concrete and previous patch repairs. This paper provides an overview of the assessment methodology that has been developed by an inter-disciplinary team of professionals working in the field of concrete conservation, and includes a variety of traditional and non-traditional non-destructive, mechanical, chemical, and electro-chemical characterization and diagnostic techniques.
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