Novel perspectives in bridges inspection using GPR A. Benedetto a *, G. Manacorda a , A. Simi b and F. Tosti a a Department of Sciences of Civil Engineering, University of Roma Tre, Via Vito Volterra 60, Rome 00146, Italy; b Ingegneria Dei Sistemi IDS Georadar Division, PISA Headquarters, Via E. Calabresi, 24 - Loc. Montacchiello, Pisa 56121, Italy (Received 9 November 2011; final version received 18 April 2012) Bridge engineers increasingly prefer to use the Ground-Penetrating Radar (GPR) technique. GPR can yield data with very high spatial resolution, the data can be acquired rapidly and even during traffic, causing very low interferences. This paper presents a novel GPR system that is designed and developed for bridge applications. In addition it proposes a new algorithm for cracks tracking in a three-dimensional domain. The effectiveness and accuracy of the procedure have been calibrated and validated on four different bridges. In this paper, three-dimensional visualisations of cracks and two-dimensional tomographies and sections are shown to demonstrate the potentialities of the GPR system associated to the signal-processing algorithm. Keywords: bridges; ground-penetrating radar; pavement engineering; bar corrosion, cracking 1. Introduction In the past decade an increasing number of bridges all over the world are always more classified as structurally deficient. In addition these structural deficiencies cause damages that are severely appearing on the top layers of pavement, having often crucial effects on safety of driving. The estimated financial cost of repairs is very high and the social costs, in terms of safety reduction, are also becoming significant [1]. Basically, corrosion associated with reinforcing bars is the most significant contributor to bridge deficiencies as well as other concrete infrastructures. The corrosion is usually caused by moisture and chloride ion exposure. It is related to the presence of excessive moisture and chloride ions in the concrete adjacent to the reinforcing steel. The acidic solution of chloride, which ingresses from the top of the concrete deck down to the reinforcement depth, depassivates the normally alkaline environment in concrete and corrosion is initiated. The solution reacts with the steel initiating intensive oxidation processes. In particular, dry corrosion produces FeO, Fe 2 O 3 , Fe 3 O 4 and other oxides along reinforcement bars. The early stage of corrosion is generally known as the initial passivity stage. Rapidly the reinforcing bars are attacked by acidic, wet corrosion and yield expansive, hydrated corrosion products, which can in turn accelerate the formation of cracks in the surrounding concrete. These oxidation products occupy a larger volume than the original intact steel and internal expansive stresses lead to cracking and debonding. ISSN 1058-9759 print/ISSN 1477-2671 online q 2012 Taylor & Francis http://dx.doi.org/10.1080/10589759.2012.694883 http://www.tandfonline.com *Corresponding author. Email: benedet@uniroma3.it Nondestructive Testing and Evaluation, Vol. 27, No. 3, September 2012, 239–251