Digital laminography assessment of the damage in concrete exposed to freezing temperatures Kentaro Wakimoto a , Joshua Blunt a , Cruz Carlos a , Paulo J.M.Monteiro a, ⁎, Claudia P.Ostertag a , Richard Albert b a Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA b Digiray Corporation, Danville,CA,USA A B S T R A C T A R T I C L E I N F O Article history: Received 24 October 2007 Accepted 15 May 2008 Keywords: Crack detection Cycles Laminography Image analysis Freezing and thawing The research explores the possibility of using digital laminography as a non-destructive inspection X-ray method to image the damage existing in concrete exposed to low temperatures. Freezing–thawing and scaling tests were performed and digital laminography was used to determine the degree of damage existing inside the concrete samples. First,digital laminography was performed on the concrete sample and then a visual inspection was done by slicing the sample after it was vacuum-impregnated with epoxy in order to compare the differences in crack width. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction The successfulevaluation of the extent and severity of cracks caused by frost action is important for determining the life cycle of concrete structures. Visual inspection of concrete surfaces has been standard practice because it is the simplest method, and up until now it has been difficult to evaluate damage inside the concrete. Any robust evaluation ofthe long-term performance ofa structure is difficult without knowing what is happening inside the material. Therefore, non-destructive methods to evaluate the internal damage of concrete structures have been developed to meet these needs. Typical non-destructive inspection techniques include stress wave propagation and electricalmethods [1]. While these methods can evaluate the internaldamage ofa concrete structure non-destruc- tively,their spatialresolution is low,and visualization using three- dimensionalreconstruction is difficult. To complement these meth- ods, X-ray imaging, such as computed tomography and laminography, are being studied [2].Computed tomography makes it possible to evaluate the internal three-dimensional damage in materials, but the technique has low portability making it hard to transport to the field. The complex geometry and the large dimensions existing in civil engineering structures often prevent the complete distribution of the detectors around the structure, which is required to obtain a sharp image.On the other hand, digital laminography,which is used in dentistry and for inspection of circuit boards, is an attractive methodology to inspect reinforced concrete structures. This paper reports on the use of digital laminography as a means to determine the presence of cracks and delaminations in concrete exposed to low temperatures. Two specimen types were prepared in order to explore a range of crack types associated with freezing damage.These include internalmicrocracking and surface scaling [3–5]. Internal cracking from freeze–thaw cycling results in expan- sion, loss in mechanical properties, and eventually the destruction of concrete [3]. The leading mechanism of destruction is caused by the phase transformation of water into ice, which has a 9% volume expansion. In fully saturated pores of concrete exposed to low temperatures, as volume expansion occurs, the space gets taken up by ice and the unfrozen water is pushed away from the freezing site. The water travels through the porous cement paste until it reaches an air-filled void (escape boundary) where the water freezes avoiding the development of large stress in the matrix [3,6]. If the concrete does not have an adequate air void system, ice is formed in the matrix generating cracks. Surface scaling, however, is characterized by the loss of small flakes of cement paste or mortar and is limited to a few millimeters near the concrete surface [3,4]. In cold climate conditions,ice forms on the surfaces of bridges and highways. Salt is placed on these surfaces to lower the freezing-point temperature which causesice to melt, thereby increasing friction on the roadway. A recently proposed mechanism for surface scaling is the bi-material effect. The mechan- ism of destruction is caused by mismatch in thermal expansion of the Cement and Concrete Research 38 (2008) 1232–1245 ⁎ Corresponding author. E-mail address: monteiro@ce.berkeley.edu (P.J.M. Monteiro). 0008-8846/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2008.05.003 Contents lists available at ScienceDirect Cement and Concrete Research j o u r n a l h o m e p a g e : h t t p : / / e e s. e l s ev i e r. c o m / C E M C O N / d e f a u l t . a s p