Assessing concrete density using infrared thermographic (IRT) images Luai M. Al-Hadhrami a,⇑ , M. Maslehuddin b , Mohammed Shameem b , Mohammed Rizwan Ali b a Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia b Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia article info Article history: Received 16 October 2011 Available online 24 May 2012 Keywords: Portland cement concrete Infrared thermography Consolidation Cement content Water to cement ratio abstract This paper presents the results of a study conducted to evaluate the possibility of utilizing infrared ther- mography to assess the quality of concrete. Concrete specimens were prepared with varying water to cement (w/c) ratio, cement content and consolidation effort. The concrete specimens were heated and the IRT images were recorded as they cooled down. The IR thermographs indicated a good variation in the surface temperature with varying concrete composition and consolidation effort. Concrete with sim- ilar composition exhibited a greater variation in surface temperature as the consolidation effort was decreased; indicating the presence of less dense structure in the specimens prepared with low consoli- dation effort. An increase in the water–cement ratio also increases the temperature variation indicating a decrease in the concrete denseness. The variation in cement content also influenced the denseness of concrete as indicated by the enhanced variation in the surface temperature. Concrete specimens with cement content of 300 kg/m 3 (less dense) exhibited a greater temperature variation compared to those prepared with cement content of 400 kg/m 3 (more dense). Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Concrete is an artificial stone, created by binding of aggregates with the use of cement paste. It is a heterogeneous mixture of coarse and fine aggregates and cement paste. The aggregates are properly graded so that the spaces created by the large fractions are filled by the smaller ones. However, air voids and honey combs are formed if the aggregate gradation is not proper and/or concrete is not adequately consolidated (usually done by vibration or rod- ing). The process of removing air by vibration or roding, known as consolidation, is an essential part of the process to produce dense concrete. Insufficient or excessive consolidation or leakage of cement paste from the formwork results in the formation of voids and honey combs. The voids and honey combs entrap mois- ture and oxygen in their skeleton thereby encouraging the deteri- oration processes, particularly reinforcement corrosion. Concrete quality is also influenced by its composition, namely the quantity of cement and the water/cement ratio. Curing is another process that controls the quality of the hard- ened concrete. Insufficient consolidation will lead to the formation of honey combs and voids while inadequate curing results in a porous structure. Both these phenomena, particularly the former, significantly decrease the durability of concrete. Often, it becomes necessary to quantify these inhomoginities in order to pinpoint the source of failure. The presently available techniques, such as pulse velocity, hammer soundness, and radar analysis do not provide adequate information regarding the extent and nature of inhomoginities. Infrared thermography has been utilized to a certain extent for the detection of inhomoginities in concrete, particularly in in situ structures. Bhaskar et al. [1] reported a case study of the assess- ment of a 30 year old overhead reinforced concrete reservoir by non-destructive test (NDT) methods. The main aim of the study was to highlight the importance and significance of different test methods employed to assess the condition of the reservoir. A ra- tional and systematic approach for the interpretation of test results based on NDT was presented for economical repair and rehabilita- tion procedures. Necessary repair measures were suggested to en- hance the service life of the structure. Clark and Forde [2] reported the use of infrared thermography for the detection of moisture behind the surface of masonry arch bridges. The laboratory experiments and two case studies of masonry arch bridges in Scot- land were described. It was reported that infrared thermography 1350-4495/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.infrared.2012.04.004 ⇑ Corresponding author. Tel.: +966 3860 2888; fax: +966 3860 3966. E-mail addresses: luaimalh@kfupm.edu.sa (L.M. Al-Hadhrami), muddin@kfup- m.edu.sa (M. Maslehuddin), mshameem@kfupm.edu.sa (M. Shameem), riz- wanm@kfupm.edu.sa (M.R. Ali). Infrared Physics & Technology 55 (2012) 442–448 Contents lists available at SciVerse ScienceDirect Infrared Physics & Technology journal homepage: www.elsevier.com/locate/infrared