Assessing concrete density using infrared thermographic (IRT) images

Infrared Physics & Technology 55 (2012) 442–448

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Infrared Physics & Technology

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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 Arabiab Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

a r t i c l e i n f o a b s t r a c t

Article history:Received 16 October 2011Available online 24 May 2012

Keywords:Portland cement concreteInfrared thermographyConsolidationCement contentWater to cement ratio

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⇑ Corresponding author. Tel.: +966 3860 2888; fax:E-mail addresses: [email protected] (L.M. A

m.edu.sa (M. Maslehuddin), [email protected]@kfupm.edu.sa (M.R. Ali).

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 tocement (w/c) ratio, cement content and consolidation effort. The concrete specimens were heated andthe IRT images were recorded as they cooled down. The IR thermographs indicated a good variation inthe 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 wasdecreased; 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 indicatinga decrease in the concrete denseness. The variation in cement content also influenced the denseness ofconcrete as indicated by the enhanced variation in the surface temperature. Concrete specimens withcement content of 300 kg/m3 (less dense) exhibited a greater temperature variation compared to thoseprepared with cement content of 400 kg/m3 (more dense).

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1. Introduction

Concrete is an artificial stone, created by binding of aggregateswith the use of cement paste. It is a heterogeneous mixture ofcoarse and fine aggregates and cement paste. The aggregates areproperly graded so that the spaces created by the large fractionsare filled by the smaller ones. However, air voids and honey combsare formed if the aggregate gradation is not proper and/or concreteis not adequately consolidated (usually done by vibration or rod-ing). The process of removing air by vibration or roding, knownas consolidation, is an essential part of the process to producedense concrete. Insufficient or excessive consolidation or leakageof cement paste from the formwork results in the formation ofvoids 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. Concretequality is also influenced by its composition, namely the quantityof cement and the water/cement ratio.

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Curing is another process that controls the quality of the hard-ened concrete. Insufficient consolidation will lead to the formationof honey combs and voids while inadequate curing results in aporous structure. Both these phenomena, particularly the former,significantly decrease the durability of concrete. Often, it becomesnecessary to quantify these inhomoginities in order to pinpoint thesource of failure. The presently available techniques, such aspulse velocity, hammer soundness, and radar analysis do notprovide adequate information regarding the extent and nature ofinhomoginities.

Infrared thermography has been utilized to a certain extent forthe detection of inhomoginities in concrete, particularly in in situstructures. Bhaskar et al. [1] reported a case study of the assess-ment of a 30 year old overhead reinforced concrete reservoir bynon-destructive test (NDT) methods. The main aim of the studywas to highlight the importance and significance of different testmethods employed to assess the condition of the reservoir. A ra-tional and systematic approach for the interpretation of test resultsbased 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] reportedthe use of infrared thermography for the detection of moisturebehind the surface of masonry arch bridges. The laboratoryexperiments and two case studies of masonry arch bridges in Scot-land were described. It was reported that infrared thermography

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Table 1Details of concrete mixture variables.

Variable Values

Cement content (kg/m3) 300 and 400Water/cement ratio 0.35, 0.4, 0.45, 0.50, 0.55, 0.60Degree of consolidation (%) 50, 60, 70, 80, 90, 100

Table 2Weights of constituents used in the concrete specimens.

Ingredients Mixture designation

#1 #2 #3 #4 #5 #6

Cement (kg) 300 300 300 400 400 400W/c ratio 0.4 0.5 0.6 0.4 0.5 0.6Water total (L) 138.6 167.7 197 176.8 215.8 254.9Coarse aggregate (kg)1.275 mm 565.9 544.3 522.6 514.7 485.3 456.59.54 mm 188.6 181.4 174.2 171.4 161.8 152.24.77 mm 377.3 362.9 348.4 342.8 323.6 304.32.38 mm 125.8 121.0 116.0 114.3 107.7 101.4Sand (kg) 770.8 741.3 711.8 700.3 661.0 621.7Super plasticizer (L) 2.8 1.0 0 2.2 0 0

L.M. Al-Hadhrami et al. / Infrared Physics & Technology 55 (2012) 442–448 443

can generally be used to determine the presence of moisture with-in the fill of a masonry arch bridge, even in unfavorable weatherconditions, as found in Scotland. According to the authors thethermal images offer an excellent means of making a qualitativemeasurement of the temperature of a surface, but absolute tem-perature measurement is fraught with difficulties [2]. Stimolo [3]reported the use of mobile IR test equipment for the detection ofdamages. The effects of the environment on the measurementand some general aspects of bridge and road pavements andof detectable subsurface defects or discontinuities werediscussed [3]. Some examples of application of the IR-technologyin road and bridge pavements were presented. It was statedthat the assessment of the condition of road and bridge pavementsby IRT is a powerful tool as it assists in planning the managementstrategy (program of maintenance, rehabilitation, and/orreplacement).

Kamoi et al. [4] studied the possibility of utilizing transient IRTto detect buried defects in concrete structures for health monitor-ing purposes. According to the authors the health monitoring todetect hidden defects in concrete structures is essential in orderto prevent additional incidents [4]. The reported study was de-voted to the analysis of the limits of detectability of air defects inmortar using thermography with both external lamp (long pulse)and flash heating, and monitoring temperature distributions onthe mortar surface by means of different infrared cameras. The re-sults indicated that IRT could be utilized for detecting flaws inconcrete.

Starnes et al. [5] conducted a preliminary thermographic studyfor the quality control of concrete structures strengthened with fi-ber-reinforced polymer composites. An experimental setup wasdescribed for measuring the emissivity of a carbon FRP compositeand for obtaining a well-defined heat pulse. The authors report agood agreement between the experimental thermal responseparameters and those calculated from finite-element models ofcontrolled-flaw specimens.

Avedilidis and Moropoulo [6] evaluated the feasibility of utiliz-ing IRT in evaluating the structural integrity of historical buildings.In particular, this non-destructive technique was utilized for theassessment of various traditional–historical materials and struc-tures after they had been conserved, restored or repaired using,depending on the case, different treatments. Non-destructive test-ing and evaluation was performed on the materials and structuresin order to assess the physico–chemical behavior of conservationtreatments, such as stone cleaning, stone consolidation, repairmortars, as well as to disclose any substrate features, such as voidson plastered mosaic surfaces. The outcome of that work providedstrong evidence that IRT is an effective technique for the evaluationof historic buildings and sites.

As stated earlier, some work has been done on the use of IRTtechnique for assessing the defects in concrete structures. How-ever, further work in this direction was not conducted may bedue to the fact that the technology had not developed significantlyat that time and portable IRT cameras were not easily available.Now with the advancement in the technology there is a need toconduct studies to relate concrete quality and/or inhomoginitieswith the IRT images.

The reported study was conducted to develop IRT images ofconcrete specimens prepared with varying composition and con-solidation effort. The developed images would be useful for assess-ing concrete quality in the field.

Fig. 1. Set of concrete specimens utilized in the study.

2. Methodology

Several concrete specimens were prepared with a varying de-gree of mixture design parameters, such as cement content and

water/cement ratio, and consolidation effort. Table 1 details themixture design parameters and the extent of consolidation thatwere adopted to prepare the concrete specimens. Table 2 showsthe weights of constituents utilized in each of the concrete mix-tures. Concrete slab specimens measuring 300 � 300 � 100 mmwere prepared. In order to minimize shrinkage, a steel mesh of12 mm diameter bars at a spacing of 150 mm in both directionswas placed in the mid depth of each specimen.

The concrete constituents were mixed in a revolving drum mix-er till a uniform color was obtained. The prepared concrete waspoured in the molds and they were vibrated on a vibrating table tillthe required degree of consolidation was achieved. The time to100% consolidation, till a shiny layer of water was noted on thespecimen surface, was noted and the time of vibration of speci-mens with 25%, 50% and 75% consolidation was adjusted in propor-tion to the 100% consolidation time. After consolidation, thesurface of the specimen was leveled and covered with a plasticsheet. After 24 h the specimens were demolded and cured in waterfor 7 days. The specimens were subsequently cured in air for 7 daysand consequently they were utilized for IR imaging work. Theywere heated to 70 �C in an oven for 24 h and then placed in a

Fig. 2. Experimental setup utilized in the reported study.

444 L.M. Al-Hadhrami et al. / Infrared Physics & Technology 55 (2012) 442–448

wooden box to record the thermal images at the surface of con-crete specimen. The thermal images were recorded utilizing a FLIRsystem camera that was connected to a personal computer loadedwith a ThermaCAM Researcher 2002 IR software. The thermalimages were recorded at intervals of 10 min. However, the con-crete surface temperature after 30 min of starting the cooling isutilized for discussion in this paper.

Fig. 1 shows a set of concrete specimens utilized in the studywhile Fig. 2 shows the experimental setup.

3. Results and discussion

Figs. 3 through 8 show the IRT images of concrete specimensprepared with varying cement content (300 and 400 kg/m3) and

Consolidation: 100%

Standard deviation: 0.3 °C

Consolidation: 50%Standard deviation: 0.6 °C

Fig. 3. IRT images of concrete specimens prepared w

water/cement ratio (0.4, 0.5 and 0.6) and consolidation effort(25%, 50%, 75% and 100%). As stated earlier the IRT images were re-corded at intervals of 10 min but images after 30 min are com-pared in these figures. A temperature scale is also included foreach of the specimen to show the thermal variation on the surfaceof the specimen. Also, provided in these figures is the details of theconcrete specimens, such as concrete composition and consolida-tion effort. The standard deviation in the surface temperature after30 min of starting the cooling is also provided. The auto tempera-ture scale option was selected to appreciate the variations in thesurface temperature in each of the specimen. Adopting a fixed scalewould have masked the temperature variations in some of thespecimens. The central body of the specimen generally exhibits ahigher temperature compared to the edges. This is understandablesince the heat tends to dissipate through the edges. The areas withlow temperature are indicative of less dense zones in a concretespecimen. Also, the temperature differential tends to increase withan increase in the water to cement ratio and a decrease in the con-solidation effort. Further, concrete specimens with cement contentof 300 kg/m3 exhibited more of low temperature areas than theconcrete specimens with cement content of 400 kg/m3.

A detailed discussion of the IR thermograms for each of the con-crete specimens investigated in this study is provided in the fol-lowing paragraphs.

The IR thermograms for the concrete specimens prepared withcement content of 300 kg/m3 and water/cement ratio of 0.40 aredepicted in Fig. 3. The intensity of temperature variation increasedwith a decrease in the consolidation effort, this evident by theincrease in the standard deviation of temperature measured after30 min of starting the cooling. The high variations in the tempera-ture are indicative of the presence of coarse pores in the concretedue to insufficient consolidation, such as 25%. This indicates theimportance of consolidation even in low water/cement ratio

Consolidation: 75%

Standard deviation: 0.5 °C

Consolidation: 25% Standard deviation: 0.6 °C

ith cement content of 300 kg/m3 and w/c of 0.4.

Consolidation: 100% Consolidation: 75%

Standard deviation: 0.3 °C Standard deviation: 0.4 °C

Consolidation: 50% Consolidation: 25% Standard deviation: 0.5 °C Standard deviation: 0.5 °C

Fig. 4. IRT images of concrete specimens prepared with cement content of 300 kg/m3 and w/c of 0.5.

Consolidation: 100% Consolidation: 75%Standard deviation: 0.5 °C Standard deviation: 0.5 °C

Consolidation: 50% Consolidation: 25% Standard deviation: 0.5 °C Standard deviation: 0.6 °C

Fig. 5. IRT images of concrete specimens prepared with cement content of 300 kg/m3 and w/c 0.6.






Fig. 6. IRT image of concrete specimens prepared with cement content of 400 kg/m3 and w/c of 0.4.





Fig. 7. IRT images of concrete specimens prepared with cement content of 400 kg/m3 and w/c of 0.5.






Fig. 8. IRT images of specimens prepared with cement content of 400 kg/m3 and w/c 0.6.


concrete. Concrete with low water–cement ratio and good consoli-dation effort is expected to possess a dense structure, as is indicatedin the IR thermograms for the specimen with a water/cement ratioof 0.4 and consolidation effort of 100%. The IR thermograms (Figs. 4and 5) for the concrete specimens prepared with other water/ce-ment ratios, 0.5 and 0.6, but similar cement content (300 kg/m3),however with varying consolidation effort, also indicate the effectof the consolidation effort on the pore structure of concrete. Thoughthe effect of water/cement ratio is also noticeable, the influence ofconsolidation effort on the concrete pore structure appears to bepredominant. For concrete specimens with similar cement contentand water cement ratio, the standard deviation of surface temper-ature increases with a decrease in the consolidation effort. This alsoindicates the formation of a porous structure in the concrete spec-imens prepared with insufficient consolidation.

The IR thermograms for the concrete specimens prepared withcement content of 400 kg/m3, water–cement ratio of 0.40 andvarying consolidation effort are depicted in Fig. 6. The variationin the surface temperature, indicative of varying denseness, wasalso noted in this batch of specimens. The thermograms indicateda less dense structure with decreasing consolidation effort andincreasing water to cement ratio. However, the temperature gradi-ent (high to low) in these specimens was not that high compared tothat noted in the concrete specimens prepared with cement con-tent of 300 kg/m3 (Figs. 3 through 5). This is probably due to thehigh cement content in the former specimens compared to the lat-ter. The increase in the quantity of cement provides sufficient ce-ment paste for filling the pores between the aggregate particlesand it also enhances the cohesiveness of the mix; thereby facilitat-ing the consolidation process. If concrete has voids caused by del-aminations or insufficient consolidation, the conduction paths aredisrupted. The disruptions in the flow of thermal energy lead tothe temperature differences on the surface, which can be detected

by IRT. As the specimen gets heated, the subsurface anomalies,including coarse pores, cause localized increase in heat absorption,consequently the surface above these areas are warmer than thesurrounding areas. As the specimen is allowed to cool, the anoma-lies, including coarse pores, cause the surface above them to dissi-pate heat faster than the surrounding solid areas, so they register acooler temperature. Consequently, the specimens with low cementcontent, high water to cement ratio and/or insufficient consolida-tion tend to show more cooler areas than dense specimens (withhigh cement content, low water cement ratio and/or sufficient con-solidation). It was also reported that the debonded areas filled withmoisture or water will lead to a lower surface temperature, whilethe debonded areas filled with air will lead to a higher surface tem-perature during the heating transient stage or vice versa during thecooling transient stage [7]. The standard deviation of temperatureis the same (0.3 �C) for the specimens with a consolidation of up to50%. However, it increases to 0.4 �C in the specimens with 25% con-solidation. The marginal change in the standard deviation in thetemperature may be attributed to the high cement content, in thiscase 400 kg/m3, that offsets the effect of low consolidation.

Figs. 7 and 8 show the IR thermograms for concrete specimensprepared with water–cement ratio of 0.5 and 0.6, respectively. Thetrend of these data is similar to that noted in the specimens with awater–cement ratio of 0.4 (Fig. 6).

4. Conclusions

This study was conducted to assess the quality of concrete uti-lizing IRT images. The concrete specimens were prepared withvarying cement content, water/cement ratio and consolidation ef-fort. The following conclusions can be made from the data devel-oped in this study.


1. A significant variation in the surface temperature was notedwith varying concrete composition and consolidation effort.Concrete specimens with similar composition exhibitedincreased temperature variation as the consolidation effortwas decreased; indicating the presence of less dense structureor coarser pores in these specimens prepared with insufficientconsolidation.

2. An increase in the water–cement ratio tended to create a largervariation in the surface temperature, indicating that the con-crete becomes less dense as the w/c ratio increases.

3. The variation in cement content also influenced the pore struc-ture, as indicated by an enhanced variation in the surface tem-perature. The temperature variation in the concrete specimensprepared with cement content of 300 kg/m3 was more than thatin the specimens prepared with cement content of 400 kg/m3.

The data developed in this study indicated that IR thermogramscould be utilized to evaluate the denseness of concrete. However,further studies are recommended for correlating the IR thermo-grams with the extent of concrete porosity and/or defects.

Acknowledgements

Authors acknowledge the Grant provided by King Fahd Univer-sity of Petroleum and Minerals, Dhahran, Saudi Arabia, under

Project # SB080022, for the conduct of study reported in this paper.The support provided by the Center for Engineering Research isalso acknowledged.

References

[1] S. Bhaskar, P. Srinivasan, A. Chellappan, Condition assessment of 30 years oldoverhead RCC reservoir, in: Proc. National Seminar on Non-DestructiveEvaluation, December 7–9, 2006, Hyderabad, India.

[2] M. Clark, M.C. Forde, Infrared thermography assessment of masonry archbridges laboratory and field case studies, in: International Symposium (NDT-CE2003), Non-Destructive Testing in Civil Engineering, 2003.

[3] M. Stimolo, Bridge and road construction, Passive infrared thermography ainspection and observation tool in bridge and road construction, in:International Symposium (NDT-CE-2003), Non-Destructive Testing in CivilEngineering, 2003.

[4] A. Kamoi, M. Yamad, Y. Okamoto, S.M. Shepard, Study on the detectability ofburied defects in concrete structures by using transient infrared thermographyfor health monitoring, 16th World Conference on NDT, August 30–September 3,2044, Montreal, Canada.

[5] M.A. Starnes, N.J. Carino, E.A. Kausel, Preliminary thermography studies forquality control of concrete structures strengthened with fiber-reinforcedpolymer composites, Journals of Materials in Civil Engineering 15 (3) (2003)266–273.

[6] N.P. Avedilidis, A. Moropouloou, Application of infrared thermography for theinvestigation of historic structures, Journal of Cultural Heritage 5 (2000) 119–127.

[7] Z. Li, W. Yao, S. Lee, C. Lee, Z. Yang, Application of infrared thermograpytechnique in building finish evaluation, Journal of Nondestructive Evaluation 19(1) (2000).

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Assessing concrete density using infrared thermographic (IRT) images