Infrared thermography has applications in assessment of properties of construction substances and structures in civil engineering and construction.
In the civil engineering construction field, it is not only necessary to built up structures as per plan, but also to be sure that with age the building is performing the same as estimated. For this, building assessment is a necessary factor.
In this generation, equal importance is given for both building building study as well as building evaluation studies. This has lead to much sophisticated, but accurate methods to evaluate the present structural condition of the building, to save it for the future.
Infrared Thermography is such a great innovation which help in the investigation of what condition the construction is in and guide in damage fixing. This method is a kind of non-destructive method which evaluates without any contact. But its prominence in construction investigation is still growing. They have a huge demand to carry out rapid investigations.
The method of infrared thermography involves the data acquisition and its analysis with the help of thermal imaging devices that works without any contact with the substance to be analyzed.
With years, the method has been developed into more proficient manner as excellent infrared cameras were developed, that supports the method by converting the radiations into images (thermal images).
The method involves the conversion of infrared radiations that are emitted (by the body under observation) into thermal images or thermographs. The concept of working is simple. Thermography means writing with heat.
The data is obtained from the substance observed based on the thermal radiation emitted by them. The characteristics of the radiation emitted are based on the body temperature, their surface condition as well their thermal properties.
The emitted energy may be due to reflection or transmission or directly radiated energies. An infrared camera here has the role in sensing the thermal energy from the body. This sensed data is converted into thermographs or thermal images. These only bring the results based on the radiant energy and no visible light is considered.
Thermal images are entirely different from visual images. These images can be taken under total darkness.
Fig. An Infrared Camera
One of the main application of infrared thermography in the civil engineering is depended on the construction thermography. As the results are based on the emission properties of the substances, a good assessment of that area has to be performed.
The emission properties of building substances are represented in terms of emission coefficients, which mainly range between 0.90 and 0.96. The emission coefficients of construction substances are given in table1.
The Infrared thermography possesses a wide variety of application in the civil engineering field, which is explained in the following section.
The method shows the variation in moisture through photos, called the thermographs. These images show the different color of shades for respective temperature. Now a substance under normal temperature if subjected to any kind of moisture penetration will be at a lower temperature. Figure-1 shows the thermograph of moisture penetration in a canopy. This differences can be evident in the thermographs.
Fig.1: Thermograph of moisture penetration
The temperature for respective band colors is shown. The masonry structure in the majority is subjected to a temperature of 47 o C due to solar radiation. The image was obtained in the evening on a summer day.
From a closer observation, it was found that the brick structure has three free sides that were exposed to rainwater. With this muck and dust got deposited along the lines that created a decrease in temperature, which is shown by the dark bands.
Figure 2 represents the moisture penetration at the bottom of the window of a masonry structure at a temperature lower than 31 degree Celsius. Rest at a temperature of about 34 degree Celsius.
Fig.2: The moisture penetration under the windows of a masonry framework represented by dark bands
The thermographs help in assessing the performance of conduits and pipelines. The images were taken on a hot day. Figure 3 represents the visual and the thermograph of a control valve.
The water flowing is hot, due to the water tank located on the terrace is exposed to the sun. From the figure, the wall is at 31 degree Celsius, the concealed pipe, and exposed pipe are at 32 and 33 degree Celsius respectively.
Fig.3: (a) Visual Image (b)Thermal Image
It is observed that the truck tyre is at 46 degree Celsius, the pump at 50 degrees and drum of the truck is at 38 degrees. Figure 4 shows the thermal image of a ready mix concrete delivery truck at the site during a hot climate. But the uniform color of the drum makes it clear that it has a good mixing and quality.
Fig.4: The thermal image of ready mix concrete truck drum
Figure 5 shows the concrete flow through the pipe. There are certain patches seen, that shows leakage of the slurry at the joints
Fig.5: The thermal image of concrete flowing through the pipe
It is clear that any obstruction in the flow can be seen at the spot and corrective measure can be taken accordingly.
The system can be applied in the casting of the slab. During compaction, how the temperature is varying through the large area can be studied simultaneously, which help in knowing the faster evaporation problems resulting in inadequate hydration of concrete.
The approach is applied to know the effect of curing. Columns curing with gunny bags and by spraying can be differentiated by the different color shades shown for different temperature.
And the section fails at this neck formed. We know that the reinforcing bars fail for tension test by the formation of the neck. The normal tensile tests do not give us an idea about the yield point precisely.
Fig.6: The thermal image of a deformed bar under the tension test
It is observed that the tip of the failed section is at a higher temperature when compared with any point of the specimen. So, this method helps in giving more accurate strain measurements, compared to conventional methods.
The approach can also be used to determine the existence of voids in the concrete. This also measures the compaction effectiveness hence the workmanship. This can be tested to determine the quality of a hardened concrete.