Using DIC to determine modulus elasticity of concrete

A study compares a non-contact measurement technique, Digital Image Correlation (DIC), with a conventional contact-based method, Linear Variable Displacement Transducer (LVDT), for determining the modulus of elasticity of concrete.

Introduction

A team of researchers from Newcastle University of Singapore and National University of Singapore, has developed a novel and practical method of assessing the mechanical properties of structures, with potential application to structural health monitoring of large structures, such as bridges and viaducts in Singapore.

The team has presented their findings exploring whether DIC is a comparabe technique to conventional contactable methods for indictaing the stiffness of a material.¹ A uniaxial compression test was set up to measure the displacement of a concrete sample under load. This study presents whether DIC can be used to obtain the static modulus of elasticity of concrete accurately.

Research methods

A cyclindrical concrete sample with a height of 300 mm and a diameter of 100 mm was loaded by a universal testing machine. Two methods, one contact-based (DIC) and one non-contact based (LVDT), were used to measure the displacement of the object’s surface.

DIC system

The non-contact based method used in the experimental setup was Imetrum’s Flexi (DIC) System.

DIC concrete test — Fig.1. (a) Schematic and (b) photo of equipment setup showing the position of the DIC camera, (c) field of view of natural targets captured by Video Gauge^TM software.

The hardware consists of a computer processing unit connected to a monochrome camera and 25 mm lens. Imetrum’s Video Gauge^TM software tool was used to capture, process and analyse the non-contact measurements. The camera was positioned at a distance of 1M from the targets set at the surface of the sample (fig.1).

Results

The sample was pre-loaded to a compressive stress of 36 MPa and held for 50 seconds before unloading. Figure 2 shows the strain values measured by both methods.

DIC concrete test data — Fig.2. (a) comparison of deformation measurement using DIC and LVDT (b) comparison of the stress/strain curve using DIC and LVDT

The DIC results from both the strain measurement and comparison of modulus of elasticity show a comparable correlation to the LVDT.

Strain and elasticity of concrete table — Table 1. Comparion of strain measurement using DIC and LVDT; Table 2. Comparison of modulus of elasticity calculated from DIC and LVDT measurement.

Conclusion

This study shows that the DIC method can be used to obtain the static modulus of elasticity of concrete accurately. DIC also has the advantage over contacting methods, like LVDTs, that you are able to directly measure the deformation on the surface of the concrete sample.

¹Loh TB, Wu Y, Goh SH, Kong KH, Goh KL and Chong JJ. Determination of Static Modulus of Elasticity of Concrete in Compression using Digital Image Correlation (DIC) Method. 2022

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