Data Logger usage in Concrete tests

Data Logger usage in Concrete tests

A data logger or data recorder is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they are based on a digital

processor (or computer). They are generally small, battery powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors.

Acquirement of Data from the Data Logger

The displacement transducers or strain gage-based transducers are connected with a state of the art data acquisition system called “Data Logger” (Data logger Kyowa UCAM-70A with strain gage-based transducers attached through Transducers cables). The displacement transducers are connected to the data logger through transducer cable and measurement could be made afterwards. A dial gage is connected with the concrete cylinder to record displacement and a steel plate of flat surface is placed on the cylinder for the uniform distribution of load. The load cell is placed over the steel plate. Load is applied by the universal testing machine till failure of the sample. The load vs. displacement data recorded in the data logger is transferred to computer and then analyzed. Stress-strain curves for the concrete cylinders are drawn after the data analysis.

Modulus of Elasticity

It is the measure of the elastic property of a material. It is the ratio of the applied load and the resulting strain which disappears on the removal of load. It is equal to stress divided by strain and is generally designated by the letter ‘E’. Modulus of elasticity of concrete is frequently expressed in terms of compressive strength. Modulus of elasticity of concrete is a key factor for estimating the deformation of structures and its members.

Modulus of Elasticity of Concrete

The modulus of elasticity of concrete E_c, adopted in modified form by the ACI Code is given by;

For normal-weight, normal-density concrete these two relations can be simplified to;

Where E_c = modulus of elasticity of concrete and f_c’= specified 28 days compressive strength of concrete. The ACI Building code 318-83 gives the following expression for the static modulus (GPa or psi) of normal weigh concrete.

In SI units: E_c = 4.70 f_cyl ^0.5

In psi: E_c = 0.057 f_cyl ^0.5

Modulus of Elasticity Value for the Samples Tested:

Modulus of elasticity for the concrete cylinders that are tested is calculated from the stress strain curves plotted. For obtaining the E_c value, only the linear part of the curve is observed. Values of stress and strain are noted at the end point of linear portion and E_c is calculated as follows.