A device for measuring the compression creep of concrete

A device for measuring the compression creep of concrete

In the Institute of Building Testing of the Faculty of Civil Engineering of BUT, a device which will enable the monitoring of the strain of fine concrete and mortar has been projected. The inventor of this equipment is Prof. Ing. Jiří Adámek, CSc., along with his colleague Jaroslav Šefc, who both participated in the development of the equipment and made the prototype by themselves. 

The advantage of the new equipment is that, when compared to standard devices, it can exert a much higher pressure, which is necessary for the testing of high-quality concretes (identified as HSC, HPC). Another advantage of the testing equipment is its small size and an option to use samples of a smaller size  compared to the present methods. These advantages can be used in testing rooms and laboratories.

The life span of concrete structures is affected by a range of various factors. It is above all its composition, the method of reinforcement and also external factors such as the environment in which the material is used and, obviously, time. The behaviour of materials and structures which are affected by these factors is monitored as early as during the process of concrete setting (e.g. occurrence and progression of fissures) and for the whole of its life span. The most important concrete parameters include compressive strength and flexural and tensile strength.

The problem, particularly in large concrete structures, is deformation caused by the effect of external stress (final shaping of concrete). More specifically, creep is a rheological property of material characterizing the rate of compression of material as a consequence of the long-term effect of pressure (pressure forces). Deformation after unloading remains partly irreversible and represents a value of creep that is an important factor, particularly in pre-stressed concrete where the value is counted on both in the projecting of pre-stress and in the static calculation.

obr do textu

Fig. 1 Side view of the device for the measuring of pressure creep of concrete in a partial cross-section
3 - leverage beam, 20 - spring, 40 - measured sample

The above-mentioned equipment was designed for the testing of this property of concretes and mortars. The known testing products require great strength for the pre-loading of a working spring. Moreover, those devices are not able to exert the sufficient adherence pressure necessary for the loading of test joists prepared of high-strength concretes (HSC) and high-performance concretes (HPC). The system of the new device designed by Prof. Adámek in cooperation with Mr. Šefc uses a combination of a compressed helical spring and a leverage beam, which multiplies the adherence pressure by a factor of three. The advantage of this new device is its small size (approx. 290 mm x 140 mm x 20 mm) and therefore a lower consumption of material for production of the whole equipment, and therefore the price. A standard device also working on the principle of leverage is incomparably larger in size (it normally takes a whole room). The device can be advantageously used for the measuring of creep of fine concretes and mortars with a maximum grain size of 8 mm. Use of the new device is assumed in testing laboratories.

The device is protected by a utility model.

Source of the general photo: commons.wikimedia.org
Source of the picture in text: archives of the Utility model authors

FaLang translation system by Faboba